Microbiology Week 0 Flashcards Preview

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Flashcards in Microbiology Week 0 Deck (304):
1

Define congenital infection

Infection transmitted vertically from mother to babies

2

What congenital infections are currently screened in mothers during pregnancy?

Hepatitis B
HIV
Rubella
Syphilis

3

What congenital infections are currently not screened in mothers during pregnancy but are possible?

CMV
Toxoplasmosis
Hepatitis C
Group B Streptococcus

4

Congenital toxoplasmosis may be asymptomatic at birth but 60% may still go on to suffer long-term sequelae such as....

Deafness
Low IQ
Microcephaly

5

Congenital toxoplasmosis is symptomatic at birth in 40%. What are examples of symptoms?

Choroidoretinitis
Microcephaly/hydrocephalus
Intracranial calcifications
Seizures
Hepatosplenomegaly/jaundice

6

What is the mechanism of congenital rubella syndrome?

The mitotic arrest of cells
Angiopathy
Growth inhibitor effect

7

How does congenital rubella syndrome affect the eyes?

Cataracts
Microphthalmia
Glaucoma
Retinopathy

8

How does congenital rubella syndrome affect the CVS?

Patent ductus arteriosis
Atrial/ventricular septal defect

9

How does congenital rubella syndrome affect the ears?

Deafness

10

How does congenital rubella syndrome affect the brain?

Microcephaly
Meningoencephalitis
Developmental delay

11

What are some other symptoms of congenital rubella syndrome (not including eyes, CVS, ears, brain)?

Growth retardation
Bone disease
Hepatosplenomegaly
Thrombocytopenia
Rash

12

Chlamydia trachomatis is a congenital infection transmitted during delivery. The mother may be asymptomatic but the neonate may show...?

Neonatal conjunctivitis
Rarely pneumonia


Treat with erythromycin

13

What is the neonatal period?

First 4-6weeks of life
n.b. if the baby is born early (premature), the neonatal period is longer and adjusted for expected birth date

14

Which organisms are typically involved with neonatal infections?

Group B streptococci
E coli
Listeria monocytogenes

15

What type bacteria and shape are Group B streptococci?

Gram +ve coccus
Catalase -ve
B-haemolytic

16

In neonates, Group B streptococci causes....?

Bacteraemia
Meningitis
Disseminated infection e.g. joint infections

17

What type bacteria and shape is E coli?

Gram -ve rod

18

What can E coli lead to in neonates?

Bacteraemia
Meningitis
UTI

19

What are early onset sepsis-risk factors (maternal)?

Premature labour
Fever
Foetal distress
Meconium staining
Previous Hx

20

What are early onset sepsis-risk factors (baby)?

Birth asphyxia
Resp distress
Low BP
Acidosis
Hypoglycaemia
Neutropenia
Rash
Hepatosplenomegaly
Jaundice

21

What are investigations used for suspected early onset sepsis?

FBC
C-reactive protein
Blood culture
Deep ear swab
Lumbar puncture (CSF)
Surface swabs
CXR (full body)

22

What is the treatment for early onset neonatal sepsis?

Supportive mgmt
- Ventilation
- Circulation
- Nutrition
- Antibiotics e.g. benzylpenicillin and gentamicin

23

What bacteria are causes of late onset sepsis in neonates (after 48-72 hours)?

Coagulase negative staphylococci (CoNS)

(Less commonly:
Group B strep
E coli
Listeria monocytogenes
Staph aureus
Enterococcus sp.
Gram negatives (Klebsiella etc)
Candida)

24

What are clinical features of late onset sepsis in neonates?

Bradycardia
Apnoea
Poor feeding/bilious aspirates/abdo distension
Irritability
Convulsions
Jaundice
Resp distress
Increased CRP
Sudden changes in WCC/platelets
Focal inflammation e.g. umbilicus, drip sites etc

25

What are investigations used for suspected late onset sepsis?

FBC
CRP
Blood cultures
Urine
ET secretions if ventilated
Swabs from any infected sites

26

What is the treatment for late onset neonatal sepsis?

Treat early
Review and stop Abx if cultures are negative and clinically stable
1st line Abx - cefotaxime and vancomycin
2nd line - meropenem

27

What is the choice of antibiotics for community acquired late onset neonatal sepsis infections?

Cefotaxime, amoxicillin ± gentamicin

28

Viral infections are very common during childhood. What are some examples?

Chickenpox (VZV)
HSV (coldsores/stomatitis)
HHV6, HHV8, EBV, CMV, RSV, enteroviruses etc

29

Bacterial infections may cause secondary infection in childhood after viral illness. An example is....

iGAS disease post-VZV infection

30

What are investigations for infections during childhood?

FBC
CRP
Blood cultures
Urine
± sputum/throat swabs etc

31

What is the most important bacterial cause of paediatric morbidity and mortality?

Meningitis

32

Diagnosis of meningitis in paeds is confirmed by...?

Clinical features
Blood cultures
Throat swab
LP for CSF if possible
Rapid Ag screen
EDTA blood for PCR
Clotted serum for serology if needed later

33

What can Streptococcus pneumonia cause?

Meningitis
Bacteraemia
Pneumonia

34

What bacteria is Gram +ve diploccous, a-haemolytic and has >90 capsular serotypes?

Streptococcus pneumoniae

35

What is the leading cause of morbidity and mortality especially in those <2years old?

Streptococcus pneumoniae

36

Streptococcus pneumoniae has increasing resistance to which drug?

Penicillin

37

What are the bacteria that can cause meningitis at <3 months?

Neisseria meningitidis
Streptococcus pneumoniae
Haemophilus influenzae (if unvaccinated)
GBS
E coli
Listeria sp

38

What are the bacteria that can cause meningitis at 3months-5years of age?

Neisseria meningitidis
Streptococcus pneumoniae
Haemophilus influenzae (if unvaccinated)

39

Respiratory tract infections account for what proportion of childhood illnesses?

1/3

(most viral and upper RTIs)

40

What is the most important bacterial cause of RTIs in children?

Streptococcus pneumoniae

Most UK strains remain sensitive to penicillin or amoxicillin

41

Mycoplasma pneumonia causes RTIs in which age group?

Older children
>4years

42

What is the choice of treatment for myocplasma pneumonia RTIs in children?

Macrolides
e.g. azithromycin

43

What are some classical presentations of mycoplasma pneumonia RTIs in school age children/young adults?

Fever
Headache
Myalgia
Pharyngitis
Dry cough
Incubation period = 2-3weeks

n.b. many are asymptomatic

44

What are the extrapulmonary manifestations of mycoplasma pneumonia?

Haemolysis
Neurological
Cardiac
Polyarthralgia
Myalgia
Arthritis
Otitis media
Bullous myringitis

45

What is the mechanism of haemolysis due to mycoplasma pneumonia?

IgM antibodies bind to the I antigen on erythrocytes
Cold agglutinins in 60% patients occur

46

What are some extra-pulmonary neurological signs in patients with mycoplasma pneumonia?

Encephalitis (most common)
Aseptic meningitis
Peripheral neuropathy
Transverse myelitis
Cerebellar ataxia

47

What do recurrent or persistent infections in children indicate?

A sign of immunodeficiency (congenital or acquired) e.g. HIV, SCID

Paediatric Infectious Diseases doctors investigate these cases

48

What is the treatment for UTIs in children?

Early diagnosis and antibiotics
Renal tract imaging
Antibiotic prophylaxis after treatment of the infection

49

What are the organisms that can cause UTIs?

E coli
Other coliforms e.g. Proteus species, Klebsiella, Enterococcus
Coagulas negative Staphylococcus

50

How are UTIs diagnosed in children?

Symptoms if child can give clear Hx
Pure growth >10^5cfu/ml
Pyuria - pus cells on urine microscopy

51

UTIs are common in children and occur in what % in girls and boys by age 11?

Up to 3% girls by age 11
Up to 1% boys by age 11

52

If treatment for children's RTI for streptococcus pneumoniae and mycoplasma pneumonia fails to respond, we must consider the bacterial cause to be....?

Whooping cough (Bordetella pertussis especially if child is not vaccinated)
Tuberculosis (including MDRTB and XDRTB)

53

What is the mechanism of neurological manifestations due to mycoplasma pneumonia?

The MoA is currently unknown but it is thought that antibodies cross-react with galactocerebroside

54

What are 4 important types of CNS infections?

1. Meningitis
2. Encephalitis
3. Brain abscess
4. Spinal infections

55

What are the 4 routes of entry for CNS infection?

1. Haematogenous spread
2. Direct implantation
3. Local extension
4. PNS into CNS

56

What are the typical signs and symptoms of meningitis?

Fever
Headache
Stiff neck
Vomiting

Light aversion
Drowsiness
Seizures
Non-blanching (petechial/purpuric) rash (in 80% of children)

57

What are the signs and symptoms of encephalitis?

Disturbance of brain function

58

What are the causative agents of encephalitis?

Rabies virus
Arboviruses
Trupanosoma species
Prions
Amoeba

59

What are the causative agent(s) of myelitis?

Poliovirus

60

What are the signs and symptoms of myelitis?

Disturbance of nerve transmission

61

What region is affected in (i) meningitis, (ii) encephalitis, (iii) myelitis, and (iv) with neurotoxins?

(i) Meninges
(ii) Brain
(iii) Spinal cord
(iv) CNS & PNS

62

What are the signs and symptoms of neurotoxin syndromes?

Paralysis
Rigid (tetanus)
OR flaccid (botulism)

63

What are the causative agents of neurotoxin syndrome?

Clostridium tetani
Clostridium botulinum

64

What is the difference between meningitis and meningoencephalitis?

Meningitis is the inflammatory process of meninges and CSF. Meningoencephalitis is the inflammation of meninges AND brain parenchyma.

65

What mechanisms does neurological damage occur in meningitis?

Direct bacterial toxicity
Indirect inflammation with cytokine release and oedema
Shock, seizures and cerebral hypoperfusion

66

What is the mortality rate of meningitis?

Around 10%

67

In the UK, around 5% meningitis survivors have long-term neurological sequelae, mainly....

Sensorineural deafness

68

What is a way to classify meningitis?

Acute
Chronic
Aseptic

69

What are some common causative agents of acute meningitis?

Neisseria meningitidis
Strep pneumoniae
Haemophilus influenzae
Listeria monocytogenes
Group B Streptococcus
E coli

70

How is Neisseria meningitidis transmitted?

Person-to-person
Through nasopharyngeal mucosa
From asymptomatic carriers

71

Pathogenic strains of Neisseria meningitidis are found in what % of carriers?

1% of N.meningitidis are pathogenic

72

Neisseria meningitidis can cause....

Meningitis (50% cases)
Septicaemia (7-10%)
Septicaemia AND meningitis (40%)

These clinical differences are important for treatment choice for shock vs only increased ICP.

73

What 4 processes produce the clinical spectrum for septicaemia?

1. Capillary leak
2. Coagulopathy
3. Metabolic derangement (namely acidosis)
4. Myocardial failure (i.e. multi-organ failure)

74

How does the capillary leakage process contribute to septicaemia?

Leakage of albumin and other plasma proteins results in hypovolaemia

75

How does the coagulopathy process contribute to septicaemia?

Bleeding and thrombosis occur
Due to endothelial injury and platelet-release reactions
Protein C pathway and plasma anticoagulants are also involved

76

What is an example of chronic meningitis?

Tuberculous chronic meningitis

77

Tuberculous chronic meningitis is more common in which cohort of patients?

Immunosuppressed

78

Which regions does tuberculous chronic meningitis involve?

Meninges and basal cisterns of the brain and spinal cord

79

What can tuberculous chronic meningitis result in?

Tuberculous granulomas
Tuberculous abscesses
Cerebritis

80

What is the most common infection of the CNS?

Aseptic meningitis

PC: headache, stiff neck and photophobia ± rash.

81

What are the causative organism(s) of aseptic meningitis in 80-90% cases?

Coxsackievirus group B
Echoviruses

(often in children <1yr)

82

How is encephalitis transmitted?

Commonly from person to person
Or through vectors (mosquitoes, lice, ticks)

83

West Nile virus is an international cause of which infection?

Encephalitis

84

What organism can cause bacterial encephalitis?

Listeria monocytogenes

85

What organism(s) can cause amoebic encephalitis?

Naegleria fowleri (lives in warm water)
Acanthamoeba
Balamuthia mandrillaris

These can cause brain abscesses, aseptic or chronic meningitis

86

Toxoplasmosis is an example of...?

other CNS encephalitis

87

A focal CNS infection may be indicated by the presence of....?

Brain abscess

88

What are some disorders involved with the pathophysiology of brain abscesses?

1. Otitis media; mastoiditis; paranasal sinuses
2. Endocarditis (haematogenous spread)

89

What are some causative organisms involved with brain abscesses?

Strep (aerobic + anaerobic)
Straph
Gram -ve organisms (esp in neonates)
Mycobacterium TB
Fungi
Parasites
Actinomyces + Nocardia species

90

What is the most common form of spinal vertebral infection?

Pyogenic vertebral osteomyelitis

91

What are the causes of spinal infection (i.e. pyogenic vertebral osteomyelitis)?

Direct open spinal trauma
Infections in adjacent structures
Haematogenous spread of bacteria to a vertebra

92

If pyogenic vertebral osteomyelitis (spinal infection) is left untreated, what can result?

Permanent neurological deficits
Significant spinal deformity
Death

93

What are some risk factors for spinal infections?

Advanced age
IV drug use
Long-term systemic steroids
Diabetes mellitus
Organ transplant
Malnutrition
Cancer

94

What investigation is the best for detecting parenchymal abnormalities e.g. abscesses and infarction?

MRI

95

What investigations are useful for CNS infections?

CSF sample
Brain tissue
MRI (for parenchymal abnormalities e.g. abscesses and infarction)

96

A 20 year old woman presents with headache and neck stiffness. Gram stain shows Gram +ve cocci. What is the causative pathogen?

Strep pneumoniae

97

A 18 year old man present with headache and neck stiffness. Gram stain shows Gram -ve cocci. What is the causative pathogen?

N. meningitidis

98

A 65 year old presents with headache and neck stiffness. Gram stain shows Gram +ve bacillus/rods. What is the causative pathogen?

Listeria monocytogenes

99

A 45 year old presents with headache and neck stiffness. A Ziehl-Neelsen stain was done and was positive. What is the causative pathogen?

Mycobacterium TB

100

A 35 year old presents with headache and neck stiffness. Indian ink stain tests were done and were positive. What is the causative pathogen?

Cryptococcus neoformans

Increased risk in HIV patients

101

What is the generic treatment plan for meningitis?

Ceftriaxone 2g IV bd

If >50yrs or immunocompromised add:
amoxicillin 2g IV 4hourly

102

What is the generic treatment plan for meningo-encephalitis?

Aciclovir 10mg/kg IV tds
Ceftriaxone 2g IV bd

If >50yrs or immunocompromised add:
amoxicillin 2g IV 4hourly

103

What is the adjunctive therapy for CNS infections alongside the main generic treatment plan?

Corticosteroids
Consider repeating lumbar puncture

(if causative organism is identified, more specific Rx can be given)

104

Define bacteriuria

The presence of bacteria in the urine

105

Define cystitis

Inflammation of the bladder caused by infection

106

Define uncomplicated urinary tract infection

Infection in a structurally and neurologically normal urinary tract

107

Define complicated urinary tract infection

Infection in a urinary tract with functional or structural abnormalities (including indwelling catheters and calculi).

108

Complicated urinary tract infections tend to occur in which groups of patients?

Men
Pregnant women
Children
Patients who are hospitalised/in healthcare associated settings

109

Up to what % of the female population will experience a symptomatic urinary tract infection at some time during their life?

40-50%

110

More than 95% of urinary tract infections are caused by a single bacterial species. What is the most frequent infecting organism in acute infection?

E.coli

111

Apart from E.coli causing the majority of UTIs, what other organisms can cause them?

Proteus mirabilis
Klebsiella aerogenes
Enterococcus faecalis
Staphylococcus saprophyticus
Staphylococcus epidermis

112

What are 3 antibacterial host defences in the urinary tract?

1. Urine (osmolality, pH, organic acids)
2. Urine flow and micturition
3. Urinary tract mucosa (bactericidal activity, cytokines)

113

What is the urethra usually colonised with?

BActeria

114

The female urethra is short and in promiximity to what?

The warm and moist vulvar and perianal areas

This makes contamination likely. Bacteria is pushed into the female bladder (risk increases during sex)

115

Organisms that cause UTIs in women tend to colonise which regions before the urinary infection results?

Vaginal introitus
Periurethral area

116

Once bacteria is within the bladder, bacteria may multiply and where can it pass up?

Ureters
Especially if vesicoureteral reflux is present, up to the renal pelvis and parenchyma

117

How do renal/urinary tract abnormalities interfere and increase infection risk?

Obstrcution inhibits natural urine flow and resulting stasis occurs

118

How can we classify obstruction of the urinary tract into 3 categories?

1. Extra-renal causes
2. Intra-renal causes
3. Neurogenic malfunction

119

Name the extra-renal causes of obstruction of the renal/urinary tract that can increase UTI risk?

- Valves, stenosis, or bands
- Calculi
- Extrinsic ureteral compression from a variety of causes
- Benign prostatic hypertrophy

120

Name the intra-renal causes of obstruction of the renal/urinary tract that can increase UTI risk?

- Nephrocalcinosis
- Uric acid nephropathy
- Analgesic nephropathy
- Polycystic kidney disease
- Hypokalemic nephropathy
- Renal lesions of sickle cell trait/disease

121

Name the neurogenic malfunction causes of obstruction of the renal/urinary tract that can increase UTI risk?

Poliomyelitis
Tabes dorsalis,
Diabetic neuropathy
Spinal cord injury

122

How does vesicoureteral reflux increase the risk of urinary tract infection?

A residual pool of infected urine in the bladder is maintained after voiding

123

The kidney is frequently the site of abscesses in patients with what infections?

Staphylococcus aureus bacteremia
Or endocarditis
(Or both. This is by the haematogenous route)

124

Infection of the kidney with which type of bacteria RARELY occurs by the haematogenous route?

Gram-negative bacilli

(it is more common with Staph aureus or endocarditis)

125

What are the symptoms of urinary tract infections in neonates and children younger than 2 years?

Non-specific

Failure to thrive
Vomiting
Fever

126

What are the symptoms of urinary tract infections in children older than 2 years?

More localised symptoms compared with children <2yrs.

Frequency
Dysuria
Abdominal/flank pain

127

What do the lower urinary tract symptoms result from?

Bacteria causing irritation of urethral and vesical mucosa, causing frequent and painful urination of small amounts of turbid urine

128

What are the lower UTI symptoms present in patients?

Frequency
Painful urination
Small amounts of turbid urine
Suprapubic heaviness/pain
Grossly bloody urine/bloody tinge at end of micturition

(fever tends to be absent in infections limited to the lower tract)

129

What are the upper UTI symptoms present in patients?

Fever (±rigors)
Flank pain
Frequently lower UTI symptoms too (frequency, urgency, dysuria) - these may occur before the upper tract symptoms by 1-2 days

130

What are the symptoms of UTIs in older/elderly patients?

- Majority are asymptomatic
- When they are present, are not diagnostic as many old people have frequency, dysuria, hesitancy, incontinence anyway
- Atypical upper UTI symptoms e.g. abdo pain, change in mental status

131

What are the investigations for (i) uncomplicated UTIs/pyelonephritis and (ii) complicated UTIs?

(i) Urine dipstick
MSU for urine MC&S
Bloods (FBC, U&Es, CRP, inflammatory markers + renal function)
(ii) The above investigations but also renal USS and IV urography

132

How can we sample urine for testing in UTIs?

- Midstream clean catch (MSU)
- Catherisation
- Suprapubic aspiration

133

The presence of white cells (pyuria) in the urine under the microscope indicates what?

Infection

134

The presence of squamous epithelial cells in the urine under the microscope indicates what?

Contamination of the sample

135

What are some causes of sterile pyuria (presence of white cells in urine without any apparent infection)?

- Prior treatment with antibiotics
- Calculi
- Catheterisation
- Bladder neoplasm
- TB
- Sexually transmitted diseases

136

The treatment for UTIs is empirical therapy, community based for lower UTIs and local guidance. How many days of therapy should be given for UTIs?

- 3 days of therapy with standard doses for treatment of uncomplicated lower UTIs in women
- Longer therapy for those with H/O previous UTIs, Abx resistance, >7days symptoms
- 7 days of therapy in men

137

What is the treatment for catheter-associated UTIs?

- Remove catheter
- Aminoglycosides (e.g. gentamin, amikacin) before catheter removal
- Oral fluconazole is NO more effective than no therapy

138

Most UTIs with indwelling catheters are caused by which organism?

Candida fungal infection

139

Oral fluconazole is not given to those with Candida fungal UTIs caused by catheters, except in which patients?

Renal transplant patients
Patients who are about to undergo elective urinary tract surgery

140

Inflammation and infection of the kidney is referred to as...?

pyelonephritis

141

The kidney itself is NOT uniformly susceptible to infection. What is the susceptibility in the medulla vs the cortex?

- Few organisms are needed to infect the medulla
- 10,000x are needed to infect the cortex

142

What is pyelonephritis commonly associated with?

Sepsis

143

Pyelonephritis is commonly associated with sepsis so it needs more aggressive treatment such as....?

Broad spectrum Abx
Co-amoxiclav ±/gentamicin

Imaging: calculi, structural cause

144

What are the complications of pyelonephritis?

- Perinephric abscess
- Chronic pyelonephritis (scarring, chronic renal impairment)
- Septic shock
- Acute papillary necrosis

145

What are 3 major pathogens in surgical site infections?

1. Staph aureus (MSSA and MRSA)
2. E.coli
3. Psuedomonas aeruginosa

146

What is the pathogenesis mechanism of surgical site infections?

1. Contamination of wound at operation
2. Pathogenicity and innoculum of microorganisms
3. Host immune response

147

The risk of surgical site infection is increased at what dose of contaminating bacteria at the surgical site?

Normally >10^5 microorganisms per gram of tissue

The dose required to cause infection is much lower if there is foreign material e.g. silk suture

148

What are the 3 levels of surgical site infection?

1. Superficial incisional - skin and subcutaneous tissue
2. Deep incisional - fascial and muscle layers
3. Organ/space infection

149

The presence of pus with cluster cocci with a surgical site infection is most likely to be which of the organisms:
(a) E.coli
(b) Enterobacter
(c) Neisseria meningitides
(d) MRSA

MRSA

150

As well as age, what underlying illnesses/causes of surgical site infections can increase its risk?

- ASA score >3
- Diabetes
- Malnutrition/obesity
- Low serum albumin
- Radiotherapy and steroid use
- RhA
- Smoking

151

Diabetes increases the risk of surgical site infection by 2-3x. How can this be managed?

Control blood glucose
Aim for HbA1C <7

This is because DM is associated with post-operative hyperglycaemia

152

Rheumatoid arthritis increases the risks of surgical site infections. How can this be managed?

Stop disease modifying agents for 4 weeks pre- and 8 weeks post-operatively.

153

Patients with a BMI of >35 have an increased risk of surgical site infection by how many times?

2-7x greater risk

154

Why is there greater risk of surgical site infection in patients with obesity?

Adipose tissue is poorly vascularised
Poor oxygenation of tissues and functioning of the immune response increases SSI risk

155

Why is there greater risk of surgical site infection in patients who smoke?

Nicotine delays primary wound healing
Peripheral vascular disease
Therefore encourage tobacco cessation

156

Why is pre-operative showering encouraged?

- Microorganisms colonising skin may contaminate exposed tissues and cause surgical site infections
- Patients should wash using soap on operation day or the day before

157

Why is hair removal is not encouraged before operations?

Micro-abrasions caused by shaving with a razor may lead to multiplication of bacteria in surgical site infections
(Use electric clippers on the day of surgery with single-use head)

158

Staph aureus contaminates the nasal region in what % of people?

20-30%

High RF for surgical site infections

159

Why does mild hypothermia during surgery appear to increase the risk of surgical site infections?

Vasoconstriction
Decreased O2 delivery to the wound space
Subsequent impairment of neutrophil function

160

Optimal oxygenation during surgery can have what effect on surgical site infections?

Higher inspired O2 concentrations peri-operatively reduces SSIs

161

Give 4 bone and joints infections that will increase the risks of surgical site infections?

1. Septic arthritis
2. Vertebral osteomyelitis
3. Chronic osteomyelitis
4. Prosthetic joint infection

162

What is the incidence of septic arthritis?

2-10 cases per 100,000

In patients with rheumatic arthritis, it increases to 28-38 per 100,000.

163

What is the (i) mortality and (ii) morbidity of septic arthritis?

(i) Mortality is 7-15%
(ii) Morbidity is 50%

164

What are the risk factors for septic arthritis?

- RhA, OA, crystal-induced arthritis
- Joint prosthesis
- IV drug abuse
- Diabetes, chronic renal disease, chronic liver disease
- Immunosuppression, steroids
- Trauma: intra-articular injection, penetrating injury

165

What is the pathophysiology of septic arthritis?

Organisms adhere to the synovial membrane
Bacteria proliferate in synovial fluid and generate a host inflammatory response
Joint damage exposes host-derived proteins e.g. fibronectin, to which bacteria adhere

166

Staph aureus has receptors that can recognise selected host proteins. What is an example of a receptor that it has?

Fibronectin binding protein

(binds to fibronectin which is a host-derived protein that is exposed from joint damage)

167

Kingella kingae is a bacteria that can adhere to the synovial membrane in septic arthritis. How does it adhere?

Bacterial pili

168

Some strains of Staph aureus produce what cytotoxin that has been associated with fulminant infections in septic arthritis?

Cytotoxin PVL
(Panton-Valentine Leucocidin)

169

What are the causative organisms of septic arthritis?

1. Staph aureus (46%)
2. Coagulase negative staph (4%)
3. Streptococci (22%) - pyogenes, pneumoniae, agalactiae
4. Gram negative organisms - E.coli, HI, Neisseria, Salmonella
5. Rare: Lyme, brucellosis, mycobacteria, fungi

170

What are the clinical features of septic arthritis?

- 1-2 week H/O red, painful, swollen restricted joint
- Monoarticular in 90%
- Knee is involved in 50%
- Patients with rheumatoid arthritis may show more subtle signs of joint infection

171

Is septic arthritis polyarticular or monoarticular?

Monoarticular in 90%

172

What investigations are appropriate for septic arthritis?

- Blood culture before antibiotics given
- Synovial fluid aspiration for MC&S
- ESR,CRP
- >50,000 WBC cells/mm3 suggest septic arthritis
- Negative culture result does not exclude septic arthritis
- Imaging: US, CT, MRI

173

What signs may be present on imaging of septic arthritis?

US - joint effusion
CT - erosive bone change, periarticular soft tissue extension
MRI - effusion, articular cartilage destruction, abscess, contiguous osteomyelitis

174

What is the treatment for septic arthritis?

- Antibiotics (up to 6 weeks therapy can be given)
- Drainage

175

Vertebral osteomyelitis can be classified into which 2 categories?

1. Acute haematogenous
2. Exogenous - after disc surgery, or implant associated

176

What are the causative organisms of vertebral osteomyelitis?

1. Staph aureus (48.3%)
2. Coagulase negative staph
3. Gram negative rods
4. Strep

177

Where can vertebral osteomyelitis infections be localised to and in what %?

Cervical (10.6%)
Cervico-thoraco (0.4%)
Lumbar (43.1%)

178

What are the symptoms of vertebral osteomyelitis?

Back pain (86%)
Fever (60%)
Neurological impairment (34%)

179

How is vertebral osteomyelitis diagnosed?

MRI - 90% sensitive
Blood cultures
CT/open biopsy

180

What is the treatment for vertebral osteomyelitis?

6 weeks of treatment
Longer treatment if undrained abscesses or implant associated

181

What are 3 characteristic features of chronic osteomyelitis?

Pain
Brodies abscess
Sinus tract

182

How is chronic osteomyelitis diagnosed?

MRI
Bone biopsy for culture and histology

183

What is the treatment for chronic osteomyelitis?

Radical debridement down to living bone

Remove sequestra, and remove infected bone and soft tissue

184

What are signs of prothetic joint infections?

Pain
Patient complains that the joint was 'never right'
Early failure
Sinus tract

185

Define sinus tract

A narrow opening or passageway under the skin that can extend in any direction through soft tissue and results in dead space with potential for abscess formation

186

What are the causative organisms for prosthetic joint infections?

- Gram +ve cocci (CoNS, Staph aureus, strep, entero)
- Aerobic gram -ve bacilli (entero, pseudomonas)
- Anerobes
- Polymicrobial
- Cultural negative
- Fungi

187

How are prosthetic joint infections diagnosed?

- Radiology: loosening
- CRP >13.5 (prosthetic knee joint)
- CRP >5 (hip joint)
- Joint aspiration where WCC >1700/ml (knee)
- WCC >4200/ml (hip)

188

Intraoperative microbiological sampling is important during prosthetic joint implantation collecting tissue specimens from how many sites?

Tissue specimens from least 5 sites around the implant

If 3 or more specimens have identical organisms = highly predictive of infection

189

What is infection defined as in the histopathology of the tissue specimens collected from at least 5 sites around the prosthetic implant?

>5 neutrophils per high power field

190

What does the 'Endo Klinik single stage revision' treatment for prosthetic joint infection involve?

- Aspirate joint to identify pathogen
- Removal of infected tissue, foreign material, dead bone
- Re-implant new prosthesis with antibiotic impregnated cement
- IV antibiotics

191

What does the 'two stage revision' treatment for prosthetic joint infection involve?

- Remove prosthesis
- Take samples for MC&S and histology
- 6 weeks IV antibiotics
- Stop Abx for 2 weeks
- Re-debride and sample at second stage
- Re-implant with antibiotic impregnated cement
- No further antibiotics if samples clear

192

A 70year old women had a 1994 right total hip replacement, and 1998 revision of acetabular component. X-ray shows lysis around the distal part of the femoral component. H/O diabetes. What is the likely pathogen involved here:
(a) Coagulase negative staphylococci
(b) Staph aureus
(c) E.coli
(d) Haemophilus influenzae

Coagulase negative staphylococci

Rx: IV vancomycin and oral rifampicin

8 weeks later had second stage revision and cultures showed no growth.

193

How do leucocyte derived proteases and cytokines act as host factors contributing to the pathogenesis?

Cartilage degradation
Bone loss

194

How does raised intra-articular pressure (a host factor) contribute to the pathogenesis of septic arthritis?

Impaired capillary blood flow
Cartilage and bone ischaemia and necrosis

195

Name 4 host factors involved in the pathogenesis of septic arthritis

(n.b. bacterial factors include binding proteins, synovial membrane adherence and cytotoxins)

- Leucocyte derived proteases and cytokines
- Raised intra-articular pressure
- Genetic deletion of macropage-derived cytokines
- Absence of IL-10

196

How does the genetic deletion of macrophage-derived cytokines (a host factor) contribute to the pathogenesis of septic arthritis?

E.g. lymphotoxin-a, TNF-a, IL-1 receptor

When present, these reduce host response normally in S.aureus sepsis in animal models.

i.e. genetic variation in cytokine expression increases susceptibility to septic arthritis

197

How does the absence of IL-10 (a host factor) contribute to the pathogenesis of septic arthritis?

IL-10 absence in KO mice increases the severity of staphylococcal joint disease

i.e. genetic variation in cytokine expression increases susceptibility to septic arthritis

198

Which groups are the most vulnerable to GI infections?

Infants
Elderly

199

Developing countries have high levels of GI infection such as cholera due to what reasons?

No access to clean drinking water and sanitation

200

What are 6 reportable GI infections?

Campylobacter
Salmonella
Shigella
E.coli 0157
Listeria
Norovirus

201

For Campylobacter, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 1-10 days
(b) 2-20 days
(c) Poultry

202

For E.coli 0157, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 1-5 days
(b) 1-4 days
(c) HUS, verotoxin

203

For Shigella, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 12-96hrs
(b) 5-7 days
(c) Small infective dose, outbreaks

204

For Salmonella (non-typhoidal, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 8-48hrs
(b) 4-7 days
(c) Rare cause systemic diagnosis

205

For Vibrio parahaemolyticus, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 24-72hrs
(b) 2-10 days
(c) Shellfish

206

For Vibrio cholera, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 1-5 days
(b) Variable
(c) 'Ricewater stools', endemic

207

For Bacillus cereus, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 1-6hrs
(b) <1 day
(c) Heat stable emetic toxin i.e. rice

208

For Staph aureus, what is the:
(a) incubation period
(b) duration (days)
(c) associated risk factors?

(a) 2-7hrs
(b) <1 day
(c) Preformed toxins

209

What does the mechanism of cholera GI infection involve?

- Cholera (secretory-diarrhoea) toxin
- Superantigens
- Host responses causing inflammation

210

Describe the mechanism of cholera disease involving cholera toxin (secretory diarrhoea toxin)?

- Cholera toxin binds to proteins
- Via cAMP, Cl- channels open at the apical membrane of enterocytes
- Cl- efflux into the lumen occurs
- H2O and electrolytes are lost

211

Describe the mechanism of cholera disease involving superantigens?

- Superantigens bind directly to T-cell receptors and MHC molecules
- This occurs OUTSIDE the peptide binding site
- Massive cytokine production by CD4 cells occur
- This causes systemic toxicity and suppression of adaptive response

212

Describe the host responses in bacteraemia mechanism of disease?

Inflammatory diarrhoea or enteric fever (interstitial inflammation)

213

Staphylococcus aureus can cause food poisoning. What is its method of transmission?

1/3 of the population are chronic carriers, and 1/3 transiently carry it.
It is spread by skin lesions on food handlers.

214

What features do Staphylococcus aureus bacteria (that cause food poisoning) show on MC&S?

- Catalase, coagulase positive Gram positive coccus
- In tetrads/clusters on Gram stain
- Yellow colonies on blood agar

215

Staphylococcus aureus bacteria (that cause food poisoning) produces what toxin, which induces what clinical features?

- An enterotoxin (exotoxin) that can act as a superantigen in the GI tract is produced
- Releases IL-1 and IL-2
- Causes prominent vomiting and watery, non-bloody diarrhoea

216

What is the treatment for the prominent vomiting, and watery, non-bloody diarrhoea caused by the enterotoxins and superantigens in Staph aureus food poisoning?

Do not treat
Self-limiting

217

What are gram-positive rods (spore-forming) that cause food poisoning?

Bacillus cereus

(spores germinate in reheated fried rice)

218

What are the 2 toxins involved in Bacillus cereus?

- Heat stable emetic toxin (not destroyed by reheating rice)
- Heat labile diarrhoeal toxin (food is not cooked to a high enough temperature)

219

What are the clinical features of Bacillus cereus?

Watery, non-bloody diarrhoea (self-limiting)
Rare cause of bacteraemia in vulnerable populations
Cerebral abscesses (rare)

220

What is a gram-positive anaerobe that can cause botulism and food poisoning?

Clostridia
- Clostridium botulinum = botulism
- Clostridium pefringens = food poisoning

221

What is the source of clostridium botulinum (botulism)?

Canned or vacuum packed foods
Ingestion of preformed toxin (inactivated by cooking)
e.g. in honey for infants

222

What is the mechanism of clostridium botulinum gram +ve anaerobe that causes botulism, and the treatment?

- Blockade of ACh release from peripheral nerve synapses
- Treat with antitoxin

223

What is the source of Clostridium pefringens (food poisoning)?

Reheated food (meat)

224

What is the incubation period and clinical features for Clostridium perfringens (food poisoning, Gram +ve anaerobe)?

Incubation = 8-16hours
Watery diarrhoea
Cramps
Little vomiting lasting 24hrs

225

What is the mechanism of clostridium botulism (gram +ve anaerobe) causing food poisoning?

The enterotoxin acts as a superantigen, and affects the colon (but not the small bowel small bowel)

226

Pseudomembranous colitis can occur with Clostridium difficile which is antibiotic-related colitis. This occurs in how many hospitalised patients, and mainly with which antibiotics?

3-30% patients

Cephalosporins, cipro and clindamycin are often involved

227

What is the treatment for closteridium difficile?

Metrodinadazole
Vancomycin
(taken orally)
Stop other Abx where possible

228

Listeria monocytogenes presents in a population as...?

Outbreaks of febrile gastroenteritis

229

What does the stain for Listeria monocytogenes show?

Gram-positive rod
B-haemolytic
Aersculin positive
Tumbling motility

230

What is the source for Listeria monocytogenes GI infection?

Refrigerated food (cold enhancement) i.e. unpasteurised dairy
Vegetables
(Grows at 4 degrees c)

231

What are the clinical symptoms of Listeria monocytogenes?

Watery diarrhoea
Cramps
Headache
Fever
Little vomiting

232

What patient groups are particularly susceptible to Listeria monocytogenes?

Perinatal infection (pregnant women)
Immunocompromised patients

233

What is the treatment for Listeria monocytogenes?

Ampicillin

234

Describe features of enterobacteriacae?

Facultative anerobes
Glucose/actose fermenters (LF)
Oxidase negative

235

E.coli is also described as traveller's diarrhoea. What is the source of E.coli?

Food/water contaminated with human faeces

236

What are the enterotoxins involved with the mechanism of disease in E.coli and where do they act?

- Heat labile stimulates adenyl cyclase and cAMP
- Heat stable stimulates guanylate cyclase

These act on jejeunum and ileum, not on colon

237

Name the various types of E.coli that match up with the features:
(a) Toxigenic, main cause of traveller's diarrhoea
(b) Pathogenic, infantile diarrhoea
(c) Invasive, dysentery
(d) Haemorrhagic, can cause HUS

(a) ETEC = toxigenic, main cause of traveller's diarrhoea
(b) EPEC = pathogenic, infantile diarrhoea
(c) EIEC = invasive, dysentery
(d) EHEC = haemorrhagic (O157), can cause HUS (H7)

238

What is the treatment for Escherichia coli?

AVOID antibiotics

239

What bacteria is a non-lactose fermenter and H2S producer?

Salmonella

(tests use TSI agar, XLD agar and selenite F broth)

240

What are the 3 species of Salmonellae?

1. S. typhi (and paratyphi)
2. S. enteritidis
3. S. cholerasuis

241

What antigens are produced by Salmonellae?

- Cell wall O (groups A-I)
- Flagellar H
- Capsular Vi (virulence, anti-phagocytic)

242

How is Salmonella enteritidis (enterocolitis) transmitted?

Poultry
Eggs
Meat

243

How is Salmonella typhi (typhoid/enteric fever) transmitted?

Only by humans
Multiplies in Payer's patches

244

What regions does Salmonella enteritidis invade to cause enterocolitis?

Epithelial and sub-epithelial tissue of small and large bowel

245

What are the clinical symptoms and signs of enterocolitis (Salmonella enteritidis)?

Non-bloody diarrhoea (self-limiting, no treatment needed)
Bacteraemia is rare
Stool positivity diagnoses

246

What are the clinical symptoms and signs of typhoid/enteric fever (Salmonella typhi)?

Slow onset fever
Constipation
Splenomegaly
Rose spots
Anaemia + leukopenia
Bradycardia
Haemorrhage and perforation

247

How is salmonella typhi (typhoid/enteric fever) diagnosed and treated?

Diagnosis is with a positive blood culture

Treatment = ceftriaxone

248

What bacteria is a non-lactose fermenter, non-H2S producer and non-motile?

Shigellae

249

What antigens are present with Shigellae?

- Cell wall O antigens
- Polysaccharide (groups A-D): S.sonnei, S.dysenteriae, S.flexneri (MSM)

250

What is the most effective enteric pathogen?

Shigella

Due to low infectious dose required (50)
n.b. it has no animal reservoir or carrier state

251

Dysentery (caused by Shigellae dysenteriae) involves what processes?

- Invasion of cells of mucosa of distal ileum and colon
- Shiga enterotoxin is produced

252

What is the treatment for Shigellae infections?

Avoid antibiotics
But ciprogloxacin given if required

253

What are some features of Vibrios (cholera) bacteria?

Curved
Comma-shaped
Late lactose fermenters
Oxidase positive

254

What are the types of Vibrio cholera?

- O1 group = endemics, with various biotypes and serotypes
- Non-O1 group = sporadic or non-pathogens

255

How is vibrio transmitted?

Contamination of water and food from human faeces (shellfish, oysters, shrimp)

256

What is the mechanism of action for vibrio cholerae?

Colonisation of small bowel
Secretion of enterotoxin with A and B subunit, which persistently stimulate adenylate cyclase and cAMP
Opens Cl- channels and causes massive diarrhoea (rice water stool) without inflammatory cells

257

What is the treatment for vibrio cholerae infection?

Treat the losses (i.e. supportive)
± Doxycycline

258

What are the species of Vibrios?

- Vibrios cholera (O1 and non-O1 group)
- Vibrio parahaemolyticus
- Vibrio vulnificus

259

How is Vibrio parahaemolyticus transmitted?

Ingestion of raw or undercooked seafood (i.e. oysters)
Major cause of diarrhoea in Japan
Self-limiting (3days)

260

Vibrio cholerae will grow in salty environments, what % of NaCl?

8.5% NaCl

261

How is vibrio vulnificus transmitted?

Cellulitis in shellfish handlers

262

What does vibrio vulnificus induce in HIV patients?

Fatal septicaemia
Diarrhoea and vomiting

263

What is the treatment for vibrios pathogens?

Doxycycline

264

What are the features of. Campylobacter bacteria?

Curved, comma or S-shaped
Micro-aerophilic
C.jejuni at 42 degrees C
Oxidase positive
Motile

265

Campylobacter is self-limiting but symptoms can last for weeks (up to 20 days). We only treat campylobacter in which patients and using which treatment?

Only treat if immunocompromised

Rx macrolides

266

How is campylobacter transmitted?

Contaminated food and water with animal faeces

(poultry, meat, unpasteurised milk)

267

What are the clinical features of Campylobacter?

Watery, foul-smelling diarrhoea
Bloody stool
Fever and severe abdominal pain

268

What are 3 long-term sequelae that may occur post-Campylobacter infection?

GBS syndrome
Reactive arthritis
Reiter's syndrome

269

What is the treatment for campylobacter?

Erythromycin or ciprofloxacin if infection is in the first 4-5 days

270

What can Yersinia enterocolitica cause?

Enterocolitis
Mesenteric adenitis

271

What conditions is Yersinia enterocolitica associated with?

Reactive arthritis
Reiter's syndrome

272

What are some features of Yersinia enterocolitica bacteria?

Non-lactose fermenter
Prefers 4 degrees C i.e. 'cold enrichment'

273

How is Yersinia enterocolitica transmitted?

Via contaminated food with domestic animal faeces

274

What condition is caused by Mycobacteria (M.Tuberculosis, M.Avium Intracellulare)?

Tuberculosis

275

Give 3 examples of protozoa

Entamoeba histolytica
Giardia lamblia
Cruptosporidium parvum

276

What are the features of the protozoa, entamoeba histolytica, in (i) diarrhoea, and (ii) non-diarrhoeal illness?

(i) Motile trophozoite in diarrhoea
(ii) Non-motile cyst in non-dirrhoeal illness

4 nuclei, no animal resevoir

277

How is entamoeba histolytica removed normally?

Killed by boiling or removed by water filters

278

What is the mechanism of action of entamoeba histolytica?

Ingestion of cysts leads to trophozoites in the ileum
These colonise the caecum and colon
Results in 'flask-shaped' ulcers

279

What are the acute and chronic clinical features of entamoeba histolytrica?

Acute: dysentery, flatulence, tenesmus
Chronic: weight loss, ±diarrhoea, liver abscess

280

How is entamoeba histolytica confirmed on diagnosis?

Stool microbiology shows wet mount, iodine and trichrome
Serology confirms in invasive disease

281

What is the treatment for entamoeba histolytica protozoal infection?

Metronidazole and peromomycin in luminal disease

282

What protozoa has the features of a 'pear-shaped' trophozoite, 2 nuclei, 4 flagella and a suction disc?

Giardia lamblia

283

How is giardia lamblia protozoal infection transmitted?

Ingestion of cyst from faecally contaminated water or food

284

What is the mechanism of action of giadia lamblia infection?

Excystation at duodenum
Pear-shaped trophozoite attaches
No invasion
Results in malabsorption of protein and fat

285

What groups of people are likely to suffer from Giardia lamblia infection?

Travellers
Hikers
Day-care
Psychiatric hospitals
MSM

286

What are the clinical features of giardia lamblia?

Foul-smelling, non-bloody diarrhoea
Cramps
Flatulence
No fever

287

How is the diagnosis made for giardia lamblia, and what is the treatment?

Stool MC&S
ELISA
'String test'

Rx = metronidazole

288

Cryptosporidum parvum is a protozoall infection that infects what region?

Jejunum

289

Stool MC&S for using the modified Kinyoun acid fast stain is used for the diagnosis of which infection, and what is shown?

Oocysts are seen in the stool by modified Kinyoun acid fast stain with Cryptosporidium parvum (protozoal infection)

290

What is the treatment for Cruptosporidium parvum infection?

Reconstitution of the immune system

291

Give 3 reasons why norovirus tends to cause outbreaks?

- Low infectious dose needed (18-1000 viral particles)
- Environmental resilience (survives in 0-60 degrees)
- No long immunity against it

292

GII.4 is currently the predominant stain of what infection?

Norovirus

293

A dsRNA 'wheel-like' virus refers to which virus?

Rotavirus

294

Rotavirus replicates in which region?

The mucosa of the small intestine

295

What are the clinical features of rotavirus?

- Secretory diarrhoea (with no inflammation)
- Watery diarrhoea (mechanism unknown, but may be caused by stimulation of the enteric nervous system)

296

Rotavirus is common and by age 6 most children globally have antibodies to at least one type. What confers lifelong immunity to rotavirus?

Exposure to natural rotavirus infection twice confers lifelong immunity

297

What types of adenovirus cause non-bloody diarrhoea below 2 years of age?

Types 40 and 41

298

In immunocompromised patients, what types of adenovirus cause non-bloody diarrhoea and infection?

ANY type

299

Using which investigations can we detect and diagnose adenovirus GI infections?

Stool MC&S
Antigen detection
PCR

300

Poliovirus, enteroviruses (coxsackie, ECHO), hepatitis A are all transmitted via which route?

Faecal-oral route

301

Vaccines for cholera exist for serogroups O1 and O139 in which 2 forms?

(a) Inactivated, whole cell with B-subunit of toxins
(b) Live attenuated, but not recommended

302

Vaccines are available/being tested for which GI infection pathogens?

- Cholera
- Campylobacter
- ETEC
- Salmonella typhi
- Rotavirus

303

Bacterial organisms that can cause vertebral oseomyelitis include...

Brucella
Salmonella

304

What two techniques can be used for the surgical treatment of chronic osteomyelitis?

- Modified Lautenbach technique
- Papineau technique (this has a higher success rate)