Microbiology Flashcards
(128 cards)
1
Q
Normal flora of the skin
A
- Coagulase-negative staphylococci
- Diptheroids
2
Q
Normal flora of the nostrils
A
- Staphylococcus aureus
3
Q
Normal flora of the oral cavity
A
- Streptococci
- Anaerobes
4
Q
Normal flora of the upper respiratory tract
A
- Viridans streptococci
- Diptheroids
- Anaerobes
- Commensal neisseria
5
Q
Normal flora of the lower GI tract
A
- Coliforms
- Faecal enterococci
- Anaerobes (bacteroides, clostridia)
6
Q
Normal flora of the anterior urethra
A
- Skin flora
- Faecal flora
7
Q
How does commensal infection occur
A
- If an organism breaches the defence of a site where it is not commensal (e.g. E.coli is normal in the gut, but can breach the urinary tract)
- Normal flora altered by broad-spectrum antibiotics
- ‘Replacement’ pathogens resulting from antibiotics
8
Q
List the sources of wound infection
A
- Direct inoculation
- Airborne contamination
- Haematogenous spread
9
Q
Why should skin shaving occur immediately before surgery and not more in advance
A
Doesn’t give time for staphylococci to colonise small lacerations in the skin
10
Q
Where does MRSA typically colonise
A
- Inguinal
- Perineal
- Axillary
- Anterior nares
11
Q
How may MRSA present
A
- Pneumonia
- Line sepsis
- Surgical site infection
- Intra-abdominal sepsis
- Osteomyelitis
- Toxic shock syndrome
12
Q
How are MRSA carriers treated
A
- Antiseptics e.g. mupirocin to nose
- Antiseptic soap and shampoos
- 3 weeks treatment
- Check swabs at 3 days and 3 weeks after use of antiseptics
13
Q
How are MRSA patients treated
A
- Barrier nurse
- Vancomycin or Teicoplanin are most often used
- Linezolid is a new alternative
14
Q
What is a conventional pathogen
A
Pathogen that may cause infection in the previously healthy person
15
Q
What is a conditional pathogen
A
Pathogen that causes infection in those who have a predisposition to infection
16
Q
What is a opportunistic pathogen
A
Pathogen that is usually of low virulence but will cause infection in the immunocompromised patient
17
Q
What shape are bacilli
A
Rods
18
Q
What shape are cocci
A
Spherical
19
Q
What colour are gram-positive
A
Blue
20
Q
What colour are gram-negative
A
Pink
21
Q
What are coagulase-positive staphylococci known as and what is their significance
A
- Staphylococcus aureus
- More likely to cause infection than coagulase-negative staphylococci
22
Q
What infections is staphylococcus aureus typically responsible for
A
- Superficial infections = boils, abscesses, styes, conjunctiviitis, wound infection
- Deep infection = septicaemia, endocarditis, osteomyelitis, pneumonia
- Food poisoning
- Toxic shock syndrome
23
Q
What infections are Staphylococcus epidermidis associated with
A
Infection in association with foreign bodies:
- Prosthetic valves
- Pacemakers
- Prosthetic joints
- IV lines
- Peritoneal dialysis
- Vascular grafts
- Breast implants
24
Q
Is staphylococcus epidermidis coagulase negative or positive
A
Negative
25
Staphylococcus may cause pneumonia with what histological features
Cavitating lesions
26
Consequences of staphylococcus aureus endotoxin
Causes rapid onset of symptoms
27
How does PVL-producing staphylococcus aureus spread
Associated with community-acquired infections:
- Contact sports
- Sharing towels
28
What antibiotics are active against S. aureus
- Penicillin (90% resistant)
- Flucloxacillin (active against beta-lactamase-producing organisms)
- Erythromycin
- Clindamycin
- Fusidic acid
- Cephalosporins
- Vancomycin
29
How are streptococci and enterococci classified
Lancefield groups - on the basis of polysaccharide antigens on their surface
30
What species of streptococci are responsible for sepsis
Beta-haemolytic strains where colonies completely lyse the blood cells on a cultured plate
31
What does strep pyogenes cause
- Necrotising fasciitis
- Wound infection with cellulitis and lymphangitis
- Tonsilitis and pharyngitis
- Peritonsillar abscess (quinsy)
- Otitis media
- Mastoiditis
32
How should strep pyogenes be treated
- All are sensitive to penicillin
| - Clindamycin may be used second-line
33
Significance of enterococcus faecalis
Causes:
- UTIs
- Abdominal wound infections
- May be isolated from the bile in acute cholecystitis
34
How are enterococci managed
- Sensitive to ampicillin
- Moderately resistant to penicillin
- Resistance to cephalosporins
35
How does Viridans streptococci appear on culture plates
Alpha-haemolysis on blood-containing plates with a green discolouration (hence viridans)
36
Significance of Viridans streptococci
Can colonise abnormal heart valves causing endocarditis
37
What is streptococcus pneumoniae
- Pneumococcus
| - Encapsulated diplococci
38
What may streptococcus pneumoniae cause
- Lobar pneumonia
- Chronic bronchitis
- Meningitis
- Sinusitis
- Conjunctivitis
- Septicaemia (especially in splenectomy patients)
39
What is clostridium perfringens associated with
Gas gangrene
40
What is clostridium difficile associated with
Pseudomembranous colitis
41
How is C. diff diagnosed
Detection of toxin in stool
42
Which antibiotics specifically predispose to C. diff
- Cephalosporins
- Quinolones
- Clindamycin
43
How is C. diff treated
- Metronidazole in mild cases
| - Vancomycin in more serious cases
44
E.coli causes sepsis in
- UTI
- Wound infection
- Peritonitis
- Biliary tract infections
- Septicaemia
45
What is Proteus spp associated with
Staghorn calculi and UTI
46
What toxin does E.coli produce
Viratoxin
47
Clinical features of salmonella infection
- Headache, fever, arthralgia
- Relative bradycardia
- Abdominal pain
- Rose spots on the trunk
48
How is salmonella typically transmitted
Infected meat (especially poultry) and eggs
49
Clinical features of Shigella spp
- Dysentery
- Shigella soneii causes mild illness
- Shigella dysentriae produces endotoxin and severe illness
50
What causes HUS
E.coli 0157
51
Features of campylobacter
- Most common cause of acute infective diarrhoea
- Usually infects caecum and terminal ileum
- Local lymphadenopathy is common
- May mimic appendicitis
- Birds are a reservoir
52
How is Vibrio cholera transmitted
- Contaminated water
| - Seafood
53
How does cholera present
- Sudden onset effortless vomiting
| - Profuse watery diarrhoea
54
Which patients are most susceptible to pseudomonas infection
- Burns
| - Malignancies
55
What does pseudomonas colonise
- Catheters
- ET tubes
- Vascular grafts
56
What are non-capsulated strains of Haemophilus influenzae associated with
- Exacerbations of COPD
| - Bronchiectasis
57
What are capsulated strains of Haemophilus influenzae associated with
Severe illness in children:
- Meningitis
- Epiglottitis
- Osteomyelitis
- Orbital cellulitis
Post-splenectomy sepsis
58
How is H. pylori transmitted
- Faecal-oral
- Oral-oral
- Iatrogenic e.g. endoscopes
59
What conditions are associated with H. pylori
- Gastritis
- Peptic ulceration
- Gastric lymphoma
- Gastric cancer
60
SIRS criteria
- Temp >38 or <36
- Tachy >90bpm
- Tachypnoea >20 or PaCO2 <4.25
- WBC >12 or <4
61
Describe Stage 1 of SIRS
Result of local insult, the local environment produces cytokines which:
- Provoke and inflammatory response
- Promote wound repair
- Recruit reticuloendothelial cells
62
Describe Stage 2 of SIRS
- Cytokines are released into the circulation
- Macrophages and platelets are recruited
- Growth factor is produced
- Acute phase response is controlled by a decrease in pro-inflammatory mediators and release of endogenous antagonists
63
Describe Stage 3 of SIRS
- Occurs if homeostasis is not restored
- Massive systemic reaction and cytokines become destructive
- Dysfunction of various distant organs
64
Define septic shock
Severe sepsis with refractory hypotension
65
Define sepsis
SIRS resulting from documented infection
66
Define MODS
Diagnosed dysfunction of two or more organ systems
67
How may mortality be predicted in sepsis
Proportional to the number of organs that are failing
68
Define a boil (furuncle)
Infection of a hair follicle
69
Define a stye (hordoleum)
Infection in a hair follicle on an eyelid
70
Define a carbuncle
Group of boils interconnected in the subcutaneous tissue by tracts
71
What bacteria is typically responsible for boils, styes, carbuncles
S. aureus
72
Describe Erysipelas
- Spreading infection of the skin due to strep pyogenes
| - Presents as a red, raised indurated area of skin with sharp demarcation
73
Describe Necrotizing fasciitis
- Infection spreads along fascial planes, causing extensive necrosis
- Overlying skin becomes devoid of its blood supply and turns purple/black
74
Where does Meleney's gangrene occur
Site of abdominal surgery or accidental abrasion of the skin
75
Define lymphangitis
Non-suppurative infection of lymphatic vessels that drain an area of cellulitis
76
How does lymphangitis present
- Red, tender streaks along the lines of lymphatics
| - Spreads from site of cellulitis to regional lymph nodes
77
What causes tetanus
- C. tetani
| - Produces neurotoxin that blocks the inhibitory activity of spinal reflexes
78
How does tetanus present
- Facial spasm produces trismus
- Lockjaw
- Arching of neck and back from spasm
- Neck stiffness
79
Define an abscess
A localised collection of pus, walled off by a barrier inflammatory reaction
80
How many air changes per hour do theatres undergo
15 per hour (3 of which are fresh air)
81
Describe air movement in theatres
- Filtered with HEPA filter
| - Enters at ceiling height and leaves at floor level
82
When are laminar airflow systems required
Arthroplasty
83
Define 'clean' surgery
An operation carried out through a clean skin incision under sterile conditions, where the GI/GU/respiratory tracts are not breached
84
Define 'clean-contaminated' surgery
An operation carried out under sterile conditions with breaching of a hollow viscus other than the colon, where contamination is minimal
85
Define 'contaminated' surgery
An operation carried out where contamination has occurred e.g. opening of colon, open fracture, bites
86
What is the wound infection rate in contaminated surgery
15%
87
Define 'dirty' surgery
Operation carried out in the presence of pus or a perforated viscus
88
Risk of wound infection in dirty surgery
>25%
89
How does alcohol work in skin preparation
Denatures proteins
90
Mechanism of action of chlorhexadine
- Causes bacterial cell wall disruption
- Bactericidal
- Most active against gram-positive organisms
91
How long does chlorhexadine have an effect
6 hours
92
Difference between disinfection and sterilisation
Sterilisation is the complete destruction of all viable microorganisms, including spores, cysts and viruses
93
What are destroyed in autoclave
Bacteria, fungi, spores, viruses
94
What monitors the efficacy of autoclave
Brown's tube
95
Role of Bowie-Dickie test
Identifies when equipment is appropriately sterilised
96
Why is moist heat better than dry heat
Penetrates material better and denatures the protein of the cell walls of micro-organisms
97
What is used to sterilise endoscopes and some laparoscopic items
Glutaraldehyde solution
98
Which antibiotic is first-line in animal and human bite injuries
Co-Amoxiclav
99
When is Co-amoxiclav useful as a prophylactic antibiotic
Bowel, hepatobiliary, and GU surgery
100
When is Cefuroxime useful as a prophylactic antibiotic
Used in combination with metronidazole in colorectal and biliary surgery
101
Precautions to be aware of with Cephalosporins
- <10% of those who are penicillin allergic are also allergic to cephalosporins
- Those with renal impairment will require dose adjustment
- Mild transient rise in liver enzymes may occur
102
List the common macrolides
- Erythromycin
| - Clarithromycin
103
What are the first choice antibiotics for severe gram negative infections
Aminoglycosides e.g. Gentamicin
104
What are the side effects of aminoglycosides
- Ototoxicity
| - Nephrotoxicity
105
What type of antibiotic is Ciprofloxacin
Quniolone
106
What is Ciprofloxacin typically used for
- UTIs (especially those that are catheter related)
- Prostatitis
- Skin and soft tissue with P. aeruginosa
- Gram negative chest infections
107
What common drug does Ciprofloxacin potentiate
Warfarin
108
What is Metronidazole active against
- Anaerobes - e.g. bacteroides, clostridia
| - Protozoal organisms - e.g. Entamoeba histolytica, Giardia lamblia
109
What antibiotic causes 'red man syndrome'
Vancomycin
110
When is Clindamycin used in surgery
Skin and soft tissue infections where penicillin is not an option or severe streptococcal cellulitis including necrotising fasciitis
111
Define intrinsic (innate) antibiotic resistance
Occurs when the organism lacks the target site for the agent or is impermeable to the antibiotic
112
Define acquired antibiotic resistance
Refers to organisms that were previously susceptible to the agent in question
113
Antibiotic prophylaxis in biliary tract surgery
Co-amoxiclav
114
Antibiotic prophylaxis in colorectal surgery
Cefuroxime and Metronidazole
115
Antibiotic prophylaxis for GU surgery
Co-amoxiclav or Gentamicin
116
Antibiotic prophylaxis for limb amputation
Penicillin
117
Antibiotic prophylaxis for GU instrumentation
Co-amoxiclav and Gentamicin
118
Which antibiotics inhibit cell wall formation
- Penicillins
| - Cephalosporins
119
Which antibiotics inhibit protein synthesis
- Aminoglycosides
- Chloramphenicol
- Macrolides
- Tetracylines
- Fusidic acid
120
Which antibiotics inhibit DNA synthesis
- Quinolones
- Metronidazole
- Sulphonamides
- Trimethorpim
121
Which antibiotics inhibit RNA synthesis
Rifampicin
122
What type of virus is Hepatitis B
Double-stranded DNA virus
123
What percentage of Hep B patients become chronic carriers
10%
124
Serology for Hep B infected persons and carriers
- HBsAg
| - Anti-HBcAg
125
What does the presence of HBeAg imply
High levels of circulating viral DNA and this high infectivity
126
What serology implies vaccination to Hep B
Anti-HBsAg in isolation
127
What type of virus is Hepatitis C
Single-stranded RNA virus
128
What is the treatment for Hepatitis C
- Interferon-alpha
| - Ribavirin
