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Bacteria Flashcards

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1
Q

What are the 5 steps in Gram stain?

A 
1 - fixation
2 - crystal violet
3 - iodine treatment
4 - decolorization with acetone
5 - counter stain safranin
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2
Q

What organisms are bacterial spores found in?

A

Some Gram +ve

e.g. bacillus, clostridium

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3
Q

three main classes of gram positive cocci

A

staphylococci

  • S. aureus
  • Coagulase negative staph

Streptococci

  • Beta hemolytic (groups A, B, C, F, G)
  • Alpha haemolytic (strep. pneumonia, Viridans streptococci)

Enterococci

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4
Q

What is the shape of staphylococcus?

A

Grape-like clusters

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5
Q

Staph aureus

  • coagulase +ve or -ve?
  • pus forming?
  • what type of infections does it commonly cause?
  • any related syndromes?
A

Coagulase +ve

Pus forming infections

blood stream infections - often device related
Soft tissue infections - cellulitis, impetigo

Toxic illnesses e.g. scalded skin syndrome

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6
Q

Coagulase negative staph

  • examples of species
  • when are they pathogenic?
  • normally present on skin?
  • form biofilm?
A

Lots of different species - Staph epidermis, S capitis

Normally only pathogenic with foreign body - prosthetic joint

Have these on our skin

Form biofilm

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7
Q

Virulence factors of S aureus

A

Cell wall
Protein A - prevents phagocytosis

Coagulase - converts fibrinogen into fibrin which coats bacteria and cells evade phagocytosis

Hyalurorindase - hydrolyses host tissue

Haemolysins

Enterotoxins -> gastroenteritis

Exotoxins -> toxic shock syndrome

Panton-Valentine Leukocyten (PVL) - recurrent boils

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8
Q

Possible causes of very acute food poisoning

A

Staph aureus - 1 hour post

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9
Q

Shape of streptococcus

A

chains

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10
Q

How is beta-hemolysis seen

A

complete hemolysis - can see through it

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11
Q

Group A Strep = strep pyogenes

  • catalase -ve or +ve?
  • infections it causes
  • antibiotic of choice? alternative?
  • Virulence factors
A

Catalse negative

Tonsilitis - strep throat
cellulitis
SST -> necrotizing fascitis
puerperal sepsis

Sensitive to penicillin - macrolides = alternative

Group A most virulent compared to Group C and G

Cell wall - M protein - anti-phagocytic wall protein
Toxins - streptomycin O and S

Streptococcal exotoxins cause rash in scarlet fever and involved in toxic shock syndrome

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12
Q

Group B streptococcus

  • other name?
  • normally found where?
  • infections it causes
A

Strep. agalactiae

normal rectal and vaginal flora

Neonatal meningitis, bacteraemia, pneumonia

Occasionally pathogen in adults if immunocompromised

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13
Q

Enterococci

  • shape
  • where found normally
  • resistant strain?
  • infections it cases
A

Gram +ve cocci in chains (like streptococci)

found in gut

More resistant to antibiotics - vancomycin resistant enterococci (VRE)

Intra-abdominal sepsis, ITU, bacteraemia

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14
Q

Examples of gram+ve bacilli

A

bacillus
Corynebacterium
Listeria

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15
Q

Bacillus anthracis

  • what species does this disease normally affect?
  • What is the reservoir?
  • how are humans infected?
  • pathogenicity
A

disease of herbivores -> human = incidental host

reservoir = soil

infected by cutaneous inoculation (IVDU - contaminated heroine) or inhalation (necrotizing pneumonia)

Multiple toxins and virulence factors

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16
Q

Listeria monocytogenes

  • what infections does it cause?
  • what temperature do they multiply at?
  • Eating what food is risky during pregnancy?
A

meningitis, intrauterine, neonatal

can multiply at 4C

Risk in pregnancy from foods like soft cheese, coleslaw

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17
Q

Corynebacterium diphtheria

  • transmission
  • pathology
  • signs to look out for
  • treatment & prevention
A

transmitted by person-to-person by respiratory droplets

pathology
1 - bacteria in pseudomembrane in throat - potential suffocation
2 - diphtheria toxin produced in throat via bloodstream then inhibits protein syntheses in heart (leading to cardiac failure) and peripheral nerve

Signs: pseudomembrane and bullock

Treatment = antibiotics
Prevention = vaccine
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18
Q

What antibiotic are most anaerobes sensitive to?

A

Metronidazole

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19
Q

Clostridium tetanus

  • transmission
  • pathology
  • symptoms
  • treatment
  • prevention
A

Transmission: spores ubiquitous in soil, soil then contaminates wounds esp. devitalised tissue (falls into manure, open wound contaminated → may present once wound has healed)

Toxin-mediated disease: bacteria produces neuro-toxin → excitation of motor neurones by blocking release of inhibitory neurotransmitter GABA

Symptoms: spasms/rigidity of voluntary muscle e.g. “lock jaw” and autonomic system: hyper-sympathetic state as catelcholamine release not inhibited

No cure

Prevention: vaccine against toxin

Neonatal: baby born → cord may be cut with non-sterile equipment

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20
Q

C botulinum

  • where does infection come from usually?
  • pathology
  • symptoms
  • prevention
A

Usually food-borne: spores germinate in food in anaerobic conditions; IVDU – spore contamination → inflamed injection site

Toxin-mediated disease: neuro-toxin prevents release of acetylcholine

Symptoms: symmetrical flaccid paralysis (cannot open eyes, cannot swallow → respiratory failure) “opposite of tetanus”

Therapeutic use as Botox

Prevention: standards of food preparation

Must notify public health when found!

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21
Q

C difficile

  • major cause of what infections?
  • transmission
  • severe cases
A

Major cause of health-care associated infection

Transmission: ingestion of spores in (hospital) environment.; spores survive alcohol
Prevention: reduced host susceptibility (antibiotic prescribing) & reduced exposure by cleaning

Severe cases – “pseudomembrane”

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22
Q

Clostridium perfringens

  • what infections does it cause?
  • transmission?
  • pathology?
Study These Flashcards
A

Gas gangrene and other soft tissue infections

Transmission: spores ubiquitous in soil and human gut

Toxin-mediated disease: main toxin is α-toxin. This is lecithinase – damages cell membranes inc. haemolysis
-Other toxins have more minor role

23
Q

Gram negative cocci

Study These Flashcards
A

Neisseria gonorrhoeae

Neisseria meningitidis

Moraxella cattharalis (COPD exaccerbations)

Other (Commensal) Neisseria in the mouth

24
Q

Neisseria gonorrhoeae

- shape

Study These Flashcards
A

Gram -ve, diplococci

25
What kind of rash is seen in Neisseria gonorrhoeae infection?
non-blanching
26
Common features of Aerobic Gram negative Bacilli
Lipopolysaccharide (LPS) – endotoxin Sometimes protein exo-toxins implicated The very common ones are major hospital pathogens and acquire antibiotic resistance easily Resistance to some antibiotics
27
Escherichia coli - is it normally found in gut? - which strain may cause HUS? - What infections are commonly caused? - Is resistance to antibiotics an issue?
Normal human gut flora: E coli = commonest aerobic GNB, rod in gut E coli O 157→ lethal toxins → haemolytic-uraemic syndrome Most strains cause UTI - P fimbriae – filamentous surface organelles → increases virulence - Capsule protects against phagocytosis - Hemolysin production Common cause of bacteraemia secondary to UTI of gut perforation - Enterotoxigenic → enterotoxin (ST) → large volume fluid secretion into gut lumen via cAMP activation - Enteropathogenic E-Coli binds to intestinal cells → structural damage & moderate (or in case of enteroinvasive E-Coli significant) invasive component → enteritis & large volume diarrhoea & fever. Resistant to many antibiotics used to treat gram +ve infections & acquire resistance rapidly- recognised as producing beta-lactamases
28
Klebsiella - what infections does it cause? - Treatment?
Klebsiella = 2nd commonest coliform causing UTI and bacteraemia etc. Hospitals: often antibiotic-resistant, spread easily between patients Many other “cousins” – enterobacter, proteus citrobacter, serratia
29
Salmonella and Shigella - what infections does it cause? - hosts of salmonella?
Important causes of gastroenteritis Shigella – human reservoir only → Causes colitis Salmonella – multiple species whose hosts include all mammals, birds, reptiles → special human one is S typhi, cause of typhoid Salmonella: spectrum of invasiveness S typhi: highly invasive, causes typhoid, control exposure to human faeces S typhimurium and S enteritidis: gastroenteritis
30
Non-typhoid salmonella gastroenteritis - what bacteria is the most common cause? - what animal harbours it?
S enteridis and S typhimurium commonest Salmonella common in poultry, destroyed by proper cooking Reptiles pets harbor other Salmonella
31
Pseudomonas aeruginosa - reservoir? - what infections does it cause? - what are the RF for infection?
Most important non-fermentor Reservoir: environment especially water Human respiratory pathogen where biofilms form - Cystic Fibrosis (CF) - Ventilator assoc pneumonia in ITU Bacteremia in immunocompromised e.g. leukaemia Common colonizer e.g. leg ulcers (biofilm)
32
Burkholderia cepacia - reservoir - what patient group is at risk of infection?
An important non-fastidious non-fermentor Long recognized as plant pathogen Reservoir: soil, plants Now a pathogen in CF - Very difficult to treat & reduces survival
33
Vibrio Cholerae - reservoir - pathology - culture agar used? - treatment
Reservoir: (warm) salt water Toxin-mediated disease. increased cAMP within cells: reduced Na uptake and increased Cl secretion → massive water loss – “rice water stool” →Profuse watery diarrhoea Death from dehydration & electrolyte imbalance Selective agar: TCBS (alkaline, lots of salt) Treat with oral re-hydration as Na/glucose transporter not affected
34
Campylobacter - what infection does it cause? - symptoms? - natural hosts? - treatment?
Commonest bacterial cause of bacterial diarrhoea in UK Diffuse diarrhea, may be bloody Natural host = birds - Carried in 80% of chickens Lab - best results with incubator at bird temp (42C) rather than human temp (37C) Self-limiting so antibiotics not usually advised – quinolones effective
35
Haemophilus Influenzae - what infections does it cause? - what agar should be used?
Unencapsulated strain are common: respiratory tract e.g. COPD, pneumonia (especially in smokers) Capsulated serotype b (Hib) → meningitis in young children. Now rare in UK due to vaccine Cultivation chocolate agar
36
Legionella - when did it first outbreak? - what infection does it cause? - diagnosis?
1976: outbreak of pneumonia - US Legionnaires, conference, Philadelphia Causative organism now a recognized cause of sever pneumonia Difficult to grow in lab - Grows slowly on enriched agar Lab diagnosis: urinary antigen or PCR Lives in natural and engineered water systems, inside amoebae - Contaminated water reservoirs Temperature control – cold water below 25C and hot water above 51C
37
Helicobacter - shape, gram stain - what does it infect? - pathology
Gram –ve, helix shaped rod Infects antrum Produces urease, hydrogenase. Breaks down urea to ammonia. Buffers stomach acid, allowing it to survive in stomach increased gastrin & gastric acid→ inflammation of gastric mucosa leading to ulceration (Cag A gene)
38
Gram Negative Anaerobes - commensals where? - what infections are they involved in?
Commensals of gut, mouth, etc Difficult to grow as the majority die in contact with oxygen Involved in poly-microbial infections e.g. abscesses, peritonitis
39
Bacteroides: - infections caused? - treatment?
Associated with intraabdominal, skin & soft tissue infections below the waist Resistant to peniciliin
40
Fusobacterium - shape - infections caused
Long filamentous rods Head and neck infections including brain abscesses Mixed intraabdominal infections Perirectal abscesses
41
Mycoplasma pneumoniae | - what infection does it cause?
Very small bacterium, no cell wall A common cause of pneumonia word-wide
42
Rickettsia - what type of microbe is it? - infections it causes? - R ricketsia - how is it transmitted?
Obligate intracellular parasites Predilection for endothelial cells with skin lesions and vasculitis Multiple hosts, geographical restrictions R. rickettsii – rocky mountain spotted fever - Maintained in animal reservoirs - Transmitted by ticks & lice
43
Candida | - type of infections it causes?
Athlete’s foot Mucosal - Oropharyngeal candidiasis; Candida oesophagitis; Vulvovaginitis Candidemia – high mortality; complications: Infective endocarditis; Endopthalmitis: treatable cause of blindness; Hepatosplenic candidiasis
44
Aspergillus species
Allergic bronchopulmonary aspegillosis (ABPA) Invasive Aspergillosis - Pulmonary or extrapulmonary - Post-transplant - Post-chemotherapy - High mortality - Monitoring using galactomannan antigen
45
Cryptococcus neoformans - RF for infection - infections it causes
Immunocompromised AIDS defining illness Fungaemia Meningitis
46
Pneumocystis jirovecci
Immunocompromised → Severe pneumonia (main feature is hypoxia); Transplant: prophylaxis; AIDS
47
Prions - pathology - What does it cause? - how does it spread?
Proteinaceous infectious agents Comprising single host-coded protein (PrP) protein folded abnormally “infectious” by causing refolding of other molecules - Forms fibrils in brain - Resistant to inactivation by physical or chemical methods Probable cause of CJD and nvCJD Spread by eating contaminated food, use of contaminated medical products or surgical instruments Prions can cross species barrier
48
Poliovirus - what type of virus is it? - structure - where does it replicate? - what can it infect? - presentation?
ss+ve RNA strand Non-enveloped icosahedron made up of 4 capsid proteins Replicates in cytoplasm Infects gut and replicates in GALT (gut-associated lymphoid tissue) Can infect (and destroy) motor neurons Asymptomatic/ mild-infections in approx. 99% of cases Meningitis Paralytic poliomyelitis (1:1,000 of poliovirus infections in children) WHO polio eradication set for 2005, not yet reached
49
Herpes simplex virus - what type of virus is it? - structure? - where does it replicate? - what can it infect?
dsDN Enveloped icosahedron (162 capsomeres) Replicates in nucleus Infects epithelium, enters and ascends axons Establishes latent infection (non- integrated) in neural ganglia Reactivation results in descent along same axons and replication in epithelium (‘cold sore’)
50
Possible causes of bloody diarrhoea
``` Shigella (usually travel related) Salmonella Campylobacter E coli 0157 (UK) Amoebic dysentery (travel related and seen in men who have sex with men) ```
51
What are gram +ve organisms most sensitive to?
penicillin | vancomycin
52
Staph. aureus - what mediates methicillin resistance?
mec operon | - PBP altered
53
Gram +ve rods
ABCDL ``` Actinomyces Bacillus anthraces Clostridium Diptheriae Listeria monocytogenes ```

Infection (8 decks)

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