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Microbiology/Infectious Disease > Bacteria > Flashcards

Bacteria Flashcards

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Biology 101 flashcards
1
Q

What is a commensal?

A

Organism that colonises the host but causes no disease in normal circumstances

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2
Q

With gram stain, what colour will gram negative and gram positive bacteria stain

A

Gram negative = pink

Gram positive = Purple

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3
Q

What type of organism are bacteria?

A

Prokaryotes- have no nuclear membrane

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4
Q

What is the purpose of their outer capsule?

A

Prevents phagocytosis/ recognition by complement

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5
Q

What stain would you use for mycobacteria?

A

Ziehl-Neelson

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6
Q

Which type of bacteria has a single cytoplasmic membrane?

A

Gram +ve

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7
Q

In gram -ve bacteria, what lies between the two membranes?

A

Periplasmic space

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8
Q

Is there more peptidoglycan in gram +ve or gram -ve bacteria?

A

Gram +ve

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9
Q

What types of organisms produce spores?

A

Fungi and gram +ve bacteria (in hard conditions)

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10
Q

Give the doubling time for each of the following:

a) e.coli/staph aureus
b) fungi
c) viruses
d) mycobacteria tuberculosis and leprae

A

a) 20-30min
b) 30 min
c) under 1 hour
d) 24 hours and 2 weeks

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11
Q

What are the 4 stages in the growth curve for bacteria dividing by binary fission?

A
  1. lag
  2. exponential
  3. stationary
  4. death
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12
Q

Give 4 ways in which genetic variation occurs in bacteria

A
  1. Mutation (base substitution, insertion, deletion)
  2. Plasmid
  3. Conjugation (via sex pillus)
  4. Transduction (virus vector - bacteriophage)
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13
Q

What is added to crystal violet to fix it to cell walls in the gram stain?

A

Iodide

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14
Q

Why do gram -ve bacteria turn pink?

A

Decolouriser (ethanol/acetone) interacts with lipids and the cells lose their outer LPS membrane and therefore CVI complexes, so pick up counterstain instead (safranin)

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15
Q

What does the catalase test distinguish between?

A

Staphylococcus (+ve) and streptococcus (-ve)

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16
Q

What does the coagulase test distinguish between?

A

Staph. aureus (+ve) and other types of staphylococcus (-ve)

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17
Q

What organisms will ferment lactose on CLED agar, and what is the colour change?

A

E.coli, Klebsiella, Citrobacter, enterobacter

Colour change = blue –> yellow

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18
Q

Name 4 antibiotics that MRSA is resistant to

A

B-lactams, gentamycin, erythromycin, tetracycline

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19
Q

How is staph. aureus spread?

A

Aerosol and touch

20
Q

Name 4 virulence factors of staph. aureus

A
  1. Pore forming toxins
  2. Proteases - EXFOLIATIN (cadherin desmoglein)
  3. TSS toxin –> cytokine release
  4. Protein A binds Ig’s wrong way so can’t be recognised
21
Q

Name at least 5 assosciated conditions of staph. aureus

A
  1. Septicaemia
  2. Endocarditis
  3. TSS
  4. Scalded skin syndrome
  5. Infected implants
  6. Pneumonia
  7. Absesses/wound infections
  8. Impetigo
  9. Osteomyelitis
22
Q

What is the main virulence factor of S.epidermidis?

A

Forms biofilms

23
Q

What is s. saprophyticus usually associated with?

A

UTI

24
Q

What class of streptococcus does S. pyogenes fall into?

A

B-haemolytic

25
Q

In the Lancefield grouping system, which group would S.pyogenes and S. agalactiae fall into?

A

A

B

26
Q

Give 3 examples of infections caused by S. pyogenes

A
  1. Tonsilitis/pharygitis
  2. Wound infections –> cellulitis
  3. Impetigo

complications: rheumatic fever, glomerulonephritis

27
Q

Give 3 predisposing factors to S.pneumoniae infection

A
  1. Impaired mucus trapping
  2. Hypogammaglobulinaemia
  3. Asplenia
28
Q

Give 3 main virulence factors of S.pyogenes

A
  1. M protein on surface (complement degradation)
  2. Capsule
  3. Enzymes and toxins released (Streptolysins O&S)
29
Q

How does S. pneumoniae appear under the microscope?

A

Draughtsman colonies

30
Q

Give the 2 main virulence factors of S.pneumoniae

A
  1. Polysaccharide capsule

2. Cytotoxin (pneumolysin)

31
Q

What is viridans streptococci a collective name for? And what conditions can they cause?

A

Oral streptococci - dental caries/abscesses and deep organ abscesses (brain liver)

32
Q

Strep. sanguinis and strep. oralis are both classed as viridans streptococci and are important in what clinical condition?

A

Infective endocarditis

33
Q

What group of bacteria within Viridans strep. are the most virulent?

A

‘Milleri group’ - s. intermedius. s. anginosus, s.constellatus

34
Q

A child is brought into clinic with malaise, severe sore throat, fever for two days. Lymphadenopathy is noticeable. The child also has very rapid breathing. On examination there is a thick grey membrane on tonsils. Swab showed gram positive rods. What is the most likely cause, and how would you treat this?

A

Corynebacterium dipheriae - treated with anti-toxin and erythromycin

35
Q

What type of vaccine is given for diptheria?

A

Toxoid

36
Q

How is diptheria spread and what organism causes it?

A

Droplet spread, caused by corynebacterium dipheriae

37
Q

What is a virulence factor?

A

Any product or strategy that contributes to the pathogenicity

38
Q

Using an optochin test, if the area around the optochin disc was clear, what bacteria would this therefore be?

A

Strep. pneumoniae (otherwise would be strep viridans)

39
Q

Looking at cell surface antigens of gram negative bacteria; Shigella would be easy to identify. Why is this?

A

Shigella do not have flagella so no H antigen would be present

40
Q

Give the 3 principal infections of e.coli

A
  1. Wound infections (surgical)
  2. UTI (cystitis or cathetirisation)
  3. Gastroenteritis
41
Q

Describe the virulence mechanism for ETEC

A
  1. Heat labile toxin (LT) secreted by e.coli
  2. Taken up by s.i.
  3. Binds to Gs and adds ADP
  4. Stimulates adenylate cyclase which increases production of cAMP, and then increases PK-A
  5. This secretes Cl- into the lumen, H2O follows
42
Q

Describe the virulence mechanism for EHEC/EPEC

A
  1. Bundle forming pili on bacteria attach to microvilli
  2. Effector protein injected into cell using T3SS
  3. Creates Tir (translocated intimin receptor) on surface which binds to intimin on ecoli
  4. This combined with actin rearrangement forms a pedestal
43
Q

What is the main symptom of shigellosis?

A

Severe bloody diarrhoea

44
Q

How does shigella invade the colonic mucosa?

A

Induces its own uptake, causes macrophage to apoptose, releasing cytokines and recruiting PMN, which further damages the epithelium. Moves into adjacent cells via basolateral membrane.

45
Q

How is shigella spread?

A

From person to person or in contaminated water or food

46
Q

Give two potential effects of shiga toxin on the body

A
  1. Hydrolyses 28s rRNA, which blocks protein synthesis and kills cells
  2. If absorbed systemically, will target the kidney and cause HUS (haemolytic uraemic syndrome) which is microvascular thrombosis in the kidneys. Leads to kidney failure
47
Q

What are the two most likely bacterial causes of cellulitis

A
  1. S. aureus

2. Beta-haemolytic strep

Microbiology/Infectious Disease (5 decks)

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