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Phase 2A > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Function of the bacterial cell wall

A

strong outer cover that maintains bacterial shape & protects against osmotic pressure

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2
Q

Ways bacteria may use its morphology to survive (3)

A
  • having a **capsule** that protects against phagocytosis
  • flagella (longer) or pili / fimbriae (shorter) that enables them to move or deliver toxins to host
  • **two membranes** for protection
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3
Q

Describe the variations in cell wall structure accounting for gram-positive and negative staining

A

pos = single ; neg = double

gram positive = thick, single peptidoglycan layer made of repeating sugar subunits cross linked by peptide chains in cell wall

gram negative = thin peptidoglycan layer & an additional outer membrane containing lipopolysaccharides = endotoxins

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4
Q

Function of flagella on bacteria

A

allows for movement

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5
Q

Function of fimbriae / pili on bacteria

A
  • allow bacteria to adhere to cell surfaces & exchange plasmids with other bacteria
  • allows for the delivery of endotoxins to host (?)
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6
Q

Ways bacteria can be classified

A

Shape, staining, biochemical tests, sensitivity tests & culture techniques

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7
Q

Round, spherical bacteria are known as?

A

Coccus / cocci

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8
Q

Rod bacteria are generally known as?

A

Bacilli

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9
Q

Curved rod bacteria are known as?

A

vibrio

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10
Q

Spiral rod bacteria are known as?

A

spirochaete

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11
Q

Temperature range for bacterial survival, and for spores>

A

-80 to +80 degree Celcius, spores = up to 120 degree Celcius

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12
Q

How do you measure growth rate of bacteria?

A

Measured by shining light on bacteria and measuring absorption

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13
Q

Briefly describe the three ways bacteria performs gene transfer

A
  • transformation - pick up DNA from environment - via plasmid
  • transduction - when virus infects bacteria - via phage
  • conjugation - exchange of plasmid between bac cells - via sex pilus
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14
Q

How does bacteria achieve genetic variation (3+3)

A
  • mutations: baseline substitution, deletion, insertion
  • gene transfer: transformation, transduction, conjugation
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15
Q

How does the gram stain differentiate bacteria?

A

PINK = negative = double membrane bacteria = endotoxins and exotoxins

PURPLE = positive = single membrane bacteria = exotoxins only

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16
Q

Briefly describe the gram staining technique?

A
  • heat fix sample to slide
  • add methyl violet (blue / purple)
  • add iodine → fixes methyl violet to gram pos samples
  • add alcohol to decolorize gram neg samples
  • counterstain with basic fuschin (red)
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17
Q

What does it mean if the gram stain returned positive?

A
  • sample will be purple
  • sample is a single membraned bacteria which will produce exotoxins only
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18
Q

What does it mean if the gram stain returned negative?

A
  • sample will be pink
  • sample is a double membraned bacteria which will produce both exo and endotoxins
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19
Q

What are endotoxins?

A
  • Component of the outer membrane of bacteria that is released when bac is damaged
  • Specific components of this is recognised by the immune system → will have huge reaction = endotoxic shock
  • Work is non-specific
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20
Q

What are exotoxins?

A
  • proteins secreted by both bacteria.
  • action is specific: inhibit (botulism) or stimulate (tetanus) nervous system
  • unstable exposure to heat
  • can be converted to a toxoid → non-active toxin
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21
Q

What colour will the bacteria stain with Gram stain if it only produces exotoxins?

A

Purple = gram-positive bacteria = single membrane

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22
Q

What colour will the bacteria stain with Gram stain if it produces both endotoxins and exotoxins?

A

Pink = gram-negative bacteria = double membrane

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23
Q

When should you not use the gram stain to group bacteria (i.e. when will it not work)

A
  • for cell walls that contains mycotic acids (‘acid fast bacilli’) which the gram stain cannot get in to
  • e.g. mycobacteria spp.

→ Ziehl-Neelsen staining should be used

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24
Q

What stain is used for mycobacteria spp.?

A

Ziehl-Neelsen staining
result = red or blue

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25
Q

What does it mean if an organism stains blue on Ziehl-Neelsen stain?

A

= non acid fast bacteria = not mycobacteria spp.

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26
Q

What does it mean if an organism stains red on Ziehl-Neelsen stain?

A

= mycobacteria spp as they are acid fast so will retain the red/pink dye

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27
Q

Why is gram staining not used for mycobacteria spp.?

A

cell wall of mycobacteria contains mycolic acids - hard to penetrate for gram stain

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28
Q

6 species of gram positive bacteria

(Sexy Students Can Look Bad Come morning!)

A

Streptococcus, staphylococcus, corynebacterium, listeria, bacillus, clostridium

sexy students can look bad come morning

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29
Q

Ideas for gram positive bacilli?

A
  • bacillus
  • corynebacteria
  • listeria

& anaerobic bacilli

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30
Q

Ideas for gram positive cocci?

A
  • Staphylococci
  • Streptococci
  • Enterococci
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31
Q

What will the gram test results be for Streptococcus spp. ?

A
  • positive (purple) (single layer)
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32
Q

What does the catalase test differentiate between?

A
  • Staphylococci → positive
  • Streptococcus & enterococci → negative
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33
Q

What is the catalase test?

A

Catalase = enzyme following 2H2O2 → 2H2O + O2

Tests if bacteria produces the catalase which protects Staphylococci against hydrogen peroxide (converts it to gas and water = gas bubbles)

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34
Q

Which bacteria spp will test positive for the catalase test and how will it return?

A

Staphylococci → positive

When placed in hydrogen peroxide it will produce gas bubbles where others will have no reaction

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35
Q

Which bacteria spp will test negative for the catalase test and how will it return?

A

Streptococcus & enterococci → negative

When placed in H2O2 it will not have any reactions

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36
Q

What is haemolysis and what will the test for?

A

haemolysis = RBC breakdown in blood agar

tests are done in blood agar, if positive it is mostly to group bacteria according to antigen groups (e.g. alpha, beta & gamma), or no haemolysis

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37
Q

What is the optochin test and what does it test for?

A
  • Optochin = chemical used for identification of streptococcus pneumoniae from other alpha haemolytic streptococci
  • disc is placed in agar & formation of inhibition zones (lysis) is the test
    formation = positive = strep pneumoniae;
    no inhibition = other alpha haemolytic strp
38
Q

How will streptococci spp. test for

  • catalase test?
  • optochin test?
A

catalase: ❌ negative (only staph is pos)

optochin:
strep pneumoniae will be ✅ positive
other alpha haemolytic strep will be ❌ negative

39
Q

How would you differentiate between the alpha and beta haemolytic groups of strep?

A

Using the blood agar (mammalian blood)

40
Q

How would alpha haemolytic (viridians) streptococci present on blood agar?

A

greenish white colonies
due to partial erythrocyte and Hb breakdown

41
Q

How would beta haemolytic streptococci present on blood agar?

A

yellowish white, opaque colonies
due to complete erythrocyte lysis

strep pyogenes & agalactiae!

42
Q

How would gamma haemolysis present on blood agar?

A

dotted / no colonic growth

43
Q

How would you further classify alpha haemolytic streptococci?

A

Optochin test - differentiates stroptococci pneumoniae from other alpha haemolytic streptococci

44
Q

How will the optochin separate streptococci pneumoniae from the rest?

A

Streptococci pneumoniae are sensitive to optochin → lysis (clear zone no growth) = positive

45
Q

How will other alpha haemolytic streptococci appear on optochin?

A

there will be growth as not sensitive = no lysis

46
Q

How would you further classify beta haemolytic streptococci?

A

Lancefield grouping, by detecting surface antigens

(so, aka Antigenic grouping)

47
Q

Important groups in Lancefield Grouping & ex?

A

A - Strep pyogenes

B - Strep agalactiae

D - Enterococcus genus

48
Q

Strep pneumoniae - tests? diseases? tx?

A

gram pos, optochin sensitive

community acquired pneumonia, bacterial meningitis, COPD exacerbate, sinusitis, otitis media

penicillin or erythromycin

49
Q

alpha haemolytic streptococcus - test? disease? tx?

A

group
alpha haemolysis = green colonies on blood agar

bacterial endocarditis, dental caries

penicillin / amoxicillin
b. endocarditis = penicillin & gentomycin

50
Q

enterococcus spp. - test? diseases? tx?

A

non haemolytic, Lancefield group D, McConkey growth

Infective - endocarditis, UTI, wound, IV catheter

penicillin / vancomycin (± gentamycin)

51
Q

🌟 General treatment options for streptococcus spp.?

A

penicillin / amoxicillin
erythromycin if allergic
erythromycin / vancomycin if resistant

52
Q

What does the MacConkey agar test for?

A

isolates & identifies enteric bacteria,
as it contains

bile salts - only permits growth of enteric bacteria

lactose & pH indicator - fermentation fo lactose produces an acidic environment → red / pink color

53
Q

What does the color change mean on MacConkey agar?

A

pH indicator, as if lactose fermenting, will produce an acidic environment

54
Q

Which bacteria will grow red / pink colonies on MacConkey agar?

A

E coli, Enterococcus spp., Klebsiella spp.

55
Q

Which bacteria will turn MacConkey agar clear / yellowish but will grow in colonies?

A

Salmonella spp., Shigella spp., Psuedomonas spp

56
Q

Which bacteria will turn MacConkey into a pinkish colour but will have no growth?

A

Staphylococcus aureus (latin for gold!)

57
Q

Which test separates Staphylococcus aureus from other staph spp.?

A

Coagulase test

58
Q

How does a coagulase work?

A

coagulase = enzyme causing fibrin to clot, preventing phagocytosis;
so test is bacteria sample + plasma

only staph aureus will form a clot, every other staph = no clot

59
Q

Staphylococcus aureus. - test? disease? tx?

A

catalase positive, coagulase positive (only staph to be)

skin infections, osteomyelitis, septic arthritis, septicaemia, bac endo, conjunc, pneumonia, toxic shock!

flucloxacillin, if MRSA = vancomycin

60
Q

Listeria spp. - tests, diseases, tx?

A

gram pos

  • *pregnancy** - miscar and still-b;
  • *young old immunecomp** - pneumonia, meningitis, encephalitis, sepsis

tx ampicillin / erythromycin and gentamycin

61
Q

Tetanus - bac name, transmission, present, treat?

A

clostridium tetani - transmit through spores entering open wounds!

tx - human tetanus immunoglobulin, benzodiazepines!

62
Q

How would tetanus present?

A

SPASMS and CONTRACTS

  • locked jaw - trismus
    • if sustained - sardonic smile - risus sardonicus
  • persistent spam of the back muscles - opisthotonos
  • painful contraction and spasms at site of injury
  • flunctuating BP, tachy, arrhy, fever
63
Q

Tx tetanus?

A

IV high dose benzodiazepine for spasms

human tetanus immunoglobulin

antimicrobial to mop up remaining: penicillin, metronidazole

64
Q

Benzodiazepine - ex, mechanism?

A

facilitate and enhance binding of GABA to receptor → systemic synaptic transmission depression

ex diazepam, lorazepam, midazolam

65
Q

clostridium difficile - disease, transmission, tx?

A

pseudomembranous colitis - diarrhoea following antibiotic therapy

trans - spores via faecal-oral route

tx vancomycin

66
Q

clostridium botulinum - disease, transmission, tx?

A

botulinism - descending paralysis secondary to botulinum toxin

trans - food ingest, wound contamination

tx - vancomycin or metronidazole

67
Q

Free card

A
68
Q

Gram negative stains?

A

pink!

69
Q

6 important gram neg bacteria?

A

neisseria spp
enterobacteriaceae
parvobacteria
helicobacter spp.
vibrio spp.
pseudomonas spp.

70
Q

gram negative cocci - ideas?

A

neisseria

moraxella

anaerobic cocci

71
Q

gram negative bacilli - ideas?

A

e. coli
campylobacter
pseudomonas
salmonella
shigella
proteus

72
Q

If a gram negative bacilli is lactose fermenting what could they be?

A

in pink colour!

e coli or klebsiella pneumoniae!

73
Q

If a gram negative bacilli stains pale / yellow in McConkey agar with growth what could they be?

A

Shigella, salmonella, proteus

74
Q

If a gram negative bacilli does not grow or turn MacConkey agar into any colour what could they be?

A

Pseudomonas or vibrio

75
Q

Neisseria meningitidis - special presenting feature?

A

If meningitis triad (fever, headache, neck stiffness / leg pains, photophobia) + purpuric rash = this bacteria as it is most likely to cause rash

or septicaemia :’)

76
Q

tx neisseria meningitidis?

A

cefotaxime or benzylpenicillin

close contacts rifampicin, ciprofloxacin or ceftriaxone

vaccine for A & C strain available

77
Q

Neisseria gonorrhoea - disease, trans, tx?

A

direct mucosal contact

gonorrhoea, reiter’s syndrome (urethritis, conjunctivitis and arthritis)

tx ciprofloxacin or cefixime

78
Q

free card

e coli treatment is dependent on site

A

UTI: trimethoprim

Pneumonia: Cephalosporin

79
Q

Klebsiella pneumonia - disease, tx?

A

Hospital acquired pneumonia, UTI, neonate meningitis

tx cephalosporins

80
Q

Typhoid & paratyphoid - cause, aka, trans, tx?

A

Salmonella typhi and paratyphi (A, B & C)

aka enteric fever

trans - faecal oral

tx - ciprofloxacin

81
Q

Salmonella enteritidis - disease, trans, tx?

A

causes ‘salmonella’ or gastroenteritis ± bacteraemia

inadequately cooked food contaminating w/ infected animal faeces, e.g. poultry & eggs

self limiting disease!

82
Q

Shigella dysenteriae - trans, disease, tx?

A

faecal-oral

bacillary dysentry

ciprofloxacin

83
Q

Campylobacter jejuni & coli - trans, disease, tx?

A

trans - contaminated poulty (jejuni) or pig meat (coli), unpasteurised milk

most common cause of diarr in england + wales!!!!

gastroenteritis ± dysentery / reactive arthritis / guillan barre (watery diarr + CNS)

tx - self limiting but if severe cirpofloxacin

84
Q

summary of food poisoning / diarrhoea related bacteria (and virus?) !

A

salmonella, shigella, campylobacter jejuni, norovirus (elderly), rotavirus (child)

85
Q

Proteus mirabellis - disease, tx?

A

UTI in young females (‘mirabelles’), wound and IV catheter infection

tx trimethoprim

86
Q

Haemophilius influenza - disease, tx, special?

A

mening, pneumo. osteomy + septic arth. acute epiglottitis, otitis media, cellulitis

cefotaxime or ceftriaxone

if children + non-typable = this. rare tho coz HiB vaccine

87
Q

Whooping cough - cause, trans, tx?

A

NOTIFIABLE

bordetella pertussis

airborne droplet transmission

diagnose ELISA for pertussis toxin
tx clarythromycin, erythromycin

88
Q

Severe pneumonia with a high fever, has been near warm water (AC units, water tanks) recently - bacteria, trans, tx?

A

Legionella pneumophila
= Legionnaires disease (pneumonia), also causes Pontiac fever = flu like illness

inhalation of aerosolised droplet (also holiday home shower)

tx - erythromycin but if severe rifampicin or cirpofloxacin

89
Q

Helicobacter pylori - everyone’s fav

disease, trans, tx

A

chronic gastritis, duodenal and gastric ulcers

tx Clarithromycin, amoxicillin / metronidazole + PPI (omeprazole)

90
Q

Cholera - type of bacteria, location, trans, present, tx?

A

vibrio cholerae

in water & seafood, transmit through faecal-oral & seafood

present = rice water diarrhoea, up to 25 litres fluids lost per day

tx = rehydrate, severe = ciprofloxacin

91
Q

pseudomonas aeruginosa - diseases, trans, tx?

A

pneumonia esp in those with cystic fibrosis
UTI & catheter infections
wound / burn / IV line infect

trans is hand borne & thru direct contact

tx fentamycin or ceftazidime
if child with CF / adult with bronch then ciprofloxacin

Phase 2A (12 decks)

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