bacteriology Flashcards

1
Q

when is blood culture used? what are the sites?

A
  • used to determine antimicrobial resistance
  • sterile sites e.g. blood and CSF
  • non-sterile sites
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2
Q

what is the problem with non-sterile sites?

A
  • usually a lot of bacteria here so culturing is difficult
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3
Q

what is serology used to determine?

A

the body’s response to an infection

so measuring the body’s response by doing a blood at beginning of chickenpox and at end

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4
Q

what do molecular techniques do?

A

detect resistance genes

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5
Q

what does antimicrobial susceptibility testing do?

A

used to test AB resistance

but takes a long time

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6
Q

what are the different types of agar?

A
  • chocolate agar: cooked blood, let’s bacteria use blood nutrients to grow
  • MacConkey agar: designed to grow gram -ve bacteria
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7
Q

describe the cell walls of gram +ve and -ve

A

gram +ve = thick wall, purple stain, retains dye

gram -ve =thin wall, pink stain, loses dye

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8
Q

how can different forms of staphylococci be distinguished?

A

coagulase test to test between coagulase +/- staphylococci

  • coagulase + = staphylococci aureus
  • coagulase - = common skin microbes
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9
Q

what is the normal presentation of staphylocci?

A

form clumps

look like bunches of grapes as they bud divide

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10
Q

what is the normal presentation of streptococci?

A
  • generally forms chains in the gram stain
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11
Q

on blood agar, what are th 2 groups streptococci separate into?

A
  • alpha haemolysis: incomplete haemolysis, turns green e.g. Strep pneumoniae
  • beta haemolysis: complete haemolysis, clears agar
    e. g. Group A - Strep Pyogenes, group B - strep agalactiae
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12
Q

what is important to remember about gram negative bacilli?

A

do not take up gram stain
so appear pink
e.g. E coli

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13
Q

what are the possible causes of diarrhoea?

A
  • bacteria: salmonella, shigella, campylobacter, E. coli, C. difficle
  • parasites: amoeba, giardia, cryptosporidium
  • viruses
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14
Q

what does salmonella, campylobacter and virbrio cholerae look like on agar?

A
  • salmonella: colonies are black due to hydrogen sulphide production
  • campylobacter: can survive at 48 degrees so heat to kill other bacteria
  • virbrio cholerae: cholera makes agar turn green
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15
Q

what is PPV and what does it depend on?

A
  • depends on pre-test probability of the sample being positive
  • more likely a pt is to have disease, more likely a positive test represents a true positive
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16
Q

what is MIC? what is used clinically instead?

A

MIC = lowest amount of AB required to inhibit growth of bacteria in vitro
- use breakpoints clinically which correlate MIC with clinical success as an AM

17
Q

what does it mean when a bacterium has an MIC below the breakpoint?

A

good chance of success with that AB

18
Q

what is a bacterium with a MIC above breakpoint?

A

resistant