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MCDone > Bacteriology > Flashcards

Bacteriology Flashcards

1
Q

Common diagnostic techniques for bacteria

A

Cultures
Serology
Molecular techniques
Antimicrobial susceptobility testing

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2
Q

2 different types of culture

A

Sterile- like blood and CSF
Non sterile sites- sites of infection
NOTE- skin is not sterile as million of commensal bacteria here

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3
Q

How are blood cultures tested as positive

A

The blood is put in tubs containing nutrients for bacteria and intubated at 37C- they are left and after time the bacteria produce waste products that change the colour of indicator at the bottom of the tubs

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4
Q

What happens to tubs containing blood cultures after their intubation

A

They are put in a machine with sensors to tell if there is a change in the colour of the indicator

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5
Q

What do you do if blood tests positive for bacteria and why

A

Carry out gram staining to work out what antibiotics would be best appropriate

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6
Q

Gnerally speaking where do gram positive infect

A

Skin and soft tissue

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7
Q

Generally speaking where do gram negative bacteria infect

A

abdomen and urinary tract

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8
Q

Cases where should give antibiotics regardless of if tests have come back

A

Meningitis and meningococcoal spticaemia

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9
Q

Why can you use non-selective agar plates for blood cultures

A

Blood should be sterile anyway

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10
Q

What is chocolate agar

A

Where the blood on agar is cooked

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11
Q

Why is chocolate agar cooked

A

Some bacteria are unable to lyse to RBCs to gain nutrients so cooking blood does this for them

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12
Q

Common example of bacteria growing on chocolate agar

A

Haemophilus influenzae

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13
Q

What grows on macconkey agar

A

Gram negative bacteria

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14
Q

Problem of gram negative bacteria

A

Most antibiotics target cell wall which in gram negative bacteria antibiotics are unable to reach because of its lipopolysaccaride outer membrane

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15
Q

Most common bacteria seen

A

gram positive cocci- easy to identify on cultures as have distinguishable growing pattens which can help drive antibiotic treatment

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16
Q

Growing pattern of staphylococci

A

Divide in 2 and from clumps of four- they look like a bunch of grapes

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17
Q

Growing pattern of streptococci

A

Divide end on end so form chains

18
Q

Test carried out on staphylococci bacteria

A

Coagulase test

19
Q

What is purpose of coagulase test

A

Distinguish between virulent staphylococci and commensal bacteria

20
Q

Positive coagulase test

A

This indicates virulence as coagulase is virulence factor

21
Q

Negative coagulase tests

A

Sign of commensal bacteria

22
Q

Test carried on streptococci bacteria

A

Haemolytic test- depends on how they appear on blood agar

23
Q

Potential results of haemolytic agar tests

A

Can either be alpha or beta haemolysis

24
Q

Alpha haemolysis test result

A

Appear green as there is incmplete haemolysis

25
Q

Beta haemolysis

A

Clear agar as complete heamolysus

26
Q

3 main bacteria stool is tested for in diarrorhoea

A

Salmonella
Shigella
Campylobacter

27
Q

What tests are used to diagnose C.difficile

A

Antigen and toxin gene PCR

28
Q

Why arent cultures used to diagnose C.difficile

A

Very difficult to grow hence the name so use detection of their toxin

29
Q

Test for salmonella

A

Grow on XLD agar

30
Q

Positive salmonella test

A

Goes pink as unable to ferment xylose.
Black colonies also form as salmonella forms hydrogen sulfide
VERY SPECIFIC TEST

31
Q

Negative salmonella test

A

Goes yellow as other bacteria are unalbe to ferment Xylose

32
Q

Campylobacter test

A

Intubate stool sample at 42 degrees as campylobacter able to grow at this temperature. Then put remaining bacteria on a selvetive agar and see if grows

33
Q

Test for cholera

A

Grow on TCBS agar- green if postive

34
Q

What is minimum inhibitory concentration (MIC)

A

Lowest amount of antibiotic required to inhibit growth of bacteria in vitro

35
Q

How is MIC used clinically

A

Set breakpoints and if concentration is below breakpoint then will have postive clinical success in treating bacteria
If above then then should be reported as resistant

36
Q

Traditional way of testing sensitivity of antibiotics

A

Disc diffusion

37
Q

What is carbapenemase

A

Beta lactamase- breaks down all beta lactams making it untreatable

38
Q

Benefits of disc diffusion

A

Able to test multiple antibiotics quickly

39
Q

How does disc diffusion work

A
  • There is a set concentration of antibiotic on each disc which is then placed on the agar and incubated for 24 hours
  • The zone size is interpreted using the breakpoints in the above table (interpretation of zone diameters)
  • The zone diameter can be used to determine whether it is sensitive or resistant
40
Q

What do disc diffusion and MIC test

A

Sensitivity of antibiotics

MCDone (43 decks)

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