Bacteriology lab

Question 1

Line cocci vs clumped cocci (gram +ve)

Answer 1

Lines= strep

Clumped=Staph

Question 2

For staph. What type of test

Answer 2

Coagulase….. +ve= staph aureus, -ve=low pathological potential (apart from prosthetic material)

Question 3

Gram -ve bacilli

Answer 3

E. Coli, klebsiella

Question 4

How is brucellosis caught

Answer 4

Animals (think bruce)
Poorly cooked meat
Unpasteurised milk or cheese

Question 5

How is melliodosis caught

Answer 5

Soil

Question 6

Which diagnositc techniques can be used in bacteriology lab

Answer 6

CULTURE (sterile=blood/CSF, non sterile)

SEROLOGY

MOLECULAR TECHNIQUE

ANTIMICROBIAL SUSCEPTIBILITY TESTING

Question 7

Differentiate gram pos and gram neg

Answer 7

Pos means thick cell wall (cos this absorbs the dye)….. so cell membrane then thick cell wall

Neg means think cell wall, so 2 cell membranes. HAS LPS

Question 8

What are bacterial cell walls composed of

Answer 8

NAM and NAG alternating units

Question 9

After positive blood culture then what

Answer 9

Then smear onto agar plates

Question 10

After smearing onto agar plates then what

Answer 10

Look under microscope

Question 11

What are the 3 bacteria morphology

Answer 11

Cocci (round)
Bacillus (rod)
Spiral

Question 12

If there are gram positive cocci, what is indicated if these cocci are in clumps

Answer 12

Clumps of gram +ve cocci is staphylococci

Question 13

If there are gram positive cocci, what is indicated if these cocci are in chains

Answer 13

Chains of gram +ve is streptococci

Question 14

What is indicated by gram +ve bacillus

Answer 14

Clostridium or listeria

Question 15

What would be the next test if you had gram +ve clumps of cocci

Answer 15

Coagulase test

Question 16

What is indicated by coagulase +ve and coagulase -ve

Answer 16

COAGULASE DONE ON STAPHYLOCOCCUS

COAG +VE= Staph Aureus (severe infections….. skin/soft tissue, endocarditis and osteomyelitis)

COAG -VE= skin commensals of low pathogenic potential

Question 17

Is coag -ve bacteria ever harmful?

Answer 17

Normally skin commensals, BUT can infect prosthetic material causing line, pacemaker infections and endocarditis

Question 18

Other than looking at clumps and chains, how can you confirm whether a gram pos is strep or staph

Answer 18

Catalase

Cat positive is staph

Cat neg is strep

Question 19

What tests can be done on catalase negatives to determine the bacteria type

Answer 19

So it’s strep….

then do haemolysis….

Question 20

How is does haemolysis work, including the colour of each

Answer 20

Strep induce haemolysis to underlying erthrocytes when placed on a blood agar

Alpha –> green… PARTIAL haemolysis

Beta –> yellow… COMPLETE haemolysis

Gamma –> no haemolysis so stays red

Question 21

Examples of alpha and each type of beta haemolytic strep

Answer 21

Alpha= Strep pneumonia or strep viridans (–> subacute endocarditis SBE

Beta split into group A, group B and group C

A: strep pyogenes

B: S. agalactiae, or group B Streptococcus causes pneumonia and meningitis in newborn and elderly

C: not important in humans

Goes up to F

Question 22

Gram negative bacilli example

Answer 22

Enterobacteriae including E. Coli, shigella, salmonella

Question 23

Bacterial and parasitic and viral cause of diarrohea

Answer 23

Bacteria:
Salmonella (inc S. typhi ), Shigella, Campylobacter,
E coli O157, C difficile, Cholera

Parasites:
Amoeba, Giardia, Cryptosporidium

Viruses:
Norwalk virus, cytomegalovirus and viral hepatitis. Rotavirus is a common cause of acute childhood diarrhea.

Question 24

In stool sample what bacteria are routinely tested for

Answer 24

Culture, then

Only Salmonella, Shigella and Campylobacter
looked for routinely.

Question 25

How is clostridium difficile tested for as it is not tested routinely

Answer 25

toxin detection or PCR for

toxin gene

Question 26

How do you test AB suitability

Answer 26

Gradient minimum inhibotry concentration strips

Question 27

T/f IgM will rise in the secondary and primary response to infection

Answer 27

T… but second exposure causes much greater IgG than IgM response

Question 28

Why are samples taken prior to AB

Answer 28

So that the AB doesn’t kill the organism before being able to work out what it was!

Question 29

Why do we look for NITRITES in the urine

Answer 29

Nitrites strongly suggest bacteriuria as many species of gramnegative bacteria convert nitrates to nitrites.

Question 30

What might we look for in urine as evidence of infection

Answer 30

nitrites, leucocytes, blood, protein, bilirubin, ketones

Question 31

How can we possibly culture stool samples when there are so many pathogens there

Give examples of the agar used

Answer 31

Culture on inhibitory media – e.g. deoxycholatecitrate agar (DCA), selenite (Faeces contains 1012-14 bacteria per gram, so selective media are used to suppress background ‘flora’ organisms)

Question 32

What substances can be used for microscopy

Answer 32

Gram stain of CSF, joint fluid, purulent exudates

ZN/auramine stain of e.g. sputum, for TB

Question 33

When is FTA used

Answer 33

To check for antibodies to T. pallidum

Question 34

What is the ZN/auramine stain sed for

Answer 34

e.g. sputum, for TB

Question 35

Examples of direct antigen detection

Answer 35

Meningococcal antigen in CSF
C. difficile toxin in faeces
Legionella and Pneumococcal antigen in urine

Question 36

Examples of PCR

Answer 36

Chlamydia in genital specimens

Rapid PCR for MRSA