Bacteriology

Question 1

What are the 4 most common diagnostic techniques?

Answer 1

Culture (sterile or nonsterile sites)
Serology
Molecular techniques e.g. PCR
Antimicrobial susceptibility testing

Question 2

What are the different types of agar plate that can grow bacteria?

Answer 2

Chocolate agar
Macconkey agar
Neomycin agar

Question 3

What is the chocoalte agar plate and what is the most common bacteria that grows on it?

Answer 3

haemolysed blood

Haemophilus Influenzae

Question 4

What is the maccokey agar plate for?

Answer 4

Gram negative bacteria

Should be in done before giving antibiotics except for meningitis and meningococcal septicaemia

Question 5

What is the neomycin agar plate for?

Answer 5

Anaerobic bacteria

Question 6

What is the difference in gram negative and gram positive bacteria?

Answer 6

Gram positive has large peitdoglycan wall. Gram negative has smaller, outer membrane and LPS.

Question 7

What is the gram stain useful for?

Answer 7

Selecting antibiotics. Some antibiotics target the cell wall and so they won’t be very good for gram negative bacteria e.g. vancomycin

Question 8

What colour are gram positive bacteria and why?

Answer 8

Purple as they hold the gram stain

Question 9

What colour are the gram negative bacteria and why?

Answer 9

Pink (counterstain) as they have an outer membrane which stops them taking up the stain

Question 10

What is the staphylococci coagulase test for and what are the results?

Answer 10

Differentiate between the different Staphyloccoci bacteria. Coagulase positive = Staphyloccocus aureus. (MRSA)
Coagulase negactive - common skin microbes

Question 11

How are the two groups of streptoccoci identified?

Answer 11

Grow them on blood agar.
Alpha haemolysis - incomplete haemolysis, green colour. Streptococcus pneumoniae.
Beta haemolysis - complete haemolysis, clear the agar. Group A - Streptocuccos pyogenes. Group B - Streptococcus agalaticae.

Question 12

What pathogens can cause diarrhoea?

Answer 12

Bacteria - salmonella, shigella, campylobacter, E.coli, C diff, cholera

Parasites - amoeba, giarda, cyrptosporidium

Viruses

Question 13

What 3 pathogens are routinely checked for in stools in the UK?

Answer 13

Salmonella, camplyobacter and shigella

Question 14

How is C diff identified?

Answer 14

Difficult to grow on plates. So mixture of toxin detection and PCR toxin gene

Question 15

What special agar plate is used for salmonella and what are the results?

Answer 15

Xylose lysine deoxylate

Balck colonies formed - cannot ferment xylos

Question 16

How long does campylobacter take to grow?

Answer 16

48hrs

Question 17

What special agar plate is used for cholera?

Answer 17

TCBS - thiosulphate citrate bile salts sucrose. Green colour

Question 18

What is the minimum inhibitory concentration?

Answer 18

the lowest amount of antibiotics required to inhibit the growth of bacteria?

Question 19

What does it mean when the MIC is above the breakpoint?

Answer 19

it should be reported as resistant

Question 20

What is the traditional way of testing antibiotic sensitivity?

Answer 20

Disc diffusion - place discs of different antibiotic concentration on agar plate of bacteria and incubate for 24hrs. The zone size is interpreted using the breakpoints.