MB practical 1 - bacterial detection

Question 1

name the clinically important gram negative cocci that are identified as diplococci (in pairs).

Answer 1

• N. meningitidis
• N. gonorrhoea

Question 2

when identifying gram negative bacilli what is the first step to identify?

Answer 2

• check their appearance on McConkey agar CLED (cytosine lactose electrolyte deficient agar) and XLD (Xylose Lysine Deoxycholate)
• if it is non-lactose fermenting it could be salmonella, shigella, pseudomonas or proteus ect
• if its lactose fermenting it could be enterobacteriase eg e.coli, klebsiella

Question 3

if the bacillus is non-fermenting, what further lactase tests can be conducted?

Answer 3

oxidase test:
positive - pseudomas
negative - enterobacteriase

if its negative and therefore identified as enterobacteriase - can do XLD agar to distinguish salmonella from shigella

• to identify further can use a serology test

Question 4

if the bacillus is fermenting, what further lactase tests can be conducted?

Answer 4

biochemical ID and sensitivity test

Question 5

how do vibros appear on agar?

Answer 5

slightly curved comma shaped

Question 6

how do you identify camplobacter and what features about it make it hard to distinguish on other tests?

Answer 6

• doesnt ferment lactose
• doesnt oxidise carbohydrates
• thy obtain energy from amino acids
• selective charcoal cefazolin sodium deoxycholate agar

Question 7

what tests to conduct when identifying anaerobes (bacteriodes)?

Answer 7

• blood agar in aerobic conditions with metronidazole antibiotic disc on the plate
• anearobes will grow on the agar except in the zone around the metrodiazole disc