Micro - Clinical Bacteriology (Gram - Basics)

Question 1

What color is a gram negative stain? What are the morphology categories of gram negative bacteria?

Answer 1

Pink; (1) Comma-shaped (oxidase +) (2) Diplococci (3) “Coccoid” rods (4) Rods

Question 2

What are the oxidase positive, comma-shaped gram negative bacteria? How can you differentiate them?

Answer 2

(1) Camplyobacter jejuni - Grows in 42C (2) Vibrio cholerae - Grows in alkaline media (3) Helicobacter pylori - Produces urease

Question 3

What are the gram negative diplococci? How can you differentiate them?

Answer 3

(1) Neisseria meningitidis - Maltose fermenter (2) Neisseria gonorrhoeae - Maltose nonfermenter

Question 4

What are the gram negative “coccoid” rods? Which of these are the most important pathogens to know?

Answer 4

(1) Haemophilus influenzae - IMPORTANT PATHOGEN (2) Bordetella pertussis - IMPORTANT PATHOGEN (3) Brucella (4) Pasteurella

Question 5

What kind of bacteria is Haemophilus influenzae? What are its growth requirements?

Answer 5

Gram negative “coccoid” rod; Factors V and X

Question 6

What kind of bacteria is Pasteurella? With what kind of exposure is it associated?

Answer 6

Gram negative “coccoid” rod; Animal bites

Question 7

What kind of bacteria is Brucella? What disease does it cause?

Answer 7

Gram negative “coccoid” rod; Brucellosis

Question 8

What are the steps involved in differentiating gram negative rods?

Answer 8

(1) Lactose: Lactose fermenter versus Lactose nonfermenter (2) For Lactose fermenters: Fast fermenter versus Slow fermenter (3) For Lactose nonfermenters: Oxidase negative versus Oxidase positive

Question 9

What are the gram negative rod lactose fermenters? Divide them into fast versus slow fermenters.

Answer 9

LACTOSE FERMENTERS - FAST: (1) Klebsiella (2) E. coli (3) Enterobacter, SLOW: Citrobacter, Serratia, Others

Question 10

What are the gram negative rod lactose nonfermenters? Divide them into oxidase negative versus positive.

Answer 10

LACTOSE NON-FERMENTERS - OXIDASE (-): (1) Shigella (2) Salmonella (3) Proteus (4) Yersinia; OXIDASE (+): (1) Pseudomonas

Question 11

How do lactose-fermenting enteric bacteria appear on MacConkey’s agar? What are examples of such bacteria?

Answer 11

Pink; (1) Citrobacter (2) Klebsiella (3) E. Coli (4) Enterobacter (5) Serratia; Think: “Lactose is KEE (fast fermenters), test with maConKEE’S agar (slow and fast fermenters)”

Question 12

In terms of lactose fermentation, what enzyme does E. Coli produce? What role does this enzyme play?

Answer 12

Beta-galactosidase; Lactose –> Glucose + Galactose

Question 13

How do lactose fermenters grow on EMB agar? More particularly, how does E. Coli grown on EMB agar?

Answer 13

Purple/black colonies; Purple colonies with green sheen

Question 14

To what antibiotics do the gram-negative outer membrane layer inhibit entry?

Answer 14

Penicillin G and vancomycin

Question 15

To what penicillins are gram negative bacilli resistant versus susceptible?

Answer 15

Resistant to Penicillin G but may be susceptible to penicillin derivatives such as ampicillin and amoxicillin