Gram Negative Rods

Question 1

What groups can GN Rods be split into?

Answer 1

(1) Glucose Fermenters - Oxidase Positive or Negative.

(2) Non-Fermenters - Oxidase Positive

Question 2

What are the important Glucose Fermenters?

Answer 2

1) Oxidase Positive - Pasteurella

2) Oxidase Neg - E.Coli, Salmonella, Actinobacillus

Question 3

What are the important Non fermenters?

Answer 3

Pseudomonas, Bordatella, Brucellus

Question 4

How can Oxidase Negative Glucose fermenters further be split, and then this further?

Answer 4

1) Enteric
a. Lactose fermenter - E.Coli
b. Non-lactose fermenter - Salmonella
2) Non-Enteric e.g. Actinobacillus

Question 5

Pseudomonas is…

Answer 5

Non-fermenter. P. aeruginosa is opportunistic infections involving damaged tissue. Also, otitis externa. Multiple antibiotic resistance.

Question 6

Bordatella is…

Answer 6

Strict aerobe, Non fermenter. B. bronchiseptica causes respiratory infections (Kennel cough)

Question 7

Pasteurella is…

Answer 7

Glucose fermenter - large grey colonies on blood agar. P. multocida is important, causes fowl cholera and other disease.

Question 8

Mannheimia haemolytica is…

Answer 8

Glucose fermenter. Causes pneumonic pasteurellosis in Cattle and sheep. Opportunistic.

Question 9

Campylobacter (curved rods) are…

Answer 9

C. jejuni is important intestinal bacteria in poultry (+ other species) and man. Largest cause of food poisoning in the UK.

Question 10

Enterobacteria (coliforms) are… and include…

Answer 10

Enterobacteria are GN, facultative anaerobes, commensals of GIT, glucose fermenters. Include: E.coli and Salmonella.

Question 11

How can you distinguish between E.Coli and Salmonella?

Answer 11

1) E.Coli - Lactose fermenter. Traditionally harmless commensals of gut.
2) Salmonella - Non lactose fermenter. Tradtionally gut pathogens.

Question 12

How can you distinguish between Lactose fermenters and Non lactose fermenters in culture?

Answer 12

Lactose fermenters - appear pink.

Non-lactose fermenters - appear yellow.

Question 13

Escheria coli…

Answer 13

Normally inhabits large intestine. Can cause UTI, Pyelonephritis, Colsepticaemia, Pyometra etc.

Question 14

Salmonella enterica…

Answer 14

Non-lactose fermenters. Produces H2S. Most important pathogens of Enterbacteria. No not produce urease.

Question 15

How can you differentiate Enterobacteria from other Gram-negative bacteria?

Answer 15

Enterobacteria are gram negative rods, that are ALWAYS oxidase negative. They grow on MacConkey (in presence of bile salts)