Enterobacteriaceae and Pseudomonas

Question 1

What are 4 characteristic of enteric bacteria?

Answer 1

1. Gram (-)
2. Rod shaped
3. Found as part of the normal flora or as a pathogen in the GI tract of both humans and animals
4. Facultative anaerobes

Question 2

What are the 6 features of enterobacteriaceae?

Answer 2

1. Can ferment glucose (thus making them facultative anaerobes)
2. Oxidase (-): no cytochrome C oxidase
3. Motility in some species
4. Ability to ferment lactose in some species
5. Many possess common and sex pili
6. Gram (-) with bipolar staining pattern

Question 3

What are the 6 genus of enterobacteriaceae which are found in the normal flora?

Answer 3

Found in the normal flora
1. Escherichia
2. Klebsiella
3. Proteus
Not found in the normal flora
1. Shigella
2. Salmonella
3. Yersinia

Question 4

How are enterobacteriaceae serologically classified? 3 things

Answer 4

Based on O, H, and K antigens
O (somatic) antigen: O side chains of LPS
H antigen: flagellar antigen
K antigen: capsular antigen, type specific polysaccharide

Question 5

How are enterobacteriaceae biochemically classified? 2 ways

Answer 5

1. Lactose fermentation: preliminary step in the identification of gram (-) enteric rods
2. Resistance to bile salts: separates Shigella and Salmonella from the commensals

Question 6

Which enterobacteriaceae are lactose fermenters and which are non-lactose fermenters?

Answer 6

Lactose fermenters:
1. Escherichia
2. Enterobacter
3. Klebsiella
Non-Lactose fermenters:
1. Salmonella
2. Shigella
3. Proteus

Question 7

How is a MacConkey agar selective and differential?

Answer 7

Contains bile salts which is selective for the growth on gram negative bacteria
Contains a selective compound which reacts to lactose fermentation by products such that lactose fermenters are pink and non-lactose fermenters are colorless