Family Enterobacteriaceae: General

Question 1

Classification

Answer 1

Large family

> 30 genera
120 species
95% of isolates belong to:

• 10 genera
• 25 species

Part of the normal intestinal flora —> except:
Salmonella, shigella and Yersinia

These are pathogenic

Question 2

Group 1

Answer 2

Genus:

Escherichia
Edwardsiella
Citrobacter
Salmonella
Shigella

Question 3

Group II

Answer 3

Klebsiellae

Genus
Klebsiella
S: K.pneumoniae
SS: pneumoniae; ozaenae; rhinoscleromatis

Genus
Enterobacter
E.Cloacae
E.aerogenes

Genus
Hafnia

Genus
Serratia:
S.Marcescens

Question 4

Group III

Answer 4

Proteae

Genus
Proteus:
P.miravulis
P.vulgaria

Genus
Morgenella
M.morganii

Genus
Providencia:
P.rettgeri

Question 5

Group IV

Answer 5

Yersinieae

Genus Yersinia

Question 6

Group V

Answer 6

Erwinieae

Genus erwinia

Question 7

Morphology

Answer 7

Gram - rods
Non-spore forming
Motile, peritrichous
> only shigella spp. And Klebsiella spp. Are non-motile
Only Klebsiella spp. Form a well-defined capsule
- other genera form loose, slime layer

Question 8

Growth characteristics

Answer 8

Facultative anaerobes

Non-fastidious

Main characteristics:

• ferment glucose
• reduce nitrates to nitrites
• oxidase negative

Lactose positive:
Escherichia
Klebsiella
Enterobacter

Lactose negative: 
Shigella
Salmonella
Proteus group
Yersinia
Serratia

Question 9

Antigenic structure

Answer 9

Capsular (K) antigens —> polysaccharides

Flagella (H) antigens —> proteins
- phase variation in salmonella

Somatic (O) antigens —> outer polysaccharide portion of the LPS

Large number:
> 1500 in Salmonella
> 164 in E.Coli

Question 10

Virulence factors

Answer 10

Endotoxin 
Exotoxins:
> enterotoxins:
Affect small intestine (cause diarrhea)
Enterotoxin-producing strains of:
- E.coli
- shigella 
- salmonella 

Shiga toxins and shiga-like toxins:

• interfere with mammalian protein synthesis —> development of:
• hemorrhagic colitis
• haemolytic uremic syndrome

Shigella: shiga-toxins
E.coli: shiga-like toxins

Colonization factors:
Pili (fimbriae)
O antigens = outer polysaccharide chains of LPS

Invasiveness

Characteristic sign of Shigella and Salmonella (some strains)

Question 11

Microbiological diagnosis

Answer 11

1) specimen
Depends on the type of infections: urine, blood …

2) microscopic examination
- useful for extraintestinal infections
- lack of morphological difference between different species (except Yersinia pestis)

3) culture

Extraintestinal infections:

• blood agar plate
• differential media

Intestinal infections:

• differential media
• selective media

Blood agar plate: morphologically indistinguishable colonies of different species

Differential media: lactose positive and lactose negative colonies

4) identification

Extraintestinal isolates: only on the basis of biochemical tests

Intestinal isolates: on the basis of:

• biochemical tests
• detection of bacterial Ag by agglutination tests

Question 12

Treatment and prevention

Answer 12

Major therapeutic problem
Choice of drug depends on susceptibility testing

Variable resistance among the member of one species

Producers of ESBLs among:

• E.coli
• Klebsiella spp.
• enterobacter spp.

Most strains are susceptible to:

• broad spectrum penicillins
• 2nd and 3rd generation of cephalosporins (ceftazidine)
• aminoglycosides
• ciprofloxacin