Enterobacteriaceae

Question 1

General and specific characteristic of enterobacteriaceae

Answer 1

• Gram negative & rod-shaped bacteria
• Aerobe and facultative anaerobic
• Usually motile (petrichous flagella); some are non-motile (Klebsiella sp & Shigella sp)
• Non- spore forming
• Non-capsulated (except Klebsiella sp & Salmonella typhi)
• Oxidase negative, catalase positive, able to reduce nitrate to nitrite

Question 2

Natural Habitat

Answer 2

Some being saprophytes, some others being human, animal and plant pathogen

Opportunistic pathogen; in stress, no food
- normal commensals in intestines of both man and animal (Coliform group)
- Some are saprophytes in water, soil and plants (Proteus sp)

Question 3

Medical and economic importance

Answer 3

Fecal contamination indicator (natural habitat in intestinal tract)
Pathogenic eggect on human and livestock; eg. Salmonella, shigella, yersinia sp
Resistant to many antibiotic

Question 4

Major pathogen category

Answer 4

E.coli, salmonella and yersinia spp cause both systemic and enteric system

Shiella spp cause diarrhea in human

Question 5

Opportunistic pathogen category

Answer 5

Proteus spp in liver, enterobacter spp, klebsiella spp. in lung

Cause disease in location other than alimentary tract

Question 6

Non pathogen

Answer 6

Without pathogen significance for animal and human.
Can be isolated from feces and the environment and may contaminated clinical specimens (may cause faulty diagnosis)

Question 7

Virulence Factors

Answer 7

1. Endotoxin - wide ranging effect on host
2. Capsule - antiphagocytic
3. Antigenic phase variation - capability to alternately express or not express either capsule or flagella and thus avoid host immunity
4. Resistant to serum killing - ability to resist the bactericidal activity of serum > survive in bloodstream
5. Antimicrobial resistant - carbapenem resistant
6. True pathogenic contains adhesins (fimbriae or pili)
   and exotoxins (enterotoxin which act in small intestine)
7. Stimulate antibody production by host including K-polysaccharide, H-flagella antigen and O-somatic polysaccharide antigen

Question 8

Lactose fermentation in MacConkey agar (within 18 hours)

Answer 8

Lactose fermenter ; colonies and surrounding are pink
> E. coli and klebsiella

Non-lactose fermenter; pale colonies and surrouding medium
> Salmonella

Question 9

Colony morphology

Answer 9

Mucoid and glistening colonies > klebsiella, enterobacter

Swarming bacteria > proteus

Question 10

Reaction in TSI agar

Answer 10

E coli > acidd butt/acid slant/ no H2s production
Salmonella > acid butt/alkaline slant/ h2s production

Question 11

Reaction on selective/indicator media

Answer 11

BGA - Salmonella shown red alkaline reaction
XLD - salmonella are red with black centres due to hydrogen sulphide production
EMB - E.coli have metalic sheen colonies
MacConkey agar

Question 12

Escherichia coli

characters

Answer 12

motile with peritrichous flagella and often fimbriate

Question 13

Culturation result of ecoli

Answer 13

Pink colonies on macconkey agar
Haemolytic activity on blood agar

Question 14

Serotyping based on