Enterobacteriaceae:
· Facultative anaerobic
· gram-negative
· Rode (bacilli)
· Some are motile
· Oxidase negative
· Many are normal inhabitants of the intestinal tract of man
· Some are enteric pathogens and others are urinary or respiratory tract pathogens
Classification of Enterobacter :
· Classification based on: Lactose fermentation
1. Lactose fermenters:
ü E.coli
ü Klabsiella
2. Non lactose farmenters:
ü Salmonella
ü Shigella
Antigenic structure of enterobact.:
· Three antigens:
1. Somatic antigen (o-antigen)
2. Flagellar antigen (h-antigen)
3. Capsular antigen (k-antigen)
Colicins (bacteriocins):
· Bactericidal substances
· Produce by certain strains of bacteria
· Active against other species
· Controlled by plasmids
· Bacteriocin-prouducing strains are resistant to their own bacteriocin
Toxins of Enterobacteriaceae:
· Most gram-negative bacteria possess
· Lipopolysaccharides in their cell wall
Escherichia coli (E.coli):
· Motile
· Gram-negative rods
· Lactose fermenter
· Normal member of intestinal flora. Some can cause disease in human.
· Common cause of opportunistic infections
· Used as indicator of faecal pollution
· Over 700 serotypes
Antigenic structure of E.coli
· Three antigens:
1. Somatic antigen (o-antigen)
2. Flagellar antigen (h-antigen)
3. Capsular antigen (k-antigen)
Diseased caused by E.coli:
1. Urinary tract infection:
o Cause 90% of urinary tract infection in young women
o The symptoms include:
Dysuria
Haematuria
Pyuria
Flank pain
2. E.coli associated diarrhoeal diseases:
a) .Enteropathogenic (EPEC):
Watery diarrhea
b) Enterotoxigenic (ETEC):
COMMON CAUSE OF DIARRHOEA IN INFANTS AND TRAVELERS IN DEVELOPING COUNTRIES
c) Enteroinvasive (EIEC)
:Samilar to shigellosis
Cause dysentery and fever
d) Enterohaemorrhagic (EHEC):
Produce Verotoxin similar to shiga toxin
Causes haemorrhagic colitis, severe diarrhea and haemolytic syndrome that all lead to uremic renal failure
e) Enteroaggregative (EAEC):
Cause persistent diarrhea in young children
3. Neonatal meningitis:
o E.coli strain K1 are common cause of neonatal meningitis
o E.coli invade the blood from nasopharynx or GIT and carried to meninges
4. Nosocomial (hospital acquired) infections
Laboratory Diagnosis:
1. Clinical specimens:
Urine, pus, CSF and stools
2. Direct smears:
Gram negative rods
3. Culture:
MacConkey's agar (pink colonies)
4. Colonies are identified biochemically
5. Serotyping:
By O, H and K antisera
Treatment:
Trimethoprim + Sulfamethoxazole
Cefotaxime
Ampicillin
Urease positive Enterobacteriaceae (Proteus):
· Gram negative rods
· Motile
· Swarm across the agar surface
· Diseases caused by Proteus:
o Cystitis
o Pyelonephritis
o Prostatitis
o Neonatal meningoencephalitis
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