Picture 17
This picture shows Escherichia coli (in red) and Salmonella typhi (in yellow) cultured in MacConkey's agar. E. coli ferments lactose and therefore appears red in the neutral red indicator found in the culture medium, whereas S. typhi does not and remains yellow.
Escherichia coli
Morphology: Gram negative cocci that are facultative anaerobes, ferment lactose, are commensals in human gastrointestinal tract
Route of transmission: Food borne
Investigations: Gram stain, organism cultured on MacConkey's agar
Diseases:
Urinary tract infections
Neonatal meningitis
Enteric infections (Traveler's diarrhoea)
Treatment:
Penicillin
Cefotaxime
Salmonella typhi
Morphology: Gram negative cocci that do not ferment lactose, do not produce gas like other species of Salmonella but produce H2S in small quantities
Route of transmission: Food borne
Investigations: Gram stain, organism cultured on MacConkey's agar and Triple Sugar Iron (TSI) medium
Diseases:
Gastroenteritis, from diarrhea to dysentery
Enteric fever (Typhoid fever)
Septicemia
Treatment:
Gastroenteritis is a self-limiting disease, so no treatment is needed
Ceftriaxone and ciprofloxacin are prescribed for enteric fevers and septicemia