Microbiology Flashcard #5


MacConkey agar

MiF #5
Clinical Features :
Frequent loose scanty feces with blood & mucus, abdominal cramps, tenesmus, fever & vomiting maybe, Gay bowel syndrome
Complications : arthritis, toxic neuritis, parotitis, intussusception in children, HUS in severe cases

Additional points :
Incubation period short, 1-7days, usually 48hrs.
Infective dose 10-100 bacilli
Invade by binding to M cells by Virulence Marker Antigens (VMA)
Exotoxin similar to EHEC verotoxin (inhibit protein synthesis; has A and B units).
Endotoxin (LPS)

Culture & Gram Reaction
Specimen : fresh feces
Transport media : Sachs’ bufferred glycerol saline or Gram negative broth
Microscopy – plenty of pus cells
Pale colonies on MacConkey and DCA agar
colonies are small. 2mm, circular, convex, smooth, translucent
Other media : XLD, SS agar (colorless), HE agar (green colonies)
Growth inhibited on Wilson-Blair medium
Gram negative bacilli, non motile, non capsulated

Biochemicals :
MR +
Catalase +
Nitrate reduced to nitrite
Glucose fermented with acid but no gas
Urease, H2S, KCN, citrate negative

Not required
Severe debilitating cases – First line : Ciprofloxacin Second line – Ceftriaxone, Azithromycin

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