A Medium for the Rapid Recognition of Penicillin-resistant Coagulase-positive Staphylococci

Abstract

Because ofthegrowing importance ofstaphylococcalcross-infection in hospitals, a simple, reliable, and rapidmethodfortheprimary isolation of theseorganisms from wounds, carriers, clothing, bedding, anddustisneeded. Thatmostwidely usedisgrowth onplain orblood agarplates, fromwhichsuspect colonies are pickedandtested by either thetubeorslide coagulase test.Theaddition ofsalttonutrient agartoafinal concentration of70,%' suppresses the growth ofother bacteria, andisofgreat valuein recovering staphylococci fromfaeces, butithas thedisadvantage that colonies maynotappear for 48hours, anddonotalways givea positive slide coagulase test unless subcultured onnutrient agar. A great improvement istheuseofnutrient agar containing phenolphthalein phosphate asemployed byBarber andBurston (1955) intheir studies of hospital infections. Afterincubation theplates wereexposed toammoniavapour, whenphosphatase-producing colonies, mainly coagulase-positive staphylococci, gavea reddish colour, andwere later tested forcoagulase production bythetube test. Duthie andLorenz(1952) addedsterile human fibrinogen witha little humanplasma tomolten agarat50°C.,after whichplates wererapidly poured.Suchplates gaveopaquerings offibrin aroundcoagulase-positive