New selective and differential medium for coagulase-positive staphlococci allowing rapid growth and strain differentiation.

Staphylococcal infection and cross-infection in hospitals is a very important problem. Investigation and management of such infection and cross-infection would be facilitated by a simple, rapid, and reliable method for the primary isolation of Staphylococcus aureus from body fluids and exudates, from feces, from carriers, from the air, and from various surfaces and fomites in the hospital environment. It is common for staphylococci to be present in mixed culture with a variety of other organisms in many of these sites. The total number of organisms present may be very large (108 to 1010 per gram in the case of feces, for example) and staphylococci may form a relatively small percentage of the total bacterial population. Furthermore, when staphylcocci are present in mixed culture with certain gram-negative bacilli, the staphylococei may be suppressed so that recovery is difficult or impossible except by use of selective media. Such media offer certain other advantages. A high degree of selectivity allows larger samples to be examined without the danger of overgrowth by extraneous organisms. Where mixtures of organisms are not a problem, a selective medium may provide more rapid presumptive and definitive identification of organisms than nonselective media. Chapman (1945, 1946) has proposed media that are selective for staphylococei and have some value in differentiating between coagulasepositive and coagulase-negative strains. These media are selective chiefly because of a high sodium chloride content; differentiation is based on pigmentation and acid production from mannitol. A more selective medium using tellurite and lithium chloride and a high pH