New method for detecting slime production by coagulase negative staphylococci.

An alternative method for detecting the production of slime by coagulase negative staphylococci was compared with the routinely used Christensen method on 124 isolates of coagulase negative staphylococci from carriage sites, blood cultures, and infected peritoneal dialysis fluids. The alternative method requires the use of a specially prepared solid medium--brain heart infusion broth, supplemented with 5% sucrose, and Congo red stain. Of the 124 tests, there was complete agreement between methods in 107 and only one strain was clearly negative by Christensen's method while positive on Congo red agar. The Congo red method is rapid, sensitive, and reproducible and has the advantage that colonies remain viable on the medium. It is also not subject ot interbatch variation of media which sometimes affects the reproducibility of the Christensen method.