Use of colony morphology to characterize carriage profiles of coagulase negative staphylococci

The absence of a reliable method to distinguish among coagulase negative staphylococcal strains in mixed culture hinders elucidation of colonization traits and precise tracking of colonization. This study examined whether colonial morphology could be used to correctly identify coagulase negative staphylococcal strains in mixed cultures. Staphylococci were isolated from nasal and hand cultures of ten subjects at 0 and 3 months. Samples were initially screened for the predominant coagulase negative staphylococcal strain by colonial morphology. The strains were subsequently identified by phenotypic and biochemical testing. Pulsed field gel electrophoresis demonstrated that the morphologic criteria correctly grouped the strains in 91.1% (41/45) of samples. This study suggests that colonial morphology is a reliable method for the initial characterization of coagulase negative staphylococcal strains. This approach has potential value for epidemiological studies that involve establishing links between commensal flora and their potential role as pathogens in subsequent clinical infections.