A comparative study on growth in soft-agar, adherence to glass and haemolysis types of coagulase-negative staphylococci.

Growth properties of coagulase-negative staphylococci in the presence and in the absence of human and rabbit serum in soft-agar prepared in modified Staphylococcus 110 broth were studied. The adherent growth was examined in modified Staphylococcus 110 broth and 1% glucose-meat broth. Of 100 strains examined 69% exhibited diffuse, 18% compact, 7% transient and 6% mixed growth. Compact type colonies were mainly characteristic of Staphylococcus haemolyticus strains. The presence of serum failed to influence the types of colony morphology in any of the strains. Sixty-three percent of the strains showed adherent growth; none of the S. haemolyticus strains produced adherent growth. The glucose-meat broth, unlike modified Staphylococcus 110 broth, was suitable to study adherence. The coincidence of the compact colony morphology in soft-agar and the absence of adherent growth seems to be a taxonomic sign for the species S. haemolyticus and differentiate it from the species Staphylococcus epidermidis.