Compact growth of Staphylococcus haemolyticus in soft agar is not due to hydrophobic interaction between the cocci

It was hypothesized that the formation of compact colony in soft-agar both in the presence and absence of serum, characteristic mainly for strains of the species Staphylococcus haemolyticus among coagulase-negative staphylococci [Szúcs et al. Acta Microbiologica Hungarica 40:181-189 (1993)] was due to hydrophobic interaction between cocci. The effect of a number of surface active agents on this phenomenon was examined. Neither 0.1% and 1%. Tween-80 nor 5% and 10% ethylene glycol and polyethylene glycol nor 0.1%-4% trypsin influenced the colony morphology in soft-agar prepared in modified Staphylococcus 110 broth. Bovine lactoferrin and apolactoferrin at concentrations of 0.1%-0.4% made compact colonies transient to diffuse ones. Thus, cocci are not adhered to each other in compact ball-like colonies by hydrophobic interaction or trypsin-sensitive proteins. It is possible that still unknown polysaccharide-binding proteins or other trypsin-resistant proteins are responsible for the formation of compact colonies by Staphylococcus haemolyticus in soft-agar.