Pathogenicity and virulence of methicillin resistant Staphylococcus aureus: slime layer production

Nine methicillin-resistant (MR) mutants and three methicillin-sensitive (MS) substrains, all derived from naturally occurring heteroresistant isolates of Staphylococcus aureus were examined for slime production. All strains showed an increased mucoid character when cultured on a modified Staphylococcus Medium No. 110. The uranic acid content of the slime layer ranged from 2% to 6% in the MR mutants and from 1.3% to 5.1% in the MS substrains. The amount of uronic acid per g of dry bacteria ranged from 82.5 mg to 143.8 mg in the MR mutants, and between 51.4 mg and 98.8 mg in the MS substrains. In 3 pairs of MR mutants and MS substrains originating from the same parents, the MR cells possessed more of uronic acid than their MS counterparts. The partially purified polysaccharide part of the slime contained D-galactose, D-mannose, D-xylose, D-galacturonic acid, D-galactosamine and D-glucuronic acid in all strains studied. Its quantitative composition was identical in each pair of the MR mutant and MS substrain; there were, however, considerable differences among the strains and between the pairs. Methicillin resistance and slime formation seem to be independent properties in S. aureus. The presumable significance of the readiness of slime production by MR cocci during infections is discussed.