Influence of Sub-Inhibitory Concentrations of Penicillin G on Surface Properties of Iron-Deprived Staphylococcus Aureus NCTC 6571

Abstract

The surface properties of batch cultures of Staphylococcus aureus NCTC 6571 (OXFORD) grown with 48- and 24-minute doubling times in iron-depleted Tryptone Soy Broth were studied after treatment with 1/16 MIC of penicillin G. Growth rate influenced surface hydrophobicity. Slow-grown phenotypes, particularly iron-poor ones, had low contact angles generally, but these were increased by iron excess and/or penicillin. Opsonisation also significantly increased contact angles. All fast-grown phenotypes had much higher, uniform contact angles regardless of iron or penicillin status. Low numbers (10–20 cocci:1 neutrophil) of the slow-grown iron-poor phenotype provoked the least chemiluminescence, had the lowest neutrophil association values, and were least susceptible to whole blood killing. The other phenotypes behaved in a manner that generally reflected their relative hydrophobicities. Alterations in growth rate significantly affected Protein A production and adherence to polyvinyl chloride catheters, whilst iron deprivation and/or penicillin induced minor changes. Little effect was noted upon the production of staphylocoagulase and alpha-haemolysin. Immunoblotting profiles were greatly simplified by iron deprivation and/or penicillin treatment. Growth rate alterations had no effect. Non-immune sera recognised the iron-poor preparations better than the iron-rich. Analysis of iron-poor and iron-rich preparations of S. aureus Hopewell, an endocarditis isolate, using the patient’s immune serum, also confirmed this trend in both immunoblotting and ELISA.