Partial characterization of an endemic strain of a methicillin- and aminoglycoside-resistant Staphylococcus aureus (MARSA) homogeneously resistant to β-lactam antibiotics

Abstract

Selected strains of methicillin- and aminoglycoside-resistant Staphylococcus aureus (MARSA) were subjected to a preliminary examination. They were representative of a larger group collected in a routine clinical microbiology laboratory over a period of 2 years. MARSA was endemic in the associated hospital. The characteristics investigated were antimicrobial resistance, the production of β-lactamase, free and bound coagulase, protein A, DNA-ase, urease, lipase and pigment. The MARSA strains were generally indistinguishable, other than in their antimicrobial resistances. The resistance to methicillin was completely homogeneous. Except with imipenem, growth extended to the edge of discs containing methicillin and the other β-lactam antibiotics tested when the strains were cultured at 37°C on media without added salt. Homogeneous resistance may confer an epidemiological advantage on strains of this phenotype.