Metal Susceptibility of a Hetero-Vancomycin-Intermediate Methicillin-Resistant Staphylococcus aureus Isolate

The Gram-positive bacterium Staphylococcus aureus is well known for its ability to develop resistance to various antimicrobial substances. Methicillin-resistant S. aureus (MRSA), a cause of nosocomial infections worldwide, is becoming increasingly resistant to the glycopeptide antibiotic vancomycin, one of few antibiotics used to treat serious multiple-antibiotic-resistant staphylococcal infections. With the increase in the number of MRSA strains showing reduced sensitivity to vancomycin, it has become important to investigate alternative treatment options. In this study, we examined the effects of five metals: silver, copper, arsenate, zinc, and cadmium on the growth of a clinical MRSA strain MM66 demonstrating heterogeneous intermediatelevel resistance to vancomycin. Disc diffusion and gradient plate experiments were used to compare the metal susceptibility levels of strain MM66 to that of the methicillin-resistant S. aureus laboratory control strain. MM66 grew less successfully when exposed to metals, and showed an overall increased level of susceptibility to metals compared to the laboratory control strain. Of the metals tested, silver exerted the highest inhibitory effect on the growth of MM66.