MRSA bacteria. Coloured transmission electron micrograph (TEM) of dividing methicillin-resistant Staphylococcus aureus (MRSA) bacteria. Strains of MRSA are resistant to most antibiotic drug agents; although some are susceptible to vancomycin. S. aureus is a Gram-positive, spherical bacterium. It can cause boils, abscesses and wound infections. MRSA is of particular concern in hospitals, where outbreaks may be hard to control among susceptible patients. The problem is made worse because the bacteria reproduce rapidly by cell division. Magnification: x21,250 when printed 10cm high.