[Methicillin-resistant Staphylococcus aureus forming the fried egg appearance colonies isolated from a patient with septicemia].

Slower growing and peculiar colonies, "fried egg" appearance, of different sizes were temporally grown on a sheep blood agar plate from a clinical blood sample obtained from a patient with mediastinitis due to infection by methicillin-resistant Staphylococcus aureus (MRSA) following the graft replacement of thoracic aorta. The organisms revealed morphologically characteristic "fried egg" appearance, mainly Gram-positive cocci including some Gram-negative cells and cell-debris, catalase test positive and coagulase test positive as well as having the identical profiles for S. aureus on biochemical examination with VITEK Systems. The rough surfaced cell walls with unequal thickness of the organisms were observed in an electronmicroscope. According to these bacteriological studies, the organisms were identified as a mutant of S. aureus which had many similarities to staphylococcal L-form. Being resistant to oxacillin, instead of methicillin susceptibility test, and possessing a mecA gene, the organisms were confirmed to belong to MRSA. It is likely that this mutant of S. aureus was induced by a long term medication of sulfamethoxazole-trimetoprim, since the patient had been receiving the drug during 5 weeks when the colonies were first detected.