Nontypeable bacteriophage patterns of methicillin-resistant Staphylococcus aureus involved in a hospital outbreak.

Of 93 strains of Staphylococcus aureus isolated from inpatient wards of Ismailia General Hospital, 48 (51%) were proven to be methicillin resistant (MR). Of these MR S. aureus strains, 44 were isolated from patients and 4 were isolated from healthy carriers, who were newly arrived interns working in the same wards. Bacteriophage patterns of MR S. aureus were identified by using routine test dilution (RTD) and 100-fold dilutions (100 RTD) of phages. Of these 48 strains, 37 (75%) (33 from patients and 4 from interns) were nontypeable when using RTD and 100 RTD of phages. Of the other 11 strains, 8 were nontypeable by RTD of phages, but 5 of them had the phage pattern D11/1136 when tested by 100 RTD. Three strains had the phage pattern 3A/3C/55/71, and three strains had different phage patterns, 29/81, 96, and 95/D11. The finding of colonization with virulent MR S. aureus strains in interns working on the wards in which these patients were located suggested that new strategies for control of MR S. aureus nosocomial infections must be considered and evaluated.