Antibiotic susceptibility and phage typing of methicillin-resistant and -sensitive Staphylococcus aureus clinical isolates at three periods during 1991-1997.

The aim of the study presented here was to evaluate the antibiotic susceptibility of Staphylococcus aureus over a 7-year period. A total of 2,122 clinical isolates of Staphylococcus aureus were collected from hospitalized patients at 3-year intervals during the period 1991–1997. The prevalence of methicillin-resistant isolates was 41.6%, 38.2% and 36% in 1991, 1994 and 1997, respectively; all of these isolates were sensitive to vancomycin. Over the study period, resistance to pristinamycin and fusidic acid increased slightly and resistance to imipenem, rifampicin and amikacin increased greatly, while resistance to trimethoprim/sulfamethoxazole decreased. For methicillin-sensitive Staphylococcus aureus isolates, significantly increased resistance was observed against amikacin only. Phage typing was conducted using the international set of phages. All of the isolates that were sensitive to group I, group II, or group V phages were sensitive to methicillin. Of the isolates that were sensitive to group III phages, 96% were methicillin resistant, and 70.5% of them were sensitive to phages 75 and 85.