Epidemiological study of Staphylococcus aureus resistance to new quinolones in a university hospital

During a 14-month period, from December 1984 to February 1986, 630 Staphylococcus aureus isolates were identified at Broussais Hospital. Thirty-eight isolates (6%), from 35 patients, were found to be pefloxacin-resistant S. aureus (PRSA) with minimal inhibitory concentrations greater than or equal to 8 mg l-1. PRSA isolates were tested for susceptibility to 35 antibiotics, including nine quinolones, and heavy metal ions. Phage-type was determined. Out of the 38 PRSA isolates, 35 (92%) were methicillin- and multiply-resistant; however, all PRSA isolates were sensitive to vancomycin and coumermycin. Fifteen isolates (39%) had similar phage-type and identical antibiotic susceptibility pattern with high level resistance to pefloxacin (MICs equal to 64 mg l-1); they were isolated from the same surgical unit. The 23 remaining PRSA isolates differed by their phage and susceptibility patterns. Pefloxacin MICs ranged from 8 to 512 mg l-1 with a bimodal distribution; cross-resistance was observed with the eight other quinolones tested. Only nine PRSA isolates (24%), including four 'epidemic' isolates, were obtained from patients who had been treated with quinolones. From these data there is apparently no direct relationship between quinolone administration and selection of PRSA in infected patients.