Susceptibility of clinical bacterial isolates to ciprofloxacin in the United States.

In 1990-1991, in a national surveillance study of bacterial resistance, ciprofloxacin data from geographic and demographically diverse institutions were collected. Most of the isolates were from hospitalized patients. Ciprofloxacin susceptibility was obtained on 154,689 clinical isolates comprising 48 genera and 128 species or groups; 60.2% of the species or groups and 62.3% of the isolates were gram-negative. MIC tests and identification tests also were performed on 12,012 of these isolates, which had been submitted to our in-house laboratory. For all surveillance isolates, 88.2% were susceptible, 4.6% were moderately susceptible, and 7.2% were resistant to ciprofloxacin. Most isolates (96.2%) of the surveillance Enterobacteriaceae were susceptible to ciprofloxacin, as were 87.7% of the Pseudomonas aeruginosa (7.8% resistant). A majority of the methicillin-susceptible strains of Staphylococcus aureus were susceptible (95.7%) or moderately susceptible (1.4%) to ciprofloxacin. But a majority of methicillin-resistant isolates were resistant (76.4%) to ciprofloxacin. Most of the pneumococci (96.5%) were susceptible or moderately susceptible to ciprofloxacin with 92.7% of these isolates having MICs of 1 mg/l (susceptible) or 2 mg/l (moderately susceptible). The ciprofloxacin data for the isolates tested in our in-house laboratory generally confirmed the susceptibility rates of those from the surveillance data. This study shows that, with the exception of methicillin-resistant staphylococci, ciprofloxacin has retained a high level of activity against most bacterial pathogens.