Evaluation of current activities of fluoroquinolones against gram-negativebacilli using centralized in vitro testing and electronic surveillance

Given the propensity for Enterobacteriaceae and clinically significant nonf ermentative gram-negative bacilli to acquire antimicrobial resistance, cons istent surveillance of the activities of agents commonly prescribed to trea t infections arising from these organisms is imperative. This study determi ned the activities of two fluoroquinolones, levofloxacin and ciprofloxacin, and seven comparative agents against recent clinical isolates of Enterobac teriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotropho monas maltophilia using two surveillance strategies: 1) centralized in vitr o susceptibility testing of isolates collected from 27 hospital laboratorie s across the United States and 2) analysis of data from The Surveillance Ne twork Database-USA, an electronic surveillance network comprising more than 200 laboratories nationwide. Regardless of the surveillance method, Entero bacteriaceae, P. aeruginosa, and A. baumannii demonstrated similar rates of susceptibility to levofloxacin and ciprofloxacin, Susceptibilities to the fluoroquinolones approached or exceeded 90% for all Enterobacteriaceae exce pt Providencia spp. (less than or equal to 65%). Approximately 70% of P. ae ruginosa and 50% of A. baumanii isolates were susceptible to both fluoroqui nolones. Among S. maltophilia isolates, 50% more isolates were susceptible to levofloxacin than to ciprofloxacin. Overall, the rate of ceftazidime non susceptibility among Enterobacteriaceae was 8.7%, with fluoroquinolone resi stance rates notably higher among ceftazidime-nonsusceptible isolates than ceftazidime-susceptible ones. Multidrug-resistant isolates were present amo ng all species tested but were most prevalent for Klebsiella pneumoniae and Enterobacter cloacae. No gram-negative isolates resistant only to a fluoro quinolone were encountered, regardless of species. Thus, while levofloxacin and ciprofloxacin have maintained potent activity against Enterobacteriace ae, the potential for fluoroquinolone resistance, the apparent association between fluoroquinolone and cephalosporin resistance, and the presence of m ultidrug resistance in every species examined emphasize the need to maintai n active surveillance of resistance patterns among gram-negative bacilli.