Antimicrobial Susceptibility of Gram-Negative Nonurinary Bacteria to Fosfomycin and Other Antimicrobials

BACKGROUND: Fosfomycin is an antimicrobial commonly used in uncomplicated urinary tract infections. The microbiological effectiveness of fosfomycin against nonurinary Gram-negative isolates has not been widely investigated. The aim of this study was to evaluate the in vitro activity of fosfomycin against Gram-negative nonurinary isolates in a region of Greece where considerable antimicrobial resistance has been detected. METHODS: Data were retrieved from the microbiological library of the University Hospital of Heraklion, Crete. We retrospectively examined the susceptibility of all Gram-negative nonurinary isolates to fosfomycin, collected over 1 year (January-December 2008). RESULTS: A total of 594 nonurinary Gram-negative isolates were examined. Susceptibility testing was performed for 270 (45.4%) Enterobacteriaceae, 209 (35.2%) Gram-negative nonfermentative bacilli and 115 (19.4%) other Gram-negative bacteria. In total, 385 (64.8%) were susceptible to fosfomycin. Specifically, all Escherichia coli, Proteus mirabilis and Salmonella species isolates were susceptible. Additionally, 73 out of 94 (77.7%) Klebsiella pneumoniae (including carbapenem-resistant strains), 22 out of 32 (68.8%) Enterobacter species and 51 out of 79 (64.5%) Pseudomonas aeruginosa isolates were susceptible to fosfomycin. Susceptibility was highest amongst isolates (45 of 61; 73.8%) taken from outpatients and lowest for intensive care unit isolates (78 of 161; 48.4%). Isolates originating from the pediatric wards exhibited higher susceptibility (45 of 63; 71.4%) than isolates originating from other departments (340 of 531; 64%). CONCLUSION: In a region with relatively high levels of antimicrobial resistance, fosfomycin seems to exhibit good levels of in vitro activity against Gram-negative nonurinary isolates. These data justify further evaluation of its potential clinical effectiveness.