In vitro susceptibility of recent antibiotic-resistant urinary pathogens to ertapenem and 12 other antibiotics

Background: The treatment of complicated urinary tract infections may require the use of a parenteral antibiotic with potent activity against the most common urinary pathogens. Ertapenem is a broad-spectrum 1beta-methyl carbapenem with a long plasma half-life that allows administration of a single daily dose. Methods: The purpose of this work was to test the in vitro susceptibility to ertapenem, ampicillin, cefazolin, cefuroxime, cefotaxime, co-amoxiclav, piperacillin/tazobactam, imipenem, gentamicin, amikacin, fosfomycin, ciprofloxacin and co-trimoxazole of 482 strains of urinary pathogens of the family Enterobacteriaceae isolated from patients in the community of Madrid (40% from males). The distribution was as follows: Escherichia coli (n = 315), Proteus mirabilis (n = 42), Klebsiella spp. (n = 14) and AmpC-producing Enterobacteriaceae (n = 111). The strains studied were selected based on their resistance to quinolones and aminoglycosides, and their production of extended-spectrum beta-lactamases (ESBLs) or AmpC-type beta-lactamases. Results: All the strains were susceptible to ertapenem, imipenem and amikacin. The MIC90 of ertapenem ranged from a minimum of 0.03 mg/L for Proteus vulgaris and a maximum of 1 mg/L for Enterobacter spp. Ertapenem was the most active of all drugs tested in all cases. On comparing antibiotic resistance among ESBL-producing strains of E. coli (n = 35) and E. coli strains not producing ESBLs (n = 280), statistically significant differences were obtained for ciprofloxacin (P = 0.002) and gentamicin (P = 0.011). Regarding ertapenem, only a slight increase in MIC50 was seen, the value being 0.015 mg/L for strains not producing ESBLs versus 0.03 mg/L for ESBL-producing strains. Conclusions: In view of its significant antibiotic potency against antibiotic-resistant Enterobacteriaceae, ertapenem may constitute a good therapeutic alternative in urinary infections caused by these pathogens.