Purpose: To investigate the susceptibility of carbapenemase-producing Enterobacterales (CPE) to mecillinam based on the recently updated European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints for uncomplicated Urinary Tract Infection (uUTI).Methods: The challenge collection consisted of 105 molecularly characterized Enterobacterales [Klebsiella spp. (N = 49), Escherichia coli (N = 30), Enterobacter cloacae (n = 13), Citrobacter freundii (N = 9), Proteus mirabilis (N = 3), and Raoultella ornithinolytica (N = 1)]. Isolates produced OXA-48 (N = 18), OXA-48-like (N = 18), VIM (N = 22), NDM (N = 22), KPC (N = 12), IMI (N = 9), IMP (N = 6), GES (N = 1), OXA-58 (N = 2) or combinations thereof (N = 5). MICs of carbapenems were determined by agar gradient diffusion (AGD). MICs of mecillinam were assessed by agar dilution (reference method) and compared to disk diffusion (DD) and AGD.Results: Overall 23/105 CPE (21.9%) were susceptible to mecillinam. Susceptibility was observed in E. coli (N = 12), E. cloacae (N = 7), and Klebsiella pneumoniae (N = 4) producing IMI, OXA-48, OXA-48-like, and NDM-1 carbapenemases. MIC50 for mecillinam in all isolates was 128 mg/L while MIC50 for meropenem was 8 mg/L. Lower MICs for mecillinam were found in IMI (MIC50 8 mg/L) and OXA-48-like (MIC50 16 mg/L) producers. The comparison of the different susceptibility methods showed very major errors of 12.2% with AGD and 8.5% with disk diffusion when compared to the reference method.Conclusion: Mecillinam susceptibility was restricted to isolates producing IMI-, OXA-48-like, and NDM-1 carbapenemases and was documented despite high carbapenem MICs in some isolates. Mecillinam could be a promising oral antimicrobial in uUTI caused by E. coli and E. cloacae isolates carrying IMI- and OXA-48-like carbapenemases; however, susceptibility testing by AGD and disk diffusion remains problematic.
A. urinae
and
A. sanguinicola
have been increasingly recognized as causative agents in urinary tract infections. Currently, there are few data available on the activity of different antibiotics against these species and no data on nitroxoline.
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