Mecillinam: Old Molecule, New Option

Abstract

Background Mecillinam is a β-lactam antibiotic that is increasingly being used for the treatment of uncomplicated urinary tract infections. Nevertheless, the international guidelines still recommend nitrofurantoin, fosfomycin trometamol, and pivmecillinam as first-line agents in the treatment of such infections. Aim The objective of this study was to determine the in vitro efficacy of mecillinam against Escherichia coli and Klebsiella pneumoniae strains isolated from children with urinary tract infections. Materials Methods We investigated E. coli and K. pneumoniae isolates, obtained within the period from January 2016 to October 2017, from urine samples of patients aged 0 to 16 years. Antibiotics susceptibility testing was conducted through the disk diffusion method based on the guidelines provided by EUCAST (European Committee on Antimicrobial Susceptibility Testing). Extended-spectrum β-lactamase (ESBL)-positivity was detected by the double-disk synergy test. Isolates with mecillinam inhibition-zone diameter breakpoints lower than < 15 mm were considered to be resistant according to EUCAST criteria. Results A total of 450 isolates were assessed in the study, 135 of which were ESBL-producing E.coli, 230 were non-ESBL-producing E. coli, 35 were ESBL-producing K. pneumoniae, and 50 were non-ESBL-producing K. pneumoniae isolates. Mecillinam susceptibility was observed in most of the non-ESBL-producing and ESBL-producing E. coli isolates (230/230, 100% and 115/135, 85.1%, respectively). The rates of susceptibility of the non-ESBL-producing and ESBL-producing K. pneumoniae isolates were 37/50 (74%) and 24/35 (68.6%), respectively. Conclusion The in vitro susceptibility results obtained support the usage of mecillinam as a first-line agent. The high susceptibility of non-ESBL-producing E. coli and K. pneumoniae isolates established in vitro brings the hope that this antibiotic could soon be used in clinical practice in Turkey.