The antimicrobial activity of mecillinam, nitrofurantoin, temocillin and fosfomycin and comparative analysis of resistance patterns in a nationwide collection of ESBL-producing Escherichia coli in Norway 2010-2011.

BACKGROUND

The prevalence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in Norway has been steadily increasing during the last 10-15 years as part of a global pandemic. ESBL producers frequently express co-resistance to other important antimicrobial drug classes, limiting therapeutic options. This has led to regained interest in older antimicrobial agents. The aim of this study was to evaluate the antimicrobial activity of mecillinam, nitrofurantoin, temocillin and fosfomycin, as well as to perform a comparative analysis of resistance patterns in a nationwide collection of ESBL-producing E. coli.

METHODS

A nationwide collection of all 105 clinical isolates of ESBL-producing E. coli from the Norwegian Organisation for Surveillance of Antimicrobial Resistance (NORM) during 2010-2011 was analyzed. Detection and identification of ESBL-encoding genes were performed by PCR and sequencing for confirmation of ESBL variants of blaTEM and blaSHV (2010) or microarray (2011). Minimum inhibitory concentrations (MICs) or MIC correlates were determined using MIC gradient tests or VITEK 2, respectively. Comparative analysis of resistance patterns was performed.

RESULTS

All isolates were susceptible to fosfomycin, temocillin (urinary tract breakpoint) and meropenem. For mecillinam and nitrofurantoin, 6% and 9% of the isolates, respectively, were non-susceptible. A high level of susceptibility was also observed for amikacin (95%). In contrast, the non-susceptibility proportions to ampicillin (100%), cefotaxime (97%), ceftazidime (77%), aztreonam (87%), gentamicin (42%), tobramycin (52%), ciprofloxacin (76%) and trimethoprim-sulfamethoxazole (71%) were higher.

CONCLUSIONS

Overall, the in vitro susceptibility to nitrofurantoin, fosfomycin, mecillinam and temocillin was high, indicating that these drugs are good options for treating uncomplicated urinary tract infections caused by ESBL-producing E. coli.