Activity of mecillinam against Escherichia coli resistant to third-generation cephalosporins.
OBJECTIVE
To assess the activity of mecillinam against two groups of Escherichia coli: (i) a selection of international isolates with mechanisms of resistance caused by the presence of defined beta-lactamases; and (ii) isolates resistant to third-generation cephalosporins referred from across Wales.


METHODS
Antibiotic susceptibility testing with mecillinam, meropenem, amoxicillin, co-amoxiclav, cefotaxime, piperacillin/tazobactam, ciprofloxacin, nitrofurantoin, trimethoprim and gentamicin was performed using the BSAC agar dilution method against 30 international strains of E. coli with known beta-lactamase presence. Antibiotic susceptibility testing with mecillinam using the same method was performed against 325 regional isolates of E. coli resistant to third-generation cephalosporins.


RESULTS
The susceptibility results showed that the only antibiotics to which the 30 international isolates were consistently susceptible were mecillinam (100%) and meropenem (100%), irrespective of the presence of beta-lactamases. Of the local isolates, 93.5% (304/325) were susceptible to mecillinam, having MICs < 8 mg/L.


CONCLUSIONS
Our results show that mecillinam has excellent in vitro activity against a range of E. coli exhibiting beta-lactamase activity, some with the production of multiple beta-lactamases. It is time to further evaluate the clinical utility of mecillinam in the treatment of infections caused by such organisms.
Wootton
Mandy
M
NPHS Microbiology, University Hospital of Wales, Cardiff, UK.
Walsh
Tim R
TR
Macfarlane
Lorna
L
Howe
Robin A
RA
D000560:Amdinocillin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D014852:Wales; D001618:beta-Lactamases / Q000096:biosynthesis
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D001618:beta-Lactamases; D000560:Amdinocillin