Reviving the role of mecillinam against extended spectrum beta-lactamase producing enterobacterales

This study was designed to determine the in vitro efficacy of mecillinam against extended spectrum beta lactamse producing Enterobacterales.

After proper permission from Ethical Review Committee of the Institute, all samples yielding growth of ESBL producing Enterobacterales were part of the study and were processed according to routine microbiological procedures. Routine antibiotic sensitivity testing was done on Muller Hinton Agar by Modified Kirby Bauer Method. All Gram negative isolates were subjected to concomitant detection of ESBL production by double disc synergy method. All ESBL producers were then subjected to the mecillinam Minimum Inhibitory Concentration (MIC) determination by E test. The results were interpreted as per CLSI Guidelines.

A total of 120 ESBL producing Enterobacterales isolates were included in the study. The mean age of patients with ESBL infection was 45 ± 18.7 years. There were 44% male and 55% female patients. Majority of the ESBL producing Enterobacterales were isolated from urine samples (56%), followed by pus. Among the isolated organisms, Escherichia coli (45%) was the most frequently isolated organism followed by Klebsiella spp. (22%). Overall 83% of the isolates turned out to be sensitive to mecillinam. MIC50 of mecillinam against ESBL producing Gram negative rods (GNR) turned out to be 1 ug/ml and MIC90 turned out to be 2 ug/ml.

Mecillinam shows good in vitro efficacy against ESBL producing Enterobacterales in our study. Further studies with more sample size and from diverse areas across the country should be done to evaluate its efficacy.