Investigation of CTX-M Type Extended-Spectrum β-Lactamase, Carbapenem and Colistin Resistance in Enterobacterales...

The increasing prevalence of antimicrobial resistance in animals, particularly the spread of multidrug-resistant Enterobacterales, poses a significant zoonotic and public health risk.

The aim of this study was to investigate extended-spectrum β-lactamase (ESBL), carbapenem and colistin resistance among Enterobacterales in faecal swabs of dairy cattle.

A total of 400 samples were cultured on Mac Conkey screening media for ESBL, carbapenem and colistin resistance. The grown Enterobacterales were identified by MALDI-TOF-MS, followed by ceftriaxone, cefotaxime and ceftazidime resistance and double disk synergy. ESBL resistance genes were identified by polymerase chain reaction (PCR) and Sanger sequencing. Bacteria grown on colistin screening media were investigated for colistin resistance by EUCAST microbroth dilution method.

A total of 89 (22.25%) of the bacteria grown from 400 samples were identified as potential ESBL-producing Enterobacterales members. A number of 53 (59.5%) of them were identified as ESBL blaCTX-M as a result of PCR, and 10 of them were identified as blaCTX-M-15/28/36/66 as a result of sequencing. None of the samples cultured on carbapenem medium grew. A total of 18 samples grown in colistin medium were found to be colistin sensitive by broth microdilution. Genotypes were not included in the study. All isolated bacteria were identified as Escherichia coli.

In this study, blaCTX-M-15 and its derivatives, which are common in humans, were also found to be the predominant ESBL type in animals. Monitoring resistance in animals together with resistance in human infections may provide more important data on the spread of resistance.