Cefotaximase (CTX-M) and quinolone resistance genes (qnr) with additional antimicrobial resistance mechanisms in commensal Escherichia coli from healthy pigs
Concerning the importance of food producing animals as potential reservoirs of enteric bacteria with clinically relevant antimicrobial resistance traits, we tested the prevalence of extended-spectrum β-lactamase (ESBL)-producing and fluroquinolone resistant E. coli from pigs in order identify multiple resistance mechanisms circulating in pig farms in Hungary and Croatia with special regards to plasmid mediated genes encoding cefotaximases (CTX-M) and quinolone resistance (qnr). For this purpose, faecal samples were collected from pigs representing three farms from Hungary and six farms from Croatia with 45 and 60 samples respectively. Farms were located in separate regions of the countries. Cefotaxime or nalidixic acid resistance were used as prime markers for the isolation of multiresistant E. coli strains. A second selection was based on resistance to additional antimicrobials (i.e. gentamicin) aiming to reduce the collection to isolates with representative multiresistance phenotypes. In several cases more than two different multiresistance phenotypes have been isolated from the same pig, which were considered as independent E. coli isolates. This collection of multidrug resistant E. coli contained 139 strains and was tested for the presence of blaCTX-M and qnr genes by PCR. Selected isolates carrying genes blaCTX-M and/or qnr are being subjected for confirmation and further typing of antimicrobial resistance genes by using the PCR-microarray AMR05. Cefotaxim resistant E. coli have been detected in one Hungarian and one Croatian farm representing 17% of all pigs tested. In majority of the strains, the plasmid-related resistance phenotypes such as ampicillin, cefotaxim, gentamicin and tetracycline occurred in multiple combinations. In 11% of the strains the coexistence of Ctx-Nal phenotypes was detected, together with the presence of the cefotaximase gene blaCTX-M. E. coli strains with nalidixin resistance phenotype have been predominantly (70%) characterizing healthy pigs independently from the farm and country of isolation. Ciprofloxacin resistant strains occured on one farm only. The plasmid-mediated fluoroquinolone resistance gene qnrS was identified in 11% of the strains, with or without the nalidixin-ciprofloxacin resistant phenotype, while genes qnrA and qnrB were absent. Overall, our results lead to conclude that multiresistant commensal E. coli strains carrying plasmid-mediated CTX-M type cefotaximase and/or quinolone resistance genes in different combinations are widespread on some pig farms but much less on others, most likely reflecting differences in use of antimicrobials. Ama Szmolka is a holder of János Bolyai Stipend of the Hungarian Academy of Sciences
