Bats as a reservoir of resistant Escherichia coli: A methodical view. Can we fully estimate the scale of resistance in the reservoirs of free-living animals?

Bats are a poorly understood reservoir of pathogenic and multi-drug resistant microorganisms; therefore, the aim of the study was to analyze the presence of drug resistance among E. coli isolated from the species of bats occurring naturally in Poland. The strategy of isolation and identification of resistant strains from pooled and single-animal samples was based on selective media with cefotaxime, chloramphenicol, kanamycin and tetracycline, the use of the ADSRRS-fingerprinting method for genomic differentiation of isolates, and the classical methods of evaluation of phenotypic and genotypic resistance. Of the 78 isolated isolates confirmed as E. coli, there were 38 genetically distinct strains resistant at least to one antimicrobial. 71% of these strains met the multi-drug resistance criterion. Moreover, two different multidrug resistant strains were isolated from three single samples. The highest resistance was observed in the case of ampicillin (66%), kanamycin (84%), sulfamethoxazole/trimetoprim (61%/55% respectively), and streptomycin (50%), which in most cases was confirmed by the presence of an adequate gene. Two isolates from single hosts produced extended-spectrum beta-lacta- mases (bla (CTX-M-3), bla( CTX-M-15), bla (TEM-1)). With the exception of tetracycline resistance, which was dominant among isolates from single animals, no significant differences in the resistance of the strains from both groups of samples were observed. Bats should not be neglected as another environmental reservoir and as an unpredictable source of potential pathogenic and multidrug resistant bacteria and should be extensively studied to predict the direction of the development and range of spreading resistance.