CTX-M, SHV, TEM and VEB β-lactamases, and MCR-1 among multidrug-resistant Escherichia coli and Klebsiella isolates from environment near animal farms in Thailand.

Background: Currently, antimicrobial agents are widely used in both animals and agriculture, causing the crisis of multidrug-resistant (MDR) bacteria. In this study we surveyed for 4 important antimicrobial-resistant bacteria: extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, Klebsiella pneumoniae and Salmonella spp., and methicillin-resistant Staphylococcus aureus (MRSA) from the environment around chicken and pig farms.

Methods: Forty-four soils, 44 water and 15 bootstrap samples were collected from upstream and downstream of the riverside close to 22 animal farms in 2020 (9 farms) and 2023 (13 farms). The samples were cultured in appropriate media and isolated colonies were further identified. Antimicrobial susceptibility and ESBL production were tested by disk diffusion method except for colistin susceptibility determined by broth disk elution test. Common resistance genes were tested by polymerase chain reaction (PCR) methods.

Results: A total of 123 E. coli (n = 59) and Klebsiella species (n = 64) were identified and 25 isolates of them were MDR; 21 and 4 isolates from the downstream and upstream areas respectively. In addition, 13 isolates were ESBL producers, of which 12 isolates were from the downstream area. The most common ESBL gene among both organisms was bla, whereas colistin resistance gene, mcr-1, was found in 2 E. coli isolates. Salmonella spp. and MRSA were not isolated from any sample.

Conclusions: Antimicrobial-resistant bacteria were found in the environment around the animal farms especially from the downstream area, suggesting the urgent need of judicious use of antimicrobial agents in animal farms.