Multidrug-resistant Escherichia coli harbouring mcr-1 and bla_CTX-M genes isolated from swine in Argentina

Objectives: Multidrug-resistant Escherichia coli isolates recovered from food-producing animals are a global public-health concern, especially those with transferable mechanisms of antimicrobial resistance such as extended-spectrum β-lactamase (ESBL) and mcr-1 genes. Here we report for the first time E. coli recovered from diarrhoeic and healthy pigs harbouring bla_CTX-M and/or mcr-1 from Argentinean farms.

Methods: During 2017, a total of 34 E. coli were recovered from 31 faecal samples from diarrhoeic piglets and healthy fattening pigs from five pig farms in three Argentinean provinces. Antimicrobial susceptibility was evaluated by agar diffusion and resistance genes were identified by PCR. Multiplex PCR was applied to screen for ST69, ST73, ST95 and ST131 clones. Genetic relationships were evaluated by XbaI-PFGE.

Results: A high diversity of resistance profiles was observed (20 profiles among 34 isolates), and 71% of isolates were multidrug-resistant. Resistance to third-generation cephalosporins (3GCs) was observed in 28 isolates and was associated with bla_CTX-M (24), bla_CMY (3) and bla_PER-2 (1) genes. bla_CTX-M alleles were grouped by specific PCR as follow: 17 bla_CTX-M-8/25; 4 bla_CTX-M-1/15; 2 bla_CTX-M-2; and 1 bla_CTX-M-9/14. Twelve isolates were positive for mcr-1, of which six were also resistant to 3GCs and were positive for bla_CTX-M-8/25 (4), bla_CTX-M-1/15 (1) or bla_CMY (1). High genetic diversity was observed, discriminating 29 profiles. One ST131 and two ST95 human-associated clones were detected.

Conclusion: Here we describe E. coli isolates recovered from diarrhoeic piglets and healthy fattening pigs harbouring ESBL and/or mcr-1 genes. 3GC resistance was mainly associated with CTX-M, in particular with bla_CTX-M-8/25 alleles.