Colistin resistance in and in humans and backyard animals in Ecuador.

OBJECTIVE

Colistin is an antibiotic of last resort for treating serious Gram-negative bacterial infections. However, the misuse of colistin, especially as an animal growth promoter, has contributed to increasing antimicrobial resistance, mediated mainly through plasmid transfer of the gene. This study assessed the prevalence of phenotypic and molecular colistin resistance in in Ecuador in healthy humans and their chickens and pigs.

METHODS

Fecal samples were collected from humans and their chickens and pigs in two rural coastal and Amazon regions between April and August 2020. Gram-negative bacteria were isolated and identified using conventional techniques. Phenotypic resistance was determined using the broth microdilution technique, and the gene was detected using conventional polymerase chain reaction.

RESULTS

A total of 438 fecal samples were obtained from 137 humans, 147 pigs and 154 chickens. The prevalence of isolates was 86.3% (378/438) and , 37.4% (164/438). Overall, the gene was found in 90% (340/378) of isolates, with higher prevalences found in isolates from coastal regions (96.5%, 191/198), humans (95.6%, 111/116) and chickens (91.8%, 123/134); for , the gene was found in 19.5% (32/164) of isolates, with equal distribution between regions and hosts. Only four isolates, two and two , showed phenotypic resistance: was present in both strains but absent in the strains.

CONCLUSIONS

Despite a low prevalence of phenotypic resistance to colistin, the high prevalence of the gene in is of concern. Ecuador's ban on using colistin in animal husbandry must be enforced, and continual monitoring of the situation should be implemented.