MOLECULAR EPIDEMIOLOGY OF THIRD-GENERATION CEPHALOSPORIN- RESISTANT ESCHERICHIA COLI FROM PIGS AND DAIRY CATTLE IN ARGENTINA

Abstract

Intro: Argentina is one of South America's leading milk and pork producers, yet the data for antimicrobial usage and resistance in these sectors is extremely limited. Here we report third-generation cephalosporin resistance (3GC-R) rates among E. coli from pigs and dairy cattle in two Argentinian regions (La Plata and Rio Cuarto) and the resistance mechanisms found. Methods: Samples were from effluent and faecally-contaminated near-animal environments collected using sterile boot-socks, submerged in 10x w/v PBS and made to 25% v/v glycerol; 20μL was spread on Chromagar-3GCR. Up to two 3GC- R isolates representing each positive sample were sequenced (Illumina) following deduplication at farm level using multiplex β-lactamase gene PCR. Findings: A total of 413 samples across 40 pig farms (291 La Plata, 122 Rio Cuarto) and 404 samples across 30 dairy cattle farms (286 La Plata, 118 Rio Cuarto) were collected. In La Plata, 29.7% of cattle and 51.2% of pig samples were positive for 3GC-R E. coli. In Rio Cuarto, resistance was more prevalent: 55.1% and 77.9% positivity in cattle and pig samples, respectively. Sequencing 131 representative 3GC-R isolates revealed a wide range of 3GC-R mechanisms, dominated by CTX-M variants (73% of isolates); specificity at the level of animal species was seen. CMY-2 accounted for 3GC-R in 24.4% of pig but only 4.4% of dairy isolates (χ2=8.14, p=0.004). 25.6% of pig isolates but only 8.9% of dairy carried CTX-M-8 (χ2=5.17, p=0.02). 6.9% of pig but 40% of dairy isolates carried CTX-M-15 (χ2=21.5, p<0.001). There was only one significant difference in 3GC- R mechanism prevalence seen between regions: CTX-M-14 was more common in isolates from farms around Rio Cuarto than La Plata (χ2=7.45, p=0.006). Nine 3GC-R isolates from pigs and one from cattle did not carry any known 3GC-R mechanism. Conclusion: There is a considerable burden of 3GC-R in Argentina which varies significantly by region and animal.