Prevalence, risk factors and antimicrobial resistance of Salmonella and ESBL E. coli in dairy cows in Henan and Hubei Provinces, China

Jie Wang

Non-typhoidal Salmonella (NTS) has been implicated in the cases of foodborne infections in many countries. Extended-spectrum β-lactamases (ESBL) are plasmid-encoded enzymes, responsible for causing resistance to extended-spectrum cephalosporins, monobactams, and aztreonam. Commensal Escherichia coli (E. coli) is believed to be the reservoirs harboring ESBL genes. Farm animals, including dairy cattle, have been identified as reservoirs of human Salmonella and ESBL E. coli. There was limited information on the prevalence of Salmonella and ESBL E. coli from lactating dairy cattle in central China. A study with four broad objectives was designed to determine the epidemiology of Salmonella and ESBL E.coli in dairy cattle in central China. Study one assessed the fecal carriage of Salmonella spp. among culled adult dairy cows presented to an abattoir in Wuhan, China and their antimicrobial resistance profiles. The results indicated the prevalence of Salmonella fecal carriage was 29.0% (95% CI: 21.6, 37.3), with 63.4% (26/41, 95% CI: 46.9, 77.9) of the isolates identified as S. Typhimurium. Twenty multi-drug resistant (MDR) strains were detected (48.8%, 95% CI: 32.9, 64.9) and overall, a high resistance to ampicillin (36/41, 87.8%, 95% CI: 73.8, 95.9) and tetracycline (15/41, 56.1%, 95% CI: 39.7, 71.5) was observed. The occurrence of Salmonella was higher (OR: 3.3, 95% CI: 1.51, 7.40) in culled cows originating from the northeast zone of China than in cows originating from the central and north zones. Study two estimated the prevalence and antimicrobial resistance of Salmonella and enumerated ESBL E. coli in apparently healthy adult lactating dairy cows in Hubei Province. In this area, the within-herd prevalence of Salmonella ranged between 0.0% and 33.3%, and 9/15 of Salmonella isolates were resistant to ampicillin. ESBL E. coli was detected by culture in all farms (10/10) with an animal-level prevalence of 59.1%, and blaCTX-M was the main resistance gene (90.1%). Of 116 samples, 39.9% contained ESBL E. coli with a number exceeding 104 Colony-forming unit (CFU)/g feces. Study three assessed the herd prevalence of Salmonella and ESBL E. coli in 38 dairy herds in Henan Province, and a herd-level Salmonella prevalence of 13.2% (95% CI: 4.4, 28.1) was recorded. A high proportion of resistance to tetracycline (6/8) and florfenicol (6/8) was obtained in the cultured Salmonella. Multi-drug resistant isolates were observed on 4/5 Salmonella-positive farms. ESBL E. coli were identified on all 34 sampled farms, and all 238 ESBL E. coli isolates contained the blaCTX-M gene. Study four evaluated the risk factors of Salmonella in dairy herds in central China. The questionnaire results highlighted a significant association between Salmonella-positive status and the high frequency of observation of wildlife (birds and rodents) on the farms. In conclusion, the high prevalence of Salmonella and ESBL E. coli among dairy cattle farms in central China highlights food safety issues and the potential for foodborne disease outbreaks in residents. There is a need to institute appropriate on-farm control measures to reduce the risk of the outbreaks of foodborne diseases and the occurrence and spread of antimicrobial resistance.

Prevalence, risk factors and antimicrobial resistance of Salmonella and ESBL E. coli in dairy cows in Henan and Hubei Provinces, China

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