Spread of tetracycline resistance genes at a conventional dairy farm

Abstract

The use of antibiotics in animal husbandry contributes to the worldwide problem of increasing antibiotic resistance in animal and human pathogens. Intensive animal production is considered an important source of antibiotic resistance genes released to the environment, while the contribution of smaller farms remains to be evaluated. Here we monitor the spread of tetracycline resistance (TC-r) genes at a middle-size conventional dairy farm, where chlortetracycline (CTC, as intrauterine suppository) is prophylactically used after each calving. Our study has shown that animals at the farm acquired the TC-r genes in their early age (1–2 weeks), likely due to colonization with TC-resistant bacteria from their mothers and/or the farm environment. The relative abundance of the TC-r genes tet(W), tet(Q), and tet(M) in fresh excrements of calves was about 1–2 orders of magnitude higher compared to heifers and dairy cows, possibly due to the presence of antibiotic residues in milk fed to calves. The occurrence and abundance of TC-r genes in fresh excrements of heifers and adult cows remained unaffected by intrauterine CTC applications, with tet(O), tet(Q), and tet(W) representing a “core TC-resistome” of the farm, and tet(A), tet(M), tet(Y), and tet(X) occurring occasionally. The genes tet(A), tet(M), tet(Y), and tet(X) were shown to be respectively harbored by Shigella, Lactobacillus and Clostridium, Acinetobacter, and Wautersiella. Soil in the farm proximity, as well as field soil to which manure from the farm was applied, was contaminated with TC-r genes occurring in the farm, and some of the TC-r genes persisted in the field over 3 months following the manure application. Concluding, our study shows that antibiotic resistance genes may be a stable part of the intestinal metagenome of cattle even if antibiotics are not used for growth stimulation, and that smaller dairy farms may also contribute to environmental pollution with antibiotic resistance genes.

Antimicrobial resistance profiles of 5 common bovine mastitis pathogens in large Chinese dairy herds

“…(59%), NAS (34%), and Klebsiella spp. (32%), similar to a previous report for China (Yassin et al, 2017) and consistent with spread of tetracycline-resistance genes on a conventional dairy farm (Kyselková et al, 2015).…”

Metagenomic analysis of enteric bacterial pathogens affecting the performance of dairy cows in smallholder productions systems

“…These findings are in agreement with the results by Thames et al, (2012), Agga et al (2015), Gerzova et al (2015), Iweriebor et al (2015), Madoshi et al (2016) and Pitta et al (2016) who reported high presence of tetC, tetG, tetO, tetW, and tetX in their studies. The findings are also similar to the results reported by Kyselkova et al (2015) when studying the occurrence of tetracycline resistance genes at conventional dairy farm. However, Englen et al (2006) reported that Campylobacter jejuni displayed tetracycline and nalidixic acid resistance genes while C. coli indicated resistance to azithromycin, ciprofloxacin, clindamycin, erythromycin, gentamicin, and tetracycline from cow fecal isolates.…”

Review of Antimicrobial Resistance in the Environment and Its Relevance to Environmental Regulators

“…The observed transmission of resistance genes through contaminated cow and calf bedding and soil (Call et al, 2013; Kyselková et al, 2015; Liu et al, 2016), highlights the importance of biosecurity and the need to separate animals being treated for infection from the herd (where feasible), and not reusing bedding from infected and treated animals (Mitchell et al, 2015). Intramuscular treatment of healthy calves with ceftiofur or florfenicol, as per manufacturer’s recommendations, was shown to be sufficient to establish a reservoir of drug-resistant Escherichia coli in the feces, soil and bedding of treated animals (Liu et al, 2016).…”

“…The dissemination of these materials on soil increases the ARG exposure risk to: (1) (wild) animals; (2) crops; (3) adjacent surface water bodies; (4) groundwater; (5) farm workers; and (6) air as dust particles from land spreading or aeolian erosion (Heuer et al, 2011; Ferro et al, 2015; Kyselková et al, 2015). The persistence and changes in the ‘resistome’ [the collection of genes that are capable of conferring resistance toward antibiotics when expressed in a susceptible organism (Dantas and Sommer, 2012)] of sludge or manure after it is anaerobically digested or composted is only recently emerging.…”