Soil‐borne reservoirs of antibiotic‐resistant bacteria are established following therapeutic treatment of dairy calves

Abstract

SummaryWe determined if antibiotics residues that are excreted from treated animals can contribute to persistence of resistant bacteria in agricultural environments. Administration of ceftiofur, a third-generation cephalosporin, resulted in a ∼ 3 log increase in ceftiofur-resistant Escherichia coli found in the faeces and pen soils by day 10 (P = 0.005). This resistant population quickly subsided in faeces, but was sustained in the pen soil (∼ 4.5 log bacteria g −1 ) throughout the trial (1 month). Florfenicol treatment resulted in a similar pattern although the loss of florfenicol-resistant E. coli was slower for faeces and remained stable at ∼ 6 log bacteria g −1 in the soil. Calves were treated in pens where eGFP-labelled E. coli were present in the bedding (∼ 2 log g −1 ) resulting in amplification of the eGFP E. coli population ∼ 2.1 log more than eGFP E. coli populations in pens with untreated calves (day 4; P < 0.005). Excreted residues accounted for > 10-fold greater contribution to the bedding reservoir compared with shedding of resistant bacteria in faeces. Treatment with therapeutic doses of ceftiofur or florfenicol resulted in 2-3 log g −1 more bacteria than the estimated ID50 (2.83 CFU g −1 ), consistent with a soil-borne reservoir emerging after antibiotic treatment that can contribute to the long-term persistence of antibiotic resistance in animal agriculture.

Effects of In-Feed Chlortetracycline Prophylaxis in Beef Cattle on Animal Health and Antimicrobial-Resistant Escherichia coli

“…We postulate that the temporal increase in E. coli concentrations in occupied pens was due to the deposited E. coli populations themselves, increased nutrients from the deposited manure, or a combination of these factors. These findings and postulations are consistent with recent studies that found antimicrobial-resistant bacteria and antimicrobial resistance genes increased in soils from pens holding cattle that had not received antibiotics and soils fertilized with manure from dairy cattle that had not received antibiotics (30,33).…”

“…Concerns also have been raised that in-feed CTC could increase the occurrence of antimicrobial resistance in pen surface soil, possibly reinoculating cattle with resistant bacteria or increasing the occurrence of antimicrobial resistance in manure, which may impact crops or the environment (29)(30)(31)(32). To our knowledge, the impact of in-feed CTC on beef cattle feedlot pen surface generic, TET r , and 3GC r E. coli occurrences has not been reported.…”

“…A comparison of the AMR impacts of in-feed CTC prophylaxis to therapeutic treatments with highest priority critically important antimicrobials was beyond the scope of this study, and we are not aware of any published studies directly addressing this specific topic. Regardless, research is needed to address this gap, because therapeutic doses of some critically important antimicrobials have been theorized to contribute to antimicrobial resistance more than in-feed CTC (30,45).…”

Occurrence and Spread of Quinolone-Resistant Escherichia coli on Dairy Farms

“…On H farms, a high within-sample prevalence of QREC was observed in the calf feed and water troughs and in milk bucket samples. The MLVA was not used to test movement within farms; however, we can assume, based on these results, that the bacterial flora surrounding the calves may play an essential role in the presence of bacteria in their gastrointestinal (GI) tract, which was also observed in a recent study by Liu et al (13). A high prevalence of QREC in feed and water troughs may ease the fecal-oral circulation of QREC, which was also suggested by Yamamoto et al (14) to be important for the on-farm dissemination of multidrug-resistant E. coli.…”

Sustainable farming of the mealworm Tenebrio molitor for the production of food and feed

“…Antibiotics are therefore used as growth promoters and prophylactics, which has led to an explosive increase in the prevalence of antibiotic-resistant bacteria, threatening livestock and human health [71,72]. Although the use of antibiotics to promote growth is restricted in the EU [73], even the therapeutic use of antibiotics has resulted in the spread of antibiotic-resistant bacteria among livestock [74,75].…”