Invited review: Fate of antibiotic residues, antibiotic-resistant bacteria, and antibiotic resistance genes in US dairy manure management systems

Abstract

United States dairy operations use antibiotics (primarily β-lactams and tetracyclines) to manage bacterial diseases in dairy cattle. Antibiotic residues, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARG) can be found in dairy manure and may contribute to the spread of antibiotic resistance (AR). Although β-lactam residues are rarely detected in dairy manure, tetracycline residues are common and perhaps persistent. Generally, <15% of bacterial pathogen dairy manure isolates are ARB, although resistance to some antibiotics (e.g., tetracycline) can be higher. Based on available data, the prevalence of medically important ARB on dairy operations is generally static or may be declining for antibiotic-resistant Staphylococcus spp. Over 60 ARG can be found in dairy manure (including β-lactam and tetracycline resistance genes), although correlations with antibiotic usage, residues, and ARB have been inconsistent, possibly because of sampling and analytical limitations. Manure treatment systems have not been specifically designed to mitigate AR, though certain treatments have some capacity to do so. Generally, well-managed aerobic compost treatments reaching higher peak temperatures (>60°C) are more effective at mitigating antibiotic residues than static stockpiles, although this depends on the antibiotic residue and their interactions. Similarly, thermophilic anaerobic digesters operating under steady-state conditions may be more effective at mitigating antibiotic residues than mesophilic or irregularly operated digesters or anaerobic lagoons. The number of ARB may decline during composting and digestion or be enriched as the bacterial communities in these systems shift, affecting relative ARG abundance or acquire ARG during treatment. Antibiotic resistance genes often persist through these systems, although optimal management and higher operating temperature may facilitate their mitigation. Less is known about other manure treatments, although separation technologies may be unique in their ability to partition antibiotic residues based on sorption and solubility properties. Needed areas of study include determining natural levels of AR in dairy systems, standardizing and optimizing analytical techniques, and more studies of operating on-farm systems, so that treatment system performance and actual human health risks associated with levels of antibiotic residues, ARB, and ARG found in dairy manure can be accurately assessed.

Systematic analysis of occurrence, density and ecological risks of 45 veterinary antibiotics: Focused on family livestock farms in Erhai Lake basin, Yunnan, China

“…This may be due to PENG was widely used to treat infectious diseases, like cow mastitis. Oliver et al. (2020) pointed that TCs and LAs were usually used to manage bacterial disease in cows.…”

Manure as a Potential Hotspot for Antibiotic Resistance Dissemination by Horizontal Gene Transfer Events

“…β-lactams are one of the most widely used groups of antibiotics, including in veterinary medicine [77]. β-lactam residues, β-lactam-resistant bacteria and β-lactam-resistant determinants have been found in dairy cattle manure because β-lactam antibiotics are often used to treat mastitis [14,15,40,78,79]. Pig manure can also work as a reservoir for the transferable amoxicillin antibiotic resistance genes bla TEM .…”

Prevalence and antibiotic resistance of Salmonella spp. in South Punjab-Pakistan

“…Researchers have recently ascribed the presence of antibiotic residues and antibiotic resistance bacteria in the animals' manure to be the underlying cause of increased spread of antibiotic resistance. Besides, they reported a rise in antibiotic susceptibility among dairy manure isolates of bacterial pathogens with 15% of tested bacteria to be resistant against some antibiotics [38] Most of the bacterial strains have been undergoing genetic modification for evolving resistance on account of indiscriminate and injudicious use of antibiotics for treating animal and human infections. Results of the present study demonstrate similar tendencies as all five experimental sites were shown to have been contaminated with Salmonella spp.…”