Selective pressure by antibiotic use in livestock

Area of Science:

• Microbiology
• Veterinary Medicine
• Public Health

Background:

• Antibiotics used as growth promoters in food animals exert selective pressure, fostering reservoirs of transferable antibiotic resistance.
• This resistance has been observed for various antibiotics, including oxytetracycline, streptothricin, and glycopeptides, with documented transfer to human pathogens.

Purpose of the Study:

• To investigate the link between antibiotic use in animal husbandry and the emergence of transferable antibiotic resistance in bacterial populations.
• To assess the impact of specific antibiotic resistance genes and their dissemination pathways from animals to humans.

Main Methods:

• Review of existing studies on antibiotic resistance in food animals and human pathogens.
• Analysis of resistance determinants (e.g., sat genes, vanA gene cluster, vatA, vatG) and their genetic elements (e.g., plasmids).
• Correlation of antibiotic usage patterns with resistance trends in animal and human microbial communities.

Main Results:

• Transferable resistance determinants (sat, vanA) have been identified in animal ecosystems, linked to antibiotic use (nurseothricin, avoparcin).
• The vanA gene cluster in Enterococcus faecium, associated with avoparcin use, spreads to human flora via meat products.
• Streptogramin resistance (vatA, vatG) in E. faecium suggests an animal origin due to virginiamycin use.

Conclusions:

• The use of avoparcin as a feed additive created a significant reservoir of transferable glycopeptide resistance (vanA).
• The ban on avoparcin has correlated with a decrease in glycopeptide-resistant Enterococcus faecium (GREF) in both animal and human populations.
• Evidence supports the prohibition of antibacterial growth promoters that could compromise human antimicrobial chemotherapy.