Assessing the Risk of Antimicrobial Resistant Enterococcal Infections in Humans Due to Bacitracin Usage in Poultry

Area of Science:

• Veterinary Medicine
• Microbiology
• Public Health

Background:

• Bacitracin is an antimicrobial used in U.S. poultry for disease control, raising concerns about antimicrobial resistance.
• Antimicrobial-resistant bacteria from poultry could potentially transmit to humans, complicating treatment.
• Enterococcus faecalis and Enterococcus faecium are key bacteria of concern in this context.

Purpose of the Study:

• To conduct a quantitative risk assessment (QRA) on the potential U.S. human health risk from antimicrobial-resistant Enterococcus derived from poultry due to bacitracin use.
• To estimate the annual number of healthcare-associated enterococcal infections resistant to therapy linked to bacitracin in poultry.

Main Methods:

• A quantitative risk assessment modeling approach was employed.
• Parameter estimates were set to maximize risk to ensure a conservative assessment.
• Data on bacitracin resistance genes (bcrABDR) and resistance to other antimicrobials (vancomycin, linezolid) were analyzed.

Main Results:

• Approximately 60% of poultry-derived Enterococcus isolates showed bacitracin resistance, compared to very few human isolates.
• No vancomycin or linezolid-resistant Enterococcus strains were detected in poultry between 2002-2019.
• Estimated annual cases of resistant Enterococcus infections from poultry were 0.86 for E. faecalis and 0.14 for E. faecium.

Conclusions:

• The annual risk for E. faecalis and E. faecium infections resistant to therapy due to U.S. poultry bacitracin use is negligible (<1 in 350 million and <1 in 2 billion, respectively).
• Even under maximum risk assumptions, bacitracin use in U.S. poultry presents a low probability of risk to human health when used as labeled.