Increase in the Frequency of Salmonella Enteritidis with Decreased Susceptibility to Ciprofloxacin

Increase in the Frequency of Salmonella Enteritidis with Decreased Susceptibility to Ciprofloxacin

JOVITA HARO, UDAY DESSAI, GAMOLA FORTENBERRY, CATHERINE ROCKWELL, BONNIE KISSLER AND SHERYL SHAW, USDA FOOD SAFETY AND INSPECTION SERVICE

The National Antimicrobial Resistance Monitoring System, or NARMS, monitors changes in antimicrobial susceptibility among bacterial isolates (Salmonella, Campylobacter, E. coli, and Enterococcus) and communicates these findings to industry, stakeholders and the public.

NARMS identified an increase since 2017 in the proportion of Salmonella Enteritidis isolates showing decreased susceptibility to Ciprofloxacin (DSC: Resistant + Intermediate resistant categories together, MIC ≥ 0.12 µg/mL) from chicken product and cecal samples collected at federally inspected slaughter establishments (Figure 1). Decreased efficacy of ciprofloxacin is of concern as it is commonly used to treat severe Salmonella infections. This trend is also concerning as fluoroquinolone use has been prohibited in poultry in the United States since 2005 after initial increases of resistance were observed in poultry Campylobacter isolates.

Key Findings:

• The observed DSC in Enteritidis is attributed to a single point mutation in the quinolone- resistance determinant region, specifically in the gyrase A gene (gyrA).
• The increase of Enteritidis with DSC has been observed since 2017. To date, a total of 1,068 Enteritidis isolates from chicken product and chicken cecal samples have been identified as DSC.
• Most of these isolates (98.5%) do not show resistance to any other antimicrobial classes.
• Since 2017, the occurrence of DSC has been observed across geographic locations, corporations, and establishment sizes.
• FSIS' observations correlate with an increase in Enteritidis with DSC observed in samples collected from retail chicken products and ill persons.

Figure 1. DSC Frequency in S. Enteritidis from Chicken Product and Cecal Samples

NARMS continues to communicate with industry and NARMS partners to further understand this trend, understand the drivers of DSC despite the long-term prohibition in fluoroquinolones/ciprofloxacin use in poultry, and to explore mitigation strategies. For more information, please visit the NARMS Integrated Reports/Summary webpage for continued updates.