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Culture methods impact recovery of antibiotic-resistant Enterococci including Enterococcus cecorum from pre- and

M M Suyemoto¹, H J Barnes¹, L B Borst¹

¹Department of Population Health and Pathobiology, North Carolina State University, College of Veterinary Medicine, Raleigh, NC, USA.

Letters in Applied Microbiology

|December 18, 2016

Abstract:

Pathogenic strains of Enterococcus cecorum (EC) expressing multidrug resistance have emerged. In National Antimicrobial Resistance Monitoring System (NARMS) data, EC is rarely recovered from chickens. Two NARMS methodologies (FDA and USDA) were compared with standard culture (SC) techniques for recovery of EC. NARMS methods failed to detect EC in 58 caecal samples, 20 chicken breast or six whole broiler samples. EC was recovered from 1 of 38 (2·6%) and 2 of 38 (5·2%) preharvest spinal lesions (USDA and FDA method, respectively). In contrast, using the SC method, EC was recovered from 44 of 53 (83%) caecal samples, all 38 (100%) spinal lesions, 14 of 20 (70%) chicken breast samples, and all three spinal lesions identified in whole carcasses. Compared with other Enterococcus spp., EC isolates had a higher prevalence of resistance to macrolides. The NARMS methods significantly affected recovery of enterococcal species other than EC. When the postharvest FDA method was applied to preharvest caecal samples, isolates of Enterococcus faecium were preferentially recovered. All 11 E. faecium isolates were multidrug resistant, including resistance to penicillin, daptomycin and linezolid. These findings confirm that current methodologies may not accurately identify the amount and range of antimicrobial resistance of enterococci from chicken sources.

Significance And Impact Of The Study:

Enterococci are an important reservoir for antimicrobial resistance. This study demonstrates how current culture methods underreport resistance to macrolides in enterococci by selecting against strains of Enterococcus cecorum in pre- and postharvest chicken. Further, the application of postharvest surveillance methods to preharvest samples resulted in selective recovery of Enterococcus faecium over Enterococcus faecalis. Isolates of E. faecium recovered exhibited multidrug resistance including penicillin, daptomycin and linezolid resistance. These findings suggest that culture methodology significantly impacts the range and amount of antimicrobial resistance detected in enterococci isolated from chicken.

Insights

Current culture methods underestimate antimicrobial resistance in chickens by failing to detect Enterococcus cecorum. This selective detection impacts surveillance of multidrug-resistant bacteria in poultry.

Area of Science:

Veterinary Microbiology
Food Safety
Antimicrobial Resistance

Background:

Pathogenic strains of Enterococcus cecorum (EC) with multidrug resistance are emerging.
EC is infrequently detected in chickens using National Antimicrobial Resistance Monitoring System (NARMS) methodologies.

Purpose of the Study:

To compare the efficacy of two NARMS methodologies (FDA and USDA) against standard culture (SC) techniques for recovering EC from chicken samples.
To assess the impact of culture methodology on the detection of antimicrobial resistance in enterococci from chicken sources.

Main Methods:

Comparison of EC recovery rates using NARMS (FDA, USDA) and SC methods across various chicken sample types (caecal, spinal lesions, breast, whole carcasses).
Analysis of antimicrobial resistance profiles, particularly macrolide resistance in EC isolates.
Evaluation of selective recovery of other Enterococcus species (e.g., E. faecium) by NARMS methods when applied to preharvest samples.

Main Results:

NARMS methods failed to detect EC in most caecal, breast, and whole carcass samples, with low recovery rates from spinal lesions.
SC method demonstrated significantly higher recovery rates for EC across all sample types.
EC isolates exhibited a higher prevalence of macrolide resistance compared to other Enterococcus species.
NARMS methods, particularly the postharvest FDA method applied to preharvest samples, preferentially recovered multidrug-resistant Enterococcus faecium.

Conclusions:

Standard culture methods are superior for detecting Enterococcus cecorum in chicken samples compared to NARMS methodologies.
Current NARMS methods may underreport macrolide resistance in enterococci due to selective underdetection of EC.
The choice of culture methodology significantly influences the assessment of antimicrobial resistance prevalence and spectrum in enterococci from poultry.

Read full analysis

Keywords:

food safety lactic acid bacteria postharvest resistance veterinary

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