Research Note: Antimicrobial resistance profile of Enterococcus spp. isolated from the eggshell of laying hens
I P Lanza1, G R Silva2, L D M Menezes3
1Veterinary School, Federal University of Minas Gerais, Belo Horizonte, 30123-970, Brazil.
Abstract:
The occurrence of antimicrobial resistance in microorganisms isolated from eggshells, especially Enterococcus, might serve as a parameter to assess the selection of bacteria due to the use of drugs in the diet of laying hens. In order to evaluate the frequency and the antimicrobial resistance profile of Enterococcus spp. isolated from the eggshells, 225 Hy-line laying hens were submitted to a 25-d long trial. The treatments were the following: hens fed ration without antimicrobials (control) and groups that received oxytetracycline (10 mg kg-1), doxycycline (20 mg kg-1), lincomycin (50 mg kg-1), and enrofloxacin (10 mg kg-1) in the ration for 5 d. Six replications were analyzed per treatment, composed of a pool of 5 eggs each. They were collected before treatment and on days 3, 6, 15, and 25, totaling 150 samples. Eggshells were submitted to counts of Enterococcus spp., which were identified by proteomic analyses. Antimicrobial resistance was determined by the disk-diffusion test. It was observed that 97.3% (n = 146) of the samples were contaminated with Enterococcus spp. There were no differences (P > 0.05) in the bacterial counts between treatments on the same day of evaluation. E. faecalis and E. faecium were the most frequent on the eggshells of all treatments. Multiresistance to the four classes of antimicrobials was also verified in the isolated bacteria. A total of 83% of the Enterococcus isolates showed resistance to neomycin, which was not administered to the hens, demonstrating an environmental problem. Thus, feeding laying hens with diets added with antimicrobials induces drug resistance in Enterococcus spp., isolated form the eggshells.
Insights
Antimicrobial drugs in laying hen feed promote drug-resistant Enterococcus on eggshells. This resistance, particularly to non-administered drugs like neomycin, highlights an environmental issue linked to poultry farming practices.
Area of Science:
- Microbiology
- Veterinary Medicine
- Food Safety
Background:
- Antimicrobial resistance (AMR) in food-producing animals is a growing public health concern.
- Eggshells can harbor microorganisms, potentially reflecting the health status and drug exposure of laying hens.
- Enterococcus species are common commensals but can also be opportunistic pathogens and indicators of AMR.
Purpose of the Study:
- To investigate the frequency and antimicrobial resistance profiles of Enterococcus spp. on eggshells from laying hens.
- To assess the impact of dietary antimicrobials (oxytetracycline, doxycycline, lincomycin, enrofloxacin) on Enterococcus resistance.
- To determine if AMR observed on eggshells reflects the administered drugs or potential environmental contamination.
Main Methods:
- A 25-day trial involving 225 Hy-line laying hens divided into control and four treatment groups receiving different antimicrobials in their feed.
- Eggshell samples (n=150) collected over time were analyzed for Enterococcus spp. counts and identification (proteomics).
- Disk-diffusion tests were used to determine antimicrobial resistance patterns of isolated Enterococcus strains.
Main Results:
- A high prevalence of Enterococcus spp. (97.3%) was found on eggshells across all treatment groups.
- Enterococcus faecalis and Enterococcus faecium were the predominant species.
- Multidrug resistance was observed, with 83% of isolates resistant to neomycin, an antimicrobial not administered in the study, indicating environmental resistance.
Conclusions:
- Dietary administration of antimicrobials to laying hens significantly induces antimicrobial resistance in Enterococcus spp. on eggshells.
- The presence of resistance to non-administered antimicrobials (e.g., neomycin) suggests broader environmental contamination and selection pressures.
- Eggshell Enterococcus serves as a valuable indicator for monitoring AMR development linked to antimicrobial use in poultry.
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