Characterization of enterotoxin, antibiotic resistance genes, and antimicrobial susceptibility profiling of Staphylococcus aureus isolated from table eggs: Implications for food safety and public health.

Background: Staphylococcus aureus is a significant pathogen in both clinical and food safety contexts, capable of contaminating table eggs, which are a common dietary staple worldwide.

Aim: This study aimed to assess the prevalence, molecular characteristics, and antibiotic resistance profiles of S. aureus isolated from table eggs. The focus was on identifying methicillin-resistant S. aureus (MRSA) strains that produce enterotoxin (seb), resistance to β-lactam antibiotics (blaTEM), tetracycline (tetA), and vancomycin-resistant S. aureus.

Methods: A total of 200 egg samples were collected from various retail sources in Mymensingh City Corporation, Bangladesh. Swab samples (n = 100) were collected from eggshells, and another 100 samples were collected from the inner membrane, egg white, and yolk. Samples were enriched in trypticase soy broth and cultured on mannitol salt agar. Staphylococcus aureus was isolated through conventional culture techniques, confirmed by polymerase chain reaction targeting the nuc, and further screened for the mecA, seb, blaTEM, tetA, vanA, and vanC genes. Antibiotic susceptibility testing was conducted using the disc diffusion method against 13 antibiotics. Bivariate analysis is used to assess the strong and significant correlations between virulence genes and the pairs of any of two antibiotic-resistant S. aureus.

Results: Staphylococcus spp. and S. aureus were detected in 53% and 21% of eggshell samples, respectively, and 41% and 13% of egg content samples. Among 34 coagulase-positive isolates, 12 (57.14%) from eggshells and 4 (30.78%) from egg contents were positive for the nuc gene. Resistance was observed in eggshell isolates for mecA (33.33%), blaTEM (85.71%), tetA (33.33%), vanA (19.04%), vanC (33.33%), and seb (20.50%), whereas egg content isolates showed resistance to blaTEM (46.15%) and vanC (7.80%). All coagulase-positive isolates exhibited significant resistance to β-lactam antibiotics, cephalosporins, and glycopeptides, especially vancomycin. Notably, 19 (90.47%) and 12 (92.30%) eggshell and egg content isolates, respectively, were multidrug-resistant, with multiple antibiotic resistance indices ranging from 0.23 to 0.76.

Conclusion: The study revealed a high prevalence of multidrug-resistant S. aureus in table eggs, indicating a significant public health risk. The presence of MRSA and strains with enterotoxins and resistance genes underscores the need for enhanced monitoring, stricter biosecurity measures, and robust control strategies for egg production and distribution to ensure food safety.