Determination of Oxytetracycline Residues in Table Eggs from the Local Market of San Jose City: Implications for Local Farm Compliance and Food Safety Screening

Abstract

Antibiotic residues in food of animal origin present an emerging food safety concern due to their potential to promote antimicrobial resistance and cause hypersensitivity reactions in consumers. Eggs, being a staple protein source, require close monitoring for residual veterinary drugs, especially antibacterial, as their use necessitates a withdrawal period. This study aimed to detect oxytetracycline residues in table eggs sold in selected market stalls of San Jose City, Nueva Ecija, using the disc diffusion method with Escherichia coli as the indicator organism. Thirty eggs from ten randomly selected market stalls were homogenized and tested on Mueller-Hinton Agar plates. Discs were infused with homogenized egg samples, distilled water (negative control), and oxytetracycline solution (positive control). After incubation at 37 °C for 12 h, inhibition zones were measured using a caliper. The results showed that all egg samples exhibited no detectable inhibition zones, indicating the absence of oxytetracycline residues above the detection threshold (≥ 14 mm for 8 mm discs) for this assay. The findings thus suggest that eggs sold in San Jose City are likely safe from detectable oxytetracycline residues within the operational limits of the disc diffusion method, and that farms may be observing proper withdrawal periods. However, continuous surveillance and confirmatory tests such as the four-plate bioassay or liquid chromatography are recommended to validate and expand these results.