Ensuring Egg Safety: Colony Morphology and Identification of Escherichia coli and Staphylococcus spp. On Select Agar Media

Abstract

Background: Eggs are a widely consumed, nutrient‑rich food but can become contaminated with pathogenic microorganisms due to environmental exposure after laying. This poses significant food safety concerns, particularly in low‑hygiene poultry systems. Aims and Objectives: This study aimed to assess microbial contamination on quail eggshell surfaces from different poultry production systems in Ikole‑Ekiti, Nigeria. Specific objectivesincluded quantifying microbial loads, identifying prevalent bacterialspecies (Escherichia coli and Staphylococcusspp.) and evaluating the effectiveness of essential oils as natural disinfectants. Methodology: Sixty fertile quail eggs were collected from three housing systems: free‑range, battery cage (BC) and deep litter. Eggs were grouped and treated with 1% solutions of garlic, tea tree, clove and lavender oils. Microbial surface rinsates were cultured on Nutrient Agar, MacConkey Agar and Mannitol Salt Agar. Colony‑forming units (CFU/cm²) were used to determine microbial loads. Bacterial identification involved colony morphology, Gram staining and biochemical tests (coagulase and indole). Eggshell porosity was assessed using methylene blue dye penetration. Results: Eggs from BC systems exhibited the highest contamination (TVC: 150 CFU/cm²; total coliform count: 90 CFU/cm²; total staphylococcal count: 95 CFU/cm²). Staphylococcus aureus and E. coli were most frequently isolated. Statistically significant differences (P < 0.05) were found among egg types for bacterial load, shell porosity and disinfection outcomes. Clove and tea tree oilssignificantly reduced microbial counts compared to the control. Conclusion: Eggshell contamination varies with the production system. Natural essential oils offer effective, low‑cost alternativesfor reducing microbial contamination, reinforcing the need for proper hygiene practices in egg handling and storag