Dynamics of bacterial contamination and antibiotic resistance in commercially or organically farmed chicken eggs

Abstract

Eggs are one of nature’s most nutritious and economical foods. Besides their nutritional value, antioxidant, anti‐cancerous, antihypertensive activity, and immunomodulatory effects, chemical and microbial contamination of eggs pose a risk on human health. Chemical contamination is due to the abuse of antibiotics in poultry. Microbial contamination can be through horizontal or vertical transmission. Microbial contamination accompanies a high risk of spread of antibiotic resistance. Microbial contamination can be controlled by choosing the egg source wisely and by storing eggs carefully. A lot of studies have been conducted to find the most favorable farming type and storage temperature, however the outcomes appeared to be contradicting. In this study we tested the microbial and chemical contamination of eggs from different farming systems in Lebanon. We studied the microbial contamination of eggshell and content of commercial and organic eggs stored at room‐ and fridge temperature for 5 weeks. The isolated bacteria were subcultured on SS and TBX agar and then confirmed by API 20E; the serotoxicity of E.coli was tested using Antiserum Escherichia coli NONAVALENT. The antibiotic resistance was studied using disc diffusion method. Our result revealed less contamination risk on the commercial eggs in comparison to organic eggshells along with better eggshell quality and a lower pore count. No antibiotic residues were detected in the egg contents regardless of the farming system. Serotoxic E.coli, Enterobacter cloacae, and citrobacter freundii were isolated from organic eggshells. E.coli and Enterobacter cloacae seemed to also vertically contaminate the egg content of eggs stored for 2 weeks at room temperature. All eggs stored in the fridge showed eggshell contamination. All the isolated bacteria were sensitive to ENR and SPT, and resistant to Macrolide E. Isolated E. coli showed resistance to macrolides (100% to E and 71% to TL), tetracyclines (86% to O and 57% to DO), beta lactams (20%), colistin (57%), Aminoglycosides (71% to Gen and 29% to N), and COT(14%). Enterobacter cloacae appeared resistant to macrolides (100% to E and 50% to TL), betalactams (50%) and colistin (50%). Citrobacter Freundii was found resistant to betalactams, tetracyclines (100% to O) and Colistin (50%). Our study shows that the farming system greatly affects the starting microbial population of eggs, where organic eggs constitute a greater risk than commercial eggs to bacterial infection, many times resistant to antimicrobials. Eggs should be cleaned properly, without compromising the pore or protective cuticle before storage.