Abstract
Chicken eggs are important as food to humans. The present study was conducted in Kafrelsheikh governorate, Egypt. A total of 250 samples (each sample contains 3 eggs) were purchased from different retail stores (conventional and organic, 125samples for each). These samples were subjected to microbiological examination for assessment of the sanitary quality and detection of incidence, serological and molecular characterization of salmonella, and subjected to chemical examination to detect the incidence of 2 antibiotic residues (oxytetracycline and tylosin) in both types of egg. Aerobic plate count showed mean values of 8.0×102 ± 4.6×10 cfu/ml for conventional eggs and 6.2×102 ± 3.2×10 cfu/ml for organic eggs, the coliform count showed a mean value of 4.6×102 ± 3.2×10 cfu /ml and 3.7×102 ± 2.6 ×10 cfu/ml for conventional and organic eggs respectively. Staphylococcus aureus count showed a mean value of 3.1×102±3.1 ×10 cfu/ml for conventional eggs and 2.3×102 ± 2.7 ×10 cfu/ml for organic egg. Mold and yeast count showed a mean value of 7.3×10 ± 3.8×10 cfu/ml and 4.2×10 ± 1.8 ×10 cfu/ml for conventional and organic eggs respectively. Salmonella was detected in 4 samples (1.6 % from total samples). All of them were only isolated from conventional eggs with a percentage of 3.2%. Serotype identification of four isolates was S. Kentucky. Salmonella Species were not isolated from organic egg contents. Multiplex PCR detected 3 virulence genes (hila, spvC, and stn) (100% of Salmonella isolates). No positive samples for microbial inhibitor test and no antibiotic residues in organic eggs and 4 conventional egg samples were detected positive for microbial inhibitor test with bacillus subtilis, which confirmed by HPLC for detection of 2 antibiotic residues (oxytetracycline and tylosin) and results revealed that 2 out of 4 positive inhibitor test samples were positive for oxytetracycline residues (317 µg /gm and 382 µg /gm) respectively, and 3 out of the same 4 samples were positive for tylosin residues (8.6 µg /gm, 48 µg /gm, and 18.5 µg /gm) respectively, and all positive samples exceeded the maximal residues limit (MRL 0.2 µg /gm) for both oxytetracycline and tylosin residues. The rate of detection of oxytetracycline and tylosin residues was (1.60%) and (2.4%) respectively from the conventional egg. Public health and economic importance for the isolated microorganisms and antibiotic residues were investigated. Results revealed that organic egg is safer than the conventional one.

Key words: Microbial quality, Salmonellae, multiplex PCR, Bacillus subtilis antibiotic residues, organic and conventional table eggs.