Chitosan Improves the Shelf Life of Domestic Chicken (Gallus gallus) Eggs against Staphylococcus aureus Contaminations

Abstract

In this study, in-vitro antibacterial activity of four different concentrations (0.00%, 0.05%, 0.10%, and 0.15% w/v%) of chitosan, a natural biopolymer, was tested against the foodborne pathogen Staphylococcus aureus ATCC 25923 using well diffusion and colony counting methods. The organism showed the highest sensitivity to 1.50% chitosan, while the antibacterial effect was raised with increasing concentration of chitosan in the medium. Microbiological testing of randomly selected village chicken egg samples obtained from a market in Kiribathgoda, Sri Lanka revealed high cell counts of S. aureus greater than 5 log CFU/ mL, which exceeded the maximum accepted limit (3 log CFU/ g) that should be present in poultry based raw products according to SLS 1161:2003 guidelines, indicating a potential risk for presence of preformed Staphylococcal enterotoxins in these eggs. Therefore, a sample containing randomly selected, 90, six-pooled eggs from the same source was used to investigate the in-vivo antibacterial efficacy of 1.50% chitosan (coated on the surface of eggshells) against this pathogen. Both chitosan coated eggs and chitosan non-coated eggs (except raw eggs) were externally inoculated from ~ 5 log CFU/ mL of the bacterial inoculum and monitored for 28 days, where it showed a bacteriostatic activity with 4 log CFU/ mL and 3 log CFU/ mL fold growth reductions compared to chitosan non-coated eggs and raw eggs respectively. These experimental results suggest that chitosan coating is a promising method to protect the microbial quality and safety of domestic chicken eggs regarding S. aureus contaminations