Impact of decalcification on antibacterial properties of eggshell against selected poultry pathogens

Abstract

Background: Eggshell which is primarily composed of more than 98% calcium carbonate crystal, serves as the physical protective and active barrier structure of egg content. Recently, antimicrobial properties of eggshell are fast becoming center of interest among stakeholders of poultry industry. However, few studies have focused on the rigidity factor of calcium components of eggshell as antimicrobial agent. Thus, this study was designed to determine the effect of decalcification on the ability of eggshell to inhibit common poultry and egg bacterial pathogens.
Methods: Raw eggshell denoted as calcified eggshell (CES) and decalcified eggshell (DES) were extracted and made into fine powder. Standard protocol was used for preparations of CES and DES at concentrations of 10, 5, 2.5 and 1.25 mg/ml, and their antibacterial assays on selected bacterial pathogens (Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Salmonella Typhi) were performed by agar diffusion method. Gentamicin 80mg solution (CC1) and distilled water (CC2) served as controls. Data were analysed with SPSS version 20.0 and presented as mean±SD for descriptive statistics. Friedman's two-way test ANOVA was used to compare the differences in mean values between CES, DES, CC1 and CC2 at significance level of p<0.05.
Results: The mean zone diameter of inhibition produced by DES (range 13–28mm) for the isolates was significantly higher (p<0.05) than that produced by CES (range 10-21mm). However, the mean zone diameter of inhibition produced by CC1 (gentamicin) (range 16-40mm) was higher than that produced by DES or CES (p<0.05). The concentrations of DES and CES have no significant antibacterial effect on B. subtilis and K. pneumoniae (p>0.05), but had inverse effect on P. aeruginosa. Overall, DES had a better inhibitory effect than CES against B. subtilis, K. pneumoniae and P. aeruginosa, but notably, neither DES nor CES had inhibitory effect on E. coli and S. Typhi.
Conclusion: Poor antibacterial effect of CES may be attributed to the calcium-protein interactions within bacterial cell membrane, which hinders absorption or mobility mechanism of the antibacterial factor of the eggshell, but decalcification had significant impact on the antibacterial profile of the eggshell for some bacterial isolates. However, S. Typhi and E. coli were totally resistant to both DES and CES. Breed of eggs with minimal calcified eggshell to withstand transportation fragility, may enhance antibacterial index and shelf-life of table eggs.

Keywords: Decalcification; Antibacterial; Eggshell; Poultry; Pathogens