This study was conducted by Dr. Balogu, T. V. of the Department of Microbiology, Ibrahim Badamasi Babangida University, Nigeria and colleagues. The study investigated the effect of removal or loss of calcium or calcium compounds in egg shells on its ability to kill harmful or disease causing bacteria.
The authors explained that eggshell which is primarily composed of more than 98% calcium carbonate crystal, served as the physical protective and active barrier structure of egg content. And that recently, antimicrobial properties of eggshell were fast becoming a center of interest among stakeholders of poultry industry. They remarked that, however, few studies have focused on the rigidity factor of calcium components of eggshell as antimicrobial agents. As a result, their study was designed to determine the effect of decalcification on the ability of eggshell to inhibit common poultry and egg bacterial pathogens.
To begin the study, the researchers gathered raw eggshell denoted as calcified eggshell (CES) and decalcified eggshell (DES), extracted them and made them into fine powder. They employed standard protocols for the preparations of CES and DES at concentrations of 10, 5, 2.5 and 1.25 mg/ml, and the antibacterial assays on selected bacterial pathogens (Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Salmonella Typhi) were performed by agar diffusion method. They used Gentamicin 80mg solution (CC1) and distilled water (CC2) as controls. The data obtained from the study 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 from the study revealed a 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 researchers observed that the concentrations of DES and CES had no significant antibacterial effect on B. subtilis and K. pneumoniae (p>0.05), but had inverse effect on P. aeruginosa.
Overall, the researchers concluded from their research that decalcified eggshell (DES) had a better inhibitory effect than calcified eggshell (CES) against B. subtilis, K. pneumoniae and P. aeruginosa, but notably, neither DES nor CES had inhibitory effect on E. coli and S. Typhi.
The authors therefore posited that 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. They however, noted that 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.
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