High levels of bacterial and antimicrobial drug residues contamination in chicken eggs for human consumption in Morogoro municipality, Tanzania

Abstract

Eggs represent one of the most important low-cost sources of high-quality animal protein and minerals. However, the occurrence of contamination with antimicrobial drug residues and antimicrobial-resistant microorganisms has been increasing and represents a serious food safety risk. This study was carried out to assess the microbial and antimicrobial drug residue contamination of chicken eggs commercialized in selected neighbourhoods in Morogoro municipality, Tanzania. A total of two hundred and fifty-five eggs were sourced from forty-four stores in ten neighbourhoods and were examined for bacterial and antimicrobial drug residue contamination using standard microbiological assays, and the Bacillus subtilis ATCC 3491 as the test organism. Bacterial contamination was detected in 53.3% (136/255) of the egg yolk samples, with significant differences between sampling sites (p = 0.001). Bacterial total viable counts in the contaminated samples ranged from 102 to 109 CFU/mL, with a mean value of 6.42×108 CFU/mL (CI 95% = 1.45×108 – 1.60×108 CFU/mL). The most prevalent bacteria were Bacillus spp. (39.7%), followed by the Coagulase-negative Staphylococcus (16.9%), Escherichia coli (8.8%), Streptococcus spp. (5.9%), Staphylococcus aureus (4.4%), Enterobacter spp. (3.7%), Salmonella spp. (3.0%) and Pseudomonas spp. (1.5%). Antimicrobial drug residues were detected in 40.8% (104/255) of the samples in egg white and nil (0%) in the yolk. The contamination with antimicrobial residues showed significant differences between sample collection sites (p = 0.000), but not with bacterial counts (p = 0.862) and isolated bacteria in each sample collection site (p = 0.497). The presence of various bacteria and drug residues above permissible maximum residue levels in eggs predisposes consumers to poison and antimicrobial-resistant bacteria.