Bacterial contamination on egg shells
A recent publication, based on research conducted in northwestern Spain evaluated the bacterial level on the shells of eggs from hens housed in various production systems. The authors confirmed higher levels of bacterial contaminations on eggs derived from extensive (free range) systems.
Microbial counts (aerobic bacteria, psychrotrophs, Enterobacteriaceae, coliforms, Pseudomonas spp., Enterococcus spp., Staphylococcus spp., and molds and yeasts) were obtained from the shells of 240 table eggs. Eggs from six sources (40 samples in each) were analysed: chicken eggs from five different housing systems (conventional battery cages, barn, free range, organic, and domestic breeding) and quail eggs (cages). A total of 120 Escherichia coli strains (20 from each source) were tested for resistance to 12 antimicrobial drugs of veterinary and human health significance.
A second component of the survey was to determine the range of antibiotic resistance in bacteria isolated from shells. Counts for most microbial groups differed significantly between sources. Eggs from domestic production had the highest contamination loads for aerobic bacteria, Enterococcus spp., and molds and yeasts and the highest prevalence of E. coli.
Twenty-three E. coli isolates (19.17%) were susceptible to all antimicrobials tested, and 80.83 % were resistant to one (22.50%) or more (58.33%) antimicrobials. The housing system had a significant influence on the average resistance per strain, with the highest resistance in conventional cage (2.85) and barn (3.10) systems followed by free range (1.55) and quail (1.95). Eggs from organic (1.00) and domestic (0.75) production systems had the lowest resistance per strain. The highest prevalence of resistance was observed for the groups of antimicrobials more frequently used on poultry farms.
The results suggest that a relationship exists between the prevalence of antimicrobial resistance in E. coli strains and the more frequent use of antimicrobials in conventional (cage, barn, and free range) than in domestic and organic chicken housing systems.
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