title: Influence of housing systems on microbial load and antimicrobial resistance patterns of Escherichia coli isolates from eggs produced for human consumption.
abstract: Microbial counts (aerobic bacteria, psychrotrophs, Enterobacteriaceae, coliforms, Pseudomonas spp., Enterococcus spp., Staphylococcus spp., and molds and yeasts) were obtained for the shells of 240 table eggs in northwestern Spain. Eggs from six sources (40  samples in each) were analyzed: 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 by the disk diffusion method  for resistance to 12 antimicrobial drugs of veterinary and human health significance. Aerobic plate counts ranged from 1.96 ± 1.0 (barn) to 3.69 ± 0.7 (domestic) log CFU/cm(2). Counts for most microbial groups differed significantly between sources. Eggs from domestic  production had the highest contamination loads (P < 0.05) 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 (P < 0.05) 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. Our 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. Education covering good sanitary practices for handling eggs to avoid cross-contamination or  inadequate cooking is needed.
authors.affiliation: Department of Food Hygiene and Food Technology, Veterinary Faculty, University of León, 24071 León, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Alvarez-Fernández
authors.forename: Jessica
authors.initials: J
authors.lastname: Domínguez-Rodríguez
authors.forename: Rosa
authors.initials: R
authors.lastname: Capita
authors.forename: Carlos
authors.initials: C
authors.lastname: Alonso-Calleja
mesh_terms: D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002645:Chickens; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D024881:Drug Resistance, Bacterial; D004531:Eggs / Q000382:microbiology*; D004926:Escherichia coli / Q000187:drug effects / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods; D006799:Housing, Animal; D006801:Humans
chemical_list: D000900:Anti-Bacterial Agents