Prevalence of Salmonella enterica in poultry and eggs in Uruguay during an epidemic due to Salmonella enterica serovar Enteritidis

Abstract

Salmonella enterica serovar Enteritidis (S. Enteritidis) is frequently associated with food-borne disease worldwide. Poultry-derived products are a major source. An epidemic of human infection with S. Enteritidis occurred in Uruguay, and to evaluate the extent of poultry contamination, we conducted a nationwide survey over 2 years that included the analysis of sera from 5,751 birds and 12,400 eggs. Serological evidence of infection with Salmonella group O:9 was found in 24.4% of the birds. All positive sera were retested with a gm flagellum-based enzyme-linked immunosorbent assay, and based on these results, the national prevalence of S. Enteritidis infection was estimated to be 6.3%. Salmonellae were recovered from 58 of 620 pools made up of 20 eggs each, demonstrating a prevalence of at least 1 in every 214 eggs. Surprisingly, the majority of the isolates were not S. Enteritidis. Thirty-nine isolates were typed as S. Derby, 9 as S. Gallinarum, 8 as S. Enteritidis, and 2 as S. Panama. Despite the highest prevalence in eggs, S. Derby was not isolated from humans in the period of analysis, suggesting a low capacity to infect humans. Microarray-based comparative genomic hybridization analysis of S. Derby and S. Enteritidis revealed more than 350 genetic differences. S. Derby lacked pathogenicity islands 13 and 14, the fimbrial lpf operon, and other regions encoding metabolic functions. Several of these regions are present not only in serovar Enteritidis but also in all sequenced strains of S. Typhimurium, suggesting that these regions might be related to the capacity of Salmonella to cause food-borne disease.

FIG. 1.

(A) S. Enteritidis RAPD patterns obtained using the OPA-4 primer. Lanes 1 to 8, S. Enteritidis egg isolates. Lane 9, 100-bp ladder. Lane10, environmental isolate. All strains correspond to RAPD profile I. (B) S. Gallinarum RAPD patterns obtained using the OPA-4 primer. Lanes 1 to 5 and 8 correspond to RAPD profile VI. Lanes 6 and 7 correspond to RAPD profile IV. Lane 9 corresponds to RAPD profile V.

FIG. 2.

Multiplex PCR results for S. Gallinarum isolates. Lanes 1 to 5, isolates from farm G; lanes 6 and 7, isolates from farm A; lane 8, isolates from farm I; lane 9, isolates from farm C; lane 10, an S. Enteritidis isolate used as a positive control.