Salmonella enteritidis, phage type 4 (SE PT4), was isolated from five of six 27-wk-old layer chickens submitted for necropsy from a flock of 43,000. Bacteriologic and epidemiologic investigations on the ranch revealed that five of the eight flocks (n = 176,000) were infected. The prevalence of SE PT4 in randomly selected healthy birds ranged from 1.7% (in caged birds) to 50% (in free-range birds) and prevalence in culled birds (kept on dirt floor houses) ranged from 14% to 42%. The estimated overall prevalence of group D Salmonella in eggs contaminated with group D Salmonella was 2.28 per 10,000. The estimated prevalence of group D Salmonella in eggs from caged birds in three infected houses ranged from 1.5 to 4.1 per 10,000, whereas in two houses of free-range birds, prevalence was 14.9 to 19.1 per 10,000. Three of the eight flocks on the ranch remained negative for Salmonella between May 1994 and December 1995 or until removed from the ranch. Salmonella enteritidis PT4 was also isolated from 12.5% (6 of 48) of mice; 57% (four of seven) of cats; and two of two skunks tested. Environmental drag swabs and well water samples yielded multiple serotypes of Salmonella (23/180 and 5/14, respectively) but not S. enteritidis.
Between August 20, 2001, and September 17, 2002, 1429 samples including drag swabs, egg belt or egg rollout swabs, fan-blade swabs, rodent organ and intestinal pools, beetle (Alphitobius diaperinus) pools, housefly (Musca domestica) pools, chicken organ and intestinal pools, and egg pools were obtained for Salmonella culture from two flocks from two different commercial layer ranches. The two ranches were purposefully selected for the study based on their previous status of Salmonella Enteritidis isolation using environmental drag swabs in cooperation with practicing veterinarians. Salmonella sp. was isolated from 337 out of 979 (34.42%) non-egg samples. No Salmonella was isolated from 450 egg pools collected from either ranch. S. enteritidis was isolated from samples obtained from ranch 1 from manure drag swabs, 4/284 (1.4%); rodent organs, 1/24 (4.2%); and housefly pool cultures 1/21 (4.8%). Salmonella Enteritidis was isolated from ranch 2 from mouse organ and intestinal pool samples, 1/24 (4.2%). Salmonella group B was isolated from all sample types except the insects. There was a statistically significant difference in isolation rates among seven serogroups of Salmonella: groups B, C1, C2, D, E, K, and untypeable (Pearson chi-square 18.96, P = 0.002). Overall, statistically significant differences were observed with respect to Salmonella isolation among the types of samples taken (Pearson chi-square 118.54, P < 0.0001). Intensive monitoring for Salmonella Enteritidis can be used to optimize a Salmonella reduction program for an individual poultry biosecurity unit.
Following the diagnosis of Salmonella enteritidis, phage type 4, infection in a commercial layer flock in southern California, effluent from a nearby sewer treatment plant was investigated as a potential source of infection. Between July 1994 and March 1995, 68 Salmonella isolations, comprising 27 serotypes, were made from the inflow (raw sewage) and effluent (treated sewage). Thirty-nine of 68 (57%) isolations yielded six serotypes, which consisted of S. enteritidis 12% (8/68), S. cerro 10% (7/68), S. typhimurium 7.4% (5/68), S. tennessee 7.4% (5/68), S. give 7.4% (5/68), S. mbandaka 7.4% (5/68), and S. panama 6% (4/68). The remaining 43% (29/68) isolations were represented by 21 serotypes. Seventeen S. enteritidis isolates originating from the effluent (creek water), resident feral animals (rodents, stray cats, skunks), and chickens (organs, eggs) of the affected flock were subjected to plasmid profile and restriction endonuclease analysis. Twelve of the 17 isolates had identical plasmid profile and restriction digestion patterns. Two of 17 isolates showed similar patterns but both differed from the rest; and 1 of 17 did not yield plasmids. Two other isolates were found to be different from each other and from the rest of the group.
Effluents from 12 sewage treatment plants in southern California were examined for Salmonella using a Moore swab technique. Eight of the 12 plants were positive for Salmonella when sampled at the chlorination/dechlorination site (inside the plant). Effluents from 11 of 12 sewage treatment plants were positive for Salmonella when samples were analyzed downstream of the chlorination/dechlorination site, before effluents merge with the receiving stream (outside the plant). Two of the three control sites, an urban runoff, a raw potable water reservoir, and two other sites were also positive for Salmonella. A total of 683 Salmonella isolations were represented by 11 serogroups and 54 serotypes from 26 of 32 sampling sites. Effluents from three treatment plants and one control site (raw potable water resevior) yielded Salmonella enteritidis phage type 4, in addition to other serotypes.
This cross-sectional, double-blind study reports the prevalence of Salmonella enterica serotype enteritidis (SE) on California egg layer premises using single vs. pooled manure drag swabs and presents a description of egg production and management systems in the state and an initial analysis of risk factors for SE. The study included 91% of all known eligible egg premises in California, representing the majority of eggs produced in the state. The overall prevalence of SE on California egg layer premises was 10.5%, while 1.1% of all rows sampled were positive for SE. The percentage of positive rows for SE on any premises never exceeded 25% of the 16 swabs collected per premises. A description of egg production and management on California egg layer premises is presented. Statistically significant associations for SE were not evident and were limited because of sample size and the low prevalence of SE on California egg layer premises. Several biological and management factors, such as flock health, stage of production, manure management, ventilation, and watering systems, show trend associations with premises positive for SE and require further investigation. Manure drag swabs serve as a useful tool to validate the core components of an egg quality assurance program for SE based on process control principles.
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