The prevalence of Salmonella in four layer farms in eastern Japan was investigated between 2004 and 2006 to determine the role of roof rats (Rattus rattus) in the epizootology of Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis). Persistent S. Enteritidis and S. Infantis contamination of the environment and pooled egg samples were detected in three out of four layer farms. A total of 113 (13.3%) and 158 (18.6%) out of 851 rats examined were positive for S. Enteritidis and S. Infantis, respectively. By pulsed-field gel electrophoresis, only one indistinguishable pulsed-field pattern was yielded by S. Enteritidis strains from rats, eggs and environmental samples from each of the two contaminated layer farms. Although, a variety of pulsed-field patterns were generated by S. Enteritidis isolates from rats, eggs, and the environment of the other contaminated farms, there are, however, some S. Enteritidis strains that are closely related clones. These results suggest that roof rats are carriers of S. Enteritidis and S. Infantis and that persistent S. Enteritidis and S. Infantis infections in a rat population may play an important role in the spread and maintenance of these pathogens inside the layer premises.
Rodents play a major role in the transmission and maintenance of Salmonella contamination cycles in poultry facilities. However, very limited field data are available regarding the transmission routes, infection cycle, and shedding patterns of Salmonella by naturally infected wild rodents from commercial layer farms. In this study, a total of 128 resident wild roof rats (Rattus ratus) were captured from a Salmonella-contaminated layer facility. All roof rats were divided into 51 laboratory cages, and weekly monitoring of Salmonella fecal shedding patterns was conducted for 53 wk. Seven roof rats from cages that were observed to frequently shed Salmonella were isolated in individual cages, and daily Salmonella monitoring was performed for 35 days. At the end of monitoring, each roof rat was euthanatized, and isolation of Salmonella from different organs was performed. Results of weekly monitoring of Salmonella showed that 21 of 51 cages (41.2%) were positive for Salmonella Infantis, while two cages (3.92%) were positive for Salmonella Enteritidis. Moreover, 11 cages were positive for Salmonella for at least two sampling weeks. Isolation of Salmonella from fecal droppings was mainly observed during the first 12 wk of captivity. The longest interval between two Salmonella-positive fecal dropping was 24 wk. In the daily Salmonella monitoring, only Salmonella Infantis was isolated from fecal droppings, in which the highest number of Salmonella Infantis organisms per fecal dropping was at 1 x 10(8) colony-forming units (cfu), while the lowest measured quantity was 1 x 10(3) cfu. It was noted that the frequency of Salmonella shedding in fecal droppings appeared to have a linear correlation (r = 0.85) with the number of Salmonella organisms (cfu) per fecal pellet (P < 0.05). Moreover, pulsed-field gel electrophoresis analysis of Salmonella Infantis isolates revealed a single identical pulsed-field pattern. Salmonella Enteritidis isolates from fecal droppings and internal organs also generated a single identical pulsed-field pattern. Interestingly, Salmonella Infantis was not isolated from any of the organs examined, while Salmonella Enteritidis was isolated from the spleen and liver of one roof rat. These results may indicate that wild roof rats could persistently carry Salmonella and contaminate commercial poultry facilities through intermittent fecal shedding. Moreover, Salmonella Enteritidis in wild roof rats appears to be more of a systemic infection, in which isolation is most likely to occur in internal organs, whereas Salmonella Infantis is more likely an enteric type of infection, in which isolation is most likely to occur in the intestinal contents. It is very plausible that layer chickens could become infected with Salmonella through ingestion of Salmonella-positive fecal droppings or feeds contaminated with these fecal droppings from infected resident roof rats. This is likely one of the major reasons why layer houses can be persistently infected by Salmonella even if the facilities are thoroughly cleaned and ...
ABSTRACT. In order to determine the epidemiological link between the Salmonella Enteritidis contamination in a rat-infested chicken layer farm, an attached egg processing facility and liquid egg samples, several S. Enteritidis isolates were analyzed by pulsed-field gel electrophoresis (PFGE) and bacteriophage typing. A total of 33 S. Enteritidis strains were isolated from a total of 4,081 samples. Similar pulsed-field patterns were generated by S. Enteritidis isolates from liquid eggs, rats and effluent water. Additionally, only two phage types were detected among the S. Enteritidis isolates, PT 1b and PT 6. These results suggest that S. Enteritidis isolates from rats, egg processing facility, and liquid eggs are genetically related. Furthermore, S. Enteritidis infection in rats in layer farms poses a serious public health concern and should be included in future epidemiological studies. KEY WORDS: layer farm, rat, Salmonella Enteritidis.J. Vet. Med. Sci. 69(6): 649-652, 2007 Human illness caused by infection with Salmonella enterica subsp. enterica serovar Enteritidis increased worldwide beginning as early as 1970s and by 1990, became the primary cause of salmonellosis in the world [2]. A major factor in this increase has been attributed to consumption of undercooked eggs and egg products such as liquid egg, contaminated with S. Enteritidis [4]. Rodents, dirty environment, recent poultry farming practices, chicks, pullets, and feeds have all been considered as major sources for contamination with S. Enteritidis in chicken layer farms [5,7,[17][18][19]. In Japan, liquid egg is commonly used in making egg custard products. Murakami et al. [13] were able to isolate S. Enteritidis from unpasteurized liquid egg and epidemiologically linked it to isolates from human salmonellosis outbreaks. But little is known of the origin and mechanism of S. Enteritidis contamination in liquid egg.DNA-based typing by pulsed-field gel electrophoresis (PFGE) has been widely used as a molecular fingerprinting technique for the epidemiological analysis of bacterial infections. In this study, several S. Enteritidis isolates obtained from a rat-infested chicken layer farm, its attached egg processing facility and liquid egg samples from a liquid egg factory for 2 years were characterized by PFGE. The purpose of this study was to determine if there are epidemiological links between S. Enteritidis isolates obtained from layer houses, egg processing facility and liquid egg samples and more importantly to determine the mechanism of S. Enteritidis contamination in the field.A commercial chicken layer farm and an attached eggprocessing facility (GP center) were sampled regularly for S. Enteritidis contamination monitoring for 2 years. Samples for Salmonella isolation were 81 batches (6,480 eggs) of dirty and broken eggs, 130 batches (3,900 eggs) of nest run eggs, 720 environmental samples from the layer houses and 820 environmental samples from GP center, 1,436 samples of GP effluent water, 180 batches of rat fecal samples, and 87 rats. The...
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