The influence of transport, catching, and processing on contamination of broiler chickens with Salmonella and Campylobacter was investigated. Transport crates were reused with high frequency and were often still contaminated with Salmonella and Campylobacter when they arrived at the farm despite the fact that they were washed at the factory, and thus they were a potential route of infection. These organisms contaminated the feathers of previously Campylobacter-and Salmonella-negative birds going to the processing plant and were isolated from processed carcasses, albeit at a low frequency. The Campylobacter types which were the predominant organisms on the live birds when they arrived at the processing plant were not necessarily the types that were most frequently isolated from processed carcasses. This finding may reflect cross-contamination that occurred during processing or differences in the tolerance of the strains to the hostile environments that the bacteria experienced. The process of catching and putting the birds in crates significantly increased the chance of contamination with Campylobacter (P < 0.001).Human infections with Campylobacter spp. continue to be of international importance, and in England and Wales the number of confirmed cases continues to exceed 50,000 per annum (4). This is in line with the rate of Campylobacter infection in the United States, where the Centers for Disease Control and Prevention has estimated that the overall rate of infection is 1,000 cases per 100,000 people (28). Recent work on infectious intestinal disease in England and Wales (30) has indicated that cases are underreported and that the actual number of Campylobacter infections in these countries is likely to be about eight times the published number.Contaminated poultry meat is considered an important vehicle of human infection with Campylobacter (1,14,22,23), and because of the difficulties in controlling the spread of the bacteria in the kitchen (6, 7) and abattoir (17), control on the farm may be more effective. Identification of control measures requires a good understanding of the epidemiology of Campylobacter spp. in poultry meat production. There have been a number of studies of this important topic in recent years, and the environment (16), drinking water (28), and even vertical transmission (10, 24) have been suggested as possible sources of flock colonization. Improved farm hygiene measures, such as boot dipping (15) and boot changing (31), which presumably prevent the introduction of Campylobacter spp. from the external environment into a broiler chicken house, can either delay or prevent colonization. Transport vehicles and crates may be an additional source of contamination between batches of birds and farms (19). Such contamination may be particularly important for the introduction of Campylobacter into previously uninfected flocks during transport or during flock thinning (i.e., the removal of birds to reduce stock density) (12). Newell et al. (21) found that on one occasion carcasses from a Campylob...

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Two Enteritidis PT4 isolates which differed in inherent tolerance to heat, acid, H2O2 and the ability to survive on surfaces were used to infect mice, day-old chicks or laying hens. The acid-, heat-, H2O2- and surface-tolerant isolate was more virulent in mice and more invasive in laying hens, particularly in reproductive tissue. However, no significant differences were observed in behaviour in chicks. Both PT4 isolates were able to infect chicks housed in the same room as infected birds, although the heat-tolerant isolate survived significantly better than the heat-sensitive one in aerosols.

In a comparative study of different Salmonella enteritidis phage type 4 isolates we found that those isolates with enhanced heat tolerance also survived better than isolates that were heat sensitive either at pH 2.6, in 10 mM H 2 O 2 , or on surfaces. Culture to the stationary phase increased the heat tolerance of all isolates and the acid and H 2 O 2 tolerance of heat-tolerant isolates. With heat-sensitive isolates, however, extended culture had no impact on survival in H 2 O 2 and only a marginal impact on acid tolerance. The growth phase had no appreciable impact on the surface survival of any of the isolates.

Experiments with 2 wild type isolates of Salmonella enterica serotype Enteritidis PT4, which differed in RpoS expression, tolerance to certain hostile environments and pathogenicity, found that changes in in vitro acid, heat, or peroxide tolerance had no effect on the ability of the isolates to multiply in the spleens of C57/BL7/J mice infected orally. Thus, with the pathogenic RpoS-positive isolate, the infectivity of log phase chilled cells, which are profoundly acid-sensitive, was the same as that of non-chilled stationary phase cells which are acid-tolerant. Similarity the infectivity of the RpoS-negative, sensitive isolate, was not enhanced by increases in any tolerance. The ability to survive on surfaces, like infectivity, was also largely unaffected by either growth phase or cold exposure. These two attributes may thus be related and, given that the pathogenic PT4 isolate is capable of prolonged survival and the nonpathogenic isolate survives poorly, survival could serve as a potential marker of pathogenicity. Although the pathogenicity of the two isolates was very different, they showed an almost identical increase in acid tolerance following culture at pH 4.0 for up to 60 min.

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