Infection of laying hens with Salmonella enteritidis PT4 by conjunctival challenge

Genome scale reconstruction of a Salmonella metabolic model: comparison of similarity and differences with a commensal Escherichia coli strain

Salmonella are closely related to commensal Escherichia coli but have gained virulence factors enabling them to behave as enteric pathogens. Less well studied are the similarities and differences that exist between the metabolic properties of these organisms that may contribute toward niche adaptation of Salmonella pathogens. To address this, we have constructed a genome scale Salmonella metabolic model (iMA945). The model comprises 945 open reading frames or genes, 1964 reactions, and 1036 metabolites. There was significant overlap with genes present in E. coli MG1655 model iAF1260. In silico growth predictions were simulated using the model on different carbon, nitrogen, phosphorous, and sulfur sources. These were compared with substrate utilization data gathered from high throughput phenotyping microarrays revealing good agreement. Of the compounds tested, the majority were utilizable by both Salmonella and E. coli. Nevertheless a number of differences were identified both between Salmonella and E. coli and also within the Salmonella strains included. These differences provide valuable insight into differences between a commensal and a closely related pathogen and within different pathogenic strains opening new avenues for future explorations.

Comparative evaluation of a bivalent killed Salmonella vaccine to prevent egg contamination with Salmonella enterica serovars Enteritidis, Typhimurium, and Gallinarum biovar Pullorum, using 4 different challenge models

We evaluated a newly developed commercial bivalent killed Salmonella vaccine Oilvax SET for its ability to decrease contamination with Salmonella enterica serovars Enteritidis and Typhimurium in layer chickens. In either an oral or intravaginal challenge model, the fecal shedding was decreased in vaccinated hens, but egg contamination was not evaluated due to scarcity of contaminated eggs even in the unvaccinated control groups. In contrast, an intravenous and an intraperitoneal challenge resulted in the relatively high level of egg contamination in unvaccinated chickens, which was significantly reduced in vaccinated chickens. In a second experiment, 2 strains of Salmonella serovar Gallinarum biovar Pullorum, which has the common O9 antigen with SE and transmits vertically into eggs, were used to test the efficacy of the Oilvax SET against egg transmission. Vertical egg transmission by the Pullorum strain was significantly reduced in the vaccinated groups of hens. The Oilvax SET can be a useful tool in the control of Salmonella egg contamination in laying hens.

Campylobacter spp. contamination of chicken carcasses during processing in relation to flock colonisation

The presence and numbers of campylobacters on chicken carcasses from 26 slaughter groups, originating from 22 single-house flocks and processed in four UK plants, were studied in relation to the level of flock colonisation determined by examining the caecal contents of at least ten birds per group. The prevalence of campylobacters on carcasses from five campylobacter-negative flocks processed just after other negative flocks was low (</=30%). Campylobacters were isolated from 90 to 100% of carcasses from three flocks which were partly colonised, with 5, 5 and 30% of caecal contents positive, and which were processed after fully colonised flocks. All carcasses from the remaining fully colonised flocks were contaminated with campylobacters, and they had significantly (P<0.001) higher numbers per carcass (average of 5.3 log(10) cfu; range: 1.3 to >8.0 log(10) cfu) than carcasses originating from low prevalence flocks (average of 2.3 log(10) cfu; range: <1.1 to 4.1 log(10) cfu). There was a reduction in the numbers of campylobacters on carcasses between plucking and chilling in eight of ten fully colonised flocks. In another eight flocks, a significant (P<0.001) decrease (0.8 log(10) cfu) in the number of campylobacters on carcasses from just before to after chilling was detected. Campylobacter spp. could be isolated from aerosols, particles and droplets in considerable numbers in the hanging-on, defeathering and evisceration areas but not in the chillers. This was the case even when campylobacters were not isolated from the target flock. Campylobacters on carcasses from two partly colonised flocks were either the same subtype, as determined by speciation, Multi-Locus Sequence Typing (MLST) and flaA Restricted Fragment Length Polymorphism (RFLP) typing, as those in the fully colonised flocks processed previously, although not necessarily the most prevalent ones; or were the same subtypes as those found in the caeca of the flock itself. The prevalences of the different campylobacter subtypes found on carcasses from two fully colonised flocks did not closely reflect those found in the caeca. MLST combined with flaA RFLP provided a good method for ascertaining the relatedness of strains isolated from carcasses and caecal contents. This study showed that carcass contamination is related to the within-flock prevalence of campylobacter colonisation, but that contamination from previously processed flocks was also significant, especially on carcasses from low prevalence flocks. Forced dry air cooling of carcasses reduced contamination levels.

Characteristics of Salmonella enteritidis Contamination in Eggs After Oral, Aerosol, and Intravenous Inoculation of Laying Hens

Experimental infection models are useful tools for understanding how Salmonella enteritidis is deposited in eggs and for testing potential strategies to control eggborne transmission of disease to humans. Oral inoculation of laying hens is presumed to provide the closest simulation of naturally occurring infections, but alternatives such as intravenous or aerosol inoculation have sometimes been recommended as options to induce higher incidences of egg contamination. The present study compared the frequency, level, and location of S. enteritidis deposition in egg contents after experimental inoculation by three different routes. In two replicate trials, specific-pathogen-free laying hens were infected with an S. enteritidis culture mixture prepared to optimize invasive behavior. Groups of hens received either an oral dose of 10(9) S. enteritidis, an aerosol dose of 10(9) S. enteritidis, or an intravenous dose of 10(5)-10(7) S. enteritidis. Oral inoculation led to the highest incidence of fecal shedding of S. enteritidis, whereas intravenous inoculation produced the highest specific antibody titers. Eggs laid during the first 21 days postinoculation were cultured to detect and enumerate S. enteritidis in the yolk and albumen. No significant differences were observed among the three inoculation routes in the frequencies of isolation of S. enteritidis from either yolk or albumen. For all three routes of administration, S. enteritidis was recovered more often from yolk (at frequencies ranging from 4% to 7%) than from albumen (0 to 2%). Over 73% of contaminated eggs harbored fewer than 1 colony-forming unit (CFU) of S. enteritidis per milliliter, and only 3% of such eggs contained more than 100 CFUs/ml. Significantly higher levels of S. enteritidis contaminants were associated with intravenous inoculation than with the other routes. No advantage of using aerosol or intravenous administration of S. enteritidis as an alternative to oral inoculation for inducing the production of contaminated eggs was evident in this study.

The chicken, the egg and Salmonella enteritidis

Salmonella enterica serovar Enteritidis is the cause of the food-borne salmonellosis pandemic in humans, in part because it has the unique ability to contaminate eggs without causing discernible illness in the birds infected. The infection route to humans involves colonization, survival and multiplication of the pathogen in the hen house environment, the bird and, finally, the egg. This review highlights the stages of transmission and discusses evidence that altered bacterial growth patterns and specific cell surface characteristics contribute to the adaptation of S. enteritidis to these diverse environments.

Salmonella penetration of egg shells and proliferation in broiler hatching eggs--a review

The presence of salmonellae in fertile broiler hatching eggs has been clearly identified as a critical control point in the salmonellae contamination of broiler chickens. This paper reviews the published research studies on a) the penetration and proliferation of salmonellae in hatching eggs, b) the consequences of this contamination on the contamination of the final product, and c) the egg's defenses against invading salmonellae. A better understanding of the material in this review paper will assist poultry researchers and the poultry industry in continuing to make progress in reducing and eliminating salmonellae from fertile hatching eggs, hatcheries, and breeder flocks.

Cross-infection of chicks by airborne transmission of Salmonella enteritidis PT4

Airborne cross-infection by Salmonella enteritidis PT4 strains was demonstrated between sets of orally infected 1-d-old chicks and identical uninfected control chicks. Low numbers of Salm. enteritidis were detected in the air of the rooms housing the chicks. Sentinel mice within the rooms did not become infected. This study demonstrates that low levels of airborne Salm. enteritidis are a potential source of cross-infection in poultry houses.

Isolates of Salmonella enterica Enteritidis PT4 with enhanced heat and acid tolerance are more virulent in mice and more invasive in chickens

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.

Survival of Salmonella enteritidis Pt4 and Salm. typhimurium Swindon in aerosols

Small particle aerosols of plate-grown Salmonella enteritidis and Salm. typhimurium were generated and maintained within a rotating drum at 75% relative humidity and 24 degrees C for 2 h. Plate-grown organisms were found to be more aerosol-stable than broth-grown organisms. Differences were observed between the two species; plate-grown Salm. typhimurium retained 100% viability after 2 h compared to approximately 70% for plate-grown Salm. enteritidis. A large proportion of cells of both serotypes remained viable in aerosols after 2 h, confirming the potential for airborne transmission for these organisms, e.g. within henhouses and during food processing.

Observations on disinfection regimens used on Salmonella enteritidis infected poultry units

Studies carried out at the laboratory and in the field identified many potential problems during disinfection of poultry units naturally contaminated with Salmonella enteritidis. There appeared to be variations in the efficiency of commonly used disinfectants within a disinfectant group when used in a contaminated house. It was possible for Salmonella and other coliforms to be amplified during the pressure washing or steam cleaning process. If an effective terminal disinfectant was not used after this, then high levels of Salmonella were likely to persist. The efficiency of the disinfection regimen was not directly dependent on the standard of physical cleaning if this was carried out to a reasonable standard, as a high level of elimination of Salmonella could be achieved even in the presence of substantial quantities of residual organic matter. Disinfection regimens involving formaldehyde, either as part of a terminal compound disinfectant spray or as a final fogging agent, were found to be the most effective in the field.

Pathogenicity of Salmonella enteritidis in poultry

Salmonella enteritidis is a common pathogen of all species of mammals and fowls. The recent increase in the number of outbreaks of food poisoning due to S. enteritidis in man was epidemiologically analysed, and it was considered that contaminated eggs or egg products were the major source of this infection. To assist in prevention and eradication of human food poisoning many investigators have studied the pathogenicity of S. enteritidis in poultry. Gross pathological observations after natural and experimental infections with S. enteritidis in poultry revealed that this organism may cause systemic infection in chicks and laying hens accompanied by prolonged faecal shedding. Some variations in the mortality rates, clinical symptoms, faecal shedding and frequency of production of contaminated eggs were observed in the chicks and hens experimentally infected with S. enteritidis isolates. Choice of bacterial strain, phage type, age of bird and inoculum size may affect the outcome of an infection. Moreover, isolation of the organisms from the ovaries, oviducts and egg contents indicates the possibility of transovarian infection of S. enteritidis in chickens. Some virulence factors associated with S. enteritidis are also reviewed in the present paper.