HtpG contributes to Salmonella Typhimurium intestinal persistence in pigs

Salmonella enterica subspecies enterica serovar Typhimurium ( Salmonella Typhimurium) contamination of pork, is one of the major sources of human salmonellosis. The bacterium is able to persist and hide in asymptomatic carrier animals, generating a reservoir for Salmonella transmission to other animals and humans. Mechanisms involved in Salmonella persistence in pigs remain poorly understood. In the present study, we demonstrate that the Salmonella htpG gene, encoding a homologue of the eukaryotic heat shock protein 90, contributes to Salmonella Typhimurium persistence in intestine-associated tissues of pigs, but not in the tonsils. HtpG does not seem to play an important role during the acute phase of infection. The contribution to persistence was shown to be associated with htpG-dependent Salmonella invasion and survival in porcine enterocytes and macrophages. These results reveal the role of HtpG as a virulence factor contributing to Salmonella persistence in pigs

Salmonella Typhimurium interferes with the humoral immune response in pigs

Foodborne salmonellosis is one of the most important bacterial zoonotic diseases worldwide. Salmonella Typhimurium is the serovar most frequently isolated from slaughter pigs in Europe. Circumvention of the host’s immune system by Salmonella might contribute to persistent infection of pigs. We found that Salmonella Typhimurium strain 112910a, which is able to persist in pigs, was capable of downregulating the expression of major histocompatibility class II (MHC II) molecules on porcine alveolar macrophages (PAM) in a Salmonella pathogenicity island 2 (SPI-2) dependent way and that MHC II downregulation was Salmonella strain dependent. The MHC II downregulation capacity was abolished when bacteria were opsonized with Salmonella-specific antibodies. Furthermore, intracellular proliferation of Salmonella Typhimurium opsonized with Salmonella positive pig serum was significantly impaired compared to that of the bacteria opsonized with negative pig serum. In a subsequent in vivo experiment, Salmonella Typhimurium strain MB2216 that did not induce MHC II downregulation in vitro, was shed less and persisted less but induced earlier seroconversion in pigs than strain 112910a. From the in vitro data, it is proposed that Salmonella Typhimurium downregulates the humoral immune response to promote intracellular survival inside porcine macrophages, contributing to long-term Salmonella persistence in pigs. The fact that the less persistent strain MB2216 induced earlier seroconversion than strain 112910a is of major interest for Salmonella-monitoring programs primarily based on serology, since this indicates that more persisting strains are more likely to escape serological detection

Salmonella Typhimurium resides largely as an extracellular pathogen in porcine tonsils, independently of biofilm-associated genes csgA, csgD and adrA

In European countries, Salmonella enterica subspecies enterica serovar Typhimurium (Salmonella Typhimurium) is the serovar most frequently isolated from slaughter pigs1. Porcine carcass contamination with Salmonella Typhimurium can largely be attributed to persistently infected pigs. Even though tonsils are a predilection site for Salmonella persistence in pigs, virulence mechanisms necessary for cell invasion and intracellular survival do not contribute to tonsillar colonization2, suggesting that Salmonella Typhimurium resides mainly extracellularly in porcine tonsils. Biofilm formation is a mechanism used by several bacteria to survive in an extracellular context or in hostile environments3. The role of biofilm formation in Salmonella Typhimurium persistence in pigs is still unknown. It was the aim of the present study to determine whether Salmonella Typhimurium persists intracellularly or extracellularly in tonsils of pigs. Additionally, the role of biofilm formation in persistence of Salmonella Typhimurium in porcine tonsils was determined

Salmonella Infection Level in Danish Indoor and Outdoor Pig Production Systems measured by Antbodies in Meat Juice and Faecal Shedding on-farm and at Slaughter

The prevalence of Salmonella shedding was compared in 34 organic, conventional outdoor, and indoor pig herds. Individual faecal and meat juice samples from 30-50 pigs per herd were analysed for presence of Salmonella, and Salmonella antibodies, respectively. We found low levels of Salmonella shedding on farm and at slaughter in organic and conventional outdoor herds compared to indoor pigs. Overall 5,5 % of the pigs were seropositive. The serological test result was associated with Salmonella shedding at slaughter in pigs from conventional systems, but not in organic pigs. The duration of transport did not affect the risk of Salmonella shedding

Tracking of Salmonella through the Pork Slaughter Process

End of project reportTo help address the problem of salmonellosis in the Republic of Ireland (RoI), a national Salmonella control programme was introduced in 1997 with a view to reducing the prevalence of Salmonella in pigs on the farm and on pig carcasses. The primary objective of this present study was to determine the correlation between the Salmonella serological and bacteriological status of pigs presented for slaughter and the Salmonella status of pork cuts following slaughter, dressing and chilling. Two additional studies investigated the prevalence and numbers of Salmonella spp. in the boning halls of four commercial pork abattoirs and at retail level in butcher shops and supermarkets in the RoI. The results indicated that categorisation of pig herds on the basis of a historical serological test for Salmonella was not a good predictor of the bacteriological Salmonella status of individual pigs at time of slaughter. However, it is acknowledged that serological testing does help in giving a rough estimate of the overall Salmonella status of a pig herd. There was a linear correlation between prevalence of Salmonella in caecal contents and on pork cuts at factory level; therefore, if the number of herds presented for slaughter with high levels of Salmonella (category 3) was reduced, there would be less potential for contamination of the lairage, equipment etc. and so less likelihood of Salmonella contamination on pork. The impact of crosscontamination during transport, lairage, processing and distribution cannot be ignored and measures to diminish this would significantly reduce the dissemination of Salmonella in the chain and the consequent risk posed. A key finding was the considerable variation in the incidence of Salmonella on different sampling days and in different slaughter plants.National Development Plan 2007-201

Effect of pig production system and transport on the potential pathogen transfer risk into the food chain from Salmonella shed in pig faeces

The prevalence of faecal Salmonella shedding has been compared in organic, conventional outdoor, and indoor finishing pig herds in a Danish survey with participation of 34 herds. Individual faecal and meat juice samples were collected from 30-50 pigs per herd and analysed for presence of Salmonella, and Salmonella antibodies, respectively. The results showed a low level of on-farm Salmonella shedding (<0,2 %) in organic and conventional outdoor herds compared to 2,5 % in indoor pigs (P<0,0001), and also a lower prevalence of Salmonella shedding in outdoor systems at slaughter (<2 %) compared to 4,1 % in indoor systems (P<0,01). The overall seroprevalence was 8,5 % with no significant differences between systems. Seropositivity was a significant predictor of Salmonella shedding at slaughter in individual pigs from conventional systems, but not in organic pigs. The duration of transport did not affect the risk of Salmonella shedding at slaughter

High diversity of salmonella serotypes found in an experiment with outdoor pigs

Little is known about the risk of Salmonella infection in outdoor pig production, but seroprevalence data has indicated a higher occurrence of Salmonella in outdoor production systems than in conventional indoor systems. This is perhaps due to the increased exposure to the surrounding environment including contact with wildlife. An unexpected high diversity of Salmonella serotypes, as e.g. S. Uganda and S. Goldcoast, which are not normally isolated from pigs, was detected in connection with an experimental study on transmission of Salmonella in outdoor organic pigs. In order to elucidate the potential source of the different Salmonella serotypes, a small-scale examination of wildlife was performed. Salmonella was not detected in any of a total of 22 rats, mice and shrews or in 21 birds (mainly crowbirds). The unidentified source of these Salmonella serotypes implies inadequate control possibilities and may therefore pose a problem for outdoor pig production in terms of food safety

Intestinal epithelial responses to Salmonella enterica serovar Enteritidis: Effects on intestinal permeability and ion transport

Salmonella infection of chickens that leads to potential human foodborne salmonellosis continues to be a major concern. Chickens serve as carriers but, in contrast to humans, rarely show any clinical signs including diarrhea. The present investigations aimed to elucidate whether the absence of diarrhea during acute Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) infection may be linked to specific changes in the electrophysiological properties of the chicken gut. Immediately after slaughter, intestinal pieces of the mid-jejunum and cecum of either commercial broiler or specific pathogen-free (SPF) chickens were mounted in Ussing chambers in 2 separate experimental series. Living Salmonella Enteritidis (3 × 109) or Salmonella Enteritidis endotoxin (20 mg/L), or both, were added to the mucosal side for 1 h. In both experimental series, the Salmonella infection decreased the trans-epithelial ion conductance Gt (P < 0.05). In the jejunum of SPF chickens, there was also a marked decrease in net charge transfer across the epithelium, evidenced by decreased short-circuit current (Isc, P < 0.05). Interestingly, the mucosal application of Salmonella endotoxin to the epithelial preparations from jejunum and cecum of SPF chicken had an effect similar to living bacteria. However, the endotoxin had no additional effect on the intestinal function in the presence of bacteria. The decreasing effect of Salmonella and or its endotoxin on Gt could be partly reversed by serosal addition of histamine. To our knowledge, this is the first study to address the functional response of native intestinal epithelium of chicken to an in vitro Salmonella infection. For the first time, it can be reported that intestinal ion permeability of chicken decreases acutely by the presence of Salmonella. This type of response could counteract ion and fluid secretion and may thus, at least in part, explain why chickens do not develop overt diarrhea after Salmonella infection