Two separate outbreaks of Salmonella enteritidis phage type 14b food poisoning linked to the consumption of the same type of frozen food

Essential role of Salmonella Enteritidis DNA adenine methylase in modulating inflammasome activation

Background

Salmonella Enteritidis (SE) is one of the major foodborne zoonotic pathogens of worldwide importance which can induce activation of NLRC4 and NLRP3 inflammasomes during infection. Given that the inflammasomes play an essential role in resisting bacterial infection, Salmonella has evolved various strategies to regulate activation of the inflammasome, most of which largely remain unclear.

Results

A transposon mutant library in SE strain C50336 was screened for the identification of the potential factors that regulate inflammasome activation. We found that T3SS-associated genes invC, prgH, and spaN were required for inflammasome activation in vitro. Interestingly, C50336 strains with deletion or overexpression of Dam were both defective in activation of caspase-1, secretion of IL-1β and phosphorylation of c-Jun N-terminal kinase (Jnk). Transcriptome sequencing (RNA-seq) results showed that most of the differentially expressed genes and enriched KEGG pathways between the C50336-VS-C50336Δdam and C50336-VS-C50336::dam groups overlapped, which includes multiple signaling pathways related to the inflammasome. C50336Δdam and C50336::dam were both found to be defective in suppressing the expression of several anti-inflammasome factors. Moreover, overexpression of Dam in macrophages by lentiviral infection could specifically enhance the activation of NLRP3 inflammasome independently via promoting the Jnk pathway.

Conclusions

These data indicated that Dam was essential for modulating inflammasome activation during SE infection, there were complex and dynamic interplays between Dam and the inflammasome under different conditions. New insights were provided about the battle between SE and host innate immunological mechanisms.

Multi locus variable-number tandem repeat (MLVA) typing tools improved the surveillance of Salmonella enteritidis: a 6 years retrospective study

Surveillance of Salmonella enterica subsp. enterica serovar Enteritidis is generally considered to benefit from molecular techniques like multiple-locus variable-number of tandem repeats analysis (MLVA), which allow early detection and confinement of outbreaks. Here, a surveillance study, including phage typing, antimicrobial susceptibility testing and MLVA on 1,535 S. Enteritidis isolates collected between 2007 and 2012, was used to evaluate the added value of MLVA for public health surveillance in Belgium. Phage types PT4, PT8, PT21, PT1, PT6, PT14b, PT28 and PT13 dominate the Belgian S. Enteritidis population. The isolates of S. Enteritidis were most frequently susceptible to all antibiotics tested. 172 different MLVA profiles were detected, of which 9 frequent profiles included 67.2% of the S. Enteritidis population. During a serial passage experiment on selected isolates to investigate the in vitro stability of the 5 MLVA loci, no variations over time were observed indicating that the MLVA profiles were stable. The MLVA profile of isolates originating from different outbreaks in the Democratic Republic of the Congo (DRC) between 2010 and 2011 were distinct from any of the MLVA profiles found in Belgian isolates throughout the six year observational period and demonstrates that MLVA improves public health surveillance of S. Enteritidis. However, MLVA should be complemented with other subtyping methods when investigating outbreaks is caused by the most common MLVA profile.

Salmonella enterica serovar Enteritidis phage type 4 outbreak associated with eggs in a large prison, London 2009: an investigation using cohort and case/non-case study methodology

In September 2009, an outbreak of Salmonella enterica serovar Enteritidis affected 327 of 1419 inmates at a London prison. We applied a cohort design using aggregated data from the kitchen about portions of food distributed, aligned this with individual food histories from 124 cases (18 confirmed, 106 probable) and deduced the exposures of those remaining well. Results showed that prisoners eating egg cress rolls were 26 times more likely to be ill [risk ratio 25.7, 95% confidence interval (CI) 15.5-42.8, P<0.001]. In a case/non-case multivariable analysis the adjusted odds ratio for egg cress rolls was 41.1 (95% CI 10.3-249.7, P<0.001). The epidemiological investigation was strengthened by environmental and microbiological investigations. This paper outlines an approach to investigations in large complex settings where aggregate data for exposures may be available, and led to the development of guidelines for the management of future gastrointestinal outbreaks in prison settings.

Effects of fructooligosaccharide-inulin on Salmonella-killing and inflammatory gene expression in chicken macrophages

Salmonella Enteritidis (SE) is one of the leading causes of food-borne salmonellosis, and macrophages play an essential role in eliminating this pathogen. Among the interventions to improve Salmonella clearance in chickens are the use of prebiotics and direct fed microbials (DFM) in animal feed as they have immunomodulatory effects. Therefore, we tested the influence of a prebiotic fructooligosaccharide (FOS)-inulin on the ability of the chicken macrophage HD11 cell line to phagocytose and kill SE, and express selected inflammatory cytokines and chemokines in an in vitro model. There were significantly fewer viable intracellular SE in HD11 cells treated with FOS-inulin than the untreated cells. However, SE phagocytosis, nitric oxide expression or production were not influenced by the prebiotic treatment. Among the inflammatory markers tested, IL-1β expression was significantly lower in HD11 cells treated with FOS-inulin. These results suggest that FOS-inulin has the ability to modulate the innate immune system as shown by the enhanced killing of SE and decreased inflammasome activation.

Effect of long chain fatty acids on Salmonella killing, superoxide and nitric oxide production by chicken macrophages

The objective of this study was to investigate the effect of uptake of different commonly consumed long chain fatty acids on superoxide (O(2)(-)), nitric oxide (NO) production, and ability to kill Salmonella enterica serotype typhimurium (S. typhimurium) by chicken macrophages (HD11 cells). All the fatty acids were taken up by HD11 cells with stearic acid uptake higher than polyunsaturated fatty acids. Uptake of green fluorescent protein-labeled bacteria and the viability of HD11 cells (measured by flow cytometry) was not affected by any of the fatty acids tested. Bacterial clearance (measured by the plating of sorted viable infected cells) was significantly higher with n-3 fatty acids alpha-linolenic acid (ALA) and docosahexanoic acid (DHA). However, stearic acid (SA) and the n-6 fatty acid, arachidonic acid (ARA) did not influence S. typhimurium killing by HD11 cells. The improved S. typhimurium clearance by ALA and DHA was not associated with increased NO or O(2)(-) production by HD11 cells. These results suggest a role for n-3 polyunsaturated fatty acids in Salmonella clearance by chicken macrophages however in vivo studies are essential to confirm their efficacy in controlling Salmonella infection in chickens and contamination in shell eggs.

A study of 279 general outbreaks of gastrointestinal infection in the north-East region of England

All outbreaks of infectious intestinal disease reported to the authorities were entered on a computer database with outbreak control teams being established to investigate larger or more significant incidents. The outbreak database and, when set up, the notes of outbreak team meetings were examined for the 279 outbreaks reported in a three-year period (2003–2005). Faeces specimens submitted as part of an outbreak were examined for microbial pathogens and the results cross-matched to the outbreak number. Almost half of the general outbreaks reported (137) occurred in long-term care facilities for the elderly, 51 outbreaks were recorded in hospitals and 31 occurred in the wider community. In 76 outbreaks no specimen was logged. A microbial cause was confirmed in about one-third of outbreaks, with noroviruses being the most common (19%). Salmonellas accounted for 12 of the 21 community outbreaks linked to social events and all were foodborne. Suggestions for improving notification and surveillance are discussed.

Does microbiological testing of foods and the food environment have a role in the control of foodborne disease in England and Wales?

This review looks at the contribution of microbiological sampling to the safety of retail foods in England and Wales. It compares sampling methods available and assesses the value of testing as part of outbreaks of foodborne disease, as part of routine management by local authorities, as part of work done or commissioned by the food industry, and as part of research. It confirms that microbiological testing has a role during outbreaks as it makes a significant contribution to help identify foods and other areas of greatest risk for future study. The review suggests that routine testing by local authorities is often of limited use and could be improved by more targeted surveillance. Testing could be better used to validate primary control methods, such as Hazard Analysis and Critical Control Point (HACCP) system. Any public health benefit from testing in the food industry is often restricted by client confidentiality. Microbial research on foods is important as it can lead to significant improvements in safety. Current microbiological methods are slow and, in future, rapid molecular methods may make an even bigger contribution to the control of foodborne disease.