Host Stress Drives Salmonella Recrudescence

Anti-Salmonella Defence and Intestinal Homeostatic Maintenance In Vitro of a Consortium Containing Limosilactobacillus fermentum 3872 and Ligilactobacillus salivarius 7247 Strains in Human, Porcine, and Chicken Enterocytes

Limosilactobacillus fermentum strain 3872 (LF3872) was originally isolated from the breast milk of a healthy woman during lactation and the breastfeeding of a child. Ligilactobacillus salivarius strain 7247 (LS7247) was isolated at the same time from the intestines and reproductive system of a healthy woman. The genomes of these strains contain genes responsible for the production of peptidoglycan-degrading enzymes and factors that increase the permeability of the outer membrane of Gram-negative pathogens. In this work, the anti-Salmonella and intestinal homeostatic features of the LF3872 and LS7247 consortium were studied. A multi-drug resistant (MDR) strain of Salmonella enteritidis (SE) was used in the experiments. The consortium effectively inhibited the adhesion of SE to intact and activated human, porcine, and chicken enterocytes and reduced invasion. The consortium had a bactericidal effect on SE in 6 h of co-culturing. A gene expression analysis of SE showed that the cell-free supernatant (CFS) of the consortium inhibited the expression of virulence genes critical for the colonization of human and animal enterocytes. The CFS stimulated the production of an intestinal homeostatic factor-intestinal alkaline phosphatase (IAP)-in Caco-2 and HT-29 enterocytes. The consortium decreased the production of pro-inflammatory cytokines IL-8, TNF-α, and IL-1β, and TLR4 mRNA expression in human and animal enterocytes. It stimulated the expression of TLR9 in human and porcine enterocytes and stimulated the expression of TLR21 in chicken enterocytes. The consortium also protected the intestinal barrier functions through the increase of transepithelial electrical resistance (TEER) and the inhibition of paracellular permeability in the monolayers of human and animal enterocytes. The results obtained suggest that a LF3872 and LS7247 consortium can be used as an innovative feed additive to reduce the spread of MDR SE among the population and farm animals.

Regulated necrosis, a proinflammatory cell death, potentially counteracts pathogenic infections

Since the discovery of cell apoptosis, other gene-regulated cell deaths are gradually appreciated, including pyroptosis, ferroptosis, and necroptosis. Necroptosis is, so far, one of the best-characterized regulated necrosis. In response to diverse stimuli (death receptor or toll-like receptor stimulation, pathogenic infection, or other factors), necroptosis is initiated and precisely regulated by the receptor-interacting protein kinase 3 (RIPK3) with the involvement of its partners (RIPK1, TRIF, DAI, or others), ultimately leading to the activation of its downstream substrate, mixed lineage kinase domain-like (MLKL). Necroptosis plays a significant role in the host's defense against pathogenic infections. Although much has been recognized regarding modulatory mechanisms of necroptosis during pathogenic infection, the exact role of necroptosis at different stages of infectious diseases is still being unveiled, e.g., how and when pathogens utilize or evade necroptosis to facilitate their invasion and how hosts manipulate necroptosis to counteract these detrimental effects brought by pathogenic infections and further eliminate the encroaching pathogens. In this review, we summarize and discuss the recent progress in the role of necroptosis during a series of viral, bacterial, and parasitic infections with zoonotic potentials, aiming to provide references and directions for the prevention and control of infectious diseases of both human and animals.

Salmonella in Swine: Prevalence, Multidrug Resistance, and Vaccination Strategies

An estimated 1.3 million Salmonella infections and 420 deaths occur annually in the United States, with an estimated economic burden of $3.7 billion. More than 50% of US swine operations test positive for Salmonella according to the National Animal Health Monitoring System, and 20% of Salmonella from swine are multidrug resistant (resistant to ≥3 antimicrobial classes) as reported by the National Antimicrobial Resistance Monitoring System. This review on Salmonella in swine addresses the current status of these topics by discussing antimicrobial resistance and metal tolerance in Salmonella and the contribution of horizontal gene transfer. A major challenge in controlling Salmonella is that Salmonella is a foodborne pathogen in humans but is often a commensal in food animals and thereby establishes an asymptomatic reservoir state in such animals, including swine. As food animal production systems continue to expand and antimicrobial usage becomes more limited, the need for Salmonella interventions has intensified. A promising mitigation strategy is vaccination against Salmonella in swine to limit animal, environmental, and food contamination. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Understanding the effects of intramuscular injection and feed withdrawal on Salmonella Typhimurium shedding and gut microbiota in pullets

Background

Gut microbiota plays a key role in health, immunity, digestion, and production in layers. Factors such as environment, diet, diseases, stress, and flock management significantly affect gut microbiota; however, it is not known how potential stressors such as intramuscular injections or feed withdrawal alter the composition of gut microbiota that result in increased the shedding level of foodborne pathogens. In the current study, the effects of intramuscular corticosterone injection and feed withdrawal were evaluated to understand their role in Salmonella Typhimurium shedding and changes in the composition of gut microbiota in layers.

Results

Salmonella shedding was observed for 8 weeks post-infection. There was a significant increase in Salmonella Typhimurium count after intramuscular injection and feed withdrawal. The Salmonella infected and the negative control groups showed significant differences in the abundance of different genera in gut microbiota at week 1 and up to week 7 post infection. The infected group showed a significant reduction in alpha diversity of gut microbiota. Firmicutes reduced significantly (P < 0.05) after intramuscular injection, while the feed withdrawal groups did not cause any significant changes in Proteobacteria-Firmicutes ratio. Furthermore, intramuscular injection resulted in a significant change in alpha diversity of gut microbiota.

Conclusions

Exposure of chicks to relatively low dose of Salmonella Typhimurium can lead to persistent shedding in pullets. The Salmonella Typhimurium infection disrupted the gut microbiota composition immediately after infection. The potential stress of intramuscular injection and feed withdrawal significantly increased the Salmonella Typhimurium count in faeces. The intramuscular injection also resulted in a significant alteration of the Proteobacteria-Firmicutes ratio, which could increase the risk of dysbiosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00597-9.

Interkingdom Cross-Talk in Times of Stress: Salmonella Typhimurium Grown in the Presence of Catecholamines Inhibits Porcine Immune Functionality in vitro

In stressful situations, catecholamines modulate mammalian immune function, and in addition, they can be sensed by many bacteria. Catecholamine sensing was also found in the zoonotic gut pathogen Salmonella Typhimurium, probably contributing to the stress-induced increased risk of salmonellosis. Virulence traits such as proliferation and invasiveness are promoted upon bacterial catecholamine sensing, but it is unknown whether S. Typhimurium may also inhibit mammalian immune function in stressful situations. We thus investigated whether supernatants from S. Typhimurium grown in the presence of catecholamines modulate porcine mitogen-induced lymphocyte proliferation. Lymphocyte proliferation was reduced by supernatants from catecholamine-exposed Salmonella in a dose-dependent manner. We further examined whether adrenaline oxidation to adrenochrome, which is promoted by bacteria, could be responsible for the observed effect, but this molecule either enhanced lymphocyte functionality or had no effect. We could thereby exclude adrenochrome as a potential immunomodulating agent produced by S. Typhimurium. This study is the first to demonstrate that bacteria grown in the presence of catecholamine stress hormones alter their growth environment, probably by producing immunomodulating substances, in a way that host immune response is suppressed. These findings add a new dimension to interkingdom signaling and provide novel clues to explain the increased susceptibility of a stressed host to Salmonella infection.

CpxR/CpxA Controls scsABCD Transcription To Counteract Copper and Oxidative Stress in Salmonella enterica Serovar Typhimurium

Periplasmic thiol/disulfide oxidoreductases participate in the formation and isomerization of disulfide bonds and contribute to the virulence of pathogenic microorganisms. Among the systems encoded in the Salmonella genome, the system encoded by the scsABCD locus was shown to be required to cope with Cu and H₂O₂ stress. Here we report that this locus forms an operon whose transcription is driven by a promoter upstream of scsA and depends on CpxR/CpxA and on Cu. Furthermore, genes homologous to scsB, scsC, and scsD are always detected immediately downstream of scsA and in the same genetic arrangement in all scsA-harboring enterobacterial species. Also, a CpxR-binding site is detected upstream of scsA in most of those species, providing evidence of evolutionarily conserved function and regulation. Each individual scs gene shows a different role in copper and/or H₂O₂ resistance, indicating hierarchical contributions of these factors in the defense against these intoxicants. A protective effect of Cu preincubation against H₂O₂ toxicity and the increased Cu-mediated activation of cpxP in the ΔscsABCD mutant suggest that the CpxR/CpxA-controlled transcription of the ScsABCD system contributes to prevent Cu toxicity and to restore the redox balance at the Salmonella envelope.IMPORTANCE Copper intoxication triggers both specific and nonspecific responses in Salmonella The scs locus, which codes for periplasmic thiol/disulfide-oxidoreductase/isomerase-like proteins, has been the focus of attention because it is necessary for copper resistance, oxidative stress responses, and virulence and because it is not present in nonpathogenic Escherichia coli Still, the conditions under which the scs locus is expressed and the roles of its individual components remain unknown. In this report, we examine the contribution of each Scs factor to survival under H₂O₂ and copper stress. We establish that the scs genes form a copper-activated operon controlled by the CpxR/CpxA signal transduction system, and we provide evidence of its conserved gene arrangement and regulation in other bacterial pathogens.

Whole genome sequencing reveals widespread distribution of typhoidal toxin genes and VirB/D4 plasmids in bovine-associated nontyphoidal Salmonella

Nontyphoidal Salmonella (NTS) is a common pathogen in food-producing animals and a public health concern worldwide. Various NTS serovars may be present in apparently healthy animals. This could result in carcass contamination during the slaughter process leading to human exposure. While most genomic research has focused on Salmonella pathogenesis, little is known on the factors associated with subclinical infections and environmental persistence. We report here the widespread distribution of typhoidal toxin genes (i. e. the cdtB islet, hlyE, taiA), among NTS strains from a beef slaughter operation (n = 39) and from epidemiologically unconnected ground beef (n = 20). These genes were present in 76% of the strains, regardless of serovar, isolation source or geographical location. Moreover, strains that predominated in the slaughterhouse carry plasmid-borne type IV secretion systems (T4SS), which have been linked to persistent infections in numerous pathogens. Population genomics supports clonal dissemination of NTS along the food production chain, highlighting its role as reservoir of genetic variability in the environment. Overall, the study provides a thorough characterization of serovar diversity and genomic features of beef-associated NTS in Mexico. Furthermore, it reveals how common genetic factors could partially explain the emergence and persistence of certain NTS serovars in the beef industry.

In silico identification and characterization of stress and virulence associated repeats in Salmonella

So much genomic similarities yet causing different diseases, is like a paradox in Salmonella biology. Repeat is one of the probes that can explain such differences. Here, a comparative genomics approach is followed to identify and characterize repeats that might play role in adaptation and pathogenesis. Repeats are non-randomly distributed in the genomes except few typhoid causing strains. Perfect long repeats are rare compare to polymorphic ones and both are statistically consistent. Significant differences in repeat densities in stress related genes manifest its probable participation in survival and virulence. 573 and 1053 repeat loci have been identified which are exclusively associated with stress and virulent genes respectively. In Salmonella Typhi, an octameric VNTR locus is found in between acrD and yffB genes having more than 25 perfect copies across Salmonella Typhi but possesses only single copy in other serovars. This repeat can be used as a diagnostic probe for typhoid.

The in vitro and in vivo protective effects of tannin derivatives against Salmonella enterica serovar Typhimurium infection

In this study, we investigated the protective effects of tannin-derived components, gallic acid (GA) and tannic acid (TA), in vitro and in vivo against Salmonella infection in mice. Both GA and TA showed antibacterial effects against Salmonella (S.) Typhimurium as well as inhibitory effects on the adherence, invasion, and intracellular growth of the pathogens in macrophages. Following a lethal dose of Salmonella infection in mice, reduced virulence in both GA- and TA-treated groups was observed based on reduced mortality rates. In the non-infected groups, the average weights of the spleens and livers of GA- or TA-treated mice were not significantly different with the control group. In addition, the average weights of these organs in all of the Salmonella-infected groups were not significantly different but the numbers of bacteria in the spleens and livers in both GA- and TA-treated mice were significantly reduced. The levels of cytokine production in non-infected mice revealed that GA-treated and TA-treated mice elicited an increased level of IFN-γ, and both IFN-γ and MCP-1, respectively, as compared with the PBS-treated group. These findings highlight the potential of GA and TA as alternatives for the treatment of salmonellosis and as supplements to conventional antimicrobial food additives.

Correlating bacterial shedding with fecal corticosterone levels and serological responses from layer hens experimentally infected with Salmonella Typhimurium

Salmonella Enteriditis and Salmonella Typhimurium are commonly isolated during egg-related outbreaks of salmonellosis and represent a significant international public health issue. In Australia, Salmonella Typhimurium is the most common serovar identified in egg product related foodborne outbreaks. While a number of studies have investigated Salmonella shedding and host responses to infection, they have been conducted over a short time period. The present study sought to characterise bacterial shedding and host responses to infection in hens infected with only Salmonella Typhimurium or co-infected with both Salmonella Typhimurium and Salmonella Mbandaka over a 16 week period. Salmonella shedding was quantified using the most probable number and qPCR methods and was highly variable over the course of the experiment. On day 1, fecal corticosterone metabolites in birds infected with Salmonella Typhimurium (674.2 ± 109.3 pg/mg) were significantly higher than control (238.0 ± 12.62 pg/mg) or co-infected (175.4 ± 8.58 pg/mg) birds. The onset of lay occurred between weeks 6–8 post-infection (pi) and Fecal corticosterone metabolite (FCM) concentrations increased in both control and co-infected birds. Antibody responses to infection were monitored in both serum and yolk samples. Salmonella Typhimurium specific antibody was lower in co-infected animals than monoinfected animals. Bacterial loads in internal organs were characterised to determine persistence. Spleen, liver and caecal tonsils were positive for bacteria in both groups, indicating that Salmonella was not cleared from the birds and internal organ colonization could serve as a reservoir for continued bacterial shedding.

Salmonella Typhimurium and Multidirectional Communication in the Gut

The mammalian digestive tract is home to trillions of microbes, including bacteria, archaea, protozoa, fungi, and viruses. In monogastric mammals the stomach and small intestine harbor diverse bacterial populations but are typically less populated than the colon. The gut bacterial community (microbiota hereafter) varies widely among different host species and individuals within a species. It is influenced by season of the year, age of the host, stress and disease. Ideally, the host and microbiota benefit each other. The host provides nutrients to the microbiota and the microbiota assists the host with digestion and nutrient metabolism. The resident microbiota competes with pathogens for space and nutrients and, through this competition, protects the host in a phenomenon called colonization resistance. The microbiota participates in development of the host immune system, particularly regulation of autoimmunity and mucosal immune response. The microbiota also shapes gut–brain communication and host responses to stress; and, indeed, the microbiota is a newly recognized endocrine organ within mammalian hosts. Salmonella enterica serovar Typhimurium (S. Typhimurium hereafter) is a food-borne pathogen which adapts to and alters the gastrointestinal (GI) environment. In the GI tract, S. Typhimurium competes with the microbiota for nutrients and overcomes colonization resistance to establish infection. To do this, S. Typhimurium uses multiple defense mechanisms to resist environmental stressors, like the acidic pH of the stomach, and virulence mechanisms which allow it to invade the intestinal epithelium and disseminate throughout the host. To coordinate gene expression and disrupt signaling within the microbiota and between host and microbiota, S. Typhimurium employs its own chemical signaling and may regulate host hormone metabolism. This review will discuss the multidirectional interaction between S. Typhimurium, host and microbiota as well as mechanisms that allow S. Typhimurium to succeed in the gut.