Salmonella Typhimurium Infection Along the Porcine Gastrointestinal Tract and Associated Lymphoid Tissues

Prevalence and Characterization of Salmonella during Pork Sausage Manufacturing

Pork carcasses and meat may harbor Salmonella and may contaminate other products during harvest and fabrication. Sources of contamination include manure on hides, environmental contamination, ingredients from external sources, and lymph nodes. Swine lymph nodes are often incorporated into ground meat, as their anatomical location makes removal labor prohibitive. A sausage processing plant in the midwestern United States was sampled monthly (except for December) from May 2021 to April 2022 to enumerate Salmonella and Enterobacteriaceae (EB) throughout the sausage manufacturing process to determine high-risk stages and efficiency of existing in-plant interventions. Salmonella serotypes and antimicrobial susceptibility were evaluated on a subset of isolates recovered at the end phases of sausage production. In each collection, samples were taken from the carcasses of eight sows through 11 stages of sausage manufacturing. A total of 830 samples were cultured. Thirty-four Salmonella were isolated from the final three production stages; of these, there were eleven serotypes. Three isolates displayed resistance to ampicillin, whereas the remainder of the isolates were pan-susceptible to the antimicrobials tested. Salmonella and EB were significantly reduced (p < 0.001) by acid washes at different stages of production, and the results point to the beneficial effects of interventions to lessen Salmonella concentrations in retail products.

Lactiplantibacillus argentoratensis AGMB00912 alleviates salmonellosis and modulates gut microbiota in weaned piglets: a pilot study

This study aimed to evaluate the efficacy of Lactiplantibacillus argentoratensis AGMB00912 (LA) in reducing Salmonella Typhimurium infection in weaned piglets. The investigation focused on the influence of LA on the gut microbiota composition, growth performance, and Salmonella fecal shedding. The results indicated that LA supplementation significantly improved average daily gain and reduced the prevalence and severity of diarrhea. Fecal analysis revealed reduced Salmonella shedding in the LA-supplemented group. Furthermore, LA notably altered the composition of the gut microbiota, increasing the levels of beneficial Bacillus and decreasing those of harmful Proteobacteria and Spirochaetes. Histopathological examination showed less intestinal damage in LA-treated piglets than in the controls. The study also observed that LA affected metabolic functions related to carbohydrate, amino acid, and fatty acid metabolism, thereby enhancing gut health and resilience against infection. Short-chain fatty acid concentrations in the feces were higher in the LA group, suggesting improved gut microbial activity. LA supplementation enriched the population of beneficial bacteria, including Streptococcus, Clostridium, and Bifidobacterium, while reducing the number of harmful bacteria, such as Escherichia and Campylobacter. These findings indicate the potential of LA as a probiotic alternative for swine nutrition, offering protective effects to the gut microbiota against Salmonella infection.

Effect of Salmonella pathogenicity island 1 and 2 (SPI-1 and SPI-2) deletion on intestinal colonization and systemic dissemination in chickens

Salmonella's virulence genes are located in two regions known as Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2). SPI-1 allows the bacteria to invade the intestine, while SPI-2 is important for intracellular survival and replication, although it is also necessary for intestinal disease. The aim of this study was to evaluate the effect of the deletion of SPI-1 or SPI-2 genes on the intestinal and systemic salmonellosis using the avian model. Groups of chickens were orally infected with 1010 Colony-Forming Units (CFU) of S. Typhimurium SL1344 WT strain, as well as mutants ∆SPI-1 or ∆SPI-2. At different times post-infection, 5 chickens from each group were euthanized and examined postmortem. Cecum and liver were taken from each chicken for determination of CFU's, histopathological analysis and immunochemistry. Bacterial colonies were recovered from the liver and cecum samples infected with WT strain, while in the cultures from the organs infected with the mutant strains no colonies were recovered or were drastically affected in the ability to survive. In histopathological analysis, the WT strain produced lesions in liver and ceca, and it was detected by immunohistochemistry throughout the course of the infection. On the other hand, organs of chickens infected with ∆SPI-1 or ∆SPI-2 showed attenuated lesions and the immunohistochemistry revealed less bacteria compared to the WT strain. Taken together, our results show the importance of SPI-1 and SPI-2 genes for the complete intestinal and systemic disease in an in vivo avian model.

Salmonella Infection in Pigs: Disease, Prevalence, and a Link between Swine and Human Health

Salmonella is one of the most spread foodborne pathogens worldwide, and Salmonella infections in humans still represent a global health burden. The main source of Salmonella infections in humans is represented by contaminated animal-derived foodstuffs, with pork products being one of the most important players. Salmonella infection in swine is critical not only because it is one of the main causes of economic losses in the pork industry, but also because pigs can be infected by several Salmonella serovars, potentially contaminating the pig meat production chain and thus posing a significant threat to public health globally. As of now, in Europe and in the United States, swine-related Salmonella serovars, e.g., Salmonella Typhimurium and its monophasic variant Salmonella enterica subsp. enterica 1,4,[5],12:i:-, are also frequently associated with human salmonellosis cases. Moreover, multiple outbreaks have been reported in the last few decades which were triggered by the consumption of Salmonella-contaminated pig meat. Throughout the years, changes and evolution across the pork industry may have acted as triggers for new issues and obstacles hindering Salmonella control along the food chain. Gathered evidence reinforces the importance of coordinating control measures and harmonizing monitoring programs for the efficient control of Salmonella in swine. This is necessary in order to manage outbreaks of clinical disease in pigs and also to protect pork consumers by controlling Salmonella subclinical carriage and shedding. This review provides an update on Salmonella infection in pigs, with insights on Salmonella ecology, focusing mainly on Salmonella Choleraesuis, S. Typhimurium, and S. 1,4,[5],12:i:-, and their correlation to human salmonellosis cases. An update on surveillance methods for epidemiological purposes of Salmonella infection in pigs and humans, in a "One Health" approach, will also be reported.

Raw potato starch diet supplement in weaned pigs could reduce Salmonella Typhimurium infection by altering microbiome composition and improving immune status

Backgorund

Salmonella enterica serovar Typhimurium (ST) is one of the causative agents of gastroenteritis in pigs. Pigs fed a diet supplemented with raw potato starch (RPS) have improved gut health by the alteration of the microbiota composition and production of short-chain fatty acids (SCFAs). This study aimed to evaluate the effects of RPS supplementation in reducing infection severity and fecal shedding in ST-infected pigs.

Methods

The weaned experimental pigs were divided into two groups: CON (n = 6) fed a corn/soybean-based diet and TRT (n = 6) supplemented with 5% RPS. After 21 d, the pigs were inoculated with ST, and their body weight, clinical signs, and fecal shedding of ST were monitored for 14 d. At 14 d post-inoculation (dpi), the jejunum, cecum, ileum, and colon tissues were collected from euthanized pigs, and histopathological lesions and cytokine gene expression were compared. Additionally, blood samples at 2 dpi were analyzed for gene ontology enrichment. Moreover, the gutmicrobiome was analyzed using 16S rRNA metagenomic sequencing, and the SCFA concentration was measured using gas chromatography.

Results

The average daily weight gain was significantly higher in TRT than in CON during the ST infection period; however, histopathological lesion scores were significantly lower in TRT than in CON. The relative abundance of nine genera of butyrate- and acetate-producing bacteria significantly increased in TRT compared with that of only two acetate-producing bacteria in CON. Among the genes involved in the immune response, IL-18 expression level was significantly lower in the jejunum and colon in TRT than in CON. Furthermore, Reg3γ expression was significantly different in the cecum and colon of both groups.

Conclusion

The diet supplemented with RPS in weaned pigs could result in predominance of butyrate- and acetate-producing bacteria, reducing the severity of ST infection by improving the immune status.

Effect of dietary β-glucan on intestinal microbial diversity and Salmonella vaccine immunogenicity and efficacy in pigs

Alternatives to antibiotics to improve animal performance, limit the negative impact of infectious disease, and/or reduce colonization with foodborne pathogens is a major focus of animal agricultural research. β-glucans, a generally-recognized-as-safe (GRAS) product derived from various sources, are used in swine and can serve as both a prebiotic and/or stimulant of the immune system given the expression of β-glucan receptors on immune cells. When supplied in the diet of nursery pigs, it is unclear how dietary additives, particularly those known to modulate immune status, impact immunogenicity and efficacy of mucosal-delivered vaccines. Salmonellosis is one of the most common bacterial foodborne infections in the United States, and consumption of contaminated pork is a major source of human infection. Reduction of foodborne Salmonella in pigs via vaccination is one strategy to reduce contamination risk and subsequently reduce human disease. We examined the ability of dietary β-glucan to modulate fecal microbial diversity, and immunogenicity and efficacy of a mucosally-delivered, live-attenuated Salmonella vaccine during the nursery period. While dietaryβ-glucan did modulate fecal alpha diversity, it did not alter the induction of peripheral Salmonella-specific IFN-γ secreting Tcells or Salmonella-specific IgA in oral fluids. In addition, vaccination reduced Salmonella enterica serovar Typhimurium fecal shedding and tissue colonization. Overall, addition of β-glucan to the nursery diet of pigs impacted the microbiota but did not alter mucosal vaccine immunogenicity and efficacy.

Functional amino acid supplementation attenuates the negative effects of plant-based nursery diets on the response of pigs to a subsequent Salmonella Typhimurium challenge

Functional amino acids (FAA) attenuate the effects of Salmonella challenge in pigs. However, this may be affected by protein source (PS). The objective of the present study was to determine the effects of nursery dietary PS and FAA supplementation on growth performance and immune status of pigs subsequently challenged with Salmonella Typhimurium (ST). Thirty-two weanling pigs (8.7 ± 0.23 kg) were assigned to a feeding program for 31 d in a 2 × 2 factorial arrangement. Factors were dietary PS (plant-based [PB] vs. animal-based [AB]) and FAA profile (basal [FAA-] or supplemented [FAA+; Thr, Met, and Trp at 120% of requirements]). Pigs were subsequently placed on a common grower diet and, after a 7-d adaptation, were inoculated with ST and monitored for 7 d postinoculation. Growth performance, rectal temperature, fecal score, gut health, ST shedding score, intestinal colonization and translocation, and blood parameters of acute-phase response and antioxidant balance were measured pre- and postinoculation. Data were analyzed with a 2 (AB vs. PB) × 2 (FAA- vs. FAA+) factorial arrangement of treatments and differences between means were considered significant at P ≤ 0.05. Postinoculation fecal score was worse, ST shedding, cecal myeloperoxidase, and cecal and colonic ST colonization were greater in PB compared to AB pigs (P < 0.05). Translocation of ST to spleen was decreased by FAA+ (P < 0.05), regardless of dietary PS. Postinoculation, AB pigs had greater average daily gain compared to PB-FAA- (P < 0.05). Pigs fed AB-FAA- showed increased average daily feed intake compared to PB-FAA- pigs (P < 0.05) and feed efficiency was increased in AB-FAA+ compared to PB-FAA- pigs (P < 0.05). Feeding PB ingredients in nursery diets seems to increase susceptibility of pigs to Salmonella. Moreover, FAA supplementation partially attenuated the negative effects of PB diets on the response of pigs to ST challenge.

Bioactive compounds, antibiotics and heavy metals: effects on the intestinal structure and microbiome of monogastric animals – a non-systematic review

The intestinal structure and gut microbiota are essential for the animals‘ health. Chemical components taken with food provide the right environment for a specific microbiome which, together with its metabolites and the products of digestion, create an environment, which in turn is affects the population size of specific bacteria. Disturbances in the composition of the gut microbiota can be a reason for the malformation of guts, which has a decisive impact on the animal‘ health. This review aimed to analyse scientific literature, published over the past 20 years, concerning the effect of nutritional factors on gut health, determined by the intestinal structure and microbiota of monogastric animals. Several topics have been investigated: bioactive compounds (probiotics, prebiotics, organic acids, and herbal active substances), antibiotics and heavy metals (essentaial minerals and toxic heavy metals).

Functional amino acid supplementation postweaning mitigates the response of normal birth weight more than for low birth weight pigs to a subsequent Salmonella challenge

Previous work has shown that dietary supplementation with key functional amino acids (FAA) improves growth performance and immune status of disease-challenged normal birth weight (NBW) pigs. It is not known whether FAA supplementation attenuates the effects of a subsequent disease challenge or whether this response is similar in low birth weight (LBW) pigs. The objective was to determine the effects of birth weight and FAA supplementation during the postweaning period in Salmonella-challenged pigs. Thirty-two LBW (1.08 ± 0.11 kg) and NBW (1.58 ± 0.11 kg) pigs were assigned to a nursery feeding program at weaning (25 d) for 31 days in a 2 × 2 factorial arrangement. Factors were birth weight category (LBW vs. NBW) and basal (FAA-) or supplemented FAA profile (FAA+; Thr, Met, and Trp at 120% of requirements). At d 31, pigs were placed onto a common grower diet and, after a 7-d adaptation period, were inoculated with Salmonella Typhimurium (ST; 2.2 × 10⁹ colony-forming units/mL) and monitored for 7-d postinoculation. Growth performance, rectal temperature, fecal score, indicators of gut health, ST shedding score in feces, intestinal ST colonization and translocation, and blood parameters of acute-phase response and antioxidant balance were measured pre- and postinoculation. Inoculation with ST increased temperature and fecal score, and the overall rectal temperature was higher in LBW compared to NBW pigs (P < 0.05). Postinoculation (d 7), reduced:oxidized glutathione was increased in NBW compared to LBW pigs (P < 0.05). Salmonella shedding and translocation to spleen were lower in NBW-FAA+ compared to NBW-FAA- pigs (P < 0.05). Postinoculation average daily gain was higher in NBW-FAA+ (P < 0.05) compared to the other groups. Postinoculation haptoglobin, superoxide dismutase, and colonic myeloperoxidase were increased in LBW-FAA- pigs (P < 0.05). Ileal alkaline phosphatase was decreased in LBW compared to NBW (P < 0.05). Overall, FAA supplementation represents a potential strategy to mitigate the effect of enteric disease challenge in NBW, but not LBW pigs.

Inoculation of Weaned Pigs by Feed, Water, and Airborne Transmission of Salmonella enterica Serotype 4,[5],12:i:

ABSTRACT

Salmonella enterica serotype 4,[5],12:i:- (STM) has become an increasing problem for food safety and has been often detected in swine products. Weanling pigs were exposed to STM-contaminated feed, water, or air to determine possible STM transmission routes. A control group of pigs was included. STM was monitored daily in feces and rectal and nasal swabs. STM colonization was most prevalent in tissues from tonsil, lower intestine, and mesenteric lymph nodes. No differences in lesion severity were observed between inoculated and control pigs. Contaminated feed, water, and aerosolized particles caused infection in weaned pigs; however, no STM colonization was observed in skeletal muscle destined for human consumption. Based on the results from this study, STM contamination in pork products most likely results from cross-contamination of meat by digesta or lymph node tissue during processing.

HIGHLIGHTS

A longer adaptation period to a functional amino acid-supplemented diet improves growth performance and immune status of Salmonella Typhimurium-challenged pigs

We recently showed that dietary supplementation with key functional amino acids (FAA) improves growth performance and immune status of Salmonella Typhimurium (ST)-challenged pigs. It is not known if ST-challenged pigs will benefit from a longer adaptation period to FAA. The objective of this study was to evaluate the effects of different adaptation periods to diets containing FAA above requirements for growth on performance and immune response of weaned pigs subsequently challenged with ST. A total of 32 mixed-sex weanling pigs (11.6 ± 0.3 kg) were randomly assigned to 1 of 4 dietary treatments, being a basal amino acid (AA) profile fed throughout the experimental period (FAA-) or a functional AA profile (FAA+; Thr, Met, and Trp at 120% of requirements) fed only in the postinoculation (FAA+0), for 1 wk pre- and postinoculation (FAA+1), or throughout the experimental period (FAA+2). After a 14-d adaptation period, pigs were inoculated with ST (2.15 × 109 CFU/mL). Growth performance, body temperature, fecal score, acute-phase proteins, oxidant/antioxidant balance, score for ST shedding in feces and intestinal colonization, and fecal and digesta myeloperoxidase (MPO) were measured pre- and postinoculation. Postinoculation body temperature and fecal score, serum haptoglobin, plasma superoxide dismutase (SOD), malondialdehyde (MDA), and fecal MPO were increased while serum albumin and plasma reduced glutathione (GSH):oxidized glutathione (GSSG) were reduced compared to pre-inoculation (P < 0.05). Average daily gain and G:F were greater in FAA+2 pigs compared to FAA- pigs (P < 0.05). Serum albumin was higher in FAA+2 and FAA+1 compared to FAA+0 and FAA- pigs (P < 0.05) while FAA+2 pigs had lower haptoglobin compared to FAA- (P < 0.05). Plasma SOD was increased and GSH:GSSG was decreased in FAA- pigs compared to the other treatments (P < 0.05). Score for ST shedding in feces was progressively lower from d 1 to 6 regardless of treatment (P < 0.05) and was lower in FAA+2 pigs compared to FAA- and FAA+0 (P < 0.05). Counts of ST in colon digesta were higher in FAA- and FAA+0 pigs compared to FAA+2 (P < 0.05). Fecal and colonic digesta MPO were lower in FAA+2 and FAA+1 pigs compared to FAA- (P < 0.05). These results demonstrate a positive effect of a longer adaptation period to FAA-supplemented diets on performance and immune status of weaned pigs challenged with Salmonella.

Functional amino acid supplementation, regardless of dietary protein content, improves growth performance and immune status of weaned pigs challenged with Salmonella Typhimurium

High dietary protein may increase susceptibility of weaned pigs to enteric pathogens. Dietary supplementation with functional amino acids (FAA) may improve growth performance of pigs during disease challenge. The objective of this study was to evaluate the interactive effects of dietary protein content and FAA supplementation above requirements for growth on performance and immune response of weaned pigs challenged with Salmonella. Sixty-four mixed-sex weanling pigs (13.9 ± 0.82 kg) were randomly assigned to dietary treatments in a 2 × 2 factorial arrangement with low (LP) or high protein (HP) content and basal (AA-) or FAA profile (AA+; Thr, Met, and Trp at 120% of requirements) as factors. After a 7-d adaptation period, pigs were inoculated with either a sterile saline solution (CT) or saline solution containing Salmonella Typhimurium (ST; 3.3 × 109 CFU/mL). Growth performance, body temperature, fecal score, acute-phase proteins, oxidant/antioxidant balance, ST shedding score in feces and intestinal colonization, fecal and digesta myeloperoxidase (MPO), and plasma urea nitrogen (PUN) were measured pre- and postinoculation. There were no dietary effects on any measures pre-inoculation or post-CT inoculation (P > 0.05). Inoculation with ST increased body temperature and fecal score (P < 0.05), serum haptoglobin, plasma superoxide dismutase (SOD), malondialdehyde (MDA), PUN, and fecal MPO, and decreased serum albumin and plasma reduced glutathione (GSH):oxidized glutathione (GSSG) compared with CT pigs (P < 0.05). ST-inoculation reduced average daily gain (ADG) and feed intake (ADFI) vs. CT pigs (P < 0.05) but was increased by AA+ vs. AA- in ST pigs (P < 0.05). Serum albumin and GSH:GSSG were increased while haptoglobin and SOD were decreased in ST-inoculated pigs fed AA+ vs. AA- (P < 0.05). PUN was higher in HP vs. LP-fed pigs postinoculation (P < 0.05). Fecal ST score was increased in ST-inoculated pigs on days 1 and 2 postinoculation and declined by day 6 (P < 0.05) in all pigs while the overall score was reduced in AA+ vs. AA- pigs (P < 0.05). Cecal digesta ST score was higher in HP vs. LP-fed pigs and were lower in AA+ compared with AA- fed pigs in the colon (P < 0.05). Fecal and digesta MPO were reduced in ST pigs fed AA+ vs. AA- (P < 0.05). These results demonstrate a positive effect of FAA supplementation, with minimal effects of dietary protein, on performance and immune status in weaned pigs challenged with Salmonella.

Salmonella and Shiga Toxin-Producing Escherichia coli in Products Sampled in the Food Safety and Inspection Service Raw Pork Baseline Study

The Food Safety and Inspection Service (FSIS) conducts microbiological baseline studies to determine national prevalence of select foodborne pathogens in federally inspected meat and poultry products and to obtain data for risk assessments. The FSIS conducted a baseline study from 1 June 2017 through 31 May 2018 to characterize and determine the prevalence of Salmonella and assess the occurrence of Shiga toxin-producing Escherichia coli (STEC) in a variety of raw pork products. In total, 4,014 samples from slaughter and processing establishments were analyzed for Salmonella; a subset of these samples (1,395) from slaughter establishments were also analyzed for STEC. Analyses determined that the national prevalence of Salmonella in raw pork products was highest in comminuted products (28.9%), followed by intact cuts (5.3%) and nonintact cuts (3.9%). Less than 1% of samples analyzed were positive for the top seven STEC. Our findings indicate there is a need for additional pathogen reduction strategies for raw pork products.

Changes in the Hematological Variables in Pigs Supplemented With Yeast Cell Wall in Response to a Salmonella Challenge in Weaned Pigs

Stressors experienced by pigs at weaning may negatively impact health and productivity. Thus, supplements that enhance pig immunity during the early post-weaned period are of great interest to the swine industry. The objective of this experiment was to evaluate the performance and hematological responses of weaned pigs supplemented with yeast cell wall (YCW) when challenged orally with Salmonella Typhimurium. Weaned pigs were assigned to one of three treatments for 22d (n = 13/treatment): Control diet, which was a non-medicated starter diet (Control); Control diet supplemented with YCW at 250 mg/kg BW (YCW250; Phileo Lesaffre Animal Care, Milwaukee, Wisconsin, USA); and Control diet supplemented with YCW at 500 mg/kg BW (YCW500). On d19 blood samples were collected from -6 to 72 h relative to oral Salmonella Typhimurium (1 × 106 cfu/pig) challenge. Gain:feed was greater (P = 0.01) in YCW250 treatment compared to both Control and YCW500 pigs. Baseline intraperitoneal temperature was greater (P < 0.001) in YCW250 pigs than Control or YCW500 pigs. There was a treatment x time interaction for the change in intraperitoneal temperature (P < 0.01), post-challenge cortisol, white blood cell counts (WBC), neutrophils, and neutrophil:lymphocyte ratio (P ≤ 0.03). Control pigs had greater (P < 0.05) cortisol concentrations than both YCW-supplemented groups at 0 h, but Control pigs had reduced (P < 0.05) cortisol compared to YCW500 pigs at 24 and 30 h post-challenge. Control pigs had greater (P < 0.05) WBC counts than both YCW-supplemented groups 6 and 12 h post-challenge, and YCW250 pigs had reduced (P < 0.01) WBC counts than Control and YCW500 pigs 18 h post-challenge. Neutrophil counts were greater (P < 0.05) in Control pigs than both YCW-supplemented groups at 6 and 12 h post-challenge and were greater (P = 0.02) than YCW250 pigs at 18 h post-challenge. Lymphocytes were greater (P < 0.001) in Control and YCW500 pigs pre- and post-challenge compared to YCW250 pigs. Control pigs had the greatest (P < 0.001) monocyte counts compared to YCW treatments. There was no effect of yeast supplementation on fecal shedding or Salmonella counts in the rectum, colon or cecum (P ≥ 0.05). While some differences were observed in intraperitoneal temperature and some hematological variables, data suggests there were minimal effects of yeast supplementation on the acute immune response to Salmonella challenge.