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.

Food safety incidents in the red meat industry: A review of foodborne disease outbreaks linked to the consumption of red meat and its products, 1991 to 2021

Red meat is a significant source of human nutrition, and the red meat industry contributes to the economy of nations. Nonetheless, there is a widespread global concern about public health issues posed by severe food safety incidents within the red meat industry. Most of these incidents are associated with foodborne disease outbreaks that impact individual consumers, food businesses and society. This study adopts a systematic search and review approach to identify three decades of published investigation reports of global foodborne disease outbreaks linked with the consumption of red meat and products made from them. The review aims to evaluate the critical features of these outbreak incidents to get insight into their contributing factors and root causes. In particular, this review discusses the transmission setting (origin of pathogenic agents), the food vehicles mostly incriminated, the causative pathogens (bacteria, viruses, and parasites) causing the most illnesses, and the most commonly reported contributing factors to the outbreaks. This information can help researchers and food business operators (FBOs) inform future risk assessment studies and support risk management activities in developing risk-mitigating strategies for the industry. Findings from this study suggest that implementing food safety management strategies which include adequate control measures at all stages of the food chain, from farm to fork, is imperative in preventing outbreak incidents. Of equal importance is the need for enhanced and sustained public education about the risk of foodborne illnesses associated with meat and its products whilst discouraging the consumption of raw meat products, especially by high-risk groups.

Formulating Diets for Improved Health Status of Pigs: Current Knowledge and Perspectives

Our understanding of nutrition has been evolving to support both performance and immune status of pigs, particularly in disease-challenged animals which experience repartitioning of nutrients from growth towards the immune response. In this sense, it is critical to understand how stress may impact nutrient metabolism and the effects of nutritional interventions able to modulate organ (e.g., gastrointestinal tract) functionality and health. This will be pivotal in the development of effective diet formulation strategies in the context of improved animal performance and health. Therefore, this review will address qualitative and quantitative effects of immune system stimulation on voluntary feed intake and growth performance measurements in pigs. Due to the known repartitioning of nutrients, the effects of stimulating the immune system on nutrient requirements, stratified according to different challenge models, will be explored. Finally, different nutritional strategies (i.e., low protein, amino acid-supplemented diets; functional amino acid supplementation; dietary fiber level and source; diet complexity; organic acids; plant secondary metabolites) will be presented and discussed in the context of their possible role in enhancing the immune response and animal performance.

Reduction of Salmonella spp. populations in Italian salami during production process and high pressure processing treatment: Validation of processes to export to the U.S

This study involved ten enterprises producing Italian salami, 20 different samples of fermented sausages underwent challenge tests to assess and record the following parameters: time, temperature, pH, a_w, and Salmonella counts. A linear regression model was used to describe the Salmonella spp. decay: at the end of the process the result of total Salmonella reduction was 0.97-5.84 Log₁₀ CFU/g and it was significantly associated with pH at the end of acidification/drying process, a_w at the end of seasoning period, the duration of seasoning, and the caliber of salami respectively. High Pressure Processing (HPP) further reduced the Salmonella level by 2.41-5.84 Log₁₀ CFU/g with an efficacy that resulted inversely associated with a_w of salami at the end of seasoning; the objective of 5-Log reduction was always reached in all the cases tested by the production process plus HPP. This model could be a useful tool for enterprises and Authorities to evaluate the efficacy of the processes to reduce Salmonella load for exportation to the U.S.

Occurrence and traceability of Salmonella spp. in five Sardinian fermented sausage facilities

The aims of the present study were to evaluate the presence of Salmonella in five fermented sausage processing plants and their products during the production process, and to trace the possible sources of contamination. A total of 270 samples were collected: mixture of ground pork meat and fat, products at the end of acidification, sausages at the end of ripening and, during production stages, surfaces in contact with meat and surfaces not in contact with meat. For samples of ground meat, product at the end of acidification and sausages at the end of ripening, the pH and water activity (aw), were determined. All the samples were tested for the presence of Salmonella. Thirtytwo Salmonella isolates were obtained, subjected to serotyping and PFGE. The sausages at the end of ripening pH and aw mean values were 5.39±0.24 and 0.91±0.03, respectively. Salmonella was detected in three processing plants with an overall prevalence of 16.7% in food samples and 5.8% in environmental samples. Salmonella prevalence was 24% in ground meat and products at the end of acidification and was also detected in a sample of sausage at the end of ripening (2%). In environmental samples, Salmonella was detected in 6.6% of surfaces in contact with meat and 5% of surfaces not in contact with meat. Five serotypes were identified among 32 isolates: S. Derby (37.5%), S. Typhimurium and S. Rissen (both 25%), S. Give and monophasic S. Typhimurium (both 6.25%). Six different pulsotypes were obtained with PFGE. The serotypes and the PFGE pattern of the strains were specific for each facility with no overlapping between different processing plants. The same observation can be pointed out considering different sampling days for the same processing plants, thus presumably indicating the raw material (ground pork meat and fat) as the source of contamination. The detection of Salmonella in a sample of sausage at the end of ripening highlights the ability of the pathogen to survive during manufacturing process.

Non-typhoidal Salmonella in the Pig Production Chain: A Comprehensive Analysis of Its Impact on Human Health

Salmonellosis remains one of the most frequent foodborne zoonosis, constituting a worldwide major public health concern. The most frequent sources of human infections are food products of animal origin, being pork meat one of the most relevant. Currently, particular pig food production well-adapted and persistent Salmonella enterica serotypes (e.g., Salmonella Typhimurium, Salmonella 1,4,[5],12:i:-, Salmonella Derby and Salmonella Rissen) are frequently reported associated with human infections in diverse industrialized countries. The dissemination of those clinically-relevant Salmonella serotypes/clones has been related to the intensification of pig production chain and to an increase in the international trade of pigs and pork meat. Those changes that occurred over the years along the food chain may act as food chain drivers leading to new problems and challenges, compromising the successful control of Salmonella. Among those, the emergence of antibiotic resistance in non-typhoidal Salmonella associated with antimicrobials use in the pig production chain is of special concern for public health. The transmission of pig-related multidrug-resistant Salmonella serotypes, clones and/or genetic elements carrying clinically-relevant antibiotic resistance genes, frequently associated with metal tolerance genes, from pigs and pork meat to humans, has been reported and highlights the contribution of different drivers to the antibiotic resistance burden. Gathered data strengthen the need for global mandatory interventions and strategies for effective Salmonella control and surveillance across the pig production chain. The purpose of this review was to provide an overview of the role of pig and pork meat in human salmonellosis at a global scale, highlighting the main factors contributing to the persistence and dissemination of clinically-relevant pig-related Salmonella serotypes and clones.

Occurrence of Salmonella in Ready-to-Eat Meat and Poultry Product Samples from U.S. Department of Agriculture-Regulated Producing Establishments. I. Results from the ALLRTE and RTE001 Random and Risk-Based Sampling Projects, from 2005 to 2012

Ready-to-eat (RTE) meat and poultry product samples collected from RTE-producing establishments for the ALLRTE (random) and RTE001 (risk-based) sampling projects of the Food Safety and Inspection Service (FSIS) were tested for both Salmonella and Listeria monocytogenes. The FSIS analyzed Salmonella results for RTE meat and poultry product samples collected for the two sampling projects from 2005 to 2012. Data for 24,385 ALLRTE samples collected from 3,023 establishments and 66,653 RTE001 samples collected from 2,784 establishments were evaluated for the percentages of Salmonella-positive samples, product types of positive samples, and Salmonella serotypes. There also were descriptive summaries with respect to establishment hazard analysis and critical control point (HACCP) size, production volumes, L. monocytogenes control alternatives, geographic location, and season or month of sample collection. Results showed low occurrences of Salmonella-positive samples from the ALLRTE and RTE001 sampling projects, with 14 positive samples (0.06%) for ALLRTE and 33 positive samples (0.05%) for RTE001. Percentages of establishments with at least one Salmonella-positive sample averaged 0.46% for ALLRTE and 1.11% for RTE001. Three product types-sausage products, pork barbecue, and head cheese-accounted for 62% of all positive samples. There were 27 distinct serotypes from 48 Salmonella isolates, with serotypes Infantis and Typhimurium being the most common (5 isolates each). All but one of the Salmonella-positive samples were obtained from establishments with HACCP sizes of small or very small. More than half of the positive samples were obtained from establishments using L. monocytogenes control alternative 3 (sanitation only, highest-risk category). Positive Salmonella samples were found in all geographic regions at all times of the year. Information obtained from these sampling projects is relevant to the prevention of foodborne Salmonella illnesses from RTE meat and poultry products.

Sodium Chloride Does Not Ensure Microbiological Safety of Foods: Cases and Solutions

Addition of salt or salt-containing water to food is one of the oldest and most effective preservation methods in history; indeed, salt-cured foods are generally recognized as microbiologically safe due to their high salinity. However, a number of microbiological risks remain. The microbiological hazards and risks associated with salt-cured foods must be addressed more in-depth as they are likely to be underestimated by previous studies. This review examined a number of scientific reports and articles about the microbiological safety of salt-cured foods, which included salted, brined, pickled, and/or marinated vegetables, meat, and seafood. The following subjects are covered in order: (1) clinical cases and outbreaks attributed to salt-cured foods; (2) the prevalence of foodborne pathogens in such foods; (3) the molecular, physiological, and virulent responses of the pathogens to the presence of NaCl in both laboratory media and food matrices; (4) the survival and fate of microorganisms in salt-cured foods (in the presence/absence of additional processes); and (5) the interaction between NaCl and other stressors in food processes (e.g., acidification, antimicrobials, drying, and heating). The review provides a comprehensive overview of potentially hazardous pathogens associated with salt-cured foods and suggests further research into effective intervention techniques that will reduce their levels in the food chain.

Foodborne Salmonellosis in Italy: Characterization of Salmonella enterica Serovar Typhimurium and Monophasic Variant 4,[5],12:i- Isolated from Salami and Human Patients

Salmonella enterica serovar Typhimurium (STm) and its monophasic variant 4,[5],12:i:- (VMSTm) have been responsible for an increased number of foodborne infections in humans in Europe in recent years. The aim of this study was to investigate the origin of three foodborne salmonellosis outbreaks that occurred in Pavia Province (Lombardy region, northern Italy) in 2010. Phenotypic and genetic characteristics of the STm and VMSTm isolates from patients and from food that were recovered in the framework of the three outbreaks were evaluated through serotyping, phage typing, antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE), and multiple-locus variable-number tandem repeat analysis (MLVA). Salami from three artisan producers, which had all purchased meat from the same slaughterhouse, was the food source of infection in outbreak I. STm isolates were recovered from salami and patients with symptoms of gastroenteritis. These isolates had the same PFGE type and the same rare MLVA profile (3-18-9-NA-211). The same molecular profiles were found in an STm isolate from a salami, which likely was the source of another family outbreak (II). A VMSTm strain with common phenotypic and molecular profiles was isolated from three hospitalized patients and identified as the cause of another putative outbreak (III). During the following 3 years (2011 through 2013), 360 salami produced in Pavia Province were monitored for the presence of S. enterica . In 2011, no STm and VMSTm isolates were recovered from 159 salami tested. During 2012 and 2013, 13.9% of 201 tested salami harbored S. enterica , and half of the isolates were VMSTm, mainly in salami from those artisan producers involved in the previous outbreaks. These isolates were genetically variable, especially in terms of MLVA profiles. The data collected suggest that from 2012, VMSTm has replaced STm in the environments of the salami producers monitored in this study, and these data confirm the dominance of this emergent serovar along the pork supply chain.

A QMRA Model for Salmonella in Pork Products During Preparation and Consumption

As part of a quantitative microbiological risk assessment (QMRA) food chain model, this article describes a model for the consumer phase for Salmonella-contaminated pork products. Three pork products were chosen as a proxy for the entire pork product spectrum: pork cuts, minced meat patties, and fermented sausages. For pork cuts cross-contamination is considered the most important process and therefore it is modeled in detail. For minced meat, both cross-contamination and undercooking are the relevant processes. For those commodities bacterial growth during transport and storage is also modeled. Fermented sausages are eaten raw and the production may be defective. Variability between consumers' behavior and the impact of variability between production processes at the farm and abattoir are taken into account. Results indicate that Salmonella levels on products may increase significantly during transport and storage. Heating is very efficient at lowering concentrations, yet cross-contamination plays an important role in products that remain contaminated. For fermented sausage it is found that drying is important for Salmonella reduction. Sensitivity analysis revealed that cross- contamination factors "knife cleaning" and "preparation of a salad" are important parameters for pork cuts. For minced meat cleaning of the board, salad consumption, refrigerator temperature, and storage time were significant.

Prevalence of Salmonella in raw animal products in Ethiopia: a meta-analysis

BACKGROUND

The contributions of animal products to human salmonellosis differ across countries, and source attribution is a major step in prioritizing control measures. The objectives of this study were to estimate the prevalence of Salmonella in raw animal products in Ethiopia by using meta-analytical methods.

RESULTS

The odds of Salmonella contaminated meat was more than twice higher in markets than in slaughter houses [Odds ratio (OR) = 2.25 (95% Confidence Interval [CI] = 1.75, 2.89)]. The source species significantly affected meat contamination in slaughter houses (P < 0.05) but not in the markets (P > 0.05). The pooled estimates of Salmonella contaminated goat carcasses, beef carcasses, minced beef and milk were 3.86%, 4.53%, 8.34% and 10.76% respectively.

CONCLUSIONS

The estimates demonstrate the extent of contamination, and imply the need for safety intervention measures to reduce the risks of contamination of animal products and human illnesses.

DIVERSITY OF ANTIMICROBIAL RESISTANCE MECHANISMS IN SALMONELLA

Abstract. Current review presents information on the antimicrobial resistance of Salmonella of various serotypes. The phenotypes of resistance and the main resistance mechanisms to the antimicrobials of various groups are described. Comparison data on the resistance to antimicrobials of Salmonella serological variants, which circulate worldwide including the Russian Federation (S. Typhimurium DT104, S. Newport, S. Virchow, S. Enteritidis) are shown. Moreover, epidemiological characteristics of transmission factors related to these pathogens are discussed. Special attention is given to genetic determinants, which encode the resistance of Enterobacteriaceae, as well as mobile genetic elements (integrons, plasmids, pathogenicity islands), which are involved in the spread of resistance.

Distribution of Salmonella enterica isolates from human cases in Italy, 1980 to 2011

We describe trends of Salmonella enterica serovars isolated from humans in Italy from January 1980 to December 2011. A total of 229,279 Salmonella isolates were reported during this period. Serovars Enteritidis, Typhimurium, Infantis, Derby, 4,[5],12,:i:-, and Napoli accounted for 135,783 (59%) of these isolates. Temporal trends from 2000 to 2011 varied by serovar: Enteritidis and Infantis decreased significantly (with a mean of -3.0% and -2.8% isolates per year, respectively, p<0.001); Typhimurium remained stable; while 4,[5],12:i:-, Derby and Napoli increased significantly (+66.4%, p<0.001; +8.1%, p<0.001; and +28.2%, p<0.05, respectively). Since 2000, Enteritidis fell consistently below Typhimurium, which is the most reported serovar in Italy in contrast to the international situation where Enteritidis still ranks at the top despite its significant decrease. Most serovars showed a marked seasonality, increasing over the summer months and peaking in August/September. Typhimurium, 4,[5],12:i:-, and Napoli were most likely to be isolated from children, whereas Enteritidis, Derby, and Infantis from adults. We conclude that the applied control measures are not equally efficient against the considered Salmonella serovars and that sources of infection other than those of Enteritidis (laying hens and eggs) have become increasingly important. Further investigations on the emerging serovars and on the causes related to their emergence are needed to define and implement newly tailored control measures.

Nationwide outbreak of Salmonella Montevideo infections associated with contaminated imported black and red pepper: warehouse membership cards provide critical clues to identify the source

In November 2009, we initiated a multistate investigation of Salmonella Montevideo infections with pulsed-field gel electrophoresis pattern JIXX01.0011. We identified 272 cases in 44 states with illness onset dates ranging from 1 July 2009 to 14 April 2010. To help generate hypotheses, warehouse store membership card information was collected to identify products consumed by cases. These records identified 19 ill persons who purchased company A salami products before onset of illness. A case-control study was conducted. Ready-to-eat salami consumption was significantly associated with illness (matched odds ratio 8·5, 95% confidence interval 2·1–75·9). The outbreak strain was isolated from company A salami products from an environmental sample from one manufacturing plant, and sealed containers of black and red pepper at the facility. This outbreak illustrates the importance of using membership card information to assist in identifying suspect vehicles, the potential for spices to contaminate ready-to-eat products, and preventing raw ingredient contamination of these products.

Salmonella serovars and antimicrobial resistance patterns on a sample of high seroprevalence pig farms in England and Wales (2003-2008)

Following the introduction of a national abattoir-based monitoring programme for Salmonella in pigs, advisory visits were made to pig farms in England and Wales with high Salmonella seroprevalence assessed by muscle tissue fluid (meat juice) ELISA. Samples (n = 15 790), including pooled pen floor faeces (n = 12 136), were collected for Salmonella culture from 296 farms, between October 2003 and February 2008. Salmonella was isolated from 4489 (28%) of all samples collected, including 3301 (27%) of pooled pen floor faecal samples, from 270 (91%) of farms visited. Salmonella Typhimurium and S. Derby were the most prevalent serovars, representing 64% and 16% of isolates serotyped, respectively. The main phage types of S. Typhimurium identified were U288 and DT193. Antimicrobial resistance (AMR) was seen in 92% of isolates tested, with the highest frequencies of resistance occurring to tetracyclines (T), sulphonamide compounds (SU), ampicillin (AM), sulphamethoxazole/trimethoprim (SXT), streptomycin (S) and chloramphenicol (C). Fifty-nine AMR patterns were observed, the most frequent of these being T, AM, SXT, C, S, SU, seen in 35% of isolates tested. Multi-drug resistance was commonly found, with 67% of isolates submitted for AMR testing showing resistance to between four and nine antimicrobials.

Tracking the Salmonella status of pigs and pork from lairage through the slaughter process in the Republic of Ireland

Salmonella Typhimurium is the predominant serotype isolated from humans in Europe. Pork and pork products are recognized vehicles of Salmonella and are responsible for outbreaks of human salmonellosis. Pigs can become infected with Salmonella on the breeding or fattening farm and during transport, lairage, and slaughter. The aim of this study was to investigate selected points of Salmonella contamination from the time pigs entered the lairage to the time the carcass was processed in the boning hall and to determine the importance of different sources of Salmonella along the Irish pork production chain. A second objective was to evaluate whether the serological status or category of a herd influenced the levels of bacteriological contamination detected on individual carcasses and pork cuts during slaughter and dressing operations. All samples were tested for the presence and numbers of Salmonella. Enterobacteriaceae numbers were also determined. Serotype, phage type, and pulsed-field gel electrophoresis were utilized to determine similarity among Salmonella isolates. Lairage was a major source of cross-contamination with Salmonella as were the hands of evisceration operatives, conveyor belts, and equipment in the boning hall. Cross-contamination within the slaughter plant environment accounted for up to 69 % of Salmonella carcass contamination. In general, herd category reflected the bacteriological status of carcasses and pork cuts. Major findings were a strong association (P < 0.01) between Enterobacteriaceae counts and Salmonella occurrence on prechill carcasses and a significant association (P < 0.05) between Enterobacteriaceae counts and Salmonella occurrence on pork cut samples.

Multiple-locus variable-number tandem-repeat analysis for discriminating within Salmonella enterica serovar Typhimurium definitive types and investigation of outbreaks

The discriminatory power of multiple-locus variable-number tandem-repeat analysis (MLVA) needs to be evaluated for all Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) phage types so that the power of this methodology is understood and results can be interpreted correctly during outbreak investigations. We evaluated the ability of MLVA to characterize four definitive phage types (DT) problematic in New Zealand. MLVA discriminated between DT104 isolates although there was very limited variation in the MLVA profiles for isolates with an RDNC phage type (reacts but does not conform to a recognized Typhimurium phage pattern) first observed in New Zealand's Enteric Reference Laboratory in May 2006. Most DT101 isolates had indistinguishable MLVA profiles or profiles that differed at one or two loci. This was also observed in DT160 isolates. MLVA may not identify all common-source outbreaks although it provided valuable data when applied to case isolates from two S. Typhimurium outbreaks.

The microbiological safety of ready-to-eat specialty meats from markets and specialty food shops: a UK wide study with a focus on Salmonella and Listeria monocytogenes

From 2359 specialty meats (continental sausages, cured/fermented, dried meats) sampled from markets and specialty food shops, 98.9% of samples were of satisfactory or acceptable microbiological quality. However, 16 (0.7%) were unsatisfactory as a result of Escherichia coli, Staphylococcus aureus or Listeria spp. contamination (>or=10(2) CFU/g), and nine (0.4%) were unacceptable due to presence of Salmonella spp. or Listeria monocytogenes (>10(2) CFU/g). Meats with unacceptable levels of L. monocytogenes were within shelf life (range: 8-143 days remaining). Nine different subtypes of L. monocytogenes were detected with sero/AFLP type 1/2c VII predominating (37%), although this subtype was not overrepresented in any particular meat type (P > 0.05). Ninety-six percent of continental sausages and cured/fermented products were stored at <8 degrees C at premises, including seven of the nine unacceptable samples. These nine meats were all pre-packed prior to supply to retail premises (OR = 0.1 P = 0.003) indicating that contamination with bacterial pathogens occurred earlier in the production chain. Most samples (72.7%, 8/11) with unsatisfactory levels of E. coli were sliced on request, suggesting cross-contamination at point of sale. This study highlights the importance of ensuring that products do not become contaminated before final packaging, that storage conditions are controlled, and that durability dates are an accurate indication of the shelf life of the product so as to minimise the potential for L. monocytogenes to be present at levels hazardous to health at the point of sale.