Salmonellosis In The United States Research Articles

Enterobacter aerogenes B199A May Be an Effective Surrogate for Quantifying Transfer of Salmonella Newport 96E01152C-TX from Cucumber Peel to Edible Flesh and Peeler during Peeling

Fresh cucumbers have been linked to multistate outbreaks of salmonellosis in the United States. Cutting, slicing, shredding, or peeling can transfer pathogens from the surface of fresh produce to the edible flesh portion through tools or hands. Different nonpathogenic surrogates have been used in various intervention studies to predict Salmonella behavior. Little is known about the degree to which pathogens or their surrogates can transfer from the surface of fresh produce to edible flesh during peeling. This study quantifies the transfer of Salmonella Newport from the surface of cucumber to the edible flesh portion or peeler during peeling and evaluates Enterobacter aerogenes B199A, as well as native mesophilic microbiota, as surrogates for Salmonella transfer. Cucumbers were dip inoculated with Salmonella Newport or E. aerogenes at 7 log CFU per cucumber. Half of each inoculated cucumber was hand peeled by using a sterilized peeler, resulting in four separate samples (unpeeled half, edible flesh half, removed peel, and used peeler) to quantify bacterial transfer. Most (>95%) of inoculated E. aerogenes, Salmonella, or native mesophilic microbiota generally remained associated with the peel during peeling. E. aerogenes transfer to cucumber flesh ranged from 0.02 to 12.9%, while transfer to the peeler ranged from 0.01 to 6.6%. Salmonella to cucumber flesh ranged from 0 to 0.6%, while transfer to the peeler ranged from 0 to 2.2%. Native microflora transfer to cucumber flesh ranged from 0.02 to 3.7%, while transfer to the peeler ranged from 0.04 to 3.7%. The log percent transfer of E. aerogenes at 24 h, as well as several shorter times, was not significantly different (P > 0.05) from that of Salmonella transferred to the edible flesh portion or peeler during peeling. E. aerogenes B199A may be a useful surrogate for Salmonella in cross-contamination studies and may help guide future risk management efforts to reduce pathogen risk associated with fresh cucumbers.

Efficacy of pectin-based caproic acid, caprylic acid, linalool, and cuminaldehyde coatings in reducing Salmonella Heidelberg on chicken eggs

Among the animal derived food products, contamination of poultry eggs, and egg shell surface is one of the major causes for foodborne salmonellosis in the United States. As a means of reducing the pathogen transfer to the internal egg contents, polysaccharide-based coatings containing antimicrobial phytochemicals could potentially serve as a biocontrol strategy for shelled egg products. The current study investigated the efficacy of four GRAS (Generally Recognized as Safe)-status plant-derived compounds, namely, caproic acid (CAO), caprylic acid (CAY), linalool (LIN) and cuminaldehyde (CUM), as pectin-based coating treatments, individually or in combination, for reducing Salmonella Heidelberg (SH) on shell eggs. A three-strain mixture of SH (~8.0 log CFU in 50 μL inoculum) was spot-inoculated on surface sterilized white-shelled eggs. Eggs were evenly coated with either pectin-based treatments of CAO (1%), CAY (1%), LIN (1%) and CUM (1%), individually, or a combination of 4 phytochemicals (COMB- each phytochemical at 0.5% v/v level of inclusion). The treated eggs were stored at 4°C and SH counts were enumerated on days 0, 1, 3, 5, 7, 14, and 21 of storage. The study was replicated thrice, 3 eggs/treatment/day time point, and the data were analyzed using two-way ANOVA with significance tested at p < 0.05. On day 0, pectin-coated control eggs had ~7.6 log CFU of SH/egg. At the end of refrigerated storage (day 21), pectin-based coating of CAO and CAY at 1% level reduced SH by 2.0–2.5 log CFU/egg (P < 0.05) when compared to controls. In addition, the CUM and LIN based coatings produced 3.0 log and 3.9 log reduction, respectively, in SH counts on eggs by day 21 of storage. Among the treatments with phytochemical combinations, COMB1 [pectin (2%) + Caprylic acid, caproic acid and cuminaldehyde (each at 0.5% level)] was found to be most effective, reducing SH counts to 2.5–3.3 log CFU/egg from day 0 through day 14, and by the end of storage period (day 21), a 3.5 log CFU reduction/egg (p < 0.05) compared to untreated controls. Morphological studies of treated eggs using atomic force microscopy (AFM) have shown that the roughness of eggs can be influenced by a combination of various compounds. Results indicate the potential efficacy of the aforesaid phytochemicals in reducing SH on shell eggs; however, further studies investigating their industrial feasibility and effects on sensory attributes of eggs are warranted.

Effect of Feeding a Postbiotic Derived from Saccharomyces cerevisiae Fermentation as a Preharvest Food Safety Hurdle for Reducing Salmonella Enteritidis in the Ceca of Layer Pullets

Salmonella Enteritidis is responsible for a significant proportion of foodborne salmonellosis in the United States and continues to be attributable to table eggs despite increased federal oversight. Technologies, including feed additives, continue to be evaluated for preharvest application and their potential food safety benefits. Diamond V Original XPC, a Saccharomyces cerevisiae fermentation-based postbiotic (SCFP), was evaluated for its effectiveness in reducing Salmonella Enteritidis (SE) colonization in young layer pullets. A total of 40 day-old Hy-Line W-36 layer pullets were equally divided and randomly assigned to one of two dietary treatments, with SCFP or without SCFP (PCON), and orally gavaged on day 28 with SE at 106 CFU/mL. Another 20 day-old pullets were fed the same control feed without SCFP and blank inoculated on day 28 with 1 mL of sterile phosphate-buffered saline to serve as a negative control. Qualitative and quantitative analyses of cecal contents for Salmonella were performed for all birds on day 32. The prevalence of SE in the ceca of all directly challenged birds was 100%; however, the SE concentration in birds fed SCFP diet (3.35 log CFU/g) was significantly lower (P < 0.0001) than that of the PCON birds not fed SCFP (4.49 log CFU/g). The proportion of birds with enumerable SE concentrations was lower in SCFP-fed pullets (57.9%) than in the PCON pullets (95.0%). These data suggest that inclusion of SCFP in the diet may aid in the reduction of SE within the ceca of commercial laying hens and could serve as an additional preharvest food safety hurdle.

Quantitative transfer and sanitizer inactivation of Salmonella during simulated commercial dicing and conveying of tomatoes

Diced tomatoes have been linked to outbreaks of salmonellosis in the United States. Compared to slicing, commercial production of diced tomatoes is more complex and includes mechanical dicing as well as washing, dewatering, conveying, and packing. Consequently, this study aimed to 1) quantify Salmonella transfer during pilot-scale dicing of tomatoes, 2) assess the efficacy of three sanitizer treatments against Salmonella during flume tank washing, and 3) assess the efficacy of four sanitizers against Salmonella during conveyance of diced tomatoes. One 0.9 kg batch of Salmonella Typhimurium LT2-inoculated Roma tomatoes (∼5 log CFU/g) was mechanically diced, followed by ten batches of uninoculated tomatoes. All uninoculated tomatoes yielded Salmonella with populations decreasing from 3.3 to 1.1 log CFU/g during dicing. Flume tank washing in sanitizer-free water or water containing 80 ppm of peroxyacetic acid, mixed peracid, or total chlorine decreased Salmonella populations in diced tomatoes 1.3 ± 0.2, 2.3 ± 0.4, 2.35 ± 0.4, and 2.4 ± 0.1 log CFU/g, respectively. After processing, Salmonella populations in flume water containing a sanitizer were always below the limit of detection (−1.0 log CFU/ml) and were significantly lower (P ≤ 0.05) than for the sanitizer-free control (1.5 ± 0.3 log CFU/ml). When the same three sanitizer treatments as well as electrolyzed water (80 ppm chlorine) were applied to smooth and interlocking belts on a dual track conveyor, Salmonella reductions were greater using mixed peracid (6.49 and 6.76 log) and peroxyacetic acid (5.95 and 6.10 log) as compared to chlorine (3.72 and 5.70 log) and electrolyzed water (3.50 and 4.53 log), respectively. All four sanitizer treatments were more effective than water alone in reducing Salmonella on conveyor belt surfaces. These findings should help provide some practical guidelines for the industry and aide in the development of improved risk assessments.

Multidrug-Resistant Salmonella enterica Subspecies I Serovar 4,[5],12:i:- Isolates Recovered from Food Safety and Inspection Service-Regulated Products and Food Animal Ceca, 2007-2016.

Salmonella enterica subspecies I serovar 4,[5],12:i:- (Salmonella I 4,[5],12:i:-) is among the five most common serovars associated with human salmonellosis in the United States. In 2010, human infections with Salmonella I 4,[5],12:i:- which exhibited resistance to ampicillin, streptomycin, sulfonamides, and tetracycline (ASSuT) emerged as a public health concern. Outbreak investigations identified live animal settings, meat and poultry, and pets as confirmed and suspect sources of infection. To shed further light on possible sources of ASSuT-resistant Salmonella I 4,[5],12:i:- infections, we described isolates recovered from meat and poultry products regulated by the Food Safety and Inspection Service (FSIS) and from food animal ceca collected at FSIS-regulated slaughter establishments during 2007-2016. During the time period of interest, ASSuT-resistant Salmonella I 4,[5],12:i:- was found at low levels in multiple FSIS product classes including swine, turkey, cattle and chicken, which suggests this pathogen has a relatively wide host range. Monitoring trends in the various FSIS production classes over time and developing commodity profiles may help focus preventative strategies.

Interventions Targeting Deep Tissue Lymph Nodes May Not Effectively Reduce the Risk of Salmonellosis from Ground Pork Consumption: A Quantitative Microbial Risk Assessment.

The inclusion of deep tissue lymph nodes (DTLNs) or nonvisceral lymph nodes contaminated with Salmonella in wholesale fresh ground pork (WFGP) production may pose risks to public health. To assess the relative contribution of DTLNs to human salmonellosis occurrence associated with ground pork consumption and to investigate potential critical control points in the slaughter-to-table continuum for the control of human salmonellosis in the United States, a quantitative microbial risk assessment (QMRA) model was established. The model predicted an average of 45 cases of salmonellosis (95% CI = [19, 71]) per 100,000 Americans annually due to WFGP consumption. Sensitivity analysis of all stochastic input variables showed that cooking temperature was the most influential parameter for reducing salmonellosis cases associated with WFGP meals, followed by storage temperature and Salmonella concentration on contaminated carcass surface before fabrication. The input variables were grouped to represent three main factors along the slaughter-to-table chain influencing Salmonella doses ingested via WFGP meals: DTLN-related factors, factors at processing other than DTLNs, and consumer-related factors. The evaluation of the impact of each group of factors by second-order Monte Carlo simulation showed that DTLN-related factors had the lowest impact on the risk estimate among the three groups of factors. These findings indicate that interventions to reduce Salmonella contamination in DTLNs or to remove DTLNs from WFGP products may be less critical for reducing human infections attributable to ground pork than improving consumers' cooking habits or interventions of carcass decontamination at processing.

A Quantitative Assessment of the Risk of Human Salmonellosis Arising from the Consumption of Pecans in the United States

A quantitative risk assessment was conducted to assess the risk of human salmonellosis acquired from consumption of pecans in the United States. The model considered the potential for Salmonella survival, growth, and recontamination of pecans from the sheller to the consumer, including steps such as immersion in water, drying, conditioning, cracking, partitioning, and storage. Five theoretical microbial reduction treatment levels (1 to 5 log CFU) were modeled. Data from the 2010 to 2013 surveys by the National Pecan Shellers Association were used for initial prevalence and contamination levels. The impacts of atypical situations in the pecan production system were also evaluated. Higher initial contamination levels, recontamination during processing, and a delay in drying postconditioning were the modeled atypical situations. The baseline model predicted a mean risk of salmonellosis in the United States from consumption of in-shell and shelled pecans processed by cold conditioning with no microbial reduction treatment and no further home cooking as 1 case per 775,193 servings (95% confidence interval [CI]: 1 case per 1,915,709 to 178,253 servings). This predicted risk per serving was estimated as a mean of 529 cases of salmonellosis per year (95% CI: 213 to 2,295 cases). Hot conditioning for shelled pecans and microbial reduction treatment of both shelled and in-shell pecans had a significant impact on the predicted mean risk of illness. Assuming 77% of the shelled pecans sold at retail (i.e., 80% of the retail supply) received hot conditioning, the mean estimated salmonellosis cases per year from consumption of in-shell and shelled pecans uncooked at home was 203 (95% CI: 81 to 882 cases) if no additional microbial reduction treatment were applied. The predicted risk of illness per serving was higher for all atypical situations modeled compared with the baseline model, and delay in drying had the greatest impact on risk.

Complete Genome Sequences of Three Salmonella enterica subsp. enterica Serovar Saintpaul Isolates Associated with a 2013 Multistate Outbreak in the United States.

ABSTRACTIn 2013, a multistate outbreak of Salmonella enterica subsp. enterica serovar Saintpaul from cucumber caused 84 cases of salmonellosis in the United States. In this announcement, we report the complete genome sequences of three clinical Salmonella Saintpaul isolates associated with the 2013 outbreak.

Salmonella Enterica Serovar Pomona Infection in Farmed Juvenile American Alligators ( Alligator Mississippiensis).

A fatal epizootic of salmonellosis occurred in farmed juvenile American alligators in Louisiana. Six animals were examined. Gross lesions included severe fibrinonecrotizing enterocolitis, necrotizing splenitis, coelomic effusion, and perivisceral and pulmonary edema. Microscopic examination revealed severe necrotizing enterocolitis and splenitis with intralesional bacteria and pneumocyte necrosis with fibrin thrombi. Salmonella enterica serovar Pomona was isolated from intestine and lung. Clinical salmonellosis is a rare finding in reptiles and salmonellosis caused by S. Pomona is not previously reported in American alligators. Since S. Pomona is a commonly isolated Salmonella serotype from patients with reptile-associated salmonellosis in the United States, and since alligator meat is consumed and the skin is exported to numerous countries, risk of human and animal infection should be considered.

Quantitative transfer of Salmonella Typhimurium LT2 during mechanical slicing of tomatoes as impacted by multiple processing variables

Slicing of fresh produce can readily lead to pathogen cross-contamination with pre-sliced tomatoes having been linked to multistate outbreaks of salmonellosis in the United States. This study aimed to assess the impact of multiple processing variables on quantitative transfer of Salmonella during simulated commercial slicing of tomatoes. One red round tomato was inoculated with Salmonella Typhimurium LT2 at ~5logCFU/g and sliced using a manual or electric slicer, followed by 20 uninoculated tomatoes. Thereafter, the distribution of Salmonella on inoculated and uninoculated tomato slices was evaluated along with the transfer of Salmonella from different parts of the slicer. The impact of multiple processing variables including post-contamination hold time (0 and 30min), tomato wetness (dry and wet), processing room temperature (23, 10 and 4°C), slice thickness (0.48, 0.64, and 0.95cm), tomato variety (Torero, Rebelski, and Bigdena) and pre-wash treatment (no wash, tap water, and chlorine) was also investigated. The data were fitted to a two-parameter exponential decay model (Y=A⋅exp(BX)) with the percentage of Salmonella transferred to 20 uninoculated tomatoes then calculated. Salmonella populations on nine inoculated tomato slices ranged from 4.6±0.2 to 5.5±0.3logCFU/g, with higher populations on slices from the blossom and stem scar ends. However, Salmonella transfer to the previously uninoculated slices was similar (P>0.05), ranging from 2.1±0.2 to 3.4±0.2logCFU/g. Significantly fewer salmonellae transferred from the blade (3.4±0.4 log CFU, P≤0.05) than from the back and bottom plates (4.7±0.3 log CFU) or the whole manual slicer (5.2±0.2 log CFU) to the 20 uninoculated tomatoes. However, the blade was the primary contributor to Salmonella transfer for the electric slicer. Post-contamination hold time, processing temperature and tomato slice thickness did not significantly impact (P>0.05) the Salmonella transfer rate (parameter B) or the overall percentage of cells transferred. A significantly lower (P≤0.05) transfer rate (−0.028±0.002) was observed for wet as compared to dry tomatoes (−0.051±0.002), with a significantly higher (P≤0.05) percentage (12.2±2.4%) of Salmonella transferred to wet as opposed to dry tomatoes (1.1±0.5%). Tomato variety also impacted Salmonella transfer with significantly lower (P≤0.05) transfer rates and Salmonella transfer percentages seen for Rebelski and Bigdena than Torero. These findings will provide practical guidelines for the fresh-cut tomato industry and will also be useful in developing science-based transfer models for risk assessments.

Salmonella enterica Infections in the United States and Assessment of Coefficients of Variation: A Novel Approach to Identify Epidemiologic Characteristics of Individual Serotypes, 1996-2011.

BackgroundDespite control efforts, salmonellosis continues to cause an estimated 1.2 million infections in the United States (US) annually. We describe the incidence of salmonellosis in the US and introduce a novel approach to examine the epidemiologic similarities and differences of individual serotypes.MethodsCases of salmonellosis in humans reported to the laboratory-based National Salmonella Surveillance System during 1996–2011 from US states were included. Coefficients of variation were used to describe distribution of incidence rates of common Salmonella serotypes by geographic region, age group and sex of patient, and month of sample isolation.ResultsDuring 1996–2011, more than 600,000 Salmonella isolates from humans were reported, with an average annual incidence of 13.1 cases/100,000 persons. The annual reported rate of Salmonella infections did not decrease during the study period. The top five most commonly reported serotypes, Typhimurium, Enteritidis, Newport, Heidelberg, and Javiana, accounted for 62% of fully serotyped isolates. Coefficients of variation showed the most geographically concentrated serotypes were often clustered in Gulf Coast states and were also more frequently found to be increasing in incidence. Serotypes clustered in particular months, age groups, and sex were also identified and described.ConclusionsAlthough overall incidence rates of Salmonella did not change over time, trends and epidemiological factors differed remarkably by serotype. A better understanding of Salmonella, facilitated by this comprehensive description of overall trends and unique characteristics of individual serotypes, will assist in responding to this disease and in planning and implementing prevention activities.

Influence of Growth Temperatures of S almonella and Storage Temperatures of Alfalfa Seeds on Heat Inactivation of the Pathogen during Heat Treatment

Sprouts have been implicated in several outbreaks of salmonellosis in the United States, where the seeds are thought to be the primary source of contamination. The objectives of this study were to investigate the influence of growth temperatures of Salmonella and storage temperatures of alfalfa seeds on heat inactivation of the pathogen on seeds. Alfalfa seeds were inoculated with a composite of Salmonella, grown at temperatures of 15, 25, 35 or 40C, stored at 22C for 7 days, dry heated at 65C for up to 48 h, chilled and subsequently microbiologically analyzed. The heat resistance of Salmonella at 65C (D65) varied with the growth temperatures in the order of 15C > 25C > 35C > 40C. The effect of storage temperature of seeds on heat inactivation of Salmonella was subsequently investigated. Inoculated seeds were dried, stored for 7 days at different temperatures (22, 15, 10, 4, 0, −10 or −18C) and then heat-treated at 60, 65 or 70C. Heat inactivation of Salmonella was dependent on the storage temperature and increased in the order of 0C ≈ −18C > 4C > 10C ≈ −10C > 15C > 22C. Storage at −18 or 0C followed by dry heating at 60 for 72 h consistently inactivated the pathogen to below detectable levels (<0.7 log cfu/g) and did not significantly (P > 0.05) reduce the sprouting yield of seeds compared to their untreated counterparts. These observations will be useful when developing effective strategies and practices to enhance the microbiological safety of alfalfa sprouts. Practical Applications Sprouts are very young shoots of plants often consumed raw in salads or sandwiches. Common sprouts include mung bean, soybean and alfalfa sprouts. Unfortunately, alfalfa sprouts have been implicated in outbreaks of gastrointestinal illness where the seeds themselves are contaminated with important disease-causing microorganisms. In this study, the influence of growth temperature of Salmonella and the storage temperature of seeds on the susceptibility of the disease-causing microorganism to heat was investigated. Storage of seeds in the refrigerator or freezer for a week prior to heating for 3 days completely destroyed the microorganisms and did not have any considerable impact on the seed viability. These observations will be useful for the sprouting industry to design and optimize heat processes to improve the safety of alfalfa sprouts.

Application of Molecular Approaches for Understanding Foodborne Salmonella Establishment in Poultry Production

Salmonellosis in the United States is one of the most costly foodborne diseases. Given that Salmonella can originate from a wide variety of environments, reduction of this organism at all stages of poultry production is critical. Salmonella species can encounter various environmental stress conditions which can dramatically influence their survival and colonization. Current knowledge of Salmonella species metabolism and physiology in relation to colonization is traditionally based on studies conducted primarily with tissue culture and animal infection models. Consequently, while there is some information about environmental signals that control Salmonella growth and colonization, much still remains unknown. Genetic tools for comprehensive functional genomic analysis of Salmonella offer new opportunities for not only achieving a better understanding of Salmonella pathogens but also designing more effective intervention strategies. Now the function(s) of each single gene in the Salmonella genome can be directly assessed and previously unknown genetic factors that are required for Salmonella growth and survival in the poultry production cycle can be elucidated. In particular, delineating the host-pathogen relationships involving Salmonella is becoming very helpful for identifying optimal targeted gene mutagenesis strategies to generate improved vaccine strains. This represents an opportunity for development of novel vaccine approaches for limiting Salmonella establishment in early phases of poultry production. In this review, an overview of Salmonella issues in poultry, a general description of functional genomic technologies, and their specific application to poultry vaccine developments are discussed.

Salmonella enterica serovar enteritidis antimicrobial peptide resistance genes aid in defense against chicken innate immunity, fecal shedding, and egg deposition.

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a major etiologic agent of nontyphoid salmonellosis in the United States. S. Enteritidis persistently and silently colonizes the intestinal and reproductive tract of laying hens, resulting in contaminated poultry products. The consumption of contaminated poultry products has been identified as a significant risk factor for human salmonellosis. To understand the mechanisms S. Enteritidis utilizes to colonize and persist in laying hens, we used selective capture of transcribed sequences to identify genes overexpressed in the HD11 chicken macrophage cell line and in primary chicken oviduct epithelial cells. From the 15 genes found to be overexpressed in both cell types, we characterized the antimicrobial peptide resistance (AMPR) genes, virK and ybjX, in vitro and in vivo. In vitro, AMPR genes were required for natural morphology, motility, secretion, defense against detergents such as EDTA and bile salts, and resistance to antimicrobial peptides polymyxin B and avian β-defensins. From this, we inferred the AMPR genes play a role in outer membrane stability and/or modulation. In the intestinal tract, AMPR genes were involved in early intestinal colonization and fecal shedding. In the reproductive tract, virK was required in early colonization whereas a deletion of ybjX caused prolonged ovary colonization and egg deposition. Data from the present study indicate that AMPR genes are differentially utilized in various host environments, which may ultimately assist S. Enteritidis in persistent and silent colonization of chickens.

First detection of CMY-2 plasmid mediated β-lactamase in Salmonella Heidelberg in South America

Salmonella enterica serovar Heidelberg ranks among the most prevalent causes of human salmonellosis in the United States and Canada, although it has been infrequently reported in South American and European countries. Most Salmonella infections are self-limiting; however, some invasive infections require antimicrobial therapy. In this work we characterized an oxyimino-cephalosporin resistant S. Heidelberg isolate recovered from an inpatient in a Buenos Aires hospital. CMY-2 was responsible for the β-lactam resistance profile. S. Heidelberg contained a 97kb plasmid belonging to the Inc N group harboring blaCMY-2. ISEcp1 was located upstream blaCMY-2 driving its expression and mobilization. The isolate belonged to sequence type 15 and virotyping revealed the presence of sopE gene. In this study we identified the first CMY-2 producing isolate of S. Heidelberg in Argentina and even in South America.

Complete Genome of Salmonella enterica Serovar Enteritidis Myophage Marshall

Salmonella enterica serovar Enteritidis is a food-borne pathogen that causes salmonellosis in the United States. Bacteriophages are emerging as viable biocontrol agents against this pathogen. Here, we present the complete annotated genome sequence of Salmonella Enteritidis T4-like myophage Marshall, which has potential as a phage therapy agent.

Antibiotic Resistance in Salmonella enterica Serovar Typhimurium Associates with CRISPR Sequence Type

Salmonella enterica subsp. enterica serovar Typhimurium is a leading cause of food-borne salmonellosis in the United States. The number of antibiotic-resistant isolates identified in humans is steadily increasing, suggesting that the spread of antibiotic-resistant strains is a major threat to public health. S Typhimurium is commonly identified in a wide range of animal hosts, food sources, and environments, but little is known about the factors mediating the spread of antibiotic resistance in this ecologically complex serovar. Previously, we developed a subtyping method, CRISPR-multi-virulence-locus sequence typing (MVLST), which discriminates among strains of several common S. enterica serovars. Here, CRISPR-MVLST identified 22 sequence types within a collection of 76 S Typhimurium isolates from a variety of animal sources throughout central Pennsylvania. Six of the sequence types were identified in more than one isolate, and we observed statistically significant differences in resistance among these sequence types to 7 antibiotics commonly used in veterinary and human medicine, such as ceftiofur and ampicillin (P < 0.05). Importantly, five of these sequence types were subsequently identified in human clinical isolates, and a subset of these isolates had identical antibiotic resistance patterns, suggesting that these subpopulations are being transmitted through the food system. Therefore, CRISPR-MVLST is a promising subtyping method for monitoring the farm-to-fork spread of antibiotic resistance in S Typhimurium.

A National Outbreak of Salmonella Serotype Tennessee Infections From Contaminated Peanut Butter: A New Food Vehicle for Salmonellosis in the United States

Salmonella serotype Tennessee is a rare cause of the estimated 1 million cases of salmonellosis occurring annually in the United States. In January 2007, we began investigating a nationwide increase in Salmonella Tennessee infections. We defined a case as Salmonella Tennessee infection in a patient whose isolate demonstrated 1 of 3 closely related pulsed-field gel electrophoresis patterns and whose illness began during the period 1 August 2006 through 31 July 2007. We conducted a case-control study in 22 states and performed laboratory testing of foods and environmental samples. We identified 715 cases in 48 states; 37% of isolates were from urine specimens. Illness was associated with consuming peanut butter more than once a week (matched odds ratio [mOR], 3.5 [95% confidence interval {95% CI}, 1.4-9.9]), consuming Brand X peanut butter (mOR, 12.1 [95% CI, 3.6-66.3]), and consuming Brand Y peanut butter (mOR, 9.1 [95% CI, 1.0-433]). Brands X and Y were produced in 1 plant, which ceased production and recalled products on 14 February 2007. Laboratories isolated outbreak strains of Salmonella Tennessee from 34 Brands X and Y peanut butter jars and 2 plant environmental samples. This large, widespread outbreak of salmonellosis is the first linked to peanut butter in the United States; a nationwide recall resulted in outbreak control. Environmental contamination in the peanut butter plant likely caused this outbreak. This outbreak highlights the risk of salmonellosis from heat-processed foods of nonanimal origin previously felt to be low risk for Salmonella contamination.

Subtyping Salmonella enterica Serovar Enteritidis Isolates from Different Sources by Using Sequence Typing Based on Virulence Genes and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs)

Salmonella enterica subsp. enterica serovar Enteritidis is a major cause of food-borne salmonellosis in the United States. Two major food vehicles for S. Enteritidis are contaminated eggs and chicken meat. Improved subtyping methods are needed to accurately track specific strains of S. Enteritidis related to human salmonellosis throughout the chicken and egg food system. A sequence typing scheme based on virulence genes (fimH and sseL) and clustered regularly interspaced short palindromic repeats (CRISPRs)-CRISPR-including multi-virulence-locus sequence typing (designated CRISPR-MVLST)-was used to characterize 35 human clinical isolates, 46 chicken isolates, 24 egg isolates, and 63 hen house environment isolates of S. Enteritidis. A total of 27 sequence types (STs) were identified among the 167 isolates. CRISPR-MVLST identified three persistent and predominate STs circulating among U.S. human clinical isolates and chicken, egg, and hen house environmental isolates in Pennsylvania, and an ST that was found only in eggs and humans. It also identified a potential environment-specific sequence type. Moreover, cluster analysis based on fimH and sseL identified a number of clusters, of which several were found in more than one outbreak, as well as 11 singletons. Further research is needed to determine if CRISPR-MVLST might help identify the ecological origins of S. Enteritidis strains that contaminate chickens and eggs.

Rapid and simple detection of the invA gene in Salmonella spp. by isothermal target and probe amplification (iTPA)

Salmonella spp. are an important cause of food-borne infections throughout world, and the availability of rapid and simple detection techniques is critical for the food industry. Salmonella enterica serovars Enteritidis and Typhimurium cause the majority of human gastroenteritis infections, and there are a reported 40,000 cases of salmonellosis in the United States each year. A novel rapid and simple isothermal target and probe amplification (iTPA) assay that rapidly amplifies target DNA (Salmonella invA gene) using a FRET-based signal probe in an isothermal environment was developed for detection Salmonella spp. in pre-enriched food samples. The assay was able to specifically detect all of 10 Salmonella spp. strains without detecting 40 non-Salmonella strains. The detection limit was 4 x 10¹ CFU per assay. The iTPA assay detected at an initial inoculum level of <10 CFU in the pre-enriched food samples (egg yolk, chicken breast and peanut butter). This detection system requires only a water bath and a fluorometer and has great potential for use as a hand-held device or point-of-care-testing diagnostics. The iTPA assay is sensitive and specific and has potential for rapid screening of Salmonella spp. by food industry.