Persistence of Salmonella Senftenberg in poultry production environments and investigation of its resistance to desiccation

Genomic typing and virulence gene profile analysis of Salmonella Derby from different sources

Salmonella enterica serovar Derby (S. Derby) is one of the most common Salmonella serovars which can infect poultry, swine, and humans. With the reduction of the sequencing cost and the improvement of sequencing technology, whole genome sequencing (WGS) has become an important method for bacterial determination, molecular investigation, and pathogenic tracing analysis. In this study, we investigated S. Derby isolates from different sources in China using in-silico multilocus sequence typing (MLST), core genome MLST (cgMLST) and whole genome MLST (wgMLST) analysis based on WGS. The results showed that 21 S. Derby strains were divided into 3 STs using MLST analysis, including ST40 (n = 19, accounting for 90.48%), ST71 (n = 1, accounting for 4.76%) and ST8016 (n = 1, accounting for 4.76%). cgMLST and wgMLST analysis categorized the tested strains into 13 cgSTs and 21 wgSTs, respectively. The minimum spanning trees of cgMLST and wgMLST both divided these strains into 3 clusters and 4 singletons. In addition, virulence gene profiles of S. Derby isolates were also analyzed, and a total of 174 virulence genes belonged to 8 categories were identified. In summary, we studied genomic typing, phylogenetic relationship and virulence gene profiles of S. Derby strains from different sources in China. These findings were beneficial for the epidemiology and pathogenesis of Salmonella.

M2 Polarization and Inhibition of Host Cell Glycolysis Contributes Intracellular Survival of Salmonella Strains in Chicken Macrophage HD-11 Cells

Salmonella enterica is a group of facultative, gram-negative bacteria. Recently, new evidence indicated that Salmonella could reprogram the host metabolism to increase energy or metabolites available for intracellular replication. In this study, using a chicken-specific kinomic immunometabolism peptide array analysis, we found that infection by S. Enteritidis induced significant phosphorylation changes in many key proteins of the glycolytic pathway in chicken macrophage HD-11 cells, indicating a shift in glycolysis caused by Salmonella infection. Nitric oxide production and changes of glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) represented by extracellular acidification rate (ECAR) and oxygen consumption rate (OCR), respectively, were measured in chicken macrophages infected with three Salmonella strains (S. Enteritidis, S. Heidelberg, and S. Senftenberg). The infection reduced glycolysis and enhanced OXPHOS in chicken macrophages as indicated by changes of ECAR and OCR. Salmonella strains differentially affected macrophage polarization and glycolysis. Among three strains tested, S. Enteritidis was most effective in downregulating glycolysis and promoting M2 polarization as measured by ECAR, ORC, and NO production; while S. Senftenberg did not alter glycolysis and may promote M1 polarization. Our results suggested that downregulation of host cell glycolysis and increase of M2 polarization of macrophages may contribute to increased intracellular survival of S. Enteritidis.

The Prolonged Treatment of Salmonella enterica Strains with Human Serum Effects in Phenotype Related to Virulence

Salmonella enterica as common pathogens of humans and animals are good model organisms to conduct research on bacterial biology. Because these bacteria can multiply in both the external environments and in the living hosts, they prove their wide adaptability. It has been previously demonstrated that prolonged exposition of Salmonella serotype O48 cells to normal human serum led to an increase in resistance to sera in connection with the synthesis of very long O-antigen. In this work, we have studied the phenotype connected to virulence of Salmonella enterica strains that were subjected to consecutive passages in 50% human serum from platelet-poor plasma (SPPP). We found that eight passages in SPPP may not be enough for the bacteria to become serum-resistant (S. Typhimurium ATCC 14028, S. Senftenberg). Moreover, C1q and C3c complement components bound to Salmonellae (S. Typhimurium ATCC 14028, S. Hammonia) membrane proteins, which composition has been changed after passaging in sera. Interestingly, passages in SPPP generated genetic changes within gene fljB, which translated to cells’ motility (S. Typhimurium ATCC 14028, S. Erlangen). One strain, S. Hammonia exposed to a serum developed a multi-drug resistance (MDR) phenotype and two S. Isaszeg and S. Erlangen tolerance to disinfectants containing quaternary ammonium salts (QAS). Furthermore, colonial morphotypes of the serum adaptants were similar to those produced by starter cultures. These observations suggest that overcoming stressful conditions is manifested on many levels. Despite great phenotypic diversity occurring after prolonged exposition to SPPP, morphotypes of colonies remained unchanged in basic media. This work is an example in which stable morphotypes distinguished by altered virulence can be confusing during laboratory work with life-threatening strains.

Antimicrobial resistance and genomic characterization of Salmonella enterica serovar Senftenberg isolates in production animals from the United States

In the USA, Salmonella enterica subspecies enterica serovar Senftenberg is among the top five serovars isolated from food and the top 11 serovars isolated from clinically ill animals. Human infections are associated with exposure to farm environments or contaminated food. The objective of this study was to characterize S. Senftenberg isolates from production animals by analyzing phenotypic antimicrobial resistance profiles, genomic features and phylogeny. Salmonella Senftenberg isolates (n = 94) from 20 US states were selected from NVSL submissions (2014-2017), tested against 14 antimicrobial drugs, and resistance phenotypes determined. Resistance genotypes were determined using whole genome sequencing analysis with AMRFinder and the NCBI and ResFinder databases with ABRicate. Plasmids were detected using PlasmidFinder. Integrons were detected using IntFinder and manual alignment with reference genes. Multilocus-sequence-typing (MLST) was determined using ABRicate with PubMLST database, and phylogeny was determined using vSNP. Among 94 isolates, 60.6% were resistant to at least one antimicrobial and 39.4% showed multidrug resistance. The most prevalent resistance findings were for streptomycin (44.7%), tetracycline (42.6%), ampicillin (36.2%) and sulfisoxazole (32.9%). The most commonly found antimicrobial resistance genes were aac(6')-Iaa (100%), aph(3″)-Ib and aph(6)-Id (29.8%) for aminoglycosides, followed by bla _TEM-1 (26.6%) for penicillins, sul1 (25.5%) and sul2 (23.4%) for sulfonamides and tetA (23.4%) for tetracyclines. Quinolone-resistant isolates presented mutations in gyrA and/or parC genes. Class 1 integrons were found in 37 isolates. Thirty-six plasmid types were identified among 77.7% of the isolates. Phylogenetic analysis identified two distinct lineages of S. Senftenberg that correlated with the MLST results. Isolates were classified into two distinct sequence types (ST): ST14 (97.9%) and ST 185 (2.1%). The diversity of this serotype suggests multiple introductions into animal populations from outside sources. This study provided antimicrobial susceptibility and genomic characteristics of S. Senftenberg clinical isolates from production animals in the USA during 2014 to 2017. This study will serve as a base for future studies focused on the phenotypic and molecular antimicrobial characterization of S. Senftenberg isolates in animals. Monitoring of antimicrobial resistance to detect emergence of multidrug-resistant strains is critical.

Salmonella enterica in soybean production chain: Occurrence, characterization, and survival during soybean storage

This study aimed to determine Salmonella enterica occurrence along the soybean meal production chain (raw material, in-processing samples, final products, and in the environment of five processing plants), characterize the isolates, and assess the survival of Salmonella Senftenberg 775W in soybeans stored under different temperature conditions. Among 713 samples analyzed, 12.9% (n = 92) were positive for Salmonella enterica. Dust collected inside and outside processing plants (n = 148) comprised the samples with the highest positivity for Salmonella enterica, 47.3%. The occurrence of Salmonella enterica varied among the different processing plants. Twenty-nine (n = 29) Salmonella serotypes were isolated, with S. Mbandaka as the most frequent serotype, whereas S. Typhimurium was mainly linked to final product samples (soybean meal). S. Senftenberg 775W did not survive for a long time in soybean stored at 20-37 °C, but at 20 °C, cells were viable for more than 60 days. This study suggests that soybean meal may harbor Salmonella serotypes related to foodborne disease outbreaks in humans and can be responsible for Salmonella introduction into livestock and, consequently, in foods of animal origin. This study provides crucial data on contamination pathways of Salmonella in the soybean production chain, contributing to the understanding of Salmonella epidemiology which is strategic for the development of preventive and control measures to reduce the burden of salmonellosis linked to products of animal origin.

Observations on the distribution and control of Salmonella in commercial broiler hatcheries in Great Britain

Salmonella can enter hatcheries via contaminated eggs and other breaches of biosecurity. The study examined the prevalence and distribution of Salmonella in commercial hatcheries and assessed the effects of providing advice on Salmonella control. Intensive swab sampling was performed throughout 23 broiler hatcheries in Great Britain (GB). Swabs were cultured using a modified ISO6579:2017 method. After each visit, tailored advice on biosecurity and cleaning and disinfection procedures was provided to the hatchery managers. Repeat sampling was carried out in 10 of the 23 hatcheries. Salmonella prevalence ranged between 0% and 33.5%, with the chick handling areas, hatcher areas, macerator area, tray wash/storage areas, external areas and other waste handling areas being more contaminated than the setter areas. Salmonella Senftenberg and Salmonella 13,23:i:‐ were the most commonly isolated serovars. There was a reduction in Salmonella prevalence at the second visit in eight out of 10 premises, but prevalence values had increased again in all of the improved hatcheries that were visited a third time. One hatchery harboured a difficult‐to‐control resident Salmonella 13,23:i:‐ strain and was visited six times; by the final visit, Salmonella prevalence was 2.3%, reduced from a high of 23.1%. In conclusion, the study found low‐level Salmonella contamination in some GB broiler hatcheries, with certain hatcheries being more severely affected. Furthermore, it was shown that Salmonella typically is difficult to eradicate from contaminated hatcheries, but substantial reductions in prevalence are possible with improvements to biosecurity, cleaning and disinfection.

Contaminated in-house environment contributes to the persistence and transmission of NDM-producing bacteria in a Chinese poultry farm

While carbapenem use is prohibited in the poultry production chain and carbapenem-resistant Enterobacteriaceae (CRE) are absent from hatchery farms, New Delhi metallo-β-lactamase-producing CRE contamination of commercial broiler chicken farms (grow-out farms) can occur via living hosts such as flies. However, it is not known whether the inanimate factors from in-house environment play a role in the persistence of CRE on commercial farms. Herein, we monitored one typical broiler house in Hebei Province, China, from January 2017 to April 2018. We collected 350 cloacal samples from four broiler batches along with 582 environmental samples (194 in the raising period and 388 in the vacancy period) from sites including the surfaces of drooping boards, feeding troughs, nipple drinkers, corridor floors, sewage trenches, and air. All samples were screened for bla_NDM and cultured for NDM-producing isolates. The resistance profiles, genotypes, and genetic context of bla_NDM in CRE isolates were further characterized. Results showed that 1-day-old broilers, which were transferred from a hatchery farm and negative for CRE, acquired bla_NDM within 24 h of transfer (2 days of age), with a detection rate of up to 18.6%. High bla_NDM detection rates (26.8%-31.4%) were obtained among all environmental samples except air after standard cleaning and disinfection during the vacancy period. bla_NDM carriage rates (52.9%-72.9%) within the flocks remain stable and high across the next three broiler batches. Overall, 279 NDM-producing bacteria, including 259 Enterobacteriaceae (8 species), 14 Morganellaceae (3 species), three Alcaligenes faecalis and three Pseudomonas putida isolates, were recovered from 85 (24.3%) cloacal and 101 (17.4%) environmental samples. Three NDM variants, including NDM-5 (n = 181), NDM-1 (n = 92), and NDM-9 (n = 3), and a novel NDM-like-metallo-β-lactamase (NLM, n = 3) were identified among the samples. The predominant NDM-producing CRE species among the samples were Klebsiella pneumoniae (CRKP; 32.6%, n = 91) and Escherichia coli (CREC; 27.2%, n = 76). Both clonal and horizontal transmission of bla_NDM and an overlap of sequence types (STs) were observed in both CREC and CRKP from chicken and environmental samples. Notably, ST6751 CREC and ST37 CRKP persisted throughout the 16-month surveillance period. IncX3 (n = 197, 7 species), IncA/C₂ (n = 41, 5 species), and IncFII (n = 8, E. coli) were the three major bla_NDM-carrying plasmid types among the isolates. Although routine cleaning and disinfection procedures and "all-in/all-out" management were performed, once introduced to the farm environment, a diverse range of NDM-positive isolates may survive and persist, becoming an important reservoir of NDM-positive CRE for broiler chickens. Therefore, cleaning and disinfection procedures should be improved on poultry farms to avoid cross-contamination of NDM-producing bacteria between different batches of chickens, as well as further downstream in the poultry production chain.

Diversity of Lactobacillus Species of Stilton Cheese Relates to Site of Isolation

This study has characterized the dominant non-starter Lactobacillus species isolated from different sites in a Stilton cheese to establish its diversity, stress-tolerance, anti-microbial activity and potential contribution to quality of cheese. Fifty-nine Lactobacillus isolates were cultured from the outer crust, blue veins and white core of the cheese and were speciated phenotypically and by 16S rDNA sequence analysis. Lactobacillus plantarum was the dominant species detected with only two isolates identified as Lactobacillus brevis. Strains were typed by pulse-field gel electrophoresis (PFGE) using the enzyme NotI to examine their genomic diversity. Cluster analysis of PFGE patterns produced five major clusters which associated isolates with their sites of isolation within the cheese. One L. plantarum isolate from each cheese site was selected and evaluated for salt, acid, relative humidity, and heat tolerance to determine whether stress conditions within the isolation site selected their phenotype. D_72°C values were 6, 13, and 17 s for strains from the crust, veins and core, respectively, suggesting strains on the crust may not have been able to survive pasteurization and therefore had been added post-pasteurization. All strains recovered from heat injury within 24–48 h at 4°C. pH values of 3, 3.5, and 4 suppressed growth but strains showed a varying ability to grow at pH 4.5 and 5; isolates from the core (which has the lowest pH) were the most acid-tolerant. All strains grew at 3.5 and 5% salt but were suppressed at 10%; those from the crust (which has a lower water activity) were the most halo-tolerant, growing at 8% salt whereas strains from the core were sensitive to this salt concentration. All 57 L. plantarum isolates were examined for antimicrobial activity and variable activity against Lactobacillus pentosus and other genera was demonstrated; plantaricin EF genes were present in 65% of strains. It was concluded that there are varied phenotypes and genotypes of Lactobacillus in a Stilton cheese according to site of isolation. Occurrence of different L. plantarum genotypes could contribute to variation in the cheese quality from batch to batch and provides criteria for selecting isolates as potential adjunct cultures.

Research Note: Repetitive element-based polymerase chain reaction genotyping improves efficiency of Salmonella surveillance in a model broiler production system

The genetic relatedness and antimicrobial susceptibility profiles of Salmonella isolated from poultry and their environment were determined. One broiler breeder flock (BBF1) and 2 broiler flocks (BF1 and BF2) were reared over a 1.75-year period on the same poultry research farm. Hatching eggs were obtained from BBF1 to produce BF1 chicks, while BF2 chicks were progeny of a separate, unsampled broiler breeder flock. BF1 and BF2 were reared in the same housing facilities but 6 mo apart. Salmonella isolates were collected via litter sock sampling (BF1), cecal excision (BF1 and BF2), or cloacal swabs (BBF1). Serotyping identified Salmonella enterica subsp. enterica serovar Altona (SA) in BBF1 and S. enterica subsp. enterica serovar Senftenberg (SS) in BF1 and BF2. Genotypic fingerprinting was achieved with Rep-PCR using the (GTG)₅ primer and revealed sequence homology among Senftenberg isolates from BF1 and BF2. For each isolate, the minimum inhibitory concentration was determined for 27 antimicrobial agents using Sensititre plates with formularies specific to antimicrobials used in poultry production or those used to control gram negative pathogens. Isolates from the 3 flocks were resistant to clindamycin, erythromycin, novobiocin, penicillin, and tylosin tartrate and demonstrated intermediate resistance to azithromycin, florfenicol, and spectinomycin. These data demonstrated that serovar Altona and Senftenberg were harbored by poultry, the latter appeared to persist in broiler flocks, and both serotypes shared similar patterns of antimicrobial susceptibility in an integrated research operation. In the case of multiple Salmonella isolates, combining genotypic fingerprinting methods with serotyping of representative isolates would reduce the number of samples required for serotyping and more clearly identify relatedness of isolates. These methods facilitate effective surveillance in poultry production systems, thus allowing for implementation of precise Salmonella control measures.

Longitudinal study reveals persistent environmental Salmonella Heidelberg in Brazilian broiler farms

The vast capacity for maintenance and dissemination in the environment are major challenges for the control of Salmonella spp. in poultry farms. The aim of this study was to assess environmental contamination by non-typhoidal Salmonella in successive broiler flocks in nine commercial broiler farms integrated with three companies in the south of Brazil, for a twelve-month production period. Recycled broiler litter, feed and swabs from the evaporative cooling system pads were analyzed, and the total enterobacteria count in the litter samples was ascertained. Positive broiler houses were identified in two of the three broiler companies studied, in which non-typhoidal Salmonella were detected for the first time in the first or second flock, and recurred in the recycled litter of subsequent flocks. Feed and evaporative cooling pad swab samples were also positive in at least one of the assessed flocks. The majority of the isolates (87.5%) originating from different flocks, broiler houses and companies that were sampled were identified as S. Heidelberg, with the prevalence of one single genotype. The total enterobacteria levels in the litter diminished as the flocks progressed, but the presence of Salmonella spp. was constant over the course of time, indicating that the litter management procedures were not capable of interrupting the cycle of residual contamination. The predominance of S. Heidelberg highlights its emergence and dissemination in this region, as well as its resistance and maintenance in the environment, and reinforces the need to improve prevention and recycled litter management measures.

"Omics" of Food-Borne Gastroenteritis: Global Proteomic and Mutagenic Analysis of Salmonella enterica Serovar Enteritidis

Salmonella Enteritidis causes food-borne gastroenteritis by the two type three secretion systems (TTSS). TTSS-1 mediates invasion through intestinal lining, and TTSS-2 facilitates phagocytic survival. The pathogens' ability to infect effectively under TTSS-1-deficient background in host's phagocytes is poorly understood. Therefore, pathobiological understanding of TTSS-1-defective nontyphoidal Salmonellosis is highly important. We performed a comparative global proteomic analysis of the isogenic TTSS-1 mutant of Salmonella Enteritidis (M1511) and its wild-type isolate P125109. Our results showed 43 proteins were differentially expressed. Functional annotation further revealed that differentially expressed proteins belong to pathogenesis, tRNA and ncRNA metabolic processes. Three proteins, tryptophan subunit alpha chain, citrate lyase subunit alpha, and hypothetical protein 3202, were selected for in vitro analysis based on their functional annotations. Deletion mutants generated for the above proteins in the M1511 strain showed reduced intracellular survival inside macrophages in vitro. In sum, this study provides mass spectrometry-based evidence for seven hypothetical proteins, which will be subject of future investigations. Our study identifies proteins influencing virulence of Salmonella in the host. The study complements and further strengthens previously published research on proteins involved in enteropathogenesis of Salmonella and extends their role in noninvasive Salmonellosis.

Reducing Foodborne Pathogen Persistence and Transmission in Animal Production Environments: Challenges and Opportunities

Preharvest strategies to reduce zoonotic pathogens in food animals are important components of the farm-to-table food safety continuum. The problem is complex; there are multiple pathogens of concern, multiple animal species under different production and management systems, and a variety of sources of pathogens, including other livestock and domestic animals, wild animals and birds, insects, water, and feed. Preharvest food safety research has identified a number of intervention strategies, including probiotics, direct-fed microbials, competitive exclusion cultures, vaccines, and bacteriophages, in addition to factors that can impact pathogens on-farm, such as seasonality, production systems, diet, and dietary additives. Moreover, this work has revealed both challenges and opportunities for reducing pathogens in food animals. Animals that shed high levels of pathogens and predominant pathogen strains that exhibit long-term persistence appear to play significant roles in maintaining the prevalence of pathogens in animals and their production environment. Continued investigation and advancements in sequencing and other technologies are expected to reveal the mechanisms that result in super-shedding and persistence, in addition to increasing the prospects for selection of pathogen-resistant food animals and understanding of the microbial ecology of the gastrointestinal tract with regard to zoonotic pathogen colonization. It is likely that this continued research will reveal other challenges, which may further indicate potential targets or critical control points for pathogen reduction in livestock. Additional benefits of the preharvest reduction of pathogens in food animals are the reduction of produce, water, and environmental contamination, and thereby lower risk for human illnesses linked to these sources.

Observations on the distribution and control of Salmonella in commercial duck hatcheries in the UK

Salmonella infection causes a significant number of cases of gastroenteritis and more serious illnesses in people in the UK and EU. The serovars Salmonella Enteritidis and Salmonella Typhimurium are most frequently associated with foodborne illness in Europe. Whilst control programmes exist to monitor these serovars in the chicken and turkey sectors, no regulatory programme is currently in place for the duck sector. A voluntary industry scheme (Duck Assurance Scheme) was launched in the UK in 2010. Hatcheries act as focal points of Salmonella contamination, in particular if Salmonella-contaminated eggs from positive breeding farms enter the hatchery. Five duck hatcheries were visited in this study and four were positive for Salmonella. S. Typhimurium DT8 and S. Indiana were isolated from hatchery 1 and S. Typhimurium DT41 and S. Senftenberg were isolated from hatchery 3. S. Kottbus, S. Bovismorbificans and S. Senftenberg were isolated from hatchery 2 and S. Kedougou was isolated from hatchery 4. Advice on the control/elimination of Salmonella was provided at each visit and a longitudinal study was undertaken to monitor its effectiveness. Extensive sampling was carried out in the hatcheries visited and the tray wash area and waste/external areas had the highest probability of being contaminated. The hatcher area was also found to be a primary focus of contamination. Improvements of farm and hatchery biosecurity standards have resulted in a reduction of hatchery contamination in this study and in previous investigations. Hatcheries 1 and 5 were cleared of Salmonella, demonstrating that elimination of Salmonella contamination from duck hatcheries is achievable.

Induction of Viable but Nonculturable Salmonella in Exponentially Grown Cells by Exposure to a Low-Humidity Environment and Their Resuscitation by Catalase

Salmonella is a major cause of foodborne disease that sometimes occurs in massive outbreaks around the world. This pathogen is tolerant of low-humidity conditions. We previously described a method for induction of viable but nonculturable (VBNC) Salmonella enterica serovar Enteritidis by treatment with hydrogen peroxide (H₂O₂) and subsequent resuscitation with 0.3 mM sodium pyruvate. Here, we report a new method for the induction of the VBNC state in Salmonella Enteritidis cells, one involving dehydration. Exposure of Salmonella Enteritidis cells to dehydration stress under poor nutritional conditions (0.9% [wt/vol] NaCl) and 10 to 20% relative humidity at room temperature decreased the presence of culturable population to 0.0067%, but respiratory and glucose uptake active populations were maintained at 0.46 and 1.12%, respectively, meaning that approximately 1% may have entered the VBNC state. Furthermore, these VBNC cells could be resuscitated to acquire culturability by incubation with catalase in M9 minimal medium without glucose in a manner dependent on the dose of catalase but not sodium pyruvate. These results suggest that a low-humidity environment could cause Salmonella Enteritidis cells to enter the VBNC state and the cells could then be resuscitated for growth by treatment with catalase, suggesting a potential risk of Salmonella Enteritidis to survive in low water activity foods in the VBNC state and to start regrowth for foodborne illness.

Homologous prime-boost immunization with live attenuated Salmonella enterica serovar Senftenberg and its preventive efficacy against experimental challenge with various strains of S. Senftenberg

Background

The heterogeneity observed regarding persistence, and subsequent fecal shedding pattern of the Salmonella Senftenberg (S. Senftenberg) serovar in chicken’s calls for development of the optimized immunization strategy which can provide protection against various S. Senftenberg isolated. Optimization of an immunization strategy with a live attenuated S. Senftenberg (Δlon and ΔcpxR) vaccine candidate (JOL1587) was undertaken in this study to evaluate the ability of a homologous prime-boost immunization strategy (using JOL1587) to confer protection against four different S. Senftenberg isolates in chickens.

Results

After oral immunization with JOL1587, the humoral, mucosal and cell-mediated immune responses were significantly higher in double immunized chickens than in single immunized and control group chickens. A significant increase in the multifunctional cytokine IL-6 and in helper and cytotoxic T cell populations after a booster immunization also indicated the advantage of double over single immunization. The four different S. Senftenberg field isolates were characterized by their persistence levels in chickens, and were subsequently used for challenge experiments to evaluate the differences in protective efficacy conferred by single and double immunization. Chickens from the doubleimmunized group exhibited significant reduction in the shedding of all four wild-type S. Senftenberg challenge strains below the detection limit in the fecal samples. Single immunized chickens showed a decrease in fecal shedding, but failed to exhibit complete protection against all the challenge strains.

Conclusion

Although single immunization with JOL1587 showed a reduction in the fecal shedding of challenge strains, only the homologous prime-boost immunization strategy provided an adequate immune response for increased protection against all four challenge strains of S. Senftenberg from the feces of chickens.

Low Prevalence of Salmonella Enterica in Cull Dairy Cattle at Slaughter in Northern Italy

In order to evaluate Salmonella carrier status of cull dairy cattle at slaughter, 125 animals were randomly selected during the period February-May 2016. Dairy cows were reared in 89 farms located in two regions of Northern Italy (Lombardy and Emilia-Romagna regions), where bovine milk is primarily used for Parmigiano-Reggiano cheese and Grana Padano cheese production. Samples were collected by swabbing a 400-cm2 area of the brisket hide and by rectoanal mucosal swabs. They were tested following the reference ISO 6579 method and the isolates were serotyped following the Kauffmann-White-Le Minor scheme and genotyped by XbaI PFGE. Salmonella was detected in 1.6% of the brisket hide samples (2/125) (95% CI: 0.4-5.6) and never found in faecal samples (95% CI: 0-3%). The positive cattle were reared in two farms located only in Emilia-Romagna region. The isolates were typed as S. Derby and S. Seftenberg. The comparison of the pulsed-field gel electrophoresis (PFGE) patterns of the bovine strains with all the PFGE patterns of the same serotypes responsible for human salmonellosis cases notified in Emilia-Romagna region in the years 2013-2015 did not find any correspondence. Therefore, the role of cull dairy cattle in transmitting Salmonella to humans seems to be less important than those of pigs and poultry in EU, but more data are needed for completing attribution source studies.

Antimicrobial Susceptibility and Molecular Typing of Salmonella Senftenberg Isolated from Humans and Other Sources in Shanghai, China, 2005 to 2011

Salmonella Senftenberg is an important nontyphoidal Salmonella serovar that causes gastrointestinal disease worldwide. In total, 130 Salmonella Senftenberg strains obtained from humans, food, and the environment in Shanghai, People's Republic of China, were characterized for antimicrobial susceptibility and subjected to molecular typing. Our findings indicated that most (96 of 130, 73.8%) of the strains were susceptible to all 13 antimicrobial compounds tested, whereas only two strains (1.5%) were resistant to two antimicrobial compounds. In total, 56 pulsed-field gel electrophoresis profiles were identified, including four main pulsed-field gel electrophoresis profiles (X2, X3, X4, and X5) that showed 95.7% genetic similarity. Our study revealed that the strains of Salmonella Senftenberg from food and the environment shared a high correlation of genetic similarity with those from humans, highlighting the potential links that exist among the strains recovered from different sources in Shanghai.

Characterization and Evaluation of a Salmonella enterica Serotype Senftenberg Mutant Created by Deletion of Virulence-Related Genes for Use as a Live Attenuated Vaccine

Natural infections of chickens with Salmonella enterica subsp. enterica serovar Senftenberg (S. Senftenberg) are characterized by low-level intestinal invasiveness and insignificant production of antibodies. In this study, we investigated the potential effects of lon and cpxR gene deletions on the invasiveness of S Senftenberg into the intestinal epithelium of chickens and its ability to induce an immune response, conferring protection against S Senftenberg infection. With the allelic exchange method, we developed JOL1596 (Δlon), JOL1571 (ΔcpxR), and JOL1587 (Δlon ΔcpxR) deletion mutants from wild-type S Senftenberg. Deletion of the lon gene from S Senftenberg produced increased frequency of elongated cells, with significantly greater amounts of exopolysaccharide (EPS) than in the cpxR-deleted strain and the wild-type strain. The in vivo intestinal loop invasion assay showed a significant increase in epithelial invasiveness for JOL1596 (Δlon) and JOL1587 (Δlon ΔcpxR), compared to JOL1571 (ΔcpxR) and the wild-type strain. Furthermore, the S Senftenberg wild-type and mutant strains were internalized at high levels inside activated abdominal macrophages from chicken. The in vivo inoculation of JOL1587 (Δlon ΔcpxR) into chickens led to colonization of the liver, spleen, and cecum for a short time. Chickens inoculated with JOL1587 (Δlon ΔcpxR) showed significant increases in humoral, mucosal, and cellular immune responses specific to S Senftenberg antigens. Postchallenge, compared to the control group, the JOL1587 (Δlon ΔcpxR)-inoculated chickens showed not only lower persistence but also faster clearance of wild-type S Senftenberg from the cecum. We conclude that the increased intestinal invasiveness and colonization of internal organs exhibited by JOL1587 (Δlon ΔcpxR) led to the establishment of immunogenicity and conferred protective efficacy against S Senftenberg infections in chickens.

Genomic and Phenotypic Analyses Reveal the Emergence of an Atypical Salmonella enterica Serovar Senftenberg Variant in China

Human infections with Salmonella enterica subspecies enterica serovar Senftenberg are often associated with exposure to poultry flocks, farm environments, or contaminated food. The recent emergence of multidrug-resistant isolates has raised public health concerns. In this study, comparative genomics and phenotypic analysis were used to characterize 14 Salmonella Senftenberg clinical isolates recovered from multiple outbreaks in Shenzhen and Shanghai, China, between 2002 and 2011. Single-nucleotide polymorphism analyses identified two phylogenetically distinct clades of S Senftenberg, designated SC1 and SC2, harboring variations in Salmonella pathogenicity island 1 (SPI-1) and SPI-2 and exhibiting distinct biochemical and phenotypic signatures. Although the two variants shared the same serotype, the SC2 isolates of sequence type 14 (ST14) harbored intact SPI-1 and -2 and hence were characterized by possessing efficient invasion capabilities. In contrast, the SC1 isolates had structural deletion patterns in both SPI-1 and -2 that correlated with an impaired capacity to invade cultured human cells and also the year of their isolation. These atypical SC1 isolates also lacked the capacity to produce hydrogen sulfide. These findings highlight the emergence of atypical Salmonella Senftenberg variants in China and provide genetic validation that variants lacking SPI-1 and regions of SPI-2, which leads to impaired invasion capacity, can still cause clinical disease. These data have identified an emerging public health concern and highlight the need to strengthen surveillance to detect the prevalence and transmission of nontyphoidal Salmonella species.

Genomic evidence reveals numerous Salmonella enterica serovar Newport reintroduction events in Suwannee watershed irrigation ponds

Our previous work indicated a predominance (56.8%) of Salmonella enterica serovar Newport among isolates recovered from irrigation ponds used in produce farms over a 2-year period (B. Li et al., Appl Environ Microbiol 80:6355-6365, http://dx.doi.org/10.1128/AEM.02063-14). This observation provided a valuable set of metrics to explore an underaddressed issue of environmental survival of Salmonella by DNA microarray. Microarray analysis correctly identified all the isolates (n = 53) and differentiated the S. Newport isolates into two phylogenetic lineages (S. Newport II and S. Newport III). Serovar distribution analysis showed no instances where the same serovar was recovered from a pond for more than a month. Furthermore, during the study, numerous isolates with an indistinguishable genotype were recovered from different ponds as far as 180 km apart for time intervals as long as 2 years. Although isolates within either lineage were phylogenetically related as determined by microarray analysis, subtle genotypic differences were detected within the lineages, suggesting that isolates in either lineage could have come from several unique hosts. For example, strains in four different subgroups (A, B, C, and D) possessed an indistinguishable genotype within their subgroups as measured by gene differences, suggesting that strains in each subgroup shared a common host. Based on this comparative genomic evidence and the spatial and temporal factors, we speculated that the presence of Salmonella in the ponds was likely due to numerous punctuated reintroduction events associated with several different but common hosts in the environment. These findings may have implications for the development of strategies for efficient and safe irrigation to minimize the risk of Salmonella outbreaks associated with fresh produce.

Salmonella enterica: survival, colonization, and virulence differences among serovars

Data indicate that prevalence of specific serovars of Salmonella enterica in human foodborne illness is not correlated with their prevalence in feed. Given that feed is a suboptimal environment for S. enterica, it appears that survival in poultry feed may be an independent factor unrelated to virulence of specific serovars of Salmonella. Additionally, S. enterica serovars appear to have different host specificity and the ability to cause disease in those hosts is also serovar dependent. These differences among the serovars may be related to gene presence or absence and expression levels of those genes. With a better understanding of serovar specificity, mitigation methods can be implemented to control Salmonella at preharvest and postharvest levels.

Evaluation of respiratory route as a viable portal of entry for Salmonella in poultry

With increasing reports of Salmonella infection, we are forced to question whether the fecal-oral route is the major route of infection and consider the possibility that airborne Salmonella infections might have a major unappreciated role. Today's large-scale poultry production, with densely stocked and enclosed production buildings, is often accompanied by very high concentrations of airborne microorganisms. Considering that the upper and lower respiratory lymphoid tissue requires up to 6 weeks to be fully developed, these immune structures seem to have a very minor role in preventing pathogen infection. In addition, the avian respiratory system in commercial poultry has anatomic and physiologic properties that present no challenge to the highly adapted Salmonella. The present review evaluates the hypothesis that transmission by the fecal-respiratory route may theoretically be a viable portal of entry for Salmonella in poultry. First, we update the current knowledge on generation of Salmonella bioaerosols, and the transport and fate of Salmonella at various stages of commercial poultry production. Further, emphasis is placed on survivability of Salmonella in these bioaerosols, as a means to assess the transport and subsequent risk of exposure and infection of poultry. Additionally, the main anatomic structures, physiologic functions, and immunologic defense in the avian respiratory system are discussed to understand the potential entry points inherent in each component that could potentially lead to infection and subsequent systemic infection of poultry by Salmonella. In this context, we also evaluate the role of the mucosal immune system as essentially one large interconnected network that shares information distally, since understanding of this sort of communication between mucosal sites is fundamental to establish the next phase of disease characterization, and perhaps immunization and vaccine development. Further characterization of the respiratory tract with regard to transmission of Salmonella under field conditions may be of critical importance in developing interventional strategies to reduce transmission of this important zoonotic pathogen in poultry.

Survival and death kinetics of Salmonella strains at low relative humidity, attached to stainless steel surfaces

Salmonella is a major pathogen of concern for low water activity foods and understanding its persistence in dry food processing environments is important for producing safe food. The studies sought to assess the survival of 15 isolates of Salmonella on stainless steel surfaces. Additionally, the aim was to select a suitable model to describe and understand the strains' survival kinetics. Salmonella isolates were dried onto stainless steel surfaces, placed in controlled temperature (25°C) and humidity (33%) conditions and their viability assessed at times from 1h to 30days. The highest survival rate was associated with S. Typhimurium DT104, S. Muenchen, and S. Typhimurium (NCTC 12023), where, after 30days, the reduction ranged from 1.3log10 cfu/surface to 1.6log10 cfu/surface. The lowest survival was linked to a S. Typhimurium strain used in European Standard disinfectant approval tests and S. Typhimurium isolated from whey powder. For most of the strains, following an initial reduction in viability in the first hours (<72h), no further reduction was seen over the 30day period; therefore a 2-population Weibull model was fitted to model the survival kinetics. The overall survival was neither serotype nor time related. All strains had two different subpopulations, one more resistant to desiccation than the other. The results indicate the possibility of the long term survival of Salmonella on environmental surfaces (at least 30days) and suggest the most suitable model to describe and predict survival kinetics. The results also identify strains that may be used to study stress response mechanisms and potential factory control measures in future studies.

Emergence and prevalence of non-H2S-producing Salmonella enterica serovar Senftenberg isolates belonging to novel sequence type 1751 in China

Salmonella enterica serovar Senftenberg is a common nontyphoidal Salmonella serotype which causes human Salmonella infections worldwide. In this study, 182 S. Senftenberg isolates, including 17 atypical non-hydrogen sulfide (H2S)-producing isolates, were detected in China from 2005 to 2011. The microbiological and genetic characteristics of the non-H2S-producing and selected H2S-producing isolates were determined by using pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and clustered regularly interspaced short palindromic repeat (CRISPR) analysis. The phs operons were amplified and sequenced. The 17 non-H2S-producing and 36 H2S-producing isolates belonged to 7 sequence types (STs), including 3 new STs, ST1751, ST1757, and ST1758. Fourteen of the 17 non-H2S-producing isolates belonged to ST1751 and had very similar PFGE patterns. All 17 non-H2S-producing isolates had a nonsense mutation at position 1621 of phsA. H2S-producing and non-H2S-producing S. Senftenberg isolates were isolated from the same stool sample from three patients; isolates from the same patients displayed the same antimicrobial susceptibility, ST, and PFGE pattern but could be discriminated based on CRISPR spacers. Non-H2S-producing S. Senftenberg isolates belonging to ST1751 have been prevalent in Shanghai, China. It is possible that these emerging organisms will disseminate further, because they are difficult to detect. Thus, we should strengthen the surveillance for the spread of this atypical S. Senftenberg variant.

Fate of Salmonella Senftenberg in broiler chickens evaluated by challenge experiments

Experimental and epidemiological evidence has indicated the respiratory route to be a potential portal of entry for salmonellas in poultry. The purpose of this study was to evaluate and compare the infectivity of Salmonella enterica serovar Senftenberg following oral gavage, intratracheal or intravenous challenge in chickens. Seven-day-old chicks were challenged with either 10(4) or 10(6) colony-forming units of S. Senftenberg per chick by oral gavage, intratracheal or intravenous challenge, respectively, in two independent trials. Chickens were humanely killed 24 h post challenge and S. Senftenberg was cultured and enumerated from caecal contents, caecal tissue-caecal tonsils and liver and spleen. In both trials, intratracheal delivery of S. Senftenberg was the only route that allowed colonization of the caeca of chickens when compared with oral gavage or intravenous challenge in a dose response fashion (P < 0.05). Liver and spleen samples yielded no S. Seftenberg after the lower dose challenge by the oral or intratracheal route and only low levels following the high-dose administration by these routes, whereas intravenous challenge resulted in recovery of the organisms after both doses. The results of the present study suggest that S. Senftenberg entering the blood is likely to be cleared and will not be able to colonize caeca to the same extent as compared with intratracheal challenge. Clarification of the potential importance of the respiratory tract for transmission of salmonellas under field conditions may be of critical importance to develop intervention strategies to reduce the transmission in poultry.

Antibacterial activity of silver nanoparticles: sensitivity of different Salmonella serovars

Salmonella spp. is one of the main causes of foodborne illnesses in humans worldwide. Consequently, great interest exists in reducing its impact on human health by lowering its prevalence in the food chain. Antimicrobial formulations in the form of nanoparticles exert bactericidal action due to their enhanced reactivity resultant from their high surface/volume ratio. Silver nanoparticles (AgNPs) are known to be highly toxic to Gram-negative and Gram-positive microorganisms, including multidrug resistant bacteria. However, few data concerning their success against different Salmonella serovars are available. Aims of the present study were to test the antimicrobial effectiveness of AgNPs, against Salmonella Enteritidis, Hadar, and Senftenberg, and to investigate the causes of their different survival abilities from a molecular point of view. Results showed an immediate, time-limited and serovar-dependent reduction of bacterial viability. In the case of S. Senftenberg, the reduction in numbers was observed for up to 4 h of incubation in the presence of 200 mg/l of AgNPs; on the contrary, S. Enteritidis and S. Hadar resulted to be inhibited for up to 48 h. Reverse transcription and polymerase chain reaction experiments demonstrated the constitutive expression of the plasmidic silver resistance determinant (SilB) by S. Senftenberg, thus suggesting the importance of a cautious use of AgNPs.

Laboratory monitoring of bacterial gastroenteric pathogens Salmonella and Shigella in Shanghai, China 2006-2012

In 2006 we initiated an enhanced laboratory-based surveillance of Salmonella and Shigella infections in Shanghai, China. A total of 4483 Salmonella and 2226 Shigella isolates were recovered from stool specimens by 2012. In 80 identified Salmonella serovars, Enteritidis (34·5%) and Typhimurium (26·2%) were the most common. Shigella (S.) sonnei accounted for 63·9% of human Shigella infections over the same time period, and replaced S. flexneri to become the primary cause of shigellosis since 2010. Overall, a high level of antimicrobial resistance was observed in Salmonella and Shigella, particularly to nalidixic acid, ampicillin, and tetracycline. Ciprofloxacin resistance was common in Salmonella Typhimurium (21·0%) and S. flexneri (37·6%). The cephalosporin resistance in both pathogens also increased over the years, ranging from 3·4% to 7·0% in Salmonella, and from 10·4% to 28·6% in Shigella. Resistance to multiple antimicrobials was also identified in a large number of the isolates. This study provides insight into the distribution of Salmonella and Shigella in diarrhoeal diseases.

Differential resuscitative effect of pyruvate and its analogues on VBNC (viable but non-culturable) Salmonella

An environmental isolate of Salmonella Enteritidis (SE), grown to the logarithmic phase, rapidly lost culturability by the addition of 3 mM H2O2 to cultures grown in Luria-Bertani (LB) medium; however, some H2O2-treated bacteria regained their culturability in M9 minimal medium, if sodium pyruvate was present at at least 0.3 mM. In addition, most pyruvate analogues, such as bromopyruvate or phenylpyruvate, did not show restoration activity similar to that of pyruvate, except in the case of α-ketobutyrate. Further analysis of the mechanism underlying the resuscitation by pyruvate revealed that although many of the bacteria showed respiratory activity on CTC (5-cyano-2,3-di-(p-tolyl) tetrazolium chloride) reduction with or without pyruvate, the biosynthesis of DNA and protein synthesis were quite different in the presence or absence of pyruvate, i.e., pyruvate endowed the cells with the ability to incorporate much more radio-label into precursors during the resuscitation process. These results suggest that pyruvate is one of the key molecules working in the resuscitation process by taking bacteria from the non-culturable state to the growing and colony-forming state by triggering the synthesis of macromolecules such as DNA and protein.

Epizootiologic role of feeds in the epidemiology of Salmonella Senftenberg contamination in commercial layer farms in eastern Japan

In total, 40 commercial layer farms and 32 replacement pullet farms with a combined population of 7.5 million adult layers and 6.6 million replacement pullets from six prefectures in eastern Japan were investigated for Salmonella Senftenberg contamination. We randomly collected 17,956 environmental samples, 5816 feed samples, and 218,470 egg samples from commercial layer farms; and 427 feed samples and 2896 environmental samples from replacement pullet farms. We monitored all samples for Salmonella. Samples were primarily enriched in Hajna tetrathinoate broth for 24 hr at 37 C followed by incubation in desoxycholate hydrogen sulfide lactose agar for 18 hr at 37 C. Salmonella colonies were confirmed and identified by biochemical tests and serotyped using Salmonella O and H antigens. We recorded 171 environmental samples (0.95%) and 10 feed samples (0.17%) that were positive for Salmonella spp. in which 36 environmental samples (0.20%) and six feed samples (0.10%) were identified as Salmonella Senftenberg. All Salmonella Senftenberg strains were isolated from nine replacement pullet farms. No Salmonella Senftenberg strains were isolated from adult layer farms and from eggs. Pulse field gel electrophoresis of BlnI-digested chromosomal DNA of 19 Salmonella Senftenberg isolates from feeds and environmental samples yielded a single identical DNA pattern. Traceback information showed that all positive feed samples were from a single feed source. Timeline studies showed that Salmonella Senftenberg contamination occurred first mostly in the feeds and then spread to the environment and other farms. This study demonstrated that the prevalence of Salmonella Senftenberg contamination in commercial layer facilities in eastern Japan is very low. Moreover, feed contamination played a major role in the epizootiology and spread of this pathogen in commercial poultry flocks. Given the resilient and persistent nature of this particular Salmonella serotype, routine monitoring and strict quality control measures at the feed level are recommended to prevent the colonization of poultry facilities with Salmonella Senftenberg that may lead to future outbreaks.

A comparative study on invasion, survival, modulation of oxidative burst, and nitric oxide responses of macrophages (HD11), and systemic infection in chickens by prevalent poultry Salmonella serovars

Poultry is a major reservoir for foodborne Salmonella serovars. Salmonella Typhimurium, Salmonella Enteritidis, Salmonella Heidelberg, Salmonella Kentucky, and Salmonella Senftenberg are the most prevalent serovars in U.S. poultry. Information concerning the interactions between different Salmonella species and host cells in poultry is lacking. In the present study, the above mentioned Salmonella serovars were examined for invasion, intracellular survival, and their ability to modulate oxidative burst and nitric oxide (NO) responses in chicken macrophage HD11 cells. All Salmonella serovars demonstrated similar capacity to invade HD11 cells. At 24 h post-infection, a 36-43% reduction of intracellular bacteria, in log(10)(CFU), was observed for Salmonella Typhimurium, Salmonella Heidelberg, Salmonella Kentucky, and Salmonella Senftenberg, whereas a significantly lower reduction (16%) was observed for Salmonella Enteritidis, indicating its higher resistance to the killing by HD11 cells. Production of NO was completely diminished in HD11 cells infected with Salmonella Typhimurium and Salmonella Enteritidis, but remained intact when infected with Salmonella Heidelberg, Salmonella Kentucky, and Salmonella Senftenberg. Phorbol myristate acetate-stimulated oxidative burst in HD11 cells was greatly impaired after infection by each of the five serovars. When newly hatched chickens were challenged orally, a high rate (86-98%) of systemic infection (Salmonella positive in liver/spleen) was observed in birds challenged with Salmonella Typhimurium, Salmonella Enteritidis, Salmonella Heidelberg, and Salmonella Kentucky, while only 14% of the birds were Salmonella Senftenberg positive. However, there was no direct correlation between systemic infection and in vitro differential intracellular survival and modulation of NO response among the tested serovars.

Genome sequence of the persistent Salmonella enterica subsp. enterica serotype Senftenberg strain SS209

Salmonella enterica subsp. enterica serotype Senftenberg is an emerging serotype in poultry production which has been found to persist in animals and the farm environment. We report the genome sequence and annotation of the SS209 strain of S. Senftenberg, isolated from a hatchery, which was identified as persistent in broiler chickens.

Heterogeneity of persistence of Salmonella enterica serotype Senftenberg strains could explain the emergence of this serotype in poultry flocks

Salmonella enterica serotype Senftenberg (S. Senftenberg) has recently become more frequent in poultry flocks. Moreover some strains have been implicated in severe clinical cases. To explain the causes of this emergence in farm animals, 134 S. Senftenberg isolates from hatcheries, poultry farms and human clinical cases were analyzed. Persistent and non-persistent strains were identified in chicks. The non-persistent strains disappeared from ceca a few weeks post inoculation. This lack of persistence could be related to the disappearance of this serotype from poultry farms in the past. In contrast, persistent S. Senftenberg strains induced an intestinal asymptomatic carrier state in chicks similar to S. Enteritidis, but a weaker systemic infection than S. Enteritidis in chicks and mice. An in vitro analysis showed that the low infectivity of S. Senftenberg is in part related to its low capacity to invade enterocytes and thus to translocate the intestinal barrier. The higher capacity of persistent than non-persistent strains to colonize and persist in the ceca of chickens could explain the increased persistence of S. Senftenberg in poultry flocks. This trait might thus present a human health risk as these bacteria could be present in animals before slaughter and during food processing.

Development and validation of a drag swab method using tampons and different diluents for the detection of members of Salmonella in broiler houses

Members of the genus Salmonella represent a significant public health concern and also a colonizer of commercial poultry. Therefore, the early detection and management of colonized broiler breeders and their progeny is essential. There have been numerous methods for farm-based detection, with gauze-based drag swabs being the most commonly used. In the present study, the wet (boiled water, buffered peptone water and double-strength skin milk) tampon was compared with the gauze to determine the recovery rate (10(2) colony-forming units/swab) of five common poultry serovars of Salmonella and after cold (4°C/48 h) storage. The recovery was found to be equivalent when tested using the ISO6572:2002 method, for all diluents (Cohen's κ =1.0; sensitivity = 1.0; specificity = 1.0). The subsequent field trial (n = 15 farms) compared the tampon drag swab (TDS) with a statistically appropriate (90% confidence, detect 10% prevalence) number of faecal swabs (n = 22), which also showed high agreement between the TDS and faecal sampling (κ = 0.86; McNemar's χ(2) = 1.0; sensitivity = 0.9; specificity = 1.0). However, direct faecal sampling showed a wider diversity of serovars of Salmonella than the corresponding TDS. The TDS is a very sensitive, readily available and cost-effective screening method for salmonellas in broiler breeder houses. This TDS technique may be used for routinely screening of broiler houses, and faecal sampling would only be used to confirm colonization or contamination, and to measure flock serovar variance.

Molecular and comparative analysis of Salmonella enterica Senftenberg from humans and animals using PFGE, MLST and NARMS

BACKGROUND

Salmonella species are recognized worldwide as a significant cause of human and animal disease. In this study the molecular profiles and characteristics of Salmonella enterica Senftenberg isolated from human cases of illness and those recovered from healthy or diagnostic cases in animals were assessed. Included in the study was a comparison with our own sequenced strain of S. Senfteberg recovered from production turkeys in North Dakota. Isolates examined in this study were subjected to antimicrobial susceptibility profiling using the National Antimicrobial Resistance Monitoring System (NARMS) panel which tested susceptibility to 15 different antimicrobial agents. The molecular profiles of all isolates were determined using Pulsed Field Gel Electrophoresis (PFGE) and the sequence types of the strains were obtained using Multi-Locus Sequence Type (MLST) analysis based on amplification and sequence interrogation of seven housekeeping genes (aroC, dnaN, hemD, hisD, purE, sucA, and thrA). PFGE data was input into BioNumerics analysis software to generate a dendrogram of relatedness among the strains.

RESULTS

The study found 93 profiles among 98 S. Senftenberg isolates tested and there were primarily two sequence types associated with humans and animals (ST185 and ST14) with overlap observed in all host types suggesting that the distribution of S. Senftenberg sequence types is not host dependent. Antimicrobial resistance was observed among the animal strains, however no resistance was detected in human isolates suggesting that animal husbandry has a significant influence on the selection and promotion of antimicrobial resistance.

CONCLUSION

The data demonstrates the circulation of at least two strain types in both animal and human health suggesting that S. Senftenberg is relatively homogeneous in its distribution. The data generated in this study could be used towards defining a pathotype for this serovar.

Pulsed-field gel electrophoresis diversity of human and bovine clinical Salmonella isolates

Pulsed-field gel electrophoresis (PFGE) characterization of 335 temporally and spatially matched clinical, bovine, and human Salmonella enterica subsp. enterica isolates revealed 167 XbaI PFGE patterns. These isolates were previously classified into 51 serotypes and 73 sequence types, as determined by multilocus sequence typing. Discriminatory power of PFGE (Simpson's index, D = 0.991) was considerably higher than that of multilocus sequence typing (D = 0.920) or serotyping (D = 0.913). Although 128 PFGE types each only represented a single isolate, 8 PFGE types represented >4 isolates, including (i) three serotype Enteritidis and Heidelberg patterns that were only identified among human isolates, (ii) two PFGE patterns (each representing serotypes Bardo and Newport) that were significantly more common among bovine isolates as compared with human isolates; (iii) two PFGE types that each includes two serotypes (4,5,12:i:- and Typhimurium; Thompson and 1,7:-:1,5); and (iv) one PFGE type that includes eight Typhimurium isolates from humans and cattle. Characterization of isolates collected over multiple farm visits indicated that given specific PFGE types persisted over time on 11 farms. On an additional seven farms, isolates with a given sequence type represented multiple PFGE type, which typically only differed by <3 bands, suggesting PFGE type diversification during strain persistence. Sixteen PFGE types were isolated from 2 or more farms, including two widely distributed serotype Newport-associated PFGE types each found on 10 farms. In six instances two or three human isolates collected in the same county in the same or consecutive months represented the same subtypes, suggesting small human case clusters. PFGE-based characterization and surveillance of human and animal isolates can provide improved understanding of Salmonella diversity and epidemiology, including identification of possible host-associated and common, widely distributed PFGE types.

Mechanically ventilated broiler sheds: a possible source of aerosolized Salmonella, Campylobacter, and Escherichia coli

This study assessed the levels of two key pathogens, Salmonella and Campylobacter, along with the indicator organism Escherichia coli in aerosols within and outside poultry sheds. The study ranged over a 3-year period on four poultry farms and consisted of six trials across the boiler production cycle of around 55 days. Weekly testing of litter and aerosols was carried out through the cycle. A key point that emerged is that the levels of airborne bacteria are linked to the levels of these bacteria in litter. This hypothesis was demonstrated by E. coli. The typical levels of E. coli in litter were approximately 10(8) CFU g(-1) and, as a consequence, were in the range of 10(2) to 10(4) CFU m(-3) in aerosols, both inside and outside the shed. The external levels were always lower than the internal levels. Salmonella was only present intermittently in litter and at lower levels (10(3) to 10(5) most probable number [MPN] g(-1)) and consequently present only intermittently and at low levels in air inside (range of 0.65 to 4.4 MPN m(-3)) and once outside (2.3 MPN m(-3)). The Salmonella serovars isolated in litter were generally also isolated from aerosols and dust, with the Salmonella serovars Chester and Sofia being the dominant serovars across these interfaces. Campylobacter was detected late in the production cycle, in litter at levels of around 10(7) MPN g(-1). Campylobacter was detected only once inside the shed and then at low levels of 2.2 MPN m(-3). Thus, the public health risk from these organisms in poultry environments via the aerosol pathway is minimal.

Development of rapid detection and genetic characterization of salmonella in poultry breeder feeds

Salmonella is a leading cause of foodborne illness in the United States, with poultry and poultry products being a primary source of infection to humans. Poultry may carry some Salmonella serovars without any signs or symptoms of disease and without causing any adverse effects to the health of the bird. Salmonella may be introduced to a flock by multiple environmental sources, but poultry feed is suspected to be a leading source. Detecting Salmonella in feed can be challenging because low levels of the bacteria may not be recovered using traditional culturing techniques. Numerous detection methodologies have been examined over the years for quantifying Salmonella in feeds and many have proven to be effective for Salmonella isolation and detection in a variety of feeds. However, given the potential need for increased detection sensitivity, molecular detection technologies may the best candidate for developing rapid sensitive methods for identifying small numbers of Salmonella in the background of large volumes of feed. Several studies have been done using polymerase chain reaction (PCR) assays and commercial kits to detect Salmonella spp. in a wide variety of feed sources. In addition, DNA array technology has recently been utilized to track the dissemination of a specific Salmonella serotype in feed mills. This review will discuss the processing of feeds and potential points in the process that may introduce Salmonella contamination to the feed. Detection methods currently used and the need for advances in these methods also will be discussed. Finally, implementation of rapid detection for optimizing control methods to prevent and remove any Salmonella contamination of feeds will be considered.