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Background For many putative Salmonella enterica subsp. enterica virulence genes, functional characterization across serovars has been limited. Cytolethal distending toxin B (CdtB) is an incompletely characterized virulence factor that is found not only in Salmonella enterica subsp. enterica serovar Typhi (Salmonella Typhi) and dozens of Gram negative bacterial pathogens, but also in non-typhoidal Salmonella (NTS) serovars. Methods A comparative genomics approach was performed to characterize sequence conservation of the typhoid toxin (TT), encoded in the CdtB-islet, between Salmonella Typhi and NTS serovars. The cytotoxic activity of representative Salmonella enterica subsp. enterica serovars Javiana, Montevideo and Schwarzengrund strains and their respective isogenic cdtB mutants was determined in human intestinal epithelial Henle-407 cells by assessment of cell cycle progression of infected cells using fluorescence-activated cell sorting (FACS). Two-way analysis of variance (ANOVA) was used to determine whether cdtB deletion had a significant (p < 0.05) effect on the percentage of Henle-407 cells at each stage of the cell cycle. Results Here we show that a CdtB-islet encoding the cytolethal distending toxin B (CdtB), pertussis-like toxin A (PltA), and pertussis-like toxin B (PltB) is present in a dozen NTS serovars and that these proteins have a high level of sequence conservation and each form monophyletic clades with corresponding Salmonella Typhi genes. Human epithelial Henle-407 cells infected with three representative CdtB-encoding NTS serovars displayed G.sub.2/M phase cell cycle arrest that was absent in cells infected with corresponding isogenic cdtB null mutants (p < 0.0001 for the factor [DELA]cdtB deletion). Conclusion Our results show that CdtB encoded by NTS serovars has a genomic organization, amino acid sequence conservation and biological activity similar to the TT, and thus, may contribute to disease pathogenesis. Keywords: Salmonella, Non-typhoidal, Typhi, Toxin, Typhoid toxin, CdtB, PltA, PltB, Author(s): Lorraine D Rodriguez-Rivera[sup.1,3] , Barbara M Bowen[sup.1] , Henk C den Bakker[sup.1,4] , Gerald E Duhamel[sup.2] and Martin Wiedmann[sup.1] Background The cytolethal distending toxin B (CdtB) is a recently [...]

Abstract Background Divergence of bacterial populations into distinct subpopulations is often the result of ecological isolation. While some studies have suggested the existence of Salmonella enterica subsp. enterica subclades, evidence for these subdivisions has been ambiguous. Here we used a comparative genomics approach to define the population structure of Salmonella enterica subsp. enterica, and identify clade-specific genes that may be the result of ecological specialization. Results Multi-locus sequence analysis (MLSA) and single nucleotide polymorphisms (SNPs) data for 16 newly sequenced and 30 publicly available genomes showed an unambiguous subdivision of S. enterica subsp. enterica into at least two subpopulations, which we refer to as clade A and clade B. Clade B strains contain several clade-specific genes or operons, including a β-glucuronidase operon, a S-fimbrial operon, and cell surface related genes, which strongly suggests niche specialization of this subpopulation. An additional set of 123 isolates was assigned to clades A and B by using qPCR assays targeting subpopulation-specific SNPs and genes of interest. Among 98 serovars examined, approximately 20% belonged to clade B. All clade B isolates contained two pathogenicity related genomic islands, SPI-18 and a cytolethal distending toxin islet; a combination of these two islands was previously thought to be exclusive to serovars Typhi and Paratyphi A. Presence of β-glucuronidase in clade B isolates specifically suggests an adaptation of this clade to the vertebrate gastrointestinal environment. Conclusions S. enterica subsp. enterica consists of at least two subpopulations that differ specifically in genes involved in host and tissue tropism, utilization of host specific carbon and nitrogen sources and are therefore likely to differ in ecology and transmission characteristics.

Abstract Background The bacterium Salmonella enterica includes a diversity of serotypes that cause disease in humans and different animal species. Some Salmonella serotypes show a broad host range, some are host restricted and exclusively associated with one particular host, and some are associated with one particular host species, but able to cause disease in other host species and are thus considered "host adapted". Five Salmonella genome sequences, representing a broad host range serotype (Typhimurium), two host restricted serotypes (Typhi [two genomes] and Paratyphi) and one host adapted serotype (Choleraesuis) were used to identify core genome genes that show evidence for recombination and positive selection. Results Overall, 3323 orthologous genes were identified in all 5 Salmonella genomes analyzed. Use of four different methods to assess homologous recombination identified 270 genes that showed evidence for recombination with at least one of these methods (false discovery rate [FDR] ompC, a gene encoding an outer membrane protein, which has also been found to be under positive selection in other bacteria. A total of 8, 16, 7, and 5 genes showed evidence for positive selection in Choleraesuis, Typhi, Typhimurium, and Paratyphi branch analyses, respectively. Sequencing and evolutionary analyses of four genes in an additional 42 isolates representing 23 serotypes confirmed branch specific positive selection and recombination patterns. Conclusion Our data show that, among the four serotypes analyzed, (i) less than 10% of Salmonella genes in the core genome show evidence for homologous recombination, (ii) a number of Salmonella genes are under positive selection, including genes that appear to contribute to virulence, and (iii) branch specific positive selection contributes to the evolution of host restricted Salmonella serotypes.

There are few epidemiologic studies on the shedding of Campylobacter among dogs in the United States, despite the potential public health implications. Our objectives were to estimate the prevalence of faecal Campylobacter shedding among Texas shelter dogs as detected by culture methods and to characterize the isolates by species and antimicrobial susceptibility. Using a cross‐sectional study design, faecal samples were collected from 185 dogs in six animal shelters throughout Texas between May and December 2014. Four culture methods were used to isolate Campylobacter from samples, and isolates were characterized. The prevalence of Campylobacter shedding was 45.4% (84/185; 95% CI, 38.1%–52.9%). Of 294 isolates from the 84 positive dogs, 26 (8.8%) isolates from seven dogs were identified as Campylobacter jejuni. Two of the isolates from one dog demonstrated resistance to ciprofloxacin and nalidixic acid. Direct plating on mCCDA‐CAT agar without enrichment identified the highest number of positive dogs (62%; 52/84). Incidence of ciprofloxacin‐resistant Campylobacter infections among humans has increased over the last several years. Canine shedding of Campylobacter is a potential source of zoonotic transmission. [ABSTRACT FROM AUTHOR]

The population size and geographic range of feral pigs in the United States are rapidly expanding. Nevertheless, the role of this invasive species in the ecology and transmission of zoonotic enteric pathogens is poorly understood. Our objectives were to describe the prevalence and diversity of Cryptosporidium and Giardia shedding among feral pigs throughout Texas and to identify risk factors for infection. Fecal samples were collected from feral pigs in Texas from February 2014 through May 2015. Cryptosporidium oocysts and Giardia cysts were detected using a direct immunofluorescence assay, and genotyping of positive samples was performed. The prevalence of Cryptosporidium shedding was 1.6% (6/370), and C. scrofarum and C. suis were identified. The prevalence of Giardia shedding was 4.3% (16/370), and assemblages A and E were identified. Cryptosporidium shedding was significantly more common among juvenile and subadult pigs than among adult pigs, but age group was not associated with Giardia shedding status. Feral pigs may serve as a source of Cryptosporidium and Giardia transmission to humans and livestock. [ABSTRACT FROM AUTHOR]

The genetic diversity represented by >2,500 different Salmonella serovars provides a yet largely uncharacterized reservoir of mobile elements that can contribute to the frequent emergence of new pathogenic strains of this important zoonotic pathogen. Currently, our understanding of Salmonella mobile elements is skewed by the fact that most studies have focused on highly virulent or common serovars. To gain a more global picture of mobile elements in Salmonella, we used prediction algorithms to screen for mobile elements in 16 sequenced Salmonella genomes representing serovars for which no prior genome scale mobile element data were available. From these results, selected mobile elements underwent further analyses in the form of validation studies, comparative analyses, and PCR-based population screens. Through this analysis we identified a novel plasmid that has two cointegrated replicons (IncI1-IncFIB); this plasmid type was found in four genomes representing different Salmonella serovars and contained a virulence gene array that had not been previously identified. A Salmonella Montevideo isolate contained an IncHI and an IncN2 plasmid, which both encoded antimicrobial resistance genes. We also identified two novel genomic islands (SGI2 and SGI3), and 42 prophages with mosaic architecture, seven of them harboring known virulence genes. Finally, we identified a novel integrative conjugative element (ICE) encoding a type IVb pilus operon in three non-typhoidal Salmonella serovars. Our analyses not only identified a considerable number of mobile elements that have not been previously reported in Salmonella, but also found evidence that these elements facilitate transfer of genes that were previously thought to be limited in their distribution among Salmonella serovars. The abundance of mobile elements encoding pathogenic properties may facilitate the emergence of strains with novel combinations of pathogenic traits. [ABSTRACT FROM AUTHOR]