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Salmonella is a common cause of human foodborne illness, which is frequently associated with consumption of contaminated or undercooked poultry meat. Serotype Infantis is among the most common serotypes isolated from poultry meat products globally. Isolates of serotype Infantis carrying the pESI plasmid, the most dominant strain of Infantis, have been shown to exhibit oxidizer tolerance. Therefore, 16 strains of Salmonella with and without pESI carriage were investigated for susceptibility to biocide chemical processing aids approved for use in US poultry meat processing: peracetic acid (PAA), cetylpyridinium chloride (CPC), calcium hypochlorite, and sodium hypochlorite. Strains were exposed for 15 s to simulate spray application and 90 min to simulate application in an immersion chiller. All strains tested were susceptible to all concentrations of PAA, CPC, and sodium hypochlorite when applied for 90 min. When CPC, calcium hypochlorite, and sodium hypochlorite were applied for 15 s to simulate spray time, strains responded similarly to each other. However, strains responded variably to exposure to PAA. The variation was not statistically significant and appears unrelated to pESI carriage. Results highlight the necessity of testing biocide susceptibility in the presence of organic material and in relevant in situ applications. [ABSTRACT FROM AUTHOR]

The bacterium Helicobacter pylori is remarkable for its ability to persist in the human stomach for decades without provoking sterilizing immunity. Since repetitive DNA can facilitate adaptive genomic flexibility via increased recombination, insertion, and deletion, we searched the genomes of two H. pylori strains for nucleotide repeats. We discovered a family of genes with extensive repetitive DNA that we have termed the H. pylori RD gene family. Each gene of this family is composed of a conserved 3' region, a variable mid-region encoding 7 and 11 amino acid repeats, and a 5' region containing one of two possible alleles. Analysis of five complete genome sequences and PCR genotyping of 42 H. pylori strains revealed extensive variation between strains in the number, location, and arrangement of RD genes. Furthermore, examination of multiple strains isolated from a single subject's stomach revealed intrahost variation in repeat number and composition. Despite prior evidence that the protein products of this gene family are expressed at the bacterial cell surface, enzyme-linked immunosorbent assay and immunoblot studies revealed no consistent seroreactivity to a recombinant RD protein by H. pylori-positive hosts. The pattern of repeats uncovered in the RD gene family appears to reflect slipped-strand mispairing or domain duplication, allowing for redundancy and subsequent diversity in genotype and phenotype. This novel family of hypervariable genes with conserved, repetitive, and allelic domains may represent an important locus for understanding H. pylori persistence in its natural host. doi:10.1128/JB.00706-09

Inheritance, mutation and horizontal gene transfer in Listeria monocytogenes and the recombinant construction of mosaic genes in three different patterns for each of the three Listeria monocytogenes lineages is studied using multilocus sequence typing analysis. Results show that the different lineages of Listeria monocytogenes can share habitats but their horizontal gene transfer histories are different.

The flaA and flaB flagellin genes of Campylobacter are not entirely identical. One segment of the flagellin sequence evolves while the other segment is maintained by conversion or recombination.

A reliable and standardized classification of Listeria monocytogenes is important for accurate strain identification during outbreak investigations. Current whole-genome sequencing (WGS)-based approaches for strain characterization are either difficult to standardize, rendering them less suitable for data exchange, or are not freely available. Thus, we developed a portable and open-source tool, Haplo-ST, to improve standardization and provide maximum discriminatory potential to WGS data tied to a multilocus sequence typing (MLST) framework. Haplo-ST performs whole-genome MLST (wgMLST) for L. monocytogenes while allowing for data exchangeability worldwide. This tool takes in (i) raw WGS reads as input, (ii) cleans the raw data according to user-specified parameters, (iii) assembles genes across loci by mapping to genes from reference strains, and (iv) assigns allelic profiles to assembled genes and provides a wgMLST subtyping for each isolate. Data exchangeability relies on the tool assigning allelic profiles based on a centralized nomenclature defined by the widely used BIGSdb-Lm database. Tests of Haplo-ST's performance with simulated reads from L. monocytogenes reference strains demonstrated high sensitivity (97.5%), and coverage depths of ≥20X were found to be sufficient for wgMLST profiling. We then used Haplo-ST to characterize and differentiate between two groups of L. monocytogenes isolates derived from the natural environment and poultry processing plants. Phylogenetic reconstruction identified lineages within each group, and no lineage specificity was observed with isolate phenotypes (transient versus persistent) or origins. Genetic differentiation analyses between isolate groups identified 21 significantly differentiated loci, potentially enriched for adaptation and persistence of L. monocytogenes within poultry processing plants. [ABSTRACT FROM AUTHOR]

Bactivory by protozoa is a major factor that limits the number of bacteria in nature and may control the presence of Listeria monocytogenes. The effectiveness of Tetrahymena pyriformis destruction of L. monocytogenes was measured. Within 1 hr, 35–40 T. pyriformis cells ingested an average of 1,219 CFU of L. monocytogenes. Gentamicin was then added to kill un‐ingested Listeria. In 24 hr, the recoverable bacteria were reduced at an exponential rate to undetectable levels (<1 per culture). A genetically diverse set of L. monocytogenes cultures all reduced Listeria recovery by the same degree. In assays without addition of gentamicin, numbers of attached L. monocytogenes cells were lessened from an average of log 6.5 CFU/2 ml culture to log 4.7 CFU/2 ml culture. T. pyriformis was capable of lowering numbers of both free‐swimming and attached L. monocytogenes. This technology may have applications to control L. monocytogenes in food processing environments. [ABSTRACT FROM AUTHOR]

The prevalence of kanamycin resistance ([Kan.sup.r]) ColE1-like plasmids in Salmonella serovars is studied. The ColE1-like plasmids have played a vital role in transmission of antibiotic resistance genes among enteric pathogens due to their high copy number and mobility.

The microarray comparative genomic hybridization methodology is employed to study the evolution of the various Campylobacter coli isolated obtained from multiple hosts. The molecular variance associated with these isolates is also analyzed.

A pulsed-field gel electrophoresis (PFGE) method was used to characterize a collection of 437 Salmonella enterica isolates from different animal sources for their antimicrobial resistance phenotypes and plasmid replicon types and gain insight into the distribution of multidrug resistance in relation to replicon types. The results indicated that some strains, particularly serovar Typhimurium and closely related types might have once carried the plasmid but the resistance genes were transferred to the chromosome with the subsequent loss of the plasmid.

The DNA sequence of a flaA short variable region (SVR) was used to analyze random population of Campylobacter isolates to investigate the weakly clonal population structure of members of the genus. The rate of migration between populations appears to limit the distribution of sequences and results in a weakly clonal population structure.