In vitro invasion capacity of Salmonella Typhimurium DT9 isolates sourced from humans and layer hen environments.

In Australia, Salmonella Typhimurium definitive type 9 is frequently isolated during foodborne outbreaks of salmonellosis. Multiple-locus variable number tandem repeat analysis (MLVA) trace back investigations frequently identify isolate distribution patterns that may be epidemiologically linked to disease outbreaks. In this study, the in vitro virulence potential of S. Typhimurium DT9 isolates possessing different MLVA patterns (03 15 07 11 550, 03 24 11 10 523, 03 15 08 11 550 and 03 14 08 11 550) isolated from either humans or layer hens was assessed using a human colon carcinoma cell line. Four strains per MLVA from each host for a total of 32 isolates were included in these experiments. Bacteria were grown to stationary phase and added to cells at a multiplicity of infection of 100. Across all isolates, mean percent recovery ranged from 7.1 ± 1.1 to 33.3 ± 7.1%. The layer hen isolate, KC900 (MLVA profile 03 15 08 11 550), exhibited the greatest invasion with a mean percent recovery of 33.3 ± 7.1%. Overall, layer hen isolates of S. Typhimurium DT9 had significantly higher invasion into Caco2 cells than human isolates (p = .0021). RAPD and enterobacterial repetitive intergenic consensus genomic fingerprinting was also performed. Irrespective of source, the SalmonellaDT9 isolates included in this study exhibited similar fingerprint patterns.

The genome of murine cytomegalovirus is shaped by purifying selection and extensive recombination.

The herpesvirus lifestyle results in a long-term interaction between host and invading pathogen, resulting in exquisite adaptation of virus to host. We have sequenced the genomes of nine strains of murine cytomegalovirus (a betaherpesvirus), isolated from free-living mice trapped at locations separated geographically and temporally. Despite this separation these genomes were found to have low levels of nucleotide variation. Of the more than 160 open reading frames, almost 90% had a dN/dS ratio of amino acid substitutions of less than 0.6, indicating the level of purifying selection on the coding potential of MCMV. Examination of selection acting on individual genes at the codon level however indicates some level of positive selection, with 0.03% of codons showing strong evidence for positive selection. Conversely, 1.3% of codons show strong evidence of purifying selection. Alignments of both genome sequences and coding regions suggested that high levels of recombination have shaped the MCMV genome.

Laboratory strains of murine cytomegalovirus are genetically similar to but phenotypically distinct from wild strains of virus.

Murine cytomegalovirus (MCMV) is widely used to model human cytomegalovirus (HCMV) infection. However, it is known that serially passaged laboratory strains of HCMV differ significantly from recently isolated clinical strains of HCMV. It is therefore axiomatic that clinical models of HCMV using serially passaged strains of MCMV may not be able to fully represent the complexities of the system they are attempting to model and may not fully represent the complex biology of MCMV. To determine whether genotypic and phenotypic differences also exist between laboratory strains of MCMV and wild derived strains of MCMV, we sequenced the genomes of three low-passage strains of MCMV, plus the laboratory strain, K181. We coupled this genetic characterization to their phenotypic characteristics. In contrast to what is seen with HCMV (and rhesus CMV), there were no major genomic rearrangements in the MCMV genomes. In addition, the genome size was remarkably conserved between MCMV strains with no major insertions or deletions. There was, however, significant sequence variation between strains of MCMV, particularly at the genomic termini. These more subtle genetic differences led to considerable differences in in vivo replication with some strains of MCMV, such as WP15B, replicating preferentially in otherwise-MCMV-resistant C57BL/6 mice. CBA mice were no more resistant to MCMV than C57BL/6 mice and for some MCMV strains appeared to control infection less well than C57BL/6 mice. It is apparent that the previously described host resistance patterns of inbred mice and MCMV are not consistently applicable for all MCMV strains.