Prevalence and virulence characteristics of enteroaggregative Escherichia coli in a case-control study among patients from Iran.

Enteroaggregative Escherichia coli (EAEC) is an important agent of diarrhoeal diseases worldwide. The role of EAEC virulence factors in the clinical outcome of infection is not completely defined. This case-control study investigated the prevalence of EAEC, its virulence genes and the antimicrobial resistance profile of adult patients with and without diarrhoea attending three different hospitals in Zanjan, Iran. A total of 550 individual stool specimens (350 from diarrhoeal patients and 200 from patients without diarrhoea) were collected. One hundred and forty-one EAEC isolates were identified by a HEp-2 cell assay and PCR. EAEC isolates were detected with slightly higher frequency in patients with (27.7%) than in patients without (22%) diarrhoea (P ≥ 0.05). The EAEC genes aggR, aap and pet were identified more frequently in case patients compared with controls (P ≤ 0.05). Many of the EAEC isolates from the diarrhoeal patients had two or more virulence genes compared with those without diarrhoea (P ≤ 0.05). EAEC isolates exhibited high-level resistance to amoxicillin (82.3%), co-amoxiclav (78%), aztreonam (73.8%), tetracycline (66.6%) and ceftazidime (63.8%). In addition, 53.2% of isolates were resistant to at least three different classes of antimicrobial agents and were considered to be multidrug resistant. These results indicate a high prevalence and heterogeneity of gene profiles of EAEC in diarrhoeal and control patients, and suggest that the presence of aggR, aap and pet, the number of genes present and the antimicrobial resistance profile may be markers for more-virulent EAEC isolates.

Identification of a virulence-related surface protein XF in piscine Streptococcus agalactiae by pre-absorbed immunoproteomics.

BACKGROUND: Since 2009, large-scale Streptococcus agalactiae infections have broken out in cultured tilapia farms in China, resulting in considerable economic losses. Screening of the surface proteins is required to identify virulence factors or protective antigens involved in piscine S.agalactiae infections in tilapia. Pre-absorbed immunoproteomics method (PAIM) is a useful method previously established in our laboratory for identifying bacterial surface proteins. RESULTS: A serine-rich repeat protein family 1 (Srr-1), designated XF, was identified by PAIM in piscine S. agalactiae isolate GD201008-001. To investigate the role of XF in the pathogenesis of piscine S. agalactiae, an isogenic xf mutant strain (Δxf) and a complemented strain (CΔxf) were successfully constructed. The Δxf mutant and CΔxf showed no significant differences in growth characteristics and adherence to HEp-2 cells compared with the wild-type strain. However the 50% lethal dose of Δxf was increased (4-fold) compared with that of the parental strain in a zebrafish infection model. CONCLUSIONS: The findings demonstrated that XF is a virulence-related, highly immunoreactive surface protein and is involved in the pathogenicity of S. agalactiae infections in fish.

Contributions of six lineage-specific internalin-like genes to invasion efficiency of Listeria monocytogenes.

Listeria monocytogenes strains are divided into at least three lineages, which seem to differ in virulence. Internalins are surface-attached or secreted proteins that encode leucine-rich repeats, and L. monocytogenes encodes species-specific as well as lineage-specific internalin and internalin-like genes. Internalins A and B have previously been shown to be critical for L. monocytogenes host cell invasion. Transcription of selected internalins is regulated by the virulence gene regulator PrfA and/or the stress-responsive alternative sigma factor sigma(B). We hypothesized that lineage-specific internalin-like genes may contribute to differential virulence and niche adaptation of the L. monocytogenes lineages. Initial quantitative real time, reverse transcriptase PCR (RT-PCR) showed that the six selected lineage-specific internalin-like genes were transcribed in cells grown at 16 degrees and 37 degrees C. Lineage-specific internalin-like gene, lineage II (lsiIIX) showed significantly higher transcript levels in log-phase cells grown at 37 degrees C as compared to 16 degrees C. The gene lsiIA was preceded by a putative sigma(B)-dependent promoter and showed sigma(B)-dependent transcription. None of the null mutants in lineage-specific internalin-like genes differed from their respective parent strain in ability to invade either human intestinal epithelial or hepatocyte-like cell lines. All three mutants in lineage I-specific internalin-like genes exhibited the same growth condition-dependent invasion phenotype as their parent strain ( approximately 1.5 log higher invasion efficiency when grown at 30 degrees C without aeration versus 37 degrees C with aeration). Despite structural similarities to internalins with known roles in host cell attachment and invasion, none of the six lineage-specific internalin-like genes characterized here appear to contribute to invasion. Combined with the observation that some nonpathogenic Listeria species also carry internalin genes, our findings suggest a broad role of Listeria internalins, not limited to attachment and invasion of human cells. Due to the wide host range of L. monocytogenes and the fact that transcription of internalin-like genes can differ considerably depending on growth condition, elucidating the function of different internalins and internalin-like genes will remain a challenge.