Association of a Bacteriophage with Meningococcal Disease in Young Adults

Despite being the agent of life-threatening meningitis, Neisseria meningitidis is usually carried asymptomatically in the nasopharynx of humans and only occasionally causes disease. The genetic bases for virulence have not been entirely elucidated and the search for new virulence factors in this species is hampered by the lack of an animal model representative of the human disease. As an alternative strategy we employ a molecular epidemiological approach to establish a statistical association of a candidate virulence gene with disease in the human population. We examine the distribution of a previously-identified genetic element, a temperate bacteriophage, in 1288 meningococci isolated from cases of disease and asymptomatic carriage. The phage was over-represented in disease isolates from young adults indicating that it may contribute to invasive disease in this age group. Further statistical analysis indicated that between 20% and 45% of the pathogenic potential of the five most common disease-causing meningococcal groups was linked to the presence of the phage. In the absence of an animal model of human disease, this molecular epidemiological approach permitted the estimation of the influence of the candidate virulence factor. Such an approach is particularly valuable in the investigation of exclusively human diseases

A Unique Regulator Contributes to Quorum Sensing and Virulence in Burkholderia cenocepacia

Burkholderia cenocepacia causes chronic and life-threatening respiratory infections in immunocompromized people. The B. cenocepacia N-acyl-homoserine lactone (AHL)-dependent quorum sensing system relies on the production of AHLs by the synthases CepI and CciI while CepR, CciR and CepR2 control expression of many genes important for pathogenesis. Downstream from, and co-transcribed with cepI, lies BCAM1871 encoding a hypothetical protein that was uncharacterized prior to this study. Orthologs of B. cenocepacia BCAM1871 are uniquely found in Burkholderia spp and are conserved in their genomic locations in pathogenic Burkholderia. We observed significant effects on AHL activity upon mutation or overexpression of BCAM1871, although these effects were more subtle than those observed for CepI indicating BCAM1871 acts as an enhancer of AHL activity. Transcription of cepI, cepR and cciIR was significantly reduced in the BCAM1871 mutant. Swimming and swarming motilities as well as transcription of fliC, encoding flagellin, were significantly reduced in the BCAM1871 mutant. Protease activity and transcription of zmpA and zmpB, encoding extracellular zinc metalloproteases, were undetectable in the BCAM1871 mutant indicating a more significant effect of mutating BCAM1871 than cepI. Exogenous addition of OHL restored cepI, cepR and fliC transcription but had no effect on motility, protease activity or zmpA or zmpB transcription suggesting AHL-independent effects. The BCAM1871 mutant exhibited significantly reduced virulence in rat chronic respiratory and nematode infection models. Gene expression and phenotypic assays as well as vertebrate and invertebrate infection models showed that BCAM1871 significantly contributes to pathogenesis in B. cenocepacia

Purification and partial characterization of the OmpA family of proteins of Pasteurella haemolytica

This study was conducted to partially characterize and identify the purity of two major outer membrane proteins (OMPs) (with molecular weights of 32,000 and 35,000 [32K and 35K, respectively]) of Pasteurella haemolytica. The 35K and 32K major OMPs, designated Pasteurella outer membrane proteins A and B (PomA and PomB, respectively), were extracted from P. haemolytica by solubilization in N-octyl polyoxyl ethylene. The P. haemolytica strain used was a mutant serotype A1 from which the genes expressing the 30-kDa lipoproteins had been deleted. PomA and PomB were separated and partially purified by anion-exchange chromatography. PomA but not PomB was heat modifiable. The N-terminal amino acid sequences of the two proteins were determined and compared with reported sequences of other known proteins. PomA had significant N-terminal sequence homology with the OmpA protein of Escherichia coli and related proteins from other gram-negative bacteria. Moreover, polyclonal antiserum raised against the E. coli OmpA protein reacted with this protein. PomA was surface exposed, was conserved among P. haemolytica biotype A serotypes, and had porin activity in planar bilayers. No homology between the N-terminal amino acid sequence of PomB and those of other known bacterial proteins was found. Cattle vaccinated with live P. haemolytica developed a significant increase in serum antibodies to partially purified PomA, as shown by enzyme-linked immunosorbent assays, and to purified PomA and PomB, as detected on Western blots and by densitometry.Peer reviewedAnatomy, Pathology and PharmacologyInfectious Disease and Physiolog