Porins of Neisseria Meningitidis

Abstract

Neisseria meningitidis is a Gram-negative diplococcal bacterium responsible for causing septicaemia and meningococcal disease. It is carried commensally in the nasopharyngeal region by ~10% of the general population. It is unknown why the organism turns virulent and often meningococcal disease strikes those in the < 5 years and 15 - 20 years age groups, although infection can occur at any stage of life. Treatment of infection is with cephalosporins or penicillin, while prophylactic treatment of close contacts is with rifampin. The closest relative of Neisseria meningitidis is Neisseria gonorrhoeae, the organism responsible for causing gonorrhoea. N. meningitidis expresses two major porins in its outer membrane – PorA and PorB, while N. gonorrhoeae expresses one major porin in its outer membrane – PIA or PIB. These porins are 16-stranded beta-barrel monomeric proteins that are assembled into trimers and positioned within the outer membrane. To date there have been few studies which have examined the porin functions of PorA or PorB and determined their importance to the viability of the organism. In this study we were able to show that PorA plays no role in the viability of N. meningitidis and that it plays no role in the entry of antibiotics. A previously generated ¢9∆PorA (Peak, unpublished) strain and ¢9 wild type strain (Virji, et al., 1995) were used to conduct growth curves. Growth curve results showed that there was no significant difference in growth (when the strains were cultured in BHI broth supplemented with Levinthals (p >0.005), however when cultured in unsupplemented BHI broth, some timepoints were significantly different between the ¢9 and ¢9∆PorA strains. This could indicate that a nutrient (possibly iron) in the Levinthals supplement improved the growth of the ¢9∆PorA strain. MIC studies with these two strains showed that there was no difference between the two in terms of antibiotic entry and that PorA was not prone to phase variation under antibiotic selection.