Investigation of the basis for persistent porin serotypes of Neisseria gonorrhoeae /

by Garvin, Lotisha Erin

Title of Thesis: Investigation of the Basis for Persistent Porin Serotypes of Neisseria gonorrhoeae in Community Infections Lotisha Erin Garvin, Master Degree, 2006 Thesis directed by: Ann Jerse, Ph. D. Associate Professor, Department of Microbiology and Immunology Uniformed Services University Neisseria gonorrhoeae porin (por), a major outer membrane protein, has been studied extensively in vaccine research and is the basis of many gonococcal typing schemes. Epidemiological studies which utilize the porin-based typing method called variable region (VR) typing have shown certain VR types of the porB1A allele occur more frequently. Additionally, certain types may persist within communities as suggested by one study in which two P1A VR types were represented over ten years among isolates from two Baltimore clinics. Here we examined a set of isolates from this study to address the hypothesis that certain porin types give strains a functional advantage. Alternatively, porin may just be a marker of more fit clones. To investigate the issue of clonality, we utilized pulsed field gel electrophoresis (PFGE). Isolates of the first and second most common VR types (1;2;1;1;1 and 1;1;1;1,4;1, respectively) fell into a total of six different PFGE clusters, which were > 85% similar in band patterns. From these results, we concluded that a porin-mediated advantage may exist in these strains. The best characterized porin-mediated phenotype that may confer a fitness advantage is the capacity of some porins to mediate resistance to the bactericidal activity of normal human serum. Accordingly, we performed bactericidal assays to determine whether there is a link between VR type and serum resistance. Fifteen of 17 (88%) isolates with the two iii most common VR types were serum resistant, in contrast to 5 of 9 (55%) isolates with less common VR types. As a control, we also investigated a non porin-mediated phenotype that might confer an advantage to N. gonorrhoeae, namely the ability to use lactoferrin (LF) as an iron source. We found that 10 of 26 (38%) isolates had the capacity to use LF and, as predicted, the LF phenotype correlated closely with PFGE cluster but not VR type. Another interesting finding of our study was that isolates with a less common VR type (2;4;3;3;3), which appeared only during the first 3 years of this 10 year study, were both more serum sensitive and less able to use LF than other strains tested. Isolates of this transient VR type fell within a single cluster, and therefore may represent a strain that is functionally disadvantaged in at least two phenotypes. In conclusion, the persistence of certain VR types among P1A strains of various ancestral backgrounds is evidence that certain porins may play an important role in survival or transmission, perhaps due to conferring increased resistance to host complement. An increased understanding of the role of porin in pathogenesis may provide invaluable insight into the success of certain strains within communities and the study of porin as a possible vaccine target. iv