PI/PD: Alex Duncan, Ph.D., M.D.
The University of North Carolina at Chapel Hill
Neisseria gonorrhoeae and Chlamydia trachomatis are two of the most common sexually transmitted pathogens in the world. N. gonorrhoeae depends on numerous, highly adapted host-pathogen interactions to persist in the human urogenital tract. Uncomplicated gonococcal infection of the urethra or cervix leads to limited, and non-protective, adaptive immune responses. The mechanisms by which N. gonorrhoeae evades host immunity are thought to include both antigenic variation and active manipulation of immune system signaling by the infecting bacteria. Our preliminary data demonstrates that N. gonorrhoeae inhibits the ability of antigen presenting cells to stimulate CD4+ T lymphocyte proliferation. N. gonorrhoeae accomplishes this through the shedding of outer membrane vesicles and anhydrous peptidoglycan fragments from its cell wall. Some C. trachomatis infected individuals appear to develop protective immunity to the infection. In animal models, CD4+ T lymphocytes directed towards chlamydial antigens can mediate protective immuniity in chlamydial infection. Our preliminary data suggest that N. gonorrhoeae is able to cross suppress T lymphocyte proliferation directed towards chlamydial antigens. We propose to identify the signaling mechanisms and consequences to the immune response that are activated by N. gonorrheoeae. Further we will determine the impact of N. gonorrhoeae-mediated immune suppression in both N. gonorrhoeae infection and N. gonorrhoeae/Chlamydia co-infection.
PI/PD: Robert Nicholas, Ph.D.
University of North Carolina at Chapel Hill
PI/PD: William Shafer, Ph.D.
The sexually transmitted human pathogens Neisseria gonorrhoeae and Chalmydia tracomatis each cause over 100 million infections worldwide each year. Since the 1940s individuals with gonorrhea have been cured of this disease by antibiotic therapy, which commonly includes treatment with antimicrobials against chlamydial co-infections. However, with the recent emergence of ceftriaxone-resistant (CroR) strains of N. gonorrhoeae, it is of great concern that in the absence of new antibiotics, gonorrhea may soon become an untreatable disease. The central hypothesis of this proposal is that antibiotic-resistant variants of N. gonorrhoeae evolve due to the selective pressure exerted by both antibiotic therapy and host antimicrobials that are produced during infection. We further posit that mutations in penicillin-binding protein 2 (PBP2), the lethal target of ceftriaxone, can negatively influence in vivo fitness, but that compensatory mutations develop to reverse this defect. To test these hypotheses, we will examine the fitness consequences for gonococci when they acquire resistance to cephalosporins. Ceftriaxone-resistant (CroR) gonococcal strains obtained from patients differ from susceptible strains in two ways: a) they contain a highly mosaic penA allele (e.g., penA41) encoding an extensively remodeled PBP2 that is poorly acylated by ceftriaxone, and b) they have regulatory mtr mutations that enhance expression of the MtrC-MtrD-MtrE efflux pump operon and confer resistance to host-derived antimicrobials, including cationic antimicrobial peptides (CAMPs), and antibiotics, including beta-lactams. Our preliminary data reveal that strains harboring a mosaic penA have a fitness defect compared to wild-type strains both in vitro and in the female mouse model of gonococcal infection, thereby reducing their potential for persistence in the host and transmission in the community, but that they acquire mutations that increase their biological fitness, potentially mimicking what occurs in humans. We aim to: i) identify the mutation(s) in compensatory mutants of FA19 penA41 and elucidate the mechanisms by which these mutations increase fitness (Specific Aim 1); ii) define the role of mtr mutations in fitness of gonococci with a mosaic penA allele and identify the changes in transcription following acquisition of a mosaic penA allele (Specific Aim 2); and iii) examine if genes known to be important in gonococcal resistance to CAMPs (e.g. mtr or lptA) contribute to fitness advantages in CroRpenA mutant strains, particularly under conditions (e.g. during a chlamydial co-infection) that decrease the production of CAMPs in the host (Specific Aim 3). We also employ biochemical studies to define the alterations in peptidoglycan structure due to acquisition of a mosaic penA allele and to delineate whether the changes in peptidoglycan structure alter pro-inflammatory responses in host cells. Working closely with other members of the AC STI CRC, we will employ an experimental murine model of gonococcal infection, including co-infection with Chlamydia, to test the importance of the host response in the selection of CroR gonococci with enhanced fitness during infection. The results obtained from our work will advance our knowledge of the factors important in the emergence and spread of antibiotic resistant gonococci, as well as provide insights for the development of novel antimicrobials effective against such strains. Such studies are critical in this era when antibiotic resistance threatens the future of effective therapy against gonorrhea.