Virginia L. Clark, Ph.D.

Research Overview
Neisseria gonorrhoeae (GC) is the etiologic agent of gonorrhea, still one of the most prevalent infectious diseases in the U.S. Untreated infections in women can lead to pelvic inflammatory disease (PID), a significant cause of infertility in this country. N. gonorrhoeae is often isolated along with obligate anaerobes, which presents a conundrum, as the gonococcus has been considered to be an obligate aerobe. We demonstrated that GC is actually a facultative anaerobic that can utilize nitrite as a terminal electron acceptor. An examination of genes that are only expressed anaerobically may reveal new virulence factors that are important in gonococcal pathogenesis.

N. gonorrhoeae grows anaerobically by using the central two reactions of the denitrification pathway, reduction of nitrite by AniA and reduction of nitric oxide by NorB. The gonococcus does not produce energy from these two reactions, but the pathway does enable the organism to maintain an oxidation/reduction balance anaerobically. The presence of AniA and NorB allows the gonococcus to produce and degrade nitric oxide (NO), known to be an important modulator of the host innate immune system and signal transduction pathways. This ability to keep NO at a low level may be responsible for the fact that most gonococcal infections in women are asymptomatic.

We are using a combination of genetic, physiologic, and cell biology techniques to better understand the role of the denitrification pathway in gonococcal virulence. We have elucidated the regulatory pathway for aniA and have identified the regulator of norB. Regulation of these two genes is complex, involving 2 activators and 3 repressors of transcription. We are currently working to identify the anaerobic regulon and the function of anaerobically regulated genes.

We have determined that gonococci establish a NO steady state in the presence of a long half-lived NO donor, reducing the NO level from a pro-inflammatory concentration to an anti-inflammatory concentration. Thus. NO metabolism may enable gonococci to alter the host immune response. NO and its relative peroxynitrite are reactive nitrogen species that are toxic to many bacteria. We have determined that gonococci are highly resistant to the toxic effects of both of these compounds. We are currently working to identify the mechanism of peroxynitrite resistance in N. gonorrhoeae.