The Composition and Metabolic Phenotype of Neisseria gonorrhoeae Biofilms

review Article published: 18 April 2011 doi: 10.3389/fmicb.2011.00075 The composition and metabolic phenotype of Neisseria gonorrhoeae biofilms Megan L. Falsetta1†, Christopher T. Steichen1†, Alastair G. McEwan2, Christine Cho1, Margaret Ketterer1, Jianqiang Shao1, Jason Hunt1, Michael P. Jennings3 and Michael A. Apicella1* Department of Microbiology, The University of Iowa, Iowa City, IA, USA School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, Australia 3 Institute for Glycomics, Griffith University, Gold Coast, QLD, Australia 1 2 Edited by: Cynthia N. Cornelissen, Virginia Commonwealth University School of Medicine, USA Reviewed by: Robert A. Nicholas, University of North Carolina at Chapel Hill, USA Virginia Clark, University of Rochester, USA *Correspondence: Michael A. Apicella, Department of Microbiology, The University of Iowa, 51 Newton Road, BSB 3-403, Iowa City, IA 52242, USA. e-mail: Megan L. Falsetta and Christopher T. Steichen have contributed equally to this work. † Neisseria gonorrhoeae has been shown to form biofilms during cervical infection. Thus, biofilm formation may play an important role in the infection of women. The ability of N. gonorrhoeae to form membrane blebs is crucial to biofilm formation. Blebs contain DNA and outer membrane structures, which have been shown to be major constituents of the biofilm matrix. The organism expresses a DNA thermonuclease that is involved in remodeling of the biofilm matrix. Comparison of the transcriptional profiles of gonococcal biofilms and planktonic runoff indicate that genes involved in anaerobic metabolism and oxidative stress tolerance are more highly expressed in biofilm. The expression of aniA, ccp, and norB, which encode nitrite reductase, cytochrome c peroxidase, and nitric oxide reductase respectively, is required for mature biofilm formation over glass and human cervical cells. In addition, anaerobic respiration occurs in the substratum of gonococcal biofilms and disruption of the norB gene required for anaerobic respiration, results in a severe biofilm attenuation phenotype. It has been demonstrated that accumulation of nitric oxide (NO) contributes to the phenotype of a norB mutant and can retard biofilm formation. However, NO can also enhance biofilm formation, and this is largely dependent on the concentration and donation rate or steady-state kinetics of NO. The majority of the genes involved in gonococcal oxidative stress tolerance are also required for normal biofilm formation, as mutations in the following genes result in attenuated biofilm formation over cervical cells and/or glass: oxyR, gor, prx, mntABC, trxB, and estD. Overall, biofilm formation appears to be an adaptation for coping with the environmental stresses present in the female genitourinary tract. Therefore, this review will discuss the studies, which describe the composition and metabolic phenotype of gonococcal biofilms. Keywords: Neisseria gonorrhoeae, biofilm, DNA, thermonuclease, matrix, anaerobic, enzymes Introduction Gonococcal infection has been recognized by different human societies as a distinct disease for over 4,000 years (Handsfield and Sparling, 2005). Gonorrhea, the infection caused by the Neisseria gonorrhoeae, is the second most commonly reported notifiable disease in the United States today with 355,991 cases of gonorrhea reported in 2007 (Anonymous, 2008). The infection rate in the United States has not changed since 1994 (Anonymous, 2008). Gonococcal disease in young women (age 15–25) has many consequences including increasing the risk for infertility, ectopic pregnancy, tubo-ovarian abscesses, and HIV infection (Holmes et al., 1999). In some cities in the US, infection rates in this age group approaches and exceeds 1.5% of the population (Jennings et al., 2010). Annually worldwide, approximately 69 million new cases of gonorrhea occur with the greatest number in Southeast Asia and Sub-Saharan Africa (Gerbase et al., 1998). Infection in 99% of men is symptomatic and treatment is sought quickly (Holmes et al., 1999). In contrast, up to 40% of infected women frequently exhibit no noticeable symptoms and are susceptible to chronic complications from undiagnosed gonorrhea (Holmes et al., 1999; Anonymous, 2008). The reservoir of www.frontiersin.org asymptomatic infected individuals and antimicrobial resistance are two of the major contributors to the spread of gonorrhea (Holmes et al., 1999). Our laboratory has shown that cervical gonorrhea involves a biofilm component (Greiner et al., 2005; Steichen et al., 2008). This contributes to persistence, and it has been established in the literature that biofilms are inherently resistant to antimicrobials (Ceri et al., 1999; Schierholz et al., 1999; Dunne, 2002), although this has not been directly tested for Neisseria. We now have evidence that the gonococcal biofilm matrix is composed of shed N. gonorrhoeae outer membrane and DNA, which can be remodeled by a chromosomally encoded nuclease. In addition, nitric oxide (NO) appears to be a factor that stimulates biofilm dispersal (Falsetta et al., 2010). The consequences of gonorrhea are significant, negatively affecting the reproductive health of infected individuals and helping to increase the spread of other sexually transmitted diseases, such as HIV1 (Holmes et al., 1999). Since this organism is an obligate human pathogen, the potential to eliminate gonorrhea with an effective vaccine is theoretically possible. However, through its close association with the human, the organism has evolved a repertoire of mechanisms to evade the human immune system including April 2011 | Volume 2 | Article 75 | 1 Falsetta et al. antigenic and phase variation, molecular mimicry, resistance to host oxidative processes and the ability to incorporate DNA from its environment all of which make effective vaccine development problematic and unlikely to occur in the near future (Handsfield and Sparling, 2005). Two features of this infection make eradication very difficult: asymptomatic carriage and an increasing number of antimicrobial resistance strains (Holmes et al., 1999). Every decade since the 1950s, the CDC recommendations for the treatment of gonorrhea have become more aggressive and more expensive, from low dose penicillin G in the 1950s to comparatively expensive, injectable, long acting cephalosporins today (Anonymous, 2008). Resistance to these cephalosporins is now being reported (Bala and Sood, 2010; Golparian et al., 2010). Novel approaches to therapy are needed, and it is possible that greater understanding of the critical points in the pathogenesis of human infection, as well as improving the methods of diagnosis in asymptomatic women, may enable better multi-drug therapies to be applied. New multi-drug therapies would ideally reduce the emergence of resistance and eliminate the asymptomatic (female) carrier. Since its discovery in 1879 until the 1990s, N. gonorrhoeae w (...truncated)