Insights into the Enhanced in vivo Fitness of Neisseria gonorrhoeae Driven by a Fluoroquinolone Resistance-Conferring Mutant DNA Gyrase

Abstract

With no vaccine available, control of gonorrhea is seriously threatened by the evolution of heightened antibiotic resistance. The fluoroquinolone class of antibiotics served as a first-line treatment option for gonorrhea for only a limited period of time due to the proliferation of resistance mutations. Resistance to fluoroquinolones in Neisseria gonorrhoeae is achieved in a two-step process in which mutations in the quinolone resistance-determining regions of the genes encoding GyrA and ParC confer intermediate and full resistance, respectively. A clinically relevant gyrA 91/95 mutation was previously demonstrated by our laboratory to confer increased in vivo fitness to N. gonorrhoeae strain FA19, leading us to hypothesize that the resistance-conferring gyrA 91/95 mutations are sufficient to alter the in vivo fitness of other N. gonorrhoeae strains. We found that the presence of this allele in two additional strains of N. gonorrhoeae (FA1090 and vi MS11) not only enhanced in vivo fitness, but did so at a level that was 10-fold higher than that reported in strain FA19. We further speculated that the enhanced in vivo fitness phenotype arose through the altered enzymatic behavior of mutant DNA gyrase, leading to a transcriptional profile better suited for bacterial survival or growth within the host.To test this hypothesis, transcriptome signatures were captured and compared between mutant and parent bacteria using total RNA sequencing as a means of identifying potential mechanisms of gyrA 91/95 -driven enhanced in vivo fitness. In vitro assays were also conducted to compare wild-type and gyrA mutant bacterial phenotypes that might explain the enhanced fitness phenotype. We showed that genome-wide expression patterns differed across three sets of mutant and parent strains. Additionally, the mutant that showed the most robust enhancement in fitness relative to its parent strain was also more resistant to human and bacterial antimicrobial peptides, including the cathelicidins and H 2 O 2 in vitro, and the fitness advantage of this mutant was not observed in cathelicidin-deficient mice. Collectively, these results suggest that a fluoroquinolone resistance-conferring mutations in GyrA condition the N. gonorrhoeae genome for increased survival or growth in vivo, and in the case of one strain background, these mutations increase resistance to host assault, allowing enhanced survivability over susceptible wild type bacteria. vii

In Vivo -Selected Compensatory Mutations Restore the Fitness Cost of Mosaic penA Alleles That Confer Ceftriaxone Resistance in Neisseria gonorrhoeae

“…mtrR mutations are likely to increase fitness due to overproduction of the MtrC-MtrD-MtrE efflux pump, which protects the gonococcus from innate antimicrobial effectors (25). The basis of the fitness advantage conferred by gyrA mutations (S91F/D95N) is unknown but may be a consequence of global changes in gene expression (27). In contrast to mtrR and gyrA mutations, PBP mutations that confer resistance to ␤-lactams are predicted to have a negative impact on gonococcal fitness based on fitness studies in Gram-positive organisms (28)(29)(30) and the importance of these enzymes in cell wall biosynthesis.…”

Addressing Sexually Transmitted Infections Due to Neisseria gonorrhoeae in the Present and Future

“…Thus, multiple research groups have focused on the study of these fitness costs. D'Ambrozio et al found that a specific mutation in gyrA conferred a fitness advantage in vivo because of its effects on genome regulation [61,66]. These findings are supported by the fact that fluoroquinolone-resistant NG strains remain prevalent even after fluoroquinolones were discarded as primary treatment options.…”