Neisseria meningitidis – evolving to cause STIs?

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Neisseria meningitidis, a bacteria usually associated with meningitis and sepsis, has been the cause of recent cluster of sexually-transmitted infections in the USA. New research analyzing the genomes of these pathogens suggests these bacteria may have evolved to adapt to the genitourinary niche.

Cases of N. meningitidis first appeared in heterosexual men in Columbus (OH, USA) causing urethritis. More than 100 cases have now been reported around the USA prompting researchers to investigate the evolution of these bacteria.

In the study, published recently in the Proceedings of the National Academy of Sciences, the researchers analyzed the genomes of 52 N. meningitis samples from Columbus, two from Indianapolis (IN, USA) and two from Atlanta (GA, USA).

On initial screening the team could not assign the bacteria identified in these samples to any known serogroup of N. meningitidis. In addition, all 56 genomes had many common features, demonstrating they are closely related.

The researchers identified alterations in the genome of this new clade of N. meningitis, which held similarities to related genitourinary bacteria N. gonorrhoeae. For example, the team discovered the N. meningitidis had lost genes encoding the outer coat capsules, potentially enhancing their ability to adhere to mucosal surfaces. In addition, the team observed the bacteria had gained enzymes that promote growth in low-oxygen environments.

The team hypothesized that some of these changes may have been transferred directly from N. gonorrhoeae, raising concerns about the spread of resistance genes. Author Yih-Ling Tzeng (Emory University, GA, USA) explained: “All the urethritis patients responded to standard treatments for gonorrhea and there were no alarming resistance markers.

“However, as the gene conversion demonstrates, this clade can readily take up DNA from gonococci and it is not unthinkable that gonococcal antibiotic resistance genes could jump into this clade by gene transfer, if it is to its advantage.”

Despite these concerns, the researchers commented that the observed adaptations mean the bacteria are less likely to cause severe invasive diseases, such as meningitis, as the capsule normally functions to protect against the immune system. In addition, the team hope that approved vaccines against the B serogroup might still be effective against this novel meningococcal clade.

Sources: Tzeng YL, Bazan JA, Turner AN et al. Emergence of a new Neisseria meningitidis clonal complex 11 lineage 11.2 clade as an effective urogenital pathogen. Proc. Natl Acad. Sci. USA. doi:10.1073/pnas.1620971114 (2017) (Epub ahead of print); http://news.emory.edu/stories/2017/04/mening_pnas/index.html

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