Neisseria gonorrhoeae

Neisseria gonorrhoeae has evolved perhaps the most sophisticated immune evasion system in the bacterial world: programmed antigenic variation. Rather than relying on random mutations, this bacterium carries silent gene copies encoding variants of its surface proteins. Through directed recombination, it continuously shuffles these variants into expression sites, presenting an ever-changing face to the immune system. A single gonococcal infection can generate millions of surface protein variants, making effective immune memory nearly impossible.

This isn't random genetic chaos—it's precisely controlled diversity. The bacterium maintains a library of pre-tested protein variants, each functional and each different enough to escape antibodies targeting other variants. The system resembles a fashion house with an extensive archive: rather than designing new styles from scratch, it recombines existing elements into novel combinations. This strategy explains why natural immunity to gonorrhea doesn't develop despite repeated infections and why vaccine development has proven extraordinarily difficult.

N. gonorrhoeae is also naturally competent, continuously importing DNA from its environment, but with remarkable specificity. It preferentially takes up DNA containing a specific 10-base sequence found throughout its own genome, essentially filtering for DNA from its own species. This creates a genetic commons among gonococcal strains—innovations in antibiotic resistance or immune evasion spread rapidly through the population. The combination of internal variation generation and external gene acquisition makes this bacterium a formidable adversary that has developed resistance to every antibiotic ever used against it.