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Neisseria is a genus of bacteria containing both disease-associated species and species that commonly inhabit human mucosal surfaces without causing the corresponding disease. Neisseria gonorrhoeae is one pathogenic member; the behaviour of one species should not be assigned automatically to the entire genus.

Comparative genome sequencing found substantial sharing of genetic variants between human-associated commensal and pathogenic Neisseria. ^[ref] This makes the genus useful for studying how a shared genetic background interacts with host association. Possession of a gene associated with disease in another strain does not by itself establish that its new host has the same disease-causing phenotype.

Neisseria gonorrhoeae is the bacterium causing gonorrhoea, an infection of mucosal surfaces that can also produce complications beyond the original site. Some infections cause few recognizable symptoms, so symptom frequency and infection frequency need not coincide. ^[ref]

It belongs to Neisseria, a genus that also includes human-associated commensal species. Shared ancestry therefore does not mean identical interactions with a host. Comparing genomes across the genus reveals genetic exchange, but the clinical behaviour of a strain depends on the organization and regulation of its genome as well as on host and tissue context. The disease name identifies a clinical entity; the species name identifies an organism.

Pradeep Reddy Marri led a comparative whole-genome sequencing study of commensal and pathogenic Neisseria. The 2010 paper found that commensal species carry many virulence alleles and have extensive genetic exchange with other Neisseria. A harmless colonizer can therefore be a reservoir of genetic variants relevant to a pathogenic relative.^[ref]

This connects horizontal gene transfer to the evolution of disease-associated traits. Possessing a particular allele does not by itself establish pathogenicity: its genomic context, regulation and host interaction also matter.