Neisseriaceae

Neisseriaceae
Name	Neisseriaceae
Taxon	Family
Authority	Prévot 1933
Subdivision ranks	Genera
Subdivision	See text.

Neisseriaceae. The Neisseriaceae are a family of Gram-negative bacteria within the order Neisseriales of the class Betaproteobacteria. This family encompasses a diverse group of aerobic or facultative anaerobic organisms, many of which are commensal residents of the mucous membranes in animals, including humans. While several genera are harmless, the family includes notable pathogens responsible for significant human diseases, driving extensive research in medical microbiology and epidemiology.

Taxonomy and classification

The family Neisseriaceae was formally proposed by the French microbiologist Émile Prévot in 1933. Its classification has been refined through advances in molecular phylogenetics, particularly 16S ribosomal RNA gene sequencing. The family resides within the order Neisseriales in the class Betaproteobacteria, a group that also includes families like Chromobacteriaceae. Historically, classification relied on phenotypic traits, but modern polyphasic taxonomy integrates genomic data for more accurate delineation. The List of Prokaryotic names with Standing in Nomenclature (LPSN) and the Bergey's Manual of Systematic Bacteriology are key resources for its current taxonomic structure. Revisions have occasionally transferred genera, such as Kingella, in and out of the family based on phylogenetic evidence.

Description and characteristics

Members of the Neisseriaceae are typically cocci or short rods, often appearing in pairs (diplococci), a characteristic morphology of the genus Neisseria. They are Gram-negative bacteria, possessing an outer membrane containing lipopolysaccharide (LPS), though the LPS of pathogenic *Neisseria* species is a less toxic lipooligosaccharide. They are generally oxidase-positive and catalase-positive, key biochemical tests for preliminary identification. Most are capnophilic, thriving in environments enriched with carbon dioxide. Their metabolism is respiratory, never fermentative, and they utilize a variety of carbohydrates through oxidative pathways.

Genera and species

The family comprises several genera, with *Neisseria* being the most prominent. This genus includes the major pathogens Neisseria gonorrhoeae, the causative agent of gonorrhea, and Neisseria meningitidis, responsible for meningococcal disease and meningitis. Other medically relevant genera include Kingella, with species like Kingella kingae associated with pediatric osteomyelitis and septic arthritis; Eikenella, containing Eikenella corrodens, part of the HACEK organisms and implicated in human bite wound infections; and Simonsiella, which are large, multicellular bacteria found in the oral cavities of animals. The genus Alysiella is also recognized, often isolated from the bovine rumen.

Ecology and habitat

Neisseriaceae exhibit a primarily commensal relationship with host animals, colonizing mucous membranes of the nasopharynx, oropharynx, urogenital tract, and gastrointestinal tract. *Neisseria meningitidis*, for instance, can asymptomatically colonize the human nasopharynx in a significant portion of the population, acting as a reservoir for transmission. Some members, like certain *Simonsiella* species, are found specifically in the oral cavities of mammals and reptiles. Environmental isolates are less common, though some non-pathogenic species may be found in water or soil, but the family is predominantly associated with animal hosts.

Pathogenicity and clinical significance

The pathogenic members of Neisseriaceae are of profound clinical importance. Neisseria gonorrhoeae causes the sexually transmitted infection gonorrhea, which can lead to pelvic inflammatory disease, epididymitis, and disseminated infections. Neisseria meningitidis is a leading cause of bacterial meningitis and septicemia, with potential for rapid progression and outbreaks, particularly in settings like the meningitis belt of sub-Saharan Africa. Kingella kingae is increasingly recognized as a cause of invasive disease in young children. Virulence factors include pili for adhesion, outer membrane proteins like porins, capsule production in *N. meningitidis*, and the secretion of immunoglobulin A1 protease.

Genomics and evolution

Genomic studies, such as those enabled by the Neisseria gonorrhoeae FA 1090 genome project, have provided deep insights into the evolution and adaptability of this family. Pathogenic *Neisseria* species exhibit high genomic plasticity through natural transformation and horizontal gene transfer, facilitating antigenic variation and antibiotic resistance. The presence of pathogenicity islands and prophage elements is common. Comparative genomics with commensal species, like Neisseria lactamica, helps elucidate the evolutionary paths to virulence. Research into the pan-genome of *Neisseria* reveals a core genome essential for basic function and a large accessory genome contributing to niche adaptation and pathogenicity.

Category:Betaproteobacteria Category:Bacterial families