Neisseria бактериялары: түрлері, қасиеттері және маңызы

Genus of bacteria

Neisseria is a large genus of bacteria that colonize the mucosal surfaces of many animals. Of the 11 species that colonize humans, only two are pathogens, N. meningitidis and N. gonorrhoeae. Neisseria species are Gram negative bacteria included among the Pseudomonadota, a large group of Gram negative forms. Neisseria diplococci resemble coffee beans when viewed microscopically.

All the medically significant species of Neisseria are positive for both catalase and oxidase. Different Neisseria species can be identified by the sets of sugars from which they will produce acid. For example, N. gonorrhoeae makes acid from only glucose, but N. meningitidis produces acid from both glucose and maltose. Polysaccharide capsule. N. meningitidis has a polysaccharide capsule that surrounds the outer membrane of the bacterium and protects against soluble immune effector mechanisms within the serum. It is considered to be an essential virulence factor for the bacteria. N. gonorrhoeae possesses no such capsule. Unlike most other Gram negative bacteria, which possess lipopolysaccharide (LPS), both pathogenic and commensal species of Neisseria have a lipooligosaccharide (LOS) which consists of a core polysaccharide and lipid A. It functions as an endotoxin, protects against antimicrobial peptides, and adheres to the asialoglycoprotein receptor on urethral epithelium. LOS is highly stimulatory to the human immune system. LOS sialylation (by the enzyme Lst) prevents phagocytosis by neutrophils and complement deposition. LOS modification by phosphoethanolamine (by the enzyme LptA) provides resistance to antimicrobial peptides and complement. Strains of the same species have the ability to produce different LOS glycoforms.

The genus Neisseria is named after the German bacteriologist Albert Neisser, who in 1879 discovered its first example, Neisseria gonorrhoeae, the pathogen which causes the human disease gonorrhea. Neisser also co discovered the pathogen that causes leprosy, Mycobacterium leprae. These discoveries were made possible by the development of new staining techniques which he helped to develop.

The genomes of at least 10 Neisseria species have been completely sequenced. The best studied species are N. meningitidis with more than 70 strains and N. gonorrhoeae with at least 10 strains completely sequenced. Other complete genomes are available for N. elongata, N. lactamica, and N. weaveri. Whole genome shotgun sequences are available for hundreds of other species and strains. N. meningitidis encodes 2,440 to 2,854 proteins while N. gonorrhoeae encodes from 2,603 to 2,871 proteins. N. weaveri (strain NCTC 13585) has the smallest known genome with only 2,060 encoded proteins although N. meningitidis MC58 has been reported to have only 2049 genes. However, the prospect of developing a gonococcal vaccine is remote.

The acquisition of cephalosporin resistance in N. gonorrhoeae, particularly ceftriaxone resistance, has greatly complicated the treatment of gonorrhea, with the gonococcus now being classified as a "superbug".

Genetic transformation is the process by which a recipient bacterial cell takes up DNA from a neighboring cell and integrates this DNA into the recipient’s genome by recombination. In N. meningitidis and N. gonorrhoeae, DNA transformation requires the presence of short DNA sequences (9 10 monomers residing in coding regions) of the donor DNA. These sequences are called DNA uptake sequences (DUSs). Specific recognition of DUSs is mediated by a type IV pilin. Davidsen et al. reported that in N. meningitidis and N. gonorrhoeae, DUSs occur at a significantly higher density in genes involved in DNA repair and recombination (as well as in restriction modification and replication) than in other annotated gene groups. These authors proposed that the over representation of DUS in DNA repair and recombination genes may reflect the benefit of maintaining the integrity of the DNA repair and recombination machinery by preferentially taking up genome maintenance genes that could replace their damaged counterparts in the recipient cell. Caugant and Maiden noted that the distribution of DUS is consistent with recombination being primarily a mechanism for genome repair that can occasionally result in generation of diversity, which even more occasionally, is adaptive. It was also suggested by Michod et al. that an important benefit of transformation in N. gonorrhoeae is recombinational repair of oxidative DNA damages caused by oxidative attack by the host’s phagocytic cells.

The International Pathogenic Neisseria Conference (IPNC), occurring every two years, is a forum for the presentation of cutting edge research on all aspects of the genus Neisseria. This includes immunology, vaccinology, and physiology and metabolism of N. meningitidis, N. gonorrhoeae and the commensal species. The first IPNC took place in 1978, and the most recent one was in September 2016. Normally, the location of the conference switches between North America and Europe, but it took place in Australia for the first time in 2006, where the venue was located in Cairns.