Gardnerella vaginalis

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Gardnerella
Gardnerella vaginalis
Gardnerella vaginalis
Scientific classification
Kingdom: Bacteria
Phylum: Actinobacteria
Order: Bifidobacteriales
Family: Bifidobacteriaceae
Genus: Gardnerella
Species: G. vaginalis
Binomial name
Gardnerella vaginalis
(Gardner and Dukes 1955) Greenwood and Pickett 1980

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];

Overview

Gardnerella is a genus of gram-variable bacteria of which Gardnerella vaginalis is the only species. Gardnerella vaginalis can cause bacterial vaginosis in some women.

Microbiology

Gardnerella vaginalis, formerly known as Haemophilus vaginalis and Corynebacterium vaginale, is a facultative anaerobic, nonmotile, pleomorphic gram-negative to gram-variable rod bacteria. It is a well-recognized colonizer of the female genital tract and survives high pH.[1] It also survives poorly in human urine at 37 degrees C.[2] G. vaginalis was first recognized by Leopold and named Haemophilus vaginalis by Gardner and Dukes in 1955 because it was isolated on human blood bilayer agar media.[3] This method of isolation did not yield great amounts of bacteria and therefore, was introduced with Tween 80 (HBT medium) or without Tween 80 (HB medium). HB medium consists of a basal layer of Columbia agar base containing colistin and naladixic acid with added amphotericin B and an overlayer of the same composition plus 5% human blood. HBT agar also contains Proteose Peptone No. 3 (Difco Laboratories) and Tween 80 in the basal layer and the overlayer. Both Tween 80 and the bilayer composition enhanced G. vaginalis production of human blood hemolysis, permitting detection of this organism even in the presence of heavy growth of other vaginal flora. G. vaginalis is resistant to lactobacillus and many antibiotics such as tetracycline. Thus, it is important to sequence its genome to find out what makes it resistant and what genes are expressed in the genome that makes it resistant.[4]

Genome structure

The Gardnerella vaginalis genome is a circular DNA that ranges between 1.67 Mb and 1.72 Mb in size, with a 42-44% G+C content.[5] It is obvious that it codes for genes that help it adhere to epithelial cells and proliferate despite in the presence of lactobaccilus (probiotics) and antibiotics. Due to the difficulties experienced in lysing the microbe, the investigations have been limited. No plasmids have been discovered yet but a procedure described by a few researchers for isolating DNA should facilitate restriction endonuclease analyses of choromosomal DNA from clinical isolates and exploration for extrachromosomal plasmids.[3]

Cell structure and metabolism

Gardnerella vaginalis is a gram-variable microbe, and therefore displays both, gram-negative and gram-positive bacteria characteristics. When analyzing its culture, it may appear gram positive during the exponential growth phase but gram negative as it ages because peptidoglycan layer becomes too thin to retain the crystal-violet iodine aggregates.[3] These organisms are surrounded by an exopolysaccharide layer and pili that aid in adhering to the epithelial cells of the vagina. The cell wall is comprised of straight chain saturated and unsaturated non-hydroxylated fatty acids with hexadecanoic acid and octadecenoic acid along with major amounts of alanine, glycine, glutamic acid and lysine.[6] G. vaginalis has a very complex metabolism. Gardnerella vaginalis are facultative anaerobes, which means that they can metabolism glucose (and other simple sugars) in under both aerobic and anaerobic conditions. Under both, aerobic and anaerobic metabolism of glucose, G. vaginalis forms lactic acid.

Pathology

G. vaginalis is one of few microorganisms that are found in women diagnosed with bacterial vaginosis. They are found in humans and some animals such as mares, and horses. Apart from the urinary tract and the bladder, they are also found in the endometrium, fetal membranes, and newborn infants and are caused by maternal infections, neonatal infections, and suppurative lesions. It can also be transmitted through sexual intercourse.[3] Gardnerella vaginalis attaches better to urogenital squamous epithelial cells due to the exopolysaccharide layer and pili. It forms biofilms that are resistant to antibiotic treatment and induce inflammatory processes that displace indigenous lactobacilli from its habitat.[6] This attachment provides a means of migration from the genitourinary tract to the primary colonization site in the bladder. Women have squamous cells in their genitourinary and their bladder and these cells are absent in a man's bladder, therefore, they are less susceptible to this pathogen.[3] The presence of clue cell-like squamous epithelial cells are observed in bladder urine by suprapubic aspiration in women affected with G. vaginalis and none are observed in men. Overall there is little information concerning the pathogenic mechanisms of G. vaginalis. G. vaginalis secretes a 60-kDa hemolysin which lyses human erythrocytes, neutrophils, and endothelial cells and thus, is a potential virulence factor.[7] Some symptoms associated with vaginosis in women caused by G. vaginalis may include Gray, foul smelling vaginal discharge (the smell is particularly noticeable after intercourse, because semen is alkaline and reacts with the bacteria, causing the release of chemicals that produce the fishy smell), may have vaginal itching or burning, may have burning or discomfort on urination, and may have pain with sexual intercourse.[3] Men may not have physical symptoms.

Clue cells (Gardnerella Vaginalis)

Reactions

Infections with G. vaginalis go along with proteolysis, giving nitrous products such as cadaverines and putrescines, which can cause a bad smell and loss of water.

References

  1. Smith SM, Ogbara T, Eng RH (1992). "Involvement of Gardnerella vaginalis in urinary tract infections in men.". J Clin Microbiol 30 (6): 1575-7. PMID 1624577.
  2. Lam MH, Birch DF (1991). "Survival of Gardnerella vaginalis in human urine.". Am J Clin Pathol 95 (2): 234-9. PMID 1992615.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Catlin BW (1992). "Gardnerella vaginalis: characteristics, clinical considerations, and controversies.". Clin Microbiol Rev 5 (3): 213-37. PMID 1498765.
  4. Totten PA, R Amsel, J Hale, PPiot, KK Holmes. "Selective differential human blood bilayer media for isolation of Gardnerella (Haemophilus) vaginalis." J Clin Microbiol. 1982 Jan ;15 (1):141-7
  5. Lim D, Trivedi H, Nath K (1994). "Determination of Gardnerella vaginalis genome size by pulsed-field gel electrophoresis.". DNA Res 1 (3): 115-22. PMID 7584037.
  6. 6.0 6.1 O'Donnell AG, Minnikin DE, Goodfellow M, Piot P (1984). "Fatty acid, polar lipid and wall amino acid composition of Gardnerella vaginalis.". Arch Microbiol 138 (1): 68-71. PMID 6611140.
  7. Jarosik GP, Land CB, Duhon P, Chandler R, Mercer T (1998). "Acquisition of iron by Gardnerella vaginalis.". Infect Immun 66 (10): 5041-7. PMID 9746616.

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