Gardenerella vaginalis
A Microbial Biorealm page on the genus Gardenerella vaginalis
Classification
Higher order taxa
Bacteria; Actinobacteria; Actinobacteridae; Bifidobacteriales; Bifidobacteriaceae; Gardnerella
Species
Gardnerella vaginalis
Description and significance
Gardnerella vaginalis, formerly known as Haemophilus vaginalis and Corynebacterium vaginale, is a facultative anaerobic, nonmotile, pleomorphic gram-negative to gram-variable rod. It is a well-recognized colonizer of the female genital tract and survives high pH (2). It also survives poorly in human urine at 37 degrees C (3).
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. 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.
Genome structure
The G. 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. The genome encodes a variety of surface proteins and toxins. This explains why G. vaginalis can adhere to epithelial cells and proliferate despite in the presence of lactobaccilus (probiotics) and antibiotics. Investigations have been limited by difficulties experienced in lysing the microbe. No plasmids have been discovered yet but a procedure described by Nath, Choi and Devlin for isolating DNA should facilitate restrictiong endonuclease analyses of choromosomal DNA from clinical isolates and exploration for extrachromosomal plasmids.
Cell structure and metabolism
Gardnerella vaginalis is a gram-variable microbe, and therefore displays both, gram-negative and gram-positive bacteria characteristics. When analyzing a culture, it may appear gram positive during the exponential growth phase but gram negative as it ages because the peptidoglycan layer becomes too thin to retain the crystal-violet iodine aggregates(5). These organisms are surrounded by a 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(4). 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 the aerobic metabolism of glucose, G. vaginalis forms lactic acid and acetic acid. However, under anaerobic conditions, the metabolism of glucose yields only lactic acid.
Ecology
Bacterial vaginosis (BV) is a polymicrobial, noninflammatory syndrome involving the lower genital tract that is characterized by a microecologic imbalance (including pH disturbance) and the replacement of lactobacilli-predominant flora with G. vaginalis, anaerobes, and Mycoplasma hominis. Microbial analysis has shown G. vaginalis to be the most causative agent but it exists in a symbiotic relationship with other anaerobes. Enzymes and decarboxylases produced by these anaerobic bacteria are thought to degrade proteins and convert the amino acids to amines. These amines raise the vaginal pH greater than 4.5 and produce a characteristic fishy odor and enhance the growth of Prevotella bivia and Gardnerella vaginalis. It also seen that G. vaginalis inhabits an environment where it can potentially be exposed to a variety of iron-containing compounds, including heme, lactoferrin, and hemoglobin and it sequesters iron by releasing toxins, and hemolysins. G. vaginalis adhere to squamous epithelium and appear to form "clue" cells under a microscope.
G. vaginalis is present in low concentrations in a healthy female but is present in extremely high concentrations in women with BV. Healthy women have high concentrations of Lactobaccilus crispatus and Lactobaccilus jensenii that produce hydrogen peroxide that keep harmful organisms from proliferating.
Pathology
G. vaginalis is one of few microorganisms that cause Vaginal Bacteriosis. They are found in humans and some animals such as mares. Apart from the urinary 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.
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. And 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 vagina and their bladder and these cells are absent in a man's bladder, therefore, they are less susceptible to this pathogen. 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.
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, May have pain with sexual intercours(5). Men may not have physical symptoms.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
Current Research
1. A recent research that just ended in April 2007 by Lawson Health Research Institute tested the effect of Lactobacillus challenge on Gardnerella vaginalis biofilms. They used to microscopy analysis to view the onset of biofilm formation within 72 hours, viable G. vaginalis covered surface area of 567 microm, reached a depth of 16 microm and a density of approximately 104 microm. It was witnessed that they maintained these levels unless challenged with lactobacilli strains. Lactobacillus reuteri RC-14 produced the biggest displacement of Gardnerella. This displacement is is not due to pH (remained constant), not by hydrogen peroxide which usually attempted by other species of lactobacillus. Therefore, this research is important in providing insight into the clinical situation in which probiotic and indigenous vaginal lactobacilli can interfere with the presence of G. vaginalis and reduce the risk of bacterial vaginosis.
2. The American Journal of Obstetrics and Gynecology recently researched bacteriocin susceptibility of G. vaginalis and its relationship to biotype, genotype, and metronidazole susceptibility. Bacteriocin susceptibility of 36 G vaginalis clinical Isolates was tested against a vaginal strain of Lactobacillus acidophilus by a growth-inhibition method. The relationship to biotype, genotype, and resistance to metronidazole were analyzed by the chi (2) test and Fisher exact test. The isolates were classified as Biotype 5, 6, and 7. Biotype 5 was found in higher prevalence among the isolates resistant to bacteriocin than among the susceptible isolates. An association between biotype of G. vaginalis and an increased resistance to bacteriocin was found. The ability of G vaginalis to resist the antibacterial activity of Lactobacillus bacteriocin may be a pivotal factor in understanding bacterial vaginosis. This could help researchers determine what biotype to expect when dealing with high concentrations of G. vaginalis and avoid giving certain antibiotics.
3. A recent research at University of Udine, Italy tested to see if activation of vaginal hydrolytic enzymes, immunoglobulin A against G. vaginalis increases the risk of early preterm birth in women with bacterial vaginosis. Two hundred eighteen women in preterm labor with intact membranes had a vaginal Gram stain performed, and hydrolytic enzymes and IgA concentrations were determined. It was found that women with bacterial vaginosis had a significantly higher hydrolytic enzymes (sialidase and prolidase) concentrations than women with normal flora. Among women with bacterial vaginosis, those that had high concentrations of sialidase had a higher rate of early preterm birth whereas those with higher levels of prolidase and IgA did not pretict early preterm birth. The significant of this research is that it gives doctors to reduce preterm birth among women with bacterial vaginosis without fighting the extremely resistant G. vaginalis and by simply eliminating sialidase.
References
1. Joe Bischoff, Mikhail Domrachev, Scott Federhen, Carol Hotton, Detlef Leipe, Vladimir Soussov, Richard Sternberg, Sean Turner. "Gardnerella Vaginalis" <http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2702>
2. S M Smith, T Ogbara, and R H Eng. "Involvement of Gardnerella vaginalis in urinary tract infections in men." J Clin Microbiol Volume 30. p. 1575–1577. <http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=265332>
3. Lam MH, and Birch DF. "Survival of Gardnerella vaginalis in human urine." American journal of clinical pathology. 1991 Feb;95(2):234-9. http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=1992615&dopt=AbstractPlus
4. O'Donnell AG, Minnikin DE, Goodfellow M, Piot P. "Fatty acid, polar lipid and wall amino acid composition of Gardnerella vaginalis." Archives of microbiology. 1984 May;138(1):68-71. http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=6611140&ordinalpos=3&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
5. B W Catlin. "Gardnerella vaginalis: characteristics, clinical considerations, and controversies." Clinical Microbiology Reviews. 1992 July; 5(3): 213–237. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=358241
Edited by Jaspreet Singh, student of Rachel Larsen
