Gardenerella vaginalis

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A Microbial Biorealm page on the genus Gardenerella vaginalis

Classification

Higher order taxa

Bacteria; Actinobacteria; Actinobacteridae; Bifidobacteriales; Bifidobacteriaceae; Gardnerella (2)

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 bacteria. It is a well-recognized colonizer of the female genital tract and survives high pH (11). It also survives poorly in human urine at 37 degrees C (6).

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 (12).

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 (7). The genome is currently being sequenced at Stanford University. But 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(8). 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.

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 that 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 is 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. It sequesters iron from these iron-containing compounds by releasing toxins, and hemolysins (8). 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 are found in women diagnosed with Vaginal Bacteriosis. 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 (9). 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 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 (5).

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 intercours(3). Men may not have physical symptoms.

Application to Biotechnology

Production of useful enzymes or compounds by G. vaginalis are yet to be discovered. Presently, the concentration of G. vaginalis is only used for the diagnosis of Bacterial Vaginosis.

Current Research

1. A recent study that just ended in April 2007 by Lawson Health Research Institute tested the effect of Lactobacillus challenge on Gardnerella vaginalis biofilms. They used 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 was not due to pH, which remained constant, and 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 (9).

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, while concentrating on others(10).

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 (4).

References

1. Aroutcheva AA, Jose A. Simoes, Kian Behbakht, and Sebastian Faro. "Gardnerella vaginalis Isolated from Patients with Bacterial Vaginosis and from patients with Healthy Vaginal Ecosystems." CID 2001:33. http://www.journals.uchicago.edu/CID/journal/issues/v33n7/010132/010132.web.pdf

2. Bischoff J, 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>

3. Catlin BW. "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

4. Cauci S, Hitti J, Noonan C, Agnew K, Quadrifoglio F, Hillier SL, Eschenbach DA. "Vaginal hydrolytic enzymes, immunoglobulin A against Gardnerella vaginalis toxin, and risk of early preterm birth among women in preterm labor with bacterial vaginosis or intermediate flora." American journal of obstetrics and gynecology. 2002 Oct;187(4):877-81. http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=12388968&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVAbstractPlus

5. Jarosik GP, Carol Beth Land, Patrice Duhon, Roderick Chandler, Jr., and Tammy Mercer. "Acquisition of Iron by Gardnerella vaginalis." Infection and Immunity. 1998 October; 66(10): 5041–5047. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=108627

6. 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

7. Lim D, Trivedi H, Nath K. "Determination of Gardnerella vaginalis genome size by pulsed-field gel electrophoresis." DNA research : an international journal for rapid publication of reports on genes and genomes. 1994;1(3):115-22. http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=retrieve&db=pubmed&list_uids=7584037&dopt=AbstractPlus

8. 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

9. Saunders S, Bocking A, Challis J, Reid G. "Effect of Lactobacillus challenge on Gardnerella vaginalis biofilms." Colloids and surfaces. B, Biointerfaces. 2007 Apr 1;55(2):138-42. http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=17234391&ordinalpos=15&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

10. Simoes, JA; Aroutcheva, A; Heimler, I; Shott, S; Faro, S. "Bacteriocin susceptibility of Gardnerella vaginalis and its relationship to biotype, genotype, and metronidazole susceptibility. American Journal of Obstetrics AND Gynecology. volume: 185, 2001:1186-1190. http://serials.cib.unibo.it/cgi-ser/start/it/spogli/df-s.tcl?prog_art=4560116&language=ITALIANO&view=articoli

11. Smith SM, 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>

12. 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. http://lib.bioinfo.pl/pmid:6764766

Edited by Jaspreet Singh, student of Rachel Larsen

Edited by KLB