A SHORT NOTE ON Gardnerella vaginalis
Gardnerella vaginalis
Compiled by: Zenisha Acharya
Tulasi Chamling Rai
Central Department of Microbiology, Kirtipur
INTRODUCTION
• Gardnerella
vaginalis is Gram negative or Gram variable bacillus.
• It
is facultative anaerobe.
• G.
vagnalis is colonizer in vagina of 40% of normal woman.
• However,
it is found to be mainly associated with bacterial vaginosis (BV) and is not
considered as normal vaginal flora.
• Bacterial
vaginosis (BV) is a clinical symptomatic condition where there is malodorous
vaginal discharge.
• Formerly,
it was termed as non-bacterial vaginitis.
• BV
occurs in women of child-bearing years
• Other
BV causing organism are Prevotella, Mobiluncus.
HISTORY
• G.
vaginalis was first described by Gardner and Dukes in 1955 and was named
Haemophilus vaginalis.
• But
its growth didn’t require neither X nor V factor.
• Later
on, Zinneman and Turner(1963) classified it on genus Corynebacterium as
some strains were observed as Gram positive rod.
• Greenwood
and Pickett(1980) finally proposed its removal to new genus, Gardnerella based
on its cell wall composition, electron microscopic appearance and (G+C)
content.
• G.
vaginalis is the only species under genus Gardnerella.
CLASSIFICATION
Domain Bacteria
Phylum Actinobacteria
Class Actinobacteria
Order Bifidobacteriales
Family Bifidobacteriaceae
Genus Gardnerella
Species Gardnerella vaginalis
MORPHOLOGY
• G.
vaginalis is Gram negative or Gram variable rod with dimension 1.5-2.5µm X
0.5µm.
• It
is facultatively anaerobic in nature.
• It
is non-spore forming and non-motile bacilli.
CULTURAL AND BIOCHEMICAL CHARACTERISTICS
• G.
vaginalis doesn’t grow on nutrient agar(NA) but on chocolate agar(CA) and
blood agar(BA).
• Growth
is more prominent on human and rabbit blood agar rather than sheep and horse
blood agar.
• The
bacterial growth occurs between 25
ͦC-40 ͦC while optimum at 35 ͦC- 37
ͦC.
• Increased carbon-dioxide enhances growth that maintaining anaerobic environment.
• Colonies
on CA is pin point after 24 hrs of incubation.
• After
48 hrs of incubation colonies measures 0.5mm in diameter, circular, convex and
grey colored.
• On
BA, the colonies are β-haemolytic.
• Characteristic
β-haemolysis is more clear on
two layer plates with Columbia agar alone as a base and a top layer of Columbia
agar containing 5% outdated banked human blood.
• Tween
80 and 1% proteose peptone enhance the haemolysis.
• G.
vaginalis utilizes various sugar like fructose, galactose, mannose, ribose
and starch with acid production.
• But
variable results are obtained from lactose, sucrose and xylose.
• Hence,
carbohydrate fermentation test is not considered to be reliable test.
• It
is negative for catalase, oxidase, indole, urease test and nitrate reduction
test.
• H₂S
gas production is also negative.
• Organism
hydrolyses hippurate.
PATHOGENESIS
• G.
vaginalis is acquired during sexual activities.
• Invasion
is initiated by the adherence of organism on the squamous epithelial cells of
vagina.
• Organism
then produces, vaginolysin a cholesterol dependent cytolysin which is specific
to host receptor site.
• It
encodes a pore forming toxin that binds to the CD59 human complementary
regulatory molecule.
• This
cytotoxin aid in the initial adherence.
• Production
of biofilm further assist in the successful colonization which is achieved
through sialidase enzyme.
• Moreover,
G. vaginalis shows symbiosis relation with other anaerobes like Atopobium,
Prevotella and Mobiluncus.
• Prevotella like species synthesizes exogenous protein.
• G.
vaginalis causes proteolysis of these exogenous protein for energy.
• This
in turn causes increment in ph value of vaginal environment.
• On
the other hand, G. vaginalis shows antagonism with vaginal normal flora Lactobacillus.
• Antagonistic
relation is maintained by the production of bacteriocin by G. vaginalis that
inhibit the growth of Lactobacilli.
• Finally, these all series of events result in the
subsiding of Lactobacilli with the successful establishment and
flourishment of BV causing G. vaginalis.
MEDICAL IMPORTANCE
• BV
is more likely to occur among women who have sex with women(WSW) and person
having multiple sex partners.
• BV
is characterised with abnormal vaginal discharge which is fishy in odour, increased
Ph and clue cells.
• Clue
cells are actually the sloughing of vaginal epithelial cells.
• It
is visualized as squamous epithelial cells surrounded by Gram variable rod
shaped bacterium.
Fig: Clue cells (squamous epithelial cells surrounded by
Gram variable bacterium)
• Its
complication may lead to urinary tract infection, amnionitis, preterm birth and
post-caesarean endometritis.
• Condition
is worsen during the menstrual period.
• In
men, balanoposthitis is found to occur rarely.
• It
remains asymptomatic in male urethra and may serve as carrier but still its
epidemiology is unclear.
LABORATORY DIAGNOSIS
• Organism
can be isolated from vaginal discharge. Other samples may include blood, urine
and pharynx.
• It
grows well on CA and BA with β-haemolytic
colonies supported with 5-10% CO₂.
• Columbia
agar contaning colistin and nalidix acid is prefered more.
• On
performing mnicroscopy, clue cells is significant observation for BV caused by
G. vaginalis.
• Organism
is catalse and oxidase test negative.
• Also,
negative for urease, indole test and nitrate reduction test.
• Hippurate
hydrolysis is positive.
• Along
with these test, production of ammonical fishy smell when 10% sodium hydroxide
is added to vaginal discharge confirm G. vaginalis.
• PCR
can be done to detect genes encoding 60kDa heat-shock protein chaperonin (Cpn
60).
TREATMENT
• G.
vaginalis is susceptible to penicillin, ampicillin, vancomycin and
clindamycin.
• Nearly
all strains are inhibited by metronidazole 128mg/l.
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