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Inge Dorthe
LadyBalance
One of the characteristics of bacterial vaginosis (BV) is the unpleasant smell from thevaginal discharge described as similar to the smell from rotten fish. For womenaffected by BV, this odor is the main direct nuisance encountered.
The description “smell like fish” is very precise, as the component mainly responsible for the smell is trimethyle amine (TMA) – the same component present in rottenseawater fish, and here constitute a major part of the smell picture in thesefish.
Tri-methylamine is a small molecule consisting of three units of methyle (CH3)all linked to the same nitrogen (N)-atom. The formula is thus N(CH3)3.
The samecomponent also exists in an oxidized form TMA oxide. This compound has verylittle smelling capacity.
Not only women affected by BV can have a fish smell problem. There is a syndrome calledtrimethylaminuria – or fish odour syndrome (Rehman, 1999). Affected peopleexcrete TMA in breath, sweat, saliva and vaginal excretions. Most knowledgeabout how TMA and it’s oxide are metabolized in the human body come fromstudies of this syndrome.
In short –the trimethyl amine smells like fish, and can be recognized by human nose at aconcentration less than 1 ppm (mg/kg). Trimethyle amine has a 100-fold greaterolfactory potency than the oxide.
For normalpeople TMA is oxidized in the liver to TMA oxide, and excreted in urine,vaginal secretions etc. People with trimethylaminuria lack the capacity totransform TMA to the non-smelling oxide form.
Sources
Trimethylamin oxid is a compound found in abundance in seawater fishes. Moreover it is acomponent that can be produced by microbial activity (normally in the gut) fromcertain nitrogen-containing compounds:
Choline from egg yolk, soy beans, peas, beans, peanuts, liver, kidney and other offal,and brassicas such as rapeseed.
Carnitine from red meat (beef, pork).
Transformation
Trimethylamine oxide thus normally circulates in the bloodstream, and is excreted in theurine.
Bacteria present in the vagina may convert the TMAO to TMA, and the smell of fish occursin vaginal secretions. Cruden and Galask (1988) found, that Mobiluncus spp. quantitatively convertsTMAO to TMA, whereas the same activity could not be identified with Gardnerella spp. This research pointsout Mobiluncus to be the origin ofthe fishy smell.
TMA is aweak base. . The lowered pH converts tri-methylamine from a volatile base form to a soluble acid form, reducing therecognisable smell (Philips & Shephard, 2011). After the introduction oflactose into a vagina affected by BV, the following is expected: Lactosefermenting organisms present in the vagina start converting lactose into lacticacid, this process is accomplished within hours to days. The low pH andavailability of fermentable carbohydrates provide a favourable environment forlactic acid bacteria, which, over days to weeks, will dominate the vaginalmicrobiota. There are no active killing processes aimed at eliminating unwantedbacteria, such as G. vaginalis, butin a hostile environment with a low pH and dominant, competing microbiota, theywill be eliminated within weeks to months.
References:
Rehman HU(1999): Fish Odour syndrome. Postgrad. Med J. 75: 451 – 452
DLCruden RP Galask (1988): Reduction ofTMAO to TMA by Mobiluncus strains isolated from patients with BV. Microb. Eco.In Health and Disease 1: 95-100
Phillips IR, Shephard EA (2011) Trimethylaminuria. Synonyms: Fish OdorSyndrome, TMAuria, TMAU. 2011th ed. Pagon R, Adam M, Ardinger H, editors.Seattle: University of Washington, Seattle.
