Lactobacilli in the Vagina Utilize an Arsenal of Defensive
Tactics
Some release powerful chemicals that stunt the growth of potential pathogens.
Others stubbornly cling to strategic positions in the inner lining of an organ,
preventing harmful microorganisms from gaining a foothold. Still others knock
loose "bad" bacteria already fastened to cell receptors. These are just some of
the tricky defense strategies used by "good" Lactobacillus bacteria to ward off
potential pathogens and keep them from overpopulating - in the gastrointestinal
tract as well as in the vagina. Mounting evidence indicates that the outcome of
this bacterial "push and shove" plays an important role in the sexual and
reproductive health of women.
A new study published in the Journal of Infectious Diseases suggests that
various strains of Lactobacillus are critical for maintaining a healthy
ecosystem in the vagina. Researchers measured the in-vitro of ability of
lactobacilli to block uropathogens – infectious microrganisms that cause urinary
tract infections - from colonizing the cells that form the protective outer
layer of the vagina.
They found that lactobaccilli had the capacity to block uropathogen growth from
50% to as much as 74%. The protective bacteria were most effective against
Pseudomonas aeruginosa and Klebsiella pneumoniae -microbial agents that commonly
spur infection when there is a defect in host defense mechanisms.
Interestingly, the defense strategy of lactobacilli seems to adapt to the body's
immediate needs. When the vagina is healthy, lactobacilli chiefly use adhesion
to block uropathogens from gaining access to the epithelium. When microbial
imbalances create a high risk of urinary tract infection, however, lactobacilli
may employ another tactic - "bumping off" infectious microrganisms that are
already occupying positions within the vaginal lining. "… Lactobacillus strains
are able to block the attachment of uropathogens to vaginal epithelium and,
moreover, are able to excrete substances that inhibit their multiplication,
which are 2 important steps in the pathogenesis of urinary infection,"
investigators concluded ( mechanisms observed in other friendly bacteria are --
adhesion to epithelial cells, inhibition of pathogen growth, and production of a
biosurfactant protein to resist pathogen adhesion.)
L reuteri is described as the synthesizer of a broad-spectrum antimicrobial
substance (reuterin). In vitro conditions for synthesis are compared to pH,
temperature, and relatively anaerobic conditions similar to those in parts of
the GI ecosystem (precisely where it thrives is not known). Concentrations of 15
to 30 micrograms/milliliter inhibit growth of gram-negative and –positive
bacteria, yeasts, fungi, and protozoa. At concentrations four to five times that
level, it can kill lactic acid bacteria. It has also been shown to lower levels
of Salmonella typhimurium.
L. reuteri has also been identified in the vagina. In the most recent issue of
Journal of Infectious Diseases, it is one of seven strains described as having
"sufficiently substantial data published on their properties that are required
of an antipathogen probiotic." The others are L. rhamnosus GG, L. acidophilus
NCFM, L. casei Shirota, L. casei CRL-431, L. rhamnosus GR-1, and L. fermentum
RC-14.
Sources: Casas IA, Edens FW, Dobrogosz WJ. Lactobacillus reuteri: An effective
probiotic for poultry and other animals. In Salminen S, von Wright A, editors.
Lactic Acid Bacteria: Microbiology and Functional
Aspects. 2nd ed. New York: Marcel Dekker, Inc., 1998.
Reid G. Probiotic agents to protect the urogenital tract against infection. Am J
Clin Nutr 2001;73(Suppl):437S-43S.
Reid G, Bruce AW. Selection of Lactobacillus strains for urogenital probiotic
applications. J Infect Dis 2001;183(Suppl 1): S77-80.
NOTE: The Vaginosis Profile features a microscopic examination for bacteria such
as beneficial Lactobacillus, which may play an important role in influencing
mechanisms of vaginal infection and disease. Based on levels of bacteria,
including Gardnerella, Mobiluncus (curved gram negative rods), and
Lactobacillus, a Bacterial Vaginosis Index is computed to indicate the balance
of microbial flora in the vagina. http://www.gsdl.com/assessments/vaginosis/
Source: Osset J, Bartolome RM, Garcia E. Assessment of the capacity of
Lactobacillus to inhibit the growth of uropathogens and block their adhesion to
vaginal epithelial cells. J Infect Dis 2001;183:485-91.