the microbial species that inhabit the vaginal tract play 
 an important role in the maintenance of health , and prevention of infection . 
 over 50 microbial species have been recovered from the vaginal tract [ 13 ] . these species 
 do not exist independently , and studies in 
 vitro and in humans have shown that a multispecies microbiota , usually 
 associated with bacterial vaginosis ( bv ) , are present in dense biofilms [ 47 ] , while a 
 lactobacilli dominant microbiota can be sparsely distributed on the epithelium 
 [ 4 , 5 , 8 ] .   in comparison , the gut is 
 populated with more than 800 species of microbes , the majority of which are 
 excreted in feces , and a number of which are well equipped to be pathogenic . despite the close proximity of the vagina to the anus , the diversity of 
 microbes present in the vagina is much lower than in the gut . the reason for 
 this lower diversity is still unclear , but may involve poor receptivity of the 
 vagina , different nutrient availability compared to the gut , and competition 
 with indigenous organisms . some species found in the gut , such as e. coli and streptococcus , can also be found in the vagina , indicating the 
 proper receptors , nutrients , and oxygen tension are present for these organisms 
 to grow . culture - based methods allow strains to be 
 identified and used for further experimentation . however , as there remains a 
 major defect in our ability to grow many bacterial species , we must rely on 
 nonculture methods to identify the breadth of vaginal microbiota . this has been 
 achieved by analyzing their ribosomal dna sequences [ 3 , 9 ] , using a combination 
 of pcr and denaturing gel gradient electrophoresis ( dgge ) [ 2 , 5 , 1012 ] , and by using 
 degenerate , universal polymerase chain reaction primers to amplify an 
 approximately 555 base - pair regions of the universal chaperonin-60 gene . the species that are present in the vaginal mucosa 
 vary between premenopausal woman and those who have gone through menopause . the 
 microbiota of healthy premenopausal woman is generally dominated by lactobacillus species , the most common 
 of which are l. iners , l. crispatus , l. gasseri , l. jenesenii , followed 
 by l. acidophilus , l. fermentum , l. 
 plantarum , l. brevis , l. casei , l. vaginalis , l. delbrueckii , l. salivarius , l. 
 reuteri , and l. rhamnosus [ 2 , 5 , 916 ] . as more 
 studies are performed on the vaginal organisms in healthy women , it is possible 
 that some women will be identified , who do not have a lactobacilli - dominated 
 microbiota . however , until we know more about the dynamics of such a 
 population , and are sure that it does not increase the risk of the disease , lactobacilli will 
 remain the organisms of most importance to vaginal health . factors such as hormonal changes ( particularly 
 estrogen ) , vaginal ph , and glycogen content can all affect the ability of 
 lactobacilli to adhere to epithelial cells and colonize the vagina . the 
 menstrual cycle can also cause changes in the vaginal microbiota , with high 
 concentrations of estrogen increasing adherence of lactobacilli to vaginal 
 epithelial cells . with the decrease in estrogen levels associated with 
 menopause , there is also a decrease in lactobacilli present in the vaginal 
 tract of postmenopausal women [ 5 , 11 , 12 , 19 ] . postmenopausal women are also more 
 susceptible to urogenital infections , supporting the theory that colonization 
 of the vagina by commensal lactobacilli serves as a protection from these 
 pathogens [ 19 , 20 ] . although the methods by which these organisms do this are still unclear , it 
 appears to involve an ability to adhere to and to populate the vaginal epithelium and mucin layer , to 
 inhibit pathogens from taking over [ 2124 ] , to reduce pathogen 
 virulence [ 25 , 26 ] , and to modulate host defenses . hormone replacement therapy ( hrt ) alters the 
 bacterial profile of the vaginal tract of postmenopausal women , and restores a 
 lactobacilli - dominated state , as well as reduces the incidence of urinary tract 
 infections ( uti ) . in a study of women taking combination conjugated equine 
 estrogen and progesterone hrt , only 1 to 3 species of bacteria , mainly lactobacillus , were detected in the vaginal 
 mucosa of 87% of the women . in postmenopausal women not receiving hrt , 
 almost all subjects had vaginal mucosa populated with more than 1 organism , 
 many of which had pathogenic potential such as bacteroides , prevotella , and gardnerella , 
 associated with bacterial vaginosis ( bv ) , and e. coli and enterococcus , associated 
 with uti . while a vaginal 
 tract dominated by lactobacilli appears to protect the host against some 
 vaginal infections , it does not fully prevent colonization by other species . pathogens are still able to coexist with these commensal organisms , as shown by 
 burton and reid , where g. 
 vaginalis , a pathogen associated with bv , was detected in a vaginal sample 
 which also contained a species of lactobacillus . interestingly , g. vaginalis was 
 displaced beyond detectable limits for 21 days , following a single intravaginal 
 instillation of probiotic lactobacilli . as more and more studies are 
 uncovering the diversity microbiota of the vagina , it seems apparent that the 
 balance between a healthy and diseased state involves some sort of equilibrium 
 or see - saw effect , which can swing in either direction depending on a number of 
 factors , such as hormone levels , douching , sexual practices , as well bacterial 
 interactions and host defenses [ 20 , 21 ] . have proposed that innate immunity plays an important 
 role in the switch to bv from a healthy state . the mechanism they propose is through 
 microbial - induced inhibition of toll - like receptor expression and/or activity 
 blocking proinflammatory immunity , as well as a lack of 70-kda heat - shock 
 protein production , and a deficit in vaginal mannose - binding lectin 
 concentrations decreasing the capacity for microbial killing . three recent 
 studies have provided further insight into the host 's role . in a study of women 
 susceptible to uti , it was discovered that immunological defects in peripheral blood coexisted with a persistently 
 aberrant microbiota ( kirjavainen et al . ) . in postmenopausal women , bv 
 was associated with apparent 
 reduced expression of host antimicrobial factors . when probiotic l. rhamnosus gr-1 was administered to the vagina of premenopausal women , it resulted in 3 536 gene expression changes and increased 
 expression levels of some antimicrobial defenses . pathogenic 
 organisms are able to infect the vagina , with bv , yeast vaginitis , and utis 
 causing an estimated one billion or more cases per year [ 3235 ] . while there 
 is some evidence that the causative organisms can be transmitted by sexual 
 partners , these conditions will be discussed here as nonsexually transmitted . the majority 
 of cases are caused by candida albicans , 
 but c. glabrata , c. krusei , and c. tropicalis can be problematic . it is diagnosed by microscopic detection of dense 
 numbers of yeast cells on a vaginal smear , and by physical examination and the 
 presence of a white , mucous - like yeast discharge . of note , lactobacilli are 
 often found in patients with yeast vaginitis , therefore , the induction of 
 infection does not appear to require the yeast displacing or killing off the 
 lactobacilli . urinary tract infections 
 occur when pathogenic bacteria ascend from the vagina and replicate on , and 
 sometimes within , the bladder urothelium [ 32 , 38 , 39 ] . these infections are frequent 
 among women , with an estimated 50% suffering at some time in their life . symptoms 
 and signs include suprapubic pain , dysuria , pyuria , frequency and painful micturition , 
 and occasionally hematuria . the most frequent pathogen is e. coli , followed by enterococcus faecalis , and staphylococcus saprophyticus . diagnosis 
 can be achieved by presence of symptoms and signs , and urine samples containing 
 over 10 organisms / ml of the pathogens . in a portion of patients , the e. coli invade the bladder epithelium and 
 form dense biofilms that are recalcitrant to antibiotics . in women with no 
 history of uti , their vagina and perineum is most commonly colonized by 
 lactobacilli , while in women with recurrent uti there is an inverse 
 association between lactobacilli and e. 
 coli , suggesting that lactobacilli play a role in preventing 
 infection . the most common 
 urogenital disorder in women of reproductive age is bv , a condition discussed 
 above . the vaginal microbiota of bv patients typically contains a broader range 
 of species than found under healthy conditions , with atopobium vaginae , bacteroides spp . , gardnerella vaginalis , mobiluncus , megasphera , mycoplasma 
 hominis , peptostreptococcus , and prevotella being particularly prevalent [ 3 , 4246 ] . bv is 
 associated with multiple species of bacteria that occur in 90% of the cases , and essentially 
 consists of an elevated vaginal ph ( > 4.5 ) and depletion of lactobacilli . when symptoms and 
 signs do occur , they include fishy odor , discharge , and vaginal ph above 4.5 . 
 indeed , this formed the basis of the often - used amsel criteria for bv diagnosis : 
 presence of at least 3 of the following criteria : ( 1 ) release of an amine or 
 fishy odor upon addition of 10% potassium hydroxide , ( 2 ) a vaginal ph higher than 
 4.5 , ( 3 ) detection of at least 20% of clue cells ( which are vaginal cells 
 colonized by gram - negative rods ) , and ( 4 ) a milky homogeneous vaginal discharge 
 .   a gram - staining method called the 
 nugent score has also been used . it comprises a scoring system based on the 
 morphology of bacteria present in vaginal swab samples . a normal score is given 
 to samples showing predominantly gram - positive rods indicative of lactobacilli , 
 while the presence of predominantly small and curved shaped gram - negative rods 
 and gram - positive cocci , along with the absence of lactobacilli , is indicative 
 of bv . the bvblue test is another kit used to diagnose bv , and works by 
 detecting sialidase produced by pathogens associated with the condition [ 49 , 50 ] .   of note , aerobic vaginitis has also been 
 described in which the vagina is colonized by organisms such as e. coli and enterococci . during 
 pregnancy , bv can increase the risk of preterm labor and low birth weight [ 52 , 53 ] . other problems associated with bv include pelvic inflammatory disease , uti , and 
 increased susceptibility to sexually transmitted diseases , including hiv [ 5457 ] . the organisms associated with bv form dense biofilms on 
 the vaginal epithelium , and these are associated with increased resistance to lactobacilli - produced 
 lactic acid and hydrogen peroxide ( h2o2 ) which are 
 normally antagonistic to planktonic organisms . the biofilms are also able 
 to induce host expression of certain inflammatory factors , such as il-1 and 
 il-8 . it is not currently known whether the production of h2o2 by lactobacilli has a clinically protective role against bv . the increased 
 prevalence of h2o2-peroxide producing vaginal 
 lactobacilli in healthy women has been given as a reason to believe that it is 
 a protective factor , however , those studies used culture to recover the 
 lactobacilli , and arguably had they used nonculture methods , l. iners would have been the most 
 commonly isolated and it does not appear to produce h2o2 . it is possible to isolate l. iners by 
 culture , but it requires selective media and extensive incubation . the same 
 group found that women with the h2o2-producing vaginal l. crispatus or l. jensenii had a 
 significantly lower incidence of bv than women with a different vaginal flora 
 . however , alvarez - olmos et al . 
  and rosenstein et al . 
 found h2o2-producing lactobacilli in 85% and 91.7% , respectively , of women 
 with bv . it could be argued that the high prevalence of h2o2-producing 
 lactobacilli shows that this compound is not protective . mclean 
 and mcgroarty   conducted an in vitro study showing that increasing culture ph 
 reduced the bacteriostatic effects of l. acidophilus on g. vaginalis nctc 11292 by 60% ; a 30% reduction in bacteriostatic effects was seen when 
 catalase was introduced to degrade h2o2 . klebanoff et al . 
 found that the toxicity of h2o2-producing lactobacilli was inhibited by 
 the presence of catalase but lactobacilli that do not produce h2o2 were not affected . high concentration of h2o2-producing lactobacilli inhibits the 
 growth of both g. vaginalis and bacteroides bivius . however , low 
 concentrations of h2o2-producing lactobacilli must be combined 
 with myeloperoxidase and chloride in vaginal mucus , to be toxic toward g. vaginalis , with a maximum toxicity in a ph range of 5 to 6 . a ph of   4.5 inhibited the growth of g. vaginalis on its own and this effect 
 increased with the addition of the above combination . suffice to say , h2o2 is likely one of 
 several factors involved in competition with other organisms in the vagina . as antimicrobial treatment of urogenital infections is not always 
 effective , and problems remain due to bacterial and yeast resistance , recurrent 
 infections [ 65 , 66 ] , as well as side effects , it is no surprise that 
 alternative remedies are of interest to patients and their caregivers . it is 
 assumed that recurrences are due to antimicrobials failing to eradicate the 
 pathogens , perhaps because of biofilm resistance , or that the virulent 
 organisms come back from their source ( the person 's gut , or a sex partner ) and 
 attack a host whose defenses are suboptimal . young girls who suffer from uti 
 are more likely to have repeated episodes in adulthood , and overall many uti , 
 bv , and yeast vaginitis patients will have a recurrence [ 21 , 67 ] . recurrent 
 infection may also be due to the elimination of the commensal organisms in the vagina 
 by the antimicrobial , thereby increasing susceptibility to recolonization by 
 pathogens [ 68 , 69 ] . this is one of the main reasons for considering the use of 
 probiotics , to replenish the commensal microbes as a way to lower the risk of 
 reinfection . in a study of 120 children with persistent primary 
 vesicoureteral reflux , l. acidophilus treatment daily was as effective as trimethoprim / sulfamethoxazole in reducing 
 the rate of uti ( p = .926 ) , suggesting that probiotics could provide a 
 prophylactic option . the route of delivery of probiotic lactobacilli has 
 intuitively been via direct instillation into the vagina . for example , the 
 weekly application of l. rhamnosus gr-1 and l. fermentum b-54 was shown 
 to reduce uti recurrences from an average of 6 to 1.6 per year . the ability 
 of a given strain of lactobacilli to adhere to vaginal cells was considered an 
 advantage in temporarily populating the vaginal [ 71 , 72 ] and creating an 
 environment conducive to the restoration of the host 's indigenous lactobacilli 
 rather than a return of pathogens . the adhesion of lactobacilli to the 
 uroepithelium varies among species and strains , as shown by in vitro studies , and may be 
 mediated by glycoprotein and carbohydrate adhesins binding to glycolipid receptors . 
 still , it is unclear the extent to which a difference in in vitro adhesion , say of 10 per 
 cell , means that an organism will succeed or fail to protect the host if 
 instilled into the vagina . thus , adhesion per se is not the definitive criteria 
 to predict success . once administered in a viable count of one billion or more , l. rhamnosus gr-1 and l. reuteri ( formerly fermentum ) rc-14 have been found to be detectable for three weeks 
 or more , depending on the host [ 74 , 75 ] . the concept of delivering lactobacilli orally to repopulate 
 the vagina was first reported in 2001 , and based upon the question  if 
 urogenital pathogens can do this , why can not lactobacilli  ? the organisms were 
 delivered in a milk base and shown to be recovered from the rectum ; therefore 
 supporting the concept that ingested strains could pass through the intestine , 
 reach the rectum , and potentially ascend to the vagina . this was confirmed 
 independently by others . in order to conduct clinical studies with the view of providing more women 
 with access to these strains , a two - year shelf life capsule formulation was 
 then developed and used successfully in a number of studies . an oral dose of 
 over one billion organisms per day was found to maintain a lactobacilli - dominated 
 vaginal presence . the time for this intervention to affect the vaginal 
 tract is obviously longer than direct vaginal instillation , and will depend on 
 viability of the strains as they pass through the stomach and gut . in 
 addition , the load of lactobacilli that can be delivered this way is clearly lower 
 than via vaginal administration . however , an advantage of the oral approach may 
 be the ability of the lactobacilli to reduce the transfer of yeast and pathogenic 
 bacteria from the rectum to the vagina , which could potentially lower the 
 risk of infection . in that randomized , placebo - controlled trial of 64 healthy 
 women ,   37% of the patients in the l. rhamnosus gr-1 and l. reuteri rc-14 probiotic group had a lactobacilli - dominated 
 normal vaginal microbiota restored from a bv vaginal flora compared to 13% in 
 the placebo group ( p = .02 ) . at both the 28-day and 60-day test points , 
 women in the lactobacilli treatment group had a greater number of vaginal lactobacilli 
 than women in the control group ( p = .08 and p = .05 , resp . ) as shown 
 by microscopy and culture . the ability of this oral probiotic therapy to create 
 a lactobacilli normal flora and convert some subjects from a bv status to 
 normal   goes beyond the proof - of - concept stage and provides a method for 
 women to help maintain vaginal health . failure of l. rhamnosus gg to be effective , at least in one small study , emphasizes the strain - specific 
 aspects of probiotic use . thus , one can not and should not utilize the data from 
 one strain to infer that another untested strain will provide the same 
 benefits . the mechanisms whereby lactobacilli function as anti - infective defenses 
 are still not fully understood . as discussed above , this may involve production 
 of antimicrobial factors , and maintenance of a 
 vaginal ph of   4.5 . it could also be due to biosurfactants 
 which alter the surrounding surface tension and reduce the ability of a wide 
 range of pathogens to adhere [ 82 , 83 ] . this might explain the relatively sparse 
 coverage of epithelial cells noted in healthy women . in addition , lactobacilli have been shown to bind ( coaggregate ) 
 some pathogens and this may be a means to block their adhesion , kill them 
 through production of antimicrobials , and prevent their spread to other areas 
 of the vagina and bladder . among 10 strains of lactobacilli .   found , 
 in vitro , that lactobacillus 
 gasseri 335 and lactobacillus salivarius fv2 were able to coaggregate 
 with g. vaginalis . when these strains of lactobacilli were combined with lactobacillus brevis cd2 in a vaginal tablet , adhesion of g. 
 vaginalis boris et al . found that the adherent properties g. vaginalis were similarly affected by lactobacillus acidophilus . it 
 has been known for some time that lactobacilllus produce bacteriocins that can inhibit the 
 growth of pathogens , including some associated with bv , such as g. vaginalis . only relatively recently has a study shown in animals that bacteriocin 
 production might have an effect in vivo . a stable mutant of lactobacillus salivarius ucc118 that did 
 not produce a specific bacteriocin was unable to protect mice against listeria intestinal infection , while the 
 wild type did , thereby leading the authors to conclude that bacteriocin 
 production can be a primary mediator of anti - infective defense . shalev 
 et al .   assessed 46 premenopausal 
 women with   4 episodes of bv and/or vaginal 
 candidiasis in the previous year , to compare the recurrence of bv using a probiotic 
 yoghurt versus one that was pasteurized . patients were not receiving long - term 
 antibiotics or immunosuppressive therapy and had not consumed yoghurt prior to 
 the commencement of the study . they were randomly assigned to one of two 
 treatment groups and ingested 150 ml of either pasteurized yoghurt ( n = 23 ) or 
 yoghurt containing l. acidophilus at   > 1.0  10 colony - forming units ( n = 23 ) . yoghurt was consumed 
 daily for two months followed by two months of no yoghurt . there was a 60% 
 reduction in bv episodes among patients consuming probiotic yoghurt after one 
 month while only a 25% reduction occurred in subjects who received pasteurized 
 yoghurt ( p = .004 ) . after two months of yoghurt consumption , the results 
 were similar ; however , 25% of patients from both groups had left the study . product integrity was only assessed prior to the study and no adverse effects 
 were reported . neri 
 et al .   studied 84 women in the first trimester of pregnancy to 
 observe the effects of probiotic - containing yoghurt on bv . the subjects were randomized to one of three treatment 
 groups : inserting a tampon containing 5% acetic acid ( n = 32 ) , a 10 to 15 ml 
 vaginal douche containing   > 1.0  10   colony - forming units / ml of l. acidophilus ( n = 32 ) , or no treatment 
 ( n = 20 ) . amsel criteria ( three of five findings : release of an amine fishy odor ; 
 release of amine odor after the addition of 10% potassium hydroxide ; vaginal ph 
 greater than 4.5 ; clue cells in the vaginal fluid ; milky homogenous vaginal 
 discharge ) were absent in 88% , 38% , and 15% of subjects 
 who received intravaginal lactobacilli , acetic acid tampons , and placebo , 
 respectively , after 30 days . there was a significant difference in the cure 
 rate between probiotic and control groups ( p < .005 ) , and lactobacilli 
 and acetic acid groups ( p = .004 ) . fredricsson et al .   conducted an 
 open - label trial to compare the cure rates of 61 women with bv given one of 
 four intravaginal products . each of the four 
 treatments that patients were randomized to receive was administered twice a day for 
 seven days : 5 ml of fermented milk containing between 5.0  10 and   2.0  10 colony - forming units / ml of l. 
 acidophilus ncdo 1748 ( n = 13 ) , 5 ml of acetic jelly ( n = 15 ) , 5 ml of estrogen 
 cream ( n = 16 ) , or 500 mg metronidazole vaginal tablets ( n = 15 ) . bv was considered 
 to have been cured if   1 amsel criterion was present at 4 and 8 weeks . after 
 both 4 and 8 weeks from the initiation of treatment , the cure rates in the 
 metronidazole , acetic acid , probiotic , and estrogen groups were 93% , 18% , 7% , 
 and 6% , respectively ; no statistical analysis was reported . in this case the cure rates of bv in 57 women with a mean age of 
 24 were studied following treatment with either  probiotics  or placebo in a 
 double - blind trial . subjects were randomized 
 to receive either a vaginal suppository containing 1.0  10 colony - forming 
 units of l. acidophilus ( n = 28 ) or 
 placebo ( n = 29 ) . symptom resolution , which was not clearly defined , was used to evaluate 
 the cure of bv . at 710 days after the 
 commencement of treatment , bv symptoms were absent in 57% of women in the 
 probiotic group and 0% of women in the placebo group ( p < .005 ) . after 
 20 to 40 from the initiation of treatment , the cure rate in the probiotic group 
 fell to 21% and remained at 0% in the placebo group ( p = ns ) . this poorly 
 conceived study is hard to interpret and is insufficient to verify efficacy of 
 the product . eriksson et 
 al .   studied how lactobacilli augmented antibiotics in curing bv 
 through a double - blind , placebo - controlled trial including 187 women with a 
 median age of 32 over two menstrual periods . open - label 
 treatment with 100 mg / d of clindamycin was administered to all patients for 3 
 days . the subjects were then randomized to one of two treatment groups which 
 required at least five tampons to be inserted during the next menstrual period . the treatment groups were placebo tampons ( n = 96 ) and tampons impregnated with l. fermentum , l. gasseri , and l. rhamnosus at 1.0  10 colony - forming 
 units per tampon ( n = 91 ) . cure rates of bv were assessed by the absence of amsel 
 criteria after the second menstrual period in both the probiotic and placebo groups , 
 and found to be 56% and 62% , respectively , ( p = ns ) . infection with candida was reported in 14.3% of subjects 
 in the probiotic group and 13.5% of patients in the placebo group . the viable 
 number of bacteria per tampon diminished to 10 colony - forming units 
 by the end of the study . in short , the 
 rationale for administering lactobacilli during menses could be questioned , as 
 it exposes the users ' blood stream directly to the organisms , and the flushing 
 effect of menstruation may be nonconducive to lactobacilli repopulating the 
 vagina . a comparison of 
 intravaginal probiotics and metronidazole gel in treating 40 women ( ages 18 to 
 50 ) with bv was conducted by a single - blind study by anukam et al . . the presence of   3 amsel 
 criteria , a nugent score of   7 , and a positive sialidase test led to a 
 diagnosis of bv . they either inserted an intravaginal capsule with l. rhamnosus gr-1 and l. reuteri rc-14 at 1.0  10 colony - forming 
 units nightly ( n = 20 ) or applied a 0.75% metronidazole gel twice daily ( n = 20 ) . a 
 nugent score of   3 at 30 days indicated a cure of bv . a bv cure rate of 88% in 
 the probiotic group and 50% in the metronidazole group was found ( p = ns ) . treatment was prematurely discontinued by patients in both the metronidazole 
 and probiotic groups at 10% and 15% , respectively . this study , albeit small in 
 size , showed the potential of probiotics to cure bv . the 
 efficacy of combining probiotics or placebo with oral metronidazole was assessed 
 in 125 women aged 18 to 44 . oral 
 metronidazole was administered at 500 mg twice daily to all patients for 7 days , 
 and they were randomized to receive twice - daily oral capsules containing either 
 a placebo ( n = 60 ) or l. rhamnosus gr-1 
 and l. reuteri rc-14 at 1.0  10 colony - forming units ( n = 65 ) for a total treatment duration of 30 days . at the 
 end of 30 days , bv was considered absent if the patient had a negative sialidase 
 test and a nugent score of <3 . ( p < .001 ) . if an intermediate nugent score was 
 regarded as  cure of bv  , the cure rate was 100% with metronidazole and 
 probiotics versus 70% with metronidazole and placebo . this study is important 
 as it implies that probiotics can augment the effects of antibiotics in 
 treatment of disease . annually , over one billion doses of probiotics are 
 administered worldwide , and those administered for urogenital health have been 
 well tolerated [ 11 , 75 , 9396 ] . in addition , 
 the mouth , gastrointestinal tract , and female genitourinary tract are inhabited 
 by lactobacillus . yet , most cases occur in patients 
 with chronic diseases or debilitating conditions that provide direct access to 
 the bloodstream from a leaky gut . only 1.7% of 241 cases of bacteremia , 
 endocarditis , and localized infections associated with lactobacillus that were investigated by cannon et al . were considered to have a 
 possible link with heavy consumption of dairy products . only one case had 
 a lactobacillus isolate that was 
 indistinguishable from a probiotic strain . there was no connection between the 
 species of lactobacillus isolated and 
 the type of infection or mortality . a recent study that directly instilled a 
 six - strain bacterial product into the intestine of patients with severe , potentially 
 fatal pancreatitis portrayed probiotics as being dangerous . however , the 
 product had never been proven to be probiotic , it was administered as a drug 
 unlike 99.9% of probiotics , the randomization process led to patients with 
 multiorgan failure being given large doses of live bacteria , and the authors 
 failed to provide a rationale for the study in an appropriate animal model . nevertheless , safety of probiotic use must 
 continually be monitored and considered when doing clinical studies . the 
 potential for transfer of antibiotic resistance is one factor to consider , 
 although it remains to be proven that probiotics have contributed in any way to 
 drug resistance , or disease . rather , the overuse of antibiotics , especially in 
 livestock feed and long - term prevention of infection , remains a root cause of 
 the increasing concerns over drug resistance . efforts to substitute 
 prophylactic antibiotics with probiotics , especially in children with recurrent 
 uti   and perhaps some patients preparing to undergo surgery , are 
 worthy of pursuit . molecular 
 methodologies are providing a greater understanding of the dynamic microbial 
 presence , both short and long term , in the vagina . the defenses of the host 
 which include some of these microbes perform a remarkable function given the 
 opportunity of pathogens to cause infection . the use of probiotic lactobacilli 
 to prevent infection has a good rationale , and an excellent safety record , but 
 so far only a few strains have been clinically proven to be effective , in 
 particular to prevent bv . it is critically important that strains be 
 characterized and tested clinically using the delivery system of choice ( oral , 
 vaginal , dried powder , or in suspension ) . many more studies are needed to optimize the 
 defensive properties of the vaginal microbiota , but the potential remains that 
 the health of many women can be improved by probiotic intervention .
the human vagina is inhabited by a range of microbes from a pool of over 50 species . 
 lactobacilli are the most common , particularly in healthy women 
 . the microbiota can change composition rapidly , for reasons that are not fully clear . 
 this can lead to infection or to a state in which organisms with pathogenic potential coexist with other commensals . 
 the most common urogenital infection in premenopausal women is bacterial vaginosis ( bv ) , a condition characterized by a depletion of lactobacilli population and the presence of gram - negative anaerobes , or in some cases gram - positive cocci , and aerobic pathogens . 
 treatment of bv traditionally involves the antibiotics metronidazole or clindamycin , however , the recurrence rate remains high , and this treatment is not designed to restore the lactobacilli . in vitro studies have shown that lactobacillus strains can disrupt bv and yeast biofilms and inhibit the growth of urogenital pathogens . the use of probiotics to populate the vagina and prevent or treat infection has been considered for some time , but only quite recently have data emerged to show efficacy , including supplementation of antimicrobial treatment to improve cure rates and prevent recurrences .