ORIGINAL ARTICLE Influence of probiotic vaginal lactobacilli on in vitro adhesion of urogenital pathogens to vaginal epithelial cells G. Za ´ rate and M.E. Nader-Macias Centro de Referencia para Lactobacilos (CERELA)-CONICET, San Miguel de Tucuman, Argentina Introduction The human vagina is a complex ecosystem composed by a stratified squamous nonkeratinized epithelium and its indigenous microbiota. In healthy premenopausal women, the vaginal bacterial microbiota is dominated by Lactoba- cillus species, mainly Lactobacillus crispatus, Lactobacillus jensenii and Lactobacillus gasseri at a level of 10 7 – 10 8 CFU g )1 of fluid (Pavlova et al. 2002). It is generally accepted that lactobacilli play a major role in maintaining the urogenital health by preventing the overgrowth and invasion of pathogenic bacteria (Lepargneur and Rous- seau 2002) by a combination of competitive exclusion, competition for nutrients and antimicrobial substances production such as hydrogen peroxide, organic acids, bacteriocins and biosurfactants (Velraeds et al. 1998; Boris and Barbe ´s 2000; Lepargneur and Rousseau 2002; Reid and Burton 2002). In fact, it has been observed that a disruption of the population balance and particularly a depletion of vaginal lactobacilli is associated with an increase in the incidence of bacterial vaginosis, yeast vagi- nitis, urinary infections and sexually transmitted diseases (Redondo-Lo ´ pez et al. 1990; Hawes et al. 1996; Gupta et al. 1998; Martin et al. 1999). For these reasons, in the Keywords adhesion, genitouropathogens, lactobacilli, probiotics, vagina, vaginal epithelium. Correspondence M.E. Nader-Macias, Centro de Referencia para Lactobacilos (CERELA)-CONICET, Chacabuco 145, 4000 San Miguel de Tucuman, Argentina. E-mail: fnader@cerela.org.ar 2005/1388: received 21 November 2005, revised 10 February 2006 and accepted 23 February 2006 doi:10.1111/j.1472-765X.2006.01934.x Abstract Aims: Lactobacilli, the predominant micro-organisms of the vaginal microbio- ta, play a major role in the maintenance of a healthy urogenital tract by pre- venting the colonization of pathogenic bacteria. The aim of the present study was to assess the ability of four vaginal Lactobacillus strains, previously selected for their probiotic features, to block in vitro the adherence of three human urogenital pathogens to vaginal epithelial cells (VEC). Methods and Results: Three types of assays were performed in order to deter- mine the inhibitory effect of lactobacilli on adhesion of urogenital pathogens to VEC: blockage by exclusion (lactobacilli and VEC followed by pathogens), competition (lactobacilli, VEC and pathogens together) and displacement (pathogens and VEC followed by the addition of lactobacilli). Bacterial adhe- sion to VEC was quantified by microscopy (·1000) after Gram’s stain. All the strains were able to inhibit by exclusion and competition the adhesion of Sta- phylococcus aureus to VEC but none was able to decrease the attachment of Escherichia coli by neither of the mechanisms assayed. Only Lactobacillus acid- ophillus CRL 1259 and Lactobacillus paracasei CRL 1289 inhibited the attach- ment of Group B streptococci (GBS) to VEC by exclusion and competition respectively. Conclusions: Lactobacillus of vaginal origin were able to inhibit the attachment of genitouropathogenic Staph. aureus and GBS to the vaginal epithelium. Significance and Impact of the Study: The results support the probiotic poten- tial of these Lactobacillus strains as anti-infective agents in the vagina and encourage further studies about their capacity to prevent and manage urogeni- tal tract infections in females. Letters in Applied Microbiology ISSN 0266-8254 174 Journal compilation ª 2006 The Society for Applied Microbiology, Letters in Applied Microbiology 43 (2006) 174–180 ª 2006 The Authors