Hindawi Publishing Corporation Infectious Diseases in Obstetrics and Gynecology Volume 2006, Article ID 18182, Pages 1–6 DOI 10.1155/IDOG/2006/18182 Review Article Antibiotic Susceptibility of Potentially Probiotic Vaginal Lactobacilli Virginia Oca n˜a,1 Clara Silva,2 and Mar´ıa Elena Nader-Mac´ıas3 1 Nuevo Hospital El Milagro, Salta 4400, Argentina 2 Facultad de Bioqu´ımica, Qu´ımica y Farmacia, Universidad Nacional de Tucuma´n, Tucuma´n 4000, Argentina 3 Centro de Referencia para Lactobacilos (CERELA-CONICET), Chacabuco 145, Tucuma´n 4000, Argentina Received 2 June 2006; Accepted 14 July 2006 Objective. To study the antimicrobial susceptibility of six vaginal probiotic lactobacilli. Methods. The disc diﬀusion method in M u¨eller Hinton, LAPTg and MRS agars by the NCCLS (National Committee for Clinical Laboratory Standards) procedure was performed. Due to the absence of a Lactobacillus reference strains, the results were compared to those of Staphylococcus aureus ATCC29213. Minimal Inhibitory Concentration (MIC) with 21 diﬀerent antibiotics in LAPTg agar and broth was also deter- mined. Results. LAPTg and MRS agars are suitable media to study antimicrobial susceptibility of lactobacilli. However, the NCCLS procedure needs to be standardized for this genus. The MICs have shown that all Lactobacillus strains grew at concentrations above 10 µg/mL of chloramphenicol, aztreonam, norﬂoxacin, ciproﬂoxacin, ceftazidime, ceftriaxone, streptomycin and kanamycin. Four lactobacilli were sensitive to 1 µg/mL vancomycin and all of them were resistant to 1000 µg/mL of metronidazole. Sensitivity to other antibiotics depended on each particular strain. Conclusions. The NCCLS method needs to be standardized in an appropri- ate medium to determine the antimicrobial susceptibility of Lactobacillus. Vaginal probiotic lactobacilli do not display uniform susceptibility to antibiotics. Resistance to high concentrations of metronidazole suggests that lactobacilli could be simultaneously used with a bacterial vaginosis treatment to restore the vaginal normal ﬂora. Copyright © 2006 Virginia Ocan˜a et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. INTRODUCTION Bacteria of the genus Lactobacillus have been proposed as probiotic microorganisms to restore the ecological equilib- rium of the intestinal, respiratory, and urogenital tracts [1]. This type of bacterial replacement therapy has been widely used as fermented milks to prevent diarrhea in humans and animals [2, 3]. They have also been increasingly considered for their use in women to prevent genital and urinary tract infections [4–8]. It has been found that administration of antimicrobial substances alters the microbial balance of the vagina and sup- presses certain bacterial groups [4]. The eﬀect of these sub- stances on autochthonous Lactobacillus is of interest in un- derstanding the development of genital and urinary tract in- fections related with the lack of these bacteria [9]. The present study was conducted to determine the an- timicrobial susceptibility of six candidate probiotic Lacto- bacillus strains. These lactobacilli have been previously se- lected for probiotic properties as surface hydrophobicity [10], self-and coaggregation [11], adhesion to vaginal ep- ithelial cells [12], and production of antimicrobial substances [13–15]. The main aims of knowing the behavior of exoge- nously applied Lactobacillus under the eﬀect of antimicrobial substances are to have an approach of the response of lacto- bacilli administered to patients subjected to some kind of an- tibiotic therapy and to consider the concomitant use of lac- tobacilli and an antibiotic to restore the disrupted ecological environment. Having in mind that a method to study antimicrobial susceptibility of genus Lactobacillus has not been standard- ized yet, diﬀerent techniques were assayed. The results ob- tained by using the disc diﬀusion method with culture media diﬀerent from Mu¨ ller Hinton agar proposed by the NCCLS (National Committee for Clinical Laboratory Standards) and the determination of the minimal inhibitory concentrations in an enriched medium are described in this paper. MATERIALS AND METHODS Microorganisms and growth conditions The microorganisms used in this study were Lactobacillus acidophilus CRL1251 (Centro de Referencia para Lactobaci- los Culture Collection), Lactobacillus paracasei ssp paracasei