Virginia Ocan˜a et al Klein et al [19] who have used the same base media with horse blood (3%). More recently, Klare et al [28] proposed a mixed formulation of Iso-Sensitest broth and MRS with or without supplementation with L-cysteine and Delgado et al [27] the use of MRS. In order to know if LAPTg or MRS could substitute Mu¨ller Hinton as a standard medium, the size of the ha- los obtained with a closely phylogenetic-related type mi- croorganism, S aureus ATCC29213 was determined. Diﬀer- ent publications have cited the use of related type strains for this type of studies. Klein et al [19] have reported the use of Enterococcus and Felten et al [26] the use of Staphylococcus strains. In this study it was observed that the diameters of the inhibition halos for S aureus ATCC 29213 in LAPTg or MRS were diﬀerent to those obtained in Mu¨ller Hinton. These ob- servations conﬁrm that the characteristic of “susceptible” or “resistant” deﬁned by NCCLS for assays performed with type strains in Mu¨ller Hinton agar cannot be considered when other media are being employed. The MICs values obtained were dependant on the lac- tobacilli under consideration as it has also been reported by Danielsen and Wind [30]. Most of the strains have been found to be resistant to high concentrations of chloram- phenicol, aztreonam, norﬂoxacin, ciproﬂoxacin, ceftazidime, ceftriaxone, and metronidazole. Susceptibility to other an- tibiotics (rifampicin, erytromicin, novobiocin, vancomycin, ampicillin, tetracycline, clarithromycin, imipenem, and cefo- taxime) depended on each particular Lactobacillus strain. On the other hand, no correlation had been obtained with the disc diﬀusion method and the MICs results. Resistance or susceptibility to vancomycin has deserved a special consideration in terms of classiﬁcation of lactic acid bacteria, mainly for lactobacilli associated with human in- fections or isolated from food [26, 34–36]. Hamilton and Shah [37] have used the susceptibility to vancomycin as an aid to identify Lactobacillus species. Simpson [35] and Fel- ten et al [26] have associated sensitivity to vancomycin with the Lactobacillus acidophilus group or those originally called “Thermobacteria” while Simpson [35] has observed resis- tance to vancomycin in lactic acid bacteria belonging to the “Betabacteria” group. However, Klein et al [19] and Griﬃths et al [20] have reported resistance to vancomycin in diﬀerent L acidophilus strains isolated from clinical samples. Accord- ing to the results obtained in this work, 4 of 6 lactobacilli were able to grow at concentrations lower than 1 µ g/mL of vancomycin. L crispatus and L salivarius, both homofermen- tatives (Thermobacteria), were able to grow at vancomycin concentrations higher than 10 and 1000 µg, respectively. Metronidazole and clindamycin are the most commonly used antibiotics for the treatment of bacterial vaginosis. Can- didate probiotic Lactobacillus strains were able to grow at high concentrations of metronidazole and clindamycin, ex- cept for L acidophilus CRL1251 and L salivarius CRL1328 that did not grow at concentrations as low as 0.1 µg/mL of the last antibiotic. These results suggest that selected strains could be used for a restoration therapy together with the antimicrobial bacterial vaginosis treatment. Simoes et al [9] have also studied the eﬀect of metronidazole on the growth 5 of vaginal lactobacilli. These authors have observed partial and complete inhibition at concentration above 1000 µg/mL while they have reported a stimulating eﬀect at concentra- tions between 128 µg/mL and 256 µg/mL. Carlstedt-Duke et al [38] have observed a low eﬀect of clindamycin on lacto- bacilli when employing this antibiotic simultaneously with the lactic acid bacteria to restore the normal ﬂora of the gut of rats. Antimicrobial resistance of candidate probiotic lacto- bacilli was found to be not associated with extra chromo- somal elements, as plasmids were not found in the strains, by applying the technique of Maniatis et al [39] (data not shown). This observation would indicate a low probability of antibiotic resistance transmission to pathogenic microor- ganisms. However, other diﬀerent methods should be tested to conﬁrm the absence of plasmids, mainly considering that L salivarius CRL1328 is an aggregating strain able to produce bacteriocins, both characteristics frequently associated with extra chromosomal DNA [40, 41]. More studies must be undertaken to deﬁne the adequate and standardized method to study the antimicrobial suscep- tibility of the Lactobacillus genus. The use of LAPTg and MRS as base media for the disc diﬀusion method deserves further studies. However, determination of the MICs is, up to date, the only reliable test to predict the susceptibility or the resis- tance to antibiotics of Lactobacillus strains. ACKNOWLEDGMENTS This paper was supported by grants from Consejo Na- cional de Investigaciones Cient´ıﬁcas y Te´cnicas de Argentina (CONICET). The Lactobacillus strains employed in this study were licensed to ANIDRAL (Italy). REFERENCES [1] Hammes W, Weiss N, Holzapfel W. The genera Lactobacillus and Carnobacterium. In: Balows A, Tru¨per H, Dworkin M, Harder W, Schleifer KH, eds. The Prokaryotes. A Handbook on the Biology of Bacteria: Ecophysiology, Isolation, Applications. Vol II. 2nd ed. New York, NY: Springer; 1995:1536–1594. [2] Fuller R. Probiotics: their development and use. In: Fuller R, Heidt PJ, Rusch V, Van der Waaij D, eds. Probiotics: Prospects of Use in Opportunistic Infections. 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