Virginia Ocan˜a et al Strain CRL 1251 CRL 1266 CRL 1289 CRL 1328 Media LAPTg MRS LAPTg MRS LAPTg MRS LAPTg MRS SXT 23/25 > 40 20/22 > 28 30/30 > 34 26/28 29/31 Table 1: Diameters of the halos obtained for lactobacilli included into LAPTg and MRS agars and tested with antibiotics employed in am- bulatory UTI treatment. TMS: trimethoprim-sulfamethoxazole (25 µg), CEC: cefaclor (30 µg), NOR: norﬂoxacin (10 µg), NAL: nalidixic acid (30 µg), PMD: pipemidic acid (20 µg), AMN: ampicillin (10 µg), CEF: cephalosporin (30 µg), NIT: nitrofurantoin (300 µg), AMS: aminopenicillin-sulbactam (20 µg). Note: commercial discs do not specify the type of cephalosporin employed. Table 2: Inhibition halos for Staphylococcus aureus ATCC29213 in LAPT and MRS agars compared to results published for NCCLS reference media using antibiotics for UTI treatment. SXT: trimethoprim-sulfamethoxazole, CEC: cefaclor, NOR: norﬂoxacin, NAL: nalidixic acid, PMD: pipemidic acid, AMP: ampicillin, CEP: cephalosporin, NIT: nitrofurantoin, SAM: aminopenicillin-sulbactam. Means of the diameters obtained in LAPTg and MRS agar from the assays performed by duplicate are shown. Note: commercial discs do not have the speciﬁcation of the type of cephalosporin employed. AMP 37/39 > 40 30/34 40/40 36/36 33/35 30/34 37/39 CEP 39/41 > 40 30/32 > 30 30/36 27/29 36/38 39/41 NIT 30/30 > 40 20–26 > 30 30/30 21/23 24/26 27/29 AMS > 39 > 40 34–36 > 28 40/40 40/40 34734 35/37 3 CEC 29/31 > 40 30/34 > 30 36/36 > 34 34/34 23/25 AMP 10 16 27–35 NOR 19/21 31/33 16/22 21/23 24/30 33/35 16/18 27/29 PMD 21 24 NP Antibiotic NAL 17/19 25/27 18/20 19/21 20/30 29/31 11/12 17/19 NAL 22 14 NP PMD 21/23 30/30 20/24 17/19 30/34 29/31 18/22 27/29 NOR 22 32 17–28 Halo diameter (mm) SAM 18 24 29–37 NIT 20 34 18–22 CEP 18 28 27–31 ∗Media recommended by NCCLS1. NP: data not published. were of the same diameters to those obtained in Mu¨ller Hin- ton agar, it would suggest that the disc diﬀusion method could be performed in LAPTg or MRS with NCCLS refer- ence strain. S aureus ATCC25922 was inoculated in LAPTg and MRS agar and the diameters of the halos obtained with antibiotic discs were compared to those of Mu¨ller Hinton. It was observed that S aureus ATCC25922 was able to grow on LAPTg and MRS agars. However, the diameters of the halos were diﬀerent to those published by the NCCLS for Mu¨ller Hinton. The diameters obtained in a Mu¨ller Hinton, MRS, and LAPTg agar are shown in Table 2. MICs Considering that the six Lactobacillus strains were able to grow in LAPTg, this medium was selected to study the MICs. LAPTg agar or broth was employed and the obtained results are shown in Tables 3 and 4. All the tested lacto- bacilli were able to grow at elevated concentration of metron- idazole (> 1000 µg/mL). They were also able to grow at high concentration of streptomycin (50–100 µg/mL), kan- amycin (100–500 µg/mL), quinolones (norﬂoxacin, 250– 1000 µg/mL, and ciproﬂoxacin, 10–100 µg/mL), chloramph- enicol (250 µg/mL), cephalosporins (ceftriaxone, 100 µg/mL; ceftazidime,100 µg/mL), and aztreonam (100 µg/mL). For the other antibiotics assayed, the susceptibility depended on CEC 26 36 29–37 SXT 14 38 24–32 LAPTg MRS Mu¨ller Hinton∗ each particular strain. L johnsonii CRL1294 and L paracasei CRL1289 did not grow at concentrations of 1 µg/mL of novo- biocin and vancomycin, but were able to grow at higher con- centrations of almost all the other antibiotics (> 100 µg/mL). L acidophilus CRL1266 and L salivarius CRL1328 were able to grow at 10 and 1000 µg/mL of vancomycin, respectively. DISCUSSION In this paper, the antimicrobial susceptibility of six probi- otic vaginal Lactobacillus strains was studied. The knowledge of the antimicrobial susceptibility or resistance is of inter- est to predict the behavior of an exogenously applied pro- biotic formula in patients subject to any type of chemother- apy, as well as to consider the concomitant use of the pro- biotic and antibiotics for the restoration of the normal uro- genital ﬂora. On the other side, antimicrobial susceptibility of exogenously applied microorganisms needs to be known for treating eventual collateral eﬀects [19–22]. In this regard, the performance of antimicrobial susceptibility testing may be considered as both a necessary selection criterion for pro- biotic cultures and an eﬀective guide for speciﬁc antimicro- bial therapy [23]. Up to date, a standardized method to study the antimi- crobial susceptibility of microorganisms belonging to the genus Lactobacillus has not been published, probably because