In vitro antibiotic susceptibility of lactobacilli isolated from commercial products containing active lactobacilli

To survey the antibiotic susceptibility patterns of some commercially available Lactobacillus, we collected four commercial products that contain active Lactobacillus. We incubated individual product and identified these colonies by the methods of API50 CH test kit and RAPID ID 32A kit. Strains of Streptococcus thermophilus, Bifidobacterium infantis, Lactobacillus acidophilus and Lactobacillus casei were collected. By agar dilution method, each identified strain was inoculated to Brucella blood agar-MIC plates. Each plate contained one of the following antibiotics with different concentrations: amoxicillin, cephalothin, gentamicin, vancomycin, erythromycin, rifampin, tetracyclin and penicillin G, clindamycin, chloramphenicol, cefmetazole, metronidazole, ampicillin/sulbactum, cefoxtin, etc. After incubation, the growth condition of each Brucella blood agar-MIC plate was observed and the breakpoint of each antibiotic to different Lactobacillus products determined. The MICs of amoxicillin, ampicillin/sulbactum and penicillin-G to all identified strains were < or =2 microg/ml and those of vancomycin, clindamycin, erythromycin, metronidazole, cefmetazole and cefoxtin for L. casei were >32 microg/ml. L. casei was more resistant to all the testing antibiotics than the other strains. According to the MICs of the above antibiotics, proper active lactobacillus products could be chosen to prevent antibiotic-associated diarrhea in the pediatric field.