Abstract

Ehab Essa Kheadr

The present study was conducted to determine the susceptibility of 13 Lactobacillus strains to 14 antibiotics and to evaluate the impact of some gastrointestinal stressful conditions, particularly acid and bile stress, as well as acid adaptation on their antibiogram profiles. The strains tested were 2 of Lactobacillus acidophilus, 1 Lb. delbrueckii subsp. bulgaricus, 2 Lb. casei, 1 Lb. casei paracasei subsp. paracasei, 1 Lb. delbrueckii subsp. lactis, 4 Lb. plantarum and 2 Lb. rhamnosus. In control trails, the majority of the strains tested were susceptible to ampicillin, penicillin, chloramphenicol, erythromycin, novobiocin and nisin A, but resistant to vancomycin, kanamycin, neomycin, paromomycin, streptomycin and nalidixic acid. Lactobacilli strains showed variable susceptibility to cloxacilline and tetracycline. Acid-adaptation (strains adapted to grow at pH 4.0) resulted in increased resistance to cloxacilline, erythromycin and tetracycline, in strain dependent manner. Acid- stressed (exposure to pH 2 for 90 min at 37Ë?C) lactobacilli appeared to be more resistant to ampicillin, cloxacilline, chloramphenicol and tetracycline compared with un-stressed strains. In the presence of 0.3% (w/v) oxgall, lactobacilli became more susceptible to aminoglycosides and slightly resistant to cell wall-targeted antibiotics. However, oxgall stress (exposure to 0.3% (w/v) oxgall for 90 min at 37Ë?C) slightly modified antibiogram profile depending on the strain tested. Results reported in this study showed that acid and oxgall stresses could substantially modify antibiotic susceptibility/resistance profile of lactobacilli, which may thus affect their probiotic capacity especially when used along with antibiotics.