Lactobacillus plantarum strains were isolated from fully ripened, white brined Bulgarian home-made cheeses. Strains were derived from phenotypically homogenous Lactobacillus group and were identified as L. plantarum based on both phenotypic and molecular identification (species-specific and multiplex PCR) methods. Heterogeneity of L. plantarum isolates was evaluated by Rep-PCR analysis. Further antimicrobial activity, antibiotic susceptibility and transit tolerance of the strains were evaluated. Most of them showed broad spectrum of activity against Gram-negative bacteria (including human pathogens) independent on the presence of organic acids or hydrogen peroxide. All strains were sensitive to amoxicillin and sulfamethoxazole/trimethoprim, resistant to clinically relevant beta -lactame antibiotics (penicillin and ampicillin) and to nalidixic acid, ciprofloxacin, streptomycin, and vancomycin. Significant variability in the sensitivity to tetracycline was noted. The tolerance to low pH, bile salts, pepsin and pancreatin at concentrations similar to those in the gastrointestinal tract was strain-dependent. The exposure to bile salts was less destructive than exposure to pH 2.0 for all tested strains. Based on their combined responses to the above selection criteria, four L. plantarum strains, RL29, RL34, RL36 and RL37, were selected as potential probiotics for in vivo studies.

The antimicrobial activity of 18 different extracts from in vivo and in vitro grown L. album L. plants was evaluated against clinical bacteria and yeasts using the well diffusion method. All the used extracts demonstrated antibacterial activity, whereas only the water extracts from leaves (in vivo) possessed antifungal activity against Candida albicans NBIMCC 72 and Candida glabrata NBIMCC 8673 (14 and 20 mm diameter of inhibition zones and MIC 10 mg/ml, respectively). The methanol and ethanol extracts obtained from the in vitro propagated plants had a broader spectrum of antibacterial activity than those from in vivo plants, while the opposite tendency was observed for the chloroform extracts. All tested flower extracts possessed antimicrobial activity. The chloroform extract from in vivo flowers demonstrated the highest activity against E. faecalis NBIMCC 3915, S. aureus NBIMCC 3703, P. hauseri NBIMCC 1339 and P. aeruginosa NBIMCC 3700 (22 mm, 13 mm, 11 mm, 23 mm zone diameter of inhibition and MIC 0.313 mg/ml, respectively). The water extracts from leaves (both in vivo and in vitro) possessed higher antibacterial activity than extract from flowers. The obtained results showed that both in vivo and in vitro propagated L. album L. could be used as a source of antibacterial substances.

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Eight genera (Lactobacillus, Leuconostoc, Staphylococcus, Enterococcus, Lactococcus, Micrococcus, Streptococcus)