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The aim of the study was a detail evaluation of genetic diversity among the lactic acid bacteria (LAB) strains having an advantage of a starter culture in order to select genotypically diverse strains with enhanced antimicrobial effect on some harmfull and pathogenic microorganisms. Antimicrobial activity of LAB was performed by the agar well diffusion method and was examined against the reference strains and foodborne isolates of Bacillus cereus, Listeria monocytogenes, Escherichia coli, Staphylococcus aureus and Salmonella Typhimurium. Antifungal activity was tested against the foodborne isolates of Candida parapsilosis, Debaromyces hansenii, Kluyveromyces marxianus, Pichia guilliermondii, Yarowia lipolytica, Aspergillus brasiliensis, Aspergillus versicolor, Cladosporium herbarum, Penicillium chrysogenum and Scopulariopsis brevicaulis.A total 40 LAB strains representing Lactobacillus (23 strains), Lactococcus (13 strains) and Streptococcus spp. (4 strains) were characterised by repetitive sequence based polymerase chain reaction fingerprinting which generated highly discriminatory profiles, confirmed the identity and revealed high genotypic heterogeneity among the strains. Many of tested LAB demonstrated strong antimicrobial activity specialised against one or few indicator strains. Twelve LAB strains were superior in suppressing growth of the whole complex of pathogenic bacteria and fungi. These results demonstrated that separate taxonomic units offered different possibilities of selection for novel LAB strains could be used as starter cultures enhancing food preservation.

This study was the first attempt to find out if the phenotypic plant response to the short-term ozone exposure might be altered by the presence of systemic viroid infection in plants. Model pathosystem used in these experiments was formed from the tomato (Lycopersicon esculentum Mill.) cv. 'Micro-Tom' and potato spindle tuber viroid. Viroid-infected plants were exposed to chronic, acute and extreme ozone treatments in order to find out if the elevated concentration of ozone could have any significant impact on the pathogenicity and spread of sub-viral pathogen. The results revealed that phenotypic alterations caused by the presence of viroid infection in plants were highly dependent on the dose of ozone received by plants. Only slight yellowing of the plant top leaves was detected in plants exposed to 80 ppb of ozone for 8 hours. No significant differences between viroid-inoculated and uninoculated plants were observed in the phenotypic appearance as well as in plant growth after application of this treatment suggesting that naturally occurring single short-term peaks of elevated ozone concentration could have no significant impact on viroid and host interaction. There were no significant differences observed in the degree of visible ozone injury between viroid-inoculated and uninoculated plants just after the short-term acute (400 ppb × 6 h) and extreme (300 ppb × 13 h) ozone treatments were applied. However, in the end of the growth period clearly expressed differences in plant growth, degree of defoliation and the regeneration capacity were revealed between viroid-inoculated and uninoculated plants submitted to these treatments, indicating that pathogenicity of potato spindle tuber viroid could be altered by the exposure of inoculated plants to the severe ozone stress.