The aim of this master's thesis was to investigate whether lactic acid bacteria, especially lactobacilli, and bifidobacteria from human milk, colostrum and mature milk, contain tetracycline and erythromycin resistance genes, which presents a certain risk of spread of antibiotic resistance to pathogenic bacteria in the infant's gut. Kanamycin was subsequently added to the study for a reason that in previous studies the resistance of lactobacili to this antibiotic was unexpectedly frequent. Thus, we investigated whether the genes associated with the resistance to selected antibiotics are present in the genome of lactic acid bacteria and bifidobacteria. One sample of colostrum and 38 samples of milk were plated on Rogosa and WCA-mup medium. 243 bacterial strains were isolated. The results of the sequencing of isolated DNA showed that bacteria belonged to the genera Lactobacillus, Propionibacterium, Streptococcus, Bifidobacterium and Actinomyces. We also included 56 pre-isolated bacterial strains from the genera Lactobacillus and Bifidobacterium. Phenotypic resistance was determined by microdilution. In phenotypic resistant strains we investigated the presence of the most well-known genes associated with resistance to a particular antibiotic with PCR. Phenotypic resistance to erythromycin was detected in 3 strains, tetracycline in 10 strains, and kanamycin in 52 strains, while the presence of investigated genes erm(A), erm(B), erm(C), erm(T), tet(A), tet(B), tet(C), tet(M), tet(O), tet(W), aac(6')-aph(2''), ant(6)-Ia and aph(3')-IIIa has not been confirmed in any of the strains.
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