Milk is a nutrient-rich food containing a diverse microbiota. In Slovenia and some other EU countries, raw milk can be purchased in stores but also in milk vending machines. In addition to potentially pathogenic bacteria, the presence of transmissible antibiotic resistance in the milk microbiota poses a risk when raw milk is consumed. In this MSc thesis, we analysed 112 isolates from 50 milk vending machines that had been identified in previous studies using MALDI-TOF MS. Species were confirmed or refuted by species-specific PCR (in the case of Lactococcus lactis and Leuconostoc mesenteroides) and/or 16S rDNA sequencing. The milk isolates were classified into 14 different genera. The phenotypic tests for antimicrobial resistance were then performed by the microdilution method using pre-prepared microtiter plates with added antibiotics. The tests carried out as part of this work showed that the microbiota of raw milk also contains bacteria resistant to antibiotics. These included both lactic acid bacteria and potentially pathogenic bacteris. Among the Enterobacteriaceae, only one isolate of E. coli showed multiple antimicrobial resistance (MDR). No MDR strains were detected among staphylococci, enterococci and listeria. Two MDR strains were detected among Leuconostoc representatives. All eight isolates from the genus Weisella were also classified as MDR. Considering the potential risk of antimicrobial resistance spreading in the food chain, these could pose a risk for human health. The assessment of this risk would require whole genome analyses to demonstrate the actual presence of antimicrobial resistance genes and other genes associated with the transmissibility of resistance.
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