Identification of aerobic mesophilic bacteria using the maldi-tof technique in milk from milk vending machine

U mlijeku dobivenom higijenskom mužnjom zdravih krava dozvoljeno je prema Pravilniku o kakvoći svježeg sirovog mlijeka do 100 000 mikroorganizama/mL što predstavlja prirodnu mikrobiotu mlijeka i nema negativan utjecaj na ukupnu kvalitetu mlijeka. Međutim, nestručnim rukovanjem tijekom i nakon mužnje ono se lako kontaminira te postaje potencijalan medij za rast i razmnožavanje mikroorganizama od kojih mogu biti štetni po zdravlje ljudi. Budući je broj aerobno mezofilnih bakterija u mlijeku jedan od pokazatelja higijenske kvalitete mlijeka, njihova je brojnost i identifikacija temeljna u kontroli sirovog mlijeka iz mljekomata. Iz pet različitih mljekomata prikupljeno je 30 uzoraka kojima je određivan ukupni broj aerobno mezofilnih bakterija metodom protočne citometrije. Identifikacija se provodila usporedbom MALDI-TOF spektra masa s referentnim spektrima pohranjenim u biblioteci mikroorganizama i obradom pomoću MALDI Biotyper računalnog programa. Uspješno je identificirano 30 rodova i 51 bakterijska vrsta. Rodovi koji prevladavaju su Lactococcus lactis, Leuconostoc mesenteroides, Kluyveromyces lactis, Staphylococcus aureus.According to the Regulation on the Quality of Fresh Raw Milk, up to 100 000 microorganisms/mL are allowed in milk obtained by hygienic milking of healthy cows, which represents the natural microbiota of milk and has no negative impact on the overall quality of milk. However, with unprofessional handling during and after milking, it is easily contaminated and becomes a potential medium for the growth and reproduction of microorganisms, some of which can be harmful to human health. Since the number of aerobic mesophilic bacteria in milk is one of the indicators of the hygienic quality of milk, their number and identification are fundamental in the control of raw milk from milk vending machine. From five different milk vending machines, 30 samples were collected from which the total number of aerobic mesophilic bacteria was determined using the flow cytometry method and the classic method of counting colonies on a nutrient medium. Identification was performed by comparing MALDI-TOF mass spectra with reference spectra stored in the microorganism library and processing using the MALDI Biotyper computer program. 30 genus and 51 bacterial species were successfully identified. Genus that predominate are Lactococcus lactis, Leuconostoc mesenteroides, Kluyveromyces lactis, Staphylococcus aureus