Atividade antimicrobiana de microrganismos presentes nos grãos de kefir

Abstract

Kefir is fermented milk, acid, slightly alcoholic, home made from grains that contain a relatively stable population of symbiotic microorganisms, embedded in a matrix composed of polysaccharides and proteins. Servings of milk added kefir grains were experimentally contaminated with Escherichia coli O157:H7, Salmonella enterica subsp. enterica serotypes Typhimurium and Enteritidis, Staphylococcus aureus and Listeria monocytogenes. Samples were analyzed for the presence of microorganisms after 0, 6, 12, 24, 48 and 72 hours of fermentation. Sixty bacterial strains isolated from kefir grains were tested for antimicrobial activity against the same pathogens. From grains were sown by spreading in MRS agar to obtain isolated colonies. The antimicrobial activity was studied through the test of antagonism. The antimicrobial activity of supernatants of lactic acid bacteria that were active in the test of antagonism was tested. The experiment was repeated using supernatants neutralized with pH. Salmonella Typhimurium and Enteritidis survived for 24 hours in the kefir fermentation. E. coli O157:H7, S. aureus and L. monocytogenes were recovered by 72 after the start of fermentation. All isolates showed antimicrobial activity against at least one of the pathogens used in the test of antagonism. Supernatants of 25 isolates showed inhibitory activity. However, only three retained the activity at pH neutralized. Pathogenic bacteria studied survived for longer than the time normally used for kefir fermentation of artisanal, characterizing potential danger to the consumer when the raw material does not provide health security. Lactobacillus isolated from kefir grains exhibit antimicrobial activity against strains of Escherichia coli O157:H7, Salmonella enterica subsp. enterica serotypes Typhimurium and Enteritidis, Staphylococcus aureus and Listeria monocytogenes in addition to that exerted by the lower pH values.