Antimicrobial Activity of Kefir against Various Food Pathogens and Spoilage Bacteria.

Kefir is a unique fermented dairy product produced by a mixture of lactic acid bacteria, acetic acid bacteria, and yeast. Here, we compared the antimicrobial spectra of four types of kefirs (A, L, M, and S) fermented for 24, 36, 48, or 72 h against eight food-borne pathogens. , , , , , , , and were used as test strains, and antibacterial activity was investigated by the spot on lawn method. The spectra, potencies, and onsets of activity varied according to the type of kefir and the fermentation time. The broadest and strongest antimicrobial spectrum was obtained after at least 36-48 h of fermentation for all kefirs, although the traditional fermentation method of kefir is for 18-24 h at 25℃. For kefir A, , , . Enteritidis, , and were inhibited, while , , , . Enteritidis, , and were inhibited to different extents by kefirs L, M, and S. Remarkably, , . Enteritidis, and were only inhibited by kefirs L, M, and S, and by kefir M after fermentation for specific times, suggesting that the antimicrobial activity is attributable not only to a low pH but also to antimicrobial substances secreted during the fermentation.