Isolation and Characterization of the Bacteriophages of Lactic Streptococci

Abstract

Four virulent phages of lactic streptococci were isolated from 245 samples of butter, buttermilk, curd, cheese, cheese whey, raw milk, and Srikhand Three of these phages, i.e., FRC1, FRC2, and FRC3 isolated from buttermilk, curd, and Srikhand, respectively, lysed Streptococcus cremoris strains, and phage FRC4 isolated from cheese whey was specific for Streptococcus lactis ssp. diacetylactis. Phages were examined by electron microscopy. Isolated phages comprised of two morphological types. Phages FRC1 and FRC3 possessed prolate head, whereas polyhedral capsids were exhibited by phages FRC2 and FRC4. Noncontractile tails of all phages were 2 to 2.5 times longer than the head diameter, exhibiting regular fine striations and 20 to 30 annuli. Base plates with three or four spikes were visible in all phages. A structure of plug type was observed in phages FRC1 and FRC3. All phages were classified into group B of Bradley. Phages FRC1, FRC2, and FRC3 exhibited a latent period of 40 min, rise period of 20 min, and average burst size of 70 to 110 phage particles. Phage FRC4 possessed a latent period of 45 min, rise period of 15 min, and average burst size of 100 to 150 phage particles. Further differentiation among these phages was on the basis of eclipse phases, which were in the range of 26 to 32 min. © 1991, American Dairy Science Association. All rights reserved.