Streptococcus salivarius subsp. thermophilus virulent fajlarının izolasyonu ve yoğurt starter kültürleri üzerine litik etkilerinin belirlenmesi

Abstract

Phages of Streptococcus salivarius subsp. thermophilus (JS. thermophilus) from raw milk were isolated. 30 native S. thermophilus strains which were previously isolated from raw milk were used as host and 19 raw milk samples used as phage isolation material. However no isolates could be obtained by using Chr. Hansen Laboratory ATL phage test After this result, 9 different S. thermophilus strains were isolated successfully from 9 lyophilized mixed yogurt cultures taken from different dairy factories. Then, those 9 strain were used as host for isolation of phages from 34 different materials including yogurt, bulk, whey, airan. In experiments, 23 S. thermophilus phages could be isolated by 3 of 9 strains; 709, 231 and B3. Modified M17 (th M 17) Agar and th M 17 Broth medias and double layer agar method were applied for growth and isolation. It is noteworthy that while all native strains of S. thermophilus were found to be resistant for phages which were tested, starter originated strains 709, 23 1 and B3 were found to be very sensitive against almost all phages. Opposingly VI, V2, Yİ, Y4, 632 and CH-1 strains were found to be resistant as native strains. Other than their homolog hosts, phages were also detected using other two strains as heterolog host. Starter originated S. thermophilus strains exhibited three different lytic spectrum. Also it was shown that the phages of Lactobacillus delbrueckii subsp. bulgaricus did not produce any lysis on any S. thermophilus strains meaning not to use as their heterolog hosts. In order to isolation of temperate phages mitomicin C (MC) concentration (0,05; 0,1; 0,2 ug/ml) were determined by using reference lysogenic strain of 5. thermophilus CNRZ 1205 and these concentrations applied for all of S. thermophilus strains. Neither native strains nor starter originated strains found in lysogenic character. By this study it was shown that the culture which was suggested in prospectus of starter producing company for the rotation, is a wrong suggestion when the native phages are regarded. 2001, 78 pages Key Words: Streptococcus salivarius subsp. thermophilus, virulent phage, lysogeny