Phage Resistance in a Phage-Insensitive Strain of Streptococcus lactis: Temperature-Dependent Phage Development and Host-Controlled Phage Replication.

Streptococcus lactis ME2 is a dairy starter strain that is insensitive to a variety of phage, including phi18. The efficiency of plating of phi18 on ME2 and N1 could be increased from <1 x 10 to 5.0 x 10 and from 7.

Mutation and Selection of Lactobacillus plantarum Strains That Do Not Produce Carbon Dioxide from Malate.

A differential medium was developed to distinguish between malate-decarboxylating (MDC) and -non-decarboxylating (MDC) strains of Lactobacillus plantarum. MDC strains produced a visible acid reaction in the medium, whereas MDC strains did not. Use of the medium allowed for rapid screening and isolation of mutagenized cells that had lost the ability to produce CO(2) from malate.

Characterization of Phage-Sensitive Mutants from a Phage-Insensitive Strain of Streptococcus lactis: Evidence for a Plasmid Determinant that Prevents Phage Adsorption.

A phage-insensitive strain of Streptococcus lactis, designated ME2, was used as a prototype strain for the study of mechanisms and genetics of phage resistance in the lactic streptococci. Mutants sensitive to a Streptococcus cremoris phage, varphi18, were isolated at a level of 17% from cultures of ME2 after sequential transfer at 30 degrees C. Phage-sensitive mutants of ME2 were not fully permissive to varphi18.

Influence of Calcium and Manganese on Dechaining of Lactobacillus bulgaricus.

The events responsible for the transition of Lactobacillus bulgaricus 1243-F from long filamentous chains to short bacilloid rods were examined in a cation-depleted liquid medium. In the presence of magnesium only, cells grew as long chains of unseparated cells. The addition of 100 muM to 1 mM calcium or manganese to this medium resulted in the dechaining of these cells to short bacilloid rods.

Detection and activity of lactacin B, a bacteriocin produced by Lactobacillus acidophilus.

A total of 52 strains of Lactobacillus acidophilus were examined for production of bacteriocins. A majority (63%) demonstrated inhibitory activity against all members of a four-species grouping of Lactobacillus leichmannii, Lactobacillus bulgaricus, Lactobacillus helveticus, and Lactobacillus lactis. Four L.

Adherence of Lactobacillus species to human fetal intestinal cells.

Thirty-two lactobacilli were tested for ability to adhere to a human fetal intestinal epithelial cell line. By an in vitro system, two adherence mechanisms were found. One mechanism, requiring calcium in the adherence reaction, was nonspecific and allowed all lactobacilli tested to adhere.

Evidence for Plasmid Linkage of Restriction and Modification in Streptococcus cremoris KH.

Restriction and modification have been demonstrated in Streptococcus cremoris KH cells when infected by Streptococcus lactis C2 phage (designated c2) at an efficiency of plating of 2 x 10. The growth of c2 phage through KH cells produces modified progeny phage capable of unrestricted growth on KH cells. The ability of single-colony isolates of S.

Growth Characteristics, Bile Sensitivity, and Freeze Damage in Colonial Variants of Lactobacillus acidophilus.

Rough (R) and smooth (S) colonial variants were isolated from a heterogeneous culture of Lactobacillus acidophilus RL8K. R and S types were stable upon repeated transfer on agar, but revertant colonies did appear after broth transfers. When propagated in commercial MRS broth, R and S cultures showed similar growth characteristics, and both cell types were insensitive to freezing and frozen storage at -20 degrees C.

Calcium-Induced Alteration of Cellular Morphology Affecting the Resistance of Lactobacillus acidophilus to Freezing.

Examination of factors affecting the resistance of Lactobacillus acidophilus NCFM culture concentrates to freeze injury induced during frozen storage at -20 degrees C revealed that calcium supplementation of the growth medium contributed to the storage stability of cells prepared in static culture. Culture concentrates of L. acidophilus NCFM were prepared from cells propagated in MRS broth or MRS broth supplemented with 0.

Restriction and modification in group N streptococci: effect of heat on development of modified lytic bacteriophage.

The appearance of lytic bacteriophage against newly introduced starter strains used during commercial cheese manufacture occurs rapidly, and their origin is not well understood. In this study, members of the group N streptococci were examined for the presence of bacteriophage restriction and modification systems. Two streptococcal phages from Streptococcus cremoris TR and Streptococcus lactis C2 (phage designations tr and c2) showed restricted lytic development on S.

Detection of plasmid deoxyribonucleic acid in an isolate of Lactobacillus acidophilus.

Eight strains of Lactobacillus acidophilus were examined for the presence of plasmid deoxyribonucleic acid, and one, a pig intestinal isolate, showed the presence of a 13.7- and a 6.3-megadalton plasmid.

Improved lysis of group N streptococci for isolation and rapid characterization of plasmid deoxyribonucleic acid.

Procedures for effective cellular lysis and plasmid deoxyribonucleic acid (DNA) isolation from group N streptococci were developed. Cells were grown at 32 degrees C for 4 h in a modified Elliker broth containing 20 mM DL-threonine. After cellular digestion with 2 mg of lysozyme per ml for 7 min at 37 degrees C, 1% sodium dodecyl sulfate exposure resulted in complete and immediate lysis.

Isolation and examination of transducing bacteriophage particles from Streptococcus lactis C2.

Two defective transducing bacteriophages induced by exposure of Streptococcus lactis C2 to ultraviolet irradiation have been isolated and characterized. These temperate phages designated c2t1 and c2t2 were isolated by cesium chloride equilibrium density gradient centrifugation of phage preparations concentrated by polyethylene glycol precipitation. The equilibrium gradient contained two visually apparent phage bands positioned at densities of 1.