Current methods of intraspecies typing of Shigella sonnei. 3. Bacteriophage typing]

Data are presented concerning the study of the phage type of Sh. sonnei isolated in various regions of the USSR. The strains isolated belonged to 64 phage types corresponding to the Hammarstr?m's scheme. A variety of Shigella sonnei phage types both in one and in different territories of the country provided future prospects for successful use of phage typing for the purpose of epidemiological supervision and analysis of dysentery morbidity.     

Specificity and functions of guanine methylase of Shigella sonnei DDVI phage.

DNA methylase methylating adenine with formation of 6-methylaminopurine has been identified in Shigella sonnei 1188 cells which are the natural host of DDVI phage. At the same time, in DNA of DDVI phage replicating both in Sh. sonnei 1188 cells and in Escherichia coli B cells 7-methylguanine was found as the only minor base in amounts of 0.25 and 0.27 mol per 100 mol of nucleotides, respectively. The extract of the infected cells was found to contain both kinds of DNA methylases: virus-specific guanine methylase and cellular adenine methylase. The lack of 6-methylaminopurine in DNA of this phage is explained by reversible inhibition of the cell enzyme in the infected cells. The amount of methyl groups transferred by DDVI-specific methylase on DNA does not depend on the species of the infected cells and is similar in the case of unmodified SD phage DNA and DNA of T2 phage methylated by E. coli B enzyme. Guanine methylase has been shown to be a DDVI-induced modification enzyme and to protect against restriction of B-type. It methylates double-stranded DNAs only and is inhibited by S-adenosylhomocysteine.     

Specificity and functions of guanine methylase of Shigella sonnei DDVI phage

DNA methylase methylating adenine with formation of 6-methylamino-purine has been identified in Shigella sonnei 1188 cells which are the natural host of DDVI phage. At the same time, in DNA of DDVI phage replicating both in Sh. sonnei 1188 cells and in Escherichia coli B cells 7-methylguanine was found as the only minor base in amounts of 0.25 and 0.27 mol per 100 mol of nucleotides, respectively. The extract of the infected cells was found to contain both kinds of DNA methylase: virus-specific guanine methylase and cellular adenine methylase. The lack of 6-methylaminopurine in DNA of this phage is explained by reversible inhibition of the cell enzyme in the infected cells.The amount of methyl groups transferred by DDVI-specific methylase on DNA does not depdend on the species of the infected cells and is similar in the case of unmodified S_D phage DNA and DNA of T2 phage methylated by E. coli B enzyme. Guanine methylase has been shown to be a DDVI-induced modification enzyme and to protect against restriction of B-type. It methylates double-stranded DNAs only and is inhibited by S-adenosylhomocysteine.     

Lipopolysaccharides of Shigella sonnei

Immunobiological properties of native lipopolysaccharides (LPS) from virulent and avirulent strains of Shigella sonnei bacteria (LPS-V and LPS-A, respectively) were studied. In avirulent bacteria, LPS-V induced immunosuppressive activity specific of the virulent strain. LPS of the avirulent strain, whereas LPS-A lacked this property. Native LPS-V with immunosuppressive activity were isolated from the virulent strain by and immune affinity method. Treatment of LPS-V with phenol or TCA abolished its activity and converted it into the LPS-A form. The data showed that LPS-A can be converted back to the LPS-V form by redox treatment. This approach seems to be promising for activating LPS extracted from cells with TCA or a water-phenol mixture.     

Acid tolerance of Shigella sonnei and Shigella flexneri

AIMS: Determination of the behaviour of Shigella sonnei and Sh. flexneri under acid conditions. METHODS AND RESULTS: The growth and survival of Shigella spp. (9 isolates) in acidified Brain Heart Infusion (BHI) (pH 5.0-3.25 with pH intervals of 0.25) was determined after 6, 24 and 30 h incubation at 37 degrees C. Subsequently, survival of shigellae was studied in apple juice and tomato juice stored at 7 degrees C and 22 degrees C for up to 14 days and in strawberries and a fresh fruit salad, kept at 4 degrees C for 4 and 48 h. CONCLUSIONS: The minimum pH for growth in acidified BHI for Sh. flexneri and Sh. sonnei was, respectively, pH 4.75 and pH 4.50. Survival in fruit juices and fresh fruits depended upon their pH, the type of strain and the incubation temperature. Shigella spp. Survived for up to 14 days in tomato juice and apple juice stored at 7 degrees C. The shortest survival time (2-8 d) was observed in apple juice at 22 degrees C. Sh. sonnei but not Sh. flexneri was recovered after 48 h from strawberries and fruit salad kept at 4 degrees C. SIGNIFICANCE AND IMPACT OF THE STUDY: Acid foods, especially if kept at refrigeration temperatures, support survival of Shigella spp. and may cause Shigella food poisoning.     

Colicine Typing of Shigella sonnei

Colicine typing of Shigella sonnei using the methods of Naito et al. and Abbott and Shannon were performed in parallel on a large number of epidemic strains, the indicator strains used in both methods, and on stock strains used to test the accuracy of the indicators. The following results were obtained after typing 462 epidemic strains: by Naito's method, 18 strains were in A₁, 87 in A₂, 33 in B₁, 253 in B₂, 38 in C₁, 3 in C₂, 2 in D, and 3 in E, and 25 strains were unclassifiable; while by Abbott and Shannon's method, using the present authors' simplified designation, 189 strains were in type 6/11, 124 in type 4/14, 85 in type O, and 41 in type 8, and 23 strains were either in other types or found unclassifiable. Naito's type A was in large part, equivalent to Abbott and Shannon's type O, but included some type 6/11 and type 4/14 strains. Naito's type B consisted of types 6/11, 4/14, 3A and 13, and type E consisted of 1A, IB, 3, 5, 9, and 10. Type C coincided with type 8 and type D with type 12. In addition, there were strains determined to be Abbott and Shannon's types 6/11, 4/14, 2, 7 and 9. The Abbott and Shannon's method revealed the possibilities of these strains to be classified in further detail. This is considered to be attributable not merely to the lack of indicators in the Naito's method corresponding to those of Abbott and Shannon's, but also to insufficient production of certain colicines in the Naito's method. Because of the type distribution found in Japan at present, further investigation should be done so that types 6 and 11, and types 4 and 14 can be separated.