V. BACTERIOPHAGE TYPING OF SHIGELLA
189
techniques. Modification and restriction implies that certain phages, Rfactors, or colicin factors, when introduced into a bacterial cell reduce or
abolish its sensitivity to phages which previously were lytic on the strain
(LAsz16 and Riman6czy, 1976; Strobe1 and Nomura, 1966). Modification
and restriction is mediated by specific enzymes which recognise certain
short, recurring base pair sequences of DNA and cause either a modification or a restriction of them (Lewin, 1977). Modification in E. coli is mediated through methylation of the base recognised by the particular enzyme.
Restriction results from cleavage of both strands of the DNA duplex at the
enzyme recognition site. This is followed by degradation of the cleaved
DNA by other nucleases that are actually non-specific. The important
point is that any DNA in the cell, whether it is in principle the endogenote
or an exogenote, like a plasmid or phage, may be modified if it possesses
the decisive base sequence, the recognition sequence, at which point modification or restriction takes place. Essentially, this system distinguishes the
endogenote DNA and that of the exogenote. The above information is
derived from our particularly detailed information for E. coli (Eskridge
et al., 1967; Horn and Taubeneck, 1970; Meselson and Yuan, 1968) and
Salmonella (Lhsz16 and Riman6czy, 1976). Horn and Taubeneck (1970),
Tschape and Rische (1970a), and Rohde (1975) have demonstrated restriction also in S. sonnei and LBsz16 and Riman6czy (1976) in S. jlexneri. Host
modification has also been studied in this species (Horn and Tschape, 1969).
In S . jlexneri, R-factors that induce host restriction have been divided into
nine groups according to the changes they cause in phage susceptibility
of the recipients (Lhsz16 and Riman6czy, 1976; Lhsz16, 1973a, b).
Restriction must be distinguished from loss of phage receptor site
specificity.
The fact that R-factors may implement changes in phage type has
serious implications for the interpretation of phage typing results, since
R-factors typically spread epidemically (Tschape and Rische, 1970a, b).
R-factors are very common in Shl;gella, where 30-84% of the isolates have
such exogenote DNA (Chanishvili and Chanishvili, 1975 ; Schon and
Mandlikovh, 1975 ; Tschape and Rische, 1970b).
Host modification has been found to cause serological change of 2 of
the phages after propagation in shigellae.
C. Lysogenic conversion of bacterial antigens
Uptake of exogenote DNA may lead to changes in serotype and susceptibility to bacteriophages. This has been demonstrated in 5’. jlexneri after
conjugation with E. coli Hfr (lac+) (Slopek et al., 1972) or Hfr (C, rha)
(Jankowski et al., 1974). Transduction mediated by phage PE5 has been
noted in S. jlexneri (Financsek and KCtyi, 1976). Most of the time the
189
techniques. Modification and restriction implies that certain phages, Rfactors, or colicin factors, when introduced into a bacterial cell reduce or
abolish its sensitivity to phages which previously were lytic on the strain
(LAsz16 and Riman6czy, 1976; Strobe1 and Nomura, 1966). Modification
and restriction is mediated by specific enzymes which recognise certain
short, recurring base pair sequences of DNA and cause either a modification or a restriction of them (Lewin, 1977). Modification in E. coli is mediated through methylation of the base recognised by the particular enzyme.
Restriction results from cleavage of both strands of the DNA duplex at the
enzyme recognition site. This is followed by degradation of the cleaved
DNA by other nucleases that are actually non-specific. The important
point is that any DNA in the cell, whether it is in principle the endogenote
or an exogenote, like a plasmid or phage, may be modified if it possesses
the decisive base sequence, the recognition sequence, at which point modification or restriction takes place. Essentially, this system distinguishes the
endogenote DNA and that of the exogenote. The above information is
derived from our particularly detailed information for E. coli (Eskridge
et al., 1967; Horn and Taubeneck, 1970; Meselson and Yuan, 1968) and
Salmonella (Lhsz16 and Riman6czy, 1976). Horn and Taubeneck (1970),
Tschape and Rische (1970a), and Rohde (1975) have demonstrated restriction also in S. sonnei and LBsz16 and Riman6czy (1976) in S. jlexneri. Host
modification has also been studied in this species (Horn and Tschape, 1969).
In S . jlexneri, R-factors that induce host restriction have been divided into
nine groups according to the changes they cause in phage susceptibility
of the recipients (Lhsz16 and Riman6czy, 1976; Lhsz16, 1973a, b).
Restriction must be distinguished from loss of phage receptor site
specificity.
The fact that R-factors may implement changes in phage type has
serious implications for the interpretation of phage typing results, since
R-factors typically spread epidemically (Tschape and Rische, 1970a, b).
R-factors are very common in Shl;gella, where 30-84% of the isolates have
such exogenote DNA (Chanishvili and Chanishvili, 1975 ; Schon and
Mandlikovh, 1975 ; Tschape and Rische, 1970b).
Host modification has been found to cause serological change of 2 of
the phages after propagation in shigellae.
C. Lysogenic conversion of bacterial antigens
Uptake of exogenote DNA may lead to changes in serotype and susceptibility to bacteriophages. This has been demonstrated in 5’. jlexneri after
conjugation with E. coli Hfr (lac+) (Slopek et al., 1972) or Hfr (C, rha)
(Jankowski et al., 1974). Transduction mediated by phage PE5 has been
noted in S. jlexneri (Financsek and KCtyi, 1976). Most of the time the