Change of host range in a resistance factor

E. S. Anderson, E. J. Threlfall

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    8 Citations (Scopus)


    An R factor for ampicillin and streptomycin resistance (AS) was identified in Salmonella enteritidis. The AS factor transferred freely to Escherichia coli K12, but only two of 260 K12(AS) clones from this cross would transfer AS to S. typhimurium, although all lines tested transferred it to S. enteritidis and K12. A study of one of the two exceptional lines“ revealed that it also transferred AS to S. paratyphi B, S. thompson and S. anatum. The R factor maintained its transferability when cycled between these serotypes and K12. Transfer to S. enteritidis, however, resulted in loss of the ability of AS to transfer to the heterologous serotypes, that is, it apparently became host specific for S. enteritidis. S. paratyphi B and S. anatum also imposed host specificity on AS, but S. typhimurium and S. thompson did not. The R factor would always enter S. enteritidis, whatever its previous salmonella host but, once it had done so, it became specific for S. enteritidis. AS could always transfer to K12, which did not seem to modify its host range. These phenomena are most easily explained by analogy with host-controlled modification of phage. Their possible significance in relation to apparent host specificity of R factors is discussed.

    Original languageEnglish
    Pages (from-to)207-214
    Number of pages8
    JournalGenetical Research
    Issue number2
    Publication statusPublished - Oct 1970

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