Clonal distribution of resistance plasmid-carryingSalmonella typhimurium, mainly in the Middle East

Abstract

SUMMARYStrains ofSalmonella typhimuriumof predominantly Middle Eastern origin, but distributed from England to India, were found to carry at least three types of resistance plasmid. The most important was initially identified as an FIplasmid by compatibility tests, but differs from the F factor on the one hand and the FIfactors R162 and CoIV on the other. The three groups of FIplasmids can be distinguished by their compatibility reactions with the MP10 plasmid ofS. typhimurium(Smith, Humphreys, Grindley, Grindley & Anderson, 1973) and group H1factors: the F factor is unilaterally incompatible with group H1(Smith, Grindley, Humphreys & Anderson, 1973; Anderson, 1975b); the FIfactors are compatible with MP10 and group H1and FImefactors are incompatible with MP10 but compatible with H1. The majority ofS. typhimuriumcultures belonged to phage type 208; most of those that did not, belonged to types related to 208. Only a minority of their FImeplasmids were autotransferring. The remainder were mobilizable by F-like plasmids, and by group H1and H2factors, but not by thefi–I1facter δ, or by plasmids of the I2, B, P, W, N andcom7 groups. The compatibility reactions of the autotransferring F1meplasmids were identical with those of the non-transferring members of the group, and both were large, single-copy plasmids.TheS. typhimuriumstrains of this series carried A or AK, and SSu resistance determinants: small, probably multicopy, non-transferring plasmids similar to those originally described in phage type 29 ofS. typhimurium(Anderson & Lewis, 1965b).TheseS. typhimuriumcultures probably represent a clone of wide geographical distribution. The accurate epidemiological study of such clonal outbreaks requires, in addition to phage typing, precise identification of the plasmids harboured by the epidemic strains, and may have to be carried to the molecular level.FImeplasmids were identified in other drug-resistant salmonellas, notably in a strain ofS. wienwhich caused large outbreaks of mainly paediatric infection in Algeria, and also spread to Britain. An FImeplasmid was found inS. typhiphage type 44 from Algeria, in which the phage-restricting properties of the plasmid are responsible for the specificity of the type.