Abstract
Three hundred and eight strains of Shigella sonnei, isolated from cases of dysentery in London in 1972, were examined for colicine production, antibiotic sensitivity and ability to transfer any resistance to E. coli K12. By these means, 61 types were differentiated. Two predominated in the population, namely colicine type 3A with transferable resistance to streptomycin, tetracycline and neomycin, non-transferable resistance to ampicillin and sensitivity to sulphonamide (33.96 %) and colicine type 3A with non-transferable resistance to ampicillin and sensitivity to sulphonamide, streptomycin, tetracycline and neomycin (12.26 %). Further investigation of the multiple resistant strain revealed two different rates of transfer of the plasmid, an efficient rate (2.85 %, to 26.31%) and a much reduced rate (0.012 %, to 0.155 %). Superinfection experiments showed the presence of a plasmid of the Id type compatibility group (49.07 %), with the low transfer strains also forming an important group (38.89%). This Id plasmid was found also in colicine type 3A strains not isolated in the London outbreak and in other strains of Sh. sonnei having a variety of colicine, sensitivity and transfer patterns. An outbreak of dysentery involving Sb. sonnei, colicine type 0 with transferable resistance to sulphonamide, streptomycin, high-level ampicillin and neomycin and sensitivity to tetracycline, occurrfed mainly in and around Luton, 97%. of the isolates were shown to carry an Id plasmid. 1% of the population showed a low transfer strain. Colicine type 4 strains with transferable resistance to high-level streptomycin and ampicillin and non-transferable resistance to sulphonamide, tetracycline and neomycin, responsible for an outbreak in Aberdeen in 1973-74, possessed a plasmid of a different compatibility group. At the beginning of this investigation a type K plasmid was seen, but as the outbreak progressed, a type A and K plasmid emerged to form the predominant type. The relevance Of these findings to the study of the epidemiology of Sonne dysentery is discussed.