The Ecology of Transferable Drug Resistance in the Enterobacteria

Correlation of phage type, biotype and source in strains ofSalmonella typhimurium

“…Occasionally, however, a sub-line of an epidemic strain may be altered in phage type by a change in lysogeny, by gain or loss of a plasmid (Anderson, 1966(Anderson, , 1968a(Anderson, , 1969a or by chromosomal mutation. WVhen this happens, cultures of different phage types may be isolated from different sources in the same outbreak, and the demonstration that they belong to the same biotype suggests that they are derived from the same clone.…”

Bacteriophage restriction in Salmonella typhimurium by R factors and transfer factors

“…It has been postulated elsewhere that this outbreak was caused by a single line, in fact a clone, of type 29 (Anderson, 1968(Anderson, , 1969(Anderson, , 1971. It so happened that in the original group of drugresistant S. typhimrurium cultures isolated from November 1964 onwards on a farm in Devon, 54 belonged to phage type 29 and 35 to phage type 44.…”

“…And it is evident from earlier studies (Anderson & Lewis, 1965a, b;Anderson, 1968Anderson, , 1969Anderson, , 1971) that salmonellas carrying resistance transfer systems pass from animals to man. But the extent to which animal non-pathogens contribute to the drug-resistant enterobacterial population of the human intestine is not yet clear, although it may be substantial.…”

“…Transfer factors in drug-sensitive E. coli were detected by their ability to mobilize 'standard' streptomycin-sulphonamide (SSu) and neomycinkanamycin (K) resistance determinants by the triparental cross for determinant mobilization (Anderson, 1965), using S. typhimurium type 36 (19R689) as the final recipient. The SSu determinant is most easily mobilized by I-like transfer factors, whereas the K determinant is best mobilized by F-like transfer factors (Anderson, 1968).…”

“…Type 29, in contrast, had been uncommon before the widespread outbreak it caused in bovines and man. The first strain of this type identified in that outbreak has been intensively studied in the Enteric Reference Laboratory, and is designated RT1 (Anderson & Lewis, 1965a, b;Anderson, 1966Anderson, , 1968Anderson, , 1969. It was the source of A, the prototype of the A-like group of transfer factors.…”