Study of the association of resistance to two drugs in a transferable determinant inSalmonella typhimurium

Abstract

A strain ofS. typhimuriumcarrying transferable determinants, one for resistance to ampicillin (A), another for resistance to streptomycin and sulphonamides (SSu), was irradiated with ultraviolet light. A clone resulting from this treatment had lost streptomycin resistance and now carried the A determinant and a new determinant, ASu. Except for coding for ampicillin resistance, the ASu determinant was homologous with SSu. The A moiety of ASu produced ampicillin (penicillin) resistance of the same degree as the original A determinant. It was therefore concluded that irradiation had resulted in the elimination of the S gene in the SSu determinant and its replacement by an A gene to form ASu. Experiments with the ASu and SSu determinants suggest that there is normally only one copy of a resistance determinant in the host cell and only one cell site into which it can integrate.

Transduction of resistance determinants and R factors of the Δ transfer systems by phage P1kc

“…The R factors chosen for this study are listed in Table 1. The A-A factor, which was formed by recombination between the A resistance determinant and 3, was isolated from RTI after ultraviolet irradiation (Anderson, 1969 Anderson and Lewis (1965b) Resistance symbols: A ~ ampicillin; S ----streptomycin; Su ~ sulphonamides; T ~ tetracyclines. The A-A factor, which was formed by recombination between the A resistance determinant and 3, was isolated from RTI after ultraviolet irradiation (Anderson, 1969 Anderson and Lewis (1965b) Resistance symbols: A ~ ampicillin; S ----streptomycin; Su ~ sulphonamides; T ~ tetracyclines.…”

“…Observations on the transferable resistance systems identified in type 29 of Salmonella typhimurium led to the postulate that R factors can be divided into two classes (Anderson, 1968(Anderson, , 1969Anderson and Threlfall, 1970). In Class 1, the prototypes of which are the R factors discovered in Japan, the factor is a covalently bonded complex incorporating the resistance determinant(s) and the transfer factor.…”

“…The tetracycline R factor T-A, first isolated from type 29 (Anderson and Lewis, 1965b) class. It has been suggested that in these R factors the resistance determinant and the transfer factor are independent of each other in the host cell, and occupy different membrane attachment sites; in fact, that they are separate plasmids (Anderson, 1968(Anderson, , 1969Anderson et al, 1968). Occasionally, the transfer factor alone is transmitted to recipient cells, suggesting that the resistance determinants dissociate from the transfer factor.…”

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

“…NTP1, the standard A determinant (Anderson & Lewis, 1965b;Smith et al 1974) which is present in a multiplicity of 10-20 copies per cell (Humphreys et al 1972) produces an ampicillin MIC of 2000 ,ugIml in the host strains, and the cephaloridine MIC of such strains is 32 ,ug/ml, the same as strains carrying A or AK of Middle Eastern origin. When the A translocon of NTP1 recombines with the A transfer factor, the resultant A-A resistance plasmid (Anderson, Kelemen et al 1968; Anderson, 1969), which is present as only one copy per cell (Humphreys et al 1972), gives MICs of 250 and 4 ,tg/ml for ampicillin and cephaloridine respectively. Although the A region of F1me plasmids confers a degree of ampicillin resistance similar to that of A-A on host strains, no cephaloridine resistance was detectable in these strains.…”

Formation of Multiple Drug Resistance Factors by Recombination between Transfer Factor and Resistance Determinants

“…Consequently, the notion on R factors was quite different from our results that the R factors were single genetic elements and existed stably in a cell. The notion that the transfer factor and resistance determinant existed separately in the cell of a Salmonella strain and were easily associable when transferred [1], could be supported by the following facts: 1) the strains carried 2 types ofRfactors, i.e., transferable R, and transferable R.), in a cell, were isolated frequently [21,23] and those carrying both transferable R1 and nontransferable R., could also be isolated frequently from clinical specimens [23], and 2) the nontransferable R could be transmitted conjugally in the presence of transferable sex factors such as F, R, T and X, namely, by complementation as reported in Col factor by Ozeki et al [20].…”