Elimination of sex factors in Escherichia coli by urea

The susceptibility of conjugative resistance transfer in gram-negative bacteria to physicochemical and biochemical agents

Over thirty years of studies have established that conjugative transfer of plasmid-encoded resistance to drugs and heavy metals can take place at high frequency between various organisms under laboratory conditions. The detected transfer frequencies in soil, in aquatic environments, and in the urogenital and respiratory tracts of healthy animals and man have generally been low. However, the conversion of bacteria from susceptible to resistant to antibiotics has been observed often during antimicrobial therapy. This has formed a challenge for the antibacterial treatment of pathogenic bacteria and called for the evaluation of the extent of conjugative transfer in various environments. Several biochemical and physicochemical factors inhibit conjugation, show preferential toxicity against plasmid-bearing cells, or stimulate plasmid curing. These factors include various agents such as detergents, anesthetics, mutagens and antibiotics which affect membrane potential, membrane permeability, protein synthesis and the processing of DNA. The application of the data on these agents, summarized in this review, might be helpful in preventing drug multi-resistance from spreading. Also these data might be valuable in studies which use conjugation as a tool or which treat the molecular mechanisms involved in conjugation.

Transfer of drug-resistance plasmids by conjugation from nosocomial strains of Serratia marcescens to Escherichia coli in biological fluids of human origin

Six independent isolates of multi-resistant Serratia marcescens associated with nosocomial infections were examined for their ability to transfer drug-resistance plasmids by conjugation to Escherichia coli in biological fluids of human origin, such as normal and pathological urine, faeces, blood plasma and ascitic fluid. Luria broth was used as a control. Positive transfer was found in all media assayed. The different patterns of linked transferable resistance found in the transconjugants corresponded to the phenotypic expression of five plasmids. The frequencies of transfer varied with plasmid types and media employed. The culture media did not affect the phenotypic expression of the plasmids.

Eliminatory action of glycine on drug resistance of Escherichia coli K12 harboring an R factor

Glycine, known to inhibit the synthesis of a peptidoglycan component of the bacterial cell wall, was effective in eliminating drug resistance of Escherichia coli K12 JE2100 strain harboring theR100-1 factor although in lower frequencies than that of sodium dodecyl sulfate (SDS). The action of glycine was found to be less effective on the same R factor in JE177 strain, and not effective on the F factor in W6. Infection of R factors from R+ cells to R- cells was found to take place in the glycine broth as efficiently as in broth without glycine. This might result in lowering the apparent efficiency of the action of glycine on those plasmids. The segregation patterns of drug-susceptible clones obtained by the glycine treatment were different from those obtained after the SDS treatment. These results coupled with other evidences suggest that the mode of action of glycine on R+ cells maybe different from those of other curing agents and may involve mechanisms other than selection of R- or drug susceptible segregantsthat are present in R+ culture.

Studies on sex pili: mutants of the sex factor F in Escherichia coli defective in bacteriophage-adsorbing function of F pili

Ultraviolet irradiation or nitrosoguanidine treatment of Escherichia coli K-12 strain JE3100 (F'(8)/fla pil) led to the isolation of six mutants defective in F pili function. The defects were shown to be caused by mutations in the F factor. The mutants retained conjugal fertility, although they were less efficient than parental F'(8) strain, and continued to synthesize F pili. Three of the mutants (strains KE196, 198, and 200) had lost sensitivity to male-specific MS2 phage, and the other three (strains KE161, 163, and 164) were insensitive to Qbeta and f1 as well as MS2 phages. F pili on strains KE196, 198, and 200 cells continued to adsorb MS2 phage, whereas those of strains KE161, 163, and 164 did not adsorb MS2 phage. The correlation of the mutant phenotypes with those of other F mutants reported in the literature is discussed.

Specific role of sex pili in the effective eliminatory action of sodium dodecyl sulfate on sex and drug resistance factors in Escherichia coli

Evidence is presented for the specific role of sex pili in the eliminatory action of sodium dodecyl sulfate (SDS) on sex (F) and drug resistance (R) factors in Escherichia coli K-12 strains leading to their loss. SDS at 0.03% concentration lysed JE3100 F(8) (+) (F-gal)/gal(-)fla(-)pil(-) in Penassay broth after they had grown exponentially and reached maximum growth to the extent that the agent at concentrations higher than 1% did. However, the agent was only effective in eliminating sex factors from JE3100 in high frequencies at concentrations higher than 1%. Increase of osmotic pressure of the culture with SDS at concentrations as low as 0.03 to 0.1% by addition of sucrose led to the substantial increase of elimination efficiency. Reconstruction experiments between F(8) (+) and F(-) cells in the SDS culture revealed the selective growth of F(-) cells as well as a delay of maximum growth of F(-) variants derived from F(8) (+) cells, compared with those of F(8) (+) cells, as well as F(-) cells originally added to the culture. The agent was not very effective in eliminating sex factors from JE3427 F(8)m(+)5/fla(-)pil(-) cells which lack the function of production of F pili. F(8)m(+)5 cells showed a sensitivity toward SDS intermediate between those of F(8) (+) and F(-) cells. SDS was further effective in eliminating R factors from KE132 R(100-1) (+)/fla(-)pil(-) cells in high efficiency; however, the action was not efficient with KE133 F(100) (+) cells possibly with fewer sex pili than R(100-1) (+). Action of acridine orange on these F(+) or R(+) strains was found to be different in some aspects from that of SDS.