Uptake of tetracycline by Escherichia coli: lack of binding of tetracycline to the uptake system

Tetracycline in Combination with Sodium Dioctylsulfosuccinate Show Increased Antimicrobial Activity in Resistant Microorganisms

We present evidence that sodium dioctylsulfosuccinate, at non inhibitory concentrations (1000 mg/L), is able to increase the antimicrobial activity of tetracycline in non susceptible bacterial and fungal strains. In culture inhibition tests, pretreatment with sodium dioctylsulfosuccinate caused a 52-fold decrease in the geometric mean MIC to tetracycline in 10 Candida albicans strains (p<0.01), a 165-fold decrease in the geometric mean MIC to tetracycline in 10 E. coli strains (p<0.001) and a significant decrease in the mean MIC of 3 strains of Candida krusei and Candida glabrata. In microbicidal tests, tetracycline in association with sodium dioctylsulfosuccinate killed 10(4) cfu tetracycline-resistant Candida albicans in 15 min and 10(4) CFU resistant E. coli in 3 min (p<0.001). Furthermore, in the N-acetyl-D-glucosamine test to calculate the number of hyphal cells, a combination of tetracycline (50 mg/L) (non inhibitory concentrations) plus sodium dioctylsulfosuccinate (25 mg/L) caused a 50-fold increase in the inhibition of hyphal cells in C. albicans (p<0.001); C. albicans cells treated with tetracycline plus sodium dioctylsolfosuccinate annulled the cell surface hydrophobicity (p<0.001). This increase in antimicrobial activity may be attributed to impairment and alteration of the membrane barrier within the microorganisms and a depletion of the thiol groups (p<0.001) critical to their efficiency.

Characteristics and expression of tetracycline resistance in gram-negative bacteria carrying the Pseudomonas R factor RP1

The Pseudomonas R factor RP1 determines an inducible tetracycline resistance similar to that described for Escherichia coli R factors. The level of RP1-determined resistance measured by minimal inhibitory concentration testing is dependent on the host bacteria and corresponds to the magnitude of decrease in tetracycline accumulation by RP1-containing organisms. The tetracycline resistance mechanism is inactivated at low temperatures. The effect of metabolic inhibitors on tetracycline accumulation by susceptible organisms under various conditions indicates a possible nonspecific effect of cellular energy metabolism on tetracycline uptake.

Tetracycline uptake by susceptible Escherichia coli cells

Experiments measuring the initial uptake of commercial (3H) tetracycline exhibit two distinct kinetic phases: a rapid phase followed by a slow phase. (3H) tetracycline purified by chromatography on a Dowex 50WX2 column exhibited only monophasic rapid uptake when tested with susceptible Escherichia coli cells. Cyanide inhibited the uptake of purified (3H) tetracycline only partially while transport of proline and maltose was entirely abolished. Energy independent accumulation of tetracycline may be accounted for by binding to cellular constituents. Uptake of tetracycline--as measured by inhibition of beta-galactosidase synthesis--was strongly affected by a shift in temperature from 37 degrees C to 21 degrees C while carrier-mediated transport systems revealed only minor reductions. Taken together with the non-saturability of tetracycline uptake and the evidence for diffusion of tetracycline through phospholipid bilayers [Argast and Beck (1984) Antimicrob Agents Chemother 26:263-265] these data support the hypothesis that tetracycline enters the cytoplasm by diffusion.

Tetracycline diffusion through phospholipid bilayers and binding to phospholipids

The ability of tetracycline to pass through phospholipid bilayers by diffusion was investigated. Liposomes did not retain enclosed tetracycline. Accumulation of tetracycline was observed with liposomes containing entrapped Tet repressor protein. These results indicate that the drug can pass through lipid bilayers. The antibiotic was also shown to bind to liposomes and isolated phospholipids.

Active uptake of tetracycline by membrane vesicles from susceptible Escherichia coli

A major portion of tetracycline accumulation by susceptible bacterial cells is energy dependent. Inner membrane vesicles prepared from susceptible Escherichia coli cells concentrated tetracycline 2.5 to 5 times above the external concentration when the electron transport substrate D-lactate or reduced phenazine methosulfate was added. This stimulation was reversed by cyanide, 2,4-dinitrophenol, and carbonyl cyanide m-chlorophenyl hydrazone. These vesicles data showed that proton motive force alone could energize tetracycline uptake. The lactate-dependent uptake had a pH optimum of 6.9 and a magnesium optimum of 1 mM and was not saturable up to 400 microM tetracycline. Although the vesicles were not as active as cells in concentrating tetracycline, they were less active to a similar extent in concentrating tetracycline, they were less active to a similar extent in concentrating proline, the transport of which is known to be solely proton motive force dependent. Therefore, we concluded that the active uptake of tetracycline in susceptible cells was largely, if not solely, energized by proton motive force.

Light-induced, carrier-mediated transport of tetracycline by Rhodopseudomonas sphaeroides

Tetracycline accumulation by the phototrophic bacterium Rhodopseudomonas sphaeroides has been studied, using the fluorescence properties of the antibiotic and measuring uptake of [7- 3H]tetracycline. Accumulation was carrier mediated, with a Km of approximately 300 micronM. Efflux also appeared to be carried mediated, with a Km of 25 mM. Chlorotetracycline competitively inhibited tetracycline transport. The transport was energy dependent. Efflux occurred during the influx process, and an energy-requiring steady state was reached when influx balanced efflux. Transport was inhibited by metabolic inhibitors such as antimycin A, cyanide, and iodoacetate. Proton conductors such as carbonylcyanide m-chlorophenyl hydrazone were strongly inhibitory. Efflux was not energy dependent. Efflux is partially blocked by mercuric ions and completely blocked by an external pH of 9 to 11. Although efflux rates increased continuously with lowering of the pH, influx rates have a sharp maximum at pH 7.

Comparison of tetracycline and minocyclie transport in Escherichia Coli

Differences between minocycline and tetracycline transport were demonstrated in an Escherichia coli strain with and without an R factor (R46) which confers moderate Tc resistance. Minocycline uptake was similar in R(+) and R(-) organisms, whereas tetracycline uptake was decreased in the R(+) as compared to the R(-) organism. Sodium azide had little effect on tetracycline uptake by either strain but minocycline uptake was completely inhibited by azide. p-Chloromercuribenzoate greatly decreased tetracycline uptake in both strains while minocycline uptake was markedly augmented. Both minocycline and tetracycline were effective inducers of decreased tetracycline transport, but only tetracycline had an effect on minocycline uptake. Mutual inhibition of uptake of one antibiotic by the other could not be demonstrated. These studies indicate different mechanisms of transport of minocycline and tetracycline in E. coli.

Phenotypic characterization of R-factor tetracycline resistance determinants

The tetracycline-resistance determinants of R-factors from different compatibility groups have been tested inEscherichia coliK12 and phenotypically classified into two major classes. Class I determinants confer high-level resistance to tetracycline (> 100 μg/ml) and moderate resistance to minocycline (5–25 μg/ml) while those of Class II gave moderate resistance to tetracycline (50–70 μg/ml) and low resistance to minocycline. Each class was subdivided because of variation in resistance profiles and in the abilities of tetracycline and minocycline to induce increased resistance. Strains carrying two compatible TetrR-factors of the same or different phenotypic groups did not show increased tetracycline resistance.