Comparison of tetracycline and minocyclie transport in Escherichia Coli

Effects of minocycline and its degradation products on the growth of Microcystis aeruginosa

This work aimed to investigate the influence of Microcystis aeruginosa on the rate of minocycline (MNC) removal (abiotic degradation, physical binding or chemical transformation by cells) and the toxicity of MNC and its degradation products to the cyanobacterium. Most of the work was carried out in culture media in the presence or in the absence of M. aeruginosa. The rate of the MNC abiotic degradation in culture media strongly decreased with the increase of the MNC initial concentration. The exudates did not influence the rate of MNC degradation in the media. For concentrations ≥0.48 μM, the rate of the MNC removal from the media was faster in the presence of M. aeruginosa. Biotic MNC removal occurs by both physical binding by the cells (10%) and chemical transformations. EC(50) and EC(20) for MNC on the growth of M. aeruginosa were 0.92 and 0.13 μM, respectively. Interestingly, MNC degradation products might promote M. aeruginosa growth.

Use of potentiated antibiotics in wound management

Prevention or resolution of microbial colonization of wounds is critical to rapid and uneventful healing. The use and misuse of antimicrobial agents continues to support the evolution of multidrug resistant organisms that can cause severe or life-threatening infections. Chelating agents have been shown to potentiate the effects of antimicrobial compounds. The third generation chelating agent. Tricide has been shown to be effective against many multidrug resistant pathogens, prevents pathogens from development resistance to the antimicrobials with which it is mixed and substantially reduces the amount of antimicrobials needed to kill bacteria and fungi.

Transport of the lipophilic analog minocycline differs from that of tetracycline in susceptible and resistant Escherichia coli strains

Plasmids which specify resistance to tetracycline offer much less resistance to its more lipophilic analog, minocycline. Resistance to minocycline varies for different plasmids. In the case of plasmid R222 (bearing the class B tetracycline resistance determinant on Tn10), minocycline resistance is comparatively high (10 microgram/ml, or 6% of the tetracycline resistance level). For plasmid pIP7 (bearing the class A determinant), minocycline resistance is only 1% of the tetracycline resistance level. To understand the basis for these differences, we compared the transport of the two tetracyclines by susceptible cells and by resistant cells. Uptake of minocycline by susceptible cells was 10 to 20 times more rapid than uptake of tetracycline and occurred largely via an energy-dependent route. This host-mediated energy-dependent uptake of both analogs was still present in tetracycline-resistant cells. In resistant cells, the same plasmid-mediated active efflux system previously described for tetracycline also exported minocycline. The 15-fold greater susceptibility of tetracycline-resistant R222-bearing cells to minocycline as compared with tetracycline could be explained at least in part by the more rapid influx of minocycline, which more easily overcame the efflux system. The particularly low minocycline resistance offered by pIP7 was due to a weak efflux for minocycline, 10-fold less effective than that mediated by R222. The rate-limiting step for uptake of both analogs appeared to be the outer membrane. That the lipophilic minocycline should cross this membrane more rapidly than tetracycline stands in contrast with other studies which show the outer membrane to be a barrier for entry of lipophilic substances.

Liquid chromatographic determination of minocycline in human serum

A rapid, specific, and sensitive liquid chromatographic assay for minocycline in human serum is described. The drug and an internal standard (oxytetracycline) were extracted into ethyl acetate from 0.5 ml of buffered serum (pH 6.5). Chromatographic separation was achieved on a 10-micrometer Lichrospher 100 CH 8 column with acetonitrile--citric acid (0.1 M) as the eluent. The column effluent was monitored at 352 nm. The assay was linear up to 3 micrograms/ml with a mean coefficient of variation of 3.3% (n = 6). An extraction recovery of 89.4 +/- 3.2% (mean +/- SD, n = 17) was obtained over the 0.5--2.6 micrograms/ml range. The detection limit averaged 50 ng/ml. A serum concentration-time profile in humans after oral intake is presented.

High and low level tetracycline resistance in Shigella sonnei

The results presented in this paper confirm the existence of two types of tetracycline resistance in Shigella sonnei. One group of strains had a high level of resistance to tetracycline and oxytetracyline, with a variable level of minocycline resistance. The second group had a lower level of tetracycline resistance and were sensitive to minocycline. After conjugation with E. coli K12 the selected E. coli transconjugants had the same levels of resistance as the parent Sh. sonnei strain, with one exception. Sh. sonnei 87 was resistant to a high level of tetracycline, but was able to transfer only low level resistance. It is suggested that Sh. sonnei 87 carriers two plasmids: pSU1, a conjugative plasmid conferring a low level of tetracycline resistance, and pSU2, a non-conjugative plasmid which confers a high level of resistance to tetracycline.

Two transport systems for tetracycline in sensitive Escherichia coli: critical role for an initial rapid uptake system insensitive to energy inhibitors

Escherichia coli sensitivity to tetracycline involves transport and accumulation of the antibiotic within the cell by two different uptake systems: an initial rapid uptake, which occurs over the initial 6 min of contact of the cell with tetracycline, and a slower uptake system, which continues indefinitely and whose rate of uptake is 1/10 that of the rapid system. Only the slow uptake system is blocked by inhibitors of energy-driven systems; it appears to be particularly dependent upon energy from oxidative phosphorylation. Although both uptake systems lead to accumulation of intracellular tetracycline and contribute to the cell's sensitivity, the rapid uptake system appears to be the more important. While these studies confirm active transport of tetracycline into the cell, they demonstrate that a critical uptake system which appears insensitive to metabolic inhibitors occurs initially.

Cetocycline, tetracycline analog: in vitro studies of antimicrobial activity, serum binding, lipid solubility, and uptake by bacteria

Cetocycline (formerly chelocardin or cetotetrine) is structurally related to the tetracyclines. It was found to be more active than tetracycline against many clinical isolates of aerobic gram-negative bacilli, but is less active against staphylococci, and has no activity against Pseudomonas. It is bactericidal against susceptible enteric gram-negative bacteria at concentrations two to four times higher than the minimal inhibiting concentrations. The drug is highly lipid soluble; more than 80% is bound to serum, and it is more avidly taken up by susceptible bacteria than tetracycline. A direct correlation between drug uptake and susceptibility of bacteria was not noted, except with a strain of Proteus vulgaris.