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At least 19 recordsLinked to original sources
PubMed1988

The cryptic tetracycline resistance determinant on Tn4400 mediates tetracycline degradation as well as tetracycline efflux.

Escherichia coli containing the cryptic tetracycline resistance determinant (class F) from the Bacteroides fragilis transposon Tn4400 on plasmid pGAT400 expressed a detoxification of tetracycline as well as an active efflux of tetracycline. This finding concurs with the report of detoxification for a related tetracycline resistance determinant from B. fragilis on Tn4351 (B. S. Speer and A. Salyers, J. Bacteriol. 170:1423-1429, 1987), which specifies a 10-fold-higher resistance than Tn4400. Inactivation of tetracycline occurred at an initial rate of congruent to 0.7 micrograms of tetracycline per h per 10(8) cells, as determined by biologic assay and chromatographic analysis. The detoxification is a chemical degradation which can occur in the absence of energy-dependent efflux. The products of this degradation were not substrates for active transport into susceptible cells or out of pGAT400-containing E. coli. These results indicate that Tn4400 mediates two functionally different mechanisms for tetracycline resistance: an active efflux of tetracycline and a degradation of tetracycline.

Escherichia coli↗
PubMed2002

Toxicity of tetracyclines and tetracycline degradation products to environmentally relevant bacteria, including selected tetracycline-resistant bacteria.

Tetracyclines used in veterinary therapy invariably will find their way as parent compound and degradation products to the agricultural field. Major degradation products formed due to the limited stability of parent tetracyclines (tetracycline, chlortetracycline, and oxytetracycline) in aqueous solution were theoretically identified at various environmental conditions, such as pH, presence of chelating metals, and light. Their potency was assessed on sludge bacteria, tetracycline-sensitive soil bacteria, and tetracycline-resistant strains. Several of the degradation products had potency at the same concentration level as tetracycline, chlortetracycline, and oxytetracycline on both the sludge and the tetracycline-sensitive soil bacteria. Further, both 5a,6-anhydrotetracycline and 5a,6-anhydrochlortetracycline had potency on tetracycline-resistant bacteria supporting a mode of action different from that of the parent compounds.

Bacteria↗
PubMed1988

Metal ion-tetracycline interactions in biological fluids. Part 8. Potentiometric and spectroscopic studies on the formation of Ca(II) and Mg(II) complexes with 4-dedimethylamino-tetracycline and 6-desoxy-6-demethyl-tetracycline.

Effects of metal ion-tetracycline (TC) interactions on both gastrointestinal absorption and pharmacological activity of these drugs are well documented. In particular, recent simulation studies based on newly determined complex stability constants have drawn attention to the potential influence of Ca2+ and Mg2+ ions on the bioavailability of various TC derivatives in blood plasma. Contrary to previous thoughts, it was demonstrated in these studies that the fraction of antibiotic not bound to proteins almost exclusively occurs as calcium and magnesium complexes. Among this fraction, predominant binuclear species are electrically charged, and as such cannot passively diffuse through cell membranes. It was thus postulated that the partial blocking of one of the potential coordination sites of the TC molecule, which would favor the formation of neutral mononuclear complexes, should result in a better tissue penetration of the drug. Such correlations were recently established for specific derivatives. Before possible modifications of the TC molecule can be envisaged, it is necessary that all the chelating sites involved in the relevant complexes be properly assigned. As tetracyclines are very complex ligands, the present paper first deals with the coordination of calcium and magnesium with two simpler parent substances, i.e., 4-dedimethylamino-tetracycline (DTC) and 6-desoxy-6-demethyl-tetracycline (DSC). After the quantitative investigation of the proton and metal complex equilibria involved, UV and circular dichroism spectroscopies are used to study the corresponding structural aspects. In DTC complexes, the BCD ring system acts as the exclusive coordination site for both metals. For DSC, however, the N4 atom plays a leading role in the metal binding and would be the only donor involved in 1:1 species; in ML2 complexes, the second ligand is thought to bind through the BCD ring system.

Calcium↗
PubMed2003

Influence of tetracycline exposure on tetracycline resistance and the carriage of tetracycline resistance genes within commensal Escherichia coli populations.

AIMS: To assess the influence of incremental tetracycline exposure on the genetic basis of tetracycline resistance within faecal Escherichia coli. METHODS AND RESULTS: Through the adoption of a novel combination of multiple breakpoint selection, phenotypic characterization and the application of a polymerase chain reaction based gene identification system it proved possible to monitor the influence of antibiotic exposure on resistance gene possession. Using tetracycline as a case study a clear hierarchy was revealed between tet genes, strongly influenced by host antimicrobial exposure history. CONCLUSIONS: The antimicrobial exposure regime under which an animal is produced affects both the identity and magnitude of resistance gene possession of a selected bacterial population within its enteric microflora. Among the ramifications associated with such resistance gene selection is the degree of resistance conferred and the carriage of linked resistance determinants. This selection is applied by exposure to antibiotic concentrations well below recognized minimum inhibitory tetracycline concentration breakpoints widely adopted to characterize bacterial 'susceptibility'. SIGNIFICANCE AND IMPACT OF THE STUDY: This study confirms the ability of minimal antibiotic exposure to select for the continued persistence of resistance genes within the enteric microflora. It is clearly demonstrated that different antimicrobial regimes select for different resistance genes, the implications of which are discussed.

Animals↗
PubMed1996

Treatment of malignant pleural effusions with a combination of bleomycin and tetracycline. A comparison of bleomycin or tetracycline alone versus a combination of bleomycin and tetracycline.

BACKGROUND: Treatment of patients with malignant pleural effusions is mostly palliative. Tetracycline and bleomycin are the two most commonly used agents for the treatment of pleurodesis. In this study, the authors used a combination of the two drugs for this particular purpose. METHODS: Sixty patients with massive malignant pleural effusions were divided in 3 equal groups in a simple randomized manner. Tetracycline (20 mg/kg [maximum of 2 g] in 50 mL of normal saline) was administered through a chest tube in Group 1. Group 2 received bleomycin (1 U/kg [maximum of 60 U] in 50 mL of normal saline). Group 3 received the above 2 preparations (tetracycline, 20 mg/kg [maximum of 2 g] in 40 mL of normal saline and bleomycin, 1 U/kg [maximum of 60 U] in 30 mL of normal saline) instilled one after the other, while the chest tube was clamped for 5 minutes in the interim. Follow-up examinations were performed at 7 days, 30 days, 60 days, 90 days, and 6 months. RESULTS: There was no significant difference in the complete response rate of the 3 groups during the first 4 months. At the end of the study, Group 3 had a significantly higher complete response rate (70%) compared with Groups 1 and 2 (35% and 25%, respectively) (P = 0.02). CONCLUSIONS: The response to use of a combination of bleomycin and tetracycline for the treatment of patients with pleurodesis is superior to that achieved by either of these agents used alone.

Adult↗
PubMed1989

Novel aerobic tetracycline resistance gene that chemically modifies tetracycline.

A tetracycline resistance gene that was found originally on the Bacteroides plasmid pBF4 confers resistance on Escherichia coli but only when cells are growing aerobically. When E. coli EM24 carrying this aerobic tetracycline resistance (*Tcr) gene is grown in medium containing tetracycline, the resulting spent medium is no longer toxic to tetracycline-sensitive (Tcs) E. coli EM24 (B.S. Speer and A.A. Salyers, J. Bacteriol. 170: 1423-1429, 1988). To determine whether the *Tcr gene product modified tetracycline, we characterized the material resulting from incubation of E. coli (*Tcr) with tetracycline. When [7-3H(N)]tetracycline was added to cultures of E. coli (*Tcr), at least 90% of the label was recovered in the extracellular fluid. Therefore, tetracycline was not being sequestered by the cells. The labeled material behaved similarly to tetracycline with respect to solubility in various organic solvents. However, the UV-visible light spectrum had a single peak at 258 nm, whereas the tetracycline spectrum had a peak at 364 nm. The labeled material also had a faster migration rate than did tetracycline on thin-layer plates in a solvent system of butanol-methanol-10% citric acid (4:1:2, vol/vol/vol) and was separable from tetracycline by reverse-phase high-pressure liquid chromatography, using an acetronitrile-0.1% trifluoroacetic acid solvent system. These results demonstrate that the *Tcr gene product chemically modifies tetracycline. The *Tcr gene is the first example of a chemically modifying tetracycline resistance mechanism.

Aerobiosis↗
PubMed1990

Transport of divalent cations with tetracycline as mediated by the transposon Tn10-encoded tetracycline resistance protein.

Tetracycline uptake into inverted membrane vesicles from Tn10-bearing Escherichia coli cells required divalent cations. The degree of the stimulation of tetracycline uptake by various divalent cations showed the following decreasing order: Co2+ greater than Mn2+ greater than Mg2+ greater than Cd2+ greater than Ca2+. This order is consistent with the increasing order of the dissociation constants for metal chelate complexes of tetracycline. The Hill constants for the tetracycline uptake rate with various divalent cation concentrations were one. These observations strongly suggested that a 1:1 complex of tetracycline and a divalent cation was transported by a tetracycline resistance protein. This notion was confirmed by our observations that 60Co2+ was actively taken up with tetracycline by the membrane vesicles prepared from resistant cells. In the absence of tetracycline, no uptake of 60Co2+ was observed. It is clear that the 60Co2+ uptake was mediated by the tetracycline resistance protein, because the membrane vesicles from tetracycline-sensitive cells did not show the uptake of 60Co2+ and tetracycline. The 60Co2+ uptake was inhibited in the presence of other divalent cations, without any significant effect on tetracycline uptake, indicating that these cations are also transported with tetracycline by the tetracycline resistance protein.

Biological Transport↗
PubMed1990

A tetracycline efflux gene on Bacteroides transposon Tn4400 does not contribute to tetracycline resistance.

Previously, we demonstrated that the Bacteroides transposon Tn4351, which confers tetracycline resistance only on aerobically grown Escherichia coli, carries a gene that codes for a tetracycline-inactivating enzyme (B. S. Speer and A. A. Salyers, J. Bacteriol. 170:1423-1429, 1988). However, Park et al. (B. H. Park, M. Hendricks, M. H. Malamy, F. P. Tally, and S. B. Levy, Antimicrob. Agents Chemother. 31:1739-1743, 1987) showed that E. coli carrying a closely related transposon, Tn4400, exhibits energy-dependent efflux of tetracycline as well as tetracycline-inactivating activity (B. H. Park and S. B. Levy, Antimicrob. Agents Chemother. 32:1797-1800, 1988). This result raised the question of whether efflux or inactivation or a combination of the two was necessary for resistance conferred by both transposons. We showed that cells carrying Tn4351 did not exhibit the clear-cut efflux activity seen with cells carrying Tn4400 but rather exhibited a tetracycline accumulation profile which could be explained solely on the basis of inactivation of tetracycline in the cytoplasm and rapid diffusion of altered tetracycline out of the cell. Additionally, we were able to clone the efflux and tetracycline-modifying genes of Tn4400 separately. The region carrying the efflux gene spanned one of the two regions in which Tn4400 differs from Tn4351. A clone containing the corresponding region of Tn4351 did not exhibit efflux. Thus, it appears that Tn4351 does not have the efflux gene and that efflux makes no contribution to the resistance conferred by Tn4351. The MIC for cells carrying the subclone from Tn4400 that contained only the gene for tetracycline inactivation was the same that for cells carrying both the inactivation and efflux genes. Cells carrying only the gene for tetracycline efflux were tetracycline sensitive. This was true even when the efflux gene was on a high-copy-number plasmid which increased the level of efflux to that associated with the Tcr gene on pBR328. These results indicate that efflux activity does not contribute significantly to the tetracycline resistance conferred by Tn4400.

Bacteroides↗
PubMed1981

Minocycline treatment of tetracycline-resistant and tetracycline-responsive acne vulgaris.

The purpose of the study presented herein was to determine the safety and efficacy of minocycline in patients whose acne vulgaris failed to respond adequately to tetracycline therapy and to confirm continued improvement in tetracycline-responsive patients when minocycline was substituted for tetracycline. Thirty-six acne vulgaris patients were given oral tetracycline (250 mg four times a day) for six weeks, followed by oral minocycline (50 mg three times a day) for six weeks. An analysis of the increase or decrease in total lesion counts obtained at biweekly intervals revealed that minocycline caused statically significant improvement both in patients who did not respond to tetracycline and in patients who did respond to tetracycline. Patients who did not respond to tetracycline therapy achieved a mean decrease of 54 percent in lesions after after six weeks of minocycline treatment. In tetracycline-responsive patients, six weeks' treatment with tetracycline caused a 33.5 percent mean decrease in the lesion count. When these patients received minocycline for a subsequent six-week period, the mean lesion count decreased by an additional 60 percent. Only one patient developed a side effect: severe itching and urticaria in a minocycline-treated subject warranted discontinuance of therapy. Minocycline was a safe and effective agent in the treatment of acne both in tetracycline-resistant and in tetracycline-responsive patients.

Acne Vulgaris↗
PubMed1982

Comparison of kinetics of active tetracycline uptake and active tetracycline efflux in sensitive and plasmid RP4-containing Pseudomonas putida.

Membrane vesicles prepared from tetracycline-sensitive cells of Pseudomonas putida took up tetracycline by an active transport system with an apparent Km of 2.5 mM and a Vmax of 50 nmol min-1 mg protein-1. In contrast, resistance determinant RP4-containing P. putida had an active high-affinity efflux system for tetracycline with a Km of 2.0 to 3.54 microM and a Vmax of 0.15 nmol min-1 mg protein-1. Thus, the efflux system of tetracycline-resistant P. putida(RP4) had an average of 1,000-fold greater affinity for tetracycline than the influx system of tetracycline-sensitive cells. From these results, it is clear that a major mechanism of tetracycline resistance in RP4-containing P. putida is an active tetracycline efflux mechanism. There was also evidence for a second tetracycline efflux system with low affinity for tetracycline n P. putida(RP4). This efflux system had a Km of 0.25 mM and a Vmax of 1.45 nmol min-1 protein-1. Whether this low-affinity efflux system was also present in tetracycline-sensitive P. putida could not be discerned from these experiments.

Biological Transport, Active↗
PubMed1994

Randomised trial of mefloquine-tetracycline and quinine-tetracycline for acute uncomplicated falciparum malaria.

The combination of mefloquine plus tetracycline was compared with quinine plus tetracycline in a randomised therapeutic trial in 102 patients with acute uncomplicated falciparum malaria in Thailand. Quinine plus tetracycline is considered the standard treatment for the highly drug-resistant strains of P. falciparum found in this area. Fifty patients received mefloquine (750 mg given immediately, followed by 500 mg 6 h later) with tetracycline and 52 patients received quinine (600 mg every 8 h for seven days) with tetracycline. Tetracycline was administered to both groups in doses of 250 mg four times daily. All patients were admitted to the hospital for 28 days to exclude re-infection. Ninety-three patients completed the study; nine patients left prior to completion of follow-up for reasons unrelated to their treatment. Cure rates for the two groups were 94% (44/47) for mefloquine plus tetracycline and 98% (45/46) for quinine plus tetracycline. Parasite and fever clearance times were shorter for the group treated with mefloquine but the differences were not statistically significant. Nearly all patients (94%) treated with quinine developed cinchonism compared with only 12% treated with mefloquine; all other symptoms following treatment were similar. Thirteen patients (26%) treated with quinine also developed delayed primary attacks of P. vivax during the follow-up period; none developed in the patients treated with mefloquine. These results support the contention that the combination of mefloquine plus tetracycline is equally effective and less toxic than quinine plus tetracycline for treatment of acute uncomplicated falciparum malaria in areas requiring combination therapy for drug resistance.

Adolescent↗
PubMed1987

Cryptic tetracycline resistance determinant (class F) from Bacteroides fragilis mediates resistance in Escherichia coli by actively reducing tetracycline accumulation.

Escherichia coli bearing a cryptic tetracycline resistance determinant from Bacteroides fragilis expressed low-level constitutive resistance to tetracycline under aerobic, but not anaerobic, growth conditions and accumulated less tetracycline aerobically than did isogenic susceptible cells. This decreased uptake was energy dependent and reversible by increased concentrations of tetracycline, suggesting a saturable carrier-mediated active efflux mechanism. Decreased uptake was not seen when the cells were grown and assayed anaerobically. Other tetracycline resistance determinants (classes A to E) isolated from gram-negative enteric bacteria expressed resistance and generated active efflux of tetracycline under anaerobic as well as aerobic conditions. When the Bacteroides determinant was placed in the same cell with any of the class A to E tetracycline resistance determinants, there was an increase in resistance under aerobic conditions of as much as 48% more than was projected by adding the resistances expressed by the determinants individually. In cells bearing the class A determinant together with the Bacteroides determinant, saturation of the active efflux system required over twofold more exogenous tetracycline than did cells bearing the class A determinant alone. We have designated this new tetracycline resistance determinant class F.

Bacteroides fragilis↗
PubMed2002

Fe(2+)-tetracycline-mediated cleavage of the Tn10 tetracycline efflux protein TetA reveals a substrate binding site near glutamine 225 in transmembrane helix 7.

TetA specified by Tn10 is a class B member of a group of related bacterial transport proteins of 12 transmembrane alpha helices that mediate resistance to the antibiotic tetracycline. A tetracycline-divalent metal cation complex is expelled from the cell in exchange for a entering proton. The site(s) where tetracycline binds to this export pump is not known. We found that, when chelated to tetracycline, Fe(2+) cleaved the backbone of TetA predominantly at a single position, glutamine 225 in transmembrane helix 7. The related class D TetA protein from plasmid RA1 was cut at exactly the same position. There was no cleavage with glycylcycline, an analog of tetracycline that does not bind to TetA. The Fe(2+)-tetracycline complex was not detectably transported by TetA. However, cleavage products of the same size as with Fe(2+) occurred with Co(2+), known to be cotransported with tetracycline. The known substrate Mg (2+)-tetracycline interfered with cleavage by Fe(2+). These findings suggest that cleavage results from binding at a substrate-specific site. Fe(2+) is known to be able to cleave amide bonds in proteins at distances up to approximately 12 A. We conclude that the alpha carbon of glutamine 225 is probably within 12 A of the position of the Fe(2+) ion in the Fe(2+)-tetracycline complex bound to the protein.

Amino Acid Sequence↗
PubMed1992

Tissue concentration and localization of tetracycline following site-specific tetracycline fiber therapy.

The primary objective of this study was to evaluate the concentration and location of tetracycline hydrochloride in tissue adjacent to periodontal pockets treated with a tetracycline impregnated fiber. A secondary objective was to determine if the presurgical placement of fibers had any adverse effects on healing following periodontal surgery. The study population consisted of 10 patients with at least 2 pockets in both maxillary quadrants of > or = 5 mm in depth and exhibiting bleeding on probing. After an initial scaling and root planing, placebo or tetracycline fibers were randomly assigned by quadrant to 2 non-adjacent pockets. Fibers were removed at the time of surgery; i.e., day 8, and periodontal surgery was performed utilizing a flap incision that allowed biopsy of 1 interdental papilla from each of the 2 test sites in each quadrant. One biopsy was analyzed for tetracycline concentrations by high performance liquid chromatography (HPLC). The second biopsy was examined by both light and ultraviolet fluorescence microscopy to determine the location of residual tetracycline and the intensity of inflammatory cell infiltrates. Results showed that the tissue concentration of the antibiotic in tetracycline treated sites was 64.4 +/- 7.01 ng/mg (ng of tetracycline/mg tissue weight) which corresponds to 43 micrograms of tetracycline and was below levels of accurate measurement in placebo treated sites. Tetracycline tissue concentrations corresponded to the ultraviolet fluorescence microscopy with a Pearson correlation coefficient of r = 0.92. Tetracycline fluorescence was noted in the soft tissue wall ranging from 1 to 20 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2001

Synthesis and analysis of ethylated tetracycline, an antibiotic derivative that inhibits the growth of tetracycline-resistant XL1-Blue bacteria.

Bacterial resistance to antibiotics is a significant problem in medical care facilities, causing increased fatalities due to infection. The present study demonstrates that antibiotic structures can be selectively altered in a manner that revives their ability to inhibit bacterial growth. The antibiotic tetracycline was ethylated at the position of the phenolic hydroxy group with the use of diazoethane, forming an ethyl ether functional group. This derivative was dissolved in Luria-Bertani (LB) agar medium, then placed in tissue culture for screening against a tetracycline-resistant bacterial strain. The growth of this bacterial strain, designated XL1-Blue, was inhibited by the ethylated form of tetracycline. The procedure for synthesizing ethylated tetracycline utilizes diazoethane and is presented with the molecular structures and IR spectra. The ethylated form of tetracycline was stable at -20 degrees C for many weeks, and was soluble in LB agar plate medium. Ethylated tetracycline induced growth inhibition of XL1-Blue bacteria within the first 24 h of incubation. The level of bacterial growth inhibition was greater than 30%. Calculation of the partition coefficient, log P, was accomplished and indicates that ethylated tetracycline has an increased lipophilic tendency relative to unmodified tetracycline, and therefore has greater solubility in lipid bilayers.

Acetates↗