J Bacteriol. 1980 Oct;144(1):346-55.
Identification of a second tetracycline-inducible polypeptide encoded by Tn10.

Zupancic TJ, King SR, Pogue-Geile KL, Jaskunas SR.

Three Tn10 polypeptides were detected by analyzing the proteins synthesized in ultraviolet light-irradiated Escherichia coli cells after infection with lambda::Tn10. One of these polypeptides was the previously identified 36,000-dalton TET polypeptide. The other two had approximate sizes of 25,000 and 13,000 daltons. The syntheses of both the TET polypeptide and the 25,000-dalton polypeptide were inducible by tetracycline in lambda-immune hosts. Similarly, the synthesis of the TET polypeptide was inducible in nonimmune hosts. However, the synthesis of the 25,000-dalton polypeptide was constitutive in nonimmune hosts. An amber mutation in a gene required for tetracycline resistance on lambda::Tn10 was isolated that eliminated the synthesis of the TET polypeptide in sup+ hosts but not the synthesis of the 25,000-dalton or the 13,000-dalton polypeptides. The expression of tetracycline resistance from wild-type Tn10 was found to be anomalous in E. coli strains carrying the amber suppressors supD, supE, and supF. In general, strains containing these nonsense suppressors were less resistant to tetracycline.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6252196&dopt=Abstract antibiotics, tetracycline




Int J Food Microbiol. 1994 Dec;24(1-2):161-70.
Occurrence of plasmids and tetracycline resistance among Campylobacter jejuni and Campylobacter coli isolated from whole market chickens and clinical samples.

Lee CY, Tai CL, Lin SC, Chen YT.

Department of Agricultural Chemistry, National Taiwan University, Taipei.

Twenty whole market chickens, purchased from 10 different stores in the Taipei Metropolitan area, were examined for the presence of Campylobacter jejuni and Campylobacter coli. The microorganisms were recovered from 95% of the chickens. A survey of different sites on--breast, thigh and tail--showed that contamination was equally common on all these sites. One hundred and sixty-seven chicken isolates and the 41 clinical isolates of Campylobacter jejuni were examined for the occurrence of plasmid DNA in association with tetracycline resistance. A high plasmid occurrence rate of 91% and 44% was observed for C. jejuni from chickens and clinical isolates, respectively. Plasmids ranged in size from 16 to 208 Kb. A 61 Kb plasmid and a 50 Kb plasmid were common to the chicken isolates and clinical isolates, respectively. All chicken isolates and 78% of clinical isolates were tetracycline-resistant. The high rate of tetracycline resistance in chicken isolates probably related to use of tetracycline as a growth promoter for poultry. A tetO DNA Probe, highly specific for the detection of tetracycline resistance in C. jejuni and C. coli, was used to find the location of tetracycline resistance. Of 157 chicken isolates, 98% of isolates were positive with the tetO probe, 87% (137/157) on plasmids and 11% (17/157) on the chromosome; only three isolates did not hybridize with the tetO probe. Of 32 clinical isolates, 88% isolates hybridized with the tetO probe, 47% (15/32) on plasmids and 41% (13/32) on the chromosome; four isolates did not hybridize with the tetO probe.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7703010&dopt=Abstract antibiotics, tetracycline




J Mol Biol. 1995 Mar 24;247(2):260-80.
The complex formed between Tet repressor and tetracycline-Mg2+ reveals mechanism of antibiotic resistance.

Kisker C, Hinrichs W, Tovar K, Hillen W, Saenger W.

Institut fur Kristallographie, Freie Universitat Berlin, Germany.

In recent years Gram-negative bacteria have developed several resistance mechanisms against the broad-spectrum antibiotic tetracycline (Tc). The most abundant mechanism involves a membrane-associated protein (TetA) that exports the antibiotic out of the bacterial cell before it can attach to the ribosomes and inhibit polypeptide elongation. The expression of the TetA protein is regulated by the Tet repressor (TetR). It occurs as a homodimer and binds with two alpha-helix-turn-alpha-helix motifs (HTH) to two tandemly orientated DNA operators, thereby blocking the expression of the associated genes, one encoding for TetA and the other for TetR. If Tc in complex with a divalent cation binds to TetR, a conformational change occurs and the induced TetR is then unable to bind to DNA. TetR of class D, TEtRD, was cocrystallized with tetracycline (7HTc) and Mg2+ in space group I4(1)22 and studied by X-ray diffraction. One TetRD monomer occupies the crystal asymmetric unit, and the dimer is formed by a crystallographic 2-fold rotation. The crystal structure was determined by multiple isomorphous replacement at 2.5 A resolution, and on this basis the structure of the nearly isomorphous complex with 7-chlorotetracycline, TetRD/(Mg 7CITc)+, has been refined to an R-factor of 18.3% using all reflections to 2.1 A resolution. TetRD folds into ten alpha-helices with connecting turns and loops. The N-terminal three alpha-helices of the repressor form the DNA-binding domain, including the HTH with an inverse orientation compared with HTH in other DNA-binding proteins. The distance of 39 A between the two recognition helices explains the inability of the induced TetR to bind to B-form DNA. The core of the protein is formed by helices alpha 5 to alpha 10. It is responsible for dimerization and contains, for each monomer, a binding pocket that accommodates Tc in the presence of a divalent cation. The structure of the TetRD/(Mg 7CITc)+ complex reveals the octahedral coordination of Mg2+ by Tc (chelating O-11, and O-12), His100 N epsilon and by three water molecules; in addition there is an extended network of hydrogen bonding and van der Waals interactions formed between 7CITc and TetR. The detailed view of the Tc-binding pocket and the interactions between the antibiotic and the repressor offers the first solid basis for rational tetracycline design, with the aim of circumventing resistance.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7707374&dopt=Abstract antibiotics, tetracycline




J Bacteriol. 1996 Jun;178(11):3246-51.
Tet(M)-promoted release of tetracycline from ribosomes is GTP dependent.

Burdett V.

Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710, USA.

Tet(M) protein, which displays homology to elongation factor G (EF-G), interacts with the protein biosynthetic machinery to render this process resistant to tetracycline in vivo and in vitro. To clarify the basis of the resistance mechanism, the effects of Tet(M) on several reactions which occur during protein synthesis were examined. The mechanism of action of Tet(M) has been clarified by two observations. The protein relieves tetracycline inhibition of factor-dependent tRNA binding and dramatically reduces the affinity of ribosomes for tetracycline when GTP is present. This reduction in drug affinity appears to be due to a large increase in the rate of tetracycline dissociation. Addition of Tet(M) to ribosome-tetracycline complexes results in displacement of bound drug. And, while Tet(M) and EF-G GTPase activities are tetracycline resistant, the two proteins differ in their sensitivities to fusidic acid, with the latter activity inhibited by the drug. Furthermore, while Tet(M) protects translation from tetracycline inhibition in a defined system, it is unable to substitute for either EF-G or elongation factor Tu.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8655505&dopt=Abstract antibiotics, tetracycline




J Biol Buccale. 1982 Dec;10(4):271-9.
The microscopic distribution of tetracycline in human teeth.

Nalbandian J, Hagopian M, Patters M.

The distribution of tetracycline fluorescence was studied in a random collection of 378 teeth extracted in 1976 in Farmington, Connecticut, using ultra-violet microscopy of longitudinal ground sections. The sample consisted of 4 deciduous molars and the following numbers of permanent teeth: 72 incisors, 41 canines, 63 premolars, 26 first molars, 24 second molars, and 148 third molars. Narrow fluorescent lines reflecting short regimens of drug administration and broad bands corresponding to long term administration were identified in the dentin and tabulated in relation to their anatomical position. Fluorescence in the cementum was also noted. Of all the teeth, 33.3% exhibited tetracycline changes in either the dentin, the cementum, or both. There were 89 affected third molars. These had a mean of 3.1 (+/- 2.9) fluorescent dentin lines per tooth as well as many broad bands, largely in the root region. The teeth were subjected to an estimation of age in order to segregate those teeth whose dentin had formed prior to the advent of tetracycline usage. When this was done, the corrected incidence of tetracycline affected teeth in the collection was 45.4%. The observations show that American teeth have been extensively affected by tetracycline. The location of fluorescent markings appear to reflect reluctance to use this drug during the developmental period when cosmetic effects could result. Markings clearly indicate heavy usage of tetracycline during a later period of development corresponding to third molar root formation.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6963269&dopt=Abstract antibiotics, tetracycline




J Clin Periodontol. 1983 Jul;10(4):422-32.
Antibiotic susceptibility testing of subgingival plaque samples.

Walker CB, Gordon JM, Socransky SS.

The in vitro inhibitory effect of several antimicrobial agents was determined against dispensed dental plaque samples taken from periodontally diseased sites as an aid in the selection of antibiotics for adjunctive use in periodontal therapy. 2 groups of patients were sampled. 1 group of 10 patients with severely advanced disease had received periodontal treatment which included the frequent adjunctive use of an antibiotic. The second group consisted of 15 individuals with less severe periodontal disease; only 4 individuals had been previously treated with antibiotics for their periodontal disease. Bacterial samples of subgingival plaque were taken from each patient and tested against a battery of antibiotics to determine which agent was the most effective in suppressing bacterial growth. Each antibiotic was incorporated into Trypticase-soy blood agar at a concentration equivalent to that achieved in either gingival fluid or blood following recommended oral dosages. The inhibitory effect was determined by comparing the number of bacterial recovered on the antibiotic-containing medium to the total number of bacteria recovered on the basal medium. Penicillins, with the exception of cloxacillin, were the most effective in inhibiting bacterial growth. Benzylpenicillin consistently inhibited the growth of 90% of the isolates recovered on media free of antibiotics while ampicillin and amoxicillin frequently inhibited 99% or more of the bacteria recovered. Tetracycline was generally inhibitory for at least 90% of the isolates if the patients had not been previously treated with this agent. However, resistance to this drug was common in samples taken from patients previously treated with tetracycline. Doxycycline, a tetracycline derivative, did not inhibit significantly more isolates than tetracycline. Clindamycin was inhibitory for 90% or more of the organisms in most of the samples; and, was usually effective in inhibiting isolates in samples which exhibited large numbers of isolates resistant to tetracycline. Erythromycin was relatively ineffective against the isolates recovered from samples from the severely diseased group but was inhibitory to isolates in some samples taken from the more moderately diseased group. Metronidazole, at the concentration tested, was largely ineffective against the isolates in bacterial samples from both groups. No single antimicrobial agent was found to be inhibitory for greater than 90% of the bacteria recovered from all of the subgingival plaque samples with the possible exception of some penicillins.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6577034&dopt=Abstract antibiotics, tetracycline




J Bacteriol. 1992 Dec;174(24):7926-33.
Genetic analysis of the tetA(C) gene on plasmid pBR322.

McNicholas P, Chopra I, Rothstein DM.

Department of Microbial Genetics, Lederle Laboratories, Pearl River, New York 10965.

The TetA(C) protein, encoded by the tetA(C) gene of plasmid pBR322, is a member of a family of membrane-bound proteins that mediate energy-dependent efflux of tetracycline from the bacterial cell. The tetA(C) gene was mutagenized with hydroxylamine, and missense mutations causing the loss of tetracycline resistance were identified at 30 distinct codons. Mutations that encoded substitutions within putative membrane-spanning alpha-helical regions were scattered throughout the gene. In contrast, mutations outside the alpha-helical regions were clustered in two cytoplasmic loops, between helices 2 and 3 and helices 10 and 11, suggesting that these regions play a critical role in the recognition of tetracycline and/or energy transduction. All of the missense mutations encoded a protein that retained the ability to rescue an Escherichia coli strain defective in potassium uptake, suggesting that the loss of tetracycline resistance was not due to an unstable TetA(C) protein or to the failure of the protein to be inserted in the membrane. We postulate that the mutations encode residues that are critical for the active efflux of tetracycline, except for mutations that result in the introduction of charged residues within hydrophobic regions of the TetA(C) protein.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1459940&dopt=Abstract antibiotics, tetracycline




J Antibiot (Tokyo). 1996 Nov;49(11):1127-32.
Detection of tet(K) and tet(M) in Staphylococcus aureus of Asian countries by the polymerase chain reaction.

Warsa UC, Nonoyama M, Ida T, Okamoto R, Okubo T, Shimauchi C, Kuga A, Inoue M.

Department of Microbiology, Kitasato University School of Medicine, Sagamihara, Japan.

This study describes the use of the polymerase chain reaction (PCR) to detect the tet(K) and tet(M) tetracycline resistance genes in Staphylococcus aureus. Primers based on the DNA sequence of the tet(K) and tet(M) genes from S. aureus were used as primers in the PCR assay to detect the presence of genes for resistance to tetracycline and minocycline. Two-hundred and fifteen isolates of S. aureus from Asian countries as Japan, Indonesia, China, Korea and Thailand were examined, and the results confirm that tet(K) specifies resistance to tetracycline but not to minocycline and tet(M) specifies resistance to both tetracycline and minocycline. We observed two different types of clinical isolates of S. aureus strains resistant to minocycline and tetracycline: the first carried only the tet(M) gene, while the second carried both the tet(M) and the tet(K) genes. Almost all of the clinical isolates of S. aureus resistant to minocycline and tetracycline from Indonesia, China and Thailand carried both tet(M) and tet(K) genes, while most of clinical isolates of S. aureuss from Japan and Korea carried only tet(M) gene.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8982342&dopt=Abstract antibiotics, tetracycline