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At least 793 records · Page 44Linked to original sources
PubMed1989

Position and density effects on repression by stationary and mobile DNA-binding proteins.

We have investigated the effects of two types of DNA-binding proteins on bacterial repression. First, the effects of operator positioning on repression by stationary DNA-binding proteins, the Lac repressor and the Trp repressor, were examined in vivo. Both operator number and positioning play a role in determining in vivo levels of repression. Operators located within a promoter are more efficient regulators than those positioned at the start of transcription. Second, we investigated the effects of DNA-binding protein density on repression using a mobile DNA-binding protein, Escherichia coli RNA polymerase. We employed a transcriptional interference assay using convergent transcriptional units. The strong synthetic promoter conI and its derivatives were observed to interfere with expression of the aadA gene, which confers spectinomycin resistance upon its host. Transcriptional interference by RNA polymerase occurred only in cis and had a strong dependence on polymerase density that was modulated by varying the promoter strengths. A change in the density of approximately fourfold completely abolished the observed transcriptional interference. Several models are discussed to explain the repression patterns observed for stationary and mobile DNA-binding proteins.

Base Sequence↗
PubMed2003

Persistence of unselected transgenic DNA during a plastid transformation and segregation approach to herbicide resistance.

The use of a nonlethal selection scheme, most often using the aadA gene that confers resistance to spectinomycin and streptomycin, has been considered critical for recovery of plastid transformation events. In this study, the plastid-lethal markers, glyphosate or phosphinothricin herbicides, were used to develop a selection scheme for plastids that circumvents the need for integration of an antibiotic resistance marker. The effect of selective agents on tobacco (Nicotiana tabacum) mesophyll chloroplasts was first examined by transmission electron microscopy. We found that at concentrations typically used for selection of nuclear transformants, herbicides caused rapid disintegration of plastid membranes, whereas antibiotics had no apparent effect. To overcome this apparent herbicide lethality to plastids, a "transformation segregation" scheme was developed that used two independent transformation vectors for a cotransformation approach and two different selective agents in a phased selection scheme. One transformation vector carried an antibiotic resistance (aadA) marker used for early nonlethal selection, and the other transformation vector carried the herbicide (CP4 or bar) resistance marker for use in a subsequent lethal selection phase. Because the two markers were carried on separate plasmids and were targeted to different locations on the plastid genome, we reasoned that segregation of the two markers in some transplastomic lines could occur. We report here a plastid cotransformation frequency of 50% to 64%, with a high frequency (20%) of these giving rise to transformation segregants containing exclusively the initially nonselected herbicide resistance marker. Our studies indicate a high degree of persistence of unselected transforming DNA, providing useful insights into plastid chromosome dynamics.

Aminobutyrates↗
PubMed2004

Characterization of antimicrobial resistant Salmonella Kinshasa from dairy calves in Texas.

AIM: To determine the prevalence of antimicrobial resistance among Salmonella isolated from a central Texas dairy calf farm that raises animals for dairy-beef production. METHODS AND RESULTS: Salmonella isolates collected from 50 faecal samples were characterized for susceptibility to 20 antimicrobial agents. Seventy per cent of the faecal samples (35 of 50) tested positive for Salmonella, and high rates of resistance to the following drugs that are commonly used for treatment of bacterial enteritis in livestock were observed: ampicillin (88%), apramycin (83%), neomycin (86%), spectinomycin (91%) and oxytetracycline (90%). No resistance to the fluoroquinolone antibiotics was observed. The most prevalent Salmonella serotype was Kinshasha (22 of 35 samples), followed by Agona (4 of 35), Newport (3 of 35), Infantis (2 of 35), Montevideo (2 of 35), Lille (1 of 35) and Newington (1 of 35). The Kinshasa, Agona, Newport and Infantis serotypes all displayed resistance to ampicillin, chloramphenicol, streptomycin, sulphamethoxazole and tetracycline, and the penta-resistance phenotype was transferable to an Escherichia coli recipient strain. SIGNIFICANCE: Multi-drug resistant Salmonella in dairy calves pose a costly animal health problem and a potential risk to the public health. This study emphasizes the need for alternative, non-antimicrobial intervention strategies for the control of zoonotic pathogens.

Ampicillin↗
PubMed1993

Rapid and efficient selection of recombinant site-directed mutants of Bradyrhizobium japonicum by colony hybridization.

Due to the high incidence of spontaneous antibiotic resistance and slow growth of Bradyrhizobium japonicum strains, screening for site-directed mutants is cumbersome and time-consuming. A rapid method for selection of recombinant site-directed mutants of B. japonicum was developed. A kanamycin (Km) and a spectinomycin (Sp) cassette were each used to replace DNA fragments in the chromosome by homologous recombination. The primary new features of this method involve a simple plate selection for the antibiotic (Km or Sp) resistant mutants, then colony streaking, and lysis for DNA hybridization on a nitrocellulose filter enabling direct identification of the recombinant site-directed mutants. This method has permitted us to quickly and easily identify a large number of positive recombinant mutants from a large number of individual colonies. The procedure eliminates the need to first isolate genomic DNA from each mutant for Southern hybridization. All of the tested site-directed mutants from this method were confirmed to exhibit the expected mutant phenotype.

DNA, Bacterial↗
PubMed1998

Construction of antibiotic resistance cassettes with multiple paired restriction sites for insertional mutagenesis of Haemophilus influenzae.

Insertional mutagenesis of cloned genes coupled with site specific recombination into the genome of the parent organism is an ideal method for characterizing gene function. In this paper we describe the production and utility of two antibiotic resistance cassettes for use in Haemophilus influenzae. The mutagenic elements encode resistance to chloramphenicol or spectinomycin. Multiple paired restriction enzyme sites bound both cassettes. Use of these constructs to create mutants in H. influenzae demonstrated that the cassettes are readily incorporated into the genome in single copy and allow easy detection of mutant constructs. The insertions are stable following repeated in vitro passage. In addition, the elements are compatible with each other and allow the construction of multiple mutations within a single strain.

Chloramphenicol O-Acetyltransferase↗
PubMed1996

Factors associated with the effectiveness of antibiotic treatment for ovine virulent footrot.

Factors associated with the proportion of sheep cured of virulent footrot after antibiotic treatment were studied in a field trial under dry environmental conditions. From 2 similar flocks, 1091 Merino sheep weighing about 50 kg and infected with virulent footrot received an intramuscular injection of either 12 mL of a mixture of penicillin (250 mg/mL) and streptomycin (250 mg/mL), 6 mL of long acting oxytetracycline (200 mg/mL) or 6 mL of a mixture of lincomycin (50 mg/mL) and spectinomycin (100 mg/mL). Variables that were significantly associated with the proportion of sheep cured were: the type of antibiotic used, the number of feet infected and the flock from which the sheep came. There was an interaction between antibiotic type and number of feet infected and between antibiotic type and flock in association with the proportion of sheep cured. The extent of paring and the occurrence of blowfly strike in footrot lesions treated with diazinon had no significant association with the proportion of sheep cured.

Animals↗
PubMed1978

In vitro assays of the efficacy of antimicrobial agents in controlling Chlamydia trachomatis propagation.

The antimicrobial susceptibility of a low-laboratory-passage, slow-growing, genital Chlamydia trachomatis strain was studied by five different procedures with the use of McCoy cells pretreated with 5-iodo-2-deoxyuridine. The effects of antimicrobial agents when added to cultures on day 0 or day 2 after inoculation with C. trachomatis and the effects of washing and reincubating treated cultures in antimicrobial-free media were investigated. Tetracycline and erythromycin inhibited C. trachomatis growth at concentrations attainable in human serum, although their actions were reversible and significantly higher concentrations were needed to "cure" 48-h infected cultures. On a weight basis, spectinomycin was relatively ineffective in inhibiting C. trachomatis growth. The minimal inhibitory concentration of penicillin measured by our assay procedures was higher than that reported by other investigators. The five assay procedures used in this study were reproducible, and our results indicate that we can obtain more pertinent information about the efficacy of an antimicrobial agent in controlling C. trachomatis growth by using a combination of these assays than by simple minimal inhibitory concentration determinations, as had been previously described by other investigators. In addition, we failed to demonstrate changes in tetracycline susceptibility of C. trachomatis isolates from two patients who had received tetracycline therapy.

Animals↗
PubMed1980

Potentially synergistic antimicrobial combinations with metronidazole against Bacteroides fragilis.

Synergy studies were performed with metronidazole in combination with clindamycin, rifampin, nalidixic acid, ticarcillin, erythromycin, and spectinomycin against Bacteroides fragilis strains. An agar dilution technique was used with two inoculum sizes (10(6) to 10(7) or 10(3) to 10(4) colony-forming units per ml). None of the drugs showed synergy with metronidazole against greater than 50% of the strains, and the synergistic effect was generally less at the larger inoculum. Of the six drugs tested, nalidixic acid, clindamycin, and rifampin showed the most synergy with metronidazole. A partially synergistic or additive effect was the usual interaction occurring between metronidazole and each of the other drugs and no antagonism was seen.

Anti-Bacterial Agents↗
PubMed1985

Effectiveness of aztreonam for the treatment of gonorrhea.

Aztreonam, 1 g intramuscularly, was compared with spectinomycin, 2 g intramuscularly, for uncomplicated gonorrhea. There were no failures with either drug. For aztreonam, there were 26 urethral, 3 rectal, and 3 endocervical sites that were infected. Aztreonam in a single dose of 1 g intramuscularly is satisfactory therapy for uncomplicated urethral gonorrhea in men and may be effective for rectal and endocervical infection as well.

Adolescent↗
PubMed1987

In vitro activity of ceftriaxone, cefetamet (Ro 15-8074), ceftetrame (Ro 19-5247; T-2588), and fleroxacin (Ro 23-6240; AM-833) versus Neisseria gonorrhoeae and Haemophilus ducreyi.

We examined 300 strains of Neisseria gonorrhoeae and 100 strains of Haemophilus ducreyi to determine their in vitro susceptibility to two new cephalosporins, cefetamet (Ro 15-8074) and ceftetrame (Ro 19-5247; T-2588), and a new fluroquinolone, fleroxacin (Ro 23-6240; AM-833). Their activity was compared with that of ceftriaxone, penicillin, spectinomycin, tetracycline, and erythromycin. Cefetamet, ceftetrame, and fleroxacin had excellent in vitro activity against both groups of microorganisms. beta-Lactamase production did not significantly affect the MICs of these agents. The Mtr phenotype of N. gonorrhoeae raised the MICs two- to fourfold, but the MICs remained within the range of achievable levels in serum. These newer compounds have a distinct advantage over existing therapeutic agents in that they can be administered orally. Clinical trials are warranted to assess their usefulness in the therapy of gonorrhea and chancroid.

Cefmenoxime↗
PubMed1988

Activity of trospectomycin against Bacteroides fragilis and other Bacteroides species.

The in vitro activity of trospectomycin (U-63366; 6'-n-propyl spectinomycin pentahydrate sulfate) was evaluated against 189 clinical isolates of the Bacteroides fragilis group and 65 Bacteroides species isolates. At less than or equal to 8 micrograms/ml, the activity of trospectomycin compared favorably with those of clindamycin and cefoxitin against B. fragilis, Bacteroides distasonis, and Bacteroides vulgatus, and there was no cross resistance to these three drugs among the strains of the B. fragilis group. All the Bacteroides species were susceptible to trospectomycin. The results of this in vitro study indicate that trospectomycin possesses excellent activity against Bacteroides species.

Anti-Bacterial Agents↗
PubMed1990

Effects of trospectomycin on serum sensitivity of Escherichia coli UC 9451.

Trospectomycin sulfate, a chemically synthesized analog of spectinomycin, exhibits a broad range of activity against both aerobes and anaerobes, including the etiological agents of sexually transmitted diseases. Its activity in vitro against Escherichia coli is considered only moderate. At subinhibitory levels, however, trospectomycin induced changes in a pathogenic strain of E. coli, UC 9451, which significantly increased its sensitivity to serum lysis. This strain of E. coli shows high-level resistance to serum in vitro, typically growing twofold within a 45-min incubation period. Following exposure to one-fifth the MIC of trospectomycin, greater than 99% of the bacteria were killed in 25% serum within 15 min. Surviving bacteria were static in this level of serum for over 3 h. Killing was due to lysis mediated by both the classical and alternative complement pathways. The bacteria exposed to trospectomycin were enlarged in both diameter and length, but they still grew at rates comparable to those of untreated bacteria. No other visible morphological changes could be directly related to the increase in serum sensitivity. The profile of outer membrane proteins obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was identical for trospectomycin-treated or untreated bacteria. However, the relative proportion of four major outer membrane proteins varied considerably.

Anti-Bacterial Agents↗
PubMed1990

Emergence of aminoglycoside resistance genes aadA and aadE in the genus Campylobacter.

Resistance to streptomycin or spectinomycin or both in five Campylobacter coli strains, two Campylobacter jejuni strains, and a Campylobacter-like strain was studied by enzymatic assays and dot blot hybridization. Resistance was due to 6- or 3",9-aminoglycoside adenylyltransferases and to new types of phospho- and adenylyltransferases.

Campylobacter↗
PubMed1991

Single-dose trospectomycin for chlamydial urethritis in men.

Trospectomycin is an aminocyclitol analog of spectinomycin with significant in vitro activity against Chlamydia trachomatis. A single 1-g intramuscular dose was administered to 10 men with symptomatic, culture-positive chlamydial urethritis. Trospectomycin was well tolerated but failed to eradicate chlamydial infection, as determined by cultures obtained approximately 1 week after treatment.

Adolescent↗
PubMed1986

Plasmid-mediated changes in virulence of Vibrio cholerae.

The effects of several plasmids, including cloning vectors and R factors, on the virulence of Vibrio cholerae CA401R were determined by measuring the dose-related diarrheal response in orally challenged infant mice. The plasmids were also examined for their effects on the colonization ability of strain CA401R by joint infection experiments with a spectinomycin-resistant CA401 strain as an internal standard. One V. cholerae R factor, pVH2, enhanced the diarrheal response, while R factors Rts1 and pVH1 reduced it; plasmids RP4, pRK290, Sa, pSJ8, pSJ5, and pBR328 had no effect. The ability of the plasmids to affect in vitro toxin production by CA401R was variable. Cells containing large plasmids all showed a modest decrease in colonization ability. These results showed that some plasmids affected V. cholerae virulence, but that the cloning vectors pBR328, RP4, and pRK290 did not.

Bacterial Toxins↗