Yet Another Doctor Blog On The Internet

[Recent progress in the hormonal treatment of sterility].


In vitro activities of 13 antibiotics were assessed against 85 Brucella abortus isolates from naturally infected cattle in the Republic of Korea during 1998-2006, using broth microdilution test. Tetracyclines showed the most excellent activity against B. abortus, displaying MIC values of 0.5 μg/ml or below. In particular, minocycline showed the lowest MIC₅₀/₉₀ values (0.125/0.125 μg/ml) in this study. Among four fluoroquinolones tested, ciprofloxacin (MIC₅₀/₉₀, 0.5/1 μg/ml) and norfloxacin (MIC₅₀/₉₀, 8/8 μg/ml) had the most and the least activities, respectively. Gentamicin (MIC₅₀/₉₀, 1/1 μg/ml) was more effective than streptomycin, erythromycin, rifampin, and chloramphenicol (MIC₅₀/₉₀, 2/2 μg/ml).

Solid dispersions were prepared using hydrophilic carriers like polyethylene glycol (PEG) 4000, polyvinylpyrrolidone (PVP) k30 and carbopol 974pNF (CP) in various ratios using solvent evaporation technique. These formulations were evaluated using solubility studies, dissolution studies; Fourier transmitted infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetery (DSC). The influence of polymer type and drug to polymer ratio on the solubility and dissolution rate of norfloxacin was also evaluated.

High-level resistance to quinolones has previously been shown to occur in Campylobacter spp. both in vitro and in patients treated with quinolones. We have selected isolates that are resistant to quinolones by plating cells from a susceptible C. jejuni strain, UA535, on medium containing nalidixic acid at 32 micrograms/ml. Fluctuation analysis indicated that resistance occurred by mutation at a frequency of 5 x 10(-8) per cell plated. Unlike what is observed with other gram-negative organisms, the nalidixic acid-resistant mutants demonstrated high-level cross-resistance (MIC, greater than or equal to 4 micrograms/ml) to newer quinolones, including ciprofloxacin, norfloxacin, and temafloxacin, yet remained susceptible to coumermycin A1 and several other unrelated antibiotics. Mutants with an identical resistance phenotype could also be selected from UA535 with ciprofloxacin and norfloxacin at a similar frequency. To study the mechanism of quinolone resistance, DNA gyrases were purified from C. jejuni UA535 and two resistant mutants by heparin-agarose and novobiocin-Sepharose chromatography. After the respective enzyme concentrations were adjusted to equivalent units of activity in the DNA supercoiling reaction, the DNA gyrases from the resistant mutants were found to be 100-fold less susceptible than the wild-type enzyme to inhibition by quinolones. Subunit switching experiments with purified A and B subunits from the wild type and one of the quinolone-resistant mutants indicated that an alteration in the A subunit was responsible for resistance. These results show that a single-step mutation can occur in vitro in the gene encoding DNA gyrase in C. jejuni, producing clinically relevant levels of resistance to the newer quinolones.

A total of 347 non-duplicated isolates of Enterobacteriaceae were collected between August and October 2006 from 2 hospitals. Qnr determinant screening was conducted using PCR amplification, and all positive results were confirmed by direct sequencing. Qnr-positive strains were determined on the basis of the presence of ESBL and AmpC beta-lactamase genes.

Effects of various antimicrobials on in vitro Shiga toxin production and release by Shigella dysenteriae serotype 1 was investigated in this study with particular reference to the role of outer membrane vesicles in toxin release by the organism. Five antimicrobials, namely nalidixic acid, ciprofloxacin, norfloxacin, fosfomycin and mitomycin C, were chosen for the study and the toxin titre was measured by the reverse passive latex agglutination (RPLA) method using an available kit. Only mitomycin C was found to induce production of Shiga toxin in the bacteria and its release by outer membrane vesicles. The highest titre of toxin was obtained in vesicle fraction suggesting that the vesicles play an important role in the release of Shiga toxin from periplasmic space by the organism.

A prospective study was undertaken to determine the transcorneal penetration of three topically applied fluoroquinolones into aqueous humour.

The antimutagenic effect of this vitamin A precursor is probably due to the active molecule of vitamin A, a desmutagen with the ability of radical capture. A diet rich in beta-carotene or vitamin A could be a good alternative to reduce genotoxic risk to patients being treated with quinolone.

FR160, a catechol iron chelator, and tetracyclines or norfloxacin exert in vitro additive or synergistic activity against a chloroquine-resistant Plasmodium falciparum clone. FR160 shows antagonistic effects in association with macrolides, ofloxacin, and rifampin.

The bactericidal effects of five quinolones (at the optimum bactericidal concentration for strain AB1157) on 15 strains of Escherichia coli with mutations in genes for the SOS response or cell division was studied by a viable-count method. The kill rate data were normalized for growth rate and compared to those for the wild type, AB1157. Similar MICs of enoxacin and fleroxacin were obtained for all mutants; however, different mutants had differing susceptibilities to ciprofloxacin, norfloxacin, and nalidixic acid. Killing kinetic studies showed that mutants with constitutive RecA expression (recA730 and spr-55 mutants) survived longer than AB1157 with all quinolones. Mutants deficient in SOS induction, e.g., recA430 and lexA3 mutants, also survived longer, suggesting that induction of the SOS response by quinolones is harmful to wild-type cells. Recombination repair-deficient mutants (recB21, recC22, and recD1009 mutants) were killed more rapidly than AB1157, as were excision repair mutants, except with nalidixic acid. Mutants which were unable to filament (sfiA11 and sfiB114 mutants) survived longer than AB1157 with all agents, but a mutant defective in the Lon protease was killed more quickly. It was concluded that (i) recombination and excision repair were involved in the repair of quinolone-damaged DNA and (ii) continuous induction (in response to exposure to quinolones) of the SOS response, and hence induction of the cell division inhibitor SfiA, causes cell filamentation and thereby contributes to the bactericidal activity of quinolones.