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V Blanc

Publications and source records attributed to V Blanc.

25 records · Page 2Linked to original sources
PubMed1995

Stress-activated expression of a Streptomyces pristinaespiralis multidrug resistance gene (ptr) in various Streptomyces spp. and Escherichia coli.

A promoter which controls expression of the pristinamycin multidrug resistance gene (ptr) in Streptomyces pristinaspiralis could be induced by physiological stresses in both Streptomyces spp. and Escherichia coli. In S. pristinaspiralis, the ptr promoter (Pptr) was induced by pristinamycin I (PI) or pristinamycin II (PII). Streptomyces lividans was adopted as a convenient heterologous host for studies of Pptr regulation since it has no known pristinamycin biosynthetic genes. Two key regulatory features were documented in these studies: many (19 of 70) antibiotics and chemicals with no common targets or structural features induced the Pptr; induction with PI was most efficient during a transition phase when antibiotic biosynthetic genes are switched on. In Streptomyces coelicolor, Pptr activity was similarly inducible by PI and not dependent on sigma factors HrdA, HrdC, or HrdD. In E. coli, Pptr cloned in the bifunctional promoter probe vector pIJ2839 was functional and activated upon entry into stationary phase in the absence of exogenous inducer. Finally, gel-retardation studies demonstrated a Pptr-binding protein in S. lividans (where its activity was PI-inducible), S. coelicolor and S. pristinaespiralis. The fact that this activity was not detected in E. coli suggested the existence of another regulatory system perhaps also present in Streptomyces.

Anti-Bacterial Agents↗
PubMed1995

Cloning and analysis of structural genes from Streptomyces pristinaespiralis encoding enzymes involved in the conversion of pristinamycin IIB to pristinamycin IIA (PIIA): PIIA synthase and NADH:riboflavin 5'-phosphate oxidoreductase.

In Streptomyces pristinaespiralis, two enzymes are necessary for conversion of pristinamycin IIB (PIIB) to pristinamycin IIA (PIIA), the major component of pristinamycin (D. Thibaut, N. Ratet, D. Bisch, D. Faucher, L. Debussche, and F. Blanche, J. Bacteriol. 177:5199-5205, 1995); these enzymes are PIIA synthase, a heterodimer composed of the SnaA and SnaB proteins, which catalyzes the oxidation of PIIB to PIIA, and the NADH:riboflavin 5'-phosphate oxidoreductase (hereafter called FMN reductase), the SnaC protein, which provides the reduced form of flavin mononucleotide for the reaction. By using oligonucleotide probes designed from limited peptide sequence information of the purified proteins, the corresponding genes were cloned from a genomic library of S. pristinaespiralis. SnaA and SnaB showed no significant similarity with proteins from databases, but SnaA and SnaB had similar protein domains. Disruption of the snaA gene in S. pristinaespiralis led to accumulation of PIIB. Complementation of a S. pristinaespiralis PIIA-PIIB+ mutant with the snaA and snaB genes, cloned in a low-copy-number plasmid, partially restored production of PIIA. The deduced amino acid sequence of the snaC gene showed no similarity to the sequences of other FMN reductases but was 39% identical with the product of the actVB gene of the actinorhodin cluster of Streptomyces coelicolor A(3)2, likely to be involved in the dimerization step of actinorhodin biosynthesis. Furthermore, an S. coelicolor A(3)2 mutant blocked in this step was successfully complemented by the snaC gene, restoring the production of actinorhodin.

Amino Acid Sequence↗
PubMed1994

Restricted association between biotypes and serotypes within group A streptococci.

Investigating individual variations between different isolates of group A streptococci, we observed a close correlation between biotypes and serotypes in 46 strains from pharyngitis patients. Biotyping, carried out with a commercially available rapid identification gallery, delineated 10 different associations of characteristics, designated biotypes 1 to 10, observed both in the manufacturer's (127 strains) and our personal (98 strains) collections of group A strains. Only the most frequent biotypes (biotypes 1 to 6) were observed in the pharyngitis cohort, but the overall frequencies of the biotypes did not display striking differences compared with the control collections. Serotyping of the pharyngitis strains showed that each M type was restricted to a sole biotype. For example, M types 1, 4, and 28 were found only in biotype 1 and M type 6 was found only in biotype 6 strains. This association was not due to an epidemiologic bias, since it was also observed in a control series consisting of reference strains and isolates from distant countries (the United States and Czech Republic versus France). An exception was for M type 78, which exhibited biotype 3 or biotype 4. Investigation of the heterogeneity of the strains at the DNA level showed no significant variations of the ribotype patterns between strains of different biotypes, confirming that group A streptococci belong to a unique and homogeneous species. This previously undescribed association between serotypes and biotypes is of interest for a rapid and preliminary characterization of strains isolated in individual patients or during an outbreak. A possible pathogenic association of some biotypic characteristics with specific M proteins is envisaged.

Adolescent↗
PubMed1994

[Severe keratomycosis. Diagnosis and treatment].

We reported three consecutive cases of severe fungal keratitis initially undiagnosed by corneal scrapping. Corneal biopsy showed fungal elements of Paecilomyces lilacinus, Fusarium solani, Scedosporium apiospermum. Most cases of fungal keratitis could be treated successfully if adequate antifungal therapy were started early. Early and accurate diagnosis is of major importance. The results of our cases confirm the superiority of corneal biopsy over corneal scrapping. Corneal biopsy is a procedure of choice in suspected cases of keratomycosis in which corneal scrapings fail.

Abscess↗
PubMed1993

[Detection of the phenotypes of resistance of enterobacteriaceae to aminoglycosides with ATB Plus Expert System].

ATB Plus Expert (Biomérieux SA) is an expert system which has been developed to perform an interpretative reading of ATB susceptibility tests. The system was tested on the results obtained for 217 strains of enterobacteriaceae. These strains were selected in order to cover a maximum of bacterial species and resistance mechanisms. The isolates were tested on rapid ATB E, rapid ATB G-, rapid ATB Ur, ATB G- and ATB Ur strips. In parallel, a disc diffusion susceptibility test was performed with 5 discs of aminoglycosides (kanamycin, gentamicin, tobramycin, netilmicin, amikacin) and the interpretation was carried out according to the criteria usually followed. Of the 217 strains tested, 122 showed a resistance phenotype. Only the rapid ATB E strips included kanamycin and allowed the detection of APH(3') phenotypes. Amikacin was not included in the ATB Ur strip, consequently it was impossible to discriminate AAC(3)-II and AAC(6') + AAC(3)-I phenotypes. 12 strains did not grow within 5 hours using the rapid ATB methodology. Not taking into account the problems previously encountered, different phenotypes between the 6 susceptibility tests were found for 16 strains. In 5 cases the expert system detected an anomaly instead of the correct phenotype, and in 3 cases of unknown phenotypes, the answers were variable. In the other cases, the main difficulty was the detection of the isolated resistance to gentamicin (AAC(3)-I phenotype). The expert system automatically corrects the susceptibility test result according to the phenotype observed.

Amikacin↗
PubMedDate not supplied

The preclinical assessment of the risk for QT interval prolongation.

Some drugs have been reported to induce severe ventricular arrhythmias, including torsades de pointes, and have been responsible in some cases for sudden death of patients. Although the mechanisms of these arrhythmias are not well understood, they are often, but not always, associated with QT interval prolongation. Regulatory authorities (CPMP in Europe) have recently pointed out the necessity to assess most carefully the potential, especially of non-cardiovascular drugs, for QT interval prolongation. Different methodological approaches are presented in this paper and experimental protocols are suggested; limitations and advantages of the presently available in vitro and in vivo models are discussed. It appears that both in vitro and in vivo approaches are complementary. In particular it is pointed out that only the in vitro models using isolated cardiac tissues (Purkinje fibres or papillary muscles) enable assessment of the drug properties under low cardiac rhythm conditions. This model allows us to mimic pathological situations of long QT interval (such as acquired or congenital long QT syndrome) in which most of the major clinical problems are encountered. Finally, a strategy for the preclinical assessment of the potential of a molecule for QT interval prolongation is presented.

Animals↗