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Biomedical subjects

P Vannuffel

Publications and source records attributed to P Vannuffel.

11 recordsLinked to original sources
PubMed1997

Inhibition of protein synthesis by streptogramins and related antibiotics.

The streptogramins and related antibiotics (the lincosamides and macrolides) (MLS) are important inhibitors of bacterial protein synthesis. The key reaction in this process is the formation of a peptide bond between the growing peptide chain (peptidyl-tRNA) linked to the P-site of the 50S ribosome and aminoacyl-tRNA linked to the A site. This reaction is catalysed by the peptidyl transferase catalytic centre of the 50S ribosome. Type A and B streptogramins in particular have been shown to block this reaction through the inhibition of substrate attachment to the A and P sites and inhibition of peptide chain elongation. Synergy between type A and B components results from conformational changes imposed upon the peptidyl transferase centre by type A compounds and by inhibition of both early and late stages of protein synthesis. The conformational change increases ribosomal affinity for type B streptogramins. Microbial resistance to the MLSB antibiotics is largely attributable to mutations of rRNA bases, producing conformational changes in the peptidyl transferase centre. This can result in resistance to a single inhibitor or to a group of antibiotics (MLSB). The activity of type A streptogramin is retained thus explaining the improved inhibitory action of the combined streptogramins against macrolide and lincosamide-resistant strains. However, the development of resistance to the streptogramins may be less of a problem because of the synergic effect of type A and B compounds which has also been demonstrated in strains resistant to MLSB i.e., high level resistance to the combined streptogramins is only likely when type A streptogramin resistance determinants are present along with type B streptogramin resistance determinants.

Anti-Bacterial Agents↗
PubMed1996

Mechanism of action of streptogramins and macrolides.

Protein synthesis is catalysed by ribosomes and cytoplasmic factors. Bacterial ribosomes (70S) are made up of 2 subunits (50S and 30S) containing ribosomal RNA (rRNA) and ribosomal proteins: the 30S binds messenger RNA and begins the ribosomal cycle (initiation), whereas 50S binds transfer RNA (tRNA) derivatives and controls elongation. The key reaction, peptide bond formation, is promoted by the catalytic centre of 50S (the peptidyl transferase centre), and the growing peptide chain (peptidyl-tRNA) attached at the donor P site undergoes peptide linkage with an aminoacyl-tRNA at the acceptor A site. This reaction is inhibited by several antibiotics, the best known being chloramphenicol, and the macrolide-lincosamide-streptogramin (MLS) group. These inhibitors have a reversible action, except for streptogramins that are composed of A and B components, which are bacteriostatic alone, but bactericidal when combined. The peptidyl transferase centre has been identified at the 50S surface, and the binding sites of inhibitors have been mapped within this domain: some of these sites overlap (e.g. those of macrolides, and type B streptogramins, which compete for binding to ribosomes). Chloramphenicol blocks the catalytic portion, and A streptogramins the substrate sites of the peptidyl transferase centre. Macrolides and type B streptogramins interfere with the formation of long polypeptides and cause a premature detachment of incomplete peptide chains. The synergism between types A and B streptogramins is due to induction by type A streptogramins of an increased ribosome affinity for type B streptogramins. Microbial resistance to antibiotics mainly involves inactivation of inhibitors and modification of targets (mutations of ribosomal proteins or rRNA genes). Alterations of rRNA bases can induce resistance to a single inhibitor or to a group of antibiotics (e.g. MLSB). The impact of resistance in chemotherapy is less important for streptogramins than for other inhibitors, because the synergistic effect of A and B streptogramins also applies to strains resistant to the MLSB group. It is proposed that mutations and modifications of rRNA bases induce conformational ribosomal changes that prevent antibiotics binding to the target. Conformational changes are also triggered by type A streptogramins: they are responsible for their synergism with type B streptogramins.

Anti-Bacterial Agents↗
PubMed1995

Specific detection of methicillin-resistant Staphylococcus species by multiplex PCR.

In Staphylococcus aureus, mecA and femA are the genetic determinants of methicillin resistance. By using a multiplex PCR strategy, 310- and 686-bp regions of the mecA and femA genes, respectively, were coamplified to identify susceptible (lacking mecA) and resistant (mecA+) staphylococci and to differentiate S. aureus (femA+) from coagulase-negative staphylococci (lacking femA). A third staphylococcal genomic sequence, corresponding to IS431 and spanning 444 bp, was used as a PCR control. One hundred sixty-five staphylococcal strains were tested. All 72 methicillin-resistant strains were found to be mecA+, and 92 of the 93 susceptible isolates lacked mecA. Only one coagulase-negative Staphylococcus isolate carrying the mecA gene was highly susceptible to oxacillin. The femA determinant was a unique feature of S. aureus; it was found in 100% of the S. aureus strains tested but was undetectable in all of the coagulase-negative staphylococci tested. The possibility of directly detecting the mecA and femA genes in blood samples was also investigated. After two amplification steps, a sensitivity of 50 microorganisms per ml of freshly collected spiked blood was achieved. In conclusion, coamplification of mecA and femA determinants proved to be very reliable both for rapid detection of methicillin resistance and differential diagnosis between S. aureus and other staphylococci. This technique, which can be successfully performed with blood samples, could be a useful tool in the diagnosis and treatment monitoring of staphylococcal infections.

Bacterial Proteins↗
PubMed1994

Chemical probing of a virginiamycin M-promoted conformational change of the peptidyl-transferase domain.

Previous findings suggest the location of the central loop of domain V of 23S rRNA within the peptidyltransferase domain of ribosomes. This enzymatic activity is inhibited by some antibiotics, including type A (virginiamycin M or VM) and type B (virginiamycin S or VS) synergimycins, antibiotics endowed with a synergistic action in vivo. In the present work, the ability of VM and VS to modify the accessibility of 23S rRNA bases within ribosomes to chemical reagents has been explored. VM afforded a protection of rRNA bases A2037, A2042, G2049 and C2050. Moreover, when ribosomes were incubated with the two virginiamycin components, the base A2062, which was protected by VS alone, became accessible to dimethyl sulphate (DMS). Modified reactivity to chemical reagents of different rRNA bases located either in the central loop of domain V or in its proximity furnishes experimental evidence for conformational ribosome alterations induced by VM binding.

Aldehydes↗
PubMed1994

Occurrence, in Crohn's disease, of antibodies directed against a species-specific recombinant polypeptide of Mycobacterium paratuberculosis.

Sera from patients with Crohn's disease and control were analyzed by an enzyme-linked immunosorbent assay based on the Mycobacterium paratuberculosis-specific recombinant polypeptide a362. Anti-a362 immunoglobulin G (IgG) (P < 0.05) and IgA (P < 0.001) titers were higher in patients with Crohn's disease than in controls. A monomodal Gaussian distribution of anti-a362 IgA levels were found for controls, and a bimodal distribution was found for patients with Crohn's disease. An M. paratuberculosis etiology is suggested for the 36% of patients with Crohn's disease who had an anti-a362 IgA level higher than that of controls.

Antibodies, Bacterial↗
PubMed1994

Paratuberculosis.

Paratuberculosis (Johne's disease) is a chronic, wasting, widespread mycobacteriosis of ruminants. It involves extensive mycobacterial shedding, which accounts for the high contagiousness, and ends with a fatal enteritis. Decreases in weight, milk production, and fertility produce severe economic loss. The DNA of the etiological agent (Mycobacterium paratuberculosis) has a base composition (66 to 67% G+C) within the range of that of mycobacteria (62 to 70% G+C), a size (4.4 x 10(6) to 4.7 x 10(6) bp) larger than that of most pathogenic mycobacteria (2.0 x 10(6) to 4.2 x 10(6) bp), and a high relatedness (> 90%) to Mycobacterium avium DNA. However, the DNAs of the two organisms can be distinguished by restriction fragment length polymorphism analysis. M. paratuberculosis genes coding for a transposase, a cell wall-associated protein (P34), and two heat shock proteins have been cloned and sequenced. Nucleic acid probes (two of which are species specific) are used, after PCR amplification, for M. paratuberculosis identification in stools and milk. As in leprosy, with disease progression, cellular immune reactions decrease and humoral immune reactions increase. Cutaneous testing with sensitins, lymphocyte proliferation assays, and cytokine tests are used to monitor cellular immune reactions in paratuberculosis, but these tests lack specificity. Complement fixation, immunodiffusion, and enzymometric tests based on antibodies to M. paratuberculosis extracts, to mycobacterial antigen complex A36, to glycolipids, and to proteins help identify affected cattle but are not species specific. The carboxyl-terminal portion of the 34-kDa cell wall-associated A36 protein (P34) carries species-specific B-cell epitopes and is the basis for an enzyme-linked immunosorbent assay. Diagnostic tests for paratuberculosis are also used in Crohn's disease, a chronic human ileitis mimicking Johne's disease, in which isolates identified as M. paratuberculosis have been found.

Amino Acid Sequence↗
PubMed1994

Development of species-specific enzyme-linked immunosorbent assay for diagnosis of Johne's disease in cattle.

The previously described (M. De Kesel, P. Gilot, M.-C. Misonne, M. Coene, and C. Cocito, J. Clin. Microbiol., 31:947-954, 1993) a362 recombinant polypeptide of Mycobacterium paratuberculosis was used as reagent for an enzyme-linked immunosorbent assay (ELISA). This ELISA, which is endowed with species specificity with respect to the other mycobacteria, was applied to the analysis of bovine paratuberculosis (Johne's disease), an endemic mycobacteriosis of cattle caused by M. paratuberculosis. The distribution of anti-a362 antibodies in the cattle population was analyzed by a computer program (mixture population model) to determine a cutoff value for the test. The prevalence of a362 seropositivity in the Belgian bovine population was estimated to be 12%. The sensitivity of the a362 assay was 70%, as determined with reference sera from the U.S. National Repository of Paratuberculosis Specimens. Some 40% of the animals in the herds with paratuberculosis analyzed were found to be positive by the a362 assay. The latter proved to be 95% specific with respect to both healthy and tuberculous cattle.

Animals↗
PubMed1992

The role of rRNA bases in the interaction of peptidyltransferase inhibitors with bacterial ribosomes.

Synergism of streptogramins A (virginiamycin M, VM) and B (virginiamycin S, VS), peptidyltransferase inhibitors, was explored in EM4/pLC7-21 (wild type) and EM4/pERY (VS-resistant). These bacterial strains contained multicopy plasmids carrying an rrnH operon with wild type (pLC7-21) or mutated (A2058----U transversion) 23 S rRNA gene. Ribosomes with wild type and mutated rRNA were both present in EM4/pERY. The latter particles did not bind VS; in the presence of VM, however, high affinity VS binding occurred. As shown previously, VS protected against chemical reagents certain bases in domain V rRNA and VM in the stems flanking this loop. Differences between wild type and mutant ribosomes were observed: A2058, A2059, A2062, and G2505, protected by VS and ERY in EM4/pLC7-21, were unshielded in EM4/pERY. A2062 was shielded by VM in EM4/pERY, not in EM4/pLC7-21, and G2505 of mutant ribosomes became protected by VS when VM was simultaneously present. Induction by VM of a high affinity VS binding site in VS-sensitive and -resistant ribosomes indicates A2058 mutation to entail a conformational change of this site, which is counteracted by VM fixation. Accessibility of A2062 to chemical reagents (unlike behavior of EM4/pERY and EM4/pLC7-21 in the presence of VM) implies different conformations for wild type and mutant ribosomes.

Base Sequence↗
PubMed1992

Identification of a single base change in ribosomal RNA leading to erythromycin resistance.

The molecular basis of a mutation conferring an erythromycin-resistance phenotype was explored, as an approach to the role of 23 S rRNA in the peptidyl-transferase activity of 50 S ribosomal subunits. Mutagenization of an Escherichia coli strain, which carried the multicopy plasmid pLC7-21 containing the rrnH operon, led to the production of an erythromycin-resistant strain. Plasmid pBFL1 isolated from this mutant was able to transform the sensitive RecA- strain EM4 and to induce a "dissociated" type of antibiotic resistance. Two ribosome populations occurred in EM4/pBFL1: normal particles coded for by the seven rrn chromosomal genes and mutated particles containing rRNA of plasmid origin. The latter particles displayed in vitro lower affinity and susceptibility to erythromycin than wild type particles. The mutation within plasmid pBFL1 was mapped by a multiple primer extension technique. Three synthetic primers were used to sequence the central loop in domain V of 23 S rRNA, leading to identification of a C to U transition at position 2611. This base change was proved to be responsible for the erythromycin-resistance phenotype by the plasmid-plasmid marker rescue technique. A molecular explanation for the rrn mutations leading, respectively, to undissociated and to dissociated types of resistance to the MLSb (macrolide-lincosamide-synergimycin B) group of antibiotics is proposed. These results and some literature data support the notion that rRNA bases involved in antibiotic resistance play a conformational role in the ribosomal binding sites for the MLSb antibiotics.

Base Sequence↗
PubMed1986

Antagonistic interactions of macrolides and synergimycins on bacterial ribosomes.

The affinity of ribosomes for VS (virginiamycin S, a type B synergimycin) is known to be increased by VM (virginiamycin M, a type A synergimycin). Erythromycin, a macrolide, displaces ribosome-bound VS in the absence of VM, but is ineffective in its presence. In the present work, the ability of spiramycin and tylosin (macrolide subgroups) derivatives to displace ribosome-bound VS, in the presence and in the absence of VM, has been explored. All macrolides with in-vitro activity displaced ribosome-bound VS: the displacement curves produced by tylosin and spiramycin derivatives virtually overlapped. When VM was added to these systems, displaced VS became readily attached to ribosomes in the case of erythromycin, did not bind appreciably within 20 min incubation in the presence of tylosin, and underwent a slow binding in the case of an N-substituted tylosin. The 16-membered macrolides (leucomycin, spiramycin and tylosin subgroups) can therefore be distinguished from the 14-membered macrolides (erythromycin subgroup) by the antagonistic effect displayed toward VM.

Bacteria↗