Search

Objectives We studied the development and fitness cost of 2-deoxystreptamine aminoglycoside resistance of Mycobacterium abscessus. Methods Spontaneous 2-deoxystreptamine aminoglycoside-resistant mutants were selected and the frequency of their appearance was determined. The 3′ part of the rrs gene was sequenced to characterize mutations. Additionally, we determined the MICs of aminoglycoside drugs for the different mutants obtained. The dominance/recessivity traits of the different mutations were examined and we explored the potential cost conferred by the mutations selected in vitro on the fitness of these isolates compared with the wild-type strain. Results The in vitro mutation rate for 2-deoxystreptamine aminoglycoside resistance was ∼10−7 mutations/cell division. In addition to the known rrs A→G substitution at position 1408 (Escherichia coli numbering), which confers kanamycin resistance (KanR), three new substitutions in rrs were identified in M. abscessus KanR mutants, i.e. T→A at 1406, C→T at 1409 and G→T at 1491. Heterodiploids carrying genomic mutations T→A at 1406 and A→G at 1408 with the wild-type rrs gene carried by the pNBV1 vector showed a resistant phenotype. In contrast, heterodiploids carrying genomic mutations C→T at 1409 and G→T at 1491 with the wild-type rrs gene carried by the pNBV1 vector had a susceptible phenotype. No burden on fitness was observed for the different mutations. Conclusion Mutations in the rrs gene that confer high-level 2-deoxystreptamine aminoglycoside resistance on M. abscessus differ in their dominance/recessivity traits and have no biological cost under our experimental conditions. [ABSTRACT FROM PUBLISHER]

The intrinsic and acquired resistance of Mycobacterium abscessus to commonly used antibiotics limits the chemotherapeutic options for infections caused by these mycobacteria. Intrinsic resistance is attributed to a combination of the permeability barrier of the complex multilayer cell envelope, drug export systems, antibiotic targets with low affinity and enzymes that neutralize antibiotics in the cytoplasm. To date, acquired resistance has only been observed for aminoglycosides and macrolides, which is conferred by mutations affecting the genes encoding the antibiotic targets (rrs and rrl, respectively). Here we summarize previous and recent findings on the resistance of M. abscessus to antibiotics in light of what has been discovered for other mycobacteria. Since we can now distinguish three groups of strains belonging to M. abscessus (M. abscessus sensu stricto, Mycobacterium massiliense and Mycobacterium bolletii), studies on antibiotic susceptibility and resistance should be considered according to this new classification. This review raises the profile of this important pathogen and highlights the work needed to decipher the molecular events responsible for its extensive chemotherapeutic resistance. [ABSTRACT FROM PUBLISHER]

Objectives: We studied the development and fitness cost of 2-deoxystreptamine aminoglycoside resistance of Mycobacterium abscessus.Methods: Spontaneous 2-deoxystreptamine aminoglycoside-resistant mutants were selected and the frequency of their appearance was determined. The 3' part of the rrs gene was sequenced to characterize mutations. Additionally, we determined the MICs of aminoglycoside drugs for the different mutants obtained. The dominance/recessivity traits of the different mutations were examined and we explored the potential cost conferred by the mutations selected in vitro on the fitness of these isolates compared with the wild-type strain.Results: The in vitro mutation rate for 2-deoxystreptamine aminoglycoside resistance was ∼10(-7) mutations/cell division. In addition to the known rrs A→G substitution at position 1408 (Escherichia coli numbering), which confers kanamycin resistance (Kan(R)), three new substitutions in rrs were identified in M. abscessus Kan(R) mutants, i.e. T→A at 1406, C→T at 1409 and G→T at 1491. Heterodiploids carrying genomic mutations T→A at 1406 and A→G at 1408 with the wild-type rrs gene carried by the pNBV1 vector showed a resistant phenotype. In contrast, heterodiploids carrying genomic mutations C→T at 1409 and G→T at 1491 with the wild-type rrs gene carried by the pNBV1 vector had a susceptible phenotype. No burden on fitness was observed for the different mutations.Conclusion: Mutations in the rrs gene that confer high-level 2-deoxystreptamine aminoglycoside resistance on M. abscessus differ in their dominance/recessivity traits and have no biological cost under our experimental conditions. [ABSTRACT FROM AUTHOR]

The cell surface of mycobacteria is quite rich in lipids. Glycopeptidolipids, surface-exposed lipids that typify some mycobacterial species, have been associated with a phenotypic switch between rough and smooth colony morphotypes. This conversion in Mycobacterium smegmatis is correlated with the absence/presence of glycopeptidolipids on the cell surface and is due to insertion sequence mobility. Here, we show that the occurrence of a high amount of glycopeptidolipids in the smooth variant leads to lower invasion abilities and lower internalization by macrophages. We further show that the high production of glycopeptidolipids on the cell surface can confer a selective advantage to the smooth variant when grown in vitro. This higher fitness under the laboratory condition might explain the selection of smooth variants in several independent laboratories. The implications of these findings are discussed. [ABSTRACT FROM AUTHOR]

Erp (exported repetitive protein), also known as P36, Pirg and Rv3810, is a member of a mycobacteria-specific family of extracellular proteins. In pathogenic species, the erp gene has been described as a virulence factor. The Erp proteins comprise three domains. The N- and C-terminal domains are similar in all mycobacterial species, while the central domain consists of a repeated module that differs considerably between species. Here we show that the Erp protein is loosely attached to the surface and that the carboxy-terminal domain, which displays hydrophobic features, anchors Erp at the surface of the bacillus. The hydrophobic region is not necessary for the complementation of the altered colony morphology of a Mycobacterium smegmatis erp− mutant but proved to be necessary to achieve resistance to detergent at wild-type levels. [Copyright &y& Elsevier]

There are two functionally different alleles of the Helicobacter pylori vacA gene, which code for proteins with different in target cell specificity. The alleles (m1 and m2) differ by approximately 50% in amino acid sequence in a 300 amino acid region, the m-region, which determines specificity. An analysis of partial likelihood anomalies in a set of eight Chinese and six Western vacA genes revealed highly significant phylogenetic deviation of a region of the gene including the m-region. Phylogenetic analysis of the conserved regions of these genes failed to reveal any distinction between m1 alleles and m2 alleles, however clear cut geographic variation was observed. In the m-region, the m1 alleles also show separate clustering of Chinese and Western isolates, however the m-region of the m2 alleles has a phylogenetic structure markedly different from the rest of the gene. The data indicate that the m2 m-region was acquired and spread through the population by horizontal transfer of DNA. [Copyright &y& Elsevier]