RESUMO
We have studied the molecular structure of the gene for the penicillin binding protein (PBP 3) of the Streptococcus pneumoniae wild-type strain and a laboratory mutant strain that exhibits a reduced amount of this protein on PBP gels. This mutation affects cefotaxime resistance when transferred into resistant strains. We have sequenced the PBP3 gene, dacA, and upstream regions from the wild-type isogenic strain and the laboratory mutant. We show that a deletion of one base-pair in the upstream sequence of this gene account for the phenotype by decreasing the amount of PBP3.
Assuntos
Proteínas de Bactérias , Proteínas de Transporte , Hexosiltransferases/genética , Complexos Multienzimáticos/genética , Muramilpentapeptídeo Carboxipeptidase , Mutação , Peptidil Transferases/genética , Streptococcus pneumoniae/genética , Sequência de Bases , DNA Bacteriano , Genes Bacterianos , Dados de Sequência Molecular , Conformação de Ácido Nucleico , Resistência às Penicilinas/genética , Proteínas de Ligação às Penicilinas , Streptococcus pneumoniae/enzimologiaAssuntos
Proteínas de Bactérias , Cefotaxima/farmacologia , Resistência às Cefalosporinas/genética , Cefalosporinas/farmacologia , Muramilpentapeptídeo Carboxipeptidase , Streptococcus pneumoniae/efeitos dos fármacos , Streptococcus pneumoniae/genética , Proteínas de Transporte/genética , Genes Bacterianos , Hexosiltransferases/genética , Humanos , Complexos Multienzimáticos/genética , Mutação , Resistência às Penicilinas/genética , Proteínas de Ligação às Penicilinas , Peptidil Transferases/genética , Sorotipagem , Transdução de Sinais , Streptococcus pneumoniae/classificaçãoRESUMO
A laboratory pneumococcal strain resistant to cefotaxime was studied by DNA-induced transformation in order to characterize its genetic structure. At least three independent genes were required to confer the highest level of resistance to this beta-lactam antibiotic. The accumulation of mutations in these three genes accounted for three levels of resistance. Mutation of the gene encoding penicillin-binding protein 2x was very likely responsible for the first step of resistance, which was a prerequisite for sequential increase in resistance. Additionally, strains highly resistant to cefotaxime were defective for natural transformation. Revertants of these strains were frequently observed. Such strains had recovered full transformability, suggesting a correlation between the inability to be transformed and a high level of resistance to cefotaxime. The possibility of electrotransforming these highly resistant strains suggests that natural transformation is probably blocked at the DNA-uptake level.
Assuntos
Cefotaxima/farmacologia , Resistência Microbiana a Medicamentos/genética , Genes Bacterianos/genética , Streptococcus pneumoniae/genética , Eletroforese em Gel de Poliacrilamida , Técnicas In Vitro , Streptococcus pneumoniae/efeitos dos fármacos , Transformação BacterianaRESUMO
A pneumococcal strain, with a reduced amount of penicillin-binding protein 3 (PBP 3), permitted an analysis of the role of this protein in cefotaxime resistance. We observed that reduced amounts of PBP 3 sensitize the bacteria to high temperature, to excess glycine and to some D-amino acids. These phenotypes suggest that the amount of PBP 3 may influence the membrane properties of the bacteria. The strain with reduced PBP 3 was transformed to cefotaxime resistance. We show that the PBP 3 mutation, in certain genetic backgrounds, decreases the level of resistance to cefotaxime by a factor of 2. Models are presented to explain this result.
