Abstract
Optochin susceptibility testing is a major assay used for presumptive identification of Streptococcus pneumoniae. Still, atypical optochin-resistant (Optr) pneumococci have been reported and this phenotype has been attributed to nucleotide substitutions in the genes coding for the F0F1ATPase. While substitutions in the atpC gene (c-subunit of ATPase) are more common and better characterized, data on mutations in the atpA (a-subunit) are still limited. We have characterized five Optr isolates presenting alterations in the atpA (Trp206Cys in four isolates and Trp206Ser in one isolate), constituting the first report of such mutations in Brazil. Most of the Optr isolates consisted of heterogeneous populations. Except for Opt MICs and the nucleotide changes in the atpA gene, Optr and Opts subpopulations originating from the same culture had identical characteristics. In addition, we compared phenotypic and genetic characteristics of these atpA mutants with those of atpC mutants previously identified in Brazil. No structural alterations were detected among predicted proteins, regardless of mutations in the coding gene, suggesting that, despite the occurrence of mutations, protein structures tend to be highly conserved, ensuring their functionalities. Phylogenetic analysis revealed that atypical Optr strains are true pneumococci and Opt resistance does not represent any apparent selective advantage for clinical isolates.
Highlights
Streptococcus pneumoniae is a leading cause of invasive diseases among children and the elderly associated with considerable mortality and economic b urden[1]
We extended the spectrum of methodologies used and compared phenotypic and genetic characteristics of all O ptr pneumococcal strains described in Brazil up to now, including both atpC and atpA mutants
Opt minimal inhibitory concentrations (MICs) of O pts subpopulations were identical to those detected among optochin-susceptible reference strains of S. pneumoniae ATCC BAA-255 and ATCC 49619 (1 μg/ml)
Summary
Streptococcus pneumoniae is a leading cause of invasive diseases among children and the elderly associated with considerable mortality and economic b urden[1]. Conventional laboratory identification of S. pneumoniae usually relies on one major characteristic of this species: the susceptibility to optochin (Opt). Alterations in other subunits of this molecule are rare, and only two reports on Optr clinical strains of S. pneumoniae presenting mutations in the atpA gene (coding for the a-subunit of the bacterial F0F1ATPase) are available to date[5,13]. We describe five additional Optr isolates presenting alterations in the atpA gene, constituting the first report of such unusual mutations in pneumococcal isolates from our country. We extended the spectrum of methodologies used and compared phenotypic and genetic characteristics of all O ptr pneumococcal strains described in Brazil up to now, including both atpC and atpA mutants
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