MOLECULAR-BASES OF 3 CHARACTERISTIC PHENOTYPES OF PNEUMOCOCCUS - OPTOCHIN-SENSITIVITY, COUMARIN-SENSITIVITY, AND QUINOLONE-RESISTANCE

Streptococcus pneumoniae is uniquely sensitive to amino alcohol antima larials in the erythro configuration, such as optochin, quinine, and q uinidine. The protein responsible for the optochin (quinine)-sensitive (Opt(s), Qin(s)) phenotype of pneumococcus is the proteolipid c subun it of the F0F1 H+-ATPase. OptR/QinR isolates arose by point mutations in the atpC gene and produce different amino acid changes in one of th e two transmembrane alpha-helices of the c subunit. In addition, compa rison of the sequence of the atpCAB genes of S. pneumoniae R6 (Opt(s)) and M222 (an Opt(R) strain produced by interspecies recombination bet ween pneumococcus and S. oralis), and S. oralis (Opt(R)) revealed that , in M222, an interchange of atpC and atpA had ocurred. We also demons trate that optochin, quinine, and related compounds specifically inhib ited the membrane-bound ATPase activity. Equivalent differences betwee n Opt(s)/Qin(s) and OptR/QinR strains, both in growth inhibition and i n membrane ATPase resistance, were found. Pneumococci also show a char acteristic sensitivity to coumarin drugs, and a relatively high level of resistance to most quinolones. We have cloned and sequenced the gyr B gene, and characterized novobiocin resistant mutants. The same amino acid substitution (Ser-127 to Leu) confers novobiocin resistance on f our isolates. This residue position is equivalent to Val-120 of Escher ichia coli ryGB, a residue that lies inside the ATE-binding domain but is not involved in novobiocin binding in E. coli, as revealed by crys tallographic data. In addition, the genes encoding the ParC and ParE s ubunits of topoisomerase IV, together with the region encoding amino a cids 46 to 172 (residue numbers as in E. coli) of the pneumococcal ryG A subunit, were characterized in respect to fluoroquinolone resistance . The gyrA gene maps to a physical location distant from the gyrB and parEC loci on the chromosome. Ciprofloxacin-resistant (Cp-R) clinical isolates had mutations affecting amino acid residues of the quinolone resistance-determining region of ParC (low-level Cp-R), or in both res istance-determining regions of ParC and GyrA (high-level Cp-R). Mutati ons were found in residue positions equivalent to Ser-83 and Asp-87 of the E. coli GyrA subunit. Transformation experiments demonstrated tha t topoisomerase IV is the primary target of ciprofloxacin, DNA gyrase being a secondary one.