Characterization of Recombinant Fluoroquinolone-Resistant Pneumococcus-Like Isolates

ABSTRACTFourteen fluoroquinolone-resistant streptococcal isolates with recombinant DNA topoisomerase genes, preliminarily identified as pneumococci, were further characterized using phenotypic and genotypic approaches. Phenotypic tests classified them as atypical pneumococci. Phylogenetic relationships were analyzed by using the sequences of seven housekeeping alleles from these isolates and from isolates ofStreptococcus pneumoniae,Streptococcus mitis,Streptococcus oralis, andStreptococcus pseudopneumoniae. Four isolates grouped withS. pneumoniae, seven grouped withS. pseudopneumoniae, and three grouped withS. mitis. These results generally agreed with those obtained with an optochin susceptibility test and with the organization of theatpoperon chromosomal region, encoding the FoF1H+-ATPase (the target of optochin). All seven isolates grouping withS. pseudopneumoniaeshare the samespr1368-atpC-atpAgene order; all four grouping withS. pneumoniaeshare thespr1368-IS1239-atpC-atpAorder, and two out of the three grouping withS. mitisshare thespr1284-atpC-atpAorder. In addition, evidence for recombination within the seven housekeeping alleles of theS. pseudopneumoniaepopulation was provided by several methods: the index of association (0.4598,P< 0.001), the pairwise homoplasy index, and the split-decomposition method. This study confirms the existence of pneumococci among the alpha-hemolytic streptococci with DNA topoisomerase genes showing a mosaic structure and reveals a close relationship between atypical pneumococci andS. pseudopneumoniae.