Topoisomerase I polypeptides and DNA and RNA encoding such topoisomerase I polypeptides and a procedure for producing such polypeptides by recombinant techniques is disclosed. Also disclosed are methods for utilizing such topoisomerase I for the treatment of infection, particularly bacterial infections. Antagonists against such topoisomerase I and their use as a therapeutic to treat infections, particularly bacterial infections are also disclosed. Also disclosed are diagnostic assays for detecting diseases related to the presence of topoisomerase I nucleic acid sequences and the polypeptides in a host. Also disclosed are diagnostic assays for detecting polynucleotides encoding streptococcal topoisomerase I and for detecting the polypeptide in a host.