The Streptococcus milleri Population of a Cystic Fibrosis Clinic Reveals Patient Specificity and Intraspecies Diversity

The genetic relatedness of Streptococcus milleri group isolates from the airways of cystic fibrosis patients was determined by using pulsed-field gel electrophoresis. This study reveals no evidence for patient-to-patient transmission in our patient population; however, within individual patients, complex inter- and intraspecies diversity and dynamics can be observed. In addition to their role in purulent infections (3, 7, 11), members of the Streptococcus milleri group (SMG), also known as the Streptococcus anginosus group, comprised of Streptococ-cus constellatus, Streptococcus intermedius, and Streptococcus anginosus, have emerged as clinically relevant in chronic airway infections in cystic fibrosis (CF) patients and have been impli-cated as etiologic agents of pulmonary exacerbation (6, 10, 13, 14). We have recently described the isolation of a large number of SMG strains from a cohort of CF patients by using the semiselective medium McKay agar (12). This collection of SMG respiratory isolates was not recovered by conventiona