[Studies on clinical significance of "Streptococcus milleri group" in respiratory infections]

"Streptococcus milleri group" are the part of the indigenous oral flora, and they are proposed to contain three distinct species: Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius. Though not included in the approved lists of bacterial names, "S. milleri group" are regarded as the causative organisms of suppurative infections, such as oral abscess, brain abscess, lung abscess and empyema. I have studied the clinical significance of the "S. milleri group" in respiratory infections. An investigation was performed to confirm the incidence of "S. milleri group" colonization in healthy 120 volunteers' (20 y/o-80 y/o) throats, and it was found that 11.7% (14/120) were positive. On the other hand, attention should be paid to the fact that the "S. milleri group" was highly isolated, 24 (24.7%) in 97 purulent respiratory specimens (94 sputa and 3 throat swabs) from which no other significant microorganism was recovered. I have measured the serum antibody titers of the "S. milleri group", employing the IFA technique, in 10 patients from whose specimens "S. milleri group" was predominantly isolated, and compared with those of 18 healthy volunteers. Whereas all of the titers of healthy volunteers reveal less than 1:256, those of the patients reveal more than 1:512. And antibody titers to "S. milleri group" showed the highest in two weeks after "S. milleri group" isolation, and came down to healthy adult levels in six weeks or more. Thus far, about half of the causative organisms of acute pneumonia have been reported unknown. In this study I have suggested that the "S. milleri group" plays an important role as the causative organism in respiratory infections including pneumonia.