STREPTOCOCCUS-MILLERI STRAINS DISPLAYING A GLIDING TYPE OF MOTILITY

Isolates belonging to the ''Streptococcus milleri'' species group that appear to exhibit a gliding type of motility, which is expressed as s preading growth on certain types of agar media, are described. These s trains resembled a biotype of ''S. milleri'' that is usually isolated from genitourinary sources and is notable for its ability to ferment a wide array df carbohydrates. This biotype, which is currently include d in the species Streptococcus anginosus, has been implicated in cases of neonatal infection. The ''S. milleri'' isolates which we studied l acked any observable organelles of motility and gave negative results when they were tested in conventional motility test medium stab cultur es, Colonies growing on certain agar media, however, spread over the s urfaces of plates and increased in area with increasing time of incuba tion. Chocolate agar supported maximum spreading, while this character istic was barely discernible on blood agar. Electron microscopy studie s revealed that there was more production of extracellular glycocalyx by motile strains than by a nonmotile isolate having a similar biotype . The results of an analysis of 16S rRNA gene sequences suggested that the motile strains are closely related to S. anginosus and represent a distinct rRNA population within the ''S. milleri'' species complex.