Recognition of group B streptococci in dip-slide cultures of urine.

One hundred strains of group B streptococci isolated from human infections were tested for growth on dip-slides available for the culture of urine. All grew on CLED agar, and none grew on MacConkey agar. The colonies were barely or not at all visible to the naked eye after overnight incubation (diameter, around 0.1 mm). The colony size increased eith prolonged incubation, but not if the inoculum density exceeded 10(6)/ml. Differences were found between lots of dip-slides. Poor growth on dip-slides may explain why group B streptococci have received little attention as pathogens of the urinary tract. The dip-slide screening personnel of one laboratory were informed of the experimental findings, and they started the practice of frequent subculture and prolonged incubation. The proportion of group B streptococci in significant bacteriuria increased from 0 to about 2% of positive cultures, whereas there was no conmitant increase of group B streptococci in dip-slides screened in several other laboratories serving as controls.