Identification of a high-virulence clone of serotype III Streptococcus agalactiae by growth characteristics at 40 degrees C.

A high-virulence clone of serotype III Streptococcus agalactiae causing invasive neonatal disease was previously identified by multilocus enzyme electrophoresis. A simple procedure involving growth at 40 degrees C distinguished all isolates classified in this high-virulence clone from other serotype III isolates, which are more frequently associated with asymptomatically colonized infants, as well as the other serotypes of group B streptococci. The high-virulence clone failed to grow at 40 degrees C in FMC, a chemically defined medium, in contrast to the other organisms, which grew readily.