Association of elevated levels of extracellular neuraminidase with clinical isolates of type III group B streptococci

Abstract

The level of total extracellular neuraminidase produced by 74 clinical isolates of group B streptococci isolated from diseased or asymptomatically colonized infants was assayed. Extracellular neuraminidase was obtained from concentrated filtrates of exponentially growing cultures of group B streptococci grown in a chemically defined medium (FMC) containing supplemental protein. The total activity of extracellular enzyme produced by these clinical isolates ranged from less than 10 to 360 nmol of sialic acid released per min per mg of cell dry weight. Strains were arbitrarily classified as either nonproducers (less than 10 nmol/min per mg of cell dry weight), low producers (greater than 10 to less than or equal 140 nmol/min per mg of cell dry weight), or high producers (greater than 140 to 360 nmol/min per mg of cell dry weight). Type III isolates from diseased infants were significantly more often classified as high producers than strains of group B streptococci of other serotypes from diseased infants (P less than 0.001). Furthermore, the serotype III strains isolated from neonatal infections were more often high producers than those of the same serotype from asymptomatically colonized infants (P less than 0.025). These results suggest that the ability to produce elevated levels of neuraminidase may be related to the frequent association of type III strains with disease among neonates.