INTERACTION OF GROUP-B STREPTOCOCCAL OPACITY VARIANTS WITH THE HOST-DEFENSE SYSTEM

Group B streptococci (GBS) demonstrate high-frequency phase variation of colony opacity. Colony opacity is a function of chain length, with opaque colonies consisting of GBS that form longer chains. Because opa que variants do not grow on standard streptococcal media, the role of opacity variation in GBS infection has not been studied. We have isola ted stable variants from type III GBS that are either transparent (var iants 1.2 and 1.3) or opaque (variants 1.1 and 1.5). In this study, we evaluated the interactions of these variants with different component s of the host immune system both in vitro and in vivo. Opaque GBS were less immunogenic than transparent GBS. Opaque GBS were more susceptib le to killing by polymorphonuclear neutrophils (PMNs) and could induce a chemiluminescent response of PMNs in the absence of antibody (Ab) o r complement. Transparent GBS did not induce neutrophil chemiluminesce nce in the absence of Ab and complement. However, in the presence of A b and complement, transparent GBS induced a stronger chemiluminescent response than did opaque GBS. Scanning electron micrographs of PMNs an d GBS demonstrated differences in the attachment and engulfment of the different variants by the PMNs as well as different effects of the GB S on the PMNs themselves. Interactions with complement were affected b y GBS opacity as well, with opaque variant 1.1 initiating complement a ctivation in the absence of any Ab. The virulence of the GBS opacity v ariants was studied in vivo by inoculation of graded numbers of GBS in to newborn mice. Transparent variants 1.2 and 1.3 were most virulent, with variant 1.1 intermediate and variant 1.5 minimally virulent. Howe ver, in mixed infections, variant 1.5 greatly enhanced the virulence o f small numbers of transparent GBS. These results indicate that the op acity status of GBS can influence the interaction between the GBS and the host immune system.