title: Group B streptococcal opacity variants.
abstract: Colony opacity variants were detected for type III group B streptococci (GBS). Transparent colonies predominate in the parent GBS, with occasional colonies having opaque portions. Two stable opaque variants (1.1 and 1.5) were compared with three transparent clones (1.2, 1.3, and 1.4). All grew well on blood agar and on GC medium, but variant 1.1 failed to grow on Todd-Hewitt medium. Scanning and transmission electron microscopy demonstrated that colony opacity correlated with bacterial aggregation status, with opaque variants forming longer and more organized chains. Opaque-transparent switches were observed in both directions for most variants, with transparent to opaque noted most frequently, but 1.5 did not switch at all. Switching of the opacity phenotype was observed both in vitro and in neonatal mice. Relationships between colony opacity and several cell surface phenomena were explored. (i) Opaque variant 1.1 had two surface proteins (46 and 75 kDa) that were either unique or greatly overexpressed. (ii) Variant 1.1 was deficient in type III polysaccharide, while 1.5 lacked group B antigen. Diminished capsular polysaccharide of variant 1.1 was reflected in reduced negative electrophoretic mobility and in increased buoyant density. (iii) Transparent variant colonies growing closest to a penicillin disk were opaque, but colonial variants did not differ in their sensitivity to penicillin. These data indicate that GBS can exist in both opaque and transparent forms, with opaque appearance occurring by multiple routes. Opaque variants grow poorly on Todd-Hewitt medium generally used for isolation of GBS, so any possible relationships between opacity variation and pathogenesis of GBS infection are unknown.
authors.affiliation: Laboratory of Microbial Structure, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840.
authors.forename: S H
authors.initials: SH
authors.lastname: Pincus
authors.forename: R L
authors.initials: RL
authors.lastname: Cole
authors.forename: M R
authors.initials: MR
authors.lastname: Wessels
authors.forename: M D
authors.initials: MD
authors.lastname: Corwin
authors.forename: E
authors.initials: E
authors.lastname: Kamanga-Sollo
authors.forename: S F
authors.initials: SF
authors.lastname: Hayes
authors.forename: W
authors.initials: W
authors.lastname: Cieplak
authors.forename: J
authors.initials: J
authors.lastname: Swanson
mesh_terms: D016667:Bacterial Capsules / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D014644:Genetic Variation; D009024:Morphogenesis / Q000235:genetics*; D010406:Penicillins / Q000494:pharmacology; D010641:Phenotype; D011135:Polysaccharides, Bacterial / Q000737:chemistry / Q000235:genetics; D013292:Streptococcus agalactiae / Q000737:chemistry / Q000235:genetics* / Q000648:ultrastructure; D014774:Virulence / Q000235:genetics
chemical_list: D010406:Penicillins; D011135:Polysaccharides, Bacterial