Density profile of group B streptococci, type III, and its possible relation to enhanced virulence

Abstract

The buoyant densities of virulent and colonizing group B streptococci, type III, were determined by centrifugation of bacteria on a linear, hypotonic density gradient. A total of 28 strains were investigated. Eleven strains were obtained from blood cultures of babies with early-onset disease, and eight strains were isolated from the cerebrospinal fluid of babies with late-onset septicemia and meningitis. Nine colonizing strains were genital isolates from pregnant women subsequently giving birth to healthy children. In each strain the buoyant density was determined before and after neuraminidase treatment. All strains showed an increase in the buoyant density after enzymatic removal of sialic acid, and the density differences before and after desialylation were calculated. The mean values of these differences for blood, cerebrospinal fluid, and colonizing isolates were 23.4, 25.3, and 10.6 mg/ml, respectively. The mean value for the colonizing strains differed significantly from the mean value for each group of virulent strains. All colonizing strains banded singly in the gradient, whereas five of the virulent strains divided into two density populations. Extracts of the low-density cells produced markedly more dense immunoprecipitates with type antiserum than did extracts of the high-density bacteria. One double-banding strain was positive for R protein. After separation of the two density populations, this antigen was detected only in the low-density population. The results indicate that bacterial buoyant density is inversely related to the amount of capsular polysaccharide enveloping the cell and that a determination of the density profile of the bacteria may be used for discriminating strains with an increased pathogenic potential.

Phase variation in streptococci of serological group B

“…(1 5) demonstrated type X-specific antibodies in cows with group B streptococcal mastitis. Variation in the expression of R-protein between buoyant density subpopulations has also been noted previously (3,6).…”

“…The bacteria used in this study were a non-typable (NT/R) blood isolate of group B streptococcal strain 5531:NT from a patient with endocarditis and a group B streptococcal strain 854-75: N T with type pattern NT/X isolated from bovine mastitis. The cultures had been characterized previously (1 6,24,25). For preparation of density subpopulations the bacteria were cultivated in trypticase yeast broth (Ty) (4), pelleted, and resuspended in Percoll (Pharmacia Fine Chemicals, Uppsala, Sweden).…”

Capsule expression regulated by a two-component signal transduction system inStreptococcus iniae

“…All of the aforementioned mutants, which had reduced capsule expression, were found to be less buoyant in broth culture (Buchanan et al, 2005;Locke et al, 2007;Lowe et al, 2007). Furthermore, the presence of capsule in Streptococcus pyogenes, also known as Group A Streptococcus (GAS) and GBS, in addition to being associated with enhanced virulence and phagocytic resistance in blood, is also associated with buoyancy in broth cultures (Hakansson et al, 1987;DeAngelis & Weigel, 1994). Previous to the work published by Lowe et al, we noted that disease-associated strains of S. iniae were buoyant in broth whereas strains isolated from healthy fish (commensal) were not, suggesting the presence of a capsule or surface component in disease-associated strains which inhibits aggregation.…”

Differential Expression ofVibrio vulnificusCapsular Polysaccharide

“…The differential expression of CPS may enhance bacterial survival by alternately exposing or masking more hydrophobic surface structures needed for adhesion dur-ing colonization or for evasion of macrophages and complement during systemic infection (7,30,34). For example, decreased CPS expression in group B streptococci correlates with adhesion to mucous membranes during initial infection, whereas during systemic phases of disease the expression increases when the need for the antiphagocytic capsule is greater (13,39). CPS expression appears to be required for the virulence of V. vulnificus, and animal models have suggested that the amount of CPS expressed may be a factor in the observed differences among opaque-and translucent-phase variants.…”

“…Bacteria that produce extracellular systemic infections frequently express polysaccharide capsules on their cell surfaces for the evasion of innate host defenses (13,36). The amount of CPS expressed can vary with genetically determined phase variation (19,25) or with environmental factors such as pH, nutrient levels, metal cation availability, and growth phase (21,26,31,36).…”