Poster Presentation BACPATH 2022

Altered arrangement of the streptococcal chain identified in studies of GAPDH in Streptococcus agalactiae (#131)

Ruby Thapa 1 , Matthew Sullivan 1 2 , Kelvin Goh 1 2 , Debashish Chattopadhyay 3 , Glen Ulett 1 2 3
  1. Griffith University, Southport, 4215, QLD, Australia
  2. Menzies Health Institute, Gold Coast, QLD, Australia
  3. Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, USA

Group B Streptococcus (GBS) or Streptococcus agalactiae is a gram-positive commensal that resides in 30-40% of adult women, typically within the gastrointestinal, and/or genital tract. GBS is also an opportunistic pathogen that becomes invasive in neonates, pregnant women, nonpregnant adults particularly the elderly, people with co-morbidities, and immunocompromised individuals. Several virulence factors in GBS have been identified, however, the mechanisms by which the bacteria become invasive are not yet fully understood. In this study, the role of one potential virulence factor, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), (a glycolytic enzyme, which is also surface displayed, and encoded by gapC) in GBS pathogenesis was investigated. We used a female reproductive tract colonization model and macrophage antibiotic protection assays to explore the role of GAPDH in pathogenesis, using a GAPDH-overexpressing S. agalactiae strain (ΩgapC ) was used. The main finding of this study was that  WgapC GBS significantly altered phagocytic uptake, however, ΩgapC GBS was more significantly cleared from the female reproductive tract in mice. We also detected significant attenuation of fitness in a direct competition challenge model in vivo. During this study, we found that overexpression of GADPH caused GBS to form notably longer streptococcal chains compared to the wildtype strain (WT). We studied the impact of long chain formation on the behavior of the ΩgapC  strain using a series of assays focused on mechanical disruption of chains, quantitation, and visualization.  A significant increase in recovery of colony forming units of ΩgapC  GBS was noted compared to WT following mechanical disruption and confirmed by microscopy. These findings are important because colony count remains a widely used and reliable method for estimating the number of bacteria in assay samples. We conclude that GBS counts significantly depend on the chain length which is vital to consider in interpreting experiments and strain behaviours in assay conditions.  

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