448 - Investigating Group B Streptococcus Serotype-Specific Responses to Intestinal Physiological Stress

Publication Number: 2436.448

Annabel Guo, Rutgers New Jersey Medical School, Plainsboro, NJ, United States; Mary Caroline Hagan, University of Georgia, Athens, GA, United States; Sanjana Sankaran, Hassenfeld Children's Hospital at NYU Langone, Brooklyn, NY, United States; Michelle J. Vaz, New York University Grossman School of Medicine, New York, NY, United States; Adam J. Ratner, Hassenfeld Children's Hospital at NYU Langone, New York, NY, United States

Background: Streptococcus agalactiae (Group B Streptococcus, GBS), a major cause of neonatal sepsis, is represented by 10 different serotypes. Late-onset (LO) sepsis (occurring >7 days of life) is the most common clinical presentation of invasive GBS disease in neonates and gastrointestinal (GI) colonization is a key precursor. To establish GI colonization, GBS must pass multiple physiological host barriers such as gastric acid, bile, and antimicrobial peptides (AMPs). We evaluated GBS serotype-specific responses to physiological stress in the gut.

Objective: (1) To determine differences in GBS growth across serotypes after exposure to acid stress, bile stress and lysozyme (AMP) and (2) To determine GBS serotype-specific differences in biofilm formation with these stressors.

Design/Methods: Representative GBS strains were selected based on serotypes: Ia (A909), III (COH1), V (AR1519), and a hypervirulent V strain (CNCTC 10/84). Growth kinetics were performed in Tryptic Soy broth (TSB) with acidic pH in the range of 5.0-7.34, bile concentrations of 5 mg/mL and 10 mg/mL, and lysozyme (14 mg/ml). Biofilm formation was assessed with the same stressors in THB (Todd Hewitt Broth) supplemented with 1% glucose and visualized using crystal violet. Data from biofilm assays were analyzed using repeated two-way ANOVA.

Results: Under acidic conditions, serotype III and hypervirulent serotype V exhibited a growth advantage compared with the other serotypes (Fig. 1). Serotype III maintained a growth advantage in bile, whereas hypervirulent serotype V exhibited reduced growth during the logarithmic and stationary phases. No serotype differences in growth were noted with lysozyme exposure. Biofilm formation was markedly reduced with both acidic pH and bile (p < 0.0001), most notably in hypervirulent serotype V (Fig. 2). In contrast, serotype Ia displayed increased biofilm production when exposed to lysozyme (p < 0.0001) (Fig. 3).

Conclusion(s): There is a serotype variation in the resistance response to physiological stress in the gut. This suggests strain-specific trade-offs between stress resistance and virulence, underscoring distinct pathogenic strategies.

Figure 1. GBS Growth Curves in Acid and Bile
Growth curves of Group B Streptococcus (GBS) serotypes under standard (pH 7.3), acidic (pH 6.0 and 5.0) and bile (5 mg/mL and 10 mg/mL) conditions obtained from long-term growth assays.

Figure 2. GBS Biofilm Formation in Bile
Biofilm formation by Group B Streptococcus (GBS) serotypes under bile stress at concentrations of 10 mg/mL (left) and 5 mg/mL (right), compared with the control (THB + 1% glucose without bile).

Figure 3. GBS Biofilm Formation in Lysozyme
Biofilm formation by Group B Streptococcus (GBS) serotypes under lysozyme stress (14 mg/mL), compared with the control condition (THB + 1% glucose without lysozyme).