From the Guidelines
Pneumococcal serotype 3 infections are particularly challenging due to their specific virulence factors, including a thick polysaccharide capsule, pneumolysin, and hyaluronidase, which require targeted management strategies to reduce morbidity, mortality, and improve quality of life. The virulence factors of pneumococci serotype 3 include:
- A thick polysaccharide capsule that inhibits phagocytosis and clearance by the immune system, making it highly virulent 1
- Pneumolysin, a pore-forming toxin that damages host cells 1
- Hyaluronidase, which breaks down connective tissue barriers 1 For management of serotype 3 pneumococcal infections,
- Empiric therapy should begin with high-dose intravenous ceftriaxone (2g every 24 hours) or ampicillin (2g every 4-6 hours) plus azithromycin (500mg daily) for adults 1
- Once susceptibilities are known, therapy can be narrowed, and for penicillin-susceptible isolates, penicillin G (2 million units every 4 hours) is preferred 1
- Treatment duration typically ranges from 7-14 days depending on infection severity and site 1
- Vancomycin (15-20 mg/kg every 8-12 hours) should be added for meningitis cases or if drug-resistant pneumococci are suspected 1
- Prevention through vaccination with PCV13 and PPSV23 is crucial as these vaccines include serotype 3, though this serotype has shown lower vaccine effectiveness compared to other serotypes 1
- Supportive care including oxygen therapy, fluid management, and respiratory support may be necessary for severe infections 1 Early identification and aggressive management are essential due to serotype 3's association with higher mortality and complication rates compared to other pneumococcal serotypes.
From the Research
Virulence Factors of Pneumococci Serotype 3
- The capsular polysaccharide (CPS) is a significant contributor to the virulence of Streptococcus pneumoniae, including serotype 3 2.
- The CPS surrounds the bacteria, preventing entrapment in mucus during colonization, trapping water to protect against desiccation, serving as an energy reserve, and protecting the bacterium against complement-mediated opsonization and immune cell phagocytosis 2.
- Serotype 3 is particularly problematic due to its severe clinical manifestations, including empyema, bacteremia, cardiotoxicity, and meningitis, resulting in a fatality rate of 30%-47% 2.
- The capsule of serotype 3 pneumococci has distinct biochemical and physiological properties that facilitate its ability to cause disease, and existing vaccines are unable to confer protection against this serotype 2.
- The polysaccharide capsule of Streptococcus pneumoniae, including serotype 3, promotes intracellular survival and vascular endothelial cell translocation during invasive pneumococcal disease 3.
- The capsule has antioxidant properties that vary according to serotype, with serotype 3 having a high level of resistance to oxidative stress-mediated killing 3.
Management Strategies for Pneumococci Serotype 3 Infections
- Current pneumococcal vaccines, including the 13-valent conjugate vaccine, are unable to confer protection against serotype 3 infections 2.
- New vaccine designs are focused on surface proteins, such as PspA and PspC, and on the cytolysin, pneumolysin, which may provide protection against serotype 3 infections 4.
- The development of synthetic glycoconjugate vaccines, which involve the conjugation of capsular polysaccharides with a carrier protein, may provide a new approach to preventing serotype 3 infections 5.
- A more profound knowledge of the virulence factors responsible for the morbidity and mortality caused by Streptococcus pneumoniae, including serotype 3, is necessary to develop effective management strategies 6.