Jiri Vlach, United States of America
University of Alabama at Birmingham MicrobiologyAuthor Of 1 Presentation
ORAL STREPTOCOCCI: A SOURCE OF NEW AND VIRULENT CAPSULE FOR PNEUMOCOCCI (ID 244)
Abstract
Background
Pneumococcal conjugate vaccines have been very successful, but their use has increased infections by non-vaccine serotypes. Oral streptococci often harbor capsular polysaccharide (PS) synthesis loci (cps). If pneumococcus can replace its cps with oral streptococcal cps, it may increase its serotype repertoire.
Methods
Chemical structures of capsular PS from an oral streptococcus strain, SK95, and a pneumococcal strain, D39, were determined by 2-dimensional NMR. An acapsular pneumococcus strain was transformed with cps from SK95 and D39, which were compared for their virulence by measuring non-specific phagocytic killing and their ability to kill mice.
Results
SK95 and D39 both produce structurally identical type 2 capsules. Baby rabbit serum (BRS) at 10% non-specifically killed >50% of SK95; however, 12ยท5% BRS killed <20% of D39. Non-encapsulated pneumococci became resistant to BRS as D39 following transformation with SK95 cps. Similarly, SK95 is avirulent in well-established in vivo mouse model. When the acapsular pneumococcus was transformed with SK95 cps, the transformant became virulent and killed all mice.
Conclusions
Oral streptococcus cps can make acapsular pneumococcus virulent and inter-species cps transfer should be considered a potential mechanism for serotype replacement. Our findings highlight potential limitations of current WHO criterion for studying serotypes of pneumococci carried without first isolating bacteria.