PspA-mediated aggregation protectsStreptococcus pneumoniaeagainst desiccation on fomites

Abstract

ABSTRACTStreptococcus pneumoniae(Spn) resides in the nasopharynx where it can disseminate to cause disease. One keySpnvirulence factor is pneumococcal surface protein A (PspA), which promotes survival by blocking the antimicrobial peptide lactoferricin. PspA has also been shown to mediate attachment to dying epithelial cells in the lower airway due to its binding of cell surface-bound mammalian (m)GAPDH. Importantly, the role of PspA during colonization is not well understood. WildtypeSpnwas present in nasal lavage elutes collected from asymptomatically colonized mice at levels ∼10-fold higher that its isogenic PspA-deficient mutant (ΔpspA). WildtypeSpnalso formed aggregates in mucosal secretions composed of sloughed epithelial cells and hundreds of pneumococci, whereas ΔpspAdid not.Spnwithin the center of these aggregates better survived prolonged desiccation on fomites than individual pneumococci and were capable of infecting naïve mice, indicating PspA-mediated aggregation conferred a survival/transmission advantage. Incubation ofSpnin saline containing mGAPDH also enhanced tolerance to desiccation, but only for wildtypeSpn. mGAPDH was sufficient to cause low-level aggregation of wildtypeSpnbut not ΔpspA. In strain WU2, the subdomain of PspA responsible for binding GAPDH (aa230-281) is ensconced within the lactoferrin (LF)-binding domain (aa167-288). We observed that LF inhibited GAPDH-mediated aggregation and desiccation tolerance. Using surface plasmon resonance, we determined thatSpnforms multimeric complexes of PspA-GAPDH-LF on its surface and that LF dislodges GAPDH. Our findings have important implications regarding pneumococcal colonization/transmission processes and ongoing PspA-focused immunization efforts for this deadly pathogen.IMPORTANCEStreptococcus pneumoniae(Spn) is a dangerous human pathogen capable of causing pneumonia and invasive disease. The virulence factor pneumococcal surface protein A (PspA) has been studied for nearly four decades with well-established roles in pneumococcal evasion of C-reactive protein and neutralization of lactoferricin. Herein, we show that mammalian (m)GAPDH in mucosal secretions promotes aggregation of pneumococci in a PspA-dependent fashion, whereas lactoferrin counters this effect. PspA-mediated GAPDH-dependent bacterial aggregation protectedSpnin nasal lavage elutes and grownin vitrofrom desiccation on fomites. Furthermore, surviving pneumococci within these aggregates retained their ability to colonize naïve hosts after desiccation. We report thatSpnbinds to and forms protein complexes on its surface composed of PspA, mGAPDH, and lactoferrin. Changes in the levels of these proteins therefore most likely have critical implications onSpncolonization, survival on fomites, and transmission.