Nasal associated lymphoid tissue & M cells, a window to persistent streptococcal infections.

BACKGROUND & OBJECTIVES: Intranasal infection of mice has been used as a model of streptococcal pharyngitis, as nasal associated lymphoid tissue (NALT) in this animal is structurally and functionally analogous to human tonsils. The present study was carried out to determine whether group A streptococci preferentially colonized or invaded NALT. METHODS: Lux(+) strain Sp3 was created and exponential phase bacteria were introduced intranasally into BALB/C female mice, total photon emission from selected areas was quantified, sections of NALT tissues were used for immunofluorescent staining and M cell staining. RESULTS: Intranasal infection of mice with bioluminescent group A streptococci or unlabeled streptococci demonstrated that NALT was a primary target of this pathogen. Streptococci readily gained access to the blood stream from this site of infection. Immunofluorescence microscopy studies showed that M cells, dispersed along the mucosal epithelium adjacent to NALT, were preferentially infected and likely to provide the window through which streptococci reached the underlying tissue. INTERPRETATION & CONCLUSION: The present study suggests that this upper respiratory Gram positive pathogen uses a mechanism similar to that of enteric pathogens in the intestine to gain access to underlying tissue, lymphatics and blood.

Promotion of fibronectin independent invasion by C5a peptidase into epithelial cells in group A Streptococcus.

BACKGROUND & OBJECTIVES: Group A Streptococcus, causative agent of several clinical manifestations codes for multiple protein invasins which help the bacterium to enter non-phagocytic cells. C5a peptidase (SCPA) is a surface protein conserved among different serotypes of M1 strain. The present study was taken up to study SCPA promoted fibronectin independent entry of GAS into epithelial cells. METHODS: An isogenic 90226 emm1deltaAB (M1(-)) mutant was constructed with thermosensitive pGhost vector. This isogenic M1(-) mutant expressed SCPA on the surface as determined by Western blotting and immunofluorescence. RESULTS: On preincubation with anti-SCPA serum, the isogenic M1(-) strain exhibited 54 per cent decreased invasion as compared to the bacteria incubated with control serum. Also, purified recombinant SCPA proteins blocked internalization of M1(-) streptococci into HEp-2 cells. The M1(-) strain invaded at the same efficiency in the presence or absence of fibronectin. INTERPRETATION & CONCLUSION: These results suggested that SCPA acted as a potential invasin of group A streptococcus and promoted invasion independent of fibronectin.