Disease-Attenuated Pneumococcal Biosynthesis Gene Mutants Invade the Mucosal Epithelium and Induce Innate Immunity

Area of Science:

• Microbiology
• Immunology
• Bacterial Pathogenesis

Background:

• Nasopharyngeal colonization by Streptococcus pneumoniae involves adherence, microinvasion, and immune activation.
• Previous studies showed metabolic mutant strains colonize but do not cause invasive infection in mice.
• This study investigates if microinvasion and innate immune responses persist despite disease attenuation.

Purpose of the Study:

• To explore whether microinvasion and innate immune responses persist in attenuated Streptococcus pneumoniae strains.
• To understand the impact of specific gene mutations on bacterial virulence and host-pathogen interactions.
• To investigate the relationship between bacterial virulence, epithelial colonization, and disease development.

Main Methods:

• Utilized an experimental human pneumococcal challenge model.
• Employed ex vivo human airway cells and in vitro nasopharyngeal epithelial models.
• Analyzed bacterial virulence gene expression, oxidative stress, and metabolic pathways under serum stress.

Main Results:

• Mutations impacted pneumococcal virulence gene expression, oxidative stress, and metabolism.
• Microinvasion was not attenuated in human challenge and epithelial models.
• One mutant strain (Δfhs/piaA) showed reduced pro-inflammatory responses and altered secretion of toxins compared to wild-type.

Conclusions:

• Differences in microinvasion and epithelial responses are linked to the differential expression of bacterial virulence and metabolic pathways.
• Single gene mutations have a complex effect on bacterial virulence.
• Virulence determinants for pneumococcal colonization, microinvasion, and innate immunity are not necessarily directly linked to invasive disease.