Dynamic Pneumococcal Genetic Adaptations Support Bacterial Growth and Inflammation during Coinfection with Influenza

Area of Science:

• Microbiology
• Immunology
• Genetics

Background:

• * Streptococcus pneumoniae (pneumococcus) is a major bacterial pathogen complicating influenza virus infections.
• * Coinfections increase influenza-associated morbidity and mortality, but specific bacterial genes driving pathogenicity remain unknown.

Purpose of the Study:

• * To identify bacterial genes that enhance Streptococcus pneumoniae fitness during influenza virus infection using genome-wide screening.
• * To investigate the role of identified bacterial genes in virulence, disease severity, and host immune responses during coinfection.

Main Methods:

• * Genome-wide transposon sequencing (Tn-Seq) to screen for bacterial genes conferring fitness advantages in influenza-infected hosts.
• * Generation and characterization of single-gene deletion (SGD) mutants for key identified genes.
• * Assessment of bacterial growth, host mortality, immune cell infiltration (neutrophils, macrophages), and cytokine/chemokine profiles in vivo.

Main Results:

• * 32 bacterial genes conferring improved fitness during influenza infection were identified, many involved in metabolism (nucleotide/amino acid biosynthesis, protein translation, membrane transport).
• * SGD mutants showed slightly attenuated growth but reached high titers in lungs.
• * All SGD mutants significantly reduced or delayed mortality in coinfected mice.
• * Pulmonary neutrophils, inflammatory macrophages, and proinflammatory mediators were reduced, with altered neutrophil distribution.

Conclusions:

• * Specific bacterial genes, particularly those involved in metabolism, are critical for Streptococcus pneumoniae virulence during influenza coinfection.
• * Targeting these bacterial metabolic pathways could be a strategy to mitigate severe outcomes of influenza-bacterial pneumonia.