Influenza Promotes Pneumococcal Growth during Coinfection by Providing Host Sialylated Substrates as a Nutrient Source

Steven J. Siegel, Aoife M. Roche, and Jeffrey N. Weiser

Cell Host & Microbe. (2014) 16, 55–67

Speaker: Sheng-Wei Chen(陳維昇)                Time: 14:00~15:00, Dec. 17, 2014

Commentator: Dr. Lien-I Hor (何漣漪 老師)        Place: Room 601

Abstract:

The mortality in influenza infection is attributed to secondary bacterial pneumonia, particularly due to Streptococcus pneumoniae [1]. However, the mechanisms underlying coinfection remain unclearly. In this paper, the authors hypothesized that influenza infection leads to rapid pneumococcal growth in the nasopharynx by providing a nutrient source for replicating bacteria. To test this hypothesis, C57BL/6 mice were inoculated with influenza A virus (x31) or PBS (mock). After seven days, treated-mice were then infected with pneumococci, and the number of bacteria in nasal lavages was counted. The authors further developed a flow cytometric assay to verify a promotion of bacterial growth by influenza infection, instead of inhibiting antibacterial immunity in the nasopharynx. Besides, the sialic acid plays a nutrition role in pneumococcal growth. Sialic acid is the most common non-reducing sugar which is accessible for modification on glycoconjugates in the airway [2]. It can be used as a sole carbon source for pneumococcal growth in vitro. Pneumococci express SatABC as a sialic acid transporter [3]. To determine whether viral and bacterial neuraminidases released sialic acid from host to promote pneumococcal growth, the authors used E. cristagalli lectin to label galactose residues that are exposed when sialic acid is cleaved. Fluorescence microscopic results showed that both viral and bacterial neuraminidases contribute to the desialylation in vivo during coinfection. In addition, the authors confirmed the findings by growing WT and satABC deficient pneumococci in human nasal airway surface fluid that is the natural environment for pneumococci. Taken together, influenza promotes pneumococci growth by providing host’s sialic acid as a nutrient source.

References:

1.     McCullers, J.A. (2006). Insights into the interaction between influenza virus and pneumococcus. Clin. Microbiol. Rev. 19, 571–582.

2.     Angata, T. et al. (2002). Chemical diversity in the sialic acids and related alpha-keto acids: an evolutionary perspective. Chem. Rev. 102,439–469.

3.     Marion, C. et al. (2011). Sialic acid transport contributes to pneumococcal colonization. Infect. Immun. 79,1262–1269.