Bacteria responsible for diseases including middle ear infection may use sialic acid to colonize the upper airway, suggests research from Nationwide Children’s Hospital.
S. pneumoniae is a leading cause of death and disease worldwide and is a major source of community-acquired pneumonia, bacterial meningitis, blood poisoning (septicemia) and middle ear infection (otitis media). Sugars are fundamental to the lifestyle of S. pneumoniae and this pathogen is able to use a variety of sugars to survive. However, the concentration of free sugar in the human upper airway is generally low.
Previously, researchers from the Center for Microbial Pathogenesis at The Research Institute at Nationwide Children’s showed that S. pneumoniae can survive by “stealing sugar” from lipids and proteins found in the airway. In their recent study, which appears in Infection and Immunity, the team hypothesized that S. pneumoniae might use the carbohydrate sialic acid for growth.
“Several bacteria that are able to colonize the human airway or gut mucosa have been shown to use sialic acid as a carbon source,” said Samantha King, PhD, principal investigator in the Center for Microbial Pathogenesis and lead study author. “Sialic acid is the first sugar released when glycoproteins are broken down, so S. pneumoniae likely encounters sialic acid in the airway.” Dr. King’s team hypothesized that the release of sialic acid may provide S. pneumoniae with a source of carbohydrates necessary for growth.”
To test their hypothesis, the team grew S. pneumoniae in the lab in growth medium supplemented with sialic acid. They found that the sialic acid was able to support significant growth among multiple pneumococcal strains.
Further investigation identified a transport protein complex, SatABC, involved in S. pneumoniae’s use of sialic acid. Some mice were inoculated with S. pneumoniae strains missing the region encoding SatABC while others were inoculated with the full strain. Findings showed that the mice that were infected with the strain missing SatABC had fewer bacteria in their upper respiratory tract.
“Our data demonstrate that SatABC, and presumably the transport of sialic acid is important in S. pneumoniae’s colonization of the upper airway,” said Dr. King. “Pneumococcus encounters an excess of glycoconjugates in the human airway, so it is possible that sialic acid is not used for growth in humans; however, our findings in the mice support the idea that sialic acid is used as a carbon source in vivo. As we learn more about what resources this bacterium needs to multiply in the airway, we can potentially find ways to intervene in this process and inhibit infection.”
Marion C, Burnaugh AM, Woodiga SA, King SJ. Sialic acid transport contributes to pneumococcal colonization. Infect Immun. 2010 Dec 28. [Epub ahead of print]