Streptococcus Pneumoniae - Interaction With Haemophilus Influenzae

Interaction With Haemophilus Influenzae

Both H. influenzae and S. pneumoniae can be found in the human upper respiratory system. A study of competition in vitro revealed S. pneumoniae overpowered H. influenzae by attacking it with hydrogen peroxide.

When both bacteria are placed together into the nasal cavity of a mouse, within 2 weeks, only H. influenzae survives. When both are placed separately into a nasal cavity, each one survives. Upon examining the upper respiratory tissue from mice exposed to both bacteria, an extraordinarily large number of neutrophil immune cells were found. In mice exposed to only one bacterium, the cells were not present.

Lab tests show neutrophils that were exposed to already-dead H. influenzae were more aggressive in attacking S. pneumoniae than unexposed neutrophils. Exposure to killed H. influenzae had no effect on live H. influenzae.

Two scenarios may be responsible for this response:

1. When H. influenzae is attacked by S. pneumoniae, it signals the immune system to attack the S. pneumoniae
2. The combination of the two species sets off an immune system alarm that is not set off by either species individually.

It is unclear why H. influenzae is not affected by the immune system response.