Eliminating bacteria's DNA and boosting antimicrobial proteins that already exist may help prevent middle ear infections from reoccurring. These are the findings from a Nationwide Children's Hospital study that examined how an immune defense protein common in the middle ear interacts with a structure meant to protect a colony of bacteria.
The bacterium nontypeable Haemophilus influenzae (NTHI) causes a wide range of diseases of both the lower and upper airways, including middle ear infection. NTHI, like most other bacteria, can form a biofilm, a robust community of bacteria that allows the bacteria to evade the host's immune system and protects the bacteria from antibiotics and other therapies designed to kill them.
Human beta-defensin-3 is an antimicrobial defense protein expressed in the middle ear of humans and other mammals that kills both Gram-positive and Gram-negative bacteria. Previous research has shown that if expression of beta-defensin is disrupted, the host's ability to control the bacteria in the upper airway is altered and infection worsens.
Investigators in The Research Institute at Nationwide Children's Hospital hypothesized that human beta-defensin-3 might lose its power to kill NTHI if it got caught up within the extracellular DNA that makes up a biofilm's outer layer, thus preventing its contact with bacteria within the biofilm.
"Antimicrobial host defense proteins, like human beta-defensin-3, have been shown to bind to non-host DNA," says Lauren O. Bakaletz, PhD director of the Center for Microbial Pathogenesis "This interaction has an impact on the defense protein's ability to function."
Upon examining their animal model of middle ear infection, Dr. Bakaletz' team found that bacterial DNA and the animal's defense peptides were detected together in biofilms that developed during infection. Also, the defense peptide was predominantly co-localized with the biofilm's extracellula
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Nationwide Children's Hospital