Author: Jaelle Brealey, PhD Candidate, Young Lab, UQ School of Chemistry and Molecular Biosciences.

‚ÄčContributer Paul Young, Australian Infectious Diseases Research Centre‚Äč.

A team of researchers led by the Head of UQ’s School of Chemistry and Molecular Biosciences Professor Paul Young, are exploring what may be a previously unrecognised role for bacteria during viral respiratory infections in children.

Respiratory infections in infants and young children are a significant cause of childhood mortality and morbidity worldwide, with viruses the main cause of these respiratory infections.

In young children antibiotics are often prescribed to treat such respiratory infections without the diagnosis of a bacterial infection – this over-prescription of antibiotics could potentially contribute to the development of antibiotic resistance.

Studies of the microbiome of the upper respiratory tract in children have found that certain bacterial species become dominant in the respiratory tract during viral infections.

These bacterial species include Streptococcus pneumoniae, an opportunistic pathogen which is capable of causing diseases like pneumonia, but can also be carried harmlessly during health.

The contribution of these bacteria to disease during viral infections is currently unclear.

Professor Young said the research team were currently focusing on the role of such bacteria during infections by respiratory syncytial virus (RSV), which was an important viral pathogen of young children.

He said the team had found that S. pneumoniae is frequently detected in children with severe RSV infections and these children experienced more severe disease compared to those with either one or neither pathogen, suggesting a pathogenic role of S. pneumoniae during RSV infection.

“Our experiments with clinical strains of S. pneumoniae isolated from young children suggest that RSV infection of the epithelial cells that line the respiratory tract promote the binding of S. pneumoniae to these cells,” Professor Young said.

“The interaction appears to be strain-specific, with some clinical isolates of S. pneumoniae binding better to RSV infected cells compared to others.

“Enhanced binding to the respiratory tract may allow certain strains of S. pneumoniae to more easily colonise the airways during RSV infection, leading to an overgrowth of bacteria that could establish a co-infection, potentially augmenting the severity of the RSV infection.”

Professor Young’s team are now investigating the strain-dependent interaction between the two pathogens further, to determine whether specific S. pneumoniae strains are more associated with severe disease in young children and to identify the molecular mechanism underlying the strain-specific binding interaction with RSV.

In an environment as complex as the respiratory tract, where invading viruses and bacteria are constantly interacting with the resident microbiome and the host immune system, it is important to identify those microorganisms that contribute to disease.

To date, the team’s work demonstrates a clear association between RSV, S. pneumoniae and disease severity, suggesting that there may be a role for antibiotics in the treatment of severe RSV infections.

Image: S. pneumoniae (blue) bound to an RSV infected bronchial epithelial cell (pink) visualised by scanning electron microscopy. Taken by Keith Chappell.