A team of infectious disease researchers has developed a new method to identify virulence genes in Streptococcus pneumoniae, the leading cause of bacterial pneumonia. Using this technique in a mouse model of pneumonia, they were able to gain new insights into the progression of the disease and its interaction with the flu virus.
«Bacterial pneumonia is a lot more common, and more deadly, after a viral infection. Historically, a lot of the deaths during flu outbreaks such as the 1918 pandemic have been attributed to pneumococcal pneumonia,» said Jacqueline Kimmey, assistant professor of microbiology and environmental toxicology at UC Santa Cruz and co-first author of a paper on the new findings published October 28 in Cell Host Microbe.
Kimmey and her colleagues developed a new method for performing functional gene analysis to identify the genes that drive virulence in S. pneumoniae. Their method builds on the powerful gene editing technology known as CRISPR, which can be modified to selectively silence targeted genes with a technique called CRISPR interference. The researchers created a pooled library of S. pneumoniae strains in which each of the bacteria’s genes was targeted by CRISPR interference in one of the bacterial strains.
The CRISPR interference system was inducible by the antibiotic doxycycline, so the genes were not silenced until the bacteria (which were resistant to the antibiotic) were introduced into mice given doxycycline-containing feed. In addition, a genetic «barcode» on the guide RNAs used to target the silenced genes enabled the researchers to easily track each strain after infection. With a single sequencing step, they could identify which strains had survived and caused infections in the mice.
«It’s a very efficient way to shut off individual genes and find out which ones are important,» Kimmey explained.
The system also enabled the researchers to assess a crucial phase of the infection when most of the bacteria die off. Only a small number of bacteria survive this «bottleneck» and go on to cause invasive disease.
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Materials provided by University of California — Santa Cruz. Original written by Tim Stephens. Note: Content may be edited for style and length.