Advanced Testing Methods Uncover Previously Hidden Bacterial Genetic Variants

Scientists at Houston Methodist Research Institute have discovered that a fast‑rising strep bacterium comes in more forms than expected, including ones that may lead to life-threatening infections.  

The study, led by James Musser, M.D., Ph.D., chair of the Department of Pathology and Genomic Medicine and director of the Center for Infectious Diseases at Houston Methodist, is published in Microbiology Spectrum. It is the largest U.S. study investigating Streptococcus dysgalactiae subspecies equisimilis (SDSE) at this level, as these strep infections are increasing worldwide.  

The bacterium is most closely related to the flesh-eating Group A Strep, which causes illnesses ranging from mild strep throat and fever to severe conditions like blood infections and necrotizing fasciitis (flesh-eating disease). SDSE was originally considered rare and was believed to mostly infect people who already had other health issues. 

First author, Lydia Pouga, Ph.D., research scientist at Houston Methodist said, by using whole-genome sequencing to analyze more than 800 patient samples, the researchers discovered 44 distinct variants of the bacterium, an insight older testing methods did not provide. 

"We discovered that certain strains caused specific types of infection," Pouga said.

For example, one type of strain was associated with skin infections, another type was associated with blood infections and yet another strain was associated with throat infections. This is the first time we've seen such strong associations between strains and specific infections across a large patient population."

Lydia Pouga, Ph.D., Research Scientist at Houston Methodist 

Pouga said the study provides critical genetic data to understand how the bacterium spreads, changes and causes infections. The information will help deliver insights that can improve diagnosis, infection control and future vaccine planning. 

Musser's lab is renowned for using an integrated interdisciplinary research approach to unravel new information about infections caused by group A Streptococcus (GAS), which is responsible for more than 700 million cases of human disease each year globally. Jim Henson, creator of the Muppets, died of a similar form of the disease in 1990. 

Other authors include Houston Methodist researchers Stephen Beres, Randall Olsen, Wesley Long and Edward Graviss. The study was funded in part by the Fondren Foundation.