New species of superbug behind spike in severe human infections

 A recently emerged strain of bacteria called Streptococcus dysgalactiae subspecies equisimilis (SDSE) is leading to a concerning rise in global rates of severe invasive infections becoming resistant to key antibiotics, according to a study.

A person infected with SDSE is likely to have an infection in the skin, throat, gastrointestinal tract, and female genital tract that can range in severity from strep throat (pharyngitis) to necrotising fasciitis (flesh-eating disease).

Although SDSE is closely related to group A streptococcus (also commonly known as Streptococcus pyogenes), which has been very well studied, little is known about SDSE, said the team at the Houston Methodist Research Institute in the US.

To understand better, the team used a sophisticated integrative approach and studied 120 human isolates of a particular SDSE subtype, called stG62647.

“The stG62647 SDSE strains are important to study because they have been reported to cause unusually severe infections,” said the team described in a paper appearing in the journal mBio.

They analysed the subtype’s genome, where the information of its DNA is stored. They also decoded its transcriptome, which provided a snapshot of the complete gene expression profile at the time the SDSE cells were collected. This also helped the researchers understand SDSE’s virulence -- the degree of damage it can cause to its host.

They found “an unexpectedly wide range of virulence was identified (20-95 per cent), as assessed by near-mortality data”.

The results suggest that human genetics and underlying medical conditions contribute to disease severity.

The integrative analysis revealed new data about the important emerging human bacterial pathogen which can help in developing treatment and in vaccine research, the team said, while stressing the need for more research.