JUL 15, 2015 5:39 PM PDT

Under Construction: Genome Remodeling Makes Group A Streptococcus More Virulent

WRITTEN BY: Kerry Evans
Streptococcus pyogenes, also known as group A streptococcus (GAS), is a gram positive bacterium best known for causing pharyngitis ("strep throat"). In some cases, however, GAS causes more severe diseases such as glomerulonephritis, acute rheumatic fever, and even necrotizing fasciitis (the ever provocative "flesh eating" bacteria).

Genome remodeling made group A streptococcus emm89 more virulent.
Recently, one strain of GAS, termed emm89, has proven itself particularly successful at infecting patients across the UK and Canada. Between 1998 and 2009, clinicians at Imperial College Healthcare NHS Trust in London noticed an increase in infections caused by emm89. Curiously, this strain is not antibiotic resistant, suggesting some other mechanism by which emm89 causes invasive disease.

Researchers at Imperial College London wanted to know if specific genetic changes in emm89 contributed to its increased virulence. To answer this question, Junior Research Fellow Claire Turner and colleagues sequenced the genomes of both invasive and non-invasive emm89 isolates. They report their findings in the most recent issue of the journal mBio.

The group sequenced the genomes of emm89 samples isolated from patients between 2004 and 2013. They identified six regions in which homologous recombination had occurred when compared to a particularly virulent emm89 strain (that caused necrotizing fasciitis). The most surprising change in these invasive emm89 strains was that they lacked a capsule, the outermost layer of the cell. "The fact that it had lost its capsule was a complete surprise", says Turner, "because it was believed that the capsule was essential for group A streptococcus to cause invasive disease". Cells lacking capsule tend to stick to surfaces better, which could be one reason emm89 is more successful at infecting humans.

The invasive emm89 isolates also produced more streptolysin O and NAD(+)-glycohydrolase (NADase). Streptolysin O creates pores in host cells through which NADase enters, eventually resulting in cell death.

These findings should motivate healthcare professionals to assess the selective pressures we place on the microbes around us. According to Shiranee Sriiskanda, lead investigator of the study, "We know very little about how group A streptococcus is transmitted from person to person. We need to look into this more deeply and think about better ways to prevent transmission".

Sources: mBio ("Emergence of a New Highly Successful Acapsular Group A Streptococcus Clade of Genotype emm89 in the United Kingdom" DOI:10.1128/mBio.00622-15), Science Daily, CDC
About the Author
  • Kerry received a doctorate in microbiology from the University of Arkansas for Medical Sciences.
You May Also Like
DEC 30, 2019
Microbiology
DEC 30, 2019
Understanding How Microbes in the Body Function as a Community
Advances in genetic technologies made it possible for researchers to learn more about the vast community of microbes that resides in the human body....
JAN 12, 2020
Microbiology
JAN 12, 2020
Using Microbial Manufacturers to Create Eco-Friendly Skis
There is huge potential in microbes; researchers have long been trying to use them to produce valuable materials like medicine, polymers, and fuel....
JAN 21, 2020
Microbiology
JAN 21, 2020
New Coronavirus is Spreading in China
In late December, health officials in China notified WHO that pneumonia with an unknown cause was sickening people....
FEB 02, 2020
Microbiology
FEB 02, 2020
A Potential Treatment for MERS is Found
A coronavirus causes MERS, which currently has no treatment. This work may help change that....
FEB 03, 2020
Microbiology
FEB 03, 2020
The Switch Controlling the Stage of a Common Parasite
The parasite Toxoplasma gondii is thought to infect from one-quarter to one-third of the global population....
FEB 08, 2020
Drug Discovery & Development
FEB 08, 2020
Drug Targets Brain-Eating Amoebas
Brain-eating amoebas lead to high rates of mortality as a result of encephalitis. In fact, more than 95% of people who develop the infection will die. Unfo...
Loading Comments...