healthHealth and Medicine

Multiple Bacteria Strains Can Gang Up To Cause A Deadly Flesh-Eating Infection


Tom Hale

Senior Journalist

clockNov 13 2019, 12:57 UTC

Aeromonas hydrophila colonies on the blood agar. Stefan Walkowski CC BY-SA 4.0

Researchers have completed the story of how two different strains of bacteria ganged up on a patient resulting in a flesh-eating infection that required a quadruple amputation to save their life.

The little known phenomenon is known as a polymicrobial infection. While cases of pathogens "teaming up" on their host are nothing new, a new report used genetic analysis to show how genetic variations in a species of bacteria can actively help to amplify infections.


Researchers from the University of Maryland and the University of Texas describe how a patient arrived at the hospital with a severe and potentially deadly flesh-eating disease known as necrotizing fasciitis. Their initial diagnosis suggested the illness was caused by a straightforward infection of the bacteria Aeromonas hydrophila. However, the disease started to progress at a startling rate, infecting the patient's bloodstream and organs and becoming life-threatening, forcing them to amputate all four limbs, and leading them to question why it had resisted treatment and accelerated. 

In earlier research, the team explain how the infection was caused by two genetically distinct strains of the bacteria, dubbed necrotizing fasciitis 1 (NF1) and necrotizing fasciitis 2 (NF2). Using mouse models they discovered that each strain produced a local infection but did not spread to the bloodstream or organs and was eventually wiped out by the host mouse's immune system. When both strains occurred they worked together to become much more lethal. 

In this new study, reported in the Proceedings of the National Academy of Sciences this week, they demonstrated how exactly NF1 and NF2 worked in tandem to create an overwhelming invasion. While the body’s defenses were busy attempting to quash the NF2 bacteria, it pumped out a toxin that broke down the muscle tissue, provided NF1 with the chance to enter into the bloodstream and organs.


“This research provides clear evidence that a very severe infection considered to be caused by a single species of a naturally occurring bacterium actually had two strains,” Rita Colwell, a Distinguished University Professor at the University of Maryland Institute for Advanced Computer Studies, said in a statement

“One of the strains produces a toxin that breaks down muscle tissue and allows the other strain to migrate into the blood system and infect the organs.” 

As shown in the latest study, the different “tactics” of the two strains is all down to slight genetic variations, which can come together to create an aggressive unified force. Although this case focuses on different bacteria strains that worked together, the researchers believe it’s a similar process when different bacteria, viruses, or parasites join forces.


“We’re excited by this very elegant detective work,” Colwell added. “We now have the ability through metagenomics to determine the individual infectious agents involved in polymicrobial infections. With these powerful new methods we can determine how microbes work together, whether they’re bacteria, viruses or parasites.”

healthHealth and Medicine
  • tag
  • bacteria,

  • amputation,

  • flesh-eating,

  • infection,

  • pathogen,

  • bacterial