The chance of survival from MRSA may depend on the genetic information in each strain of the superbug, according to a new analysis.
Dr Ruth Massey of Bath University, UK, and colleagues say that increasing antibiotic resistance is making Staphylococcus aureus a major health problem.
Writing in Nature Microbiology, they say infection severity, and in particular bacteraemia-associated mortality, has been attributed to several host-related factors, such as age and the presence of comorbidities." But the role of the bacterium in infection severity "is less well understood".
So far, the links between genotype, phenotype and infection outcome have not been made clear. So the team examined samples of S. aureus isolates from patients with bloodstream infections. These strains represented two globally important clonal types, CC22 and CC30, the team report.
They were able to identify several genetic areas linked to the toxic effect of the strains on body cells, called cytolytic toxicity, and the way they attach to and grow on a cell’s surface, called biofilm formation.
Putting this information together with observed patient outcomes, the experts found that greater cytolytic toxicity with low levels of biofilm formation raised the risk of mortality in infections with the CC22 strains. But cytolytic toxicity and biofilm formation were not related to outcomes with CC30 infections.
"Our results therefore suggest that different clones may have adopted different strategies to overcome host responses and cause severe pathology," the team write.
Dr Massey said: "Our study is important because it’s the first time we’ve collected data in human patients rather than relying solely on animal models.
"We’ve combined information from real people with phenotypic and DNA sequence data from the bacteria causing the infections. For the first time we’ve been able to predict which strains are most virulent, or likely to cause disease, and the outcomes of infection."
Recker, M. et al. Clonal differences in Staphylococcus aureus bacteraemia-associated mortality. Nature Microbiology 7 August 2017; doi: 10.1038/s41564-017-0001-x [abstract]
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