An antibiotic-resistant strain of staph bacteria began its globetrotting adventures in Europe and can mutate quickly as it spreads, a new study suggests. Scientists acting as molecular historians used a new technology to decode the bacteria’s genome and follow its movements, an approach that could one day help health care workers pinpoint the origins of outbreaks and prevent further infections.
The marauding bacterium, known as methicillin-resistant Staphylococcus aureus or MRSA, changes its genetic makeup faster than previously thought by altering at least one letter in its genetic handbook about every six weeks, a new study in the Jan. 22 Science shows.
More of those mutations fall in genes involved in antibiotic resistance than would be expected if the changes had occurred randomly, “illustrating that there is an immense selective pressure from antibiotic use worldwide,” says Simon Harris, a bacterial phylogeneticist at the Wellcome Trust Sanger Institute in Hinxton, England. Bacteria that get mutations creating resistance to antibiotics are more likely to survive than are bacteria that remain sensitive to drugs.
Harris and his colleagues report analyses of 63 isolates of a strain of MRSA, all collected in hospitals around the world. The researchers decoded the entire genetic instruction book, or genome, of each sample. All the isolates are variations of a MRSA strain known as sequence type 239, or ST239. Most of the samples look genetically identical when analyzed using other DNA fingerprinting techniques. Only after determining every letter of the genetic handbook of each sample could the researchers see that each isolate is genetically distinct, Harris says.