Escaping medicine, pneumonia bacteria leave genetic paper trail

genetic paper trail

Scientists have constructed a detailed family tree for a nasty strain of Streptococcus pneumoniae, allowing them to see how the bacteria have evolved and evaded both vaccines and antibiotics in recent years.

Emory infectious disease specialist Keith Klugman was part of an international team that deciphered the entire genomes of 240 samples of S. pneumoniae. The study was published in January in the journal Science.

Researchers looked at one particular strain of S. pneumoniae, called PMEN1, which was first recognized in a Barcelona hospital in 1984. The team’s analysis indicates PMEN1 probably first arose around 1970 and then spread around the world because it was resistant to penicillin.

How PMEN1 and other strains became resistant to antibiotics comes from their ability to give their DNA to other bacteria, the study shows. Klugman says the problem of antibiotic resistance seems to rest largely on the ability of bacteria to “hand over” their DNA to other bacteria. Antibiotic resistance that results from mutations that change bacterial DNA one letter at a time occurs less often, he says.

Vaccines, in contrast, reduce the number of infections caused by S. pneumoniae with one kind of outer coat but leave the field clear for those with another kind of coat to take over.

As the cost of whole-genome sequencing continues to fall, Klugman says the study shows how public health officials might be able to more easily track how drug-resistant bacteria are spreading through hospitals or nursing homes.

“I think we’ve arrived at the point where the standard of how you identify a bacterial strain in this species has shifted to whole-genome sequencing,” he says. “In the future, sequencing of whole bacterial genomes will offer insight into the range of strategies that bacteria are able to use to evade human interventions for treatment and prevention.”—Quinn Eastman

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Emory Medicine Fall 2011