Sometimes natural selection gets a helping hand from humans. A new study tracing the genetic history of a nasty strain of pneumonia-causing bacteria shows that antibiotics and vaccines helped shape the microbe’s evolution.
In a technical tour de force, an international team of researchers deciphered the complete genetic blueprints of 240 samples of a strain of Streptococcus pneumoniae taken from sick people in 22 countries. The samples were isolated between 1984 and 2008, allowing researchers to see how the bacteria changed over time.
This strain of pneumonia, known as the Pneumococcal Molecular Epidemiology Network clone 1 or PMEN1, was first recognized in a hospital in Barcelona in 1984. But the new analysis indicates the strain probably first arose about 1970, the team reports in the Jan. 28 Science.
“When this clone emerged, it emerged into a world in which penicillin was frequently used,” says study coauthor Stephen Bentley, a molecular microbiologist at the Wellcome Trust Sanger Institute in Hinxton, England. Because the strain was not killed by penicillin, it had an advantage over strains that were susceptible and quickly spread.