By Tina Hesman Saey
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.
S. pneumoniae is a common cause of death, especially among young children. A recent estimate published in the Lancet, for example, showed the bacteria caused 14.5 million cases of serious disease in children aged 1 to 5 worldwide in 2000, killing about 826,000. The PMEN1 strain contributes to these totals and, because of its resistance to several different antibiotics, has become a public health concern. The strain is considered a major cause of pneumonia, meningitis and other infections worldwide. The new study reveals some of the genetic tricks the organism used to develop drug resistance.
Since its emergence, the strain has changed one of its DNA letters about every 15 weeks, the analysis reveals. That rate of mutation is rapid but similar to rates seen in the deadly antibiotic-resistant Staphylococcus aureus bacteria commonly called MRSA.