Pneumonia-causing bacterium ‘morphs’ to escape destruction
A common human pathogen is also a sort of microbial quick-change artist — mutating too fast for medicine to follow. The bacterium that causes pneumonia, meningitis and ear infections can quickly and nimbly dodge the vaccines and antibiotics health officials throw at it, according to an international research team.
They have documented how one particularly nasty strain of the bacterium skipped from Spain to Britain, Canada, the U.S. and Vietnam, shuffling, mutating and swapping genes as it went. It made more than 700 genetic changes, including 10 “capsule-switching events” that researchers liken to an enemy changing clothes.
“It really is an arms race,” said co-author Dr. Dylan Pillai, a medical microbiologist at the University of Toronto and the Ontario Agency for Health Protection and Promotion.
To get a better sense of the tiny adversary, the researchers examined the microbe, Streptococcus pneumoniae, in detail as never before.
They sequenced and analyzed the genomes of 240 different “isolates” or varieties of a strain known as PMEN1.
It developed so much resistance to antibiotics and caused so much misery that samples of the bug have been stashed in lab freezers around the world since 1984.
Pillai and his colleagues in Toronto thawed out their isolates, collected when the microbes started causing serious disease in Canada in the 1990s. They resuscitated the bacterium in the Petri dish, and grew enough to extract genetic material.
It was then sent off to Britain, where scientists sequenced the genomes of 240 isolates from all continents. Genomes contain the DNA that controls and orchestrates life.
The researchers combed through the DNA to find the genetic changes, tricks and swaps the bacterium used to evade antibiotics and vaccines. They found single-letter mutations — passed down when the microbe divided — and recombinations, where chunks of DNA and sometimes entire genes were passed from one bacterium to another.
It’s long been known the microbe has a tendency to mutate and pick up genes from its environment and neighbours.
“It’s a fairly promiscuous organism,” Pillai said of Streptococcus pneumoniae.
What is new, he said, is the realization that it “morphs” so rapidly.