Calgary Herald

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.

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