Scientists sequence genome of pneumonia pathogen

The sequencing will help identify new targets for drugs to treat and prevent Pneumocystis pneumonia, a common and often deadly infection in immunocompromised patients.

Scientists sequenced the genome of the pathogen Pneumocystis jirovecii.

"Recognised first among malnourished infants, P jirovecii pneumonia became a public issue with the advent of the HIV epidemic," said Philippe Hauser of the Centre Hospitalier Universitaire Vaudois and University of Lausanne, in Switzerland.

Today, the disease most commonly affects HIV-infected persons who are unaware of their status as well as solid organ transplant recipients and patients with hemato-oncologic or autoimmune diseases.

Since the organism cannot be grown in the lab for study, researchers have long made do with studying P jirovecii's lab-friendly relatives, species that infect animals and plants, in order to explore the secrets of the human disease.

"It is obviously better to study [P jirovecii's] genes rather that those of Pneumocystis species from animal models. The genome has both medical and evolutionary interests for the scientific community," Hauser said in a statement.

The study found that P jirovecii lacks the genes necessary for creating some of the essential ingredients of life, a hallmark of obligate parasites, organisms that must rely on another creature for sustenance.

"It implies that they need their host to provide these molecules. Thus, this has been quite an important finding which implied that human beings represent the reservoir of this pathogen," said Hauser.

The genome also showed that P jirovecii apparently lacks the ability to make toxins and virulence factors, molecules that enable a microbe to invade and take advantage of its host.

This makes sense, since P jirovecii does not cause disease in healthy people, but only runs out of control when it is not confronted with an immune response.

The current drugs of choice for treating Pneumocystis pneumonia are antifolates, but certain isolates of P jirovecii have already developed resistance to antifolates, an ability that is very likely to spread.

Now that the genome of P jirovecii is assembled and available to researchers all over the world, scientists can tease out clues about the organism that will help identify targets for some badly needed new drugs, researchers said.

The study will be published in a journal of the American Society for Microbiology.