Wednesday, 22 May 2019

Oral bacteria 'battle royale' helps explain how a pathogen causes hospital infections


Hundreds of different bacterial species are living inside your mouth. Some are highly abundant, while others are scarce. A few of these oral bacteria are known pathogens. Others are benign, or even beneficial.

Scientists know the genetic makeup of about 70 percent of oral bacteria. What they don't know is which species would live the longest without nutrients in a "battle royale" -- so they decided to find out. The results help explain how certain dangerous bacteria are able to persist in a sterile hospital environment and infect patients.

Researchers from the Forsyth Institute, the J. Craig Venter Institute, the University of Washington, and the University of California, Los Angeles, have described their discovery that three closely related species of bacteria belonging to the family Enterobacteriaceae outlived all other oral bacteria in long-term starvation or "doomsday" experiment.

To create a battle of bacteria, researchers placed hundreds of samples of oral bacteria from human saliva into test tubes. The bacteria, which are accustomed to living in the nutrient-rich mouth, were starved in their new environment. Each day, scientists checked the samples to see which bacteria were still alive.

Nearly every bacterial species died within the first couple of days. But three species -- Klebsiella pneumoniae, Klebsiella oxytoca, and Providencia alcalifaciens -- survived the longest, with Klebsiella pneumoniae and Klebsiella oxytoca surviving for more than 100 days.

Researchers were surprised to find that Klebsiella were among the champions of this bacterial combat. In their natural environment of the oral cavity, Klebsiella are considered an underdog. They account for only about 0.1 percent of all microbes in the mouth. But in an extreme environment deprived of all nutrients, Klebsiella reigned supreme while the bugs normally found in high abundance rapidly died off.

Scientists describe Klebsiella species as opportunistic pathogens. In healthy people, they live in the mouth peacefully, crowded by other microbes and unable to grow or cause trouble. But outside the mouth, where few other bacteria survive, Klebsiella is king. They persist on hospital surfaces, like sinks or tables. If a patient with a compromised immune system makes contact with Klebsiella, that patient could develop an infection.

Infections by Klebsiella can result in a number of dangerous conditions including pneumonia and meningitis. One of the reasons Klebsiella infections are so dangerous is that Klebsiella are particularly adept at developing resistance to antibiotics, as well as transferring this drug resistance to neighboring bacteria.

The finding that these Klebsiella species survive longer than their more benign neighbors in mixtures of saliva is likely to have a great deal of clinical significance, as multiple virulent outbreaks of antibiotic-resistant Klebsiella have been traced back to hospital sinks and drains. This research also helps illuminate a key ecological dynamic of bacterial communities.

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology

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