Amoebae: Bacteria's best friends?

University study finds soil encourages anthrax spores’ growth, multiplication

A recent University study shows that anthrax, when aided by a specific type of amoeba, can thrive and multiply in soil — a trick that could prove deadly for livestock and other mammals.

Bacillus anthracis, according to the Centers for Disease Control and Prevention, produces spores — small, dormant cells — that reanimate when exposed to optimal temperatures and environments, reproduce and form the disease Anthrax. Although there are three different ways of contracting the disease — cutaneous, inhalation and gastrointestinal — most humans acquire the disease from handling infected livestock or ingesting infected meat.

The bacteria was previously thought to lie dormant in soil, even in optimal conditions, until the soil was ingested by a mammal, triggering germination and contamination in the animal.

University researchers, however, found the bacteria are able to use the amoeba Acanthamoeba castellanii to germinate and reproduce in the soil itself. Paul S. Hoffman, a professor of infectious diseases, said in a University news release that it is not uncommon for bacteria to use amoebae at some point in their life cycle. “There’s a rich history of amoeba being associated with diseases,” Hoffman said. “We tried to make that connection with the anthrax by asking, ‘Could the amoeba have a role in the environment?’”

The researchers confirmed the amoebae were part of the process by first leaving the anthrax spores in warm, sterile water to identify whether or not the bacteria could thrive in water alone. The spores did not germinate. Next, the Acanthamoeba castellanii were added to the water/spore mixture and were allowed to sit for 72 hours. During this time, the spores increased fifty-fold in normal temperatures and a hundredfold in optimal conditions (37 degrees Celsius).

Other types of amoebae would normally consume all of the nutrients the bacteria needs for reproduction, but the Acanthamoeba castellanii seems to have something the bacteria can use instead. “We may find other species of amoeba that are even better at this than what we were using in the lab,” Hoffman said. “We may be at the tip of the iceberg.”

The danger of any spore-producing bacteria like anthrax lies in the spores’ ability to lie dormant for an extended period of time in a variety of different environments. The large population of the B. anthracis spores after interaction with the amoeba presents a very real danger to both livestock and humans.

According to the National Institute of Allergy and Infectious Diseases, the B. anthracis causes a fluid build-up in the victim’s cells and flips a molecular “switch” that regulates key cellular function, a lethal effect.

The combination of the spores and the toxins they release make this disease a deadly one, but University researchers think this newfound cooperation between B.anthracis and Acanthamoeba castellanii may help create a more effective antibiotic for the disease. “If we can figure out any way to disrupt the cycle, that would effectively eliminate the problem,” assistant professor of microbiology Ian Glomski said in the release. “If we really understand those interactions, we’ll have more and more points of intervention to think about.”

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