The bacterium that caused the deathly bubonic plague could survive within the ameba, the universal soil protozoan. It could survive through producing proteins that protect the ameba's digestion of microbes, scientists have discovered.

In a study published in Applied and Environmental Microbiology, last April 28 titled "Yersinia pestis resists predation by Acanthamoeba castellani and exhibits prolonged intracellular survival," the bacterium Yersinia pestis was reported to have the ability to spread from rodent to rodent and to human at some cases, through fleas. Viveka Vadyvaloo of Paul G. Allen School for Global Animal Health, Washington State University, Pullman said that fleas use the protective niche of the ameba to follow when conditions are unfavorable to its spread whenever rodents are few.

Ameba, the location of the bacterium, is the same to some human immune cells, the macrophages, in their ability to engulf bacteria or other items of similar size that could be nourishing. These are taken up within some special compartments called vacuoles. "With this in mind, graduate student Javier Benavides-Montaño separately cultured three distinct Y. pestis strains that have been associated with human epidemics, with a common laboratory strain of the free-living soil ameba, Acanthamoeba castellani, in a medium that supports the latter's growth," Vadyvaloo said.

"This study serves as a proof of principle that amoebae can support the prolonged survival of [the bacterium] Y. pestis in the environment," Vadyvaloo said. In an article published in Science Daily, Vadyvaloo also said that it could encourage a search for the interaction within areas of Colorado and New Mexico.

The study was deemed important due to the possibility of the plague to re-emerge in the public, Centers for Disease Control and Prevention has said. There is already 95 percent of cases reported in sub-Saharan Africa and Madagascar. Currently, modern antibiotics were used and proved to be effectiveness but without prompt treatment, this bacterium could cause serious illness, or worse, death.