The bacterium responsible for the "black plague," which led to the deaths of more than 75 million people worldwide in the 14th century, may have other nasty tricks.

Yersinia pestis can normally be treated and cured with a course of antibiotics, if caught within a few days of the symptoms. But researchers at Weill Cornell Medical College (WCMC) have located a gene that could mutate to make Y. pestis resistant to many common drugs. Scientists believe that antibiotic-resistant Y. pestis should concern the public and scientific community, because the bacterium might be used as a bioterrorism agent.

Luis Quadri, associate professor of microbiology and immunology at WCMC, and his research team located the gene that, when overexpressed or in high numbers in the body, allows the bacterium to be almost bulletproof.

The researchers scanned colonies of the bacterium E. coli , which had Y. pestis genome fragments implanted within, and found that some of the bacteria were able to resist the effects of multiple antibiotic drugs.

The researchers also found that these rare microbes contained high numbers of a Y. pestis gene called robA -- a gene that activates production of microscopic pumps that flush toxins and antibiotics from the cell. The greater the number of robA in Y. pestis , the more cellular pumps, and the easier it is for the bacterium to eliminate the antibiotics.

Because the findings' importance has generated above-average readership, the study has earned the permanent "Highly Accessed" distinction by the BioMed Central Microbiology site.