Melioidosis can mutate to become antibiotic-resistant, study warns

A new study has shown that the gram-negative bacterium that causes melioidosis, considered a major biothreat, can mutate to become resistant to the antibiotics used to treat it.

The research, conducted by a team of scientists from Colorado State University, has the potential to help scientists treat melioidosis and may also aid in discovering strategies to combat antibiotic-resistant bacteria.

Melioidosis, caused by the bacterium Burkholderia psuedomallei, is considered highly dangerous and is classified as a category B priority pathogen by the U.S. Centers for Disease Control and Prevention. It is commonly treated using the antibiotic ceftazidime.

In most cases, when bacteria mutate to become more resistant to antibiotics, they will make small but effective changes in their DNA structure. The CSU researchers discovered that B. pseudomallei completely discarded an entire section of its DNA in order to develop resistance to ceftazimide.

“Its slow growth helped it elude proper treatment because it didn’t show up on tests which depended upon seeing bacteria multiply in the test media that Burkholderia pseudomallei tipically thrives in," Herbert Schweizer, a co-director of the research, said. "This new mutant form of the bacterium we looked at in this study was likely responsible for a good portion of about 11 to 17 percent of the cases of melioidosis that did not respond to ceftazidime treatment.”

Schweizer said that it was highly unusual to see DNA changes of this magnitude that left a bacterium still able to cause disease.

“The ultimate outcome of this research is that, when patients don’t respond to ceftazidime, we now know what to look for," Schweizer said. "And hospitals can begin using new tests to diagnose the problematic mutant strains early and patients can then be treated with other antibiotics that may be more effective against the resistant strains.”

The research was conducted by scientists from CSU, as well as Mahidol University in Bangkok, the Genome University in Singapore and the Universities of Cambridge and Oxford. The study was published in the journal the Proceedings of the National Academy of Sciences.