Study casts doubt on minibacteria.

Two years ago, some scientists claimed to have found a new class of ultratiny microbes that others argued were too small to be real. A new analysis in the Oct. 10 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES suggests the naysayers were right.

Several years ago, John O. Cisar learned of Finnish scientist Olavi Kajander's reported discovery of nanobacteria, unusually small bacteria allegedly responsible for kidney stones in many people (SN: 8/1/98, p. 75). Cisar wondered whether the bacteria could be found in places other than blood, which is where Kajander had originally isolated them.

Cisar, a microbiologist at the National Institute of Dental and Craniofacial Research in Bethesda, Md., speculated that nanobacteria naturally live in the mouth and occasionally escape into the bloodstream. Indeed, Cisar and his colleagues initially found what they thought were signs of nanobacteria growing from human saliva and dental plaque. Electron micrographs showed calcified shells that the microbes were thought to make. "We began to see exactly what [Kajander] described. We were believers for a period of 2 to 3 months," says Cisar.

Follow-up work has changed his mind. In their new paper, Cisar and his colleagues describe a series of studies that convinced them that there's no compelling evidence for nanobacteria. For example, the investigators found no proteins or DNA that would indicate a life form was associated with the calcium-rich particles.

"We believe the particles are arising for some reason other than the presence of a living entity," says Cisar, suggesting they crystallize around some biological molecule.

Kajander's team had used the research technique called polymerase chain reaction (PCR) to identify DNA sequences from nanobacteria. Those sequences, notes Cisar, are virtually identical to ones from bacteria that frequently taint PCR assays. "It's pretty clear that they're contaminants," he says.

Cisar acknowledges that it's almost impossible to prove that something doesn't exist. He's discussed his results with the Finnish group and says Kajander maintains his belief in nanobacteria. (Kajander did not reply to SCIENCE NEWS'S attempts to contact him.) Cisar remains open-minded to new data, but he argues that it's premature to use antibiotics to treat kidney stones or other conditions that had been linked to nanobacteria.