The rogue's gallery of human pathogens is filled with members of the Bacteria and Eukaryota domains of life. Notably absent is the third domain: Archaea. According to a recent report in the Journal of Clinical Microbiology, however, that may no longer be the case.
When Hans-Peter Horz, an assistant professor at the University Hospital in Aachen, Germany, and colleagues used real-time quantitative PCR to survey the microbial ecology of 20 infected dental root canals, they found that five contained archaeal sequences, representing up to 2.5% of the total microbial load in these samples (J Clin Microbiol, 44:1274-82, April 2006). The predominant archaeal species was Methanobrevibacter oralis.
Healthy root canals are sterile environments, Horz says. "Microbes that are able to penetrate into this area must have some pathogenic...