3a-Negative Yersinia Pestis, China

Dear Editor, As the causative agent of plague, Yersinia pestis has killed millions of people in the three major historical pandemics and remains endemic in many natural foci around the world today. This Gram-negative bacterium is transmitted to humans and susceptible animals from the natural rodent reservoirs through the bites of infected fleas, contact with infected animals or persons, or aerosols. Because of its respiratory transmission and high pathogenicity, the potential use of Y. pestis as a bioterrorism agent is a major concern. The specific and rapid detection of Y. pestis is the key step in implementing effective countermeasures during plague epidemics. The standard culture and biochemical identification methods for Y. pestis are relatively time-consuming, so PCR assays are frequently used because they are rapid. However, the amplification targets are usually based on three plasmids, which may be lost in atypical strains, causing false-negative results. Therefore, Radnedge et al. identified a signature sequence, designated “3a”, in a chromosomal region of Y. pestis, based on the results of suppression subtractive hybridization, which was later confirmed with a microarray-based analysis. A positive 3a result has been shown to be an effective marker for the identification of Y. pestis isolates. However, the recent isolation of 3a-negative Y. pestis in China suggests that this indicator is unreliable