Molecular Detection of PersistentFrancisella tularensisSubspeciesholarcticain Natural Waters

Abstract

Tularemia, caused by the bacteriumFrancisella tularensis, whereF. tularensissubspeciesholarcticahas long been the cause of endemic disease in parts of northern Sweden. Despite this, our understanding of the natural life-cycle of the organism is still limited. During three years, we collected surface water samples (n=341) and sediment samples (n=245) in two areas in Sweden with endemic tularemia. Real-time PCR screening demonstrated the presence ofF. tularenis lpnAsequences in 108 (32%) and 48 (20%) of the samples, respectively. The 16S rRNA sequences from those samples all grouped to the speciesF. tularensis. Analysis of the FtM19InDel region oflpnA-positive samples from selected sampling points confirmed the presence ofF. tularensissubspeciesholarctica-specific sequences. These sequences were detected in water sampled during both outbreak and nonoutbreak years. Our results indicate that diverseF. tularensis-like organisms, includingF. tularensissubsp.holarctica, persist in natural waters and sediments in the investigated areas with endemic tularemia.