Isolation of Francisella tularensis by centrifugation of shell vial cell culture from an inoculation eschar

Abstract

A 52-year-old man was admitted to the hospital following the development of an inoculation eschar and fever six days after being bitten by a tick. He was clinically diagnosed as suffering from rickettsiosis. Eschar biopsy cultures on standard bacteriological media remained sterile. However, inoculation of cells with the homogenized specimen by the centrifugation- shell vial technique (M. Marrero and D. Raoult, Am. J. Trop. Med. Hyg. 40:197-199, 1989) resulted in the recovery of a bacterium. Determination of the sequence of the 16S rRNA gene amplified from the organism and comparison of the sequence to other sequences identified it as a strain of Francisella tularensis, whereas the specific serology was still negative. Our findings demonstrate that the centrifugation-cell culture, which is a tool for investigation of tick-transmitted diseases, may have the potential to serve as a method for the cultural isolation of F. tularensis.