CLPB and tularemia: To determine if the ClpB-DnaK interaction is also vital for virulence, mice were subcutaneously infected and the spread of F. novicida U112, ΔclpB, and ΔclpB/Y503Acis was followed by determining the bacterial numbers on day 3 and 5 in spleen and liver, the main target organs of tularemia.