Inflammation patterns induced by different Burkholderia species in mice

Burkholderia pseudomallei, which causes melioidosis, a severe, mainly pulmonary disease endemic in South-East Asia, is considered to be the most pathogenic of the Burkholderia genus. B. thailandensis, however, is considered avirulent. We determined differences in patterns of inflammation of B. pseudomallei 1026b (clinical virulent isolate), B. pseudomallei AJ1D8 (an in vitro invasion-deficient mutant generated from strain 1026b by Tn5-OT182 mutagenesis) and B. thailandensis by intranasally inoculating C57BL/6 mice with each strain. Mice infected with B. thailandensis showed a markedly decreased bacterial outgrowth from lungs, spleen and blood 24 h after inoculation, compared with infection with B. pseudomallei and the invasion mutant AJ1D8. Forty-eight hours after inoculation, B. thailandensis was no longer detectable. This was consistent with elevated pulmonary cytokine and chemokine concentrations after infection with B. pseudomallei 1026b and AJ1D8, and the absence of these mediators 48 h, but not 24 h, after inoculation with B. thailandensis. Histological examination, however, did show marked pulmonary inflammation in the mice infected with B. thailandensis, corresponding with substantial granulocyte influx and raised myeloperoxidase levels. Survival experiments showed that infection with 1 x 10(3) cfu B. thailandensis was not lethal, whereas inoculation with 1 x 10(6) cfu B. thailandensis was equally lethal as 1 x 10(3) cfu B. pseudomallei 1026b or AJ1D8. These data show that B. pseudomallei AJ1D8 is just as lethal as wild-type B. pseudomallei in an in vivo mouse model, and B. thailandensis is perhaps more virulent than is often recognized.