Comparative pathogenicity of bacteraemic isolates of Aeromonas hydrophila and Klebsiella pneumoniae

Two bacteraemic isolates of Aeromonas hydrophila and Klebsiella pneumoniae, Ah-2743 and Kp-129, respectively, were studied for their relative pathogenicity in comparison with Escherichia coli ATCC 25922. Ah-2743 caused significantly higher serum levels of tumour necrosis factor-α, interleukin (IL)-1β or IL-6 in human whole blood, and higher serum IL-1β and IL-6 levels in infected mice, than did Kp-129 and E. coli ATCC 25922. In addition, in BALB/c mice infected by intraperitoneal inoculation, Ah-2743 caused a higher fatality rate (80%) than did Kp-129 (0%). With intramuscular inoculation, Ah-2743 caused more rapid and intense local accumulation of inflammatory cells than did Kp-129, and myonecrosis was present only in Ah-2743-infected mice. These data indicate that Ah-2743 is more pathogenic than Kp-129 or E. coli ATCC 25922 for BALB/c mice. The cellular components or extracellular factors associated with increased cytokine induction and pathogenicity of A. hydrophila in mice merit further investigation.