Gram-negative bacteria killed by complement are associated with more severe biliary infections and produce more tumor necrosis factor-alpha in sera.

Abstract

We previously showed that gallstones contain bacteria and that illness severity correlates with bacterial presence. This study examined virulence differences of gram-negative biliary bacteria. Gallstones and bile were cultured, and sera obtained, from 210 patients. Infection severity was staged as: none-no clinical infection; moderate-fever, leukocytosis; or severe-bacteremia, cholangitis, hypotension, abscess, or organ failure. Gram-negative biliary bacteria were tested against patient (and control) serum for complement-mediated bacterial killing and induction of tumor necrosis factor-alpha (TNFalpha) production (using cultured monocytes) with and without sera. These results were correlated with infection severity. A total of 98 (47%) patients had biliary bacteria. Infection severity distribution was none, 29%; moderate, 35%; and severe, 36%. Gram-negative organisms killed by complement were associated with more severe infections as follows: 13%, none; 60%, moderate; and 88%, severe infections (P =.024 and P <.0001, respectively vs none, chi-square test). TNFalpha production in sera increased 182 pg/mL with complement resistant bacteria, but increased 546 pg/mL with bacteria killed by complement (P <.0001, killed vs not killed, Student's t test). E coli and Klebsiella were the most virulent bacterial species. They were cultured from blood, usually killed by complement, and had the largest increase in TNFalpha production in sera. Gram-negative biliary bacteria killed by complement (as opposed to complement-resistant) were associated with more serious biliary infections including bacteremia and induced more TNFalpha production in sera. This suggests a potential role for complement activation and cytokine production in biliary sepsis.