A peritonitis model with low mortality and persisting intra-abdominal abscesses

Abstract

Intra-abdominal abscesses are a potential source of recurrent or residual infection after surgical intervention for secondary peritonitis. The development of therapies requires a model which combines low mortality with the formation of persisting abscesses and which is also suitable to study the local inflammatory response. Male Wistar rats were injected intraperitoneally with a mixture of sterile rat faeces, increasing doses of E. coli (10(4)-10(8) cfu/ml) and a fixed dose of B. Fragilis (10(4) cfu/ml). After one h a laparotomy was performed and the peritoneal cavity was debrided. Blood samples were taken under anaesthesia after 6 and 24 h. Abdominal fluid samples were collected (by laparotomy) after 24 and 72 h. The rats were killed after 5 days and the abdomen was inspected for abscesses. Mortality was 90% in the two groups with the highest doses of E. coli and 30% in those with the two lowest doses. In the latter groups all surviving rats but one showed intraabdominal abscesses and bacteremia was encountered frequently, especially after 24 h in the 10(5) cfu E. coli group. The groups receiving 10(4)-10(6) cfu E. coli showed similar plasma IL-6 concentrations after 6 h which were lowered significantly after 24 h. No circulating TNF-alpha was found. Considerable concentrations of TNF-alpha, IL-6, IL-1beta, and IL-10, were found in the peritoneal fluid after 24 h but no differences were observed between the contro groups and those receiving 10(4)-10(6) cfu E. coli. At 72 h cytokine levels were reduced significantly and remained the highest in the animals dosed with 10(6) cfu E. coli. The present model is suitable to study the mechanisms involved in, and prevention of, intra-abdominal abscess formation after surgical treatment of generalized peritonitis.

Figure 1

Survival. Survival in six groups of rats inoculated on day 0 with sterile faeces (controls) or sterile faeces mixed with a fixed dose of B. fragilis and increasing doses of Escherichia coli. ▵, controls; ○, 10⁴ cfu E. coli; ×, 10⁵ cfu E. coli; ♦, 10⁶ cfu E. coli; □, 10⁷ cfu E. coli; ▿, 10⁸ cfu E. coli.

Figure 2

Course of body weight. Daily body weight in four groups of rats inoculated on day 0 with sterile faeces (controls) or sterile faeces mixed with a fixed dose of B. fragilis and increasing doses of Escherichia coli. Average weight is expressed as percentage of the weight at inoculation. ▵, controls; ○, 10⁴ cfu E. coli; ×, 10⁵ cfu E. coli; ♦, 10⁶ cfu E. coli. The results of the groups receiving 10⁷ or 10⁸ cfu E. coli are not shown since only one rat survived in each group.

Figure3

TNF-α and interleukin-6 (IL-6) in peritoneal fluid. TNF-α (A) and IL-6 (B) concentrations in peritoneal fluid collected at 24 and 72 h after inoculation in the control group and the groups receiving 10⁴, 10⁵ or 10⁶ cfu Escherichia coli. Data are depicted as medians with 25–75 percentiles in boxes and 5–95 percentiles represented as vertical lines. *P < 0.05.

Figure 4

Interleukin (IL)-1β and IL-10 in peritoneal fluid. IL-1β (A) and IL-10 (B) concentrations in peritoneal fluid collected at 24 and 72 h after inoculation in the control group and the groups receiving 10⁴, 10⁵ or 10⁶ cfu E. coli. Data are depicted as medians with 25–75 percentiles in boxes and 5–95 percentiles represented as vertical lines. *P < 0.05.

Figure 5

Interleukin-6 (IL-6) in plasma. IL-6 concentrations in plasma collected at 6 and 24 h after inoculation in the control group and the groups receiving 10⁴, 10⁵ or 10⁶ cfu Escherichia coli. Data are depicted as medians with 25–75 percentiles in boxes and 5–95 percentiles represented as vertical lines. *P < 0.01.