OBJECTIVETo reproduce a reliable rat model of burn with infection for the study of prevention and treatment of infected wound.

METHODS(1) Electrical burn producing apparatus equipped with constant temperature (80°C) and pressure (0.5 kg) was used to reproduce burn injury (with area of 4.5 cm(2)) on both sides of the back in 50 SD rats for different duration (4, 6, 8, 10, 12 s), with 10 rats for each burn duration. On post burn day (PBD) 1, gross condition of wounds was observed with naked eyes. Wounds on the left side were used to observe healing time. The wounds on the right side were used for histological observation to determine the depth of injury, and they were classified into superficial and deep partial-thickness injury. (2) Another 36 SD rats were divided into A (inflicted with superficial partial-thickness burn, n = 18) and B (inflicted with deep partial-thickness burn, n = 18) groups according to the random number table. Rats in both groups were treated in accordance with method of preliminary experiment. Immediately after burn, 0.1 mL of liquid containing 1 × 10(9), 1 × 10(7), 1 × 10(5) CFU Pseudomonas aeruginosa (PA) ATCC 27853 was respectively inoculated to the wounds on one side (with 6 rats for each amount), while the wounds on the other side were treated with the same volume of normal saline as control. Inflammatory reaction of wounds was examined with HE staining on post inoculation day (PID) 1. On PID 1, 2, 3, 5, 7, and 14, the number of subeschar bacteria was respectively counted and the bacteria were identified with Gram stain and biochemical reaction. Wound healing time was recorded. Data were processed with t test.

RESULTS(1) Burn for 6, 8 s was respectively identified as injury time resulting in superficial or deep partial-thickness injury according to histological observation and wound healing time. (2) Obvious inflammatory cell infiltration was observed in the wounds in B group which were inoculated with 1 × 10(7), 1 × 10(9) CFU PA, and the infiltration was less marked in A group with inoculation of 1 × 10(9) CFU PA. (3) The bacteria isolated from wounds of A and B groups was identified as PA. The subeschar bacteria count within PID 14 in A group, in which different amount of PA was inoculated, was mostly less than 1 × 10(5) CFU/g of tissue, while that in B group in which 1 × 10(9) CFU PA was inoculated was more than 1 × 10(5) CFU/g of tissue. (4) There was no obvious difference in wound healing time between wounds inoculated with different amount of PA and wounds treated with normal saline in A group (with t value respectively 1.26, 0.29, 1.07, P values all above 0.05). Wound healing time of wounds in B group, in which 1 × 10(9) CFU PA was inoculated, was longer as compared with that treated with normal saline [(22.5 ± 1.0) d vs. (19.4 ± 1.6) d, t = 2.73, P < 0.05].

CONCLUSIONSIn rat, deep partial-thickness burn wound inoculated with 1 × 10(9) CFU PA ATCC 27853 is a reliable model with high reproducibility for the study of infection of burn wound.