Behavioral and physiologic effects of inapparent wound infection in rats

There is a common notion that rats are resistant to postoperative wound infection because many recover from surgery performed under nonsterile conditions. As a result, nonaseptic surgical techniques are used commonly in rat surgery. Our aim was to determine if these techniques cause wound infection and, if so, whether or not the infection, inapparent to casual observation, creates measurable changes in rat physiology and behavior. Rats subjected to craniotomies or laparotomies and inoculated with 10(8) Staphylococcus aureus or Pseudomonas aeruginosa or sterile saline were tested for open-field activity, freezing behavior, home-cage behavior score, and wheel-running activity. Physiologic indices included lactate dehydrogenase, blood glucose, plasma fibrinogen, complete blood counts, wound bacterial counts and histology scores, body temperature, and body weight. Although no clinical signs were detected by postoperative observation, rats inoculated with bacteria were significantly less active in the open field and the duration of freezing behavior was shorter. Plasma fibrinogen, serum glucose, total white blood cell counts, and wound histology scores were significantly altered in the bacteria-inoculated rats. These findings underscore the need for sterile techniques in rat surgery to avoid confounding experimental data.