Effect of Operation on Persistence of Inspired Bacteria in the Lungs of Mice

Abstract

Both the bronchogenous and embolic theories of the pathogenesis of postoperative pneumonia command attention at the present time. The rôle played by bacteria already present in the respiratory tract or introduced into the body at the time of operation must be evaluated. It is probable that bacteria may enter the lungs through the air passages, that they may be removed in the lungs by some defense mechanism, and that certain factors may inhibit this defense of the lungs against the inhaled bacteria. Such a conclusion seems to be justified by the work of Stillman, 1 who subjected mice to atmosphere laden with various bacteria; when pneumococci Type I were inspired by normal mice they could later be demonstrated in the lungs, but disappeared within 3 hours. However, when alcoholized mice were subjected to the same experiment pneumococci were found in the lungs as late as 5 days after breathing the contaminated air.

Because of these facts we were led to investigate the disappearance or persistence of inspired microorganisms in the lungs of mice after operation in order to determine whether there was any delay in the removal of bacteria which might be a factor in the pathogenesis of pneumonia.

Method. The general technique was similar to that described by Stillman. 2 Mice were placed in a metal box into which broth cultures of bacteria were sprayed. Some of these mice were normal controls. Others had had operations which consisted of simple laparotomy and closure or simple incision and closure of the skin and muscles of the thorax. These procedures were carried out under novocaine infiltration anesthesia. After having been sprayed for one hour the animals were removed from the spraying chamber. They were sacrificed at definite intervals of time by strangulation and then were immersed in lysol solution for 10 minutes prior to necropsy.