Lobar pneumonia in rats produced by clinical isolates of Klebsiella pneumoniae.

Transtracheal instillation of clinical isolate Klebsiella pneumoniae serotype 1 (KP1) into the lungs of rats resulted in the production of a characteristic, chronic lobar pneumonia. To further examine this phenomenon, two variants of this organism were employed in this experimental model. These variants differed markedly in capsule size, colony morphology, and in virulence, as determined by mouse lethality tests. The ability of these strains to establish a lobar pneumonia in rats correlated with the virulence of the respective organisms as monitored by intraperitoneal injection in mice. The 50% lethal doses in mice were 4.9 x 10(1) colony-forming units (CFU) for the more virulent KP1 strain (KP1-O) and 1.42 x 10(5) CFU for the less virulent variant (KP1-T). In the rat lung model, marked lung pathology was evident by day 6 with a KP1-O inoculum of 5 x 10(2) CFU, whereas KP1-T caused little or no lung pathology when delivered transtracheally at a concentration of 7 x 10(6) CFU. Two relatively nonvirulent variants of K. pneumoniae serotype 2 were also used in this rat lung model and were found not to produce a lobar pneumonia even when delivered in large doses. These results indicate that a chronic lobar pneumonia can be established in a rat model if the appropriate organism is employed and the virulence of K. pneumoniae injected intraperitoneally into mice is an excellent indicator of an organism's potential to cause lobar pneumonia in rats.