CLINICAL AND EXPERIMENTAL STUDIES OF THE PATHOGENICITY OF ENTEROCOCCUS FAECALIS IN THE URINARY TRACT

Abstract

The pathogenicity of Enterococcus faecalis in the urinary tract was investigated clinically and experimentally.
A clinical study was performed on E. faecalis infection in the urinary tract which had been detected at the Department of Urology, Tokyo University Hospital from July 1980 to June 1984. The annual incidence of E. faecalis isolated from the urinary tract had been increased from 8.5% to 15.4% in this period. Totally, 279 strains of E. faecalis were isolated from 271 patients in the four years. Among these 271 patients, 242 (89.3%) were cases of complicated urinary tract infection, and 88 patients (32.5%) were catheter indwelt patients. The percentage of the patients with a single infection of E. faecalis was 58.7%, and the other patients showed polymicrobial infections. Antimicrobial activity tests showed that most strains of E. faecalis were highly sensitive to penicillin G and ampicillin, but were resistant to new cephems and aminoglycosides. In clinical observations, most patients had no significant symptoms but 20 patients developed fever, pain on micturition and urinary frequency. In these symptomatic cases, E. faecalis was thought to be causative in ten patients.
Experimental pyelonephritis was produced by the transurethral inoculation of the organisms into the rat urinary bladder. Two experimental designs were employed. In the first study, infection was induced by E. faecalis alone. Three to seven days after inoculation, pyelonephritis was found in 5 of 20 kidneys. These five kidneys demonstrated mild inflammatory changes localized along the renal pelvis. However, fourteen days after inoculation, no histological change was found in the kidneys and the number of organisms had decreased in the renal tissues. Then, in order to suppress the host defence mechanism, cyclophosphamide was administrered transperitoneally before the inoculation of E. faecalis. These rats showed a high incidence of pyelonephritis, and more severe lesions, some of which extended into the medulla and cortex, were seen in several kidneys. The renal enterococcal populations persisted at high levels in these kidneys. In the second study, rats were infected with both E. faecalis and Proteus mirabilis. The incidence of pyelonephritis was 79.2%, and large numbers of both strains were still present on the fourteenth day after inoculation. The infected rats were treated with latamoxef beginning three days after the inoculation with the two strains. Histological observations proved that the inflammation continued in the kidneys in which P. mirabilis had disappeared. No remarkable change was seen in the numbers of E. faecalis in the renal tissues after the administration of latamoxef.
The results of the clinical and experimental studies indicate that the pathogenicity of E. faecalis seems to be relatively low in the urinary tract. However, when the host defence mechanism is suppressed or when a polymicrobial infection with virulent strains has occurred, the pathogenicity of E. faecalis may increase.