Bacterial interference as a factor in renal infection.

These experiments have investigated the role of bacterial interference as a determinant in the epidemiology of renal infection. Two unrelated strains of Escherichia coli, E. coli 08 and 075, isolated from cases of clinical pyelonephritis were used. Although both strains had identical morphology on conventional media they could be differentiated using genetically stable markers for streptomycin resistance and arabinose utilization. When the 2 strains of E. coli were introduced into the kidney simultaneously by direct inoculation mixed infections were readily established. On the other hand, although both strains of E. coli were equally invasive as individual pathogens, pyelonephritis, when induced using a retrograde challenge with a mixed culture of the same organisms was almost invariably caused by the 08 strain alone. Further experiments showed that bacterial interference occurred within the kidney and determined the pattern of infection. When unilateral renal infections were established with E. coli 08 and the animals subsequently challenged with E. coli 075, it was found that E. coli 075 infection never occurred in kidneys infected with E. coli 08 but infection was established in the contralateral kidney. The experiments have shown that mixed renal infection with E. coli are uncommon even when both pathogens are equally nephropathogenic and are introduced simultaneously into the bladder.