Rats were injected with 25 microCi (14.2 microgram) of tritiated gentamicin and were killed 10 min, 1 hour, or 24 hours after the injection. Renal tissue was preserved by intravascular perfusion of a glutaraldehyde-containing solution. In a preliminary experiment, glutaraldehyde was found to fix gentamicin to bovine serum albumin, and this property probably accounted for the negligible loss of label during specimen preparation. By light microscopy, gentamicin appeared to be confined almost entirely to the proximal tubules. Autoradiographic grains appeared initially over the apical cytoplasm of the proximal tubule cells and, with time, moved progressively into the interior of the cell. Electron-microscopy revealed that the grains were associated with apical vesicles at 10 min and lysosomes at 1 and 24 hours. The specificity of labeling was confirmed by quantitative grain analysis. These results indicate that gentamicin is transported into the proximal tubule cell by pinocytosis and becomes sequestered in lysosomes. This process may account for the accumulation of myeloid bodies in the proximal tubule lysosomes of gentamicin-treated rats, but whether this mechanism contributes the nephrotoxicity of this drug cannot be ascertained at this time.

The degree of piliation of 20 clinical isolates of Escherichia coli was correlated with their susceptibility to phagocytosis by human polymorphonuclear leukocytes. Piliation was quantitated by negative staining, and phagocytosis was quantitated by a monolayer technique. Ingestion was confirmed by electron microscopy. In the absence of source of opsonins, there was a positive correlation between the degree of piliation and susceptibility to phagocytosis (y = 0.83x + 19.58; correlation coefficient = 0.65; P < 0.01). Heavily piliated strains were no longer phagocytized after their pili were removed by ultraviolet irradiation. Phagocytosis was reduced 75% in the presence of 0.1 M D-mannose, an agent which competitively inhibits binding of pili to cell surfaces. L-Mannose, D-glucose, and D-galactose were much less inhibitory. The viability of piliated organisms was reduced by 1 log after 1 h of incubation with polymorphonuclear leukocytes. Addition of 10% fresh human serum increased both the rate and completeness of killing. These observations suggest that polymorphonuclear leukocytes may interact with the pili of E. coli to promote phagocytosis. This phenomenon may have clinical relevance in situations where normal opsonic activity is poor, such as the renal medulla.

Escherichia coli type 1 pili, which mediate the mannose-sensitive adherence of the bacterium to eucaryotic cells, are comprised of very stable arrays of pilin protein subunits (molecular weight, approximately 17,000). Previous methods for the dissociation of pili caused their irreversible denaturation. We have found that incubation of pili in saturated guanidine hydrochloride at 37°C led to their complete dissociation, as evidenced by nephelometry and electron microscopy. Gel chromatography of the dissociated pili on a Sepharose CL-6B column in the presence of saturated guanidine hydrochloride yielded a single protein peak with a molecular weight corresponding to that of pilin. Dialysis of this peak against 5 mM tris(hydroxymethyl)aminomethane hydrochloride (pH 8.0) and rechromatography in the same buffer afforded a major protein peak, probably consisting of piln dimers. About 25% of the protein in this peak bound to a mannan-Sepharose column and could be eluted with methyl aD -mannoside. The pilin dimer gave a single protein band upon polyacrylamide gel electrophoresis in the presence of 0.1% sodium dodecyl sulfate (molecular weight, 16,600) or 10 M urea and penetrated completely into 7% gels in the absence of denaturants. Reassembly of the pilin dimers into pili was achieved upon dialysis against the tris(hydroxymethyl)aminomethane buffer containing 5 mM MgCl2, as observed by electron microscopy. Thus, the conditions used allow renaturation of the dissociated subunits and may aid in further studies of the structure-function relationship of

The ability of heavily and lightly piliated Proteus mirabilis to infect the renal parenchyma was compared in a model of hematogenous pyelonephritis. Cortical abscesses occurred in 13 of 24 rats injected with lightly piliated P. mirabilis but in none of 24 rats challenged with heavily piliated organisms (P less than 0.001). Lightly and heavily piliated organisms were cleared from the vasculature equally rapidly and were also delivered to the kidney in equal numbers. During the first 24 hr, however, titers of the lightly piliated organisms in the kidney increased by 4 logs, whereas the heavily piliated P. mirabilis were virtually all eliminated. Pili are believed to mediate attachment to cell surfaces, and heavy piliation has been correlated with enhanced virulence when P. mirabilis invades the kidney across the pelvic mucosa. The results in this study suggest, however, that pili may adversely affect bacterial survival within the renal parenchyma.

A B S T R A C T The ability of antipili antibody to prevent ascending urinary tract infection was investigated in rats. One group ofrats was immunized passively with rabbit antisera to purified pili and challenged by intravesicular inoculation of 5 x 107 heavily piliated Escherichia coli. Only 2 of 14 immunized animals developed cortical abscesses as compared to 13 of 15 control rats given normal rabbit serum (P = 0.0001). The mean log titer of bacteria in the kidneys of the immunized rats was 0.85 vs. 6.08 in the controls (P < 0.005). A second group was actively immunized with pili. 3 of 16 immunized animals became infected as compared to 10 of 15 controls (P = 0.01). The mean log titers were 2.13 and 4.54, respectively (P < 0.01). A third group was passively immunized and challenged with a strain that had different 0, K, and H antigens but shared pili antigens. Abscesses occurred in 4 of 15 immunized animals as compared to 13 of 15 controls (P = 0.001). The mean log titers were 2.37 and 5.63, respectively (P < 0.005). These results indicate that antipili antibody protects rats against ascending urinary tract infection.