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F J Silverblatt

Publications and source records attributed to F J Silverblatt.

At least 37 records · Page 2Linked to original sources
PubMed1981

Bacterial adherence to cell surface sugars.

Bacterial adherence to animal cell surfaces is of interest because of its relation to pathogenicity and the insight it provides into determinants of intercellular recognition. The attachment of various strains of Escherichia coli and Salmonella spp. to epithelial cells and phagocytes is inhibited by D-mannose, and the adherence of other bacteria is inhibited by sugars such as L-fucose and D-galactose, suggesting that sugar-mediated adherence is widespread. This intercellular recognition is thought to be mediated by sugar residues (e.g. D-mannose) on the surface of animal cells, to which bacteria attach by a sugar-binding substance on their surface. The nature of the receptors on the animal cells is unknown. There is evidence that E. coli produces lectin-like substances specific for D-mannose, by which it binds to the cells. The most common form of these lectin-like substances appears to be the bacterial pili, which can be reversibly dissociated into their protein subunits. The lectin can also be in the form of bacterial flagella or tightly attached to the outer membrane of the bacteria. Mannose-specific attachment may assist bacteria in colonizing and invading their hosts: methyl alpha-D-mannoside (but not methyl alpha-D-glucoside) significantly reduced infection of the urinary tract of mice by virulent strains of E. coli. Once bacteria penetrate the host their ability to binding sugars on phagocytes may impair their virulence by facilitating phagocytosis. Further studies of the sugar-mediated bacterial adherence by organisms growing in vivo and the structural identification of the host cell receptors may lead to the design of more effective adherence inhibitors that may help to prevent certain bacterial infections.

Adhesiveness↗
PubMed1981

Dissociation and reassembly of Escherichia coli type 1 pili.

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 degrees 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 pilin dimers. About 25% of the protein in this peak bound to a mannan-sepharose column and could be eluted with methyl alpha-D-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 pili.

Escherichia coli↗
PubMed1979

Autoradiography of gentamicin uptake by the rat proximal tubule cell.

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.

Animals↗
PubMed1979

Effect of pili on susceptibility of Escherichia coli to phagocytosis.

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.

Binding Sites↗
PubMed1979

Ultraviolet irradiation disrupts somatic pili structure and function.

Three piliated bacterial species were exposed to ultraviolet light (7 X 10(3) microW/cm2), and the effect of increasing duration of irradiation on the integrity of the somatic pili was quantitated by negative-stain electron microscopy. Heavily piliated Proteus mirabilis became devoid of pili after 20 min of irradiation, but Escherichia coli and Neisseria gonorrhoeae required 40 min for complete depiliation. Partially purified proteus pili underwent progressive loss of structural integrity with increasing doses of irradiation as determined by negative staining and nephelometry, suggesting that ultraviolet light exerted an effect directly on the pili themselves. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that new, small molecular weight fragments appeared after irradiation of purified E. coli pili, suggesting that cleavage of the peptide chain rather than disassociation of pilin monomers accounted for the loss of pili structure. Ultraviolet irradiation also inhibited the ability of piliated bacteria to bind to human buccal epithelial cells. These observations indicate that the ultrastructural integrity and function of pili can be disrupted by ultraviolet light.

Dose-Response Relationship, Radiation↗
PubMed1979

Antipili antibody affords protection against experimental ascending pyelonephritis.

The ability of antipili antibody to prevent ascending urinary tract infection was investigated in rats. One group of rats was immunized passively with rabbit antisera to purified pili and challenged by intravesicular inoculation of 5 x 10(7) 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 equals 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 less than 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 equals 0.01). The mean log titers were 2.13 and 4.54, respectively (P less than 0.01). A third group was passively immunized and challenged with a strain that had different O, K, and H antigens but shared pili antigens. Abscesses occurred in 4 of 15 immunized animals as compared to 13 of 15 controls (P equals 0.001). The mean log titers were 2.37 and 5.63, respectively (P less than 0.005). These results indicate that antipili antibody protects rats against ascending urinary tract infections.

Animals↗
PubMed1979

Binding of 125I-insulin to the isolated glomeruli of rat kidney.

To investigate a possible action of insulin on the glomerulus, the binding 125I-insulin to the isolated glomeruli prepared from rat kidney was examined. When incubated at 22 degrees C, 125I-insulin binding proceeded with time and reached a steady state at 45 min at which time nonspecific binding was less than 25% of total binding. A small fraction of 125I-insulin was degraded during incubation. This binding was specific to insulin in that it was inhibited by unlabeled porcine and beef insulins and to a lesser extent by porcine proinsulin and desalanine-desasparagine insulin, but not by glucagon, parathyroid hormone, vasopressin, calcitonin, and angiotensin II. Increasing concentrations of nonlabeled insulin displaced 125I-insulin binding in a dose-dependent fashion. Scatchard plot of the data was curvilinear consistent with either two classes of receptors with different affinities or a single class of receptors that demonstrate negative cooperativity. The addition of excess nonlabeled insulin to the glomeruli preincubated with 125I-insulin resulted in a rapid dissociation of approximately or equal to 70% of bound 125I-insulin. Insulin decreased the increments in glomerular cyclic AMP levels by epinephrine and by prostaglandin E2, but not those by histamine. These data showed the presence of specific insulin receptors in the glomeruli, and that insulin action may be, at least in part, through modulation of glomerular cyclic AMP concentrations. Such action of insulin may underlie the alteration in glomerular ultrafiltration and the glomerular ultrafiltration and the development of glomerular lesions in diabetes mellitus, a disease in which insulin deficiency or the tissue resistance to insulin exists.

Angiotensin II↗
PubMed1978

Influence of pili on the virulence of Proteus mirabilis in experimental hematogenous pyelonephritis.

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.

Animals↗
PubMed1978

Evaluation of an office method of detecting bacteriuria.

Although catheter-associated UTI continues to be the leading cause of nosocomial infection, epidemiological investigation of catheter use in many hospitals may be precluded by the reluctance of the laboratory to process the large number of urine cultures. We have evaluated the use by Nurse Epidemiologists of Bacturcult tubes for such purposes. The urine of 111 catheterized patients was cultured daily using both the Bacturcult and streak plate method until significant bacteriuria developed (greater than 10(5) colonies/ml). Bacturcult proved as accurate as the conventional technique in detecting bacteriuria. In contrast to previous studies, the daily incidence of infection rose with increasing duration of catheterization. Concomitant antibiotic usage reduced the risk of infection but selected out multi-drug resistant organisms. Older age and procedural errors also increased the risk of infection. The study took 150 hours to complete and cost about $250. It is concluded that Bacturcult is an accurate, simple and relatively inexpensive method of detecting bacteriuria and could be useful for investigating the epidemiology of catheter-associated infections in community hospitals.

Adult↗
PubMed1977

Comparison of the nephrotoxicity of netilmicin and gentamicin in rats.

The nephrotoxicity of netilmicin relative to that of gentamicin was examined in Sprague-Dawley rats. Balance studies were performed on rats injected with netilmicin or gentamicin (50 mg/kg per day for 14 days, 100 mg/kg per day for 8 days, and 150 mg/kg per day for 8 days). Control rats were injected with saline. Both drugs caused a dose-related decrease in urine osmolality and increases in urine volume, water intake, and serum creatinine; however, the magnitude of these changes was significantly less in netilmicin- than in gentamicin-injected rats. Light microscopy of renal tissue revealed less proximal tubular cell necrosis in netilmicin- than in gentamicin-injected rats. There was no significant difference between the renal cortical concentrations of the two drugs. Both drugs stimulated uptake of p-aminohippurate in rat renal cortical slices to the same degree. The data indicate that netilmicin is less nephrotoxic than gentamicin in rats, that the difference in nephrotoxicity cannot be explained by a difference in drug concentration in the renal cortex, and that the ability of aminoglycosides to stimulate the organic acid transport system of proximal tubular cells does not correlate with their nephrotoxic potential.

Animals↗
PubMed1976

Failure of vancomycin treatment in Staphylococcus aureus endocarditis. In vivo and in vitro observations.

In a case of staphylococcal endocarditis, we failed to eradicate Staphylococcus aureus from the blood stream with vancomycin hydrochloride therapy. The strain involved was sensitive to vancomycin by disk diffusion studies but showed a wide disparity between minimal inhibitory and minimal bactericidal concentrations. The lack of a bactericidal effect was probably responsible for the failure of treatment. A synergistic effect was demonstrated for the combination of gentamicin sulfate and methicillin sodium, and the patient was ultimately cured with this combination plus vancomycin. Bactericidal tests are important in choosing an antimicrobial agent for treatment of endocarditis.

Adult↗
PubMed1975

Gentamicin nephrotoxicity: failure of three cephalosporins to potentiate injury in rats.

The possibility that gentamicin and cephalosporin antibiotics may act synergistically to produce nephrotoxicity was evaluated in an experimental model. Necrosis of the proximal tubules occurred when rats were treated with 60 to 120 mg/kg of gentamicin for 5 days but not when 15 to 20 mg/kg per day was given for up to 4 weeks. In all gentamicin-treated animals lysosomes of proximal tubules were increased in size and number and the lumens of many tubules contained a granular deposit. Examination by electron microscopy revealed that the abnormal lysosomes contained membranous whorls. The luminal deposits consisted of similar material; identical bodies were also present in the urinary sediment. To determine whether concurrent administration of a cephalosporin would augment the nephrotoxic potential of gentamicin, additional rats were treated for 4 weeks with daily injections of gentamicin (20 mg/kg) and either cephaloridine, cephalothin, or cefazolin (500 mg/kg). None of the combination regimens produced any more injury than did gentamicin alone.

Animals↗
PubMed1975

Serum disappearance and catabolism of homologous immunoglobulin fragments in rats.

The serum disappearance, metabolic clearance and whole body catabolism of homologous immunoglobulin fragments were studied in rats. The rapid disappearance of Fab fragments from serum in normal animals was no longer present after nephrectomy. In contrast, the serum disappearance curve of Fc fragments was not altered by nephrectomy. The results of three different experiments, however, indicated that similar to Fab fragments, some Fc fragments underwent filtration and degradation in the kidneys. First, the amount of intact Fc fragments excreted in the first day after injection increased from 6% of the injected dose in normal rats to 17% in rats pretreated with sodium maleate. Secondly, nephrectomy eliminated the rapid phase of whole body catabolism of inected Fc fragments. Thirdly, auto-radiographic studies showed localization of Fc fragments in the renal proximal tubule cells in the first 3 hr after injection. An identical localization was seen with Fab fragments. These results support the conclusion that removal from circulation by glomerular filtration and subsequent reabsorption and degradation in proximal tubule cells represent the major mechanism for catabolism of Fab fragments. Although some Fc fragments undergo the same fate, most injected Fc fragments equilibrate with unknown sites where they are possibly bound and made unavailable for filtration in the kidneys.

Animals↗
PubMed1974

Host-parasite interaction in the rat renal pelvis: a possible role for pili in the pathogenesis of pyelonephritis.

The initial interaction between bacteria and the renal pelvic epithelium may determine whether intrarenal infection occurs. A model of retrograde pyelonephritis was employed to study these events by electron microscopy. Female rats received an intravesicular inoculation of a 0.5-ml suspension of Proteus mirabilis containing 10(8) organisms. At intervals after inoculation, the kidneys were fixed by intravascular perfusion and the tissues were prepared for electron microscopy. During the first 24 h, increasing numbers of bacteria were seen to be attached by pili to the renal pelvic epithelial cells. The organism appeared to cross the mucosal barrier by several mechanisms: (a) penetration into the cytoplasm of intact epithelial cells, (b) passage between epithelial cells that were separated by excessive hydrostatic pressure generated during bladder inoculation, (c) passage across necrotic regions of the pelvis, and (d) translocation to the cortex by calicotubular backflow. Whereas at inoculation bacteria possessed pili 40 A in diameter (type III pili) 24 h after reflux, the predominant type of pili measured 70 A in thickness (type IV pili). Repetitive subculture induced a similar transition in vitro. To assess the influence of pili type on virulence in this model, 80 rats were challenged with either type III or type IV pilated organisms and the frequency of rats with cortical abscesses were compared at 1 wk. A significantly greater number of rats inoculated with type IV pilated Proteus manifested macroscopic evidence of infection. These results suggest that pili play a role in the pathogenesis of ascending pyelonephritis.

Animals↗