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Biomedical subjects

R F Gagnon

Publications and source records attributed to R F Gagnon.

At least 37 records · Page 2Linked to original sources
PubMed1993

A mouse model of implant-associated infection.

Infections of implanted devices are of increasing frequency and importance, representing a significant limitation of many therapeutic modalities. There are puzzling features of implant-associated infection including the changes in microbial flora, the tendency to chronicity and impaired responses to conservative modes of treatment. The concept of the bacterial biofilm as a shielding mechanism generated by bacteria adherent to artificial surfaces has recently been proposed as an explanation for these features. The biofilm is a term applied to a complex comprising the implant surface, adherent bacteria and a specialized matrix enclosing the bacteria. The matrix of the biofilm is an electrostatically charged glue-like extracellular polymer derived by bacterial enzymes acting on tissue carbohydrates, formed by bacteria when adherent to surfaces. This matrix binds the bacteria to the surface providing a sequestration affording selective protection against harmful elements of the environment, especially mechanisms of host defenses and antimicrobial agents. These biological systems are complex to study because of the dynamic interaction of the microbial variables, host defenses, properties of synthetic materials and the biofilm matrix itself. There is a need for a laboratory model in which the variables can be controlled permitting the researcher to examine the outcomes of modifying one variable at a time in a planned and orderly manner. The practical way to attain this end is the conduct of studies in a stable reproducible animal model of localized biofilm-implant infection. Staphylococcus epidermidis is a representative of the class of microorganisms predominant in implant-associated infection. This paper describes the development of a model utilizing an implant-S. epidermidis-biofilm infection localized to the peritoneal cavity of the mouse. The natural history of the infection has been well documented and is stable in all respects for periods exceeding 3 months. This chronicity is especially advantageous in analyzing the impact of long-term therapeutic modalities and necessary periods of recovery and assessment. A representative example of an experimental use of this model to determine the relative efficacy of antibiotic therapeutic regimes is described, demonstrating its scope and efficacy.

Animals↗
PubMed1993

Vancomycin therapy of experimental peritoneal catheter-associated infection (Staphylococcus epidermidis) in a mouse model.

Catheter-related sepsis, principally with S. epidermidis, remains a main complication of continuous ambulatory peritoneal dialysis (CAPD). A possible reason for the antibiotic resistance often displayed by these infections is the presence of bacteria growing in a protective biofilm on the catheter surface. We developed a reproducible stable model of experimental peritoneal catheter-associated infection with S. epidermidis in the mouse and used this model to examine the therapeutic efficacy of vancomycin. The response to vancomycin treatment given daily (15 mg/kg body weight) for periods from 1-14 days, relating the proportion of successful outcome (sterilization of implant infection) over time, was typical of an S-shaped biological response curve. These results extend our previous observations in vitro of the activity of vancomycin against S. epidermidis biofilm preparations and serve as a rational basis for the experimental evaluation of synergy and antagonism in the treatment of implant-associated infection.

Animals↗
PubMed1993

The effect of peritoneal dialysis solutions on rifampin action against Staphylococcus epidermidis in the fluid and biofilm phases of growth.

Continuous ambulatory peritoneal dialysis (CAPD) catheter-associated infections can be resistant to conservative therapeutic measures despite the apparent susceptibility of the infecting bacterial strains to antibiotics. This chronicity of infection has been ascribed to the development of bacteria on the surfaces of catheter material within a protective polysaccharide shield or matrix. CAPD catheters are unique in being exposed to nonphysiological environments of dialysis fluids of varying physical properties and constitution. We determined that the rate of growth of S. epidermidis in the fluid phase in laboratory media or fresh dialysis solution was significantly influenced by pH. An acid milieu (pH 5) impaired growth compared to a neutral milieu (pH 7). Spent dialysis fluid, however, which had an approximately neutral pH, also impaired bacterial growth, the assumption being that this results from properties of spent fluid unrelated to pH. Using rifampin as the test antibiotic, we noted that its action on S. epidermidis was unaffected by pH or by the differing milieu of fresh and spent fluid. Bacterial growth was arrested regardless of the milieu. We further examined the potential of dialysis fluids to modify the interaction between rifampin and the matrix-enclosed bacteria of standardized S. epidermidis biofilms. We determined that the pH of the dialysis solution was a critical factor influencing the outcome of exposure of the biofilm to rifampin. An acid pH enhanced antibiotic activity, whereas a neutral pH was associated with antibiotic antagonism. These findings have implications in the management of S. epidermidis catheter-associated infections using rifampin.(ABSTRACT TRUNCATED AT 250 WORDS)

Dialysis Solutions↗
PubMed1993

The modulation of rifampin action against Staphylococcus epidermidis biofilms by drug additives to peritoneal dialysis solutions.

Many drugs are added to peritoneal dialysis solutions in continuous ambulatory peritoneal dialysis (CAPD) patients, principally during episodes of peritonitis when antibiotics and nonantibiotic agents are often administered together. To evaluate the influence of nonantibiotic drug additives on antibiotic action, we determined the effect of ten drug additives on the antimicrobial activity of rifampin against S. epidermidis biofilms. None of the additives had any direct effect on biofilm bacteria. While five additives did not affect rifampin action, the other five strongly antagonized rifampin. Insulin and heparin were among these five antagonists. This antagonism suggests that a significant degree of inhibition of antibiotic action may occur by the coadministration of agents in the treatment of peritonitis, particularly in diabetic patients.

Dialysis Solutions↗
PubMed1992

The modulation by fresh and spent peritoneal dialysis fluids of antibiotic kinetics directed against Staphylococcus epidermidis biofilms.

The presence of CAPD peritoneal catheters has an association with S. epidermidis infections which are relatively resistant to antibiotic therapy. This resistance has been ascribed to the formation by the bacteria of a protective matrix on the catheter surface enclosing the bacteria to form a bacterial biofilm. The rate of action of 14 antibiotics on standardized S. epidermidis bacterial biofilms over a 5 day exposure period and the modifying effects of fresh and spent peritoneal dialysis fluids were assayed. There were significant differences in the rates of antibiotic action. Fresh dialysis solution markedly augmented rifampin activity, and to a lesser extent, vancomycin, cloxacillin and teicoplanin but antagonized ciprofloxacin. Spent dialysis fluid generally augmented the activity of antibiotics, notably cloxacillin and cephalothin. Rifampin was bactericidal in both fresh and spent dialysis fluids. Fusidic acid was a poor performer in all tests.

Anti-Bacterial Agents↗
PubMed1992

Effect of lovastatin on hypercholesterolemia in chronic renal failure.

Using a mouse model of chronic renal failure (CRF), the possibility of using lovastatin to treat hypercholesterolemia associated with CRF was examined. Renal failure was induced in 5 week-old, C57BL/6J mice by electrocoagulation of the right kidney surface followed by left nephrectomy 2 weeks later. Five weeks post-nephrectomy, BUN and serum total cholesterol levels were assessed and lovastatin treatment commenced. Upon sacrifice 4 weeks later, BUN, serum total cholesterol levels and hepatic HMG-CoA reductase activity were measured. Results showed that CRF induced significant increases in serum total cholesterol levels and enzyme activity. Treatment with lovastatin led to a dose-dependent reduction in serum total cholesterol levels without affecting the enzyme activity. These results suggest that the hyper-cholesterolemia in CRF is partly due to an increase in de novo cholesterol synthesis in the liver and that the lipid-lowering effect of lovastatin is mediated by an action other than the direct reduction of hepatic HMG-CoA reductase activity.

Animals↗
PubMed1991

Natural history of chronic Staphylococcus epidermidis foreign body infection in a mouse model.

The development and characterization of a mouse model of chronic Staphylococcus epidermidis foreign body infection was done with two clinical isolates that differed in degree of extracellular slime production. Segments of Silastic catheters bearing preformed S. epidermidis biofilms were implanted intraperitoneally, and mice were assessed after 3 and 6 months. Both test strains of S. epidermidis persisted at the implant site through the 6-month follow-up in 80% of the mice, regardless of the degree of slime production. There was no evidence of overt animal morbidity, and microbiologic assessment of other peritoneal sites did not reveal dissemination of bacteria from the infected focus. In comparison with control mice, animals harboring chronic foreign body infection presented marked peripheral neutrophilia and mild anemia.

Animals↗
PubMed1990

Kinetics of Staphylococcus epidermidis clearance from the peritoneal catheter site of renal failure mice following intracatheter inoculation.

A mouse model of surgically induced renal failure harboring a peritoneal catheter implant was utilized to study the response to intracatheter (IC) peritoneal inoculation of 10(6) or 10(8) colony-forming units (CFU) Staphylococcus epidermidis. The kinetics of bacterial clearance from peritoneal structures, including the peritoneal catheter implant, was investigated in renal failure and sham-operated mice. All animals survived experimental challenge with 10(6) CFU; however, microbiological assessments conducted 1 week and 1 month after inoculation revealed that the catheter site of a small number of renal failure mice was persistently colonized. During 1 month following 10(8) CFU IC inoculation, significant animal mortality was observed in renal failure mice (29.4%), while sham-operated controls presented minimal lethality (5.9%). In surviving mice of both groups, the peritoneal catheter site proved to be a reservoir for persisting S. epidermidis, a finding confirmed by scanning electron microscopy. Throughout the study, local and systemic inflammatory responses were comparable in sham-operated and renal failure mice. Nevertheless, 3 and 4 weeks after 10(8) CFU inoculation, S. epidermidis recovery was significantly greater in sham-operated controls. Phenotypic colonial variation was observed in a majority of S. epidermidis isolates, and only in those specimens recovered 2 or more weeks after inoculation. Our results reveal that the peritoneal catheter implant provides a preferred site for persistent bacterial colonization up to 1 month after inoculation.

Animals↗
PubMed1990

Development and progression of uremic changes in the mouse with surgically induced renal failure.

Adult C57BL/6 mice with surgically induced renal failure of 1-15 weeks' duration were examined for the presence of changes caused by the renal failure. Surgery consisted of the electrocoagulation of the entire surface of the right kidney followed 3 weeks later by contralateral nephrectomy. Control groups comprised normal mice as well as sham-operated mice subjected to the right kidney electrocoagulation followed by visualization of the left kidney rather than removal. Results indicate: (1) the surgical procedures to induce renal failure were free of local and systemic infectious complications, (2) moderate to severe degree of renal failure was consistently achieved and remained stable over the study period, (3) significant growth retardation of the renal failure mice was present throughout the study whereas sham-operated mice showed catch-up growth with normal controls by the 3rd week postsurgery, (4) anemia was a very early manifestation of the disease appearing by the 1st week after the induction of renal failure to reach its nadir by the 2nd week; a mild anemia was observed transiently postsurgery in sham-operated mice and ascribed to the renal injury, and (5) renal failure mice were free of visible changes of advanced uremia such as impaired wound healing, bleeding tendency and gross neurological deficits. This new experimental model is proposed as a tool for the study of the pathogenesis and treatment of chronic uremia. While developed to study the immunological disturbances of renal failure, this model could conceivably serve for the study of other abnormalities, anemia in particular.

Anemia↗
PubMed1990

Effect of drug additives to peritoneal dialysis solutions on the viability and function of mouse peritoneal cells.

Peritoneal dialysis (PD) solutions and therapeutic drugs frequently added to PD solutions in clinical practice have been shown to reduce the viability and to impair the function of mouse peritoneal cells. The cytotoxicity of PD solutions, directly related to the dextrose concentration, was more marked towards resident than elicited peritoneal cells. None of the drug additives, heparin and insulin amongst them, were cytotoxic when tested alone or combined with 4.25% PD solution, with the exception of phosphatidylcholine which markedly enhanced the cytotoxicity of the PD solution. While the function of mouse peritoneal macrophages as measured by their hydrogen peroxide production was largely unaffected by PD solutions and drug additives when tested separately, the combination of 4.25% PD solution with any of the drug additives resulted in complete abolition of macrophage respiratory burst. The results should caution against the indiscriminate addition of drugs to PD solutions in dialysis patients.

Animals↗
PubMed1990

Macrophage secretory activity and atherosclerosis during chronic renal failure.

Accelerated atherosclerosis is a serious complication of chronic renal failure (CRF) treated by peritoneal dialysis. In order to study the pathological mechanisms underlying its development we are using an animal model, namely the C57BL/6J mouse, which develops foam cell-type atherosclerotic lesions after surgical induction of CRF. During atherogenesis, monocyte/macrophages move from the circulation to the blood vessel wall, migrate through the endothelium, imbibe lipid and transform into foam cells. Migration through the endothelium involves proteolysis by plasminogen activator (PA) and uptake of lipids involves hydrolysis of lipoproteins by lipoprotein lipase (LPL). Both of these enzymes are secreted by macrophages. In this paper we report the results of studies on the effect of uremia on the secretion of PA and LPL by macrophages from C57BL/6J mice. The secretion of PA and LPL by macrophages from uremic mice (as defined by BUN levels) was higher than that by cells from control animals. Furthermore, whereas macrophage secretion of PA and LPL was significantly less in normal mice fed a high fat diet than in mice fed rodent chow, it was increased above control levels in uremic animals fed the atherogenic diet. We conclude that increased secretion of PA and LPL by macrophages may contribute to atherogenesis in uremic C57BL/6J mice.

Animals↗
PubMed1990

Are peritoneal host defenses really important?

Peritonitis requires a constant focus of infection plus the presence of foreign material, both amply present in the CAPD patient with an indwelling catheter and universal bacterial biofilm. Amazingly the great variety of potentially cytotoxic and immunodiluent agents with which the CAPD peritoneum is confronted on a daily basis does not produce the gross rate of sepsis that might be predicted. Clearly the profound reserve capacity of the peritoneal defense mechanisms, whose functions and interactions are poorly described and understood, contribute to the continuing success of the CAPD modality.

Anti-Bacterial Agents↗
PubMed1989

Response of chronic renal failure mice to peritoneal Staphylococcus epidermidis challenge: impact of repeated peritoneal instillation of dialysis solution.

The effect of repeated instillation of peritoneal dialysis (PD) solution on the peritoneal clearance of a Staphylococcus epidermidis challenge was investigated in a mouse model of surgically induced chronic renal failure. For periods of up to 2 weeks, mice bearing peritoneal catheter implants underwent daily (3 mL) or twice daily (1.5 mL) peritoneal instillation of PD solution (4.25% dextrose) by transcutaneous injection into the catheter lumen. Peritoneal instillation of PD solution did not have a significant influence on the microbiological status of peritoneal structures of renal failure or sham-operated mice following experimental intracatheter S epidermidis inoculation with 10(6) colony-forming units (CFU) (assessment 48 hours after inoculation) or 10(8) CFU (assessment 1 week after inoculation). Microbiological and scanning electron microscopy (SEM) assessments of recovered peritoneal catheters demonstrated that S epidermidis remained associated with the catheter site after other peritoneal structures had become culture negative. SEM of the parietal peritoneum revealed striking morphologic alterations of the mesothelial surface as a consequence of daily PD solution infusion. In the absence of S epidermidis inoculation, repeated instillation of PD solution caused a marked acute peritoneal inflammation without evidence of a concomitant systemic inflammatory response. Furthermore, peritoneal inflammatory response to S epidermidis challenge was augmented by the infusion procedure. Concurrent assessments of inflammatory response and microbiological status revealed that, in spite of heightened peritoneal inflammatory response with peritoneal infusion, bacterial clearance from the catheter site was not improved. Although the animal preparation was limited to peritoneal infusion without drainage, the influence of repeated peritoneal instillation of hyperosmolar, acidic PD solution on the response of mice to S epidermidis challenge was successfully addressed.

Animals↗
PubMed1989

The activity of rifampin and analogs against Staphylococcus epidermidis biofilms in a CAPD environment model.

Rifampin has been noted to exhibit exceptional antimicrobial activity against Staphylococcus epidermidis biofilms as compared to commonly used antibiotics. To further explore this unique effect of rifampin, we evaluated the antimicrobial activity of three commercially available preparations of rifampin, two rifampin analogs (CGP29861 and rifapentine) and the parent compound rifamycin SV. These were tested against standardized S. epidermidis biofilms in various milieus. All six members of the rifamycin group tested demonstrated marked antimicrobial activity but with minor foci of resisters when tested in a peptone water environment. The microscopy of the exposed biofilms showed profound lysis and morphological distortion of the remaining cells. The synergistic elimination of the foci of resistance was achieved in an environment of fresh peritoneal dialysis (PD) solution or by the addition of vancomycin. Neither vancomycin nor fresh PD solution demonstrated significant antimicrobial activity when tested alone with biofilm preparations. Spent PD fluid markedly antagonized the activity of the rifamycins with the exception of the rifampin analogs, an effect primarily of pH. The synergistic effect of vancomycin with the rifamycins was not affected either by protein content or pH, leaving the antagonistic properties of spent PD fluid unexplained. The variable activity of the different members of the rifamycin group underlines the importance of structural differences in determining their interaction with bacterial biofilms. Further precision of the nature of these structural interactions is seen to have considerable potential for therapeutic advancement of catheter-associated sepsis.

Anti-Bacterial Agents↗
PubMed1989

Antibiotic activity against Staphylococcus epidermidis biofilms in dialysis fluids.

Infection associated with medical devices may be resistant to conventional antibiotic therapy. A potential mechanism explaining this variable therapeutic response is the presence of bacterial biofilms on the surface of the prosthetic material which may confer a biologically important protective function to the entrapped bacteria. To study these questions, we prepared standardized biofilms and conventional fluid phase cultures from a panel of ten Staphylococcus epidermidis strains. All ten strains showed in the fluid phase a variable pattern of sensitivity to seven antibiotics but were uniformly sensitive to rifampin and vancomycin. In the biofilm phase they demonstrated solid antibiotic resistance with the variable exception of rifampin. The nature of the milieu was a major variable. Fresh peritoneal dialysis solution enhanced the activity of rifampin but this effect was not present with spent or neutral dialysis fluids.

Bacterial Adhesion↗
PubMed1989

The effects of heparin on rifampin activity against Staphylococcus epidermidis biofilms.

Rifampin shows unique antimicrobial activity against Staphylococcus epidermidis biofilms, although in the in vitro situation rifampin resistance emerges rapidly by the selection of preexisting resistant mutants present in a small number in any large bacterial population. Fresh peritoneal dialysis solution is synergistic with rifampin suppressing rifampin resisters. The antimicrobial properties of rifampin are affected by heparin and protamine in entirely different directions. Heparin blocks the action of rifampin whereas protamine is synergistic producing a total bactericidal outcome. Protamine, when combined with heparin, unexpectedly did not influence the ability of heparin to antagonize rifampin. The mechanisms involved are unknown. The results are discussed in terms of known characteristics of the drugs and of the biofilm surface.

Bacterial Adhesion↗
PubMed1989

The effectiveness of protein supplementation on the nutritional management of patients on CAPD.

Repeated episodes of peritonitis cause malnutrition in CAPD patients because of increased protein loss into the dialysate, a high protein catabolic rate (PCR), and/or a decrease in appetite. The purpose of this study was to investigate whether protein supplements could improve the nutritional status of CAPD patients and secondarily reduce their incidence of peritonitis. Eight patients on CAPD were studied for 2 months as a baseline, then given protein supplementation for 4 months. There was significant (p less than .05) increase in dietary intake and nitrogen balance, with supplementation. The PCR decreased significantly (p less than .05). There was a concomitant decrease in the incidence of new episodes of peritonitis. In conclusion, protein supplementation can improve the catabolic state of CAPD patients.

Aged↗