Linezolid alone and in combination with rifampicin prevents experimental vascular graft infection due to methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis

BACKGROUND: In this report we describe the in vivo antibacterial activity of linezolid in an experimental graft infection model in rats and compare it with teicoplanin. The objective of this study was also to determine the effects of the interaction of linezolid when it was combined with rifampicin and test this effect against strains of methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis. MATERIALS AND METHODS: Graft infections were established in the subcutaneous tissue of 130 Wistar rats by implantation of Dacron grafts followed by a topical inoculation with 2 x 10(7) CFU of clinical isolates of MRSA and MRSE. The study included a control group and six groups for each of the staphylococcal strains: an inoculated group that did not receive any antibiotic prophylaxis, two inoculated groups that received intraperitoneal prophylaxis with teicoplanin or linezolid alone, an inoculated group that received rifampicin-soaked grafts, and two inoculated groups that received a combination prophylaxis consisting of intraperitoneal teicoplanin or linezolid and rifampicin-soaked grafts. RESULTS: There was a reduction in the quantitative bacterial graft cultures in all prophylaxis groups when compared with inoculated control groups. There was not a statistically significant difference between linezolid and teicoplanin prophylaxis groups. The best results were obtained by a combination of rifampicin-soaked grafts with linezolid or teicoplanin. CONCLUSIONS: We found no evidence to suggest that linezolid differs from teicoplanin regarding effectiveness in the prevention of prosthetic vascular graft infection. Linezolid plus rifampicin and teicoplanin plus rifampicin are demonstrated to be valuable prophylactic regimens.     

Temporin A as a prophylactic agent against methicillin sodium-susceptible and methicillin sodium-resistant Staphylococcus epidermidis vascular graft infection

OBJECTIVE: The purpose of this study was to investigate the efficacy of temporin A as a prophylactic agent in a rat model of vascular graft infection from methicillin sodium-susceptible and methicillin sodium-resistant Staphylococcus epidermidis. METHODS: The prospective, randomized, controlled animal study set in a research laboratory in a university hospital used 280 adult male Wistar rats (weight range, 280 to 350 g). Graft infections were established in the back subcutaneous tissue of rats with implantation of 1-cm(2) sterile Dacron grafts followed by topical inoculation with 2 x 10(7) colony-forming units of S epidermidis. The study for each staphylococcal strain included: one control group (no graft contamination), one contaminated group that did not receive any antibiotic prophylaxis, one contaminated group that received temporin A-soaked graft, two contaminated groups that received perioperative intraperitoneal cefazolin (30 mg/kg) or vancomycin hydrochloride prophylaxis (10 mg/kg), and two contaminated groups that received temporin A-soaked graft and perioperative intraperitoneal cefazolin (30 mg/kg) or vancomycin hydrochloride (10 mg/kg) prophylaxis. All grafts were explanted at 7 days after implantation. The main outcome measure was quantification of bacterial contamination. RESULTS: Overall, the perioperative prophylaxis based on soaked grafts was not significantly different to that of parenteral vancomycin hydrochloride. Only the combination between temporin A and vancomycin hydrochloride produced a complete bacterial inhibition for both strains. CONCLUSION: Temporin A showed a similar antibacterial in vitro activity against the two different strains. The in vivo results suggest its potential use in providing prophylaxis to direct graft contamination when used in combination with parenteral vancomycin hydrochloride.     

Quinupristin/dalfopristin bonding in combination with intraperitoneal antibiotics prevent infection of knitted polyester graft material in a subcutaneous rat pouch model infected with resistant Staphylococcus epidermidis.

OBJECTIVE: to investigate the efficacy of quinupristin/dalfopristin in the prevention of prosthetic graft infection in a rat subcutaneous pouch model. METHODS: graft infections were established in the subcutaneous tissue of 140 male Wistar rats by implantation of Dacron prostheses followed by topical inoculation with Staphylococcus epidermidis with intermediate resistance to glycopeptides. The study included one group without contamination, one contaminated group without prophylaxis, one contaminated group that received 50mg/l quinupristin/dalfopristin-soaked graft, one contaminated group that received 10mg/kg intraperitoneal levofloxacin, one contaminated group that received 3mg/kg intraperitoneal doxycycline, and two contaminated groups that received 50mg/l quinupristin/dalfopristin-soaked plus 10mg/kg intraperitoneal levofloxacin or 3mg/kg intraperitoneal doxycycline. Each group included 20 animals. The grafts were removed after 7 days and evaluated by quantitative culture. RESULTS: quinupristin/dalfopristin showed a significantly higher efficacy than levofloxacin and doxycycline, even though quantitative graft cultures for rats that received only quinupristin/dalfopristin-soaked graft showed bacterial growth. Otherwise, the efficacy of levofloxacin was similar to that of doxycycline. Only the group treated with quinupristin/dalfopristin combined with levofloxacin or doxycycline showed no evidence of staphylococcal infection. CONCLUSIONS: quinupristin/dalfopristin as adjunctive topical antibiotic prophylaxis can be useful for the prevention of vascular graft infections caused by staphylococcal strains with high levels of resistance.     

Prophylaxis against Staphylococcus aureus vascular graft infection with mupirocin-soaked, collagen-sealed dacron

A rat model was used to investigate the efficacy of mupirocin in the prevention of vascular prosthetic graft infections. The effect of mupirocin-soaked Dacron was compared with the effect of rifampin-soaked, collagen-sealed Dacron in the rat model of graft infection caused by methicillin-susceptible Staphylococcus aureus and methicillin-resistant S. aureus. Graft infections were established in the back subcutaneous tissue of 195 adult male Wistar rats by implantation of 1-cm(2) Dacron prostheses followed by topical inoculation with 5 x 10(7) colony-forming units of S. aureus. The study included a control group (no graft contamination), two contaminated groups that did not receive any antibiotic prophylaxis, two contaminated groups in which perioperative intraperitoneal amoxicillin clavulanate prophylaxis (50 mg/kg) was administered, four contaminated groups that received mupirocin- or rifampin-soaked graft, and four contaminated groups that received mupirocin- or rifampin-soaked graft and perioperative intraperitoneal amoxicillin clavulanate prophylaxis (50 mg/kg). The grafts were sterilely removed 7 days after implantation and the infection was evaluated by using sonication and quantitative agar culture. Data analysis showed that the efficacy of mupirocin against both strains was significantly different from that of the untreated control. In addition, mupirocin was more effective than rifampin against the methicillin-resistant strain. Finally, only the combination of mupirocin and amoxicillin clavulanate produced complete suppression of growth of all strains.     

Efficacy of Rifampin-Levofloxacin as a Prophylactic Agent in Preventing Staphylococcus epidermidis Graft Infection

OBJECTIVES: To investigate the efficacy of levofloxacin in the prevention of vascular prosthetic graft infection in a rat model. METHODS: Graft infections were established in the subcutaneous tissue of 225 male Wistar rats by implantation of Dacron prostheses followed by topical inoculation with methicillin-susceptible and methicillin-resistant S. epidermidis. The study included a group without contamination, two contaminated groups without prophylaxis, two contaminated groups with intraperitoneal levofloxacin prophylaxis, two contaminated groups with intraperitoneal cefazolin prophylaxis, two contaminated groups with intraperitoneal teicoplanin prophylaxis and six contaminated groups with rifampin-soaked graft and intraperitoneal levofloxacin, cefazolin or teicoplanin prophylaxis. The grafts were removed after 7 days and evaluated by quantitative culture. RESULTS: The efficacy of levofloxacin against the methicillin-susceptible strain was not different to that of cefazolin or teicoplanin. Levofloxacin showed slight less efficacy than teicoplanin against the methicillin-resistant strain. The combination levofloxacin-rifampin demonstrated to be similarly effective to the combination rifampin-teicoplanin and more effective than the combination rifampin-cefazolin against both strains. CONCLUSIONS: Rifampin-levofloxacin combination seems useful for the prevention of late-appearing vascular graft infections caused by S. epidermidis.     

Efficacy of vancomycin, teicoplanin and fusidic acid as prophylactic agents in prevention of vascular graft infection: an experimental study in rat.

OBJECTIVES: To compare the efficacy of a single prophylactic dose of intra-peritoneal vancomycin and teicoplanin with anti-biotic treated Dacron grafts (vancomycin, teicoplanin, 10 or 40% fusidic acid-soaked grafts) in preventing vascular graft infections in a rat model. DESIGN: Prospective, randomized, controlled animal study. MATERIALS AND METHODS: The graft infections were established in the subcutaneous tissues of 80 female Sprague-Dawley rats by the implantation of Dacron prostheses followed by the topical inoculation with methicillin-resistant Staphylococcus aureus. The study groups were as follows: (1) uncontaminated control group, (2) untreated contaminated group, (3) contaminated group with intra-peritoneal vancomycin, (4) contaminated group with intra-peritoneal teicoplanin, (5) contaminated group received vancomycin-soaked Dacron graft, (6) contaminated group received teicoplanin-soaked Dacron graft, (7) contaminated group received 40% fusidic acid-soaked Dacron graft, and (8) contaminated group received 10% fusidic acid-soaked Dacron graft prophylaxis. The grafts were removed after 7 days and evaluated by a quantitative culture analysis. RESULTS: No infection was detected in controls. The untreated contaminated group had a high bacteria count (6.0 x 10(4) CFU/cm2 Dacron graft). Groups that received intra-peritoneal vancomycin or teicoplanin had less bacterial growth (4.8 x 10(3) and 3.9 x 10(3)CFU/cm2 Dacron graft, respectively). Similarly, the group that received 10% fusidic acid-soaked graft showed less bacterial growth (3.6 x 10(3) CFU/cm2 Dacron graft). The groups with vancomycin-, teicoplanin- and 40% fusidic acid-soaked grafts showed no evidence of infection. Statistical analyses demonstrated that intra-peritoneal prophylactic antibiotic treatment was less effective in inhibiting bacterial growth than high concentration antimicrobial-soaking of grafts. CONCLUSION: The use of vancomycin-, teicoplanin- and 40% fusidic acid-soaked grafts was effective in preventing primary prosthetic vascular graft infection.     

RNAIII-inhibiting Peptide and/or Nisin Inhibit Experimental Vascular Graft Infection with Methicillin-susceptible and Methicillin-resistant Staphylococcus epidermidis

OBJECTIVE: To investigate the efficacy of RNAIII-inhibiting peptide (RIP) and nisin as prophylactic agents in a rat model of vascular graft infection. DESIGN: Prospective, randomized, controlled animal study. MATERIALS: Two hundred and twenty adult male Wistar rats. Staphylococcus epidermidis ATCC 12228 and one clinical isolate of methicillin-resistant S. epidermidis. Drugs: RIP, nisin and rifampin. METHODS: Graft infections were established in the dorsal subcutaneous tissue by implantation of 1 cm(2) sterile Dacron grafts, followed by topical bacterial inoculation: grafts were retrieved at 7 days. The study included a control group (without inoculation) and two series composed of five groups for each staphylococcal strain: one contaminated group that did not receive any antibiotic prophylaxis, three contaminated groups that received grafts soaked with 10 mg/l RIP, 10 mg/l nisin, 10 mg/l rifampin, or RIP+nisin. The main outcome measure was the extent of bacterial at graft harvest. RESULTS: The bacterial counts for methicillin-resistant S. epidermidis on explanted grafts were 6.1+/-2.8x10(2), 7.8+/-3.0x10(3) and 5.5+/-2.9x10(4) for RIP, nisin and rifampin, respectively. RIP and nisin used in combination reduced the bacterial count to <10. The results for S. epidermidis were similar. CONCLUSIONS: RIP and nisin could be used in combination to coat medical devices to prevent drug resistant S. epidermidis infections.     

Prevention of prosthetic vascular graft infection by rifampicin impregnation of a protein-sealed Dacron graft in combination with parenteral cephalosporin.

Antibiotic-impregnated prosthetic vascular grafts have been shown to be highly resistant to bacterial contamination in animal models. The aim of this study was to assess if graft infection in an animal model challenged with local bacterial contamination could be reduced further by the use of rifampicin soaking of a protein-sealed Dacron graft in addition to the prophylaxis provided by perioperative intravenous cephalosporin. Of 20 Merino sheep given cefoxitin intravenously before the induction of anaesthesia, ten had a rifampicin treated Dacron graft implanted into the common carotid artery (group 1), and ten received an untreated Dacron graft (group 2). Before wound closure the grafts were inoculated with 1 ml of 10(8) colony forming units per ml of Staphylococcus aureus. After three weeks the grafts were removed and cultured. Group 1 sheep had fewer graft infections (two of 10) compared to group 2 (six of eight survivors), this difference being statistically significant (p = 0.03; Fisher exact test). It is concluded that rifampicin treatment of protein-sealed Dacron grafts combined with intravenous cefoxitin provides more protection from contaminating Staphylococcus aureus than intravenous cefoxitin alone in this animal model.     

Prevention of graft infection by bonding of gentamycin to Dacron prostheses.

To increase the efficacy of perioperative antibiotic prophylaxis in vascular surgery an experimental study including topical application of the gentamicin derivative EMD 46/217 and fibrin sealant as antibiotic carrier to Dacron prostheses was initiated. In vitro treatment of Dacron with gentamicin and fibrin was followed by constant antibiotic release for 3 weeks. In a subsequent animal study Dacron grafts were implanted in the aorta of 10 pigs after direct contamination with Staphylococcus aureus solution. One graft was pretreated with the antibiotic/fibrin compound, a second with the antibiotic alone. Grafts 3 (no pretreatment) and 4 (fibrin alone) served as controls. After 1 week the grafts and their corresponding implantation sites were excised for measurement of antibiotic content and for culture. The antibiotic content of grafts with the antibiotic/fibrin compound was 25.0 +/- 7.2 micrograms/gm wet weight, whereas Dacron pretreated with the antibiotic alone contained no measurable drug amounts except for one specimen (0.5 microgram/gm) (antibiotic/fibrin vs antibiotic, p less than .0005). The corresponding implantation sites to antibiotic/fibrin grafts contained 1.07 +/- 0.54 microgram/gm antibiotic, whereas in only 2/10 implantation sites of antibiotic grafts low antibiotic levels were found (0.05 and 0.2 microgram/gm) (antibiotic/fibrin vs antibiotic, p less than 0.005). All control grafts and 9/10 antibiotic grafts were infected. By contrast, only five were contaminated, and 5 of 10 remained sterile after culture (antibiotic/fibrin vs antibiotic, p less than 0.05). This finding correlates with the antibiotic content in the Dacron. It is concluded that pretreatment of prosthetic Dacron grafts with the antibiotic/fibrin compound results in binding of sufficient amounts of antibiotic for at least 1 week.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prophylactic antibiotics prevent bacterial biofilm graft infection.

Bacterial biofilm graft infection is due to prostheses colonization by Staphylococcus epidermidis, a pathogen frequently recovered from perigraft tissues of man during vascular procedures despite the use of asepsis and prophylactic antibiotics. The effect of preoperative intraperitoneal cefazolin, administered at a standard (15 or 30 mg/kg) and high (120 mg/kg) dose, on the prevention of bacterial biofilm infection was studied in a rat model. Seventy-four Dacron grafts, colonized in vitro with S. epidermidis to produce an adherent biofilm (3.19 +/- 0.71 x 10(7) colony-forming units/cm2 graft), were implanted in the dorsal subcutaneous tissue at 0.5, 2, and 4 hr after antibiotic administration. The study strain was a slime-producing clinical isolate with minimum inhibitory concentration (MIC) of 15-30 micrograms/ml to cefazolin. Subcutaneous tissue antibiotic levels were determined at each time interval. One week after implantation, the concentration of bacteria in the surface biofilm by quantitative agar culture was significantly decreased (P less than 0.05) only for grafts implanted when antibiotic tissue levels were greater than or equal to the MIC of the study strain. The result of no growth by biofilm broth culture was significantly achieved (P less than 0.01) only for grafts implanted 0.5 hr after high dose cefazolin, in which the tissue antibiotic level was above the MIC of the study strain. Antibiotics can markedly reduce the bacteria concentration of a prosthetic surface biofilm. The effectiveness of prophylactic antibiotics on the prevention of graft infection is dependent upon maintaining an adequate antibiotic level in the perigraft tissues for the duration of the procedure.     

Inhibition of vascular prosthetic graft infection using a photocrosslinkable chitosan hydrogel

BACKGROUND: Despite improvements in surgical techniques and antimicrobial therapies, prosthetic aortic graft infections remain a clinical problem. It is well known that chitosan has strong antibacterial activities to a wide variety of bacteria including Staphylococcus aureus, epidermidis and Escherichia coli (E. coli). The antibacterial activity by adhering a photocrosslinkable chitosan hydrogel to Dacron grafts was investigated in vitro and in vivo using a rabbit model. MATERIALS AND METHODS: The photocrosslinkable chitosan hydrogel (50microl) coated grafts (3 x 2mm fragments) were evaluated on a resistance against E. coliin vitro. The graft infections in vivo were also initiated through implantation of a Dacron graft fragment into the infrarenal aorta of a rabbit, followed by a topical inoculation with 10(6) colony-forming units of E. coli. The graft infection was allowed to develop over the following 1 week. RESULTS: The photocrosslinkable chitosan hydrogel-coated grafts exhibited a resistance against E. coliin vitro. Furthermore, application of 0.1ml photocrosslinkable chitosan hydrogel on the Dacron implant in vivo substantially inhibited graft infection with E. coli. CONCLUSIONS: These preliminary results suggested the potential use of a photocrosslinkable chitosan hydrogel in directing graft infection prophylaxis.     

Use of an antibiotic-bonded graft for in situ reconstruction after prosthetic graft infections.

We have developed an infection resistant vascular prosthesis by bonding rifampin to Dacron grafts with the use of a collagen matrix release system. The purpose of this study was to determine the efficacy of this antibiotic-bonded graft in resisting infection after an in situ reconstruction of a previously infected prosthetic bypass. Eighty-three adult mongrel dogs underwent implantation of a 3 cm untreated Dacron graft into the infrarenal aorta. This initial graft was deliberately infected, at the time of operation, with 10(2) organisms of Staphylococcus aureus by direct inoculation. One week later, the dogs were reexplored, the retroperitoneum debrided, and the animals randomized to undergo an end-to-end in situ graft replacement with either one of two types of prosthetic grafts: group I (collagen, n = 36) received control collagen-impregnated knitted Dacron grafts; group II (rifampin, n = 47) received experimental collagen-rifampin-bonded Dacron grafts. Each group of animals was then subdivided to receive one of four treatment protocols: (a) no antibiotic therapy, (b) cephalosporin peritoneal irrigation solution (cefazolin 500 mg/1000 ml) during operation and two doses of cephalosporin (cefazolin, 500 mg intramuscularly) postoperatively, (c) treatment as in protocol group b plus 1 week of cephalosporin (cefazolin, 500 mg intramuscularly, twice daily), and (d) treatment as in protocol group b plus 2 weeks of cephalosporin (cefazolin, 500 mg intramuscularly, twice daily). All grafts were sterilely removed between 3 and 4 weeks after implantation. There were no anastomotic disruptions and all grafts were patent at the time of removal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Laser-induced shock waves enhance sterilization of infected vascular prosthetic grafts

BACKGROUND AND OBJECTIVE: Bacteria that cause infection of vascular prosthetic grafts produce an exopolysaccharide matrix known as biofilm. Growth in biofilms protects the bacteria from leukocytes, antibodies and antimicrobial drugs. Laser-generated shock waves (SW) can disrupt biofilms and increase drug penetration. This study investigates the possibility of increasing antibiotic delivery and sterilization of vascular prosthetic graft. STUDY DESIGN/MATERIALS AND METHODS: Strains of Staphylococcus epidermidis and S. aureus were isolated from infected prosthetic grafts obtained directly from patients. Dacron grafts were inoculated with the isolated bacteria, which were allowed to form adherent bacterial colonies. The colonized grafts underwent the following treatments: (a) antibiotic (vancomycin) alone; (b) antibiotic and SW (c) saline only; and (d) saline and SW. Six hours after treatment, the grafts were sonicated, the effluent was cultured and the colony forming units (CFU) were counted. RESULTS: CFU recovered from control grafts colonized by S. epidermidis were comparable: saline, 3.05 x 10(8) and saline+SW 3.31 x 10(8). The number of S. epidermidis CFU diminished to 7.61 x 10(6) after antibiotic treatment but the combined antibiotic+SW treatment synergistically decreased CFU number to 1.27 x 10(4) (P<0.001). S. aureus showed a higher susceptibility to the antibiotic: 2.26 x 10(6) CFU; antibiotic +SW treatment also had an incremental effect: 8.27 x 10(4) CFU (P<0.001). CONCLUSIONS: This study demonstrates that laser-generated shock waves have no effects alone, but can enhance the effectiveness of antibiotics against bacteria associated with prosthetic vascular graft biofilms, suggesting that this treatment may be of value as adjunctive therapy for prosthetic graft infections.     

Vascular prosthetic infection with Staphylococcus epidermidis: experimental study of pathogenesis and therapy

To determine whether a slime-producing strain of Staphylococcus epidermidis was capable of producing acute infection of a prosthetic vascular graft, 5 cm segments of knitted Dacron were implanted in the infrarenal aortic position of dogs in three groups of animals. These included a control group (no graft contamination), a contaminated group that received a graft soaked in an S. epidermidis solution (untreated group), and a contaminated group in which perioperative antibiotics (three doses of cefamandole, 100 mg/kg) were administered (prophylaxis group). In all the animals reexploration and graft removal were performed at 10 days, with replacement of the defect being achieved with a new uncontaminated graft. These animals underwent exploration a third time after an additional 10-day period. S. epidermidis was not grown from the control animals (n = 7) but was cultured in 44% of the prophylaxis group (n = 9) and 88% of the untreated group (n = 16) during at least one of the operative procedures (chi 2 = 15.859; p less than 0.001). The pathologic features of acute S. epidermidis infection were best seen in the untreated animals and included anastomotic disruption (56%), periaortic hematoma, and lymphadenopathy (94%). Microscopic examination of the aortic tissues revealed extensive infiltrates of leukocytes, macrophages, and foreign body giant cells with aortic necrosis. These features were less prominent in the prophylaxis animals. We conclude that S. epidermidis is capable of producing acute graft infection with perigraft inflammation and anastomotic disruption. The administration of perioperative antibiotics reduced but did not abolish these effects of bacterial contamination of prosthetic vascular grafts.     

Local application of vancomycin for prophylaxis of graft infection: Release of vancomycin from antibiotic-bonded dacron grafts,toxicity in endothelial cell culture,and efficacy against graft infection in an animal model

Methicillin-resistant strains ofStaphylococcus epidermidis cause an increasing number of prosthetic infections. This prompted us to test the uptake of vancomycin in various graft materials in vitro, its influence on graft healing, and its efficacy against graft infection in pigs. Incubation of six different Dacron graft materials in a vancomycin solution (20 gm/L) was performed. Grafts were then placed in plasma, and samples were taken over 72 hours to determine vancomycin levels. Release of vancomycin ranged from 775 µg/cm² to 3691 µg/cm² after 1 hour of incubation. Gelatin-covered grafts increased release of vancomycin fourfold when incubation time was extended to 24 hours; uncovered grafts or the collagen-covered graft did not. Graft healing was not complicated when a vancomycin-bonded, gelatin-impregnated Dacron graft was implanted to replace the common femoral artery in pigs. Four weeks after implantation, histologic examination revealed normal development of neointima and perigraft scar tissue in the vancomycin-treated (n=4) and untreated (n=5) grafts. To test the efficacy of local vancomycin against graft infection, grafts were implanted in the groin of pigs and contaminated with 2 × 10⁷ colony-forming units ofStaphylococcus aureus. Four weeks after implantation, all grafts were infected in the untreated group (n=6), with abscess, nonincorporated graft, and detection ofS. aureus from the graft. In the treatment group (n=6) vancomycin was added to the contaminated grafts. As a carrier for the vancomycin, we used a resorbable gelatin-glycerol foam. All grafts healed without infection. The difference between the treated and untreated groups is statistically significant (p<0.05). We conclude that it may be effective to prevent graft infection with local application of vancomycin if an in situ replacement of infected graft (infected by gram-positive bacteria) is necessary or if there is a high risk of infection by methicillin-resistant staphylococci.     

Systemic and local antibiotic prophylaxis in the prevention of prosthetic vascular graft infection: an experimental study.

AIM: to determine if local, in addition to systemic antibiotic prophylaxis (compared to that provided by systemic prophylaxis alone) provides additional benefit in terms of reducing graft infection. METHODS: gelatin-sealed Dacron grafts were interposed in the infrarenal aorta of 36 mongrels and inoculated with 1 ml of a S. aureus suspension. Group 1 (control group) received no prophylaxis and were inoculated with 1 ml containing 10(9)cfu/ml. Group 2 (n=6) received systemic prophylaxis (1 g cephamandole) and were inoculated with 10(5) cfu/ml (n=3) or 10(7) cfu/ml (n=3). Group 3 received systemic prophylaxis (1 g cephamandole) and were inoculated with 109 cfu/ml. Group 4 received systemic prophylaxis (2 g cephamandole) and were inoculated with 10(9)cfu/ml. In group 5 and 6 grafts were soaked in a rifampicin solution before use and inoculated with 10(9) cfu/ml. Group 5 received no systemic prophylaxis and group 6 received systemic prophylaxis (1 g cephamandole). Grafts were harvested at 2 weeks, and peritonitis, perigraft abscess, anastomotic disruption and graft occlusion recorded. Swabs were taken of the graft, the perigraft tissues and the peritoneal fluid. Graft segments were incubated in broth medium. RESULTS: inoculation with 10(9) cfu/ml ensured graft infection. Systemic or local prophylaxis alone failed to prevent graft infection. Only systemic and local antibiotic prophylaxis provided significant better results than no prophylaxis at all (p<0.01) and local prophylaxis alone (p<0.05). However, total "graft sterility" was not achieved as bacteriologic analysis of the graft segments showed low bacterial counts (<10 bacteria/graft) in 5 of 6 grafts. CONCLUSION: local and systemic prophylaxis provided more protection as demonstrated by the significant decrease in the incidence of "overt" graft infection. Total "graft sterility" cannot be expected in the case of an overwhelming bacterial challenge.     

Experimental examination concerning the efficacy of silver-coated Dacron prostheses in vascular graft infections following subcutaneous implantation in a standardized infection model

It was the aim of the study to examine the efficacy of silver coated prostheses in comparison to Rifampin in impregnated prostheses in the prevention of vascular graft infections. MATERIAL AND METHODS: 24 C3H/HcN mice with a bodyweight between 24 and 27 grams were assigned to four different groups. GROUP I: control gel-sealed Dacron graft (Uni-Graft DV) (6), GROUP II: gel-sealed Dacron graft (Uni-Graft DV) contaminated locally with 2 x 10(7) CFU/1.2 ml Staphylococcus aureus ATCC 25923 (6), GROUP III: silver prosthesis (Intergard Silver) contaminated locally with 2 x 10(7) CFU/0.2 ml Staphylococcus aureus ATCC 25923 (6), GROUP IV: Rifampin impregnated prosthesis contaminated locally with 2 x 10(7) CFU/0.2 ml Staphylococcus aureus ATCC 25923 (6). 14 days after primary operation all animals were euthanized and the grafts harvested. Specimens were examined for signs of infections by histology and microbiology. RESULTS: At termination of the trial on day 14 none of the grafts of group I were contaminated. 6 out of 6 grafts in group II, 6 out of 6 grafts in group III and 1 out of 6 grafts in group IV presented with infected grafts. The use of antimicrobial Rifampin could significantly prevent infection after bacterial challenge in group IV. CONCLUSION: The silver protected prosthesis (Intergard Silver) seems to be not effective in protecting vascular infection in vivo. However, the Rifampin group showed excellent results. In conclusion Rifampin bonded gelatin-sealed Dacron grafts are significantly more resistant to bacteremic infection than are silver/collagen-coated Dacron grafts.     

A rat model of polypropylene graft infection caused by Staphylococcus epidermidis

BACKGROUND: The aim of this study was to constitute a valid graft infection model with Staphylococcus epidermidis in rats. METHODS: Rats were divided into seven groups. In groups 1 and 2, 2 cm x 2 cm polypropylene grafts were incubated with 10(8) c.f.u./mL slime-positive S. epidermidis at 37 degrees C for 2 and 24 h and were then placed subfascially to the groins of rats. In the third group, naive grafts were placed and 0.5 mL of 3 x 10(7) c.f.u. slime-positive S. epidermidis were injected on the inside of the wounds. Rifampicin (30 mg/kg) in group 4 and teicoplanin (20 mg/kg) in group 5 were applied i.p. to rats with 2-h incubated grafts for prophylaxis. The same prophylactic regimens were given to groups 6 and 7 in which rats were incubated for 24 h. At eighth day, rats were killed and wounds were assessed with macroscopic evaluation and cultures. RESULTS: No death occurred in any of the groups. In groups 1 and 2, 100% infection rates were achieved. However, graft infection was detected in only two (20%) of the rats in group 3 (P = 0.001). Prophylactic application of teicoplanin or rifampicin decreased the infection rates significantly in the short-incubation groups. CONCLUSION: Incubation of polypropylene grafts with slime-producing S. epidermidis for 2 and 24 h in the pre-application period achieved the occurrence of a standardized graft infection. Prophylactic use of teicoplanin and rifampicin decreased the infection rates. We propose to use this reproducible and reliable animal model of graft infection in future studies.     

Impact of postantibiotic effect on bacterial adherence to vascular prostheses

The brief exposure of bacteria to high antibiotic concentrations can result in prolonged suppression of bacterial growth termed postantibiotic effect (PAE). A pathogenic Staphylococcus epidermidis strain (RP-62) was exposed to 2X and 6X minimum inhibitory concentrations (MIC) of cefazolin, vancomycin, or rifampin for 1 hr and incubated for 2 to 24 hr in inhibitory-free broth. PAE was defined as the difference in time required for a 1.0 log increase in test (T) vs control (C) cultures (PAE = T-C). PAE was observed only for rifampin: 6 hr at 2X MIC and 8 hr at 6X MIC. Bacterial adherence to Dacron grafts was calculated in PAE vs control cultures by a quantitative culture technique for graft specimens incubated 2 to 24 hr. A demonstrable PAE and its impact on adherence were found to be both antimicrobial and concentration dependent. A significant decrease in staphylococcal adherence to velour-knitted Dacron was demonstrated by rifampin at 2X MIC (P less than 0.05) and 6X MIC (P less than 0.01). This phenomena may be useful in reducing bacterial adherence and colonization of bioprosthetics in the perioperative period. Preoperative suppression of staphylococcal skin flora by high dose antimicrobials can alter the capacity of these organisms to adhere to vascular prosthetic grafts and, if incorporated into antibiotic prophylaxis regimens, may reduce graft colonization.     

Prosthetic vascular conduit in contaminated fields: a new technology to decrease ePTFE infections

Vascular reconstruction using prosthetic materials in contaminated fields can lead to infection, graft loss, and subsequent amputation. We hypothesized that minocycline and rifampin bound to an ePTFE graft using a unique methacrylate technology would provide for resistance from infection and controlled antibiotic elution. Kirby Bauer susceptibility testing was performed on plates overlaid with Staph aureus (SA) and Staph epidermidis (SE) using 6 mm diameter discs of uncoated graft or antibiotic coated graft (ABX). Zones of inhibition (ZIH) were determined after 24 hours. ABX grafts were then placed in a continuous water bath and a recirculating, pulsatile flow device. Susceptibility testing and high performance liquid chromatography with mass spectroscopy was performed to determine graft performance and antibiotic elution rate. ABX grafts had an average ZIH of 35 mm for SA and 44 mm for SE (each P < 0.0001). After the 1 week water bath, the ZIH of the ABX grafts was 23 mm on both the SA and SE plates. The high performance liquid chromatography with mass spectroscopy revealed that after 24 hours, 50 per cent of the antibiotics remained on the graft, and there was a sustained elution for 7 days. Minocycline and rifampin can be bound to ePTFE vascular grafts using a unique methacrylate method. In vitro, the grafts provide a slow elution of antibiotics that provide resistance from infection by SA and SE for up to 2 weeks after graft insertion.