In vitro infectability of prosthetic mesh by methicillin-resistant Staphylococcus aureus

Although mesh use is important for effective herniorrhaphy in adults, prosthetic infections can cause serious morbidity. Bacterial adherence to the mesh is a known precursor to prosthetic infection. We compared the ability of common mesh prosthetics to resist bacterial adherence. The meshes studied included polypropylene (Marlex^®), expanded polytetrafluoroethylene (PTFE) with and without silver chlorhexidine coating (DualMesh Plus^® and Dualmesh^®) composite meshes (Composix E/X^®, Proceed^?, and Parietex Composite^®) and lightweight polypropylene meshes (TiMesh^®, Ultrapro^®, and Vypro^®). Fifteen samples of each mesh type were individually inoculated with a suspension of 10⁸ methicillin-resistant Staphylococcus aureus (MRSA) in tryptic soy broth. After incubation at 37°C for 1 h, the mesh pieces were then removed and serially washed. The colony-forming units (CFU) of MRSA present in the initial inoculum, at the end of the 1-h warm-water bath (broth count), and the pooled washes (wash count), were determined using serial dilutions and spot plating. The bacteria not accounted for in the broth or wash counts were considered adhered to the mesh. Samples of each mesh type were also analyzed using scanning electron microscopy (SEM). Data are presented as the mean percentage adherence with ANOVA and Tukey’s test used to determine significance (P<0.05). The DualMesh Plus^® mesh had no detectable MRSA in the broth or the pooled wash samples. Dualmesh^® had less adherence compared with Marlex^®, Proceed^?, and Vypro^® (P<0.05). Conversely, Vypro^® had a statistically higher adherence (96%, P<0.05) as compared to TiMesh^®, Ultrapro^®, Composix E/X^®, and Parietex Composite^®. SEM confirmed bacterial adherence to all the mesh types except DualMesh Plus^®. The ability of a biomaterial to resist infection has an important clinical significance. DualMesh Plus^®, due to its antimicrobial coating, is the only mesh type of the nine tested that demonstrated a bactericidal property. Standard PTFE (Dualmesh^®) also had less bacterial adherence. Vypro^® demonstrated an increase in bacterial adherence; this was possibly due to the multifilament polyglactin 910 weaved within the prolene component of the mesh.     

Experimental colonization of a polyester vascular graft with Staphylococcus aureus: a quantitative and morphologic study

Colonization of a polyester (Dacron) vascular graft by Staphylococcus aureus 209P-R was studied. Twenty-five dogs had thoracoabdominal aortic bypass. After intervals of 2 hours (three dogs), 8 days (five dogs), 1 month (six dogs), 2 months (six dogs), or 6 months (five dogs), a bacteremic challenge was produced by intravenous injection of 6 x 10(8) colony-forming units of S. aureus. Two hours later grafts were removed and cut into 10 fragments, each submitted to bacterial counts and scanning electron microscopic studies. Results of bacterial counts were expressed in colony-forming units (CFU) per square centimeter of graft segment (median [lower to upper quartiles]). Normal canine aortas (n = 2) used as controls trapped no bacteria. Colonization of Dacron grafts varied according to the duration of graft function (p less than 0.01): after 2 hours, 4416.5 CFU (1158 to 9073 CFU); after 8 days, 1515 CFU (963 to 2893 CFU); after 1 month, 199 CFU (86 to 538 CFU); after 2 months, 615 CFU (243 to 1407 CFU); and after 6 months, 1 CFU (1 to 5 CFU). Heavily colonized fragments were observed for duration of graft function of 2 months or less, whereas at 6 months all the fragments trapped fewer than 50 CFU/cm2 of graft segment. Scanning electron microscopy showed that colonization was closely associated with healing. Staphylococcal entrapment was related to the amount of fibrin deposits, which were especially abundant where the thrombotic matrix was unorganized and on bare polyester filaments. Graft colonization is especially to be feared in the first weeks after graft implantation, an observation which may help to define guidelines for preventing hematogenous vascular graft infection.     

Prevention of Staphylococcus aureus graft infection by a new gelatin-sealed vascular graft prebonded with antibiotics

OBJECTIVE: The aim of this study was to evaluate the efficacy of a new gelatin-sealed graft prebonded with two antibiotics in resisting infection with Staphylococcus aureus (S aureus) A980142 after direct bacterial application in a dog model. METHODS: Twelve 6.0-mm polyester grafts were implanted in dogs end-to-end into the infrarenal aorta. The dogs were divided into two groups. A test group (n = 6) received experimental antibiotic-bonded gelatin-sealed knitted polyester grafts, loaded with two antibiotics, rifampin and tobramycin. A control group (n = 6) received commercial gelatin-sealed knitted polyester grafts. At the end of graft implantation, 50 mul of a 1.8 x 10(4) CFU/mL S aureus solution were instilled directly over the graft. One week after implantation, grafts were harvested with sterile technique. Quantitative cultures were obtained from all the harvested grafts. The results were expressed as colony-forming units per cm(2) of surface of the graft. Bacteriological study was also performed on various tissue samples. The chi(2) test was used to compare the culture proven infection of control and antibiotics-bonded grafts. RESULTS: Mean inoculum size was similar in the two groups of dogs. Five of the six control grafts grew S aureus A980142 at the time of graft removal, whereas none of the six antibiotic-bonded gelatin-sealed grafts were infected (P = .0192). None of the organ samples were infected in the group implanted with antibiotic-bonded grafts, whereas 15/34 samples grew S. aureus in the control group. CONCLUSION: These results indicate that this gelatin sealed graft prebonded with two antibiotics resists infection caused by S aureus graft contamination in a dog model.     

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.     

Improved management of infrainguinal bypass graft infection with methicillin-resistant Staphylococcus aureus

BACKGROUND: There is considerable debate over the management of infected infrainguinal grafts. This report describes recent experience in this field and documents the change in clinical practice needed to deal with methicillin-resistant Staphylococcus aureus (MRSA). METHODS: All infected infrainguinal grafts between January 1991 and July 1997 were reviewed. In the light of the findings, clinical practice was modified considerably. A further 1 year was audited prospectively up to August 1998. RESULTS: Twenty-six patients were treated for 27 infrainguinal graft infections (25 prosthetic, two vein). Twenty were treated by complete graft excision as the initial therapy; graft preservation was attempted in six patients. Before 1995, the infecting organisms were predominantly Pseudomonas aeruginosa or methicillin-sensitive staphylococci. Subsequently all 14 patients treated up to 1997 had infection with MRSA. The overall amputation rate was 17 of 26; ten amputations were in patients with MRSA. Four patients died, all with MRSA sepsis. As a result of this experience a policy of complete isolation was adopted for all patients infected with MRSA. In the 12 months since this policy was introduced, 77 infrainguinal grafts (61 vein, 16 prosthetic) have been inserted. Two grafts (3 per cent) have become infected, necessitating graft excision and amputation. CONCLUSION: MRSA infection of an infrainguinal graft is a serious complication with high associated amputation and mortality rates. Isolation and barrier nursing appeared to contain the problem.     

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.     

Twenty years of countermeasures against postoperative methicillin-resistant Staphylococcus aureus infections

Purpose

A total of 7345 cases of digestive organ surgery were investigated over the course of 20 years.

Methods

Owing to the increasing incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections, we classified our countermeasures into periods A (September 1987 to February 1990), B (March 1990 to February 1997), C (March 1997 to February 1999), D (March 1999 to October 2004), and E (November 2004 to August 2007), and compared the number of infections during these periods. In period B, cefazolin and cefotiam were administered as prophylaxes. The treatment continued for 4 days, including the day of surgery. The patients undergoing endotracheal intubation or tracheotomy were managed with nonscreening pre-emptive isolation and cohorting (NSPEI&;C), regardless of whether MRSA was present. However, NSPEI&;C was halted in period C, but it was thereafter implemented again, and prophylactic antibiotics were administered only on the day of surgery during period D. In period E, prophylactic antibiotics were administered for 3 days.

Results

In period A, MRSA was contracted in 4.1% (34/833) of patients. In period B, the MRSA isolation rate decreased to 0.3% (8/2722). In period C, the MRSA isolation rate increased to 3.4% (23/681). In period D, the MRSA isolation rate fell to 2.2% (40/1807). In period E, MRSA isolation cases significantly decreased to 0.4% (5/1302; P < 0.002 vs period D).

Conclusion

The comprehensive management, selection of prophylactic antibiotics, and NSPEI&;C were all considered to be effective.     

Dealing with biofilms of Pseudomonas aeruginosa and Staphylococcus aureus: In vitro evaluation of a novel aerosol formulation of silver sulfadiazine

The risk of infection of skin and soft tissue chronic wounds by gram-negative and gram-positive pathogens growing in biofilms is a major health-care concern. In this study we test a formulation of silver sulfadiazine, vitamin A and lidocaine (AF-SSD) for aerosol administration against biofilms of Pseudomonas aeruginosa and biofilms of methicillin-resistant (MRSA) and methicillin-sensitive (MSSA) strains of Staphylococcus aureus. The aerosol allows the administration of AF-SSD without the direct contact with the wound and avoids contamination of the product after reiterative usage. We evaluated in vitro the anti-biofilm activity of AF-SSD by carrying out different technical approaches such as resazurin assays to measure metabolic activity/viability, crystal violet staining assays to determine biofilm biomass, counting of CFUs and live/dead staining for confocal microscopy analysis. AF-SSD clearly affected biofilm viability, biomass and structure, in the three bacterial strains tested. AF-SSD displayed a strong anti-biofilm effect, showing total bactericidal activity on biofilms of P. aeruginosa at a 400-fold dilution of the product, and after a 100-fold and 10-fold dilution for MRSA and MSSA, respectively. Considering the benefits of aerosol administration, our results support this kind of formulation as a potential improvement over conventional treatments with silver sulfadiazine.     

The acquisition of methicillin-resistant Staphylococcus aureus (MRSA) in vascular patients.

OBJECTIVE: the aim of this study was to establish at which point during a hospital admission MRSA acquisition occurs in vascular patients. METHOD: a consecutive series of 100 patients undergoing arterial surgery were screened for MRSA carriage on admission to hospital, on exit from theatre, on discharge from ITU, weekly whilst an inpatient and on hospital discharge. Screening was with moistened swabs from nose, throat, perineum and open wounds that were pooled for microbiological culture. RESULTS: four patients (4%) screened positive for MRSA on admission to hospital. Of the remaining 96, 16 (17%) acquired MRSA during their hospital stay as follows: exit from theatre, one; exit from ITU, six; on the ward postoperatively, nine. Comparing MRSA acquisition (n=16) with non acquisition (n = 80) the following characteristics were noted, length of stay 16 (4-66) vs 7 (2-50) days (Mann-Whitney p < 0.001); admission to ITU 13/16 vs 46/80 (Fishers chi-squared p = 0.10); length of ITU stay 3 (1-20) vs 3 (1-14) days (Mann-Whitney p = 0.41). Frequent hospital attendance, age, emergency admission, diabetes or renal failure were not commoner in those with MRSA acquisition. CONCLUSIONS: these data indicate that 4% of patients undergoing arterial surgery are pre-existing carriers of MRSA. Length of hospital stay is the single most important determinant of MRSA acquisition.     

Evaluating antimicrobial efficacy of new commercially available silver dressings

Prevention and treatment of bacterial colonised/infected wounds are critical. Many commercially available silver dressings claim broad‐spectrum bactericidal activity over days and are indicated for serious conditions including burns and ulcers. However, there is no peer‐reviewed literature available for many newer dressings. This study compared the activity of some of these dressings. Six silver‐containing dressings were compared using log reduction, silver release and corrected zone of inhibition assays. Only the nanocrystalline silver dressing was bactericidal against Staphylococcus aureus, and the only other dressing that produced any log reduction was a silver collagen matrix dressing. These two dressings and a silver alginate dressing produced zones of inhibition, although the collagen matrix and alginate dressings had decreasing zone sizes over time, and the latter liquefied after five transfers. The remaining dressings (two ionic silver foam dressings and a silver sulphate dressing) did not produce zones of inhibition. For the foam, alginate and collagen matrix dressings, antimicrobial activity was related to silver release. The silver sulphate dressing released large quantities of silver, but only through the dressing edges, as the wound‐contacting surface appeared to be hydrophobic. The results of this study emphasise the importance of confirming product claims regarding silver dressing efficacy.     

In vitro study of the antimicrobial properties of a silver ion-releasing polyurethane foam

Introduction

The antimicrobial properties of a silver ion (Ag+)-releasing polyurethane foam were evaluated using different microorganisms. The diffusion of Ag+ from the medium, as well as any possible cytotoxicity on human cells, was also studied.

Material and methods

Silver release from V.A.C. GranuFoam Silver^® was assessed by using inductively coupled plasma mass spectrometry (ICP-MS). An in vitro experimental study was designed to evaluate the bactericide capacity using lethal dose curves on A. baumannii, P. aeruginosa, S. maltophilia, K. pneumoniae, E. coli, P. mirabilis, methicillin resistant S. aureus, E. faecium, S. pyogenes and C. minutissimum. A cytotoxicity study was also performed on human fibroblasts.

Results

The silver release showed an exponential curve with a stable meseta phase after 3 hours, with levels of 0.22-0.24 mg/l. A reduction of 99.9% of all the gram-negatives was achieved at 3 hours. The reduction was greater than 99% at 2 hours in S. pyogenes and C. minutissimum, at 6 h in S. aureus and at 14 h in E. faecium. In an in vivo simulation model, these reductions were achieved in 6 hours in the gram negatives and 24 h in the gram positives. The silver concentrations were no cytotoxic to human fibroblasts, with no differences being observed between the cells exposed to Ag+ and the controls (p = .7)

Conclusion

V.A.C. Granufoam Silver^® releases bactericide concentrations of Ag+ that did not damage human fibroblasts. It appears to be a good alternative for the control and prevention of local infections.     

Experimental treatment of vascular graft infection due to Staphylococcus epidermidis by in situ replacement with a rifampin-bonded polyester graft

In situ prosthetic graft replacement (ISPGR) of an infected prosthesis raises the risk of recurrent infection in the new graft, especially in cases involving drug-resistant microorganisms. The purpose of this animal study was to evaluate in situ replacement of a vascular graft infected by a highly rifampin-resistant strain of Staphylococcus epidermidis with the use of a rifampin-bonded polyester graft. Antibiotic bonding was obtained by soaking grafts in a high dose of rifampin solution (60 mg/mL). The infrarenal abdominal aorta of 20 dogs was replaced using a polyester prosthesis infected with a highly rifampin-resistant strain of Staphylococcus epidermidis. One week later, the 18 surviving animals were randomized into three groups. Group I (n = 6) did not undergo reoperation. Group II (n = 6) underwent ISPGR using a rifampin-bonded prosthesis. Group III (n = 6) underwent ISPGR using an untreated prosthesis. All surviving animals were killed 28 days after the first procedure. Infectious signs were noted and bacteriological study was carried out on explanted prostheses and various tissue samples. The findings of this experimental study show that soaking a polyester prosthesis in a high-dose rifampin solution can prevent reinfection after in situ replacement of a prosthesis infected by a highly rifampin-resistant Staphylococcus epidermidis.     

Daptomycin for methicillin-resistant Staphylococcus aureus infections of the spine

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) infection is increasingly common. Treatment with vancomycin-based therapy is often unsuccessful. Daptomycin is a relatively new lipopeptide antibiotic with potent activity against MRSA.PurposeTo describe the successful management of MRSA infection involving the spine.Study designTwo case reports of MRSA infection, one involving epidural and lumbar subdural abscesses, the other with osteomyelitis and discitis.MethodsTwo cases are described, one with lumbar epidural and subdural abscesses and the other with osteomyelitis and discitis of the spine. Switching from vancomycin to daptomycin plus rifampin-based therapy resulted in patient improvement that allowed discharge from the hospital.ResultsBoth patients recovered fully from their infection.ConclusionsDaptomycin is a safe and effective option for the treatment of MRSA infection involving the spine.     

Clinical experiences of a new vascular graft prosthesis fabricated from ultrafine polyester fiber (Toray graft)]

A new low porous vascular prosthesis made of a textile of ultra-fine fiber was used clinically in ten patients for whom replacement of the ascending and/or arch aorta were performed. There were no operative deaths after initial operations, but one patient died after a second operation in which replacement of the thoraco-abdominal aorta was performed. Nine survived patients are well for 50 days to 10 months postoperatively. The new vascular graft prosthesis was very soft and pliable in clinical use, and the surgical needle penetrates easily the prosthesis. Although the new graft prosthesis can be used without preclotting under full heparinization, porosity of the graft, 100 ml/min/cm, revealed initial oozing of blood for a while just after releasing an aortic clamp. Therefore, preclotting of the graft is recommended under full heparinization. Because of rapid, even, and stable formation of neo-intima in the new graft confirmed by experimental studies of Noishiki et al., and soft and pliable characteristics of the graft, a wide-spread clinical use of the new graft is recommended in the surgery of aortic aneurysms as well as reconstruction of the congenital malformations.     

Increasing incidence of methicillin-resistant Staphylococcus aureus skin and soft-tissue infections: reconsideration of empiric antimicrobial therapy

BACKGROUND: Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) rates are at an all time high. MRSA rates as high as 60% have been reported in patients presenting with skin and soft-tissue infections (SSTIs). Our objectives were to (1) examine the incidence of MRSA over a 7-year period in surgical patients with SSTIs, (2) examine the choice of empiric antibiotic therapy, and (3) evaluate the vancomycin minimum inhibitory concentration (MIC) in MRSA isolates. METHODS: The medical records of all patients who underwent operative debridement of SSTIs from 2000 to 2006 were retrospectively reviewed. Demographic data such as age, race, and gender as well as co-morbid risk factors were collected. Preoperative American Society of Anesthesiologists (ASA) score, temperature, WBC, creatinine, HgbA1c, albumin, and empiric antimicrobial of choice were also included. Microbiology of all operative cultures was recorded. Available vancomycin MIC data were collected. All data are presented as mean +/- standard error of the mean. A chi-square test was used for statistical analysis. RESULTS: From 2000 to 2006, 288 patients with operative debridement for SSTIs were identified. The mean age was 54 +/- 11 years. Fifty-two percent of patients had diabetes mellitus, 55% were tobacco users, 34% alcohol users, and 23% had hepatitis C. The mean temperature at presentation was 99.2 degrees +/- 1.5 degrees F. The mean white blood cell count was 13.8 +/- .9. The mean HgbA1c was 8.6 +/- 2.5. The mean body mass index was 30.1 +/- 8. Sixty-seven percent of patients had an ASA > or = 3. There was a significant increase in MRSA SSTIs in 2006 (77%) compared with 2000 (34%, P < .001). Correspondingly, there was a significant increase in empiric administration of vancomycin in 2006 (93%) compared with 2000 (18%, P < .001). The examination of vancomycin MIC shows a shift for MRSA isolates over this time period (MIC < or = .5 microg/mL, 62%, MIC = 1 microg/mL, 7%, and MIC = 2 microg/mL, 31%). CONCLUSION: Our study shows a significant and ongoing increase in the incidence of MRSA in patients with SSTIs. Empiric coverage with an MRSA antimicrobial should be used as first-line therapy. However, given the observed increase in vancomycin MIC, alternative MRSA antimicrobials should be considered.     

Preventing methicillin-resistant Staphylococcus aureus infection in joint replacements: a new problem requiring old solutions

AIM: To analyse prospectively the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonisation and infection in wounds and surgical vacuum drains. METHODS: The study group was 100 patients undergoing primary total hip and total knee replacements in a single orthopaedic unit. RESULTS: Two patients had undergone revision joint surgery within the same unit in the year prior to the study due to confirmed MRSA infection. Following a change in the unit's infection control policy, joint replacement surgery continued within the unit even when there were cases of active MRSA present on the same ward. None of the patients undergoing joint replacement grew MRSA in their postoperative drain tips or wound cultures. CONCLUSIONS: It is safe to continue with joint replacement surgery when other patients on the same ward have active MRSA as long as strict infection control measures are followed as outlined.     

Impact of new methicillin-resistant Staphylococcus aureus carriage postoperatively after living donor liver transplantation

BACKGROUND: Preoperative carriage of methicillin-resistant Staphylococcus aureus (MRSA) is associated with an increased risk of MRSA infection after liver transplantation. It is not known, however, whether new MRSA carriage postoperatively also increases the risk of MRSA infection after liver transplantation. METHODS: We retrospectively reviewed the data from 242 adult patients who underwent living donor liver transplantation (LDLT) including microbiological and medical records from admission to 3 months after LDLT. Uni and multivariate analyses were performed to identify independent risk factors for postoperative MRSA infection among preoperative noncarriers of MRSA. RESULTS: Postoperative MRSA infection occurred in 18 of 219 preoperative noncarriers of MRSA by median postoperative day 26. Operation time of at least 16 hours and postoperative colonization with MRSA independently predicted postoperative MRSA infection. CONCLUSION: Postoperative surveillance cultures should be performed periodically after liver transplantation to identify high-risk candidates for postoperative MRSA infection, even among preoperative noncarriers of MRSA.