Pseudomonas aeruginosa biofilm formation and slime excretion on antibiotic-loaded bone cement

Background Infection is an infrequent but serious complication of prosthetic joint surgery. These infections will usually not clear until the implant is removed and re-implantation has a high failure rate, especially when Pseudomonas aeruginosa is involved. Material and methods We examined Pseudomonas aeruginosa biofilm formation on plain and gentamicin-loaded bone cement with confocal scanning laser microscopy (CSLM). Two different stains were applied in order to visualize and quantify the distribution of bacterial cells and extracellular polymeric substances (slime) from the bone cement surface to the top of the biofilm. Staining with LIVE/DEAD viability stain differentiated between live and dead bacteria within the biofilm, and slime production was evaluated after staining with Calcofluor white. Results CSLM showed that the biofilm was a nonuniform structure of variable thickness, with differences in local bacterial cell and slime densities. Incorporation of gentamicin in bone cement resulted in a 44% reduction in bacterial viability, while the slime density increased significantly. In addition, conventional plate counting showed the development of small-colony variants on gentamicin-loaded bone cement with a decreased sensitivity for gentamicin (MIC: 8 mg/L), as compared with normal-sized colonies taken from plain and gentamicin-loaded bone cement (MIC: 3 mg/L). The enhanced slime production on antibiotic-loaded bone cement, together with the formation of small-colony variants, resulted in decreased susceptibility to antibiotics-probably concomitant with the onset of persistent and relapsing infections. Interpretation In the clinical situation, our findings help to explain the frequent re-implantation failure of joint replacements infected with P. aeruginosa when the procedure has been performed using antibiotic-loaded bone cement

Familial congenital bilateral agenesis of the acromion:a radiologically illustrated case report

Familial congenital bilateral acromion absence was found in four members of one family. Only one of them presented with gradually increasing pain in his left shoulder, resembling a shoulder impingement syndrome. The other members did not have any symptoms. This is the first report of familial occurrence of this extremely rare congenital anomaly

Backgrounds of antibiotic-loaded bone cement and prosthesis-related infection

Antibiotic-loaded bone cement has been in use for over 30 years for the fixation of total joint arthroplasties, although its mechanism of action is still poorly understood. This review presents the backgrounds of bone cements, prosthesis-related infection and antibiotic-loaded bone cements. It is shown that antibiotic-loaded bone cement has a significant effect on bacteria, particularly in animal and clinical studies. However, recently, antimicrobial resistance among bacteria has been ascribed to the antibiotic-loaded bone cement. The unresolved issues both regarding the action of antibiotic-loaded bone cement and the nature of the antimicrobial resistance necessitate further research into the interaction of antibiotic-loaded bone cement and bacteria. (C) 2003 Elsevier Ltd. All rights reserved

Bacterial survival in the interfacial gap in gentamicin-loaded acrylic bone cements

Clinical experience indicates the beneficial effects of antibiotic-loaded bone cement. Although in vitro studies have shown the formation of a biofilm on its surface they have not considered the gap between the cement and the bone. We have investigated bacterial survival in that gap. Samples with gaps 200 gm wide were made of different bone cements. These were stored dry ('pre-elution') or submersed in phosphate-buffered saline to simulate the initial release of gentamicin ('post-elution'). The gaps were subsequently inoculated with bacteria, which had been isolated from infected orthopaedic prostheses and assessed for their sensitivity to gentamicin. Bacterial survival was measured 24 hours after inoculation. All the strains survived in plain cements. In the pre-elution gentamicin-loaded cements only the most gentamicin-resistant strain, CN5115, survived, but in post-elution samples more strains did so, depending on the cement tested. Although high concentrations of gentamicin were demonstrated in the gaps only the gentamicin-sensitive strains were killed. This could explain the increased prevalence of gentamicin-resistant infections which are seen clinically

The release of gentamicin from acrylic bone cements in a simulated prosthesis-related interfacial gap

Gentamicin is added to polymethylmethacrylate bone cements in orthopedics as a measure against infection in total joint arthroplasties. Numerous studies have been published on gentamicin release from bone cements, but none have been able to estimate the local concentrations in the prosthesis-related interfacial gap, present after implantation. The aim of this study was to develop a method allowing determination of antibiotic release in such a gap. Two-hundred-micrometer-wide gaps with a volume of 6 mul and a surface area of 0.6 cm(2) were created by inserting stainless-steel strips in gentamicin-loaded bone cement plugs prior to polymerization. After hardening, the gap surface was exposed to 6 mul or 10 ml of phosphate-buffered saline. Within 2 h, gentamicin concentrations in the gaps reached around 4000 mug/ml for 4 different CMW and Palamed cements and 2500 mug/ml for Palacos R. Concentrations measured in the larger volume were several hundred times lower than in the gaps. This simulated prosthesis-related interfacial gap model offers new insights in the clinical efficacy of antibiotic-loaded bone cements. It is demonstrated that concentrations up to 1000-fold the antibiotic resistance levels for most bacterial strains causing implant infection can be achieved in a realistic in vitro model. (C) 2002 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 64B: 1-5, 2003

The influence of ultrasound on the release of gentamicin from antibiotic-loaded acrylic beads and bone cements

Gentamicin-loaded acrylic beads are loosely placed in infected bone cavities, whereas gentamicin-loaded acrylic bone cement is used as a mechanical filler in bone to anchor prosthetic components. Both drug delivery systems are used to decrease infection rates by gentamicin release. The objective of this study is to investigate the effects of pulsed ultrasound on gentamicin release from both materials. Gentamicin release from gentamicin-loaded beads (Septopal) and from three commercially-available brands of gentamicin-loaded bone cement (CMW 1, Palacos R-G, and Palamed G) was measured after 18 h of exposure in PBS to an ultrasonic field of 46.5 kHz in a 1:3 duty cycle with an average acoustic intensity of 167 mW/cm(2). Samples not exposed to ultrasound were used as controls. Pulsed ultrasound significantly enhanced gentamicin release from gentamicin-loaded beads, whereas gentamicin release from the gentamicin-loaded bone cements was not significantly enhanced. Mercury intrusion porosimetry revealed an increased distribution of pores between 0.1 and 0.01 mu m in beads after gentamicin release, while in bone cements no increase in the number of pores was found. Increased gentamicin release in beads due to ultrasound may be explained by microstreaming in a porous structure, whereas the absence of changes in pore structure after gentamicin release in bone cement is concurrent with the lack of an enhanced release of the antibiotic by ultrasound. As an effective treatment of infections requires high local concentrations of antibiotic, increased gentamicin release due to ultrasound may be of clinical significance, especially since ultrasound has been demonstrated to increase bacterial killing by antibiotics. (c) 2005 Wiley Periodicals, Inc

Increased release of gentamicin from acrylic bone cements under influence of low-frequency ultrasound

The release profile of antibiotics from antibiotic-loaded bone cement, used to prevent infections in total joint arthroplasty, is neither ideal nor complete. Ultrasound has been used to allow drugs to cross otherwise impermeable barriers. The aim of this study was to establish a possible effect of ultrasound on antibiotic release from bone cements. Samples were made of three commercially available gentamicin-loaded bone cements. Part of the samples was allowed to release gentamicin for 3 weeks before insonation. An insonation device produced an ultrasound field with a time average acoustic intensity of 167 mW/cm(2) at a frequency of 46.5 kHz. The samples were exposed to the ultrasound field or not exposed to it as a control. The amount of gentamicin released was measured by fluorescence polarization immunoassay. There was a limited increase of gentamicin release with application of ultrasound in fresh samples but not in the samples that had been allowed to release gentamicin. For fresh samples, a linear regression model showed that this ultrasound effect was statistically significant. The mechanism behind these observations is not clear, but it is suggested that microstreaming or localized temperature rises may be involved. (C) 2003 Elsevier B.V. All rights reserved

Antimicrobial efficacy of gentamicin-loaded acrylic bone cements with fusidic acid or clindamycin added

The increasing gentamicin resistance among bacteria in septic joint arthroplasty has stimulated interest in adding a second antibiotic into gentamicin-loaded bone cement. A first aim of this in vitro study is to investigate whether addition of fusidic acid or clindamycin to gentamicin-loaded bone cement has an additional antimicrobial effect against a collection of 38 clinical isolates, including 16 gentamicin-resistant strains. A modified Kirby-Bauer test, involving measurement of the inhibition zone around antibiotic-loaded bone cement discs on agar plates, was used to investigate whether adding a second antibiotic has an additional antimicrobial effect. Second, a selected number of strains was used to study their survival in an interfacial gap made in the different bone cements to mimic the gap between bone and cement as existing near a prosthesis. Gentamicin loaded bone cement had an antimicrobial activity against 58% of the 38 bacterial strains included in this study, while 68% of the strains were affected by bone cement loaded with a combination of gentamicin and clindamycin. Bone cement loaded with the combination of gentamicin and fusidic acid had antimicrobial activity against 87% of the bacterial strains. In the prosthesis-related gap model, there was a clear trend toward less bacterial survival for gentamicin-loaded bone cement after adding clindamycin or fusidic acid. Addition of clindamycin or fusidic acid into gentamicin-loaded bone cement yields an additional antimicrobial effect. The combination gentamicin and fusidic acid was effective against a higher number of clinical isolates than the combination of gentamicin with clindamycin, including gentamicin-resistant strains. (c) 2005 Orthopaedic Research Society. Published by Wiley Periodicals, Inc