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Prosthetic joint infections (PJIs) are related to the formation of biofilms, mainly by Staphylococcus aureus and Staphylococcus epidermidis. Therapy is usually selected according conventional susceptibility testing, but these data may be insufficient to detect the true antibiotic susceptibility in the biofilm. In total, 32 clinical strains (17 S. aureus and 15 S. epidermidis) isolated from patients with PJIs as well as 2 collection strains (S. aureus 15981 and S. epidermidis ATCC 35984) were tested against nine antibiotics commonly used in the treatment of PJIs (rifampicin, vancomycin, tigecycline, clindamycin, trimethoprim/sulfamethoxazole, ciprofloxacin, cloxacillin, daptomycin and fosfomycin) using the Calgary Biofilm Device. None of the antibiotics proved to be totally effective against biofilms in both species, with minimum biofilm eradication concentrations (MBECs) highly above the minimum inhibitory concentrations for most of the antibiotics (>1024 mg/L). Rifampicin and tigecycline showed MBECs slightly lower, mainly against S. epidermidis biofilms, and only two strains of this staphylococcal species were susceptible to almost all of the antibiotics tested. These results show that the search for new compounds with antimicrobial and antibiofilm properties is mandatory as well as the development of other strategies that could lead to the prevention and treatment of PJIs. In addition, more studies are necessary to obtain a better understanding of the mechanisms involved in antimicrobial resistance of biofilms.

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Prosthetic joint infections (PJI) are severe complications in Orthopedics, with Staphylococcus aureus and Staphylococcus epidermidis being the most commonly isolated pathogens. The variable antimicrobial susceptibility found in these microorganisms, along with the increasing number of methicillin-resistant strains, increases the difficulty of antibiotic selection and makes it necessary to perform individual susceptibility studies to select the optimal antibiotic treatment. The aim of this study was to evaluate the in vitro susceptibility pattern of 35 clinical strains isolated from PJI (17 S. aureus and 18 S. epidermidis) against rifampin, vancomycin, tygecicline, clindamycin, cotrimoxazole, cloxacillin, ciprofloxacin, daptomycin and fosfomycin. In vitro susceptibility assays were performed using the broth microdilution method and agar dilution for fosfomycin. MBC was also determined. Tygecicline and daptomycin showed the highest antimicrobial activity with low MIC(90) values, and no resistant strains were detected. On the other hand, ciprofloxacin and cloxacillin exhibited a poor antimicrobial effect with a high percentage of nonsusceptible strains in both species. Bactericidal activity rates revealed the bacteriostatic behavior of rifampin, tygecicline, cotrimoxazole, fosfomycin and clindamycin, whereas vancomycin and cloxacillin showed species- and strain-dependent behavior. Daptomycin and ciprofloxacin were observed to be efficient bactericidal agents against the tested strains. According to our data, rifampin, tigecycline, daptomycin and fosfomycin showed high in vitro activity against most staphylococcal strains isolated from the PJIs tested, although daptomycin seems to be the best alternative to vancomycin therapy.

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Bone infections are a challenge for modern medicine. The most common pathogen is Staphylococcus aureus, which usually develops a biofilm inside the infected bone. Local release of antibiotics within the infected tissue may diminish this problem because high concentrations of the antibiotic would be delivered to the required place. This study was carried out to evaluate silica-based mesoporous material SBA-15 as a delivery system for three antibiotics with activity against S. aureus, namely vancomycin, rifampicin and linezolid, alone or in combination. SBA-15 disks were loaded with antibiotics by adsorption using a 1000 mg/L solution. Measurements of biological activity were carried out by bioassay tests, and antibiotic release was monitored by high-performance liquid chromatography (HPLC). In all cases, the ceramic disks released most of the antibiotics at the initial stage of the experiments, with concentrations above the susceptibility breakpoints. The most active antibiotic was rifampicin, with an active concentration of 96.14 mg/L at 24 h, followed by linezolid (7.2 mg/L) and vancomycin (5.5 mg/L). In the HPLC measurements, the antibiotic that showed the best release was linezolid, followed by vancomycin; rifampicin alone could not be measured by HPLC with precision. Taking into account all these results, the antibiotic that remains most active after loading and release is vancomycin (77.46%), followed by linezolid (24%). The results presented here demonstrate the efficacy of SBA-15 bioceramics for local release of antibiotics, which could be of interest in the context of bone infection.

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PURPOSE: We wanted to improve the diagnosis of implant-related infection using molecular biological techniques after sonication. METHODS: We studied 258 retrieved implant components (185 prosthetic implants and 73 osteosynthesis implants) from 126 patients. 47 patients had a clinical diagnosis of infection (108 components) and 79 patients did not (150 components). The fluids from sonication of retrieved implants were tested in culture and were also analyzed using a modified commercial PCR kit for detection of Gram-positive and Gram-negative bacteria (GenoType BC; Hain Lifescience) after extraction of the DNA. RESULTS: 38 of 47 patients with a clinical diagnosis of infection were also diagnosed as being infected using culture and/or PCR (35 by culture alone). Also, 24 patients of the 79 cases with no clinical diagnosis of infection were identified microbiologically as being infected (4 by culture, 16 by PCR, and 4 by both culture and PCR). Comparing culture and PCR, positive culture results were obtained in 28 of the 79 patients and positive PCR results were obtained in 35. There were 21 discordant results in patients who were originally clinically diagnosed as being infected and 28 discordant results in patients who had no clinical diagnosis of infection. INTERPRETATION: For prosthetic joint infections and relative to culture, molecular detection can increase (by one tenth) the number of patients diagnosed as having an infection. Positive results from patients who have no clinical diagnosis of infection must be interpreted carefully.

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Bacterial adherence on total joint replacement implants may lead to biofilm formation and implant-related osteoarticular infection. It is unclear if different biomaterials in the prosthetic components are more prone to facilitate this bacterial adherence, although ultrahigh molecular weight polyethylene (UHMWPE) component exchange in modular systems has been clinically utilized in the early management of these infections. To clarify if the amount of clinically adhered microorganisms was related to the material or the component, we investigated retrieved implants from infected joint replacements. Thirty-two patients were revised after confirmed implant-related infection through positive cultures. Eighty-seven total joint components (hip and knee) were obtained and separately sonicated following a previously published protocol. Cultures were quantified, and detected colony forming units (CFU) were adjusted according to the component surface and compared based on the component material and location. Variable adherence of bacteria to chrome cobalt alloys, UHMWPE, hydroxyapatite coated components, and titanium alloys. The commonest isolated organisms were Staphylococcus epidermidis (23 of 87 components) and Staphylococcus aureus (10 of 87). Twelve components did not show any microorganism adhered despite location in an infected joint, with positive cultures in other components. A mixed linear model adjusted for random effects (the random effect being the infected patient) obtained convergence for the CFU/mm(2) variable, but could not confirm a significantly higher adherence to a particular component or to a particular biomaterial. Therefore, the bacterial adherence primarily depends on the infective microorganism and the response of each individual patient, rather than materials or components.

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OBJECTIVES: To study the resistance of biofilms developed by non-pigmented rapidly growing mycobacteria (NPRGM) against amikacin, ciprofloxacin and clarithromycin in an in vitro model using clinical strains of different species. DESIGN: Antimicrobial susceptibilities of different clinical strains of Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium fortuitum, Mycobacterium peregrinum, Mycobacterium mucogenicum and Mycobacterium mageritense using conventional techniques were measured. Biofilm resistance was measured by using the sandwich technique developed by Anderl et al. using a concentration of antibiotic of 50mg/L. Penetration of antibiotics through biofilm was measured using the same technique with minimal modifications. RESULTS: NPRGM biofilms showed drug resistance (percentages of viable bacteria >1% of those of controls) against antibiotics that are commonly used for the treatment of infections caused by these organisms, although there are intraspecies differences between strains. We have detected differences in antibiotic penetration through biofilms with an important permeability barrier for ciprofloxacin. However, other mechanisms must be probably more important to explain the antimicrobial resistance of NPRGM biofilm. CONCLUSIONS: Biofilms formed by NPRGM are resistant to amikacin, ciprofloxacin and clarithromycin. As no resistance differences between the tested antibiotics have been observed, it is likely that biofilm permeability of antibiotics is of low importance for antimicrobial resistance of biofilms.

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Objectives To study the resistance of biofilms developed by non-pigmented rapidly growing mycobacteria (NPRGM) against amikacin, ciprofloxacin and clarithromycin in an in vitro model using clinical strains of different species. Design Antimicrobial susceptibilities of different clinical strains of Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium fortuitum, Mycobacterium peregrinum, Mycobacterium mucogenicum and Mycobacterium mageritense using conventional techniques were measured. Biofilm resistance was measured by using the sandwich technique developed by Anderl et al. using a concentration of antibiotic of 50mg/L. Penetration of antibiotics through biofilm was measured using the same technique with minimal modifications. Results NPRGM biofilms showed drug resistance (percentages of viable bacteria >1% of those of controls) against antibiotics that are commonly used for the treatment of infections caused by these organisms, although there are intraspecies differences between strains. We have detected differences in antibiotic penetration through biofilms with an important permeability barrier for ciprofloxacin. However, other mechanisms must be probably more important to explain the antimicrobial resistance of NPRGM biofilm. Conclusions Biofilms formed by NPRGM are resistant to amikacin, ciprofloxacin and clarithromycin. As no resistance differences between the tested antibiotics have been observed, it is likely that biofilm permeability of antibiotics is of low importance for antimicrobial resistance of biofilms (AU)

Objetivos Estudiar la resistencia de biopelículas formadas por micobacterias no pigmentadas de crecimiento rápido (MNPCR) frente amicacina, ciprofloxacino y claritromicina en in modelo in vitro empleando aislamientos clínicos de diferentes especies. Material y MétodosSe estudiaron las sensibilidades de las diferentes cepas clínicas de Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium fortuitum, Mycobacterium peregrinum, Mycobacterium mucogenicum y Mycobacterium mageritense mediante técnicas convencionales. La resistencia de dichas bacterias en la biopelícula fue estudiada mediante la técnica de sándwich descrita por Anderl et al. utilizando una concentración de antibiótico de 50mg/L. La penetración de los antibióticos a través de la biopelícula fue estudiada mediante la misma técnica con mínimas modificaciones. Resultados Las biopelículas de MNPCR presentaron resistencia (porcentajes de bacterias viables > 1% de los recuentos obtenidos en los controles) frente a todos los antibióticos que son empleados habitualmente en las infecciones causadas por estos organismos, si bien se detectaron diferencias dentro de la misma especie entre las diferentes cepas. Hemos detectado diferencias en la penetración de antibióticos a través de la biopelícula, especialmente con una importante disminución de la permeabilidad frente a ciprofloxacino. Sin embargo, otros mecanismos son, probablemente, más importantes para explicar la resistencia antimicrobiana de las biopelículas de MNPCR. Conclusiones Las biopelículas formadas por MNPCR son resistentes frente a amicacina, ciprofloxacino y claritromicina. Como no se demostraron diferencias importantes entre los distintos antibióticos, es probable que la permeabilidad de la biopelícula frente a los antibióticos tenga poca importancia en la resistencia antimicrobiana de las biopelículas (AU)

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The genus Corynebacterium includes a high number of species that are usually isolated from human skin as saprophytes. However, these microorganisms have also been reported as infectious agents in a broad group of patients and have showed broad-spectrum resistance. We studied the susceptibility profiles against macrolides, clindamycin, and streptogramins of 254 clinical strains belonging to the species Corynebacterium urealyticum (120), Corynebacterium amycolatum (66), Corynebacterium jeikeium (17), Corynebacterium striatum (20), Corynebacterium coyleae (12), Corynebacterium aurimucosum (11), and Corynebacterium afermentans subsp. afermentans (8). The MLS(B) phenotype was detected in 186 strains and was associated with the presence of methylase enzymes codified by the erm(X) gene in 171 strains. The erm(B) gene was only detected in two C. urealyticum strains. Fourteen strains showed macrolide resistance, but they did not carry erm genes. mef genes were not detected despite eight C. amycolatum strains showed the M phenotype. Also, the presence of hydrolytic enzymes codified by ere(B) was evaluated, but all results were negative. Resistance to macrolide in Corynebacterium sp. is mainly due to the presence of erm(X) methylase, although other resistance mechanisms could be involved.

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BACKGROUND: Atypical mycobacteria are a heterogeneous group of organisms that are of increasing importance because of the growing number of infections they cause. This rising rate of infection is due mainly to the increase in the number of susceptible (and especially immunosuppressed) patients. OBJECTIVE: To revise the currently used treatment schemes of the most commonly isolated atypical mycobacteria. METHODS: Literature review using reference books and PubMed with specific keywords for each mycobacteria. RESULTS/CONCLUSION: The first important step in the management of atypical mycobacteria is to recognize the true infections caused by these organisms. The treatment required varies according to species. Well-characterized combinations exist for most common isolates, with the use of first-line antituberculous drugs (isoniazid, rifampin, ethambutol), clarithromycin, aminoglycosides and/or quinolones for slowly growing species (Mycobacterium avium complex, Mycobacterium kansasii, Mycobacterium xenopi, Mycobacterium ulcerans, Mycobacterium marinum, Mycobacterium lentiflavum, Mycobacterium malmoense) and macrolides, quinolones, amikacin and other antibiotics for rapidly growing mycobacteria (Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium fortuitum). Surgical therapy is also important for some species (Mycobacterium ulcerans, Mycobacterium scrofulaceum) and for localized infections. The treatment of uncommon species is not well defined and is determined by the results of in vitro tests of individual strains. Because of the increasing number of resistant strains, new antibiotics need to be used for the treatment of these strains.

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