Methicillin-resistant Staphylococcus aureus: clinical manifestations and antimicrobial therapy

Implants coating strategies for antibacterial treatment in fracture and defect models: A systematic review of animal studies

Objective

Fracture-related infection (FRI) remains a major concern in orthopaedic trauma. Functionalizing implants with antibacterial coatings are a promising strategy in mitigating FRI. Numerous implant coatings have been reported but the preventive and therapeutic effects vary. This systematic review aimed to provide a comprehensive overview of current implant coating strategies to prevent and treat FRI in animal fracture and bone defect models.

Methods

A literature search was performed in three databases: PubMed, Web of Science and Embase, with predetermined keywords and criteria up to 28 February 2023. Preclinical studies on implant coatings in animal fracture or defect models that assessed antibacterial and bone healing effects were included.

Results

A total of 14 studies were included in this systematic review, seven of which used fracture models and seven used defect models. Passive coatings with bacteria adhesion resistance were investigated in two studies. Active coatings with bactericidal effects were investigated in 12 studies, four of which used metal ions including Ag+ and Cu2+; five studies used antibiotics including chlorhexidine, tigecycline, vancomycin, and gentamicin sulfate; and the other three studies used natural antibacterial materials including chitosan, antimicrobial peptides, and lysostaphin. Overall, these implant coatings exhibited promising efficacy in antibacterial effects and bone formation.

Conclusion

Antibacterial coating strategies reduced bacterial infections in animal models and favored bone healing in vivo. Future studies of implant coatings should focus on optimal biocompatibility, antibacterial effects against multi-drug resistant bacteria and polymicrobial infections, and osseointegration and osteogenesis promotion especially in osteoporotic bone by constructing multi-functional coatings for FRI therapy.

The translational potential of this paper

The clinical treatment of FRI is complex and challenging. This review summarizes novel orthopaedic implant coating strategies applied to FRI in preclinical studies, and offers a perspective on the future development of orthopaedic implant coatings, which can potentially contribute to alternative strategies in clinical practice.

Comparison of disease and economic burden between MRSA infection and MRSA colonization in a university hospital: a retrospective data integration study

BACKGROUND

Although there is a growing concern and policy regarding infections or colonization caused by resistant bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), the prognosis of MRSA infections compared to that of methicillin-susceptible Staphylococcus aureus (MSSA) infections remains controversial. Moreover, there have not been any studies comparing both the burden of disease and its impact on the healthcare economy between MRSA infection and colonization while adjusting for confounding factors. These comparisons are crucial for developing effective infection control measures and healthcare policies. We aimed to compare the disease and economic burden between MRSA and MSSA infections and between MRSA infection and colonization.

METHODS

We retrospectively investigated data of 496 in-patients with MRSA or MSSA infections and of 1178 in-patients with MRSA infections or MRSA colonization from a university hospital in Japan from 2016 to 2021. We compared in-hospital mortality, length of stay, and hospital charges between in-patients with MRSA and MSSA infections and those with MRSA infections and MRSA colonization using multiple regressions. We combined surveillance data, including all microbiological test results, data on patients with infections, treatment histories, and clinical outcomes, to create the datasets.

RESULTS

There was no statistically significant difference in in-hospital mortality rates between matched MRSA vs. MSSA infections and MRSA infection vs. colonization. On the contrary, the adjusted effects of the MRSA infection compared to those of MSSA infection on length of stay and hospital charges were 1.21-fold (95% confidence interval [CI] 1.03-1.42, P = 0.019) and 1.70-fold (95% CI 1.39-2.07, P < 0.00001), respectively. The adjusted effects of the MRSA infection compared to those of MRSA colonization on length of stay and hospital charges were 1.41-fold (95% CI 1.25-1.58, P < 0.00001) and 1.53-fold (95% CI 1.33-1.75, P < 0.00001), respectively. Regarding confounding factors, hemodialysis or hemofiltration was consistently identified and adjusted for in the multiple regression analyses comparing MRSA and MSSA infections, as well as MRSA infection and MRSA colonization.

CONCLUSIONS

MRSA infection was associated with longer length of stay and higher hospital charges than both MSSA infection and MRSA colonization. Furthermore, hemodialysis or hemofiltration was identified as a common underlying factor contributing to increased length of stay and hospital charges.

In vitro activity of the novel Fe-cyclam complex against clinical multidrug-resistant bacterial isolates from Brazil

Aim: To evaluate the effect of a new Fe-cyclam complex on pathogenic bacterial species, including multidrug-resistant clinical specimens. Materials & methods: The complex [Fe(cyclam)ox]PF6 (D2) was tested in cytotoxicity and MIC tests. Clinical and reference strains of Gram-negative and Gram-positive bacteria were used. Considering Staphylococcus aureus strains, the profile of antimicrobial susceptibility and time-kill kinetics for D2 was performed. An in silico analysis for D2 was also performed. Results: D2 showed broad bacterial activity, mainly against specimens of Cutibacterium acnes, S. aureus, Pseudomonas aeruginosa and Acinetobacter baumannii. Low cytotoxicity in human cells was demonstrated. Conclusion: The tested compound proved to be a promising agent against resistant bacterial infections.

Animal experimental investigation on the efficacy of antibiotic therapy with linezolid, vancomycin, cotrimoxazole, and rifampin in treatment of periprosthetic knee joint infections by MRSA

Aims

Periprosthetic joint infections (PJIs) are rare, but represent a great burden for the patient. In addition, the incidence of methicillin-resistant Staphylococcus aureus (MRSA) is increasing. The aim of this rat experiment was therefore to compare the antibiotics commonly used in the treatment of PJIs caused by MRSA.

Methods

For this purpose, sterilized steel implants were implanted into the femur of 77 rats. The metal devices were inoculated with suspensions of two different MRSA strains. The animals were divided into groups and treated with vancomycin, linezolid, cotrimoxazole, or rifampin as monotherapy, or with combination of antibiotics over a period of 14 days. After a two-day antibiotic-free interval, the implant was explanted, and bone, muscle, and periarticular tissue were microbiologically analyzed.

Results

Vancomycin and linezolid were able to significantly (p < 0.05) reduce the MRSA bacterial count at implants. No significant effect was found at the bone. Rifampin was the only monotherapy that significantly reduced the bacterial count on implant and bone. The combination with vancomycin or linezolid showed significant efficacy. Treatment with cotrimoxazole alone did not achieve a significant bacterial count reduction. The combination of linezolid plus rifampin was significantly more effective on implant and bone than the control group in both trials.

Conclusion

Although rifampicin is effective as a monotherapy, it should not be used because of the high rate of resistance development. Our animal experiments showed the great importance of combination antibiotic therapies. In the future, investigations with higher case numbers, varied bacterial concentrations, and changes in individual drug dosages will be necessary to be able to draw an exact comparison, possibly within a clinical trial.

Cite this article: Bone Joint Res 2022;11(3):143–151.

Nanobiotic formulations as promising advances for combating MRSA resistance: susceptibilities and post-antibiotic effects of clindamycin, doxycycline, and linezolid

Antimicrobial activity and post-antibiotic effects (PAEs) are both important parameters in determination of the dosage regimen of antimicrobial agents. In the present study, antimicrobial activity and PAEs of clindamycin, doxycycline, linezolid, and their nanobiotic formulations were evaluated against two methicillin resistant Staphylococcus aureus clinical isolates (MRSA) encoded (MRSA-S1 and MRSA-S2). Nanobiotic formulations increased the susceptibility of MRSA isolates by 4-64 folds as compared to their conventional ones. The PAE values were determined after exposure of MRSA isolates for 1 h to 10× the MICs of the tested antibiotics. The duration of PAEs were recorded after bacterial growth in Mueller Hinton broth (MHB) free from antibiotic has been restored. The PAE values for MRSA-S1 were 2.5 h for the conventional antibiotics. However, the PAEs for nanobiotics were 4 h for both clindamycin and linezolid, while 3 h for doxycycline. For MRSA-S2, linezolid and linezolid nanobiotics PAEs were 3 h. PAEs of clindamycin and clindamycin nanobiotics were 3.75 h and 4 h, respectively. Doxycycline and doxycycline nanobiotics revealed the same PAEs patterns of 3.5 h. The findings of the current study may positively influence the pharmacodynamics of the antibiotics and consequently the dosage regimen of nanobiotics as well as on their clinical outcome.

Antimicrobial action of autologous platelet-rich plasma on MRSA-infected skin wounds in dogs

Effective antimicrobial preparations, other than antibiotics, are important for the treatment of potentially fatal drug-resistant infections. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the leading causes of hospital-acquired and post- operative infections. Fortunately, the antimicrobial properties of platelet-rich plasma (PRP) against various microorganisms enable its potential use as an alternative to conventional antibiotics. The present work was designed to evaluate the hypothesized antimicrobial activity of PRP against MRSA infected skin wounds. Six adult male dogs were divided equally into control and PRP groups. Unilateral circular full-thickness skin wounds were created then a MRSA suspension was injected locally. Treatment started at 1st week post infection with subcutaneous infiltration of autologous activated PRP every week in the PRP group and with topical application of clindamycin cream twice daily in the control group. PRP decreased wound size and significantly increased wound contractility and re-epithelization, as confirmed by histopathological and immunohistochemical findings. Also PRP treated group showed significant decrease in ROS and redox imbalance with over expression of the TNF-α and VEGFA genes that indicate angiogenesis and maximum antibacterial activity after three weeks. In conclusion, CaCl2-activated PRP exhibited antimicrobial activity against MRSA infection, which improved the infected wound healing re-epithelization and granulation tissue formation.

Antibacterial activity of Mulinum spinosum extracts against slime-producing Staphylococcus aureus and methicillin-resistant Staphylococcus aureus isolated from nasal carriers

Nasal carriers of Staphylococcus aureus are important reservoirs with risk of developing endogenous infections or transmitting infections to susceptible individuals. Methicillin-resistant S. aureus (MRSA) are associated with higher rates of treatment failure. Some strains of S. aureus produce slime which is believed to make the microorganisms more resistant to antibiotics and host defenses. The antibacterial activity of ethyl acetate : n-hexane (EtOAc : HEX) extracts of Mulinum spinosum (5 : 95% EtOAc : HEX, 50 : 50% EtOAc : HEX, 70 : 30% EtOAc : HEX and mix 20 : 80/30 : 70% EtOAc : HEX, 50 : 50/70 : 30/100 : 0% EtOAc : HEX) were assayed against 3 slime-producing S. aureus strains and 2 MRSA strains isolated from nasal carriers. S. aureus ATCC 35556 slime-producing strain and MRSA ATCC 43300 strain were used as controls. The extracts were prepared using flash chromatography. M. spinosum 5 : 95% AcOEt : HEX showed antibacterial effect against all slime-producing strains (MIC: 500 µg/mL) and the highest activity against MRSA strains (MIC: 500 to 1000 µg/mL). All M. spinosum extracts assayed were active against slime-producing S. aureus and MRSA at doses between 500 and 4000 µg/mL. Both, slime-producing S. aureus and MRSA are highly contagious and hardly eradicated by antibiotic therapies. So, there is an increasing need to find new substances with the ability to inhibit these strains.

Minocycline, often forgotten but preferred to trimethoprim-sulfamethoxazole or doxycycline for the treatment of community-acquired meticillin-resistant Staphylococcus aureus skin and soft-tissue infections

Treatment of uncomplicated skin and soft-tissue abscesses caused by meticillin-sensitive Staphylococcus aureus or meticillin-resistant S. aureus (MRSA) is problematic. Incision and drainage aside, oral antibiotic therapy for uncomplicated community-acquired MRSA (CA-MRSA) is limited and frequent choices include clindamycin, doxycycline or trimethoprim-sulfamethoxazole (TMP-SMX). The most common oral antibiotics used for CA-MRSA are doxycycline or TMP-SMX, which often fail to eradicate the infection. With MRSA, in vitro susceptibilities do not always predict in vivo effectiveness. In situations where doxycycline or TMP-SMX fails in the treatment of uncomplicated cutaneous abscesses due to CA-MRSA, minocycline is reliably effective.

Update on the appropriate use of linezolid in clinical practice

Multi-antibiotic resistant Gram-positive cocci, which include Staphylococcus aureus, the coagulase-negative staphylococcal group, Enterococcus faecalis and Enterococcus faecium, and other streptococci, represent emerging pathogens especially in the setting of the immunocompromised, hospitalized patients, in particular when surgery, invasive procedures, or prosthetic implants are of concern, patients are admitted in intensive care units, or underlying chronic disorders and immunodeficiency are of concern, and broad-spectrum antibiotics or immunosuppressive drugs are widely administered. During the recent years, the phenomenon of multiresistant Gram-positive cocci is spreading to the community, where the retrieval of such microorganism is progressively increasing. The spectrum of available antimicrobial compounds for an effective management of these relevant infections is significantly impaired in selection and clinical efficacy by the emerging and spread of methicillin-resistant and more recently glycopeptide-resistant Gram-positive microbial strains. The first oxazolidinone derivative linezolid, together with the recently licensed quinupristin–dalfopristin, daptomycin, and tigecycline, followed by a number of glycopeptides, fluoroquinolones, and other experimental compounds on the pipeline, represent an effective response to the great majority of these concerns, due to their innovative mechanisms of action, their maintained or enhanced activity against multiresistant pathogens, their effective pharmacokinetic/pharmacodynamic properties, their frequent possibility of synergistic activity with other compounds effective against Gram-positive pathogens, and a diffuse potential for a safe and easy administration, also when compromised patients are of concern. The main problems related to the epidemiological and clinical features of multiresistant Gram-positive infection, the potential clinical indications of all recently available compounds compared with the standard of care of treatment of resistant Gram-positive infections, and updated data on efficacy and tolerability of linezolid as the golden standard compound for vancomycin-resistant Gram-positive cocci in multiple clinical situations, are outlined and updated on the ground of an extensive review of all the available, recent evidences coming from the international literature.

Clinical and cost ineffectiveness of preoperative screening for methicillin-resistant Staphylococcus aureus and intranasal mupirocin in preventing methicillin-resistant S aureus infections in cardiothoracic surgery

In our recent experience with methicillin-resistant Staphylococcus aureus (MRSA) infections in 488 patients undergoing thoracic cardiovascular surgery, we found only 2 MRSA infections (one sternal and one graft site). Both patients received preoperative bacitracin and had a negative nares culture for MRSA before the initiation of bacitracin therapy. We conclude that preoperative MRSA screening cultures and bacitracin prophylaxis are neither clinically efficacious nor cost-effective in predicting or preventing MRSA in patients undergoing thoracic cardiovascular surgery.

Prosthetic valve endocarditis

Prosthetic valve endocarditis (PVE) is associated with a high mortality during the early and midterm follow-up despite diagnostic and therapeutic improvements; its incidence is increasing and reaches 20-30% of all infective endocarditis episodes. In this review, changes in epidemiology, microbiology, diagnosis and therapy that have evolved in the past few years are analyzed. Staphylococci (both Staphylococcus aureus and coagulase-negative Staphylococcus) have emerged as the most common cause of PVE and are associated with a severe prognosis. Moreover, diagnosis may often be difficult because of its complications and extracardiac manifestations; thus, a comprehensive assessment of the clinical, echocardiographic and laboratory data must be performed. Early PVE, comorbidity, severe heart failure and new prosthetic dehiscence are predictors of mortality. Therapy is not indicated by evidence-based recommendations but mostly on identification of the high-risk conditions. A PVE is a common indication for surgery, whereas medical treatment alone may be achieved in a few instances. Systematic prophylaxis should be used to prevent this severe complication of cardiac valve replacement.

In vitro and in vivo activities of linezolid alone and combined with vancomycin and imipenem against Staphylococcus aureus with reduced susceptibility to glycopeptides

The objective of this study was to evaluate the in vitro and in vivo efficacies of linezolid (35 mg/kg/5 h), vancomycin (60 mg/kg/5 h), imipenem (30 mg/kg/5 h), linezolid+imipenem, linezolid+vancomycin and vancomycin+imipenem against two clinical Staphylococcus aureus isolates with reduced susceptibility to glycopeptides using time–kill curves and the murine peritonitis model. Time–kill curves were performed over 24 h. For the murine peritonitis model, peritonitis was induced by the intraperitoneal inoculation of 10⁸ CFU/ml of each bacterial strain. Four hours later (0 h), the mice were randomly assigned to a control group or to therapeutic groups receiving subcutaneous treatment for 25 h. Bacterial counts in peritoneal fluid, bacteraemia and mortality rates were determined. The time–kill curves showed that the addition of linezolid to imipenem yielded synergistic results after 24 h. The addition of linezolid decreased vancomycin activity. In the animal model, vancomycin and linezolid monotherapies produced comparable bacterial decreases in mice infected with each strain but linezolid achieved higher rates of blood sterilisation. Linezolid tested either in monotherapy or in combination showed similar efficacy against both strains in terms of bacterial killing, number of negative blood cultures and survival. Linezolid and vancomycin were moderately bactericidal and similar in efficacy against glycopeptide-intermediate or -resistant S. aureus. Linezolid combinations, as effective as linezolid tested alone, could be considered as alternative options for the treatment of glycopeptide-intermediate S. aureus (GISA) infections.

A European survey of antibiotic management of methicillin-resistant Staphylococcus aureus infection: current clinical opinion and practice

Although the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) varies across Europe, healthcare-associated MRSA infections are common in many countries. Despite several national guidelines, the approach to treatment of MRSA infections varies across the continent, and there are multiple areas of management uncertainty for which there is little clinical evidence to guide practice. A faculty, convened to explore some of these areas, devised a survey that was used to compare the perspectives of infection specialists from across Europe on the management of MRSA infections with those of the faculty specialists. The survey instrument, a web-based questionnaire, was sent to 3840 registered delegates of the 19th European Congress of Clinical Microbiology and Infectious Diseases, held in April 2009. Of the 501 (13%) respondents to the survey, 84% were infection/microbiology specialists and 80% were from Europe. This article reports the survey results from European respondents, and shows a broad range of opinion and practice on a variety of issues pertaining to the management of minor and serious MRSA infections, such as pneumonia, bacteraemia, and skin and soft tissue infections. The issues include changing epidemiology, when and when not to treat, choice of treatment, and duration and route of treatment. The survey identified areas where practice can be improved and where further research is needed, and also identified areas of pan-European consensus of opinion that could be applied to European guidelines for the management of MRSA infection.

A focus on intra-abdominal infections

Complicated intra-abdominal infections are an important cause of morbidity and are frequently associated with poor prognosis, particularly in higher risk patients.

Well defined evidence-based recommendations for intra-abdominal infections treatment are partially lacking because of the limited number of randomized-controlled trials.

Factors consistently associated with poor outcomes in patients with intra-abdominal infections include increased illness severity, failed source control, inadequate empiric antimicrobial therapy and healthcare-acquired infection.

Early prognostic evaluation of complicated intra-abdominal infections is important to select high-risk patients for more aggressive therapeutic procedures.

The cornerstones in the management of complicated intra-abdominal infections are both source control and antibiotic therapy.

The timing and the adequacy of source control are the most important issues in the management of intra-abdominal infections, because inadequate and late control of septic source may have a negative effect on the outcomes.

Recent advances in interventional and more aggressive techniques could significantly decrease the morbidity and mortality of physiologically severe complicated intra-abdominal infections, even if these are still being debated and are yet not validated by limited prospective trials.

Empiric antimicrobial therapy is nevertheless important in the overall management of intra-abdominal infections. Inappropriate antibiotic therapy may result in poor patient outcomes and in the appearance of bacterial resistance.

Antimicrobial management is generally standardised and many regimens, either with monotherapy or combination therapy, have proven their efficacy. Routine coverage especially against Enterococci and candida spp is not always recommended, but can be useful in particular clinical conditions. A de escalation approach may be recommended in patients with specific risk factors for multidrug resistant infections such as immunodeficiency and prolonged antibacterial exposure.

Therapy should focus on the obtainment of adequate source control and adequate use of antimicrobial therapy dictated by individual patient risk factors. Other critical issues remain debated and more controversies are still open mainly because of the limited number of randomized controlled trials.

Swine Influenza (H1N1) pneumonia: clinical considerations

Influenza is a viral zoonosis of birds and mammals that has probably existed since antiquity. Attack rates of influenza are relatively high but mortality is relatively low. Influenza mortality is highest in the very young, the very old, and the immunosuppressed. Influenza has the potential for rapid spread and may involve large populations. This article examines the swine influenza (H1N1) strain of recent origin, and compares the microbiology, epidemiology, clinical presentation, differential, clinical, and laboratory diagnosis, therapy, complications, and prognosis with previous recorded outbreaks of avian and human seasonal influenza pneumonias.

Rapid clinical diagnosis in fatal swine influenza (H1N1) pneumonia in an adult with negative rapid influenza diagnostic tests (RIDTs): diagnostic swine influenza triad

BACKGROUND

The "herald wave" of the H1N1 pandemic spread from Mexico to the United States in spring 2009. Initially, the epicenter of H1N1 in the United States was in the New York area. Our hospital, like others, was inundated with large numbers of patients who presented at the Emergency Department (ED) with influenza-like illnesses (ILIs) for swine influenza testing and evaluation.

METHODS

The Winthrop-University Hospital ED used rapid influenza (QuickVue A/B) tests to screen for H1N1 infection. Patients who were rapid influenza A test-positive were also reverse transcription-polymerase chain reaction (RT-PCR) positive for H1N1. In our ED, 30% of patients with ILIs and possible H1N1 pneumonia had negative rapid influenza A screening tests. Because H1N1 RT-PCR testing was restricted, there was no laboratory test to confirm or rule out H1N1. Other rapid influenza diagnostic tests (RIDTs), e.g., the respiratory fluorescent antibody (FA) viral panel test, were used to identify H1N1 patients with negative RIDTs.

RESULTS

Unfortunately, there was not a good correlation between RIDT results and RT-PCR results. There was a critical need to develop a clinical syndromic approach for diagnosing hospitalized adults with probable H1N1 pneumonia with negative RIDTs. Early in the pandemic, the Winthrop-University Hospital Infectious Disease Division developed a diagnostic weighted point score system to diagnose H1N1 pneumonia clinically in RIDT-negative adults. The point score system worked well, but was time-consuming. As the "herald wave" of the pandemic progressed, our ED staff needed a rapid, simplified method to diagnose probable H1N1 pneumonia in hospitalized adults with negative RIDTs. A rapid and simplified diagnosis was based on the diagnostic weighted point score system, which we simplified into a triad of key, nonspecific laboratory indicators. In adults hospitalized with an ILI, a fever >102 degrees F with severe myalgias, and a chest x-ray without focal segmental/lobar infiltrates, the presence of three indicators, i.e., otherwise unexplained relative lymphopenia, elevated serum transaminases, and an elevated creatinine phosphokinase, constituted the diagnostic swine influenza triad. The Infectious Disease Division's diagnostic swine flu triad was used effectively as the pandemic progressed, and was not only useful in correctly diagnosing probable H1N1 pneumonia in hospitalized adults with negative RIDTs, but was also in ruling out mimics of swine influenza, e.g., exacerbations of chronic bronchitis, asthma, or congestive heart failure, as well as bacterial community-acquired pneumonias (CAPs), e.g., legionnaire's disease.

CONCLUSION

Clinicians can use the Winthrop-University Hospital Infectious Disease Division's Diagnostic swine influenza triad to make a rapid clinical diagnosis of probable H1N1 pneumonia in hospitalized adult patients with negative RIDTs.

Daptomycin in bone and joint infections: a review of the literature

INTRODUCTION

To review the pharmacology, pharmacokinetics, efficacy, and safety of daptomycin, a novel antibiotic for the treatment of bone and joint infections, a literature search of relevant articles was conducted.

MATERIALS AND METHODS

A PubMed/MEDLINE search (1990-April 2008) to identify relevant English-language literature was conducted. Search terms included bone and joint infection, osteomyelitis, daptomycin, and methicillin-resistant Staphylococcus aureus (MRSA). Additional articles were identified by reviewing the bibliographies of articles cited. Programs and abstracts from infectious disease meetings were searched, and prescribing information of antibiotics indicated for bone and joint infections consulted. All articles identified from data sources published in English were evaluated.

RESULTS

Caused primarily by Gram-positive pathogens such as S. aureus and, to a lesser extent, Enterococcus faecalis, bone and joint infections are difficult to treat successfully. Surgical intervention and prolonged courses of antibiotics are frequently required, and failure of first-line antibiotic therapy is common. The emergence of S. aureus strains with reduced susceptibility to vancomycin, the longstanding gold standard for bone and joint infections, has complicated the clinical scenario. Few randomized trials comparing the efficacy of different antibiotics for bone and joint infections exist. Daptomycin, a novel intravenous lipopeptide antibiotic, has shown potent in vitro activity against a broad spectrum of Gram-positive bacteria, including many resistant pathogens commonly associated with bone and joint infections such as MRSA and vancomycin-resistant E. faecalis. Early clinical investigation of daptomycin in bone and joint infections unresponsive to antibiotics, such as vancomycin, has found a cure rate of approximately 80%, with a low incidence of adverse events and drug resistance.

CONCLUSION

Further studies are warranted to determine if limited clinical evidence, described in individual case reports and a daptomycin-specific retrospective registry, suggests daptomycin is a promising option for patients with bone and joint infections such as MRSA osteomyelitis.

Update on cutaneous manifestations of infectious diseases

Many emerging pathogens present in the skin and are of interest to dermatologists. Recent epidemics of measles, avian flu, and SARS demonstrated how an organism can rapidly spread worldwide because of airline travel. Travelers are often contagious before they are aware that they have the disease, contributing to the spread. This article reviews bacterial, mycobacterial, fungal, and viral pathogens important to dermatologists.

Addition of gentamicin or rifampin does not enhance the effectiveness of daptomycin in treatment of experimental endocarditis due to methicillin-resistant Staphylococcus aureus

This study evaluated the activity of daptomycin combined with either gentamicin or rifampin against three methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates in vitro and one isolate in vivo against a representative strain (MRSA-572). Time-kill experiments showed that daptomycin was bactericidal against these strains at concentrations over the MIC. Daptomycin at sub-MIC concentrations plus gentamicin at 1x and 2x the MIC yielded synergy, while the addition of rifampin at 2 to 4 microg/ml resulted in indifference (two strains) or antagonism (one strain). The in vivo activity of daptomycin (6 mg/kg of body weight once a day) was evaluated +/- gentamicin (1 mg/kg intravenously [i.v.] every 8 h [q8h]) or rifampin (300 mg i.v. q8h) in a rabbit model of infective endocarditis by simulating human pharmacokinetics. Daptomycin plus gentamicin (median, 0 [interquartile range, 0 to 2] log10 CFU/g vegetation) was as effective as daptomycin alone (0 [0 to 2] log10 CFU/g vegetation) in reducing the density of bacteria in valve vegetations (P = 0.83), and both were more effective than daptomycin plus rifampin (3 [2 to 3.5] log10 CFU/g vegetation; P < 0.05) for the strain studied. In addition, daptomycin sterilized a ratio of vegetations that was similar to that of daptomycin plus gentamicin (10/15 [67%] versus 9/15 [60%]; P = 0.7), and both regimens did so more than daptomycin plus rifampin (3/15 [20%]; P = 0.01 and P = 0.02, respectively). No statistical difference was noted between daptomycin plus gentamicin and daptomycin alone for MRSA treatment. In the combination arm, all isolates from vegetations remained susceptible to daptomycin, gentamicin, and rifampin. Sixty-one percent of the isolates (8/13) acquired resistance to rifampin during monotherapy. In the daptomycin arm, resistance was detected in only one case, in which the daptomycin MIC rose to 2 microg/ml among the recovered bacteria. In conclusion, the addition of gentamicin or rifampin does not enhance the effectiveness of daptomycin in the treatment of experimental endocarditis due to MRSA.

Serious infections due to methicillin-resistant Staphylococcus aureus: an evolving challenge for physicians

Methicillin-resistant Staphylococcus aureus (MRSA) is a well-recognized major cause of nosocomial infection worldwide. During the past decade, however, the epidemiology of staphylococcal infections has partially changed, with an increase in the number of patients who acquire infections in the community. The changing epidemiology is a cause for concern among physicians, leading to an increase in the number of patients with infections due to MRSA diagnosed at hospital admission and in the emergency department. The aims of this article are to review the current state of knowledge regarding MRSA infections, to identify those factors which may help physicians to recognize the patients at high risk, and to manage these infections appropriately.

[In vitro activity of arbekacin against clinical isolates of Staphylococcus species and gram-negative bacilli]

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) and some gram-negative bacilli are very prevalent nosocomial pathogens, commonly causing mixed infections, and are often resistant to multiple drugs. Arbekacin is an aminoglycoside used for the treatment of MRSA infections, but is also active against some gram-negative bacilli. The aim of this study was to determine in vitro activity of arbekacin against recent clinical isolates of staphylococci and gram-negative bacilli.

MATERIALS AND METHODS

The strains were isolated from clinical specimens of patients at Severance Hospital in 2003. Antimicrobial susceptibility was tested by the Clinical and Laboratory Standards Institute agar dilution method. The following arbekacin breakpoints were used: susceptible, </=4 microg/mL; and resistant, >/=16 microg/mL .

RESULTS

All isolates of staphylococci tested were inhibited by </=4 microg/mL of arbekacin, regardless of their methicillin susceptibility. The MIC90s of arbekacin, 1-4 microg/mL, were 8->32-fold and >32-128-fold lower than those of amikacin and gentamicin, respectively. The resistance rates of MRSA, methicillin-susceptible S. aureus, methicillin-resistant coagulase-negative staphylococci (CNS) and methicillin-susceptible CNS were 0% to arbekacin, 0-54% to amikacin, and 24-79% to gentamicin. The MIC90s of arbekacin for Escherichia coli and Citrobacter freundii, 1 microg/mL and 16 microg/mL, were 2-4-fold and 8-16-fold lower than those of amikacin and gentamicin, respectively. However, The MIC90s of arbekacin for other species of gram-negative bacilli, 64->128 microg/mL, were similar to those of other aminoglycosides.

CONCLUSIONS

Arbekacin may be a useful alternative to glycopeptides for the treatment of monomicrobial methicillin-resistant staphylococcal infections, as well as mixed infections with gram-negative bacilli, as most isolates of E. coli, C. freundii and some other gram-negative bacilli were also susceptible to arbekacin.

Vascular catheter-associated infections: a microbiological and therapeutic update

The increasing incidence of central venous catheter (CVC)-related infections can be ascribed to the wider indications to central venous catheterization, to the higher attention to this issue paid by clinicians and microbiologists, and to the patient population referred to hospitals, increasingly characterized by different degrees of immunosuppression and often in critical clinical conditions. This phenomenon implies a higher health care burden and higher related costs, as well as a significant attributable mortality, that varies however according to the pathogen involved. The microorganisms most frequently involved in CVC-related infections are coagulase-negative staphylococci, Staphylococcus aureus, aerobic Gram-negative bacilli, and Candida albicans. In the management of suspected or proven central venous catheter-related infections, several issues need to be addressed: the need to remove the device or the possibility of salvage, the immediate start of calculated antibiotic therapy or the possibility of waiting for results of microbiological diagnostics and proceeding to etiologically-guided therapy. The preferred conservative method is the "Antibiotic-Lock technique" (ALT), based on the endoluminal application of antibacterials at extremely high concentrations in situ for a period of time long enough to ensure bactericidal activity. On the other hand, immediate catheter removal and initiation of appropriate calculated therapy immediately after an adequate diagnostic work-up are strongly recommended in a clinical setting of severe sepsis or septic shock.

Survival of epidemic strains of healthcare (HA-MRSA) and community-associated (CA-MRSA) meticillin-resistant Staphylococcus aureus (MRSA) in river-, sea- and swimming pool water

The aim of this study was to examine the survival dynamics of several epidemic healthcare (HA) and community-associated (CA) meticillin-resistant Staphylococcus aureus (MRSA) in river, sea and swimming pool waters. Six different phage-types of HA-MRSA (Irish 1, Irish 2, EMRSA 15, EMRSA 16, distinct type and non-typable), as well as a community-associated MRSA (CA-MRSA), were examined in this study. Two strains of each type were examined resulting in a total of 14 organisms being examined. Cells were harvested from overnight cultures of Columbia blood agar (Oxoid) supplemented with 5% [v/v] defibrinated blood to make a 0.5 McFarland inoculum standard. An inoculum of each MRSA isolate was added individually to each water microcosm to give log(10)5 (10(5)) colony forming units (cfu/ml water) and water was stored in the dark at ambient temperature for up to 14 days. Recovery experiments were unable to isolate any of HA- or CA-MRSA in the swimming pool water after 24 h storage. This study demonstrates that all 14 epidemic HA and CA MRSA studied can survive in sea and river water environments up to at least 14 days post inoculation. There was no significant differences in the survival dynamics between CA-MRSA and HA-MRSA in any water environment, but all MRSA died off more quickly in river water, compared to sea water, with decimal (D(10)) reduction values of 3.53 and 7.4 days, for river- and sea water, respectively. This study indicates that contaminated sea and river water may serve as potential reservoirs of HA- and CA-MRSA, if such water sources become contaminated with these organisms.

Vancomycin revisited: a reappraisal of clinical use

Vancomycin has been used for decades to treat serious systemic gram positive infections. Extensive use over time has demonstrated vancomycin is not nephrotoxic even when used in high dosage, i.e., twice the usual dose. Since vancomycin is not nephrotoxic, there is no rationale for dosing vancomycin based on serum vancomycin levels. Since vancomycin is eliminated by GFR, vancomycin dosing should be based on creatinine clearance. Vancomycin obeys "concentration dependent" kinetics and higher than usual doses may be useful in some infections (eg, osteomyelitis). Widespread vancomycin use has resulted in increased VRE prevalence worldwide. Among staphylococci, vancomycin induced cell wall thickening results in "permeability mediated" resistance to vancomycin, as well as other anti-staphylococcal antibiotics. "Permeability mediated" resistance accounts for the common clinical observation that MRSA infections treated with vancomycin often resolve slowly or not at all. Other effective MRSA antibiotics are available (eg, linezolid, daptomycin, minocycline, or tigecycline) and are more reliably effective, do not increase staphylococcal resistance or increase VRE prevalence.

Sepsis and septic shock: selection of empiric antimicrobial therapy

This article is a brief overview of empiric antibiotic selection for sepsis and septic shock. The article includes a differential diagnosis of the mimics of sepsis and stresses a strategy for avoiding problems associated with antibiotic resistance. Although early appropriate empiric therapy is the cornerstone of sepsis and septic shock therapy, nonantibiotic interventions are critical as well. In patients with septic shock, adequate and effective early volume replacement is essential. Early surgical intervention is critical in controlling and eliminating the septic focus if sepsis is related to perforation of a viscus (eg, the colon); obstruction of the biliary, gastrointestinal, or urinary tract; or presence of an abscess that requires drainage. If device-related infection is the cause of sepsis, device removal is essential. Empiric monotherapy for sepsis and septic shock is preferred. Multiple-drug therapy is more expensive, has an increased potential for drug-drug interactions, has a higher likelihood of side effects, and does not decrease the resistance potential of the antibiotics being used. For these reasons, early empiric monotherapy is optimal and de-escalation is not necessary if initial mono therapy was wisely selected.

Daptomycin is effective in treatment of experimental endocarditis due to methicillin-resistant and glycopeptide-intermediate Staphylococcus aureus

Daptomycin is a lipopeptide antibiotic with potent in vitro activity against gram-positive cocci, including Staphylococcus aureus. This study evaluated the in vitro and in vivo efficacies of daptomycin against two clinical isolates: methicillin-resistant S. aureus (MRSA) 277 (vancomycin MIC, 2 microg/ml) and glycopeptide-intermediate S. aureus (GISA) ATCC 700788 (vancomycin MIC, 8 microg/ml). Time-kill experiments demonstrated that daptomycin was bactericidal in vitro against these two strains. The in vivo activity of daptomycin (6 mg/kg of body weight every 24 h) was evaluated by using a rabbit model of infective endocarditis and was compared with the activities of a high-dose (HD) vancomycin regimen (1 g intravenously every 6 h), the recommended dose (RD) of vancomycin regimen (1 g intravenously every 12 h) for 48 h, and no treatment (as a control). Daptomycin was significantly more effective than the vancomycin RD in reducing the density of bacteria in the vegetations for the MRSA strains (0 [interquartile range, 0 to 1.5] versus 2 [interquartile range, 0 to 5.6] log CFU/g vegetation; P = 0.02) and GISA strains (2 [interquartile range, 0 to 2] versus 6.6 [interquartile range, 2.0 to 6.9] log CFU/g vegetation; P < 0.01) studied. In addition, daptomycin sterilized more MRSA vegetations than the vancomycin RD (13/18 [72%] versus 7/20 [35%]; P = 0.02) and sterilized more GISA vegetations than either vancomycin regimen (12/19 [63%] versus 4/20 [20%]; P < 0.01). No statistically significant difference between the vancomycin HD and the vancomycin RD for MRSA treatment was noted. These results support the use of daptomycin for the treatment of aortic valve endocarditis caused by GISA and MRSA.

Hospital-acquired infections in the NICU: epidemiology for the new millennium

Nosocomial infections are an important cause of morbidity and mortality in the preterm neonate. Extrinsic and intrinsic risk factors make the preterm neonate particularly susceptible to infection. This review focuses on two major pathogens that cause nosocomial infection, Candida and methicillin-resistant Staphylococcus aureus. The difficult diagnosis of meningitis in the neonate also is discussed.

Methicillin-resistant Staphylococcus aureus (MRSA) mitral valve acute bacterial endocarditis (ABE) in a patient with Job's syndrome (hyperimmunoglobulin E syndrome) successfully treated with linezolid and high-dose daptomycin

Job's syndrome (hyperimmunoglobulin E syndrome) is a congenitally acquired primary immune deficiency. The primary host defense defect in Job's syndrome is impaired phagocytosis. Accordingly, patients with Job's syndrome have difficulties eradicating staphylococcal infections. A continuous, high-grade Staphylococcus aureus bacteremia with a cardiac valve vegetation is the hallmark of S. aureus acute bacterial endocarditis (ABE). ABE may be caused by methicillin-sensitive Staphylococcus aureus or methicillin-resistant Staphylococcus aureus (MRSA). We report a case of Job's syndrome MRSA mitral valve ABE. Presumably because of impaired phagocytic function, his MRSA ABE was complicated by extensive metastatic septic complications manifested as brain abscess, multiple epidural abscesses, and multifocal vertebral osteomyelitis. The patient did not respond to 5 days of appropriately dosed linezolid and daptomycin and remained bacteremic because abscess drainage was not an option in this case and the continuous, high-grade MRSA bacteremia continued despite appropriate therapy. High-dose daptomycin (12 mg/kg intravenously every 24 hours) was given, and his MRSA bacteremia was rapidly terminated. Because daptomycin does not cross the blood-brain barrier in therapeutic concentrations, linezolid was used to treat the brain abscess. The extensiveness of infection in this case is remarkable and is probably related to impaired phagocytic function from Job's syndrome. High-dose daptomycin therapy rapidly cleared the bacteremia and cured the endocarditis and epidural abscesses/vertebral osteomyelitis. The patient was treated with 8 weeks of high-dose daptomycin therapy with no adverse effects. If MRSA and methicillin-sensitive S. aureus bacteremias are unresponsive to usually effective antistaphylococcal agents, and surgical drainage of abscesses and removal of infected devices are not clinically possible, then a prolonged, high dose of daptomycin is a therapeutic alternative in such situations. To the best of our knowledge, this is the first case of MRSA mitral valve ABE complicated by extensive epidural abscesses and vertebral osteomyelitis in a patient with Job's syndrome.

Bactericidal activity of denture-cleaning formulations against planktonic health care-associated and community-associated methicillin-resistant Staphylococcus aureus

The aim of this study was to examine the survival dynamics of several epidemic health care-associated (HA) and community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) in planktonic state in widely employed denture-cleaning solutions. The bacteriocidal activity of five widely employed denture-cleaning formulations were examined against five phage-types of HA-MRSA (EMRSA 15, EMRSA 16, Irish 1, Irish 2, unique type), as well as a CA-MRSA strain, in this study. Viable MRSA cells (circa 10(5) cfu/mL) were coincubated with optimum recommended working concentrations of denture-cleaning solutions for up to 17 hours (overnight). Recovery experiments were unable to isolate any of the inoculated MRSA organisms 10 minutes post inoculation. The significance and impact of this short study indicates that HA-MRSA and CA-MRSA are not able to remain culturable for 10 minutes in planktonic form, in commonly used denture-cleaning formulations widely available on the UK High Street, suggesting that these formulations may be useful in lowering the numbers of MRSA. Further work is however required to examine the more complex survival dynamics of MRSA in naturally derived denture biofilm, associated with dental plaque and the use of such cleaning formulations.

Treatment of orthopedic infections caused by resistant staphylococci

During 1999-2005 we treated 15 patients with linezolid for relevant infections of locomotion apparatus (7 cases with endoprosthesis infection, 5x osteomyelitis and 3x another infection). With the exception of one case the antibiotic therapy was always combined with appropriate surgical intervention. Average period of linezolid administration was 26 d; linezolid was applied from the beginning intravenously on average for 10 d, and then orally for 16 d (average). There were no undesirable effects in the file. Success rate reached 86.6%. MRSA strains were proved by standard methods: growth on Mueller-Hinton agar with increased concentration of NaCl and 2 mg/L of oxacilline, and measuring inhibitory zones around cephoxitine disk. The sensitivity to other antibiotics was specified by disk-diffusion test; that to linezolid was verified by E-test. Linezolid represents a medical reserve for the treatment of multiresistant Gram-positive infections or for emergencies, when allergy onset, high toxicity risk, intolerance, etc. do not allow to use other, in vitro effective, antibiotics.

Prevalence and regional variation in meticillin-resistant Staphylococcus aureus (MRSA) in the USA and comparative in vitro activity of tigecycline, a glycylcycline antimicrobial

The Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) is a surveillance study established in 2004 to monitor the activity of tigecycline, the first glycylcycline, and comparator agents [β-lactams (including penicillins, cephalosporins and carbapenems), glycopeptides, tetracyclines, fluoroquinolones and oxazolidinones] against Gram-positive and Gram-negative pathogens worldwide. This report examines 1692 isolates of Staphylococcus aureus collected in the continental United States between January 2004 and September 2005. Meticillin-resistant S. aureus (MRSA) accounted for 52.0 % of isolates. Prevalence of MRSA by state ranged from 12.5 % in New Hampshire to 100 % in Kentucky. All isolates were susceptible to tigecycline, linezolid and vancomycin. In vitro, tigecycline was potent against both meticillin-susceptible S. aureus (MSSA) (MIC50 and MIC90=0.12 μg ml−1) and MRSA (MIC50=0.12 μg ml−1; MIC90=0.25 μg ml−1). Only a single isolate was resistant to three or more antimicrobial classes. Ninety-six isolates (5.7 %) were susceptible to the complete antimicrobial panel.

Staphylococci

Staphylococci are among the leading causes of nosocomial infections. Increasing insusceptibility to beta-lactams and the glycopeptides complicates treatment of these infections. This review examines the current status and future perspectives for the therapy of infections caused by Staphylococcus aureus and coagulase-negative staphylococci.

Minocycline modulates neuroinflammation independently of its antimicrobial activity in staphylococcus aureus-induced brain abscess

Minocycline exerts beneficial immune modulatory effects in several noninfectious neurodegenerative disease models; however, its potential to influence the host immune response during central nervous system bacterial infections, such as brain abscess, has not yet been investigated. Using a minocycline-resistant strain of Staphylococcus aureus to dissect the antibiotic's bacteriostatic versus immune modulatory effects in a mouse experimental brain abscess model, we found that minocycline significantly reduced mortality rates within the first 24 hours following bacterial exposure. This protection was associated with a transient decrease in the expression of several proinflammatory mediators, including interleukin-1beta and CCL2 (MCP-1). Minocycline was also capable of protecting the brain parenchyma from necrotic damage as evident by significantly smaller abscesses in minocycline-treated mice. In addition, minocycline exerted anti-inflammatory effects when administered as late as 3 days following S. aureus infection, which correlated with a significant decrease in brain abscess size. Finally, minocycline was capable of partially attenuating S. aureus-dependent microglial and astrocyte activation. Therefore, minocycline may afford additional therapeutic benefits extending beyond its antimicrobial activity for the treatment of central nervous system infectious diseases typified by a pathogenic inflammatory component through its ability to balance beneficial versus detrimental inflammation.