Analysis of 42 cases of septicemia caused by an epidemic strain of methicillin-resistant Staphylococcus aureus: evidence of resistance to vancomycin

Interplay Between Antibiotic Resistance and Virulence During Disease Promoted by Multidrug-Resistant Bacteria

Diseases caused by antibiotic-resistant bacteria in hospitals are the outcome of complex relationships between several dynamic factors, including bacterial pathogenicity, the fitness costs of resistance in the human host, and selective forces resulting from interventions such as antibiotic therapy. The emergence and fate of mutations that drive antibiotic resistance are governed by these interactions. In this review, we will examine how different forms of antibiotic resistance modulate bacterial fitness and virulence potential, thus influencing the ability of pathogens to evolve in the context of nosocomial infections. We will focus on 3 important multidrug-resistant pathogens that are notoriously problematic in hospitals: Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus. An understanding of how antibiotic resistance mutations shape the pathobiology of multidrug-resistant infections has the potential to drive novel strategies that can control the development and spread of drug resistance.

Vancomycin pharmacokinetic models: informing the clinical management of drug-resistant bacterial infections

This review aims to critically evaluate the pharmacokinetic literature describing the use of vancomycin in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. Guidelines recommend that trough concentrations be used to guide vancomycin dosing for the treatment of MRSA infections; however, numerous in vitro, animal model and clinical studies have demonstrated that the therapeutic effectiveness of vancomycin is best described by the area under the concentration versus time curve (AUC) divided by the minimum inhibitory concentration (MIC) of the infecting organism (AUC/MIC). Among patients with lower respiratory tract infections, an AUC/MIC ≥400 was associated with a superior clinical and bacteriological response. Similarly, patients with MRSA bacteremia who achieved an Etest AUC/MIC ≥320 within 48 h were 50% less likely to experience treatment failure. For other patient populations and different clinical syndromes (e.g., children, the elderly, patients with osteomyelitis, etc.), pharmacokinetic/pharmacodynamic studies and prospective clinical trials are needed to establish appropriate therapeutic targets.

Interaction between lichen secondary metabolites and antibiotics against clinical isolates methicillin-resistant Staphylococcus aureus strains

The in vitro antimicrobial activities of five compounds isolated from lichens, collected in several Southern regions of Chile (including the Chilean Antarctic Territory), were evaluated alone and in combination with five therapeutically available antibiotics, using checkerboard microdilution assay against methicillin-resistant clinical isolates strains of Staphylococcus aureus. MIC90, MIC50, as well as MBC90 and MBC50, for the lichen compounds were evaluated. The MIC90 was ranging from 32 µg/ml for perlatolic acid to 128 µg/ml for α-collatolic acid. MBC90 was ranging from onefold up to twofold the MIC90 for each compound. A synergistic action was observed in combination with gentamicin, whilst antagonism was observed for some lichen compounds in combination with levofloxacin. All combinations with erythromycin were indifferent, whilst variability was observed for clindamycin and oxacillin combinations. Data from checkerboard assay were analysed and interpreted using the fractional inhibitory concentration index and the response surface approach using the ΔE model. Discrepancies were found between both methods for some combinations. These could mainly be explained by the failure of FIC approach, being too much subjective and sensitive to experimental errors. These findings suggest, however, that the natural compounds from lichens are good candidates for the individuation of novel templates for the development of new antimicrobial agents or combinations of drugs for chemotherapy.

Effect of Vancomycin Therapy for Osteomyelitis on Colonization by Methicillin-ResistantStaphylococcus aureus: Lack of Emergence of Glycopeptide Resistance

Background:

In treating orthopedic infections, the long-term impact of vancomycin therapy on colonization by methicillin-resistantStaphylococcus aureus(MRSA) and the emergence of vancomycin-intermediate S.aureusis unknown.

Design:

Prospective surveillance of the effect of long-term vancomycin therapy on colonization by MRSA and the emergence of vancomycin-intermediateS. aureus.

Methods:

Thirty-four patients with MRSA osteomyelitis that was microbiologically documented were longitudinally observed for the emergence of vancomycin-intermediate S.aureusat 3 body sites (wound, anterior nares, and groin) during the initial period of vancomycin therapy and at the 2-month follow-up. Twenty patients received the standard dose (20 mg/kg/d) for 34 ± 6 days and 14 patients received a high dose (40 mg/kg/d) of vancomycin for 37 ± 9 days.

Results:

During vancomycin treatment, global MRSA carriage (all body sites) fell from 100% to 25% in the group of patients receiving the standard dose of vancomycin, and from 100% to 40% in the group receiving the high dose. During the 2-month follow-up period after vancomycin therapy, global MRSA carriage increased from 25% to 55% in the group receiving the standard dose and decreased from 43% to 36% in the group receiving the high dose.

Conclusion:

Therapy with a high dose of vancomycin contributes to the sustained eradication of MRSA carriage without promoting the emergence of glycopeptide resistance.

Models matter: the search for an effective Staphylococcus aureus vaccine

Staphylococcus aureus is a highly successful bacterial pathogen owing to its abundance of cell surface and secreted virulence factors. It is estimated that 30% of the population is colonized with S. aureus, usually on mucosal surfaces, and methicillin-resistant S. aureus is a major public health concern. There have been multiple attempts to develop an S. aureus vaccine using one or more cell surface virulence factors as antigens; all of these vaccine trials have failed. In this Opinion article, we suggest that an over-reliance on rodent models and a focus on targeting cell surface components have been major contributing factors to this failure.

Effects of Essential Oils and Monolaurin on Staphylococcus aureus: In Vitro and In Vivo Studies

The antimicrobial properties of volatile aromatic oils and medium-chain fatty acids derived from edible plants have been recognized since antiquity. To give examples, Origanum oil, used as a food-flavoring agent, possesses a broad spectrum of antimicrobial activity due, at least in part, to its high content of phenolic derivatives such as carvacrol and thymol. Similarly, lauric acid, present in heavy concentrations in coconuts, forms monolaurin in the body that can inhibit the growth of pathogenic microbes. Using Staphylococcus aureus in broth cultures and a microdilution method, comparative efficacy of Origanum oil, and a constituent carvacrol, other essential oils and monolaurin were examined. Origanum oil was the most potent of the essential oils tested and proved bactericidal in culture to two strains of Staphylococcus aureus (ATCC #14154 and #14775) at 0.25 mg/mL. In vitro, monolaurin's effects mirrored Origanum oil. The combination of both was bactericidal at the 0.125 mg/mL concentration of each. In two separate In vivo experiments, injected Staphylococcus aureus (ATCC #14775) killed all 14 untreated mice within a 1-week period. In treated mice, over one third survived for 30 days when given oral Origanum oil daily for 30 days (6/14). Fifty percent of the mice survived for 30 days when receiving daily vancomycin (7/14) and monolaurin (4/8). Over 60% of mice survived when receiving a daily combination of Origanum oil and monolaurin (5/8). Origanum oil and/or monolaurin may prove to be useful antimicrobial agents for prevention and therapy of Staphylococcus aureus infections.

The interface between antibiotic resistance and virulence in Staphylococcus aureus and its impact upon clinical outcomes

The ability of Staphylococcus aureus to rapidly acquire antibiotic resistance in the face of antimicrobial challenge has enabled it to remain an ongoing, significant human pathogen. Mechanisms behind the evolution of resistance in S. aureus are well documented, but the effects of these phenotypes upon virulence are less clear. By exploring available clinical and experimental data, we have shown that a number of the major steps in the evolution of antibacterial resistance in S. aureus have been accompanied by alterations in virulence. This review also highlights that further experimentation is required to fully elucidate the mechanisms involved in the interface between virulence and antibiotic resistance, with the intention of identifying novel preventative or therapeutic strategies for this important human pathogen.

The clinical significance of vancomycin minimum inhibitory concentration in Staphylococcus aureus infections: a systematic review and meta-analysis

BACKGROUND

Emerging data suggest that vancomycin may be less effective against serious methicillin-resistant Staphylococcus aureus (MRSA) infections with minimum inhibitory concentration (MIC) values at the higher end of the susceptibility range. The purpose of this review is to examine the strength of these associations.

METHODS

All relevant studies pertaining to treatment outcomes or mortality associated with vancomycin MIC were retrieved from the medical literature from January 1996 through August 2011 and analyzed according to Cochrane guidelines.

RESULTS

Of the 270 studies identified, 48 studies were reviewed, with 22 studies included in the final meta-analysis. Vancomycin MIC was significantly associated with mortality for MRSA infection irrespective of the source of infection or MIC methodology (odds ratio [OR], 1.64; 95% confidence interval [CI], 1.14-2.37; P < .01). This mortality association was predominantly driven by bloodstream infections (BSIs; OR, 1.58; 95% CI, 1.06-2.37; P = .03) and isolates with a vancomycin MIC of 2 μg/mL by Etest (OR, 1.72; 95% CI, 1.34-2.21; P < .01). Vancomycin MIC was significantly associated with treatment failure irrespective of source of infection or MIC methodology (OR, 2.69; 95% CI, 1.60-4.51; P < .01).

CONCLUSION

High vancomycin MIC was associated with a higher mortality rate in MRSA BSI. Thus, institutions should consider conducting Etest MICs on all MRSA BSI isolates. Although these data highlight concerns about vancomycin, currently, there are no data to support better survival rates with alternative antibiotics. Data are sorely needed to determine whether other agents can remedy these outcomes observed with vancomycin for MRSA infections with elevated vancomycin MIC values.

MRSA new treatments on the horizon: current status

There is a choice of anti-MRSA antibiotic available with proven efficacy in the treatment of complicated skin and skin structure infection (cSSSI). Additional anti-MRSA antibiotics are in development, which have the potential to influence how such infections are managed. The emergence of resistance to current anti-MRSA agents, toxicity, and general lack of oral agents with proven efficacy for deep seated infection justify the development of new agents. However, there is a relative dearth of information specific to patients with orthopaedic-related infection. Combination therapy is often used in these patients, although there is a paucity of controlled trial data to support particular antibiotic combinations. As the choice of anti-MRSA agents increases, so does the need to identify which are best for the large variety of infections included in the group of cSSSIs. This is particular true for infections occurring in orthopaedic patients where poorly vascularised tissue, trauma or implanted prosthetic material, pose specific challenges.

Reduced vancomycin susceptibility in Staphylococcus aureus, including vancomycin-intermediate and heterogeneous vancomycin-intermediate strains: resistance mechanisms, laboratory detection, and clinical implications

The emergence of vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) over the past decade has provided a challenge to diagnostic microbiologists to detect these strains, clinicians treating patients with infections due to these strains, and researchers attempting to understand the resistance mechanisms. Recent data show that these strains have been detected globally and in many cases are associated with glycopeptide treatment failure; however, more rigorous clinical studies are required to clearly define the contribution of hVISA to glycopeptide treatment outcomes. It is now becoming clear that sequential point mutations in key global regulatory genes contribute to the hVISA and VISA phenotypes, which are associated predominately with cell wall thickening and restricted vancomycin access to its site of activity in the division septum; however, the phenotypic features of these strains can vary because the mutations leading to resistance can vary. Interestingly, changes in the staphylococcal surface and expression of agr are likely to impact host-pathogen interactions in hVISA and VISA infections. Given the subtleties of vancomycin susceptibility testing against S. aureus, it is imperative that diagnostic laboratories use well-standardized methods and have a framework for detecting reduced vancomycin susceptibility in S. aureus.

Treatment strategies for methicillin-resistant Staphylococcus aureus infections in pediatrics

Staphylococcus aureus is an important pathogen that frequently causes clinical disease in children. A wide array of illnesses can be caused by this common pathogen ranging from non-invasive skin infections to severe, life-threatening sepsis. Additionally, as antibacterials have been used to eradicate S. aureus, it has developed resistance to these important therapeutic agents. Methicillin-resistant S. aureus (MRSA) has become an increasing problem in pediatric patients over the past decade. In this review, we discuss the epidemiology, pathogenesis, and treatment options available in treating MRSA infections in children. Specifically, we address the importance of abscess drainage in the treatment of skin and soft tissue infections, the most common clinical manifestation of MRSA infections, and highlight the various agents that are available for treating this common infection. In severe, life-threatening invasive MRSA infections the primary therapeutic option is vancomycin. In cases of MRSA toxic shock syndrome the addition of clindamycin is necessary. In other invasive MRSA infections, such as pneumonia and musculoskeletal infections, the empiric treatment of choice is clindamycin. Finally, newer agents and additional treatment options are discussed.

Development of glycopeptide-intermediate resistance by Staphylococcus aureus leads to attenuated infectivity in a rat model of endocarditis

Glycopeptide-intermediate resistant Staphylococcus aureus (GISA) are characterized by multiple changes in the cell wall and an altered expression of global virulence regulators. We investigated whether GISA are affected in their infectivity in a rat model of experimental endocarditis. The glycopeptide-susceptible, methicillin-resistant S. aureus M1V2 and its laboratory-derived GISA M1V16 were examined for their ability to (i) adhere to fibrinogen and fibronectin in vitro, (ii) persist in the bloodstream after intravenous inoculation, (iii) colonize aortic vegetations in rats, and (iv) compete for valve colonization by co-inoculation. Both GISA M1V16 and M1V2 adhered similarly to fibrinogen and fibronectin in vitro. In rats, GISA M1V16 was cleared faster from the blood (P < 0.05) and required 100-times more bacteria than parent M1V2 (10(6) versus 10(4)CFU) to infect 90% of vegetations. GISA M1V16 also had 100 to 1000-times lower bacterial densities in vegetations. Moreover, after co-inoculation with GISA M1V16 and M1V2Rif, a rifampin-resistant variant of M1V2 to discriminate them in organ cultures, GISA M1V16 was out-competed by the glycopeptide-susceptible counterpart. Thus, in rats with experimental endocarditis, GISA showed an attenuated virulence, likely due to a faster clearance from the blood and a reduced fitness in cardiac vegetations. The GISA phenotype appeared globally detrimental to infectivity.

Outcome of patients with meticillin-resistant Staphylococcus aureus bacteraemia at an Emergency Department of a medical centre in Taiwan

The number of patients presenting to the Emergency Department (ED) with meticillin-resistant Staphylococcus aureus (MRSA) is increasing, but few studies focus on patients with bacteraemia. From January 2001 to June 2006 the clinical characteristics and outcome of 177 consecutive patients with MRSA bacteraemia visiting an ED of a university hospital were studied. The average age of the patients was 65.8 years. Healthcare-associated MRSA bacteraemia comprised 76.3% of all cases. Catheter-related bacteraemia was the most common type of infection (22.6%), followed by soft tissue infection (20.9%) and primary bacteraemia (15.3%). Different types of infection were significantly related to different outcome. In-hospital mortality was 33.3%, but the mortality decreased to 17.7% when patients with rapidly fatal disease and mortality within 3 days were excluded. All isolates exhibited lower susceptibility to vancomycin (minimum inhibitory concentration (MIC) 1–2 μg/mL). Factors associated with mortality included severity of underlying illness, severity of bacteraemia and persistent bacteraemia. A detrimental effect of elevated MIC could not be demonstrated despite applying several definitions of patient outcome. Patients admitted to the ED with MRSA bacteraemia carry high overall mortality; however, the severity of underlying illness, severity of bacteraemia and persistent bacteraemia are correlated with mortality, but not vancomycin MICs (2 μg/mL) of MRSA isolates.

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.

Antibiotic Prescribing in Critical Care: Specific Indications

This article outlines recommendations for the treatment of specific infections occurring in the setting of critical care. In the interests of brevity, a limited number of infections are discussed and recommendations are largely confined to empirical therapy. Basic principles of diagnosis and treatment apply in all cases, including appropriate de-escalation when an organism is identified. These aspects of treatment have been dealt with in part one of this article – ‘Antibiotic prescribing in critical care: general principles' published in the winter 2007 edition of JICS.

Linezolid versus glycopeptide or beta-lactam for treatment of Gram-positive bacterial infections: meta-analysis of randomised controlled trials

Linezolid has been approved for the treatment of patients with infections caused by Gram-positive cocci that are resistant to traditionally used antibiotics, including glycopeptides. This oxazolidinone antibiotic has been reported to have excellent pharmacokinetics and effectiveness. We did a meta-analysis of randomised controlled trials (RCTs) to clarify whether linezolid is superior to glycopeptides or beta-lactams for the treatment of Gram-positive infections. 12 RCTs, involving 6093 patients, were included. Overall, with respect to treatment success, linezolid was more effective than glycopeptides or beta-lactams (odds ratio [OR] 1.41 [95% CI 1.11-1.81]). Mortality was similar between the groups (OR 0.97 [0.79-1.19]). Linezolid was more effective than comparators in patients with skin and soft-tissue infections (OR 1.67 [1.31-2.12]) and bacteraemia (OR 2.07 [1.13-3.78]). However, there was no difference in treatment success for patients with pneumonia (OR 1.03 [0.75-1.42]). Treatment with linezolid was not associated with more adverse effects in general (OR 1.40 [0.95-2.06]); however, thrombocytopenia was recorded more commonly in patients receiving linezolid (OR 11.72 [3.66-37.57]). Although linezolid is more effective than its comparators for the empirical treatment of selected patients, several points, such as the use of less potent antistaphylococcal beta-lactams, the same all-cause mortality, and the higher probability of thrombocytopenia, should be taken into account and may limit the use of linezolid to specific patient populations or infections that are difficult to treat with other antibiotics.

Antibiotic resistance in Staphylococcus aureus and its relevance in therapy

Staphylococcus aureus is a major cause of infections. Only approximately 20% of the strains remain sensitive to penicillin. Beta-lactamase stable penicillins such as flucloxacillin form the mainstay of treatment of staphylococcal infection. Meticillin-resistant S. aureus (MRSA) are resistant to all beta-lactam antibiotics. Glycopeptide antibiotics are effective against most MRSA strains but, in the last few years, isolates of MRSA that have reduced susceptibility to glycopeptides (glycopeptide-intermediate S. aureus) have been isolated. Some strains exhibit frank resistance to glycopeptides (vancomycin-resistant S. aureus). Infections due to these strains are difficult to treat. This review summarises the therapeutic options for MRSA, glycopeptide-intermediate S. aureus and vancomycin-resistant S. aureus. Novel therapeutic strategies such as immunotherapy and vaccines are also discussed.

Pharmacodynamics of antibiotics to treat multidrug-resistant Gram-positive hospital infections

Hospital infection due to multidrug-resistant Gram-positive bacteria may often represent a life-threatening challenge; thus, to appropriately combat them, clinicians should be confident and systematically apply several important pharmacodynamic concepts. The concept of 'correct antibiotic treatment' should include, in addition to an appropriate choice in terms of antimicrobial susceptibility, an appropriate dosage and administration schedule consistent with the pharmacodynamic principles. In the next few years, it is expected that some of the anti-Gram-positive antimicrobial agents that are currently under investigation will be added to the therapeutic armamentarium. However, optimization of the usage of old drugs still remains a clinical priority and a scientific challenge, whose dignity may be considered of similar importance to that of the assessment of the possible therapeutic role of the new compounds.

Emerging Options for Treatment of Invasive, Multidrug-ResistantStaphylococcus aureusInfections

Limited established treatment options exist for the treatment of serious, invasive infections caused by multidrug-resistant Staphylococcus aureus, most notably nosocomially acquired methicillin-resistant S. aureus (MRSA). Although vancomycin represents the gold standard for therapy of such invasive infections, reports of increasing in vitro resistance to vancomycin, combined with reports of clinical failures (with this and other antistaphylococcal agents), underscore the need for alternative therapies. Older agents with favorable in vitro activity available in both oral and intravenous dose forms include trimethoprim-sulfamethoxazole and clindamycin. Limited clinical data exist to support their routine use as initial therapy in the treatment of invasive disease. However, these and other options (e.g., tetracyclines) are being reexplored in the setting of increasing concern over MRSA acquired in the community setting. Newer treatment options for MRSA include linezolid, quinupristin-dalfopristin, daptomycin, and tigecycline. With the exception of linezolid, these newer agents require intravenous administration. Combination therapy may be considered in select invasive diseases refractory to standard monotherapies. These diseases include infections such as endocarditis, meningitis, and prosthetic device infections. Additional alternatives to vancomycin are under clinical investigation. Those in later stages of development include oritavancin, dalbavancin, telavancin, and ceftobiprole.

Costs of hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) and its control

For most countries badly affected by methicillin-resistant Staphylococcus aureus (MRSA) there have been many years of debate about its relative virulence compared with methicillin-susceptible S. aureus (MSSA) and whether it could be controlled. Now that it is endemic in the majority of hospitals around the world, it is clear that it is at least as virulent as MSSA and is an additional burden of healthcare-acquired infection. There is increasing evidence that, despite this endemicity, control efforts can be successful, although they are often perceived as expensive. In reality, there is a large body of consistent evidence that control is highly cost effective, particularly in the context of the huge societal costs of MRSA and the future ever-greater threats that it poses.

Early experience with linezolid for infections in orthopaedics

In infections following orthopaedic surgery, isolated staphylococci are reported to be methicillin resistant (MRSA) in up to 50% of cases. Linezolid, the first in a new class of antibiotics, has excellent efficacy against gram positive organisms that are resistant to other therapies and is 100% orally bioavailable. We report early results of its use for the treatment of resistant infections in orthopaedic practice. Infections were characterised according to the UK Nosocomial Infections National Surveillance Service classification of surgical infections as superficial, deep or organ/space. Osteomyelitis, joint sepsis and deep infection involving orthopaedic implants were included into the final category. Outcome was recorded as clinical, microbiological and blood parameter cure or fail. Over the 12-month study period, 54 patients received linezolid therapy, 41% of these had significant co-morbidity that might affect their ability to fight infection. Sixty-seven percent of infections were in association with implanted metal work. The majority of patients were treated with vancomycin for a short period before linezolid was used as oral 'switch' therapy for longer-term administration, allowing early discharge in all cases. MRSA was isolated in 87% of the patients treated. The mean length of linezolid therapy was 39 days (2-151). Clinical success was achieved in 90% of patients overall. Though there were no life-threatening complications, adverse event rates were significantly higher than those recorded in the literature, with 19% of patients needing to cease therapy. Linezolid offers an alternative to traditional treatments for resistant infections and can facilitate early discharge. Patients need to be monitored closely, particularly where long-term therapy is planned.

Outbreak of epidemic methicillin-resistant Staphylococcus aureus in a regional burns unit: Management and implications

Colonization of burn patients with methicillin-resistant Staphylococcus aureus (MRSA) is not uncommon, however an outbreak that necessitates closure of a burns unit is relatively rare. The objective of this study was to present the experience of a regional adult burns unit where an outbreak of epidemic MRSA-15 (EMRSA-15) took place. During the studied period, 176 patients were admitted to the unit, 52 with burns, 48 for elective plastic surgery procedures while the remainder belonged to other specialties. Patients admitted under burns and plastic surgery were investigated together with 46 staff members to control the outbreak. MRSA was isolated in 18 patients out of which 12 had EMRSA-15. Among the staff members, MRSA was isolated in nine of which five had EMRSA-15. The burns unit was closed to all admissions to terminate this outbreak. The MRSA positive staff members were sent on "special leave" and underwent treatment with nasal mupirocin and triclosan body wash. All staff members were able to return to work after one week's treatment. The burns unit underwent re-furbishment and decontamination while it was closed. In conclusion, the study shows that an outbreak of EMRSA was controlled successfully, however, it highlights the implications of such an event for a regional burn service with regard to staff, patients and guidelines for management.

Guidelines for the prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the UK

These evidence-based guidelines have been produced after a literature review of the treatment and prophylaxis of methicillin-resistant Staphylococcus aureus (MRSA) infection. The guidelines were further informed by antibiotic susceptibility data on MRSA from the UK. Recommendations are given for the treatment of common infections caused by MRSA, elimination of MRSA from carriage sites and prophylaxis of surgical site infection. There are several antibiotics currently available that are suitable for use in the management of this problem and potentially useful new agents are continuing to emerge.

The clinical significance of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for the largest outbreak of hospital-acquired infection (HAI) that the world has ever seen. It is not replacing methicillin-susceptible S. aureus (MSSA), but seems largely to be an additional burden of HAI with double the mortality of MSSA infections, at least in the bacteraemic form. It is often highly transmissible and carriage seems to lead to clinical infection much more frequently than with MSSA carriage. Additional screening for MRSA needs to be performed, not only to establish the size of the problem and to allow initiation of decolonization measures to prevent the onset of clinical disease, but also to allow implementation of infection control precautions that will be necessary to control the epidemic. MRSA is a huge clinical burden that is causing great public and political concern. Current treatments are suboptimal. Control measures are likely to be effective and cost saving if they have a broad enough base, and should be implemented without further delay.

Management of serious nosocomial bacterial infections: do current therapeutic options meet the need?

Hospital-acquired bacterial infections pose a formidable challenge for healthcare providers, as patients often need to be treated empirically, at least initially, although delay of appropriate initial antimicrobial therapy is known to increase morbidity significantly and to increase mortality among affected patients. This elevated risk is compounded by the presence of antibiotic-resistant bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), extended-spectrum beta-lactamase-producing Enterobacteriaceae, Escherichia coli and Klebsiella pneumoniae. Prompt initiation of treatment with an appropriate antimicrobial agent that is active against both Gram-positive and Gram-negative organisms is prudent for patients with nosocomial infections. As the continued usefulness of vancomycin comes into question, the number of alternative agents that provide efficacy equal to that of vancomycin remains limited. The development of novel and effective alternative agents, such as tigecycline, is therefore important.

Unstable vancomycin heteroresistance is common among clinical isolates of methiciliin-resistant Staphylococcus aureus

We tested 109 unique, vancomycin-susceptible, methicillin-resistant Staphylococcus aureus (MRSA) strains for vancomycin heteroresistance by a selection method, i.e., step-wise exposure of large inoculums to increasing concentrations of vancomycin. Although no strains demonstrated stable heteroresistance, 81 strains (74%) demonstrated unstable heteroresistance. Unstable heteroresistance is common among clinical isolates of MRSA and may represent a cause of therapeutic failure.

Dehydroepiandosterone induction of increased resistance to vancomycin in Staphylococcus aureus clinical isolates (MSSA, MRSA)

AIMS

To investigate whether dehydroepiandosterone (DHEA), an androgen present throughout life, alters the response of Staphylococcus aureus clinical isolates to vancomycin.

METHODS AND RESULTS

DHEA in physiologically relevant concentrations (0.1, 0.5, 1.0 and 5.0 micromol l(-1)) was tested for its effect on methicillin-sensitive S. aureus (MSSA, n = 53) and methicillin-resistant S. aureus (MRSA, n = 73) response to vancomycin using standard protocols. Mutant selection was determined by serial transfer of selected isolates (n = 5). DHEA-mediated at least a fourfold increase in vancomycin MIC for 42% of MSSA and 21% of MRSA. For five of the isolates (0.1 and 0.5 micromol l(-1) DHEA) the MIC was increased to levels (8 microg ml(-1)) defined as vancomycin-intermediate resistance.

CONCLUSION

Resistance was detected only in the presence of DHEA, and was not related to altered generation time, indicating induction of phenotypic resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings require further investigation to determine what role DHEA plays in clinical vancomycin treatment failure that has been reported in the absence of vancomycin genotypic resistance or heteroresistance.

Minimum inhibitory concentrations of herbal essential oils and monolaurin for gram-positive and gram-negative bacteria

New, safe antimicrobial agents are needed to prevent and overcome severe bacterial, viral, and fungal infections. Based on our previous experience and that of others, we postulated that herbal essential oils, such as those of origanum, and monolaurin offer such possibilities. We examined in vitro the cidal and/or static effects of oil of origanum, several other essential oils, and monolaurin on Staphylococcus aureus, Bacillus anthracis Sterne, Escherichia coli, Klebsiella pneumoniae, Helicobacter pylori, and Mycobacterium terrae. Origanum proved cidal to all tested organisms with the exception of B. anthracis Sterne in which it was static. Monolaurin was cidal to S. aureus and M. terrae but not to E. coli and K. pneumoniae. Unlike the other two gram-negative organisms, H. pylori were extremely sensitive to monolaurin. Similar to origanum, monolaurin was static to B. anthracis Sterne. Because of their longstanding safety record, origanum and/or monolaurin, alone or combined with antibiotics, might prove useful in the prevention and treatment of severe bacterial infections, especially those that are difficult to treat and/or are antibiotic resistant.

Pharmacodynamics of vancomycin and other antimicrobials in patients with Staphylococcus aureus lower respiratory tract infections

BACKGROUND

Vancomycin is commonly used to treat staphylococcal infections, but there has not been a definitive analysis of the pharmacokinetics of this antibacterial in relation to minimum inhibitory concentration (MIC) that could be used to determine a target pharmacodynamic index for treatment optimisation.

OBJECTIVE

To clarify relationships between vancomycin dosage, serum concentration, MIC and antimicrobial activity by using data gathered from a therapeutic monitoring environment that observes failures in some cases.

METHODS

We investigated all patients with a Staphylococcus aureus lower respiratory tract infection at a 300-bed teaching hospital in the US during a 1-year period. Clinical and pharmacokinetic information was used to determine the following: (i) whether steady-state 24-hour area under the concentration-time curve (AUC24) divided by the MIC (AUC24/MIC) values for vancomycin could be precisely calculated with a software program; (ii) whether the percentage of time vancomycin serum concentrations were above the MIC (%Time>MIC) was an important determinant of vancomycin response; (iii) whether the time to bacterial eradication differed as the AUC24/MIC value increased; (iv) whether the time to bacterial eradication for vancomycin differed compared with other antibacterials at the same AUC24/MIC value; and (v) whether a relationship existed between time to bacterial eradication and time to significant clinical improvement of pneumonia symptoms.

RESULTS

The median age of the 108 patients studied was 74 (range 32-93) years. Measured vancomycin AUC24/MIC values were precisely predicted with the A.U.I.C. calculator in a subset of our patients (r2 = 0.935). Clinical and bacteriological response to vancomycin therapy was superior in patients with higher (> or = 400) AUC24/MIC values (p = 0.0046), but no relationship was identified between vancomycin %Time>MIC and infection response. Bacterial eradication of S. aureus (both methicillin-susceptible and methicillin-resistant) occurred more rapidly (p = 0.0402) with vancomycin when a threshold AUC24/MIC value was reached. S. aureus killing rates were slower with vancomycin than with other antistaphylococcal antibacterials (p = 0.002). There was a significant relationship (p < 0.0001) between time to bacterial eradication and the time to substantial improvement in pneumonia score.

CONCLUSIONS

Vancomycin AUC24/MIC values predict time-related clinical and bacteriological outcomes for patients with lower respiratory tract infections caused by methicillin-resistant S. aureus.

High dose vancomycin for osteomyelitis: continuous vs. intermittent infusion

OBJECTIVES

To compare the efficacy, ease of use and safety of intermittent vancomycin infusion (IVI) and continuous vancomycin infusion (CVI) in high-dose therapy of osteomyelitis.

METHODS

Forty-four patients with an osteomyelitis requiring vancomycin for more than 4 weeks were prospectively included, 21 receiving IVI and 23, CVI. The target serum concentration of vancomycin was 20-25 mg/L. Pharmacokinetics, adverse effects, and clinical efficacy were recorded.

RESULTS

The mean daily vancomycin dosing was the same in the two groups, but the serum vancomycin concentrations (trough or plateau) were lower in the IVI group than the CVI group (21.7 +/- 9.3 and 26.0 +/- 6.1 mg/L, respectively; P < 0.0001). The target concentrations were achieved quicker with CVI, and daily dosing was changed more frequently in the IVI group. After reaching the target, variability of vancomycin serum concentration (trough or plateau concentrations) was higher in the IVI group than in CVI group (standard deviation 7.9 mg/L vs. 5.6 mg/L, respectively; P = 0.001). CVI did not show clinical superiority, but adverse drug effects were more frequent in the IVI group as compared with the CVI group, 9 (42.9%) and 2 (8.7%), respectively (P = 0.03). Survival multiple regression using Cox's proportional hazard model showed that IVI (RR = 5.9, P = 0.03) and osteomyelitis of the foot (RR = 5.2, P = 0.01) were the only factors associated with adverse drug reactions leading to treatment termination.

CONCLUSIONS

CVI is practical and effective, and may be a good alternative for patients requiring prolonged treatment with high vancomycin serum levels.

New Developments in Antibacterial Choice for Lower Respiratory Tract Infections in Elderly Patients

Elderly patients are at increased risk of developing lower respiratory tract infections compared with younger patients. In this population, pneumonia is a serious illness with high rates of hospitalisation and mortality, especially in patients requiring admission to intensive care units (ICUs). A wide range of pathogens may be involved depending on different settings of acquisition and patient's health status. Streptococcus pneumoniae is the most common bacterial isolate in community-acquired pneumonia, followed by Haemophilus influenzae, Moraxella catarrhalis and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae. However, elderly patients with comorbid illness, who have been recently hospitalised or are residing in a nursing home, may develop severe pneumonia caused by multidrug resistant staphylococci or pneumococci, and enteric Gram-negative bacilli, including Pseudomonas aeruginosa. Moreover, anaerobes may be involved in aspiration pneumonia. Timely and appropriate empiric treatment is required in order to enhance the likelihood of a good clinical outcome, prevent the spread of antibacterial resistance and reduce the economic impact of pneumonia. International guidelines recommend that elderly outpatients and inpatients (not in ICU) should be treated for the most common bacterial pathogens and the possibility of atypical pathogens. The algorithm for therapy is to use either a selected beta-lactam combined with a macrolide (azithromycin or clarithromycin), or to use monotherapy with a new anti-pneumococcal quinolone, such as levofloxacin, gatifloxacin or moxifloxacin. Oral (amoxicillin, amoxicillin/clavulanic acid, cefuroxime axetil) and intravenous (sulbactam/ampicillin, ceftriaxone, cefotaxime) beta-lactams are agents of choice in outpatients and inpatients, respectively. For patients with severe pneumonia or aspiration pneumonia, the specific algorithm is to use either a macrolide or a quinolone in combination with other agents; the nature and the number of which depends on the presence of risk factors for specific pathogens. Despite these recommendations, clinical resolution of pneumonia in the elderly is often delayed with respect to younger patients, suggesting that optimisation of antibacterial therapy is needed. Recently, some new classes of antibacterials, such as ketolides, oxazolidinones and streptogramins, have been developed for the treatment of multidrug resistant Gram-positive infections. However, the efficacy and safety of these agents in the elderly is yet to be clarified. Treatment guidelines should be modified on the basis of local bacteriology and resistance patterns, while dosage and/or administration route of each antibacterial should be optimised on the basis of new insights on pharmacokinetic/pharmacodynamic parameters and drug interactions. These strategies should be able to reduce the occurrence of risk factors for a poor clinical outcome, hospitalisation and death.

Methicillin-resistant Staphylococcus aureus: impact on dermatology practice

Methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) emerged in the 1960s and is now commonly seen in hospitals, clinics and, since the mid-1990s, the community. Risk factors for the acquisition of MRSA include chronic dermatoses, underlying medical illnesses, attending healthcare facilities, use of prescription antibacterials, surgery, intravenous lines, hospitalization in an intensive care unit, and proximity to patients colonized with MRSA. Recent community-associated strains often occur in patients without these risk factors. Staphylococci are readily spread from person to person and readily contaminate the environment. Infection control measures thus involve identifying the infected patients, separating them from other non-infected patients, cleaning of the environment and, most important of all, scrupulous attention to hand hygiene. Alcoholic antiseptic hand rubs offer an alternative to antiseptic hand washes and increase compliance. Treatment of MRSA skin infections is challenging. Topical agents such as mupirocin or fusidic acid can be used, but the organisms often become resistant. Systemic therapy involves non-beta-lactams. Parenteral treatment is generally with glycopeptides such as vancomycin; oral therapy is more complex. Monotherapy with quinolones, rifampin (rifampicin), and fusidic acid often results in the development of resistance and so, if any of these agents are chosen it should be in combination. There are no data on combination therapy, although rifampin-containing combinations are often chosen. Fourth-generation quinolones and linezolid are expensive but promising alternatives.

Clinical implications of varying degrees of vancomycin susceptibility in methicillin-resistant Staphylococcus aureus bacteremia

We conducted a retrospective study of the clinical aspects of bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) with heterogeneously reduced susceptibility to vancomycin. Bloodstream MRSA isolates were screened for reduced susceptibility by using brain-heart infusion agar, including 4 mg/L vancomycin with and without 4% NaCl. Patients whose isolates exhibited growth (case-patients) were compared with those whose isolates did not (controls) for demographics, coexisting chronic conditions, hospital events, antibiotic exposures, and outcomes. Sixty-one (41%) of 149 isolates exhibited growth. Subclones from 46 (75%) of these had a higher MIC of vancomycin than did their parent isolates. No isolates met criteria for vancomycin heteroresistance. No differences in potential predictors or in outcomes were found between case-patients and controls. These data show that patients with vancomycin-susceptible MRSA bacteremia have similar baseline clinical features and outcomes whether or not their bacterial isolates exhibit growth on screening media containing vancomycin.

[Importance of a cefpirome-vancomycin combination on bactericidal kinetics in severe MRSA infections in intensive care]

Vancomycin is always the drug of choice for treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) in spite of his bactericidal kinetic.

BACKGROUND

The aim of this study was to evaluate in vivo the improvement of bactericidal kinetic of vancomycin associated with cefpirome against MRSA infection in critically ill patients.

METHODS

The prospective cross-over study was carried out in 20 patients with severe pneumonia or bacteremia. There were randomized to receive vancomycin 2 g per day (Group 1, n = 10) or vancomycin with cefpirome 2 g x 2 (Group 2, n = 10). Clinical recovery, bacteriologic parameters (bactericidal kinetic and bactericidal power in vivo at the peak and the valley), duration of ventilation and stay in ICU were comparatively explored in both groups.

RESULTS

Clinical outcome did not significantly differ between Group 1 and 2. Bactericidal kinetics were better in the Group 2 (40% vs 60% after 6 hours to the dilution for 1/8e) but the difference was not significant. However, bactericidal power in sera was also better in the Group 2 with more bactericidal dilution at 1/16e (68% vs 88.8%: NS) and overall at 1/32e (10.5% vs 50%: p < 0.05) and CRP, an inflammatory marker, was significantly lower in the Group 2 than in the Group 1 (119.5 +/- 24 mg/l vs 198.6 +/- 78 mg/l: p < 0.05) on the third day.

Combination of quinupristin-dalfopristin (Synercid) and rifampin is highly synergistic in experimental Staphylococcus aureus joint prosthesis infection

We compared the efficacies of quinupristin-dalfopristin (Q-D; 30 mg/kg of body weight every 8 h) and vancomycin (60 mg/kg twice daily), alone or in combination with rifampin (10 mg/kg twice daily), in a rabbit model of methicillin-resistant Staphylococcus aureus knee prosthesis infection. In contrast to vancomycin, Q-D significantly reduced the mean log(10) CFU per gram of bone versus that for the controls. The combination of rifampin with either Q-D or vancomycin was significantly more effective than monotherapy.

[Decreasing susceptibility to vancomycin in isogenic Staphylococcus aureus strains isolated from a single patient]

BACKGROUND

We aimed at evaluating the microbiological characteristics and clinical implication of 7 isogenic strains of Staphylococcus aureus with decreased susceptibility to vancomycin.

SUBJECT AND METHOD

A patient with nosocomial trival vularendocarditis due to methicillin-resistant S. aureus had positive blood cultures for 8 weeks despite antimicrobial therapy with vancomycin (normal serum levels) and rifampicin. The patient rejected surgical treatment but the process cured with antimicrobial therapy. The epidemiological relationship of strains was evaluated by pulsed field gel electrophoresis. The susceptibility to vancomycin was evaluated by microdilution and E-test using two different in ocula. The activity of oxacillin, ampicillin and cephalotin was evaluated in Mueller Hinton (MH) agar containing different concentrations of vancomycin (0.06 to 4 mg/l). Heteroresistant subpopulations were determined in both MH and brain heart infussion agar containing vancomycin (0.5 to 512 mg/l). All seven strains belonged to the same clone. Vancomycin MIC ranged from 1 mg/l (isolates 1 to 5) to 4 mg/l (isolates 6 and 7). Isolates 6 and 7 displayed differences in pigmentation and slower growth rates. The susceptibility of these isolates to betalactams inMH containing different concentrations of vancomycin was greater than that in controls. Subpopulations heteroresistant to vancomycin were not detected.

CONCLUSION

The decreased susceptibility of the isogenic S. aureus strains evaluated in this study was not due to heteroresistance and did not cause therapeutic failure.