Vancomycin for Staphylococcus aureus therapy of respiratory tract infections: the end of an era?

A powerful combination of copper-cysteamine nanoparticles with potassium iodide for bacterial destruction

Herein, for the first time, we demonstrate that the combination of copper-cysteamine (Cu-Cy) nanoparticles (NPs) and potassium iodide (KI) can significantly inactivate both Gram-positive MRSA and Gram-negative E. coli. To uncover the mystery of the killing, the interaction of KI with Cu-Cy NPs was investigated systematically and the products from their interaction were identified. No copper ions were released after adding KI to Cu-Cy NPs in cell-free medium and, therefore, it is reasonable to conclude that the Fenton reaction induced by copper ions is not responsible for the bacterial killing. Based on the observations, we propose that the major killing mechanism involves the generation of toxic species, such as hydrogen peroxide, triiodide ions, iodide ions, singlet oxygen, and iodine molecules. Overall, the powerful combination of Cu-Cy NPs and KI has good potential as an independent treatment or a complementary antibiotic treatment to infectious diseases.

Denis TG, Xuan Y, Huang YY, Tanaka M, Zadlo A, Sarna T, Hamblin MR. Paradoxical potentiation of methylene blue-mediated antimicrobial photodynamic inactivation by sodium azide: role of ambient oxygen and azide radicals

Sodium azide (NaN(3)) is widely employed to quench singlet oxygen during photodynamic therapy (PDT), especially when PDT is used to kill bacteria in suspension. We observed that addition of NaN(3) (100 μM or 10 mM) to gram-positive Staphylococcus aureus and gram-negative Escherichia coli incubated with methylene blue (MB) and illuminated with red light gave significantly increased bacterial killing (1-3 logs), rather than the expected protection from killing. A different antibacterial photosensitizer, the conjugate between polyethylenimine and chlorin(e6) (PEI-ce6), showed reduced PDT killing (1-2 logs) after addition of 10mM NaN(3). Azide (0.5mM) potentiated bacterial killing by Fenton reagent (hydrogen peroxide and ferrous sulfate) by up to 3 logs, but protected against killing mediated by sodium hypochlorite and hydrogen peroxide (considered to be a chemical source of singlet oxygen). The intermediacy of N(3)() was confirmed by spin-trapping and electron spin resonance studies in both MB-photosensitized reactions and Fenton reagent with addition of NaN(3). We found that N(3)() was formed and bacteria were killed even in the absence of oxygen, suggesting the direct one-electron oxidation of azide anion by photoexcited MB. This observation suggests a possible mechanism to carry out oxygen-independent PDT.

Type I and Type II mechanisms of antimicrobial photodynamic therapy: an in vitro study on gram-negative and gram-positive bacteria

BACKGROUND AND OBJECTIVES

Antimicrobial photodynamic therapy (APDT) employs a non-toxic photosensitizer (PS) and visible light, which in the presence of oxygen produce reactive oxygen species (ROS), such as singlet oxygen ((1) O(2), produced via Type II mechanism) and hydroxyl radical (HO(.), produced via Type I mechanism). This study examined the relative contributions of (1) O(2) and HO(.) to APDT killing of Gram-positive and Gram-negative bacteria.

STUDY DESIGN/MATERIALS AND METHODS

Fluorescence probes, 3'-(p-hydroxyphenyl)-fluorescein (HPF) and singlet oxygen sensor green reagent (SOSG) were used to determine HO(.) and (1) O(2) produced by illumination of two PS: tris-cationic-buckminsterfullerene (BB6) and a conjugate between polyethylenimine and chlorin(e6) (PEI-ce6). Dimethylthiourea is a HO(.) scavenger, while sodium azide (NaN(3)) is a quencher of (1) O(2). Both APDT and killing by Fenton reaction (chemical generation of HO(.)) were carried out on Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Proteus mirabilis, and Pseudomonas aeruginosa).

RESULTS

Conjugate PEI-ce6 mainly produced (1) O(2) (quenched by NaN(3)), while BB6 produced HO(.) in addition to (1) O(2) when NaN(3) potentiated probe activation. NaN(3) also potentiated HPF activation by Fenton reagent. All bacteria were killed by Fenton reagent but Gram-positive bacteria needed a higher concentration than Gram-negatives. NaN(3) potentiated Fenton-mediated killing of all bacteria. The ratio of APDT killing between Gram-positive and Gram-negative bacteria was 2 or 4:1 for BB6 and 25:1 for conjugate PEI-ce6. There was a NaN(3) dose-dependent inhibition of APDT killing using both PEI-ce6 and BB6 against Gram-negative bacteria while NaN(3) almost failed to inhibit killing of Gram-positive bacteria.

CONCLUSION

Azidyl radicals may be formed from NaN(3) and HO(.). It may be that Gram-negative bacteria are more susceptible to HO(.) while Gram-positive bacteria are more susceptible to (1) O(2). The differences in NaN(3) inhibition may reflect differences in the extent of PS binding to bacteria (microenvironment) or differences in penetration of NaN(3) into cell walls of bacteria.

In vitro efficacy of fosfomycin-containing regimens against methicillin-resistant Staphylococcus aureus in biofilms

OBJECTIVES

To compare the in vitro antibacterial efficacy of antistaphylococcal antibiotics in combination with fosfomycin or rifampicin, using a biofilm model.

METHODS

The antibacterial activities of fusidic acid, linezolid, vancomycin, teicoplanin, rifampicin, minocycline, fosfomycin and tigecycline, individually and in fosfomycin or rifampicin combinations, were measured against planktonic or biofilm-embedded methicillin-resistant Staphylococcus aureus (MRSA) with susceptible and resistant breakpoint concentrations (SBCs and RBCs, respectively), using the MTT-staining method and by counting the number of cfu in the biofilms.

RESULTS

Linezolid alone at its SBC, and fosfomycin, linezolid, minocycline and tigecycline at their RBCs, exhibited killing effects on biofilm-embedded MRSA (P < 0.0001). Of the eight fosfomycin combinations studied, fosfomycin combined with linezolid, minocycline, vancomycin or teicoplanin at their respective SBCs, exhibited enhanced antibacterial activities (P < 0.0001) when compared with the control group, and outperformed rifampicin combinations (P < 0.01). The killing effects of fosfomycin combinations at their respective RBCs were better than those at their respective SBCs (P < 0.05). Significantly enhanced killing effects were observed with fosfomycin in combination with vancomycin or teicoplanin, compared with vancomycin or teicoplanin alone. For 10 randomly selected MRSA isolates, the results of colony counting in biofilms were comparable with those of the MTT-staining method.

CONCLUSIONS

Fosfomycin enhanced the activities of linezolid, minocycline, vancomycin and teicoplanin. These combinatorial treatments were even better than rifampicin combination regimens, and may provide therapeutic advantages in catheter-related or prosthetic joint infections.

Health economic issues in the treatment of drug-resistant serious Gram-positive infections

Escalating health care costs have stimulated a paradigm change in the way health care is delivered, reimbursed, and evaluated. Reducing the length of hospital stay and controlling the cost of new technologies and therapies are major factors driving health care decisions. Economic evaluations have had variable success in the decision-making process, partly due to the overall quality, interpretation, and reporting of published analyses. Compared with other Gram-positive pathogens, the economic impact of methicillin-resistant Staphylococcus aureus (MRSA) infections remains the most studied. MRSA infections clearly represent a significant clinical and fiscal burden and future studies analyzing cost-effective strategies that encompass their prevention and optimal management would be beneficial. These studies would need to be carefully designed with clear objectives and explicit perspectives at the onset. Use of an appropriate reference group is key in the design process to measure the true impact of MRSA infections. Health-economic outcome data of the impact of linezolid compared with glycopeptides remain the most robust data available in this therapeutic area.

Point: Vancomycin is not obsolete for the treatment of infection caused by methicillin-resistant Staphylococcus aureus

Since the discovery, development, and US Food and Drug Administration approval of vancomycin in the 1950s, this agent has remained a mainstay for the treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA). However, because of the development of new antistaphylococcal antibiotics and reports of vancomycin failures, the utility of vancomycin has recently been questioned. Although vancomycin did not undergo the strict US Food and Drug Administration approval process that is in place today to demonstrate efficacy, there is considerable information available that sheds light on the role vancomycin has in infectious diseases pharmacotherapy today. In addition, although we look to in vitro susceptibility testing to assess vancomycin activity against S. aureus, we have come to appreciate that resistance of S. aureus to vancomycin can be a continuous--rather than a categorical--phenomenon. This has resulted in clinical microbiology laboratories having difficulty identifying S. aureus that may not respond to conventional doses of vancomycin. A better understanding is needed of the pharmacodynamic relationship between vancomycin and MRSA as relates to optimal dosing strategies, including consideration for loading doses, and development of rational categorical breakpoints for susceptibility based on clinical outcomes. By better understanding these critical issues, it may be possible to optimize the use of vancomycin, resulting in a cost-effective treatment option for many patients infected with MRSA.

Antimicrobial treatment for Intensive Care Unit (ICU) infections including the role of the infectious disease specialist

Between 5 and 10% of patients admitted to acute care hospitals acquire one or more infections, and the risks have steadily increased during recent decades. Three types of infection account for more than 60% of all nosocomial infections: pneumonia, urinary tract infection and primary bloodstream infection, all of them associated with the use of medical devices. Nearly 70% of infections are due to micro-organisms resistant to one or more antibiotics (multidrug resistant or MDR). A higher incidence of inappropriate antibiotic therapy is expected when infections are caused by antibiotic-resistant micro-organisms and initial inappropriate empirical therapies, and the further need to modify them substantially increases the mortality risk. Despite new antibacterial agents such as linezolid, and also tigecycline and daptomycin, now being available for the treatment of infections due to MDR micro-organisms, the best strategy for improving the cure rate and minimising the development of resistance, probably remains the infectious disease specialist consultation.

Hospital-acquired pneumonia in the 21st century: a review of existing treatment options and their impact on patient care

Hospital-acquired pneumonia is a common nosocomial infection, with significant morbidity and mortality, and represents a major therapeutic challenge to clinicians. The therapeutic approach must be patient-oriented and institution-specific. The specific risk factors of each patient, such as previous antibiotic exposure, underlying diseases, length of hospital stay and the local patterns of antimicrobial resistance, should guide physicians in their decision of the initial optimal empirical therapy. Delays in the initiation or inappropriate/inadequate initial therapy are related to increased mortality and worse outcomes. In responding patients, as soon as culture data are available, efforts should be made to change the initial broad spectrum antibiotic regimen to a more targeted one (de-escalation). The optimal duration of treatment is a matter of debate, but courses longer than 1 week are rarely justified.

Dalbavancin: A Novel Lipoglycopeptide Antibacterial

Dalbavancin is a new lipoglycopeptide antibacterial possessing in vitro activity against a variety of gram-positive pathogens. Against methicillin-susceptible and methicillin-resistant Staphylococcus aureus, it has demonstrated favorable minimum inhibitory concentration ranges compared with those of currently available agents. Dalbavancin is highly protein bound (> 90%), which may contribute to its prolonged half-life of 149-300 hours. Because of this long half-life, once-weekly dosing strategies have been used in clinical trials. Efficacy and tolerability have been demonstrated in a wide variety of animal infection models. Clinical success and safety have been shown in phase II and III trials for skin and soft-tissue infections and a phase II trial for catheter-related bloodstream infections. In these trials with vancomycin, linezolid, and various beta-lactams as comparators, comparable results have been reported. The results of further phase III trials are anxiously awaited and will more clearly define the clinical role of this novel agent.

Neumonía nosocomial causada por Staphylococcus aureus resistente a meticilina

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly common cause of hospital acquired pneumonia (HAP) and the second most frequently isolated pathogen from patients who die from HAP. High-risk units for MRSA colonization such as intensive care (ICU's) are the most affected. Multiple risk factors for transmission of MRSA have been identified, including colonization pressure and severity of illness at ICU admission. On the other hand, the most important predisposing factor for MRSA infection is prolonged mechanical ventilation and/or previous antibiotic therapy. Controlling the spread of MRSA remains a major challenge for hospitals. Screening programs, together with contact precautions for cases with MRSA and judicious antimicrobial use are major factors for a successful control. Early appropriate initial therapy is of crucial importance and improves outcome. The standard therapy has been glycopeptides but, in spite of its in vitro activity, mortality in critically ill patients treated with glycopeptides has consistently been reported high, mainly due to their poor lung penetration. Linezolid shows better clinical cure and survival rates, but further studies are needed. As the treatment options for MRSA pneumonia are limited and inadequate, development of more effective drugs is mandatory.

Pneumonia caused by oxacillin-resistant Staphylococcus aureus treated with glycopeptides*

OBJECTIVE

To determine whether ventilator-associated pneumonia caused by oxacillin-resistant Staphylococcus aureus (VAP-ORSA) treated with glycopeptides is associated with an increased mortality rate.

DESIGN

Retrospective matched cohort study.

SETTING

Four intensive care units in teaching hospitals.

PATIENTS

Seventy-five patients were matched to 75 controls.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All adult intensive care unit patients with microbiologically documented VAP-ORSA were matched to intubated controls who did not develop VAP-ORSA, based on disease severity (Acute Physiology and Chronic Health Evaluation II score) at admission (+/-3 points), diagnostic category, and length of stay before pneumonia onset. Population characteristics and intensive care unit mortality rates of patients with VAP-ORSA and their controls without pneumonia were compared. Attributable mortality was determined by subtracting the crude mortality rate of controls from the crude mortality rate of VAP-ORSA patients. Thirty-six of the 75 matched VAP-ORSA patients died, representing a crude mortality rate of 48%, whereas 19 of the 75 controls died, a crude mortality rate of 25.3% (p < .01). Excess mortality was estimated to be 22.7% (95% confidence interval, 2.4-42.9%). Median length of intensive care unit stay in the surviving pairs was 33 days (interquartile range, 25-75%: 25-45 days) for VAP-ORSA patients and 21 days (interquartile range, 25-75%: 15-34.75 days) days for controls (p = .054).

CONCLUSIONS

Despite appropriate glycopeptide therapy, there is an increased attributable mortality for pneumonia by ORSA, after careful adjustment for disease severity and diagnostic category.

The treatment of ventilator-associated pneumonia

OBJECTIVE

This manuscript attempts to provide insight into current concepts of prevention, diagnosis, and management of ventilator-associated pneumonia (VAP).

DATA SOURCES

A Medline search from 1996 to May 2004 was performed. Search terms included: ventilator-associated pneumonia with prevention, diagnosis, management, duration, resistance, and outcome.

DATA SELECTION

Emphasis was placed on the recent peer-reviewed literature. Human data were preferentially included.

DATA EXTRACTION

Where possible, recent publications (within the last year) were used in preference to older data. The references were chosen to present key citations.

DATA SYNTHESIS

Data selection was prioritized to address specific subtopics.

CONCLUSIONS

The treatment and prevention of VAP is evolving rapidly based on improved diagnostic skills and a better understanding of optimal antimicrobial therapy. An overview of new and key data guiding clinicians in the management of this important disease is presented.