Polymyxin B sulfate and colistin: old antibiotics for emerging multiresistant gram-negative bacteria

Impact of Cu(2+) ions on the structure of colistin and cell-free system nucleic acid degradation

Colistin and transition metal ions are commonly used as feed additives for livestock animals. This work presents the results of an analysis of combined potentiometric and spectroscopic (UV-vis, EPR, CD, NMR) data which lead to conclude that colistin is able to effectively chelate copper(II) ions. In cell-free system the oxidative activity of the complex manifests itself in the plasmid DNA destruction with simultaneous generation of reactive OH species, when accompanied by hydrogen peroxide or ascorbic acid. The degradation of RNA occurs most likely via a hydrolytic mechanism not only for complexed compound but also colistin alone. Therefore, huge amounts of the used antibiotic for nontherapeutic purposes might have a potential influence on livestock health.

Organic bioelectronics in infection

Organic bioelectronics is a rapidly growing field of both academic and industrial interest. Specific attributes make this class of materials particularly interesting for biomedical and medical applications, and a whole new class of biologically compatible devices is being created owing to structural and functional similarities to biological systems. In parallel, modern advances in biomedical research call for dynamically controllable systems. In infection biology, a progressing bacterial infection can be studied dynamically, at much higher resolution and on a smaller spatial scale than ever before, and it is now understood that minute changes in the tissue microenvironment play pivotal roles in the outcome of infections. This review merges the fields of infection biology and organic bioelectronics, describing the ability of conducting polymer devices to sense, modify, and interact with the infected tissue microenvironment. Though the primary focus is from the perspective of bacterial infections, general examples from cell biology and regenerative medicine are included where relevant. Spatially and temporally controlled biomimetic in vitro systems will greatly aid our molecular understanding of the infection process, thereby providing exciting opportunities for organic bioelectronics in future diagnosis and treatment of infectious diseases.

Identification of Anti-Persister Activity against Uropathogenic Escherichia coli from a Clinical Drug Library

Uropathogenic E. coli is a major cause of urinary tract infections (UTIs), but current antibiotics do not always effectively clear the persistent infection. To identify drugs that eliminate uropathogenic E. coli persisters, we screened a clinical drug library consisting of 1524 compounds using high throughput drug exposure assay in 96-well plates. Bacterial survival was assessed by growth on LB plates. We identified 14 drug candidates (tosufloxacin, colistin, sparfloxacin, moxifloxacin and gatifloxacin, enrofloxacin and sarafloxacin, octodrine, clofoctol, dibekacin, cephalosporin C, pazufloxacin, streptomycin and neomycin), which had high anti-persister activity. Among them, tosufloxacin and colistin had the highest anti-persister activity and could completely eradicate E. coli persisters in 3 days in vitro while the current UTI antibiotics failed to do so. Our findings may have implications for the development of a more effective treatment for UTIs.

Colistin, mechanisms and prevalence of resistance

BACKGROUND

Infections caused by multi-drug-resistant Gram-negative bacteria, particularly Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae, that cause nosocomial infections, represent a growing problem worldwide. The rapid increase in the prevalence of Gram-negative pathogens that are resistant to fluoroquinolones and aminoglycosides as well as all β-lactams, including carbapenems, monobactam, cephalosporins and broad-spectrum penicillins, has prompted the reconsideration of colistin as a valid therapeutic option. Colistin is an old class of cationic, which act by disrupting the bacterial membranes resulting in cellular death. Although there has been a significant recent increase in the data gathered on colistin, focusing on its chemistry, antibacterial activity, mechanism of action and resistance, pharmacokinetics, pharmacodynamics and new clinical application, the prevalence of colistin resistance has been very little reported in the literature. This review concentrates on recent literature aimed at optimizing the clinical use of this important antibiotic.

METHODS

The available evidence from various studies (microbiological and clinical studies, retrieved from the PubMed, and Scopus databases) regarding the mechanisms and prevalence of resistance was evaluated.

RESULTS

Increasing use of colistin for treatment of infections caused by these bacteria has led to the emergence of colistin resistance in several countries worldwide. Although resistance to polymyxins is generally less than 10%, it is higher in the Mediterranean and South-East Asia (Korea and Singapore), where colistin resistance rates are continually increasing.

CONCLUSION

There is a critical need for effective infection prevention and control measures and strict use of antibiotics in the world to control the rise and spread of colistin resistance.

Clinical efficacy and safety of colistin treatment in patients with pulmonary infection caused by Pseudomonas aeruginosa or Acinetobacter baumannii: a meta-analysis

INTRODUCTION

The aim of this study was to evaluate the efficacy and safety of colistin treatment in patients with pulmonary infection caused by Pseudomonas aeruginosa or Acinetobacter baumannii.

MATERIAL AND METHODS

The relevant studies were identified through a search of public databases including PubMed, MEDLINE and EMBASE up to December 2012. A meta-analysis was conducted to compare the clinical response, mortality and renal damage of colistin (colistin group) versus other effective antibiotics (control group). The odds ratio (OR) was chosen as the effect size.

RESULTS

A total of 9 studies were eventually identified. The result of the meta-analysis showed that the pooled OR of clinical response was 1.24 (95% CI = 0.68-2.27, p > 0.05) for patients in the colistin group versus the control group, indicating no significant difference in efficacy between colistin and control groups. Similar results were obtained by the further subgroup meta-analyses by sample size, research year, ethnicity and study method. Treatment with colistin versus other agents did not affect hospital mortality (OR = 1.05, 95% CI = 0.58-1.89, p > 0.05) or renal damage (OR = 1.25, 95% CI = 0.78-2.00, p > 0.05). The combined estimate of our analysis was strong across multiple sensitivity analyses and without significant publication bias.

CONCLUSIONS

Our results suggest that colistin may be as efficacious and safe as standard antibiotics for the treatment of pulmonary infection.

Colistin treatment in carbapenem-resistant Acinetobacter baumannii pneumonia patients: Incidence of nephrotoxicity and outcomes

Colistimethate sodium (CMS) is increasingly used to treat multidrug-resistant Gram-negative bacilli infections. However, the incidence of CMS-associated nephrotoxicity has not been evaluated in patients with carbapenem-resistant Acinetobacter baumannii (CRAB) pneumonia. This retrospective study included 120 patients with CRAB pneumonia treated with intravenous CMS for ≥72 h. The objective of the study was to determine risk factors for CMS-induced nephrotoxicity and 30-day mortality in patients with CRAB pneumonia. Of the 120 patients with CRAB pneumonia, 61 (51%) developed nephrotoxicity. Multivariate analysis showed that dose per ideal body weight (IBW) [odds ratio (OR)=1.28, 95% confidence interval (CI) 1.01-1.62; P=0.04], Charlson co-morbidity index (OR=1.31, 95% CI 1.06-1.60; P=0.01) and septic shock (OR=3.16, 95% CI 1.32-7.60; P=0.01) were associated with CMS-associated nephrotoxicity. Thirty-day mortality was 33% (39/120). Multivariate analysis showed that higher daily doses of CMS per IBW [hazard ratio (HR)=0.81, 95% CI 0.67-0.98; P=0.03] and longer duration of CMS therapy (HR=0.86, 95% CI 0.79-0.95; P=0.002) were associated with increased survival. Septic shock (HR=3.91, 95% CI 1.95-7.83; P<0.001) and corticosteroid use (HR=3.49, 95% CI 1.67-7.28; P=0.001) were associated with decreased survival in patients with CRAB pneumonia. Higher daily doses of CMS per IBW, Charlson comorbidity index and septic shock were significant risk factors for CMS-associated nephrotoxicity. However, CMS-associated nephrotoxicity does not appear to have an impact on mortality.

Autophagy regulates colistin-induced apoptosis in PC-12 cells

Colistin is a cyclic cationic polypeptide antibiotic with activity against multidrug-resistant Gram-negative bacteria. Our recent study demonstrated that colistin induces apoptosis in primary chick cortex neurons and PC-12 cells. Although apoptosis and autophagy have different impacts on cell fate, there is a complex interaction between them. Autophagy plays an important role as a homeostasis regulator by removing excessive or unnecessary proteins and damaged organelles. The aim of the present study was to investigate the modulation of autophagy and apoptosis regulation in PC-12 cells in response to colistin treatment. PC-12 cells were exposed to colistin (125 to 250 μg/ml), and autophagy was detected by visualization of monodansylcadaverine (MDC)-labeled vacuoles, LC3 (microtubule-associated protein 1 light chain 3) immunofluorescence microscopic examination, and Western blotting. Apoptosis was measured by flow cytometry, Hoechst 33258 staining, and Western blotting. Autophagosomes were observed after treatment with colistin for 12 h, and the levels of LC3-II gene expression were determined; observation and protein levels both indicated that colistin induced a high level of autophagy. Colistin treatment also led to apoptosis in PC-12 cells, and the level of caspase-3 expression increased over the 24-h period. Pretreatment of cells with 3-methyladenine (3-MA) increased colistin toxicity in PC-12 cells remarkably. However, rapamycin treatment significantly increased the expression levels of LC3-II and beclin 1 and decreased the rate of apoptosis of PC-12 cells. Our results demonstrate that colistin induced autophagy and apoptosis in PC-12 cells and that the latter was affected by the regulation of autophagy. It is very likely that autophagy plays a protective role in the reduction of colistin-induced cytotoxicity in neurons.

Nosocomial Outbreak of Infection With Pan–Drug-ResistantAcinetobacter baumanniiin a Tertiary Care University Hospital

Objective.

TO describe what is, to our knowledge, the first nosocomial outbreak of infection with pan–drug-resistant (including colistin-resistant)Acinetobacter baumannii,to determine the risk factors associated with these types of infections, and to determine their clinical impact.

Design.

Nested case-control cohort study and a clinical-microbiological study.

Setting.

A 1,521-bed tertiary care university hospital in Seville, Spain.

Patients.

Case patients were inpatients who had a pan-drug-resistantA. baumanniiisolate recovered from a clinical or surveillance sample obtained at least 48 hours after admission to an intensive care unit (ICU) during the time of the epidemic outbreak. Control patients were patients who were admitted to any of the “boxes” (ie, rooms that partition off a distinct area for a patient's bed and the equipment needed to care for the patient) of an ICU for at least 48 hours during the time of the epidemic outbreak.

Results.

All the clinical isolates had similar antibiotic susceptibility patterns (ie, they were resistant to all the antibiotics tested, including Colistin), and, on the basis of repetitive extragenic palindromic-polymerase chain reaction, it was determined that all of them were of the same clone. The previous use of quinolones and glycopeptides and an ICU stay were associated with the acquisition of infection or colonization with pan-drug-resistant A.baumannii.To control this outbreak, we implemented the following multicomponent intervention program: the performance of environmental decontamination of the ICUs involved, an environmental survey, a revision of cleaning protocols, active surveillance for colonization with pan-drug-resistantA. baumannii,educational programs for the staff, and the display of posters that illustrate contact isolation measures and antimicrobial use recommendations.

Conclusions.

We were not able to identify the common source for these cases of infection, but the adopted measures have proven to be effective at controlling the outbreak.

Guanidinium-pendant oligofluorene for rapid and specific identification of antibiotics with membrane-disrupting ability

A new method based on fluorescence resonance energy transfer was developed for specifically screening membrane-disrupting antibiotics.

Electrochemically monitoring the antibiotic susceptibility of Pseudomonas aeruginosa biofilms

We demonstrate a simple microfluidic system for screening antibiotic efficacy and determining minimum inhibitory concentrations forP. aeruginosabiofilms.

Multi-drug resistant gram negative infections and use of intravenous polymyxin B in critically ill children of developing country: retrospective cohort study

Background

Patients in pediatric intensive care Units (PICU) are susceptible to infections with antibiotic resistant organisms which increase the morbidity, mortality and cost of care.

To describe the clinical characteristics and mortality in patients with Multi-Drug Resistant (MDR) gram negative organisms. We also report safety of Polymyxin B use in these patients.

Methods

Files of patients admitted in PICU of Aga Khan University Hospital, from January 2010 to December 2011, one month to 15 years of age were reviewed. Demographic and clinical features of patients with MDR gram negative infections, antibiotic susceptibility pattern of isolates, discharge disposition and adverse effects of Polymyxin B were recorded.

Results

A total of 44.8/1000(36/803) admitted patients developed MDR gram negative infections, of which 47.2%(17/36) were male, with mean age of 3.4 yrs(+/−4.16). Acinetobacter Species (25.5%) was the most frequently isolated MDR organisms followed by Klebsiella Pneumoniae (17%). Sensitivity of isolates was 100% to Polymyxin B, followed by Imipenem (50%), and piperacillin/tazobactem (45%). The crude mortality rate of patients with MDR gram negative infections was 44.4% (16/36). Fourteen of 36 patients received Polymyxin B and 57.1%; (8/14) of them were cured. Nephrotoxicity was observed in 21.4% (3/14) cases, none of the patients showed signs of neuropathy.

Conclusion

Our study highlights high rates of Carbapenem resistant gram negative isolates, leading to increasing use of Polymyxin B as the only drug to combat against these critically ill children. Therefore, we emphasizeon Stewardship of Antibiotics and continuous surveillance system as strategies in overall management of these critically ill children.

Intra-Pleural Colistin Methanesulfonate Therapy for Pleural Infection caused by Carbapenem-Resistant Acinetobacter Baumannii: A Successful Case Report

Infections caused by carbapenem-resistant, Gram-negative bacteria are an increasing clinical challenge, since the antimicrobial treatment options are often limited to colistin methanesulfonate. No data are available regarding the pharmacokinetics of colistin in pleural fluid. We report the case of a 92-year old man with ventilator-associated pneumonia and pleurisy caused by Acinetobacter baumannii and Escherichia coli, which were both multidrug-resistant. After an unsuccessful treatment with intravenous colistin methanesulfonate and imipen-em-cilastatin, the addition of intra-pleural colistin methanesulfonate to the intravenous treatment led to a prompt clinical, radiological and microbiological resolution. This is the first report of a successful use of intra-pleural colistin in the literature. The intra-pleural colistin therapy should be considered in selected cases of pleurisy caused by multi-resistant Gram-negative bacteria.

Colistimethate sodium for the treatment of chronic pulmonary infection in cystic fibrosis: an evidence-based review of its place in therapy

Chronic bacterial respiratory-tract infections are a major driving force in the pathogenesis of cystic fibrosis (CF) lung disease and promote chronic lung-function decline, destruction, and progression to respiratory failure at a premature age. Gram-negative bacteria colonizing the airways in CF are a major problem in CF therapy due to their tendency to develop a high degree of resistance to antibiotic agents over time. Pseudomonas aeruginosa is the dominating bacterial strain infecting the CF lung from early childhood on, and multiresistant strains frequently develop after years of therapy. Colistin has been used for treating pulmonary bacterial infections in CF for decades due to its very good Gram-negative activity. However, drawbacks include concerns regarding toxicity when being applied systemically, and the lack of approval for application by inhalation in the USA for many years. Other antibiotic substances for systemic use are available with good to excellent Gram-negative and anti-Pseudomonas activity, while there are only three substances approved for inhalation use in the treatment of chronic pulmonary infection with proven benefit in CF. The emergence of multiresistant strains leaving nearly no antibiotic substance as a treatment option, the limited number of antibiotics with high activity against P. aeruginosa, the concerns about increasing the risk of antibiotic resistance by continuous antibiotic therapy, the development of new drug formulations and drug-delivery devices, and, finally, the differing treatment strategies used in CF centers call for defining the place of this "old" drug, colistimethate, in today's CF therapy. This article reviews the available evidence to reflect on the place of colistimethate sodium in the therapy of chronic pulmonary infection in CF.

PGE2 Inhibits IL-10 Production via EP2-Mediated β-Arrestin Signaling in Neuroinflammatory Condition

Regulatory mechanisms of the expression of interleukin-10 (IL-10) in brain inflammatory conditions remain elusive. To address this issue, we used multiple primary brain cell cultures to study the expression of IL-10 in lipopolysaccharide (LPS)-elicited inflammatory conditions. In neuron-glia cultures, LPS triggered well-orchestrated expression of various immune factors in the following order: tumor necrosis factor-α (TNF-α), cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), and lastly IL-10, and these inflammatory mediators were mainly produced from microglia. While exogenous application of individual earlier-released pro-inflammatory factors (e.g., TNF-α, IL-1β, or PGE2) failed to induce IL-10 expression, removal of LPS from the cultures showed the requirement of continuing presence of LPS for IL-10 expression. Interestingly, genetic disruption of tnf-α, its receptors tnf-r1/r2, and cox-2 and pharmacological inhibition of COX-2 activity enhanced LPS-induced IL-10 production in microglia, which suggests negative regulation of IL-10 induction by the earlier-released TNF-α and PGE2. Further studies showed that negative regulation of IL-10 production by TNF-α is mediated by PGE2. Mechanistic studies indicated that PGE2-elicited suppression of IL-10 induction was eliminated by genetic disruption of the PGE2 receptor EP2 and was mimicked by the specific agonist for the EP2, butaprost, but not agonists for the other three EP receptors. Inhibition of cAMP-dependent signal transduction failed to affect PGE2-mediated inhibition of IL-10 production, suggesting that a G protein-independent pathway was involved. Indeed, deficiency in β-arrestin-1 or β-arrestin-2 abolished PGE2-elicited suppression of IL-10 production. In conclusion, we have demonstrated that COX-2-derived PGE2 inhibits IL-10 expression in brain microglia through a novel EP2- and β-arrestin-dependent signaling pathway.

Nonattenuated Polymyxin B Used for the Treatment of Extreme-Drug Resistant Acinetobacter baumannii-Related Infections in Patients with Preexisting End Stage Renal Failure

Recent pharmacokinetic studies have suggested that nonrenal clearance predominates the elimination of polymyxin B. We present 2 patients with preexisting end stage renal failure, who were given nonattenuated doses of polymyxin B for the treatment of extreme-drug resistant organism. No evidence of adverse events occurred and microbiological clearance was documented.

Serratia marcescens arn, a PhoP-regulated locus necessary for polymyxin B resistance

Polymyxins, which are increasingly being used to treat infections caused by multidrug-resistant bacteria, perform poorly against Serratia marcescens. To investigate the underlying mechanisms, Tn5 mutagenesis was performed and two mutants exhibiting increased polymyxin B (PB) susceptibility were isolated. The mutants were found to have Tn5 inserted into the arnB and arnC genes. In other bacteria, arnB and arnC belong to the seven-gene arn operon, which is involved in lipopolysaccharide (LPS) modification. LPSs of arn mutants had greater PB-binding abilities than that of wild-type LPS. Further, we identified PhoP, a bacterial two-component response regulator, as a regulator of PB susceptibility in S. marcescens. By the reporter assay, we found PB- and low-Mg2+-induced expression of phoP and arn in the wild-type strain but not in the phoP mutant. Complementation of the phoP mutant with the full-length phoP gene restored the PB MIC and induction by PB and low Mg2+ levels, as in the wild type. An electrophoretic mobility shift assay (EMSA) further demonstrated that PhoP bound directly to the arn promoter. The PB challenge test confirmed that pretreatment with PB and low Mg2+ levels protected S. marcescens from a PB challenge in the wild-type strain but not in the phoP mutant. Real-time reverse transcriptase-PCR also indicated that PB serves as a signal to regulate expression of ugd, a gene required for LPS modification, in S. marcescens through a PhoP-dependent pathway. Finally, we found that PB-resistant clinical isolates displayed greater expression of arnA upon exposure to PB than did susceptible isolates. This is the first report to describe the role of S. marcescens arn in PB resistance and its modulation by PB and Mg2+ through the PhoP protein.

Characterization of nontypable Haemophilus influenzae isolates recovered from adult patients with underlying chronic lung disease reveals genotypic and phenotypic traits associated with persistent infection

Nontypable Haemophilus influenzae (NTHi) has emerged as an important opportunistic pathogen causing infection in adults suffering obstructive lung diseases. Existing evidence associates chronic infection by NTHi to the progression of the chronic respiratory disease, but specific features of NTHi associated with persistence have not been comprehensively addressed. To provide clues about adaptive strategies adopted by NTHi during persistent infection, we compared sequential persistent isolates with newly acquired isolates in sputa from six patients with chronic obstructive lung disease. Pulse field gel electrophoresis (PFGE) identified three patients with consecutive persistent strains and three with new strains. Phenotypic characterisation included infection of respiratory epithelial cells, bacterial self-aggregation, biofilm formation and resistance to antimicrobial peptides (AMP). Persistent isolates differed from new strains in showing low epithelial adhesion and inability to form biofilms when grown under continuous-flow culture conditions in microfermenters. Self-aggregation clustered the strains by patient, not by persistence. Increasing resistance to AMPs was observed for each series of persistent isolates; this was not associated with lipooligosaccharide decoration with phosphorylcholine or with lipid A acylation. Variation was further analyzed for the series of three persistent isolates recovered from patient 1. These isolates displayed comparable growth rate, natural transformation frequency and murine pulmonary infection. Genome sequencing of these three isolates revealed sequential acquisition of single-nucleotide variants in the AMP permease sapC, the heme acquisition systems hgpB, hgpC, hup and hxuC, the 3-deoxy-D-manno-octulosonic acid kinase kdkA, the long-chain fatty acid transporter ompP1, and the phosphoribosylamine glycine ligase purD. Collectively, we frame a range of pathogenic traits and a repertoire of genetic variants in the context of persistent infection by NTHi.

Treatment options for multidrug-resistant bacteria

As a consequence of antibiotic overuse and misuse, nosocomial infections caused by multidrug-resistant bacteria represent a physician's nightmare throughout the world. No newer antimicrobials active against Pseudomonas aeruginosa, the main multidrug-resistant nosocomial pathogen, are available or under investigation. The only exceptions are linezolid, some newer glycopeptides (dalbavancin, oritavancin and telavancin) and daptomycin (a lipopeptide), which are active against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) strains, as well as tigecycline, a potent in vitro glycylcycline against MRSA, VRE, Acinetobacter baumannii and entended-spectrum beta-lactamase (ESBL)+ Enterobacteriaceae. Colistin, an antibiotic of the 1950s has been rediscovered by intensive care unit physicians for use against ESBL+ Enterobacteriaceae, as well as against multidrug-resistant P. aeruginosa and A. baumannii isolates. Although success rates with colistin range between 50 and 73%, almost all studies are retrospective. Immunostimulation efforts against S. aureus are still under development. As antibiotic research and development stagnate, rational policies for prescribing existing antibiotics plus strict infection control are the current mainstay efforts for preventing and combating multidrug-resistant bacterial infections.

Treatment ofPseudomonas aeruginosainfection in critically ill patients

Critically ill patients are on the increase in the present clinical setting. Aging of our population and increasingly aggressive medical and therapeutic interventions, including implanted foreign bodies, organ transplantation and advances in the chemotherapy of malignant diseases, have created a cohort of particularly vulnerable patients. Pseudomonas aeruginosa is one of the leading gram-negative organisms associated with nosocomial infections. This organism is frequently feared because it causes severe hospital-acquired infections, especially in immunocompromised hosts, and is often antibiotic resistant, complicating the choice of therapy. The epidemiology, microbiology, mechanisms of resistance and currently available and future treatment options for the most relevant infections caused by P. aeruginosa are reviewed.

Antimicrobial agents, drug adverse reactions and interactions, and cancer

The intent of this chapter is to review the types of adverse drug reactions and interactions associated with antimicrobial agents, specifically in the setting of patients with malignancies. The initial sections will discuss categorizing and describing the mechanisms of adverse reactions and interactions. The later sections include a detailed discussion about adverse reactions and drug interactions associated with commonly used antibacterial, antiviral, and antifungal agents in this subpopulation. Where relevant, the clinical use and indication for the drugs will be reviewed. The antibacterial section will specifically address the emergence of antimicrobial resistance and drugs of last resort (newer agents, such as linezolid and daptomycin and novel uses of older previously retired agents, such as polymyxin B). The antifungal section will address the ramification of pharmacokinetic interactions and the need to measure drug levels. The chapter is not meant to be exhaustive and as such will not extensively address all antimicrobials or all interactions for each of these agents.

To study the clinical efficacy and nephrotoxicity along with the risk factors for acute kidney injury associated with parenteral polymyxin B

Aim:

The aim of this study was to evaluate the clinical efficacy and nephrotoxicity along with the risk factors for acute kidney injury (AKI) associated with the parenteral polymyxin B in patients with the multidrug resistance (MDR) gram −ve infections in a tertiary Intensive care unit (ICU).

Materials and Methods:

A retrospective cohort study (March 2010-October 2011) was conducted in Medical ICU of a 23 bedded tertiary care hospital in Northern India.

Results:

Out of 71 ICU patients who were administered polymyxin B, only 32 (M:F = 1:0.8) met the inclusion criteria. Patients with concurrent administration of nephrotoxic drugs were excluded from the study. Mean age of patients was 48.53 ± 13.90 years ranging from 16 years to 68 years. 6 out of 32 (18.7%) patients progressed to AKI, whereas renal functions remained normal in 26 (81.2%) patients. No statistically significant difference was observed in mortality between AKI and non AKI patients at the end of therapy (33.3% vs. 26.9%, P value 0.756). Older age (62.33 ± 11.90 vs. 45.34 ± 2.45, P value 0.005) was found to be an independent risk factor for causing nephrotoxicity.

Conclusion:

In the present scenario of rising infections with MDR gram −ve micro-organisms, this pilot study suggests that polymyxin B can be used effectively and safely in patients not receiving other nephrotoxic drugs, with cautious administration in older patients as they are more vulnerable to nephrotoxicity caused by polymyxin B.

Selective decontamination of the digestive tract in gastrointestinal surgery: useful in infection prevention? A systematic review

INTRODUCTION

Gastrointestinal surgery is associated with a high incidence of infectious complications. Selective decontamination of the digestive tract is an antimicrobial prophylaxis regimen that aims to eradicate gastrointestinal carriage of potentially pathogenic microorganisms and represents an adjunct to regular prophylaxis in surgery.

MATERIAL AND METHODS

Relevant studies were identified using bibliographic searches of MEDLINE, EMBASE, and the Cochrane database (period from 1970 to November 1, 2012). Only studies investigating selective decontamination of the digestive tract in gastrointestinal surgery were included.

RESULTS

Two randomized clinical trials and one retrospective case-control trial showed significant benefit in terms of infectious complications and anastomotic leakage in colorectal surgery. Two randomized controlled trials in esophageal surgery and two randomized clinical trials in gastric surgery reported lower levels of infectious complications.

CONCLUSION

Selective decontamination of the digestive tract reduces infections following esophageal, gastric, and colorectal surgeries and also appears to have beneficial effects on anastomotic leakage in colorectal surgery. We believe these results provide the basis for a large multicenter prospective study to investigate the role of selective decontamination of the digestive tract in colorectal surgery.

Targeted therapy against multi-resistant bacteria in leukemic and hematopoietic stem cell transplant recipients: guidelines of the 4th European Conference on Infections in Leukemia (ECIL-4, 2011)

The detection of multi-resistant bacterial pathogens, particularly those to carbapenemases, in leukemic and stem cell transplant patients forces the use of old or non-conventional agents as the only remaining treatment options. These include colistin/polymyxin B, tigecycline, fosfomycin and various anti-gram-positive agents. Data on the use of these agents in leukemic patients are scanty, with only linezolid subjected to formal trials. The Expert Group of the 4(th) European Conference on Infections in Leukemia has developed guidelines for their use in these patient populations. Targeted therapy should be based on (i) in vitro susceptibility data, (ii) knowledge of the best treatment option against the particular species or phenotype of bacteria, (iii) pharmacokinetic/pharmacodynamic data, and (iv) careful assessment of the risk-benefit balance. For infections due to resistant Gram-negative bacteria, these agents should be preferably used in combination with other agents that remain active in vitro, because of suboptimal efficacy (e.g., tigecycline) and the risk of emergent resistance (e.g., fosfomycin). The paucity of new antibacterial drugs in the near future should lead us to limit the use of these drugs to situations where no alternative exists.

Adjunctive aerosolized colistin for multi-drug resistant gram-negative pneumonia in the critically ill: a retrospective study

BACKGROUND

The incidence of multi-drug resistant (MDR) gram-negative (GN) organisms including Pseudomonas and Acinetobacter spp has increased in the last decade, prompting re-evaluation of colistin for the management of these infections. Aerosolized colistin as an adjunct to intravenous therapy is a current option for the management of MDR-GN pneumonia, although data supporting this practice is limited. This study evaluates the efficacy of adjunctive aerosolized colistin in combination with intravenous colistin in critically ill patients with MDR-GN pneumonia.

METHODS

A retrospective multi-center cohort analysis comparing critically ill patients with MDR-GN pneumonia who received intravenous colistin (IV) alone or in combination with adjunctive aerosolized colistin (IV/AER) with a primary endpoint of clinical cure at the end of colistin therapy. Secondary endpoints included microbiologic cure, duration of mechanical ventilation, length of stay, and hospital mortality. A post-hoc subgroup analysis was performed for patients with high quality cultures used for diagnosis of MDR-GN pneumonia. Dichotomous data were compared using Fisher's exact test while the student's t-test or Mann-Whitney U test were used for continuous variables.

RESULTS

Ninety-five patients met criteria for evaluation with 51 patients receiving IV and 44 receiving IV/AER. Baseline characteristics were similar between the two groups. Twenty patients (39.2%) receiving IV and 24 (54.5%) receiving IV/AER achieved clinical cure (p = 0.135). There was no difference in microbiologic cure rates between the IV and IV/AER colistin groups (40.7vs. 44.4%, p = 0.805). The IV group demonstrated a trend towards higher pneumonia attributable mortality (70.4 vs. 40%, p = 0.055). In the subgroup analysis of patients with high quality respiratory cultures, there was a significantly lower clinical cure rate for those in the IV group as compared to the IV/AER group (31.3 vs. 57.1%, p = 0.033).

CONCLUSIONS

Addition of aerosolized colistin to IV colistin may improve clinical cure and mortality for patients with MDR-GN pneumonia. Larger, prospective trials are warranted to confirm the benefit of adjunctive aerosolized colistin in critically ill patients with MDR-GN pneumonia.

Microbiological Activity and Clinical Efficacy of a Colistin and Rifampin Combination in Multidrug-ResistantPseudomonas aeruginosaInfections

The aim of the study was to assess the microbiological activity and clinical efficacy of colistin and rifampin combination against multidrug-resistant (MDR) Pseudomonas aeruginosa infections. The antimicrobial activity of the colistin/rifampin combination was evaluated using the checkerboard and time-kill curve methods against different MDR P. aeruginosa strains. The combination of rifampin and colistin resulted fully (1 strain) or partially (5 strains) synergistic for 6/7 strains and minimum inhibitory concentrations (MICs) in combination were reduced to easily obtainable therapeutic levels. The time-kill curves showed that the combination was bactericidal against the strains tested. The clinical efficacy of the combination was tested in four patients with difficult-to treat infections (sepsis or pneumonia) caused by MDR P. aeruginosa. All infections were successfully treated. Our microbiological and clinical observations suggest that the addition of rifampin to colistin may result in a synergistic bactericidal combination that may be useful in patients with infections caused by MDR P. aeruginosa which are difficult to cure.

The two peptide lantibiotic lacticin 3147 acts synergistically with polymyxin to inhibit Gram negative bacteria

BACKGROUND

The emergence of bacterial drug resistance encourages the re-evaluation of the potential of existing antimicrobials. Lantibiotics are post-translationally modified, ribosomally synthesised antimicrobial peptides with a broad spectrum antimicrobial activity. Here, we focussed on expanding the potential of lacticin 3147, one of the most studied lantibiotics and one which possesses potent activity against a wide range of Gram positive species including many nosocomial pathogens. More specifically, our aim was to investigate if lacticin 3147 activity could be enhanced when combined with a range of different clinical antibiotics.

RESULTS

Initial screening revealed that polymyxin B and polymyxin E (colistin) exhibited synergistic activity with lacticin 3147. Checkerboard assays were performed against a number of strains, including both Gram positive and Gram negative species. The resultant fractional inhibitory concentration (FIC) index values established that, while partial synergy was detected against Gram positive targets, synergy was obvious against Gram negative species, including Cronobacter and E. coli.

CONCLUSIONS

Combining lacticin 3147 with low levels of a polymyxin could provide a means of broadening target specificity of the lantibiotic, while also reducing polymyxin use due to the lower concentrations required as a result of synergy.

In vitro toxicity of colistin on primary chick cortex neurons and its potential mechanism

Colistin is increasingly used as the last-line therapy for infections caused by Gram-negative 'superbugs'. Although colistin neurotoxicity was reported in the literature, there has no data on its mechanism. In the present study, we examined the effect of colistin on primary chick neuron cells, which were treated with 0.83, 4.15 and 8.3μg/mL colistin for 6, 12 and 24h. Cell viability was evaluated with 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assays after exposure to colistin. Formation of reactive oxygen species (ROS), nuclear morphology, caspase-3 activity and internucleosomal DNA fragmentation were examined. The results showed that, compared with the control, no significant change was observed in cell viability, ROS formation and caspase-3 activity in cells treated for 6, 12 and 24h with 0.83μg/mL colistin. However, in the 4.15 and 8.3μg/mL colistin-treated groups, the viability of chick primary neurons significantly decreased at 12 and 24h, respectively; caspase-3 activities were significantly increased to 5.1 and 7.4 fold at 6h, more earlier than the changes of ROS, which was significant increased to 124.5% and 143.5% (P<0.01) of control at 12h, respectively. The apoptosis of neuron cells was revealed by both nuclear morphological observations and internucleosomal DNA fragmentation in the 4.15 and 8.3μg/mL colistin-treated groups at 6, 12 and 24h. Our data demonstrated that colistin can induce apoptosis in primary chick cortex neurons through caspase-3 activation, which may be contributed with ROS-dependent and independent mechanism.

Rapid determination of colistin resistance in clinical strains of Acinetobacter baumannii by use of the micromax assay

Colistin is an old antibiotic which has been used as a therapeutic option for carbapenem- and multidrug-resistant Gram-negative bacteria, like Acinetobacter baumannii. This pathogen produces life-threatening infections, mainly in patients admitted to intensive care units. Rapid detection of resistance to colistin may improve patient outcomes and prevent the spread of resistance. For this purpose, Micromax technology was evaluated in four isogenic A. baumannii strains with known mechanisms of resistance to colistin and in 66 isolates (50 susceptible and 16 resistant). Two parameters were determined, DNA fragmentation and cell wall damage. To assess DNA fragmentation, cells trapped in a microgel were incubated with a lysing solution to remove the cell wall, and the released nucleoids were visualized under fluorescence microscopy. Fragmented DNA was observed as spots that diffuse from the nucleoid. To assess cell wall integrity, cells were incubated with a lysis solution which removes only weakened cell walls, resulting in nucleoid release exclusively in affected cells. A dose-response relationship was demonstrated between colistin concentrations and the percentages of bacteria with DNA fragmentation and cell wall damage, antibiotic effects that were delayed and less frequent in resistant strains. Receiver operating characteristic (ROC) curves demonstrated that both DNA fragmentation and cell wall damage were excellent parameters for identifying resistant strains. Obtaining ≤11% of bacteria with cell wall damage after incubation with 0.5 μg/ml colistin identified resistant strains of A. baumannii with 100% sensitivity and 96% specificity. Results were obtained in 3 h 30 min. This is a simple, rapid, and accurate assay for detecting colistin resistance in A. baumannii, with strong potential value in critical clinical situations.

Relative contributions of lipooligosaccharide inner and outer core modifications to nontypeable Haemophilus influenzae pathogenesis

Nontypeable Haemophilus influenzae (NTHi) is a frequent commensal of the human nasopharynx that causes opportunistic infection in immunocompromised individuals. Existing evidence associates lipooligosaccharide (LOS) with disease, but the specific and relative contributions of NTHi LOS modifications to virulence properties of the bacterium have not been comprehensively addressed. Using NTHi strain 375, an isolate for which the detailed LOS structure has been determined, we compared systematically a set of isogenic mutant strains expressing sequentially truncated LOS. The relative contributions of 2-keto-3-deoxyoctulosonic acid, the triheptose inner core, oligosaccharide extensions on heptoses I and III, phosphorylcholine, digalactose, and sialic acid to NTHi resistance to antimicrobial peptides (AMP), self-aggregation, biofilm formation, cultured human respiratory epithelial infection, and murine pulmonary infection were assessed. We show that opsX, lgtF, lpsA, lic1, and lic2A contribute to bacterial resistance to AMP; lic1 is related to NTHi self-aggregation; lgtF, lic1, and siaB are involved in biofilm growth; opsX and lgtF participate in epithelial infection; and opsX, lgtF, and lpsA contribute to lung infection. Depending on the phenotype, the involvement of these LOS modifications occurs at different extents, independently or having an additive effect in combination. We discuss the relative contribution of LOS epitopes to NTHi virulence and frame a range of pathogenic traits in the context of infection.

Cell cycle arrest in a model of colistin nephrotoxicity

Colistin (polymixin E) is an antibiotic prescribed with resurging frequency for multidrug resistant gram negative bacterial infections. It is associated with nephrotoxicity in humans in up to 55% of cases. Little is known regarding genes involved in colistin nephrotoxicity. A murine model of colistin-mediated kidney injury was developed. C57/BL6 mice were administered saline or colistin at a dose of 16 mg/kg/day in 2 divided intraperitoneal doses and killed after either 3 or 15 days of colistin. After 15 days, mice exposed to colistin had elevated blood urea nitrogen (BUN), creatinine, and pathologic evidence of acute tubular necrosis and apoptosis. After 3 days, mice had neither BUN elevation nor substantial pathologic injury; however, urinary neutrophil gelatinase-associated lipocalin was elevated (P = 0.017). An Illumina gene expression array was performed on kidney RNA harvested 72 h after first colistin dose to identify differentially expressed genes early in drug treatment. Array data revealed 21 differentially expressed genes (false discovery rate < 0.1) between control and colistin-exposed mice, including LGALS3 and CCNB1. The gene signature was significantly enriched for genes involved in cell cycle proliferation. RT-PCR, immunoblot, and immunostaining validated the relevance of key genes and proteins. This murine model offers insights into the potential mechanism of colistin-mediated nephrotoxicity. Further studies will determine whether the identified genes play a causative or protective role in colistin-induced nephrotoxicity.

Post-Neurosurgical Meningitis Due to Multidrug-ResistantAcinetobacter baumaniiTreated with Intrathecal Colistin: Case Report and Review of the Literature

Intrathecal colistin (Polymxin E) is becoming an important option for the treatment of post-neurosurgical meningitis caused by multidrug resistant (MDR) Acinetobacter baumannii. We report a case of 28-year-old man who developed meningitis due to MDR A. baumannii associated with an external ventricular drain. The patient was cured using a 4-week course of intrathecal colistin 3.2 mg via external ventricular drain (EVD) daily without any serious side effects.

Intravenous colistin for multidrug-resistant gram-negative infections in critically ill pediatric patients

OBJECTIVES

Nosocomial infection due to multidrug-resistant Gram-negative pathogens in ICUs is a challenge for clinicians and microbiologists and has led to the resurgence of IV colistin use in the last decade. The aim of this study was to assess the efficacy of IV colistin in the treatment of critically ill children with multidrug-resistant Gram-negative infections.

DESIGN AND SETTING

Retrospective descriptive study conducted in the PICU of Maulana Azad Medical College and associated Chacha Nehru Bal Chikitsalaya, Delhi, India, during the period of January 2010 to December 2011.

PATIENTS

The records of critically ill children with multidrug-resistant Gram-negative infections treated with IV colistin were reviewed.

RESULTS

Fifty critically ill children received IV colistin; their median age was 36 months (range: 1 mo-12 yr), with male:female ratio of 3:2. The isolated pathogens were Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae. Mean duration of colistin therapy was 14.3 days (range, 7-21). A favorable clinical outcome occurred in 36 children (72%), and 14 children (28%) died due to severe sepsis with multiple-organ dysfunction syndrome. Renal toxicity occurred in five children and was associated with multiple-organ dysfunction syndrome in three and coadministration of vancomycin in two. No neurotoxic adverse effects due to colistin therapy were reported.

CONCLUSION

Our study suggests that IV colistin may have a role in the treatment of infections caused by multidrug-resistant Gram-negative bacteria in critically ill children, but further prospective and randomized control trials are needed to confirm its efficacy and safety in children.

Identification of a novel antimicrobial peptide from human hepatitis B virus core protein arginine-rich domain (ARD)

The rise of multidrug-resistant (MDR) pathogens causes an increasing challenge to public health. Antimicrobial peptides are considered a possible solution to this problem. HBV core protein (HBc) contains an arginine-rich domain (ARD) at its C-terminus, which consists of 16 arginine residues separated into four clusters (ARD I to IV). In this study, we demonstrated that the peptide containing the full-length ARD I–IV (HBc147-183) has a broad-spectrum antimicrobial activity at micro-molar concentrations, including some MDR and colistin (polymyxin E)-resistant Acinetobacter baumannii. Furthermore, confocal fluorescence microscopy and SYTOX Green uptake assay indicated that this peptide killed Gram-negative and Gram-positive bacteria by membrane permeabilization or DNA binding. In addition, peptide ARD II–IV (HBc153-176) and ARD I–III (HBc147-167) were found to be necessary and sufficient for the activity against P. aeruginosa and K. peumoniae. The antimicrobial activity of HBc ARD peptides can be attenuated by the addition of LPS. HBc ARD peptide was shown to be capable of direct binding to the Lipid A of lipopolysaccharide (LPS) in several in vitro binding assays. Peptide ARD I–IV (HBc147-183) had no detectable cytotoxicity in various tissue culture systems and a mouse animal model. In the mouse model by intraperitoneal (i.p.) inoculation with Staphylococcus aureus, timely treatment by i.p. injection with ARD peptide resulted in 100-fold reduction of bacteria load in blood, liver and spleen, as well as 100% protection of inoculated animals from death. If peptide was injected when bacterial load in the blood reached its peak, the protection rate dropped to 40%. Similar results were observed in K. peumoniae using an IVIS imaging system. The finding of anti-microbial HBc ARD is discussed in the context of commensal gut microbiota, development of intrahepatic anti-viral immunity and establishment of chronic infection with HBV. Our current results suggested that HBc ARD could be a new promising antimicrobial peptide.

Antibiotics-resistant pathogens have been a major problem to our public health. Recently, in our studies of human hepatitis B virus (HBV), we accidentally discovered potent and broad spectrum antimicrobial peptides from HBV core protein (HBc) arginine-rich domain (ARD). The peptides are mainly composed of SPRRR repeats and are effective against both Gram-positive and Gram-negative bacteria, as well as fungi. We found different bactericidal mechanisms of the ARD peptides, which involved LPS binding, DNA binding and membrane permeabilization in various tested bacteria, such as P. aeruginosa, K. pneumoniae, E. coli and S. aureus. We also found that this ARD peptide was effective for colistin-resistant A. baumannii. The peptides exhibited no hemolysis activity to human red blood cells and no cytotoxicity to human hepatoma cells and kidney cells. Furthermore, the ARD peptide was shown to be safe and protective in the animal model. Recently, intestinal flora was found to influence the development of immunity. We discussed here the potential involvement of the antimicrobial activity of HBc ARD in the establishment of HBV chronic infection in the newborns. We proposed here that the HBc ARD peptides could serve as an alternative to the conventional antibiotics in clinical medicine.

Macrocyclic drugs and synthetic methodologies toward macrocycles

Macrocyclic scaffolds are commonly found in bioactive natural products and pharmaceutical molecules. So far, a large number of macrocyclic natural products have been isolated and synthesized. The construction of macrocycles is generally considered as a crucial and challenging step in the synthesis of macrocyclic natural products. Over the last several decades, numerous efforts have been undertaken toward the synthesis of complex naturally occurring macrocycles and great progresses have been made to advance the field of total synthesis. The commonly used synthetic methodologies toward macrocyclization include macrolactonization, macrolactamization, transition metal-catalyzed cross coupling, ring-closing metathesis, and click reaction, among others. Selected recent examples of macrocyclic synthesis of natural products and druglike macrocycles with significant biological relevance are highlighted in each class. The primary goal of this review is to summarize currently used macrocyclic drugs, highlight the therapeutic potential of this underexplored drug class and outline the general synthetic methodologies for the synthesis of macrocycles.

High performance liquid chromatography-mass spectrometry assay for polymyxin B1 and B2 in human plasma

BACKGROUND

Polymyxin B is an old antibiotic with increasing clinical relevance in the treatment of multidrug-resistant Gram-negative bacterial infections. However, current dosing regimens are largely empiric as clinical pharmacological characterization of the drug has been hindered by the lack of assays to measure polymyxin B in human plasma.

METHODS

A high-performance liquid chromatography-mass spectrometry assay was developed to quantify polymyxin B1 and B2 in human plasma using pure calibrators. After purification with a solid-phase extraction column, polymyxin B1 and B2 were separated on a C18 column by gradient chromatography with an overall runtime of 12 minutes. Polymyxin B1 and B2 were ionized by positive electrospray ionization, and the resulting ions specific to polymyxin B1 and B2 were monitored (selected ion recording).

RESULTS

The dominant ions produced were (M + 2H) at m/z 602.6 and 595.5 for polymyxin B1 and polymyxin B2, respectively. The assay was linear between concentrations of 100 and 2500 ng/mL, with interday precision of 5.9% and 3.4% at 100 ng/mL and 5.3% and 4.0% at 2000 ng/mL for polymyxin B1 and polymyxin B2, respectively. Accuracy was 80.2% and 82.2% at 100 ng/mL and 99.9% and 109.6% at 2000 ng/mL for polymyxin B1 and polymyxin B2, respectively. No interference from other drugs commonly administered with polymyxin B was detected. The performance of the assay is affected by gross hemolysis and hyperlipemia. The method was successfully applied to patient samples. Interestingly, in a single patient the ratio of B1 and B2 did not change over a period of 12 hours after administration of the drug.

CONCLUSIONS

A simple method for the simultaneous measurement of polymyxin B1 and polymyxin B2 in human plasma is described, which has the potential to optimize clinical use of this valuable antibiotic by permitting pharmacokinetic studies and therapeutic drug monitoring.

Evaluation of the anticryptococcal activity of the antibiotic polymyxin B in vitro and in vivo

Polymyxin B (PMB), a cationic lipid oligopeptide used to treat Gram-negative bacterial infections, was previously identified to possess broad-spectrum antifungal activity and to work synergistically with azole antifungals in vitro. Here we evaluated the efficacy of PMB against Cryptococcus neoformans in vitro and in vivo and explored the mechanism of the hypersensitivity of this fungus to this compound. Using comparative time-course assays, PMB was found to kill both proliferative and quiescent cryptococcal cells in vitro. Presence of the polysaccharide capsule, a characteristic feature of Cryptococcus, significantly enhances the susceptibility of this fungus to the fungicidal activity of PMB. Furthermore, PMB is able to reduce the tissue fungal burden both in intravenous and inhalation models of murine cryptococcosis at a level comparable with the commonly used antifungal fluconazole. These findings suggest that PMB could provide an additional option for treatment against systemic cryptococcosis.

Nephrotoxicity and efficacy assessment of polymyxin use in 92 transplant patients

Polymyxins are old antimicrobials, discontinued for many years because of nephrotoxicity and neurotoxicity reports and reintroduced recently due to the increasing frequency of multiresistant Gram-negative bacterial infections. There are very few data related to toxicity and efficacy from transplanted patients, the major subjects of this study. All solid-organ-transplanted patients from our institution during January 2001 to December 2007 who used polymyxins were retrospectively assessed for nephrotoxicity and treatment efficacy. Microbiological and clinical cure rates were 100% and 77.2%, respectively. Only transplant patients subjected to at least 72 h of intravenous polymyxin were entered in the study. Overall, 92 transplant patients were included, and the nephrotoxicity rate was 32.6%. Multivariate analysis showed a statistically significant association between duration of polymyxin treatment (P = 0.037; odds ratio [OR], 1.06; 95% confidence interval [CI], 1.00 to 1.12) and significant renal dysfunction. Polymyxin use is associated with very high rates of significant decrease in renal function; therefore, polymyxin must be used only when no other option is available and for as briefly as possible in the solid organ transplant setting.