The need for new antibiotics

Increased prevalence of carbapenem resistant Enterobacteriaceae in hospital setting due to cross-species transmission of the bla NDM-1 element and clonal spread of progenitor resistant strains

This study investigated the transmission characteristics of carbapenem-resistant Enterobacteriaceae (CRE) strains collected from a hospital setting in China, in which consistent emergence of CRE strains were observable during the period of May 2013 to February 2014. Among the 45 CRE isolates tested, 21 (47%) strains were found to harbor the bla_NDM-1 element, and the rest of 24 CRE strains were all positive for bla_KPC-2. The 21 bla_NDM-1—borne strains were found to comprise multiple Enterobacteriaceae species including nine Enterobacter cloacae, three Escherichia coli, three Citrobacter freundii, two Klebsiella pneumoniae, two Klebsiella oxytoca, and two Morganella morganii strains, indicating that cross-species transmission of bla_NDM-1 is a common event. Genetic analyses by PFGE and MLST showed that, with the exception of E. coli and E. cloacae, strains belonging to the same species were often genetically unrelated. In addition to bla_NDM-1, several CRE strains were also found to harbor the bla_KPC-2, bla_VIM-1, and bla_IMP-4 elements. Conjugations experiments confirmed that the majority of carbapenem resistance determinants were transferable. Taken together, our findings suggest that transmission of mobile resistance elements among members of Enterobacteriaceae and clonal spread of CRE strains may contribute synergistically to a rapid increase in the population of CRE in clinical settings, prompting a need to implement more rigorous infection control measures to arrest such vicious transmission cycle in CRE-prevalent areas.

Biochemical characters and antibiotic susceptibility of Staphylococcus aureus isolates

OBJECTIVE

To observe the biochemical characters and antibiotic susceptibility of isolated Staphylococcus aureus (S. auerus) strains against some conventional and traditional antibiotics.

METHODS

Thirty post operative pathogenic isolated S. aureus strains were used in this study. Bacterial culture was done in Mueller-Hinton broth at 37 °C. Characters of these strains were determined by traditional biochemical tests such as hydrolysis test of gelatin, urea, galactose, starch and protein, and fermentation of lactose and sucrose. Antibiotic susceptibility were carried out by minimum inhibitory concentration test, minium bactericidal concentration test, disc agar diffusion test and brain heart infusion oxacillin screening agar.

RESULTS

From this study, it was observed that 100% S. aureus isolates showed positive results in gelatin, urea and galactose hydrolysis test, 50% isolates were positive in starch hydrolysis test, 35% in protein hydrolysis test, 100% isolates in lactose fermenting test, but no isolate was positive in sucrose fermenting test. Antibiotic susceptibility testing suggested that 20% of isolates were resistant to kanamycin and 46.67% were resistant to oxacillin.

CONCLUSIONS

These findings show that all these isolates have gelatin, urea, galactose hydrolysis and lactose fermenting activity. 20% of these isolates were resistant to kanamycin and 46.67% were resistant to oxacillin.

Antibiotic discovery: combatting bacterial resistance in cells and in biofilm communities

Bacterial resistance is a rapidly escalating threat to public health as our arsenal of effective antibiotics dwindles. Therefore, there is an urgent need for new antibiotics. Drug discovery has historically focused on bacteria growing in planktonic cultures. Many antibiotics were originally developed to target individual bacterial cells, being assessed in vitro against microorganisms in a planktonic mode of life. However, towards the end of the 20th century it became clear that many bacteria live as complex communities called biofilms in their natural habitat, and this includes habitats within a human host. The biofilm mode of life provides advantages to microorganisms, such as enhanced resistance towards environmental stresses, including antibiotic challenge. The community level resistance provided by biofilms is distinct from resistance mechanisms that operate at a cellular level, and cannot be overlooked in the development of novel strategies to combat infectious diseases. The review compares mechanisms of antibiotic resistance at cellular and community levels in the light of past and present antibiotic discovery efforts. Future perspectives on novel strategies for treatment of biofilm-related infectious diseases are explored.

Ebselen as a potent covalent inhibitor of New Delhi metallo-β-lactamase (NDM-1)

We identified a potent NDM-1 inhibitor that formed a S–Se bond with the Cys²²¹ residue at the active site, thereby exhibiting a new inhibition mechanism with broad spectrum inhibitory potential.

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.

Valuable Secondary Metabolites from Fungi

Fungi are amazing producers of natural products, including secondary metabolites. These compounds are crucial to the health and well-being of people throughout the world. They also provide agriculture and livestock with many essential products. Production of secondary metabolites is improved by mutagenesis and recombinant DNA technologies allowing commercial production of these valuable compounds. This chapter centers on these fungal beneficial products, the discovery of which goes back 85 years to the time that penicillin was discovered by Alexander Fleming.

Anti-cooperative ligand binding and dimerisation in the glycopeptide antibiotic dalbavancin

Dalbavancin, a semi-synthetic glycopeptide with enhanced antibiotic activity compared to vancomycin and teicoplanin, binds to the C-terminal lysyl-d-alanyl-d-alanine subunit of Lipid II, inhibiting peptidoglycan biosynthesis. In this study, micro-calorimetry and electrospray ionization (ESI)-MS have been used to investigate the relationship between oligomerisation of dalbavancin and binding of a Lipid II peptide mimic, diacetyl-Lys-d-Ala-d-Ala (Ac2-Kaa). Dalbavancin dimerised strongly in an anti-cooperative manner with ligand-binding, as was the case for ristocetin A, but not for vancomycin and teicoplanin. Dalbavancin and ristocetin A both adopt an 'closed' conformation upon ligand binding, suggesting anti-cooperative dimerisation with ligand-binding may be a general feature of dalbavancin/ristocetin A-like glycopeptides. Understanding these effects may provide insight into design of novel dalbavancin derivatives with cooperative ligand-binding and dimerisation characteristics that could enhance antibiotic activity.

Mecillinam resistance and outcome of pivmecillinam treatment in uncomplicated lower urinary tract infection in women

Pivmecillinam (PIV) is a first-line antimicrobial for treatment of lower urinary tract infection in women (LUTIW). Mecillinam, the active substance of PIV, is bactericidal mainly against gram-negative uropathogens, whereas gram-positive species are considered intrinsically resistant. However, successful treatment of LUTIW caused by Staphylococcus saprophyticus has been reported, but more rarely for other gram-positive species. The aim of this study was to compare clinical and bacteriological outcome of PIV vs placebo treatment among uropathogens with special focus on mecillinam-resistant isolates. We analysed data from a prospective, multicentre, placebo-controlled, primary health care, therapy study performed in Sweden in 1995–1998 that included 1143 women with symptoms suggestive of LUTIW. Urine cultures were collected and symptoms registered at inclusion and at follow-up visits. Overall, the efficacy of PIV was superior to that of placebo. Clinical and bacteriological outcomes of PIV treatment were similar for S. saprophyticus, Escherichia coli as for most other uropathogens irrespective of their susceptibility to mecillinam. However, the occurrence of enterococci increased nearly fivefold shortly post PIV treatment, although with mild symptoms and a high spontaneous eradication. As susceptibility to mecillinam in vitro did not predict bacteriological and clinical outcome of PIV treatment, we suggest that the present breakpoints for mecillinam should be revised.

Biological activity of lactoferrin-functionalized biomimetic hydroxyapatite nanocrystals

The emergence of bacterial strains resistant to antibiotics is a general public health problem. Progress in developing new molecules with antimicrobial properties has been made. In this study, we evaluated the biological activity of a hybrid nanocomposite composed of synthetic biomimetic hydroxyapatite surface-functionalized by lactoferrin (LF-HA). We evaluated the antimicrobial, anti-inflammatory, and antioxidant properties of LF-HA and found that the composite was active against both Gram-positive and Gram-negative bacteria, and that it modulated proinflammatory and anti-inflammatory responses and enhanced antioxidant properties as compared with LF alone. These results indicate the possibility of using LF-HA as an antimicrobial system and biomimetic hydroxyapatite as a candidate for innovative biomedical applications.

Treatment of infectious disease: beyond antibiotics

Several antibiotics have been discovered following the discovery of penicillin. These antibiotics had been helpful in treatment of infectious diseases considered dread for centuries. The advent of multiple drug resistance in microbes has posed new challenge to researchers. The scientists are now evaluating alternatives for combating infectious diseases. This review focuses on major alternatives to antibiotics on which preliminary work had been carried out. These promising anti-microbial include: phages, bacteriocins, killing factors, antibacterial activities of non-antibiotic drugs and quorum quenching.

Diffusible signal factor (DSF) quorum sensing signal and structurally related molecules enhance the antimicrobial efficacy of antibiotics against some bacterial pathogens

Background

Extensive use of antibiotics has fostered the emergence of superbugs that are resistant to multidrugs, which becomes a great healthcare and public concern. Previous studies showed that quorum sensing signal DSF (diffusible signal factor) not only modulates bacterial antibiotic resistance through intraspecies signaling, but also affects bacterial antibiotic tolerance through interspecies communication. These findings motivate us to exploit the possibility of using DSF and its structurally related molecules as adjuvants to influence antibiotic susceptibility of bacterial pathogens.

Results

In this study, we have demonstrated that DSF signal and its structurally related molecules could be used to induce bacterial antibiotic susceptibility. Exogenous addition of DSF signal (cis-11-methyl-2-dodecenoic acid) and its structural analogues could significantly increase the antibiotic susceptibility of Bacillus cereus, possibly through reducing drug-resistant activity, biofilm formation and bacterial fitness. The synergistic effect of DSF and its structurally related molecules with antibiotics on B. cereus is dosage-dependent. Combination of DSF with gentamicin showed an obviously synergistic effect on B. cereus pathogenicity in an in vitro model. We also found that DSF could increase the antibiotic susceptibility of other bacterial species, including Bacillus thuringiensis, Staphylococcus aureus, Mycobacterium smegmatis, Neisseria subflava and Pseudomonas aeruginosa.

Conclusion

The results indicate a promising potential of using DSF and its structurally related molecules as novel adjuvants to conventional antibiotics for treatment of infectious diseases caused by bacterial pathogens.

A de novo-designed antimicrobial peptide with activity against multiresistant Staphylococcus aureus acting on RsbW kinase

Antimicrobial peptides are a promising complement to common antibiotics, development of resistance to which is a growing problem. Here we present a de novo-designed peptide, SP1-1 (RKKRLKLLKRLL-NH2), with antimicrobial activity against multiresistant Staphylococcus aureus (minimal inhibitory concentration: 6.25 μM). Elucidation of the mode of action of this peptide revealed a strong interaction with RsbW kinase (Kd: 6.01±2.73 nM), a serine kinase negatively regulating the activity of the transcription factor σB (SigB). SP1-1 binding and functional modulation of RsbW were shown in vitro by a combination of biochemical, molecular, and biophysical methods, which were further genetically evidenced in vivo by analysis of S. aureus ΔsigB deletion mutants. Intracellular localization of the peptide was demonstrated using nanometer-scaled secondary ion mass spectrometry. Moreover, microarray analysis revealed that transcription of numerous genes, involved in cell wall and amino acid metabolism, transport mechanisms, virulence, and pigmentation, is affected. Interestingly, several WalR binding motif containing genes are induced by SP1-1. In sum, the designed peptide SP1-1 seems to have multiple modes of action, including inhibition of a kinase, and therefore might contribute to the development of new antibacterial compounds, giving bacterial kinase inhibition a closer inspection.

Candida infections, causes, targets, and resistance mechanisms: traditional and alternative antifungal agents

The genus Candida includes about 200 different species, but only a few species are human opportunistic pathogens and cause infections when the host becomes debilitated or immunocompromised. Candida infections can be superficial or invasive. Superficial infections often affect the skin or mucous membranes and can be treated successfully with topical antifungal drugs. However, invasive fungal infections are often life-threatening, probably due to inefficient diagnostic methods and inappropriate initial antifungal therapies. Here, we briefly review our current knowledge of pathogenic species of the genus Candida and yeast infection causes and then focus on current antifungal drugs and resistance mechanisms. An overview of new therapeutic alternatives for the treatment of Candida infections is also provided.

Computational Insights into the Mechanism of Inhibition of OASS-A by a Small Molecule Inhibitor

O-Acetylserine sulfhydrylase (isoform A, OASS-A) is a PLP-dependent enzyme involved in the last step of cysteine biosynthesis in many pathogens. Many microorganisms use cysteine as the main building block for sulfur-containing antioxidants, and cysteine depletion in several pathogens resulted in a reduced antibiotic resistance, thus leading to the identification of OASS as novel suitable molecular targets to overcome antimicrobial resistances. The precise molecular mechanism of OASS-A inhibition by small peptides or by small molecule inhibitors is still unclear. To shed more lights on the structural basis underlying the inhibition mechanism for OASS, we engaged ourselves in studying the dynamic properties of this enzyme. In this paper, we describe a computational study involving unbiased MD simulations of OASS-A from Haemophilus influenzae (HiOASS) in its inhibitor free, PLP-bound form, and in complex with a pentapeptide inhibitor and with UPAR40, a small molecule which we have recently reported as a potent OASS-A inhibitors. We proposed that UPAR40 inhibits HiOASS-A through the stabilization of a closed conformation. Moreover, preliminary docking studies and sequence analysis allow us to speculate about the non-specificity of UPAR40 toward a particular OASS enzyme species or isoforms.

Antibacterial Derivatives of Ciprofloxacin to Inhibit Growth of Necrotizing Fasciitis Associated Penicillin Resistant Escherichia coli

Escherichia coli (E. coli) is associated with necrotizing fasciitis (type I) and can induce enough damage to tissue causing hypoxia. Three ester derivatives of the broad-spectrum antibiotic ciprofloxacin were placed into bacteria culture simultaneously with the parent ciprofloxacin (drug 1) to ascertain the level of antibacterial activity. The n-propyl (drug 2), n-pentyl (drug 3), and n-octyl (drug 4) esters of ciprofloxacin were synthesized under mixed phase conditions and by microwave excitation. The formation of ester derivatives of ciprofloxacin modified important molecular properties such as Log P and polar surface area which improves tissue penetration, yet preserved strong antibacterial activity. The Log P values for drugs 1, 2, 3, and 4 became -0.701, 0.437, 1.50, and 3.02, respectively. The polar surface areas for drugs 1, 2, 3, and 4 were determined to be 74.6 Angstroms(2), 63.6 Angstroms(2), 63.6 Angstroms(2), and 63.6 Angstroms(2), respectively. These values of Log P and polar surface area improved tissue penetration, as indicated by the determination of dermal permeability coefficient (K p ) and subsequently into the superficial fascial layer. All drugs induced greater than 60% bacterial cell death at concentrations less than 1.0 micrograms/milliliter. The ester derivatives of ciprofloxacin showed strong antibacterial activity toward penicillin resistant E. coli.

Pseudomonas putida are environmental reservoirs of antimicrobial resistance to β-lactamic antibiotics

The adaptive flexibility of bacteria largely contributes to the emergence of antibiotic resistance, eventually leading to the predictable failure of current antimicrobial therapies. It is of utmost importance to improve current approaches and implement new ways to control bacterial growth and proliferation. A promising strategy lies in unraveling the antimicrobial resistance (AMR) dynamics in environmental reservoirs, namely in soil. Environmental microorganisms are antibiotic producers and generally also carriers of AMR mechanisms. Therefore, soil samples were collected from areas distinctly influenced by men: rural farms and urban fluvial shores. Globally, microbial communities collected in farms revealed the highest antibiotic resistance potential. Largely predominant Gram-negative isolates were further screened for their low susceptibility to β-lactamic agents, and found to belong to Pseudomonaceae family, with predominance of Pseudomonas putida (92 %). Minimal Inhibitory Concentration (MIC) was determined for five β-lactams and the distributive analysis of cefotaxime MIC performed, allowing the first report of Epidemiological Cut-OFF values for P. putida regarding such antibiotic. Hence, 46 % of the isolates from farms presented acquired resistance to cefotaxime, with fluvial strains presenting an acquisition of AMR in 22 % of the isolates. The response to β-lactams impact in P. putida is different from Pseudomonas aeruginosa's, the family type strain, showing that data determined for a species should only be extended to other bacteria with caution, even closely related. It becomes crucial to broaden present research, mainly focused on few pathogenic bacteria, to other microorganisms carrying relevant resistance tools or capable of genetic transfer to more virulent strains. Most available data on AMR so far has been obtained from studies performed in restricted clinical or veterinary context, showing the result of a strong selective pressure related to therapy but often disregarding the origin of the AMR mechanisms encountered. The strong impact that environmental microorganisms have (and probably already had in the past) on the evolution and spreading of AMR, is just beginning to be unveiled.

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.

Bacillus anthracis thioredoxin systems, characterization and role as electron donors for ribonucleotide reductase

Bacillus anthracis is the causative agent of anthrax, which is associated with a high mortality rate. Like several medically important bacteria, B. anthracis lacks glutathione but encodes many genes annotated as thioredoxins, thioredoxin reductases, and glutaredoxin-like proteins. We have cloned, expressed, and characterized three potential thioredoxins, two potential thioredoxin reductases, and three glutaredoxin-like proteins. Of these, thioredoxin 1 (Trx1) and NrdH reduced insulin, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), and the manganese-containing type Ib ribonucleotide reductase (RNR) from B. anthracis in the presence of NADPH and thioredoxin reductase 1 (TR1), whereas thioredoxin 2 (Trx2) could only reduce DTNB. Potential TR2 was verified as an FAD-containing protein reducible by dithiothreitol but not by NAD(P)H. The recently discovered monothiol bacillithiol did not work as a reductant for RNR, either directly or via any of the redoxins. The catalytic efficiency of Trx1 was 3 and 20 times higher than that of Trx2 and NrdH, respectively, as substrates for TR1. Additionally, the catalytic efficiency of Trx1 as an electron donor for RNR was 7-fold higher than that of NrdH. In extracts of B. anthracis, Trx1 was responsible for almost all of the disulfide reductase activity, whereas Western blots showed that the level of Trx1 was 15 and 60 times higher than that of Trx2 and NrdH, respectively. Our findings demonstrate that the most important general disulfide reductase system in B. anthracis is TR1/Trx1 and that Trx1 is the physiologically relevant electron donor for RNR. This information may provide a basis for the development of novel antimicrobial therapies targeting this severe pathogen.

Genomics of adaptation during experimental evolution of the opportunistic pathogen Pseudomonas aeruginosa

Adaptation is likely to be an important determinant of the success of many pathogens, for example when colonizing a new host species, when challenged by antibiotic treatment, or in governing the establishment and progress of long-term chronic infection. Yet, the genomic basis of adaptation is poorly understood in general, and for pathogens in particular. We investigated the genetics of adaptation to cystic fibrosis-like culture conditions in the presence and absence of fluoroquinolone antibiotics using the opportunistic pathogen Pseudomonas aeruginosa. Whole-genome sequencing of experimentally evolved isolates revealed parallel evolution at a handful of known antibiotic resistance genes. While the level of antibiotic resistance was largely determined by these known resistance genes, the costs of resistance were instead attributable to a number of mutations that were specific to individual experimental isolates. Notably, stereotypical quinolone resistance mutations in DNA gyrase often co-occurred with other mutations that, together, conferred high levels of resistance but no consistent cost of resistance. This result may explain why these mutations are so prevalent in clinical quinolone-resistant isolates. In addition, genes involved in cyclic-di-GMP signalling were repeatedly mutated in populations evolved in viscous culture media, suggesting a shared mechanism of adaptation to this CF–like growth environment. Experimental evolutionary approaches to understanding pathogen adaptation should provide an important complement to studies of the evolution of clinical isolates.

Pathogens face a hostile and often novel environment when infecting a new host, and adaptation to this environment can be critical to a pathogen's survival. The genetic basis of pathogen adaptation is in turn important for treatment, since the consistency with which therapies succeed may depend on the extent to which a pathogen adapts via the same routes in different patients. In this study, we investigate adaptation of the bacterium Pseudomonas aeruginosa to laboratory conditions that resemble the lungs of cystic fibrosis patients and to quinolone antibiotics. We find that a handful of genes and genetic pathways are repeatedly involved in adaptation to each condition. Nonetheless, other, less common mutations can play important roles in determining fitness, complicating strategies aimed at reducing the prevalence of antibiotic resistance.

In vitro antimicrobial activity of nanoconjugated vancomycin against drug resistant Staphylococcus aureus

The mounting problem of antibiotic resistance of Staphylococcus aureus has prompted renewed efforts toward the discovery of novel antimicrobial agents. The present study was aimed to evaluate the in vitro antimicrobial activity of nanoconjugated vancomycin against vancomycin sensitive and resistant S. aureus strains. Folic acid tagged chitosan nanoparticles are used as Trojan horse to deliver vancomycin into bacterial cells. In vitro antimicrobial activity of nanoconjugated vancomycin against VSSA and VRSA strains was determined by minimum inhibitory concentration, minimum bactericidal concentration, tolerance and disc agar diffusion test. Cell viability and biofilm formation was assessed as indicators of pathogenicity. To establish the possible antimicrobial mechanism of nanoconjugated vancomycin, the cell wall thickness was studied by TEM study. The result of the present study reveals that nano-sized vehicles enhance the transport of vancomycin across epithelial surfaces, and exhibits its efficient drug-action which has been understood from studies of MIC, MBC, DAD of chitosan derivative nanoparticle loaded with vancomycin. Tolerance values distinctly showed that vancomycin loaded into nano-conjugate is very effective and has strong bactericidal effect on VRSA. These findings strongly enhanced our understanding of the molecular mechanism of nanoconjugated vancomycin and provide additional rationale for application of antimicrobial therapeutic approaches for treatment of staphylococcal pathogenesis.

Staphylococcus aureus Infection Induced Oxidative Imbalance in Neutrophils: Possible Protective Role of Nanoconjugated Vancomycin

Staphylococcus aureus infection causes oxidative stress in neutrophils. The immune cells use reactive oxygen species (ROS) for carrying out their normal functions while an excess amount of ROS can attack cellular components that lead to cell damage. The present study was aimed to test the protective role of nanoconjugated vancomycin against vancomycin-sensitive Staphylococcus aureus (VSSA) and vancomycin-resistant Staphylococcus aureus (VRSA) infection induced oxidative stress in neutrophils. VSSA- and VRSA-infection were developed in Swiss mice by intraperitoneal injection of 5 × 10(6) CFU/mL bacterial solutions. Nanoconjugated vancomycin was treated to VSSA- and VRSA-infected mice at its effective dose for 10 days. Vancomycin was treated to VSSA and VRSA infected mice at similar dose, respectively, for 10 days. The result reveals that in vivo VSSA and VRSA infection significantly increases the level of lipid peroxidation, protein oxidation, oxidized glutathione level, and nitrite generation and decreases the level of reduced glutathione, antioxidant enzyme status, and glutathione-dependent enzymes as compared to control group; which were increased or decreased significantly near to normal in nanoconjugated vancomycin-treated group. These finding suggests the potential use and beneficial protective role of nanoconjugated vancomycin against VSSA and VRSA infection induced oxidative imbalance in neutrophils.

Introduction to antibiotic resistance

The inexorable rise in multidrug-resistant Gram-negative bacteria has been widely reported. Multiple modes of resistance often present in a single strain of bacteria, and this may also be combined with an increase in virulence, both of which are leading to a significant increase in morbidity and mortality in patients. Against this background, the absolute number of new antibiotics licensed has declined especially for Gram-negative multidrug-resistant pathogens. The reasons for this failure are presented here: market issues, big pharma changes, regulatory constraints, difficulties in finding drugable targets and, lastly, suitable compounds worthy of full development.

Leveraging structural information for the discovery of new drugs: computational methods

Escalating problems with drug resistance continue to compromise the effectiveness of commercial antibiotics, necessitating the search for novel classes of antimicrobial agents. To circumvent problems with resistance, a multitarget single-pharmacophore approach has been employed to discover inhibitors that possess balanced activity against multiple target enzymes. In this chapter, we examine the application of computational techniques, in particular, structure-based drug design approaches, to design new dual-targeting antibacterial agents against bacterial topoisomerases.

In vitro antimicrobial studies of silver carbene complexes: activity of free and nanoparticle carbene formulations against clinical isolates of pathogenic bacteria

OBJECTIVES

Silver carbenes may represent novel, broad-spectrum antimicrobial agents that have low toxicity while providing varying chemistry for targeted applications. Here, the bactericidal activity of four silver carbene complexes (SCCs) with different formulations, including nanoparticles (NPs) and micelles, was tested against a panel of clinical strains of bacteria and fungi that are the causative agents of many skin and soft tissue, respiratory, wound, blood, and nosocomial infections.

METHODS

MIC, MBC and multidose experiments were conducted against a broad range of bacteria and fungi. Time-release and cytotoxicity studies of the compounds were also carried out. Free SCCs and SCC NPs were tested against a panel of medically important pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Acinetobacter baumannii (MRAB), Pseudomonas aeruginosa, Burkholderia cepacia and Klebsiella pneumoniae.

RESULTS

All four SCCs demonstrated strong efficacy in concentration ranges of 0.5-90 mg/L. Clinical bacterial isolates with high inherent resistance to purified compounds were more effectively treated either with an NP formulation of these compounds or by repeated dosing. Overall, the compounds were active against highly resistant bacterial strains, such as MRSA and MRAB, and were active against the biodefence pathogens Bacillus anthracis and Yersinia pestis. All of the medically important bacterial strains tested play a role in many different infectious diseases.

CONCLUSIONS

The four SCCs described here, including their development as NP therapies, show great promise for treating a wide variety of bacterial and fungal pathogens that are not easily killed by routine antimicrobial agents.

Synergistic killing of multidrug-resistant Pseudomonas aeruginosa at multiple inocula by colistin combined with doripenem in an in vitro pharmacokinetic/pharmacodynamic model

Combination therapy may be required for multidrug-resistant (MDR) Pseudomonas aeruginosa. The aim of this study was to systematically investigate bacterial killing and emergence of colistin resistance with colistin and doripenem combinations against MDR P. aeruginosa. Studies were conducted in a one-compartment in vitro pharmacokinetic/pharmacodynamic model for 96 h at two inocula (~10(6) and ~10(8) CFU/ml) against a colistin-heteroresistant reference strain (ATCC 27853) and a colistin-resistant MDR clinical isolate (19147 n/m). Four combinations utilizing clinically achievable concentrations were investigated. Microbiological response was examined by log changes and population analysis profiles. Colistin (constant concentrations of 0.5 or 2 mg/liter) plus doripenem (peaks of 2.5 or 25 mg/liter every 8 h; half-life, 1.5 h) substantially increased bacterial killing against both strains at the low inoculum, while combinations containing colistin at 2 mg/liter increased activity against ATCC 27853 at the high inoculum; only colistin at 0.5 mg/liter plus doripenem at 2.5 mg/liter failed to improve activity against 19147 n/m at the high inoculum. Combinations were additive or synergistic against ATCC 27853 in 16 and 11 of 20 cases (4 combinations across 5 sample points) at the 10(6)- and 10(8)-CFU/ml inocula, respectively; the corresponding values for 19147 n/m were 16 and 9. Combinations containing doripenem at 25 mg/liter resulted in eradication of 19147 n/m at the low inoculum and substantial reductions in regrowth (including to below the limit of detection at ∼50 h) at the high inoculum. Emergence of colistin-resistant subpopulations of ATCC 27853 was substantially reduced and delayed with combination therapy. This investigation provides important information for optimization of colistin-doripenem combinations.

Sequential mechanism of assembly of multidrug efflux pump AcrAB-TolC

Multidrug efflux pumps adversely affect both the clinical effectiveness of existing antibiotics and the discovery process to find new ones. In this study, we reconstituted and characterized by surface plasmon resonance the assembly of AcrAB-TolC, the archetypal multidrug efflux pump from Escherichia coli. We report that the periplasmic AcrA and the outer membrane channel TolC assemble high-affinity complexes with AcrB transporter independently from each other. Antibiotic novobiocin and MC-207,110 inhibitor bind to the immobilized AcrB but do not affect interactions between components of the complex. In contrast, DARPin inhibits interactions between AcrA and AcrB. Mutational opening of TolC channel decreases stability of interactions and promotes disassembly of the complex. The conformation of the membrane proximal domain of AcrA is critical for the formation of AcrAB-TolC and could be targeted for the development of new inhibitors.

Clinically relevant plasma concentrations of colistin in combination with imipenem enhance pharmacodynamic activity against multidrug-resistant Pseudomonas aeruginosa at multiple inocula

The use of combination antibiotic therapy may be beneficial against rapidly emerging resistance in Pseudomonas aeruginosa. The aim of this study was to systematically investigate in vitro bacterial killing and resistance emergence with colistin alone and in combination with imipenem against multidrug-resistant (MDR) P. aeruginosa. Time-kill studies were conducted over 48 h using 5 clinical isolates and ATCC 27853 at two inocula (~10(6) and ~10(8) CFU/ml); MDR, non-MDR, and colistin-heteroresistant and -resistant strains were included. Nine colistin-imipenem combinations were investigated. Microbiological response was examined by log changes at 6, 24, and 48 h. Colistin combined with imipenem at clinically relevant concentrations increased the levels of killing of MDR and colistin-heteroresistant isolates at both inocula. Substantial improvements in activity with combinations were observed across 48 h with all colistin concentrations at the low inoculum and with colistin at 4× and 16× MIC (or 4 and 32 mg/liter) at the high inoculum. Combinations were additive or synergistic against imipenem-resistant isolates (MICs, 16 and 32 mg/liter) at the 10(6)-CFU inoculum in 9, 11, and 12 of 18 cases (i.e., 9 combinations across 2 isolates) at 6, 24, and 48 h, respectively, and against the same isolates at the 10(8)-CFU inoculum in 11, 7, and 8 cases, respectively. Against a colistin-resistant strain (MIC, 128 mg/liter), combinations were additive or synergistic in 9 and 8 of 9 cases at 24 h at the 10(6)- and 10(8)-CFU inocula, respectively, and in 5 and 7 cases at 48 h. This systematic study provides important information for optimization of colistin-imipenem combinations targeting both colistin-susceptible and colistin-resistant subpopulations.

[Shedding light on the use of colistin: still gaps to be filled]

Colistin (polymyxin E), an old antibiotic replaced by other less toxic antibiotics in the 1970s, has been increasingly used over the last decade due to multidrug-resistance in Gram-negative bacteria and lack of new antibiotics. However, there is a dearth of information on the pharmacokinetics (PK), pharmacodynamics (PD) and toxicodynamics (TD) of colistin and its non-active prodrug colistimethate sodium (CMS). Optimised dose regimens have not been established for different types of patients. Additionally, most PK data available in the literature were obtained from concentrations derived from potentially misleading microbiological assays. Therefore, it is urgent to conduct prospective studies to optimise CMS/colistin use in patients, in particular the critically ill. This review summarises recent key clinical studies evaluating the efficacy, toxicity and PK/PD of colistin/CMS.

Nitric oxide mediated Staphylococcus aureus pathogenesis and protective role of nanoconjugated vancomycin

OBJECTIVE

To test the survival of Staphylococcus aureus (S. aureus) inside lymphocyte that contributes to the pathogenesis of infection and possible anti-inflammatory and antioxidative effect of nanoconjugated vancomycin against in vivo S. aureus infection in a dose and duration dependent manner.

METHODS

5×10(6) CFU/mL vancomycin-sensitive S. aureus (VSSA) and vancomycin-resistive S. aureus (VRSA) were challenged in Swiss male mice for 3 days, 5 days, 10 days and 15 days, respectively. Bacteremia and inflammatory parameters were observed to evaluate the duration for development of VSSA and VRSA infection. 100 mg/kg bw/day and 500 mg/kg bw/day nanoconjugated vancomycin were administrated to VSSA and VRSA infected group for 5 days. Bacteremia, inflammatory parameters and oxidative stress related parameters were tested to observe the effective dose of nanoconjugated vancomycin against VSSA and VRSA infection. Nanoconjugated vancomycin was treated at a dose of 100 mg/kg bw/day and 500 mg/kg bw/day, respectively, to VSSA and VRSA infected group for successive 5 days, 10 days and 15 days. Bacteremia, inflammatory parameters and oxidative stress related parameters were observed to assess the effective duration of nanoconjugated vancomycin against VSSA and VRSA infection.

RESULTS

The result revealed that in vivo VSSA and VRSA infection developed after 5 days of challenge by elevating the NO generation in lymphocyte and serum inflammatory markers. Administration with nanoconjugated vancomycin to VSSA and VRSA infected group at a dose of 100 mg/kg bw/day and 500 mg/kg bw/day, respectively, for successive 10 days eliminated bacterimia, decreased NO generation in lymphocyte, serum inflammatory markers and increased antioxidant enzyme status.

CONCLUSIONS

These findings suggest, in vivo challenge of VSSA and VRSA for 5 days can produce the highest degree of damage in lymphocyte which can be ameliorated by treatment with nanoconjugated vancomycin for 10 successive days.

Effect of manuka honey on the expression of universal stress protein A in meticillin-resistant Staphylococcus aureus

Staphylococcus aureus is an important pathogen that can cause many problems, from impetigo to endocarditis. With its continued resistance to multiple antibiotics, S. aureus remains a serious health threat. Honey has been used to eradicate meticillin-resistant S. aureus (MRSA) strains from wounds, but its mode of action is not yet understood. Proteomics provides a potent group of techniques that can be used to analyse differences in protein expression between untreated bacterial cells and those treated with inhibitory concentrations of manuka honey. In this study, two-dimensional (2D) electrophoresis was combined with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) to determine the identities of proteins whose levels of expression were changed at least two-fold following treatment with manuka honey. Protein extracts were obtained from cells grown in tryptone soy broth (with or without manuka honey) by mechanical disruption and were separated on 2D polyacrylamide gels. A protein was isolated in gels prepared from untreated cell extract that was absent from gels made using honey-treated cell extract. Using MALDI-TOF MS, the protein was identified as universal stress protein A (UspA). Downregulation of this protein was confirmed by real-time polymerase chain reaction (PCR), which showed a 16-fold downregulation in honey-treated cells compared with untreated samples. This protein is involved in the stress stamina response and its downregulation could help to explain the inhibition of MRSA by manuka honey.

rRNA Methyltransferases and their Role in Resistance to Antibiotics

Methyltransferases (MTases), a large protein superfamily, commonly use S-adenosyl-L-methionine (SAM) as the methyl group donor. SAM-dependant MTases methylate both nucleic acids (DNA, RNA) and proteins, and thus modulate their activity, function and folding. Methylation of G1405 or A1408 nucleotides of 16S rRNA in aminoglycoside-producing microorganisms confers the resistance to their own toxic product(s). This mechanism of resistance has been considered as unique to antibiotics producers until recently. Since 2003, methylation of 16S rRNA as a mechanism of resistance is increasingly emerging in pathogenic bacteria. This represents a major threat towards the usefulness of aminoglycosides in the clinical practice. A potential solution to the problem involves the design of novel compounds that would act against new ribosomal targets. The second approach to the issue includes the development of resistance MTases' inhibitors, with the idea to prevent them from modifying the bacterial rRNA, and thus reinstate the therapeutic power of existing aminoglycosides. As the latter approach has considerable potential, it is obvious that fundamental research related to protein expression, in-depth understanding of the mechanism of action and resolving a tertiary structure of 16S rRNAs MTases are prerequisites for application in medicine.

Pharmacokinetic/pharmacodynamic investigation of colistin against Pseudomonas aeruginosa using an in vitro model

Colistin plays a key role in treatment of serious infections by Pseudomonas aeruginosa. The aims of this study were to (i) identify the pharmacokinetic/pharmacodynamic (PK/PD) index (i.e., the area under the unbound concentration-time curve to MIC ratio [fAUC/MIC], the unbound maximal concentration to MIC ratio [fC(max)/MIC], or the cumulative percentage of a 24-h period that unbound concentrations exceed the MIC [fT(>MIC)]) that best predicts colistin efficacy and (ii) determine the values for the predictive PK/PD index required to achieve various magnitudes of killing effect. Studies were conducted in a one-compartment in vitro PK/PD model for 24 h using P. aeruginosa ATCC 27853, PAO1, and the multidrug-resistant mucoid clinical isolate 19056 muc. Six intermittent dosing intervals, with a range of fC(max) colistin concentrations, and two continuous infusion regimens were examined. PK/PD indices varied from 0.06 to 18 for targeted fC(max)/MIC, 0.36 to 312 for fAUC/MIC, and 0 to 100% for fT(>MIC). A Hill-type model was fit to killing effect data, which were expressed as the log(10) ratio of the area under the CFU/ml curve for treated regimens versus control. With fC(max) values equal to or above the MIC, rapid killing was observed following the first dose; substantial regrowth occurred by 24 h with most regimens. The overall killing effect was best correlated with fAUC/MIC (R(2) = 0.931) compared to fC(max)/MIC (R(2) = 0.868) and fT(>MIC) (R(2) = 0.785). The magnitudes of fAUC/MIC required for 1- and 2-log(10) reductions in the area under the CFU/ml curve relative to growth control were 22.6 and 30.4, 27.1 and 35.7, and 5.04 and 6.81 for ATCC 27853, PAO1, and 19056 muc, respectively. The PK/PD targets identified will assist in designing optimal dosing strategies for colistin.

High yield expression of an AHL-lactonase from Bacillus sp. B546 in Pichia pastoris and its application to reduce Aeromonas hydrophila mortality in aquaculture

Background

Aeromonas hydrophila is a serious pathogen and can cause hemorrhagic septicemia in fish. To control this disease, antibiotics and chemicals are widely used which can consequently result in "superbugs" and chemical accumulation in the food chain. Though vaccine against A. hydrophila is available, its use is limited due to multiple serotypes of this pathogen and problems of safety and efficacy. Another problem with vaccination is the ability to apply it to small fish especially in high numbers. In this study, we tried a new way to attenuate the A. hydrophila infection by using a quorum quenching strategy with a recombinant AHL-lactonase expressed in Pichia pastoris.

Results

The AHL-lactonase (AiiA_B546) from Bacillus sp. B546 was produced extracellularly in P. pastoris with a yield of 3,558.4 ± 81.3 U/mL in a 3.7-L fermenter when using 3-oxo-C8-HSL as the substrate. After purification with a HiTrap Q Sepharose column, the recombinant homogenous protein showed a band of 33.6 kDa on SDS-PAGE, higher than the calculated molecular mass (28.14 kDa). Deglycosylation of AiiA_B546 with Endo H confirmed the occurrence of N-glycosylation. The purified recombinant AiiA_B546 showed optimal activity at pH 8.0 and 20°C, exhibited excellent stability at pH 8.0-12.0 and thermal stability at 70°C, was firstly confirmed to be significantly protease-resistant, and had wide substrate specificity. In application test, when co-injected with A. hydrophila in common carp, recombinant AiiA_B546 decreased the mortality rate and delayed the mortality time of fish.

Conclusions

Our results not only indicate the possibility of mass-production of AHL-lactonase at low cost, but also open up a promising foreground of application of AHL-lactonase in fish to control A. hydrophila disease by regulating its virulence. To our knowledge, this is the first report on heterologous expression of AHL-lactonase in P. pastoris and attenuating A. hydrophila virulence by co-injection with AHL-lactonase.

Expression of antimicrobial peptides in cutaneous infections after skin surgery

BACKGROUND

Increasing numbers of antibiotics have lost efficiency because of bacterial resistance. The consequences can be severe when surgical wounds become infected during postoperative care. Natural peptide antibiotics, the so-called host defence peptides (HDPs), have been investigated since the 1990s in a search for alternative treatment strategies. HDPs build up a protection shield against pathological microorganisms, especially in human epithelium. The use of HDPs is currently being discussed as a new antimicrobial therapeutic strategy. Accordingly, a profound knowledge of the quantitative relationships of the effectors is essential.

OBJECTIVES

To evaluate differences in HDP expression between postoperatively inflamed and healthy epithelium.

METHODS

Expression profiles of the genes encoding HDP human beta-defensin (hBD)-1 (DEFB1, previously known as HBD-1), hBD-2 (DEFB4A, previously known as HBD-2), hBD-3 (DEFB103A, previously known as HBD-3) and psoriasin (S100A7) were assessed in samples of surgical wound healing disorders (n = 27) and healthy epithelium (n = 16) by using real-time polymerase chain reaction. Immunohistochemical staining was performed in the same samples.

RESULTS

A significant overexpression of DEFB4A (P < 0.001), DEFB103A (P = 0.001) and S100A7 (P < 0.001) was found in cutaneous surgical site infections. Immunohistochemistry revealed intensely elevated protein levels of psoriasin in infected wounds, and differences in distribution with respect to the epithelial layers.

CONCLUSIONS

The study demonstrates upregulated mRNA expression and protein levels of HDPs in postoperatively inflamed epithelium. The results may be a starting point for novel pharmacological treatments.

Kinetic parameters of efflux of penicillins by the multidrug efflux transporter AcrAB-TolC of Escherichia coli

The multidrug efflux transporter AcrAB-TolC is known to pump out a diverse range of antibiotics, including beta-lactams. However, the kinetic constants of the efflux process, needed for the quantitative understanding of resistance, were not available until those accompanying the efflux of some cephalosporins were recently determined by combining efflux with the hydrolysis of drugs by the periplasmic beta-lactamase. In the present study we extended this approach to the study of a wide range of penicillins, from ampicillin and penicillin V to ureidopenicillins and isoxazolylpenicillins, by combining efflux with hydrolysis with the OXA-7 penicillinase. We found that the penicillins had a much stronger apparent affinity to AcrB and higher maximum rates of efflux than the cephalosporins. All penicillins showed strong positive cooperativity kinetics for export. The kinetic constants obtained were validated, as the MICs theoretically predicted on the basis of efflux and hydrolysis kinetics were remarkably similar to the observed MICs (except for the isoxazolylpenicillins). Surprisingly, however, the efflux kinetics of cloxacillin, for example, whose MIC decreased 512-fold in Escherichia coli upon the genetic deletion of the acrB gene, were quite similar to those of ampicillin, whose MIC decreased only 2-fold with the same treatment. Analysis of this phenomenon showed that the extensive decrease in the MIC for the acrB mutant is primarily due to the low permeation of the drug and that comparison of the MICs between the parent and the acrB strains is a very poor measure of the ability of AcrB to pump a drug out.

Design of O-acetylserine sulfhydrylase inhibitors by mimicking nature

The inhibition of cysteine biosynthesis in prokaryotes and protozoa has been proposed to be relevant for the development of antibiotics. Haemophilus influenzae O-acetylserine sulfhydrylase (OASS), catalyzing l-cysteine formation, is inhibited by the insertion of the C-terminal pentapeptide (MNLNI) of serine acetyltransferase into the active site. Four-hundred MNXXI pentapeptides were generated in silico, docked into OASS active site using GOLD, and scored with HINT. The terminal P5 Ile accounts for about 50% of the binding energy. Glu or Asp at position P4 and, to a lesser extent, at position P3 also significantly contribute to the binding interaction. The predicted affinity of 14 selected pentapeptides correlated well with the experimentally determined dissociation constants. The X-ray structure of three high affinity pentapeptide-OASS complexes were compared with the docked poses. These results, combined with a GRID analysis of the active site, allowed us to define a pharmacophoric scaffold for the design of peptidomimetic inhibitors.

Biophysical characterization and mutational analysis of the antibiotic resistance protein NimA from Deinococcus radiodurans

Metronidazole (MTZ) is an antibiotic commonly used to treat anaerobic bacterial infections in humans and animals. Antibiotic resistance toward this class of 5-nitroimidazole (5-Ni) drug derivatives has been related to the Nim genes thought to encode a reductase. Here we report the biophysical characteristics of the NimA protein from Deinococcus radiodurans (DrNimA) binding to MTZ and three other 5-Ni drugs. The interaction energies of the protein and antibiotic are studied by isothermal titration calorimetry (ITC) and with free energy and linear interaction energy (LIE) calculations, where the latter method revealed that the antibiotic binding is mainly of hydrophobic character. ITC measurements further found that one DrNimA dimer has two antibiotic binding sites which were not affected by mutation of the reactive His71. The observed association constants (K(a)) were in the range of 5.1-4910(4)M(-1) and the enthalpy release upon binding to DrNimA for the four drugs studied was relatively low (approximately -1 kJ/mol) but still measurable. The drug binding is mainly entropy driven and along with the hydrophobic drug binding site found by crystallography, this possibly explains the low observed enthalpy values. The effect of the His71 mutation and the presence of MTZ were studied by differential scanning calorimetry (DSC). Native DrNimA is a yellow colored protein where the interaction from His71 to the cofactor is thought to be responsible for the coloring. Mutations of His71 to Ala, Ser, Leu or Asp all gave transparent, colorless protein solutions, and the two mutant crystal structures of DrNimA-H71A and DrNimA-H71S presented revealed no cofactor binding.

Multicomponent drug efflux complexes: architecture and mechanism of assembly

Multidrug efflux pumps are major contributors to intrinsic antibiotic resistance in Gram-negative pathogens. The basic structure of these pumps comprises an inner membrane transporter, a periplasmic membrane fusion protein and an outer membrane channel. However, the architecture and composition of multidrug efflux complexes vary significantly because of the topological and functional diversity of the inner membrane transporters. This article presents the current views on architecture and assembly of multicomponent drug efflux transporters from Gram-negative bacteria.