Genomic analysis of vB_PaS-HSN4 bacteriophage and its antibacterial activity (in vivo and in vitro) against Pseudomonas aeruginosa isolated from burn

The most frequent infections caused by Pseudomonas aeruginosa are local infections in soft tissues, including burns. Today, phage use is considered a suitable alternative to cure infections caused by multi-drug-resistant (MDR) and extensively drug-resistant (XDR) bacteria. We investigated the potential of a novel phage (vB_PaS-HSN4) belonging to Caudoviricetes class, against XDR and MDR P. aeruginosa strains in vivo and in vitro. Its biological and genetic characteristics were investigated. The phage burst size and latent were 119 and 20 min, respectively. It could tolerate a broad range of salt concentrations, pH values, and temperatures. The combination with ciprofloxacin significantly enhanced biofilm removal after 24 h. The genome was dsDNA with a size of 44,534 bp and encoded 61 ORFs with 3 tRNA and 5 promoters. No virulence factor was observed in the phage genome. In the in vivo infection model, treatment with vB_PaS-HSN4 increased Galleria mellonella larvae survival (80%, 66%, and 60%) (MOI 100) and (60%, 40%, and 26%) (MOI 1) in the pre-treatment, co-treatment, and post-treatment experiments, respectively. Based on these characteristics, it can be considered for the cure of infections of burns caused by P. aeruginosa.

Multidrug-Resistant and Virulent Organisms Trauma Infections: Trauma Infectious Disease Outcomes Study Initiative

INTRODUCTION

During the wars in Iraq and Afghanistan, increased incidence of multidrug-resistant (MDR) organisms, as well as polymicrobial wounds and infections, complicated the management of combat trauma-related infections. Multidrug resistance and wound microbiology are a research focus of the Trauma Infectious Disease Outcomes Study (TIDOS), an Infectious Disease Clinical Research Program, Uniformed Services University, research protocol. To conduct comprehensive microbiological research with the goal of improving the understanding of the complicated etiology of wound infections, the TIDOS MDR and Virulent Organisms Trauma Infections Initiative (MDR/VO Initiative) was established as a collaborative effort with the Brooke Army Medical Center, Naval Medical Research Center, U.S. Army Institute of Surgical Research, and Walter Reed Army Institute of Research. We provide a review of the TIDOS MDR/VO Initiative and summarize published findings.

METHODS

Antagonism and biofilm formation of commonly isolated wound bacteria (e.g., ESKAPE pathogens-Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.), antimicrobial susceptibility patterns, and clinical outcomes are being examined. Isolates collected from admission surveillance swabs, as part of infection control policy, and clinical infection workups were retained in the TIDOS Microbiological Repository and associated clinical data in the TIDOS database.

RESULTS

Over the TIDOS study period (June 2009 to December 2014), more than 8,300 colonizing and infecting isolates were collected from military personnel injured with nearly one-third of isolates classified as MDR. At admission to participating U.S. military hospitals, 12% of wounded warriors were colonized with MDR Gram-negative bacilli. Furthermore, 27% of 913 combat casualties with ≥1 infection during their trauma hospitalization had MDR Gram-negative bacterial infections. Among 335 confirmed combat-related extremity wound infections (2009-2012), 61% were polymicrobial and comprised various combinations of Gram-negative and Gram-positive bacteria, yeast, fungi, and anaerobes. Escherichia coli was the most common Gram-negative bacilli isolated from clinical workups, as well as the most common colonizing MDR secondary to extended-spectrum β-lactamase resistance. Assessment of 479 E. coli isolates collected from wounded warriors found 188 pulsed-field types (PFTs) from colonizing isolates and 54 PFTs from infecting isolates without significant overlap across combat theaters, military hospitals, and study years. A minority of patients with colonizing E. coli isolates developed subsequent infections with the same E. coli strain. Enterococcus spp. were most commonly isolated from polymicrobial wound infections (53% of 204 polymicrobial cultures). Patients with Enterococcus infections were severely injured with a high proportion of lower extremity amputations and genitourinary injuries. Approximately 65% of polymicrobial Enterococcus infections had other ESKAPE organisms isolated. As biofilms have been suggested as a cause of delayed wound healing, wound infections with persistent recovery of bacteria (isolates of same organism collected ≥14 days apart) and nonrecurrent bacterial isolates were assessed. Biofilm production was significantly associated with recurrent bacteria isolation (97% vs. 59% with nonrecurrent isolates; P < 0.001); however, further analysis is needed to confirm biofilm formation as a predictor of persistent wound infections.

CONCLUSIONS

The TIDOS MDR/VO Initiative provides comprehensive and detailed data of major microbial threats associated with combat-related wound infections to further the understanding of wound etiology and potentially identify infectious disease countermeasures, which may lead to improvements in combat casualty care.

Atomistic insight and modeled elucidation of conessine towards Pseudomonas aeruginosa efflux pump

Drug-resistant Pseudomonas aeruginosa efflux pump extrudes antibiotics from cells for survival. Efflux pump inhibitor (EPI) thus becomes an interesting alternative to handle the drug-resistant bacteria. Conessine, a natural steroidal alkaloid from Holarrhena antidysenterica, previously exhibited efflux pump inhibitory potential. Our molecular docking and molecular dynamics (MD) studies provided atomistic information as well as the interaction of conessine with bacterial MexB efflux pump in phospholipid bilayer membrane to further the previous experimental report. Herein, the binding site and proposed mode of action of conessine were identified compared to known/commercial EPIs such as PAβN or designed-synthetic P9D. Our results explained conessine binding mode of action as an effective agent against the MexB efflux pump. The MD simulation also suggested that conessine was able to affect glycine loop (G-loop) flexibility, and the reduced G-loop flexibility due to conessine could hinder an antibiotics extrusion. In addition, our study suggested the conessine core structure buried in a hydrophobic region in the efflux pump similar to other known EPIs. Our finding could cope as a key for the design and development of the conessine derivative as novel EPI against P. aeruginosa.Communicated by Ramaswamy H. Sarma.

Identification of the PA1113 Gene Product as an ABC Transporter Involved in the Uptake of Carbenicillin in Pseudomonas aeruginosa PAO1

The resistance of Pseudomonas aeruginosa to antibiotics is multi factorial and complex. Whereas efflux pumps such as MexAB-OprM have been thought to predominate, here we show that a novel ATP Binding Cassette (ABC) transporter that mediates influx of carbenicillin from the periplasm to the cytoplasm and away from its cell wall target plays an important role in the resistance of P. aeruginosa to this antibiotic. Treatment of P. aeruginosa with verapamil, an inhibitor of ABC transporters in eukaryotic cells, increases its sensitivity to carbenicillin. Using amino acid sequence homology with known verapamil protein targets as a probe, we determined that the PA1113 gene product, an ABC transporter, mediates carbenicillin uptake into the bacterial cytoplasm. Docking and pharmacological analyses showed that verapamil and carbenicillin compete for the same site on the PA1113 gene protein, explaining the inhibitory effect of verapamil on carbenicillin uptake, and furthermore suggest that the PA1113 ABC transporter accounts for about 30% of P. aeruginosa carbenicillin resistance. Our findings demonstrate that the PA1113 gene product helps mediate carbenicillin resistance by transporting it away from its cell wall target and represents a promising new therapeutic target.

Screening of endophytic fungal metabolites from Cola nitida leaves for antimicrobial activities against clinical isolates of Pseudomonas aeruginosa

Endophytic fungi of selected Nigerian plants are important sources of bioactive products with enormous potentials for the discovery of new drug molecules for drug development. Pseudomonas aeruginosa is one of the major causes of healthcare-associated bacterial infections, leading to increased mortality and morbidity. In this study, isolated endophytic fungi from Cola nitida were screened for anti-pseudomonas properties. Endophytic fungi associated with healthy leaves of C. nitida were isolated using standard methods. Fungi were identified through their morphological, cultural and microscopic characteristics. The fungi were subjected to solid-state fermentation and secondary metabolites extracted using ethyl acetate and concentrated under vacuum. The crude extracts were screened for antimicrobial activity against clinical and laboratory strains of Pseudomonas aeruginosa using the agar diffusion method. The bioactive components of the fungal extracts were identified using High-Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD) analysis. Three endophytic fungi; Acremonium sp., Aspergillus sp. and Trichophyton sp. were isolated. At 1 mg/ml, extracts of the three fungi displayed antipseudomonal activity with inhibition zone diameter ranging from 6 - 4 mm. HPLC-DAD analysis revealed the presence of compounds, such as 4-hydroxyphenyl acetate. indole-3-acetic acid, and protocatechuic acid among others in the fungal extracts. The findings in this study reveal that endophytic fungi associated with C. nitida possess promising antipseudomonal properties. This finding can open new doors for the discovery of new agents against P. aeruginosa.

Functional properties and the oligomeric state of alkyl hydroperoxide reductase subunit F (AhpF) in Pseudomonas aeruginosa

Alkyl hydroperoxide reductase subunit F (AhpF) is a well-known flavoprotein that transfers electrons from pyridine nucleotides to the peroxidase protein AhpC via redox-active disulfide centers to detoxify hydrogen peroxide. However, study of AhpF has historically been limited to particular eubacteria, and the connection between the functional and structural properties of AhpF remains unknown. The present study demonstrates the dual function of Pseudomonas aeruginosa AhpF (PaAhpF) as a reductase and a molecular chaperone. It was observed that the functions of PaAhpF are closely linked with its structural status. The reductase and foldase chaperone function of PaAhpF predominated for its low-molecular-weight (LMW) form, whereas the holdase chaperone function of PaAhpF was found associated with its high-molecular-weight (HMW) complex. Further, the present study also demonstrates the multiple function of PaAhpF in controlling oxidative and heat stresses in P. aeruginosa resistance to oxidative and heat stress.

Assessment of Microbiological Content of Private and Public Recreational Water Facilities and Their Antimicrobial Susceptibility Pattern in Al-Ahsa

BACKGROUND

Water recreational facilities like swimming pools attract people of all ages. However, these facilities are very suitable for the transmission of various microbial diseases and have been shown to pose public health concerns.

AIMS

This study assesses the presence of different Gram-negative bacteria pathogens and their antimicrobial susceptibility pattern in both private and public pools in Al-Ahsa.

METHODS

11 private and 3 public recreational water facilities were sampled for the study. Collected water samples were inoculated into nutrient broth and incubated aerobically for 24 hours. The overnight growth was plated out on blood and MacConkey agars. Pure cultures of the bacteria samples were used for identification and antimicrobial susceptibility test using the Vitek 2 compactautomated system (BioMerieux, Marcy L'Etoile, France). Minimum inhibitory concentration was also provided by the Vitek 2 compact automated system.

RESULTS

13 different Gram-negative bacteria species isolates were encountered in both pool types sampled. More of potential pathogens were isolated from the private than the public pools, of which Klebsiella pneumoniae and Pseudomonas aeruginosa constituted 50% and 43%, respectively, of all the isolates. Findings also revealed a varied minimum inhibitory concentrations (MICs) indicating that the isolates were of different strains. Antibiotic susceptibility pattern also showed variability among the isolates.

CONCLUSIONS

This study has revealed a potential health risk associated with the use of water recreational facilities. The presence of K pneumoniae and P aeruginosa suggests a public health concern and should be looked into.

Blocking RpoN reduces virulence of Pseudomonas aeruginosa isolated from cystic fibrosis patients and increases antibiotic sensitivity in a laboratory strain

Multidrug-resistant organisms are increasing in healthcare settings, and there are few antimicrobials available to treat infections from these bacteria. Pseudomonas aeruginosa is an opportunistic pathogen in burn patients and individuals with cystic fibrosis (CF), and a leading cause of nosocomial infections. P. aeruginosa is inherently resistant to many antibiotics and can develop resistance to others, limiting treatment options. P. aeruginosa has multiple sigma factors to regulate transcription. The alternative sigma factor, RpoN (σ54), regulates many virulence genes and is linked to antibiotic resistance. Recently, we described a cis-acting peptide, RpoN*, which is a "molecular roadblock", binding consensus promoters at the -24 site, blocking transcription. RpoN* reduces virulence of P. aeruginosa laboratory strains, but its effects in clinical isolates was unknown. We investigated the effects of RpoN* on phenotypically varied P. aeruginosa strains isolated from CF patients. RpoN* expression reduced motility, biofilm formation, and pathogenesis in a P. aeruginosa-C. elegans infection model. Furthermore, we investigated RpoN* effects on antibiotic susceptibility in a laboratory strain. RpoN* expression increased susceptibility to several beta-lactam-based antibiotics in strain P. aeruginosa PA19660 Xen5. We show that using a cis-acting peptide to block RpoN consensus promoters has potential clinical implications in reducing virulence and improving antibiotic susceptibility.

Synergy of clavine alkaloid 'chanoclavine' with tetracycline against multi-drug-resistant E. coli

The emergence of multi drug resistance (MDR) in Gram-negative bacteria (GNB) and lack of novel classes of antibacterial agents have raised an immediate need to identify antibacterial agents, which can reverse the phenomenon of MDR. The purpose of present study was to evaluate synergy potential and understanding the drug resistance reversal mechanism of chanoclavine isolated from Ipomoea muricata against the multi-drug-resistant clinical isolate of Escherichia coli (MDREC). Although chanoclavine did not show antibacterial activity of its own, but in combination, it could reduce the minimum inhibitory concentration (MIC) of tetracycline (TET) up to 16-folds. Chanoclavine was found to inhibit the efflux pumps which seem to be ATPase-dependent. In real-time expression analysis, chanoclavine showed down-regulation of different efflux pump genes and decreased the mutation prevention concentration of tetracycline. Further, in silico docking studies revealed significant binding affinity of chanoclavine with different proteins known to be involved in drug resistance. In in silico ADME/toxicity studies, chanoclavine was found safe with good intestinal absorption, aqueous solubility, medium blood-brain barrier (BBB), no CYP 2D6 inhibition, no hepatotoxicity, no skin irritancy, and non-mutagenic indicating towards drug likeliness of this molecule. Based on these observations, it is hypothesized that chanoclavine might be inhibiting the efflux of tetracycline from MDREC and thus enabling the more availability of tetracycline inside the cell for its action.

Structure-functionality relationship and pharmacological profiles of Pseudomonas aeruginosa alkylquinolone quorum sensing modulators

An important paradigm in anti-infective research is the antivirulence concept. Pathoblockers are compounds which disarm bacteria of their arsenal of virulence factors. PqsR is a transcriptional regulator controlling the production of such factors in Pseudomonas aeruginosa, most prominently pyocyanin. In this work, a series of tool compounds based on the structure of the natural ligand 2-heptyl-4-quinolone (HHQ) were used for probing the structure-functionality relationship. Four different profiles are identified namely agonists, antagonists, inverse agonists and biphasic modulators. Molecular docking studies revealed that each class of the PqsR modulators showed distinctive interactions in the PqsR binding domain. It was found that the substituents in position 3 of the quinolone core act as a switch between the different profiles, according to their ability to donate or accept a hydrogen bond, or form a hydrophobic interaction. Finally, it was shown that only inverse agonists were able to strongly inhibit pyocyanin production.

Sonochemical-solvothermal synthesis of guanine embedded copper based metal-organic framework (MOF) and its effect on oprD gene expression in clinical and standard strains of Pseudomonas aeruginosa

The guanine incropped Cu based metal-organic framework (Guanine-Cu-MOF) was synthesized by facile one-step sonochemical method by simply mixing of 4-4, biphenyldicarboxylic, guanine and copper nitrate (Bio-Cu-H₂bpdc-Gu). The prepared guanine-MOF was characterized by using X-Ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Field emission scanning electron microscopy (FE-SEM) techniques. The morphology of prepared material was sponge-shaped which it was well documented, together with the presence of existing functional groups. The effect of prepared material on oprD Gene Expression was investigated in Clinical and Standard Strains of Pseudomonas aeruginosa (PAO-1) and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of prepared samples against P. aeruginosa strains were determined through the broth micro-dilution method. The expression of oprD gene in strains affected by Cu-H₂bpdc-Gu was quantitatively investigated through real-time PCR. MIC of Bio-Cu-H₂bpdc-Gu was 400 μg/mL for the standard and clinical strains of P. aeruginosa, while, MBC of this compound was 700 μg/mL for standard strain and 800 μg/mL for clinical strains. The highest and the lowest rate of oprD gene expression were found to be 3.6 and 1.1 fold in the strains, respectively.

Ultrasound assisted extraction of phenolic acids from broccoli vegetable and using sonochemistry for preparation of MOF-5 nanocubes: Comparative study based on micro-dilution broth and plate count method for synergism antibacterial effect

The aim of this work was comparison study of dilution and plating method for evaluation of the synergism effect of metal-organic framework nanocubes (MOF-5-NCs) and broccoli extract (Brassica oleracea) on antibacterial activity of standard and clinical Pseudomonas aeruginosa strains. For this purpose, sonochemical synthesis of MOF-5-NCs was performed and it was characterized using XRD, FT-IR, FESEM and EDS techniques. Maceration extraction (ME) and ultrasound assisted extraction (UAE) methods in three different solvents were prepared and applicability of their extracts were compared in some cases such as radical scavenging and antioxidant activity. The HPLC/UV analysis was applied for separation, identification and evaluation of phenolic acids in prepared broccoli extracts. Then, antimicrobial activity of MOF-5NCs and broccoli extract against gram-negative bacteria, Pseudomonas aeruginosa was evaluated by detection of minimal inhibition concentration (MIC), minimal bactericidal concentration (MBC) and zone of inhibition (ZOI). The results of in vitro assays showed that dilution method due to flase estimation of 4% viability percentage which is not logic by consideration of MBC well could not be able to estimate MBC. Therefore, plate count method was performed for precise calculation of MBC. MIC of broccoli extract and MOF-5-NCs on Pseudomonas aeruginosa strains were 7.81mgmL^-1 and 3.13mgmL^-1, respectively.

Targeting the alternative sigma factor RpoN to combat virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that infects immunocompromised and cystic fibrosis patients. Treatment is difficult due to antibiotic resistance, and new antimicrobials are needed to treat infections. The alternative sigma factor 54 (σ⁵⁴, RpoN), regulates many virulence-associated genes. Thus, we evaluated inhibition of virulence in P. aeruginosa by a designed peptide (RpoN molecular roadblock, RpoN*) which binds specifically to RpoN consensus promoters. We expected that RpoN* binding to its consensus promoter sites would repress gene expression and thus virulence by blocking RpoN and/or other transcription factors. RpoN* reduced transcription of approximately 700 genes as determined by microarray analysis, including genes related to virulence. RpoN* expression significantly reduced motility, protease secretion, pyocyanin and pyoverdine production, rhamnolipid production, and biofilm formation. Given the effectiveness of RpoN* in vitro, we explored its effects in a Caenorhabditis elegans–P. aeruginosa infection model. Expression of RpoN* protected C. elegans in a paralytic killing assay, whereas worms succumbed to paralysis and death in its absence. In a slow killing assay, which mimics establishment and proliferation of an infection, C. elegans survival was prolonged when RpoN* was expressed. Thus, blocking RpoN consensus promoter sites is an effective strategy for abrogation of P. aeruginosa virulence.

Annona glabra Flavonoids Act As Antimicrobials by Binding to Pseudomonas aeruginosa Cell Walls

Pseudomonas aeruginosa is an important pathogen in opportunistic infections in humans. The increased incidence of antimicrobial-resistant P. aeruginosa isolates has highlighted the need for novel and more potent therapies against this microorganism. Annona glabra is known for presenting different compounds with diverse biological activities, such as anti-tumor and immunomodulatory activities. Although other species of the family display antimicrobial actions, this has not yet been reported for A. glabra. Here, we investigated the antimicrobial activity of the ethyl acetate fraction (EAF) obtained from the leaf hydroalcoholic extract of A. glabra. EAF was bactericidal against different strains of P. aeruginosa. EAF also presented with a time- and concentration-dependent effect on P. aeruginosa viability. Testing of different EAF sub-fractions showed that the sub-fraction 32-33 (SF32-33) was the most effective against P. aeruginosa. Analysis of the chemical constituents of SF32-33 demonstrated a high content of flavonoids. Incubation of this active sub-fraction with P. aeruginosa ATCC 27983 triggered an endothermic reaction, which was accompanied by an increased electric charge, suggesting a high binding of SF32-33 compounds to bacterial cell walls. Collectively, our results suggest that A. glabra-derived compounds, especially flavonoids, may be useful for treating infections caused by P. aeruginosa.

Mechanistic Basis of Antimicrobial Actions of Silver Nanoparticles

Multidrug resistance of the pathogenic microorganisms to the antimicrobial drugs has become a major impediment toward successful diagnosis and management of infectious diseases. Recent advancements in nanotechnology-based medicines have opened new horizons for combating multidrug resistance in microorganisms. In particular, the use of silver nanoparticles (AgNPs) as a potent antibacterial agent has received much attention. The most critical physico-chemical parameters that affect the antimicrobial potential of AgNPs include size, shape, surface charge, concentration and colloidal state. AgNPs exhibits their antimicrobial potential through multifaceted mechanisms. AgNPs adhesion to microbial cells, penetration inside the cells, ROS and free radical generation, and modulation of microbial signal transduction pathways have been recognized as the most prominent modes of antimicrobial action. On the other side, AgNPs exposure to human cells induces cytotoxicity, genotoxicity, and inflammatory response in human cells in a cell-type dependent manner. This has raised concerns regarding use of AgNPs in therapeutics and drug delivery. We have summarized the emerging endeavors that address current challenges in relation to safe use of AgNPs in therapeutics and drug delivery platforms. Based on research done so far, we believe that AgNPs can be engineered so as to increase their efficacy, stability, specificity, biosafety and biocompatibility. In this regard, three perspectives research directions have been suggested that include (1) synthesizing AgNPs with controlled physico-chemical properties, (2) examining microbial development of resistance toward AgNPs, and (3) ascertaining the susceptibility of cytoxicity, genotoxicity, and inflammatory response to human cells upon AgNPs exposure.

Evaluation of Metallo-β-Lactamase-Production and Carriage of bla-VIM Genes in Pseudomonas aeruginosa Isolated from Burn Wound Infections in Isfahan

Background

Metallo-β-lactamase-production among Gram-negative bacteria, including Pseudomonas aeruginosa, has become a challenge for treatment of infections due to these resistant bacteria.

Objectives

The aim of the current study was to evaluate the metallo-β-lactamase-production and carriage of bla-_VIM genes among carbapenem-resistant P. aeruginosa isolated from burn wound infections.

Patients and Methods

A cross-sectional study was conducted from September 2014 to July 2015. One hundred and fifty P. aeruginosa isolates were recovered from 600 patients with burn wound infections treated at Imam-Musa-Kazem Hospital in Isfahan city, Iran. Carbapenem-resistant P. aeruginosa isolates were screened by disk diffusion using CLSI guidelines. Metallo-β-lactamase-producing P. aeruginosa isolates were identified using an imipenem-EDTA double disk synergy test (EDTA-IMP DDST). For detection of MBL genes including bla-_VIM-1 and bla-_VIM-2, polymerase chain reaction (PCR) methods and sequencing were used.

Results

Among the 150 P. aeruginosa isolates, 144 (96%) were resistant to imipenem by the disk diffusion method, all of which were identified as metallo-β-lactamase-producing P. aeruginosa isolates by EDTA-IMP DDST. Twenty-seven (18%) and 8 (5.5%) MBL-producing P. aeruginosa isolates harbored bla-_VIM-1 and bla-_VIM-2 genes, respectively.

Conclusions

Our findings showed a high occurrence of metallo-β-lactamase production among P. aeruginosa isolates in burn patient infections in our region. Also, there are P. aeruginosa isolates carrying the bla-_VIM-1 and bla-_VIM-2 genes in Isfahan province.

Antimicrobial potentials of Helicteres isora silver nanoparticles against extensively drug-resistant (XDR) clinical isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a leading opportunistic pathogen and its expanding drug resistance is a growing menace to public health. Its ubiquitous nature and multiple resistance mechanisms make it a difficult target for antimicrobial chemotherapy and require a fresh approach for developing new antimicrobial agents against it. The broad-spectrum antibacterial effects of silver nanoparticles (SNPs) make them an excellent candidate for use in the medical field. However, attempts made to check their potency against extensively drug-resistant (XDR) microbes are meager. This study describes the biosynthesis and biostabilization of SNPs by Helicteres isora aqueous fruit extract and their characterization by ultraviolet-visible spectroscopy, transmission electron microscopy, dynamic light scattering, X-ray diffraction, and Fourier transform infrared spectroscopy. Majority of SNPs synthesized were of 8--20-nm size. SNPs exhibited dose-dependent antibacterial activities against four XDR P. aeruginosa (XDR-PA) clinical isolates as revealed by growth curves, with a minimum inhibitory concentration of 300 μg/ml. The SNPs exhibited antimicrobial activity against all strains, with maximum zone of inhibition (16.4 mm) in XRD-PA-2 at 1000 μg/ml. Amongst four strains, their susceptibilities to SNPs were in the following order: XDR-PA-2 > XDR-PA-4 > XDR-PA-3 > XDR-PA-1. The exposure of bacterial cells to 300 μg/ml SNPs resulted into a substantial leakage of reducing sugars and proteins, inactivation of respiratory chain dehydrogenases, and eventual cell death. SNPs also induced lipid peroxidation, a possible underlying factor to membrane porosity. The effects were more pronounced in XDR-PA-2 which may be correlated with its higher susceptibility to SNPs. These results are indicative of SNP-induced turbulence of membranous permeability as an important causal factor in XDR-PA growth inhibition and death.

Modulation of antibiotic resistance and induction of a stress response in Pseudomonas aeruginosa by silver nanoparticles

The objective of this study was to characterize the effects of silver nanoparticles on Pseudomonas aeruginosa. Their interactions with several conventional antibiotics and ability to induce a stress response were examined. Interactions between silver nanoparticles (AgNPs) and antibiotics against free-living cells and biofilm of P. aeruginosa were studied using the chequerboard method and time-kill assays. The ability of AgNPs to induce a stress response was determined by evaluation of cellular levels of the DnaK and HtpG chaperones using SDS-PAGE and Western blot analysis. Synergistic activity against free-living P. aeruginosa between AgNPs and ampicillin, streptomycin, rifampicin and tetracycline, but not oxacillin, ciprofloxacin, meropenem or ceftazidime, was demonstrated by the chequerboard method. No such interactions were observed against P. aeruginosa biofilm. The results of time-kill assays confirmed synergy only for the AgNPs-streptomycin combination. AgNPs induced the expression of chaperone DnaK. No induction of the HtpG chaperone was detected. In conclusion, AgNPs not only display potent bactericidal activity against P. aeruginosa, but also act synergistically with several conventional antibiotics to enhance their effect against free-living bacteria as determined by the chequerboard method. The time-kill assay proved synergy between AgNPs and streptomycin only. The ability of AgNPs to induce the major chaperone protein DnaK may influence bacterial resistance to antimicrobials.