Role of reactive oxygen species in antibiotic action and resistance

Pseudomonas aeruginosa nfuA: Gene regulation and its physiological roles in sustaining growth under stress and anaerobic conditions and maintaining bacterial virulence

The role of the nfuA gene encoding an iron-sulfur ([Fe-S]) cluster-delivery protein in the pathogenic bacterium Pseudomonas aeruginosa was investigated. The analysis of nfuA expression under various stress conditions showed that superoxide generators, a thiol-depleting agent and CuCl₂ highly induced nfuA expression. The expression of nfuA was regulated by a global [2Fe-2S] cluster containing the transcription regulator IscR. Increased expression of nfuA in the ΔiscR mutant under uninduced conditions suggests that IscR acts as a transcriptional repressor. In vitro experiments revealed that IscR directly bound to a sequence homologous to the Escherichia coli Type-I IscR-binding motifs on a putative nfuA promoter that overlapped the -35 element. Binding of IscR prevented RNA polymerase from binding to the nfuA promoter, leading to repression of the nfuA transcription. Physiologically, deletion of nfuA reduced the bacterial ability to cope with oxidative stress, iron deprivation conditions and attenuated virulence in the Caenorhabditis elegans infection model. Site-directed mutagenesis analysis revealed that the conserved CXXC motif of the Nfu-type scaffold protein domain at the N-terminus was required for the NfuA functions in conferring the stress resistance phenotype. Furthermore, anaerobic growth of the ΔnfuA mutant in the presence of nitrate was drastically retarded. This phenotype was associated with a reduction in the [Fe-S] cluster containing nitrate reductase enzyme activity. However, NfuA was not required for the maturation of [Fe-S]-containing proteins such as aconitase, succinate dehydrogenase, SoxR and IscR. Taken together, our results indicate that NfuA functions in [Fe-S] cluster delivery to selected target proteins that link to many physiological processes such as anaerobic growth, bacterial virulence and stress responses in P. aeruginosa.

Evolution of Antibiotic Resistance in Biofilm and Planktonic Pseudomonas aeruginosa Populations Exposed to Subinhibitory Levels of Ciprofloxacin

The opportunistic Gram-negative pathogen Pseudomonas aeruginosa, known for its intrinsic and acquired antibiotic resistance, has a notorious ability to form biofilms, which often facilitate chronic infections. The evolutionary paths to antibiotic resistance have mainly been investigated in planktonic cultures and are less studied in biofilms. We experimentally evolved P. aeruginosa PAO1 colony biofilms and stationary-phase planktonic cultures for seven passages in the presence of subinhibitory levels (0.1 mg/liter) of ciprofloxacin (CIP) and performed a genotypic (whole-bacterial population sequencing) and phenotypic assessment of the populations. We observed a higher proportion of CIP resistance in the CIP-evolved biofilm populations than in planktonic populations exposed to the same drug concentrations. However, the MICs of ciprofloxacin were lower in CIP-resistant isolates selected from the biofilm population than the MICs of CIP-resistant isolates from the planktonic cultures. We found common evolutionary trajectories between the different lineages, with mutations in known CIP resistance determinants as well as growth condition-dependent adaptations. We observed a general trend toward a reduction in type IV-pilus-dependent motility (twitching) in CIP-evolved populations and a loss of virulence-associated traits in the populations evolved in the absence of antibiotic. In conclusion, our data indicate that biofilms facilitate the development of low-level mutational resistance, probably due to the lower effective drug exposure than in planktonic cultures. These results provide a framework for the selection process of resistant variants and the evolutionary mechanisms involved under the two different growth conditions.

Surface deposited one-dimensional copper-doped TiO2 nanomaterials for prevention of health care acquired infections

Bacterial infections acquired in healthcare facilities including hospitals, the so called healthcare acquired or nosocomial infections, are still of great concern worldwide and represent a significant economical burden. One of the major causes of morbidity is infection with Methicillin Resistant Staphylococcus aureus (MRSA), which has been reported to survive on surfaces for several months. Bactericidal activity of copper-TiO2 thin films, which release copper ions and are deposited on glass surfaces and heated to high temperatures, is well known even when illuminated with very weak UVA light of about 10 μW/cm2. Lately, there is an increased intrerest for one-dimensional TiO2 nanomaterials, due to their unique properties, low cost, and high thermal and photochemical stability. Here we show that copper doped TiO2 nanotubes produce about five times more ·OH radicals as compared to undoped TiO2 nanotubes and that effective surface disinfection, determined by a modified ISO 22196:2011 test, can be achieved even at low intensity UVA light of 30 μW/cm2. The nanotubes can be deposited on a preformed surface at room temperature, resulting in a stable deposition resistant to multiple washings. Up to 103 microorganisms per cm2 can be inactivated in 24 hours, including resistant strains such as Methicillin-resistant Staphylococcus aureus (MRSA) and Extended-spectrum beta-lactamase Escherichia coli (E. coli ESBL). This disinfection method could provide a valuable alternative to the current surface disinfection methods.

Single-Cell, Time-Lapse Reactive Oxygen Species Detection in E. coli

Detection of reactive oxygen species (ROS) in bacteria has been limited to bulk biochemical assays. Although they are powerful and quantitative tools to understand the overall production of ROS in E. coli, such assays provide limited spatial and temporal information when correlating cellular phenotype with perturbations such as antibiotics or other treatments. We have developed single-cell, time-lapse assays to detect ROS in live E. coli. The assays utilize flow systems on a fluorescence microscope to correlate symptoms aroused from biological or chemical perturbations with the in situ detection of ROS. ROS is detected by fluorogenic dyes that accumulate inside the cell, allowing detection of ROS in single cells in both homogeneous and heterogeneous samples using CellROX Green and Amplex® Red/APEX2. © 2018 by John Wiley & Sons, Inc.

The Pseudomonas Quinolone Signal (PQS): Not Just for Quorum Sensing Anymore

The Pseudomonas quinolone signal (PQS) has been studied primarily in the context of its role as a quorum-sensing signaling molecule. Recent data suggest, however, that this molecule may also function to mediate iron acquisition, cytotoxicity, outer-membrane vesicle biogenesis, or to exert host immune modulatory activities.

3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz)-capped silver nanoparticles (TzAgNPs) inhibit biofilm formation of Pseudomonas aeruginosa: a potential approach toward breaking the wall of biofilm through reactive oxygen species (ROS) generation

Microbial biofilms are factions of surface-colonized cells encompassed in a matrix of extracellular polymeric substances. Profound application of antibiotics in order to treat infections due to microbial biofilm has led to the emergence of several drug-resistant microbial strains. In this context, a novel type of 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz)-capped silver nanoparticles (TzAgNPs) was synthesized, and efforts were given to test its antimicrobial and antibiofilm activities against Pseudomonas aeruginosa, a widely used biofilm-forming pathogenic organism. The synthesized TzAgNPs showed considerable antimicrobial activity wherein the MIC value of TzAgNPs was found at 40 μg/mL against Pseudomonas aeruginosa. Antibiofilm activity of TzAgNPs was also tested against Pseudomonas aeruginosa by carrying out an array of experiments like microscopic observation, crystal violet assay, and protein count using the sub-MIC doses of TzAgNPs. Since TzAgNPs showed efficient antibiofilm activity, thus, in the present study, efforts were put together to investigate the underlying cause of biofilm attenuation of Pseudomonas aeruginosa by using TzAgNPs. To this end, we discerned that the sub-MIC doses of TzAgNPs increased ROS level considerably in the bacterial cell. The result showed that the ROS level and microbial biofilm formation are inversely proportional. Thus, the attenuation in microbial biofilm could be attributed to the accumulation of ROS level. Furthermore, it was also duly noted that microorganisms upon treatment with TzAgNPs exhibited considerable diminution in virulence factors (protease and pyocyanin) in contrast to the control where the organisms were not treated with TzAgNPs. Thus, the results indicated that TzAgNPs exhibit considerable reduction in the development of biofilms and spreading of virulence factors. Taken together, all the results indicated that TzAgNPs could be deemed to be a promising agent for the prevention of microbial biofilm development that might assist to fight against infections linked to biofilm.

Fabrication of Self-Healing Hydrogels with On-Demand Antimicrobial Activity and Sustained Biomolecule Release for Infected Skin Regeneration

Microbial infection has been considered as one of the most critical challenges in bioengineering applications especially in tissue regeneration, which engenders severe threat to public health. Herein, a hydrogel performing properties of rapid self-healing, on-demand antibiosis and controlled cargo release was fabricated by a simple assembly of Fe complex as the cross-linker and hyaluronic acid as the gel network. This hydrogel is able to locally degrade and release Fe³⁺ to kill bacteria as needed because of hyaluronidase excreted by surrounding bacteria, resulting in efficient antibacterial activity against different types of bacteria. The sustained release property of certain types of growth factors was also observed from this hydrogel owing to its dense network. Moreover, this hydrogel could repeatedly heal itself in minutes because of the coordination interaction between Fe³⁺ and COOH, exhibiting good potential in bioengineering applications on the exposed tissue, where the materials are easily damaged during daily life. When topically applied onto damaged mouse skin with infection of Staphylococcus aureus, the hydrogel is able to inhibit microbial infections, meanwhile promoting cutaneous regeneration, which formed new skin with no inflammation within a 10 day treatment. These results demonstrate the potential application of this self-healing hydrogel for the integrated therapy of antibiosis and tissue regeneration.

KatG-Mediated Oxidation Leading to Reduced Susceptibility of Bacteria to Kanamycin

Resistance to antibiotics has become a serious problem for society, and there are increasing efforts to understand the reasons for and sources of resistance. Bacterial-encoded enzymes and transport systems, both innate and acquired, are the most frequent culprits for the development of resistance, although in Mycobacterium tuberculosis, the catalase-peroxidase, KatG, has been linked to the activation of the antitubercular drug isoniazid. While investigating a possible link between aminoglycoside antibiotics and the induction of oxidative bursts, we observed that KatG reduces susceptibility to aminoglycosides. Investigation revealed that kanamycin served as an electron donor for the peroxidase reaction, reducing the oxidized ferryl intermediates of KatG to the resting state. Loss of electrons from kanamycin was accompanied by the addition of a single oxygen atom to the aminoglycoside. The oxidized form of kanamycin proved to be less effective as an antibiotic. Kanamycin inhibited the crystallization of KatG, but the smaller, structurally related glycoside maltose did cocrystallize with KatG, providing a suggestion as to the possible binding site of kanamycin.

Antimicrobial use of reactive oxygen therapy: current insights

Infections caused by drug-resistant pathogens are a global public health problem. The introduction of a new antimicrobial strategy is an unavoidable option for the management of drug-resistant pathogens. Induction of high levels of reactive oxygen species (ROS) by several procedures has been extensively studied for the treatment of infections. In this article, the general aspects of ROS production and the common procedures that exert their antimicrobial effects due to ROS formation are reviewed. ROS generation is the antimicrobial mechanism of nanoparticles, hyperbaric oxygen therapy, medical honey, and photodynamic therapy. In addition, it is an alternative bactericidal mechanism of clinically traditional antibiotics. The development of ROS delivery methods with a desirable selectivity for pathogens without side effects for the host tissue may be a promising approach for the treatment of infections, especially those caused by drug-resistant organisms.

AldB controls persister formation in Escherichia coli depending on environmental stress

Persisters are multidrug-tolerant cells that are present within antibiotic-sensitive populations. Persister formation is not induced by genetic mutations, but rather by changes in the degree of expression of some genes. High redundancy has been observed among the pathways that have been hypothesized to respond to specific stresses. In this study, we conducted RNA sequencing of Escherichia coli persisters under various stress conditions to identify common mechanisms. We induced stresses such as glucose or amino acid exhaustion, acid stress and anaerobic conditions, all of which are encountered during bacterial pathogenesis. We found that most genes are differentially expressed depending on the specific stress condition; however, some genes were commonly expressed in persisters in most stress conditions. Commonly expressed genes are expected to be promising therapeutic targets for combating persistent infections. We found that knockdown of aldehyde dehydrogenase (aldB), which was expressed in every condition except for acid stress, decreased persisters in the non-stressed condition. However, the same strain unexpectedly showed an increased number of persisters in the amino acid-limited condition. Because the increase in persister number is glycolytic metabolite-dependent, metabolic flow may play a crucial role in aldB-mediated persister formation. These data suggest that environmental stresses alter persister mechanisms. Identification of environmental influences on persister formation during pathogenesis is therefore necessary to enabling persister eradication.

Extracellular polymeric substances affect the responses of multi-species biofilms in the presence of sulfamethizole

The occurrence and transportation of antibiotics in biofilms from natural and engineered sources have attracted increasing interests. Nevertheless, the effects of extracellular polymeric substances (EPS) on the responses of biofilms to the exposure to antibiotics are not clear. In this study, the effects of EPS on the sorption and biological responses to one representative antibiotic, sulfamethizole (STZ), in model biofilms were investigated. Proteins dominated the interactions between the EPS and the STZ and the EPS from a moving bed biofilm reactor exhibited the strongest interaction with the STZ. The EPS served as important reservoirs for the STZ and the tested biofilms all showed reduced sorption capacities for the STZ after the EPS were extracted. The respiratory rates and typical enzymatic activities were reduced after the EPS were extracted. High-throughput 16S rRNA gene sequencing results confirmed that the bacterial community in the biofilm without the EPS was more vulnerable to antibiotic shock as indicated by the community diversity and richness indices. A greater increase in the abundance of susceptible species was observed in the natural biofilm. The results comprehensively suggested that the EPS played important role in biosorption of STZ and alleviated the direct damage of the antibiotic to the cells; in addition the extent of the bacterial community response was associated with the origins of the biofilms. Our study provided details on the responses of multi-species biofilms to the exposure to an antibiotic and highlighted the role of the EPS in interacting with the antibiotic, thereby providing a deeper understanding of the bioremediation of antibiotics in real-life natural and engineered biofilm systems.

Molecular mechanisms of biofilm-based antibiotic resistance and tolerance in pathogenic bacteria

Biofilms are surface-attached groups of microbial cells encased in an extracellular matrix that are significantly less susceptible to antimicrobial agents than non-adherent, planktonic cells. Biofilm-based infections are, as a result, extremely difficult to cure. A wide range of molecular mechanisms contribute to the high degree of recalcitrance that is characteristic of biofilm communities. These mechanisms include, among others, interaction of antimicrobials with biofilm matrix components, reduced growth rates and the various actions of specific genetic determinants of antibiotic resistance and tolerance. Alone, each of these mechanisms only partially accounts for the increased antimicrobial recalcitrance observed in biofilms. Acting in concert, however, these defences help to ensure the survival of biofilm cells in the face of even the most aggressive antimicrobial treatment regimens. This review summarises both historical and recent scientific data in support of the known biofilm resistance and tolerance mechanisms. Additionally, suggestions for future work in the field are provided.

The Role of NADPH Oxidase in the Inhibition of Trichophyton rubrum by 420-nm Intense Pulsed Light

Objectives: To evaluate the effect of intense pulsed light (IPL) on Trichophyton rubrum and investigate its mechanism of action.

Methods: The viability of fungi treated with IPL alone and with IPL combined with an NADPH oxidase inhibitor (DPI) pretreatment was determined by MTT assays. The reactive oxygen species (ROS) were quantified with a DCFH-DA fluorescent probe. Malondialdehyde (MDA) content and superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were determined by commercial kits. The transcription of the Nox gene was quantified using quantitative real-time PCR (qRT-PCR) analysis, and micromorphology was observed using scanning electron microscopy (SEM). In addition, fungal keratinase activity was detected by measuring dye release from keratin azure.

Results: The growth declined with statistical significance after 6 h of treatment (P < 0.001). The ROS and MDA content increased after IPL treatment, whereas the SOD and GSH-Px activity decreased. Nox gene expression was upregulated, and the micromorphology was damaged. Keratinase activity decreased. Fungi that received DPI pretreatment exhibited contrasting outcomes.

Conclusion: We found that 420-nm IPL significantly inhibited the growth and pathogenicity of T. rubrum in vitro. A suggested mechanism involves Nox as a factor that mediates 420-nm IPL-induced oxidative damage of T. rubrum.

Regulation of Class A β-Lactamase CzoA by CzoR and IscR in Comamonas testosteroni S44

A genomic analysis of Comamonas testosteroni S44 revealed a gene that encodes a LysR family transcriptional regulator (here named czoR, czo for cefazolin) located upstream of a putative class A β-lactamase encoding gene (here named czoA). A putative DNA-binding motif of the Fe-S cluster assembly regulator IscR was identified in the czoR-czoA intergenic region. Real-time RT-PCR and lacZ fusion expression assays indicated that transcription of czoA and czoR were induced by multiple β-lactams. CzoA expressed in Escherichia coli was shown to contribute to susceptibility to a wide range of β-lactams judged from minimum inhibitory concentrations. In vitro enzymatic assays showed that CzoA hydrolyzed seven β-lactams, including benzylpenicillin, ampicillin, cefalexin, cefazolin, cefuroxime, ceftriaxone, and cefepime. Deletion of either iscR or czoR increased susceptibility to cefalexin and cefazolin, while complemented strains restored their wild-type susceptibility levels. Electrophoretic mobility shift assays (EMSA) demonstrated that CzoR and IscR bind to different sites of the czoR-czoA intergenic region. Precise CzoR- and IscR-binding sites were confirmed via DNase I footprinting or short fragment EMSA. When cefalexin or cefazolin was added to cultures, czoR deletion completely inhibited czoA expression but did not affect iscR transcription, while iscR deletion decreased the expressions of both czoR and czoA. These results reveal that CzoR positively affects the expression of czoA with its own expression upregulated by IscR.

Antibiotic resistance of pathogenic Acinetobacter species and emerging combination therapy

The increasing antibiotic resistance of Acinetobacter species in both natural and hospital environments has become a serious problem worldwide in recent decades. Because of both intrinsic and acquired antimicrobial resistance (AMR) against last-resort antibiotics such as carbapenems, novel therapeutics are urgently required to treat Acinetobacter-associated infectious diseases. Among the many pathogenic Acinetobacter species, A. baumannii has been reported to be resistant to all classes of antibiotics and contains many AMR genes, such as bla _ADC (Acinetobacter-derived cephalosporinase). The AMR of pathogenic Acinetobacter species is the result of several different mechanisms, including active efflux pumps, mutations in antibiotic targets, antibiotic modification, and low antibiotic membrane permeability. To overcome the limitations of existing drugs, combination theraphy that can increase the activity of antibiotics should be considered in the treatment of Acinetobacter infections. Understanding the molecular mechanisms behind Acinetobacter AMR resistance will provide vital information for drug development and therapeutic strategies using combination treatment. Here, we summarize the classic mechanisms of Acinetobacter AMR, along with newly-discovered genetic AMR factors and currently available antimicrobial adjuvants that can enhance drug efficacy in the treatment of A. baumannii infections.

Influence of oxidative stress on the antibacterial activity of betulin, betulinic acid and ursolic acid

Contribution of reactive oxygen species and oxidative stress in the antibacterial activities of betulin, betulinic acid and ursolic acid against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus was investigated. The minimum inhibitory concentrations of betulin, betulinic acid and ursolic acid against E. coli, P. aeruginosa and S. aureus are 1024-, 256- and 1024-μg/mL; 512-, 256- and 256 μg/mL; 256-, 256- and 64 μg/mL respectively. Cell viability of betulin-, betulinic acid- and ursolic acid-treated bacteria decrease in time dependent manner. Treatment of bacteria in the presence of 2,2'-bipyrydyl increased cell viability. Superoxide anion radical production increased significantly (p < 0.05) in bacterial cells-treated with betulin, betulinic acid and ursolic acid. Furthermore, NAD+/NADH ratio increased significantly (p < 0.05) in betulin-, betulinic acid- and ursolic acid-treated bacteria. Similarly, level of reduced glutathione in E. coli, P. aeruginosa and S. aureus decreased significantly with corresponding increase in glutathione disulphide, malondialdehyde and fragmented DNA following betulin, betulinic acid and ursolic acid treatments. It is evident from the above findings that betulin, betulinic acid and ursolic acid enhanced electron transport chain activity in E. coli, P. aeruginosa and S. aureus leading to increased ROS generation, Fenton reaction, lipid peroxidation, fragmented DNA and consequentially bacterial death.

Organic compounds stimulate horizontal transfer of antibiotic resistance genes in mixed wastewater treatment systems

Domestic wastewater treatment plants as a reservoir of antibiotic resistance genes (ARGs) have received much attention, but the effect of dyes on the propagation of ARGs has rarely been investigated. In this study, we investigated the differences in distributions of ARGs and microbial communities using high-throughput qPCR and 16S rRNA gene sequencing, respectively, between mixed (dyeing and domestic) wastewater and domestic sewage. The relative abundance of ARGs in inflows of mixed wastewater (IW2 and IW3) was higher than that of domestic wastewater (IW1). The relative abundance of mobile genetic elements in the inflow of textile dyeing wastewater (IDW3) was 3- to 13-fold higher than that in other samples. Moreover, in IDW3, some distinct high abundance ARGs, particularly operons encoding efflux pumps (such as acrR-01, acrB-01 and acrF), were significantly correlated with Streptococcus of the Firmicutes. To explore why the abundance of ARGs was relatively high in mixed wastewater, six representative types of organic compounds in textile dyeing wastewater were used to test the effect on plasmid-based conjugative transfer from E. coli HB101 to E. coli NK5449. These six compounds all facilitated the transfer of resistance-carrying RP4 plasmid, and the highest transfer frequency (approximately 10^-5-10^-3) was over 4- to 200-fold higher than that in the control group (approximately 10^-6-10^-5). These results illustrated that the six common residual compounds, particularly low-dose substances in IDW3, could facilitate the dissemination of ARGs in aquatic environments. More importantly, this study revealed for the first time that dyeing contaminants influenced horizontal gene transfer (HGT) of ARGs.

Rational design of drug-like compounds targeting Mycobacterium marinum MelF protein

The mycobacterial mel2 locus (mycobacterial enhanced infection locus, Rv1936-1941) is Mycobacterium marinum and M. tuberculosis specific, which can withstand reactive oxygen species (ROS) and reactive nitrogen species (RNS) induced stress. A library of over a million compounds was screened using in silico virtual ligand screening (VLS) to identify inhibitors against the modeled structure of MelF protein expressed by melF of mel2 locus so that M. marinum’s ability to withstand ROS/RNS stress could be reduced. The top ranked 1000 compounds were further screened to identify 178 compounds to maximize the scaffold diversity by manually evaluating the interaction of each compound with the target site. M. marinum melF was cloned, expressed and purified as maltose binding protein (MBP)-tagged recombinant protein in Escherichia coli. After establishing the flavin dependent oxidoreductase activity of MelF (~ 84 kDa), the inhibitors were screened for the inhibition of enzyme activity of whole cell lysate (WCL) and the purified MelF. Amongst these, 16 compounds could significantly inhibit the enzyme activity of purified MelF. For the six best inhibitory compounds, the minimal inhibitory concentration (MIC) was determined to be 3.4–19.4 μM and 13.5–38.8 μM for M. marinum and M. tuberculosis, respectively. Similarly, the minimal bactericidal concentration (MBC) was determined to be 6.8–38.8 μM and 27–38.8 μM against M. marinum and M. tuberculosis, respectively. One compound each in combination with isoniazid (INH) also showed synergistic inhibitory effect against M. marinum and M. tuberculosis with no cytotoxicity in HeLa cells. Interestingly, these inhibitors did not display any non-specific protein-structure destabilizing effect. Such inhibitors targeting the anti-ROS/RNS machinery may facilitate the efficient killing of replicating and nonreplicating mycobacteria inside the host cells.

"On demand" redox buffering by H2S contributes to antibiotic resistance revealed by a bacteria-specific H2S donor

Understanding the mechanisms of antimicrobial resistance (AMR) will help launch a counter-offensive against human pathogens that threaten our ability to effectively treat common infections. Herein, we report bis(4-nitrobenzyl)sulfanes, which are activated by a bacterial enzyme to produce hydrogen sulfide (H2S) gas. We found that H2S helps maintain redox homeostasis and protects bacteria against antibiotic-triggered oxidative stress "on demand", through activation of alternate respiratory oxidases and cellular antioxidants. We discovered, a hitherto unknown role for this gas, that chemical inhibition of H2S biosynthesis reversed antibiotic resistance in multidrug-resistant (MDR) uropathogenic Escherichia coli strains of clinical origin, whereas exposure to the H2S donor restored drug tolerance. Together, our study provides a greater insight into the dynamic defence mechanisms of this gas, modes of antibiotic action as well as resistance while progressing towards new pharmacological targets to address AMR.

Plant-derived antifungal compounds trigger a common transcriptional response

Understanding the mechanism of action of antifungal drugs is vital for better control of mycosis, which kills >1.3 million lives every year thus remains a major health problem worldwide. In this study, we investigate the activities of three different categories of plant-derived antifungal compounds (resveratrol, honokiol and osthole) via transcriptomics and bioinformatics analysis, with the goal of discovering the common Mode-of-Action (MoA) at molecular level. The result shows that a common transcriptional response (72 gene are up-regulated while 10 genes are down-regulated, commonly) are triggered by above representative antifungal compounds in Schizosaccharomyces pombe (S. pombe) yeast. By virtue of gene set enrichment analysis (GSEA) and gene functional annotation study, we identify that the genes involved in oxidative stress response, sugar metabolism, fatty acid metabolism, amino acid metabolism and glycolysis are significantly up-regulated, while the genes involved in nucleosome assembly, transcription and RNA processing are down-regulated, by any of these antifungal compounds. These observations demonstrate that the common MoA includes a strengthened anti-oxidative cell adaptation, a faster metabolic rate and a generally suppressed gene transcriptional activity. It implies a genetically encoded common redistribution of intracellular energy flux and molecules synthesis, after the challenging of antifungal compounds.

[Effect of intense pulsed light on Trichophyton rubrum growth in vitro]

OBJECTIVE

To investigate the inhibitory effect of 420 nm intense pulsed light on Trichophyton rubrum growth in vitro and explore the mechanism.

METHODS

The fungal conidia were divided into treatment group with intense pulse light irradiation and control group without irradiation. The surface areas of the fungal colonies were photographed before irradiation and on the 2nd and 3rd days after irradiation to observe the changes in fungal growth. The viability of the fungus in suspension was detected at 6 h after irradiation using MTT assay. The intracellular reactive oxygen species (ROS) level in the fungus was determined using DCFH-DA fluorescent probe, and the MDA content was detected using TBA method.

RESULTS

Intense pulse light (420 nm) irradiation caused obvious injuries in Trichophyton rubrum with the optimal effective light dose of 12 J/cm² in 12 pulses. At 6 h after the irradiation, the fungus in suspension showed a 30% reduction of viability (P<0.05), and the fungal colonies showed obvious growth arrest without further expansion. Compared to the control group, the irradiated fungus showed significant increases in ROS level and MDA content (P<0.05).

CONCLUSION

Intense pulse light (420 nm) irradiation can induce oxidative stress in Trichophyton rubrum to lead to fungal injuries and death.

Exposure to sub-inhibitory concentrations of gentamicin, ciprofloxacin and cefotaxime induces multidrug resistance and reactive oxygen species generation in meticillin-sensitive Staphylococcus aureus

PURPOSE

The role of antibiotics below their MIC in the development of bacterial drug resistance is becoming increasingly important. We investigated the effect of sub-MICs of bactericidal antibiotics on the susceptibility pattern of Staphylococcus aureus and evaluated the role of free radicals.

METHODOLOGY

A total of 12 S. aureus strains were recovered from pus samples and their antibiograms determined. The test isolates were treated with sub-MIC levels of tetracycline, gentamicin, ciprofloxacin and cefotaxime. Alterations in their respective breakpoints were observed along with measurements of free radical generation by nitro blue tetrazolium test.Results/Key findings. Gentamicin, ciprofloxacin and cefotaxime exposure significantly altered the breakpoints of exposed isolates against several tested antibiotics and higher levels of free radicals were generated after antibiotic exposure.

CONCLUSIONS

Our study demonstrates that sub-MIC levels of antimicrobials can lead to resistance and cross-resistance across several classes of antibiotics in wild strains of S. aureus, possibly by free radical production. The molecular mechanisms behind the acquisition of drug resistance at low antibiotic concentrations and the specific target genes of reactive oxygen speciesneed to be explored further.

In vivo ROS production and use of oxidative stress-derived biomarkers to detect the onset of diseases such as Alzheimer's disease, Parkinson's disease, and diabetes

Breakthroughs in biochemistry have furthered our understanding of the onset and progression of various diseases, and have advanced the development of new therapeutics. Oxidative stress and reactive oxygen species (ROS) are ubiquitous in biological systems. ROS can be formed non-enzymatically by chemical, photochemical and electron transfer reactions, or as the byproducts of endogenous enzymatic reactions, phagocytosis, and inflammation. Imbalances in ROS homeostasis, caused by impairments in antioxidant enzymes or non-enzymatic antioxidant networks, increase oxidative stress, leading to the deleterious oxidation and chemical modification of biomacromolecules such as lipids, DNA, and proteins. While many ROS are intracellular signaling messengers and most products of oxidative metabolisms are beneficial for normal cellular function, the elevation of ROS levels by light, hyperglycemia, peroxisomes, and certain enzymes causes oxidative stress-sensitive signaling, toxicity, oncogenesis, neurodegenerative diseases, and diabetes. Although the underlying mechanisms of these diseases are manifold, oxidative stress caused by ROS is a major contributing factor in their onset. This review summarizes the relationship between ROS and oxidative stress, with special reference to recent advancements in the detection of biomarkers related to oxidative stress. Further, we will introduce biomarkers for the early detection of neurodegenerative diseases and diabetes, with a focus on our recent work.

Functional disruption of peroxiredoxin by bismuth antiulcer drugs attenuates Helicobacter pylori survival

Bismuth drugs have been used clinically to treat infections from Helicobacter pylori, a pathogen that is strongly related to gastrointestinal diseases even stomach cancer. Despite extensive studies, the mechanisms of action of bismuth drugs are not fully understood. Alkyl hydroperoxide reductase subunit C (AhpC) is the most abundant 2-cysteine peroxiredoxin, crucial for H. pylori survival in the host by defense of oxidative stress. Herein we show that a Bi(III) antiulcer drug (CBS) binds to the highly conserved cysteine residues (Cys49 and Cys169) with a dissociation constant (K _d) of Bi(III) to AhpC of 3.0 (±1.0) × 10^-24 M. Significantly the interaction of CBS with AhpC disrupts the peroxiredoxin and chaperone activities of the enzyme both in vitro and in bacterial cells, leading to attenuated bacterial survival. Moreover, using a home-made fluorescent probe, we demonstrate that Bi(III) also perturbs AhpC relocation between the cytoplasm and membrane region in decomposing the exogenous ROS. Our study suggests that disruption of redox homeostasis by bismuth drugs via interaction with key enzymes such as AhpC contributes to their antimicrobial activity.

Untargeted metabolomics analysis reveals key pathways responsible for the synergistic killing of colistin and doripenem combination against Acinetobacter baumannii

Combination therapy is deployed for the treatment of multidrug-resistant Acinetobacter baumannii, as it can rapidly develop resistance to current antibiotics. This is the first study to investigate the synergistic effect of colistin/doripenem combination on the metabolome of A. baumannii. The metabolite levels were measured using LC-MS following treatment with colistin (2 mg/L) or doripenem (25 mg/L) alone, and their combination at 15 min, 1 hr and 4 hr (n = 4). Colistin caused early (15 min and 1 hr) disruption of the bacterial outer membrane and cell wall, as demonstrated by perturbation of glycerophospholipids and fatty acids. Concentrations of peptidoglycan biosynthesis metabolites decreased at 4 hr by doripenem alone, reflecting its mechanism of action. The combination induced significant changes to more key metabolic pathways relative to either monotherapy. Down-regulation of cell wall biosynthesis (via D-sedoheptulose 7-phosphate) and nucleotide metabolism (via D-ribose 5-phosphate) was associated with perturbations in the pentose phosphate pathway induced initially by colistin (15 min and 1 hr) and later by doripenem (4 hr). We discovered that the combination synergistically killed A. baumannii via time-dependent inhibition of different key metabolic pathways. Our study highlights the significant potential of systems pharmacology in elucidating the mechanism of synergy and optimizing antibiotic pharmacokinetics/pharmacodynamics.

Global Transcriptional Responses to Osmotic, Oxidative, and Imipenem Stress Conditions in Pseudomonas putida

Bacteria cope with and adapt to stress by modulating gene expression in response to specific environmental cues. In this study, the transcriptional response of Pseudomonas putida KT2440 to osmotic, oxidative, and imipenem stress conditions at two time points was investigated via identification of differentially expressed mRNAs and small RNAs (sRNAs). A total of 440 sRNA transcripts were detected, of which 10% correspond to previously annotated sRNAs, 40% to novel intergenic transcripts, and 50% to novel transcripts antisense to annotated genes. Each stress elicits a unique response as far as the extent and dynamics of the transcriptional changes. Nearly 200 protein-encoding genes exhibited significant changes in all stress types, implicating their participation in a general stress response. Almost half of the sRNA transcripts were differentially expressed under at least one condition, suggesting possible functional roles in the cellular response to stress conditions. The data show a larger fraction of differentially expressed sRNAs than of mRNAs with >5-fold expression changes. The work provides detailed insights into the mechanisms through which P. putida responds to different stress conditions and increases understanding of bacterial adaptation in natural and industrial settings.IMPORTANCE This study maps the complete transcriptional response of P. putida KT2440 to osmotic, oxidative, and imipenem stress conditions at short and long exposure times. Over 400 sRNA transcripts, consisting of both intergenic and antisense transcripts, were detected, increasing the number of identified sRNA transcripts in the strain by a factor of 10. Unique responses to each type of stress are documented, including both the extent and dynamics of the gene expression changes. The work adds rich detail to previous knowledge of stress response mechanisms due to the depth of the RNA sequencing data. Almost half of the sRNAs exhibit significant expression changes under at least one condition, suggesting their involvement in adaptation to stress conditions and identifying interesting candidates for further functional characterization.

Graphene Quantum Dot/Silver Nanoparticle Hybrids with Oxidase Activities for Antibacterial Application

We report the first attempt of using graphene quantum dot-Ag nanoparticles (GQD/AgNP hybrids) as oxidase mimics and antibacterial agents. Unlike previous silver- and graphene-based materials, the GQD/AgNP hybrids exhibit a high oxidase-like catalytic activity and possess favorable stability in neutral medium within the range from room temperature to 60 °C. In accordance with their prominent enzyme activities, the GQD/AgNP hybrids show excellent antibacterial properties against Gram-negative and Gram-positive bacteria as well as drug resistant bacteria, with an ultralow minimal inhibitory concentration (2-4 μg/mL) against 1 × 10⁷ to 1 × 10⁸ μg/mL Escherichia coli and Staphylococcus aureus. In the presence of the GQD/AgNP hybrids, the fluorescence behavior after the introduction of 2', 7'-dichlorofluorescin diacetate demonstrated a possible role of reactive oxidative species in the GQD/AgNP hybrid-mediated antibacterial therapeutic effect. Furthermore, TEM and SEM imaging identified concomitant disruption of the bacterial cell membrane and loss of barrier function during the sterilization process. Therefore, the GQD/AgNP hybrids exhibit vast potentials for serving as highly effective, broad-spectrum antibacterial agent for sterilization use without the need of additional stimulation by laser irradiation (photosensitization) or the provision of H₂O₂, facilitating their relative ease of use and cost-effectiveness.

The Complex Relationship between Virulence and Antibiotic Resistance

Antibiotic resistance, prompted by the overuse of antimicrobial agents, may arise from a variety of mechanisms, particularly horizontal gene transfer of virulence and antibiotic resistance genes, which is often facilitated by biofilm formation. The importance of phenotypic changes seen in a biofilm, which lead to genotypic alterations, cannot be overstated. Irrespective of if the biofilm is single microbe or polymicrobial, bacteria, protected within a biofilm from the external environment, communicate through signal transduction pathways (e.g., quorum sensing or two-component systems), leading to global changes in gene expression, enhancing virulence, and expediting the acquisition of antibiotic resistance. Thus, one must examine a genetic change in virulence and resistance not only in the context of the biofilm but also as inextricably linked pathologies. Observationally, it is clear that increased virulence and the advent of antibiotic resistance often arise almost simultaneously; however, their genetic connection has been relatively ignored. Although the complexities of genetic regulation in a multispecies community may obscure a causative relationship, uncovering key genetic interactions between virulence and resistance in biofilm bacteria is essential to identifying new druggable targets, ultimately providing a drug discovery and development pathway to improve treatment options for chronic and recurring infection.

The Role of Reactive Oxygen Species in Antibiotic-Mediated Killing of Bacteria

Recently, it was proposed that there is a common mechanism behind the activity of bactericidal antibiotics, involving the production of reactive oxygen species (ROS). However, the involvement of ROS in antibiotic-mediated killing has become the subject of much debate. In the present review, we provide an overview of the data supporting the ROS hypothesis; we also present data that explain the contradictory results often obtained when studying antibiotic-induced ROS production. For this latter aspect we will focus on the importance of taking the experimental setup into consideration and on the importance of some technical aspects of the assays typically used. Finally, we discuss the link between ROS production and toxin-antitoxin modules, and present an overview of implications for treatment.

Silibinin protects Staphylococcus aureus from UVC-induced bactericide via enhanced generation of reactive oxygen species

ROS produced by silibinin suppresses UVC-inducedStaphylococcus aureuscell death.

Antibacterial efficacy of Ocimum sanctum leaf extract-treated iron oxide nanoparticles

Iron oxide nanoparticles (IONPs) were preparedviaa co-precipitation method and were then characterized and evaluated for their antibacterial activity after modification withOcimum sanctumleaf extract.

Genome-wide mapping of mutations at single-nucleotide resolution for protein, metabolic and genome engineering

Improvements in DNA synthesis and sequencing have underpinned comprehensive assessment of gene function in bacteria and eukaryotes. Genome-wide analyses require high-throughput methods to generate mutations and analyze their phenotypes, but approaches to date have been unable to efficiently link the effects of mutations in coding regions or promoter elements in a highly parallel fashion. We report that CRISPR-Cas9 gene editing in combination with massively parallel oligomer synthesis can enable trackable editing on a genome-wide scale. Our method, CRISPR-enabled trackable genome engineering (CREATE), links each guide RNA to homologous repair cassettes that both edit loci and function as barcodes to track genotype-phenotype relationships. We apply CREATE to site saturation mutagenesis for protein engineering, reconstruction of adaptive laboratory evolution experiments, and identification of stress tolerance and antibiotic resistance genes in bacteria. We provide preliminary evidence that CREATE will work in yeast. We also provide a webtool to design multiplex CREATE libraries.

Transcriptional response of Prochlorococcus to co-culture with a marine Alteromonas: differences between strains and the involvement of putative infochemicals

Interactions between marine microorganisms may determine the dynamics of microbial communities. Here, we show that two strains of the globally abundant marine cyanobacterium Prochlorococcus, MED4 and MIT9313, which belong to two different ecotypes, differ markedly in their response to co-culture with a marine heterotrophic bacterium, Alteromonas macleodii strain HOT1A3. HOT1A3 enhanced the growth of MIT9313 at low cell densities, yet inhibited it at a higher concentration, whereas it had no effect on MED4 growth. The early transcriptomic responses of Prochlorococcus cells after 20 h in co-culture showed no evidence of nutrient starvation, whereas the expression of genes involved in photosynthesis, protein synthesis and stress responses typically decreased in MED4 and increased in MIT313. Differential expression of genes involved in outer membrane modification, efflux transporters and, in MIT9313, lanthipeptides (prochlorosins) suggests that Prochlorococcus mount a specific response to the presence of the heterotroph in the cultures. Intriguingly, many of the differentially-expressed genes encoded short proteins, including two new families of co-culture responsive genes: CCRG-1, which is found across the Prochlorococcus lineage and CCRG-2, which contains a sequence motif involved in the export of prochlorosins and other bacteriocin-like peptides, and are indeed released from the cells into the media.

Bacterial Hyaluronidase Self-Triggered Prodrug Release for Chemo-Photothermal Synergistic Treatment of Bacterial Infection

A novel platform for targeted on-demand prodrug ascorbic acid (AA) delivery is fabricated using a bacterial hyaluronidase sensitive graphene-mesoporous silica nanosheet@hyaluronic acid-magnetic nanoparticles as the nanocarrier to treat bacterial infections. The released AA can be converted to detrimental •OH in situ on the surface of bacteria. With the chemo-photothermal synergistic effect, the designed antibacterial system can effectively inactivate bacteria and disperse stubborn biofilm.

Eradication of Pseudomonas aeruginosa biofilms and persister cells using an electrochemical scaffold and enhanced antibiotic susceptibility

Biofilms in chronic wounds are known to contain a persister subpopulation that exhibits enhanced multidrug tolerance and can quickly rebound after therapeutic treatment. The presence of these “persister cells” is partly responsible for the failure of antibiotic therapies and incomplete elimination of biofilms. Electrochemical methods combined with antibiotics have been suggested as an effective alternative for biofilm and persister cell elimination, yet the mechanism of action for improved antibiotic efficacy remains unclear. In this work, an electrochemical scaffold (e-scaffold) that electrochemically generates a constant concentration of H₂O₂ was investigated as a means of enhancing tobramycin susceptibility in pre-grown Pseudomonas aeruginosa PAO1 biofilms and attacking persister cells. Results showed that the e-scaffold enhanced tobramycin susceptibility in P. aeruginosa PAO1 biofilms, which reached a maximum susceptibility at 40 µg/ml tobramycin, with complete elimination (7.8-log reduction vs control biofilm cells, P ≤ 0.001). Moreover, the e-scaffold eradicated persister cells in biofilms, leaving no viable cells (5-log reduction vs control persister cells, P ≤ 0.001). It was observed that the e-scaffold induced the intracellular formation of hydroxyl free radicals and improved membrane permeability in e-scaffold treated biofilm cells, which possibly enhanced antibiotic susceptibility and eradicated persister cells. These results demonstrate a promising advantage of the e-scaffold in the treatment of persistent biofilm infections.

Using an electrically conductive fabric to generate hydrogen peroxide could eradicate persistent biofilms in chronically infected wounds. Electrochemical scaffolds (e-scaffolds) are thin networks of conductive material such as carbon fiber used to generate chemical responses in media they are in contact with. Haluk Beyenal and colleagues at Washington State University, USA, investigated the effect of a carbon fabric e-scaffold on cultured biofilms of the bacterium Pseudomonas aeruginosa. The procedure enhanced the susceptibility of this troublesome multidrug-resistant bacterium to the antibiotic tobramycin. Crucially, it eradicated so-called persister cells that can evade antibiotic treatment to reform biofilms in chronic wounds. The research suggests that the effect involves the production of hydroxyl free radicals from hydrogen peroxide and increased permeability of the bacterial cell membranes. The potential of e-scaffolds for treating infected wounds warrants further exploration.

Beauvericin counteracted multi-drug resistant Candida albicans by blocking ABC transporters

Multi-drug resistance of pathogenic microorganisms is becoming a serious threat, particularly to immunocompromised populations. The high mortality of systematic fungal infections necessitates novel antifungal drugs and therapies. Unfortunately, with traditional drug discovery approaches, only echinocandins was approved by FDA as a new class of antifungals in the past two decades. Drug efflux is one of the major contributors to multi-drug resistance, the modulator of drug efflux pumps is considered as one of the keys to conquer multi-drug resistance. In this study, we combined structure-based virtual screening and whole-cell based mechanism study, identified a natural product, beauvericin (BEA) as a drug efflux pump modulator, which can reverse the multi-drug resistant phenotype of Candida albicans by specifically blocking the ATP-binding cassette (ABC) transporters; meantime, BEA alone has fungicidal activity in vitro by elevating intracellular calcium and reactive oxygen species (ROS). It was further demonstrated by histopathological study that BEA synergizes with a sub-therapeutic dose of ketoconazole (KTC) and could cure the murine model of disseminated candidiasis. Toxicity evaluation of BEA, including acute toxicity test, Ames test, and hERG (human ether-à-go-go-related gene) test promised that BEA can be harnessed for treatment of candidiasis, especially the candidiasis caused by ABC overexpressed multi-drug resistant C. albicans.

Polymyxin: Alternative Mechanisms of Action and Resistance

Antibiotic resistance among pathogenic bacteria is an ever-increasing issue worldwide. Unfortunately, very little has been achieved in the pharmaceutical industry to combat this problem. This has led researchers and the medical field to revisit past drugs that were deemed too toxic for clinical use. In particular, the cyclic cationic peptides polymyxin B and colistin, which are specific for Gram-negative bacteria, have been used as "last resort" antimicrobials. Before the 1980s, these drugs were known for their renal and neural toxicities; however, new clinical practices and possibly improved manufacturing have made them safer to use. Previously suggested to primarily attack the membranes of Gram-negative bacteria and to not easily select for resistant mutants, recent research exploring resistance and mechanisms of action has provided new perspectives. This review focuses primarily on the proposed alternative mechanisms of action, known resistance mechanisms, and how these support the alternative mechanisms of action.

Role of catalase overproduction in drug resistance and virulence in Candida albicans

Aim: To investigate the role of Cat1 overproduction in Candida albicans. Materials & methods: Strains overproducing the CAT1 gene were constructed. Results: Cells overproducing CAT1 were found to be more resistant to some oxidants and mammalian phagocytic cells. They also showed reduced intracellular reactive oxygen species generated by amphotericin B or ciclopirox olamine. CAT1 overproduction did not change the minimum inhibitory concentration of fungal cells to fungistatic or fungicidal azoles nor to amphotericin B although increased twofold the minimum inhibitory concentration to caspofungin. The role of Cat1 overproduction in virulence and colonization was also analyzed in mouse models. Conclusion: The overproduction of Cat1 protects against oxidants, phagocytes and certain antifungals at subinhibitory concentration but does not increase virulence in a systemic infection mouse model.

Identifying and Tackling Emergent Vulnerability in Drug-Resistant Mycobacteria

The global mechanisms and associated molecular alterations that occur in drug-resistant mycobacteria are poorly understood. To address this, we obtain genomics data and then construct a genome-scale response network in isoniazid-resistant Mycobacterium smegmatis and apply a network-mining algorithm. Through this, we decipher global alterations in an unbiased manner and identify emergent vulnerabilities in resistant bacilli, of which redox response was prominent. Using phenotypic profiling, we find that resistant bacilli exhibit collateral sensitivity to several compounds that block antioxidant responses. We find that nanogram/milliliter concentrations of ebselen, vancomycin, and phenylarsine oxide, in combination with isoniazid, are highly effective against Mycobacterium tuberculosis H37Rv and three clinical drug-resistant strains. Dynamic measurements of cytoplasmic redox potential revealed a surprisingly diminished capacity of clinical drug-resistant strains to counteract oxidative stress, providing a mechanistic basis for efficient and synergistic mycobactericidal activity of the drug combinations. Ebselen and vancomycin appear to be promising repurposable drugs.

Programmed Bacteria Death Induced by Carbon Dots with Different Surface Charge

Based on a series of biochemical experiments for analysis and characterization, it is found that the uncharged C-dots have no effect on bacterial growth while the negatively charged and positively charged C-dots can induce bacteria apoptosis. For the positively charged C-dots, they can induce both bacteria apoptosis and bacteria death. These observations will provide new insights into bioapplications of carbon dots.

Dual Repression of the Multidrug Efflux Pump CmeABC by CosR and CmeR in Campylobacter jejuni

During transmission and intestinal colonization, Campylobacter jejuni, a major foodborne human pathogen, experiences oxidative stress. CosR, a response regulator in C. jejuni, modulates the oxidative stress response and represses expression of the CmeABC multidrug efflux pump. CmeABC, a key component in resistance to toxic compounds including antimicrobials and bile salts, is also under negative regulation by CmeR, a TetR family transcriptional regulator. How CosR and CmeR interact in binding to the cmeABC promoter and how CosR senses oxidative stress are still unknown. To answer these questions, we conducted various experiments utilizing electrophoretic mobility shift assays and transcriptional fusion assays. CosR and CmeR bound independently to two separate sites of the cmeABC promoter, simultaneously repressing cmeABC expression. This dual binding of CosR and CmeR is optimal with a 17 base pair space between the two binding sites as mutations that shortened the distance between the binding sites decreased binding by CmeR and enhanced cmeABC expression. Additionally, the single cysteine residue (C218) of CosR was sensitive to oxidation, which altered the DNA-binding activity of CosR and dissociated CosR from the cmeABC promoter as determined by electrophoretic mobility shift assay. Replacement of C218 with serine rendered CosR insensitive to oxidation, suggesting a potential role of C218 in sensing oxidative stress and providing a possible mechanism for CosR-mediated response to oxidative stress. These findings reveal a dual regulatory role of CosR and CmeR in modulating cmeABC expression and suggest a potential mechanism that may explain overexpression of cmeABC in response to oxidative stress. Differential expression of cmeABC mediated by CmeR and CosR in response to different signals may facilitate adaptation of Campylobacter to various environmental conditions.

Involvement of Antibiotic Efflux Machinery in Glutathione-Mediated Decreased Ciprofloxacin Activity in Escherichia coli

We have analyzed the contribution of different efflux components to glutathione-mediated abrogation of ciprofloxacin's activity in Escherichia coli and the underlying potential mechanism(s) behind this phenomenon. The results indicated that glutathione increased the total active efflux, thereby partially contributing to glutathione-mediated neutralization of ciprofloxacin's antibacterial action in E. coli However, the role of glutathione-mediated increased efflux becomes evident in the absence of a functional TolC-AcrAB efflux pump.