Antibiotic potentiating effect of Bauhinia purpurea L. against multidrug resistant Staphylococcus aureus

Bauhinia purpurea L. is a medium-sized tree from the family Fabaceae. The plant is traditionally used as medicine by different tribes in Sikkim. The present study aimed to evaluate the modulation in minimum inhibitory concentration (MIC) of the bark methanol extract of Bauhinia purpurea L. against the clinical isolates of multidrug resistant Staphylococcus aureus. The synergistic activity of the test plant extract with different classes of antibiotics was also evaluated. The methanol extract of Bauhinia purpurea exhibited modulation by a 16-fold reduction in the MIC of clindamycin against both resistant and susceptible isolates, followed by penicillin and gentamicin, whereas a maximum of only a 4-fold MIC reduction was observed with ciprofloxacin. The lowest minimum inhibitory concentration and minimum bactericidal concentration showed by the plant extract was 0.48 and 0.97 mg/mL, respectively. The methanol extract of Bauhinia purpurea exhibited synergistic activity with penicillin, gentamicin, ciprofloxacin, and clindamycin against most of the tested isolates of multidrug-resistant Staphylococcus aureus (MDR-SA). Gas chromatography-mass spectrometry analysis of Bauhinia purpurea L. bark methanol extract revealed 16 phytocompounds. The results provide an insight into the potential antibacterial property of the plant extract in terms of its antibiotic MIC modulation and synergistic properties with the selected antibiotics. This is the first report of the antibiotic potentiation property of Bauhinia purpurea L., collected from Sikkim, India.

Anti-bacterial, anti-biofilm and anti-quorum sensing activities of honey: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Man has used honey to treat diseases since ancient times, perhaps even before the history of medicine itself. Several civilizations have utilized natural honey as a functional and therapeutic food to ward off infections. Recently, researchers worldwide have been focusing on the antibacterial effects of natural honey against antibiotic-resistant bacteria.

AIM OF THE STUDY

This review aims to summarize research on the use of honey properties and constituents with their anti-bacterial, anti-biofilm, and anti-quorum sensing mechanisms of action. Further, honey's bacterial products, including probiotic organisms and antibacterial agents which are produced to curb the growth of other competitor microorganisms is addressed.

MATERIALS AND METHODS

In this review, we have provided a comprehensive overview of the antibacterial, anti-biofilm, and anti-quorum sensing activities of honey and their mechanisms of action. Furthermore, the review addressed the effects of antibacterial agents of honey from bacterial origin. Relevant information on the antibacterial activity of honey was obtained from scientific online databases such as Web of Science, Google Scholar, ScienceDirect, and PubMed.

RESULTS

Honey's antibacterial, anti-biofilm, and anti-quorum sensing activities are mostly attributed to four key components: hydrogen peroxide, methylglyoxal, bee defensin-1, and phenolic compounds. The performance of bacteria can be altered by honey components, which impact their cell cycle and cell morphology. To the best of our knowledge, this is the first review that specifically summarizes every phenolic compound identified in honey along with their potential antibacterial mechanisms of action. Furthermore, certain strains of beneficial lactic acid bacteria such as Bifidobacterium, Fructobacillus, and Lactobacillaceae, as well as Bacillus species can survive and even grow in honey, making it a potential delivery system for these agents.

CONCLUSION

Honey could be regarded as one of the best complementary and alternative medicines. The data presented in this review will enhance our knowledge of some of honey's therapeutic properties as well as its antibacterial activities.

Inhibition of Multidrug Efflux Pumps Belonging to the Major Facilitator Superfamily in Bacterial Pathogens

Bacterial pathogens resistant to multiple structurally distinct antimicrobial agents are causative agents of infectious disease, and they thus constitute a serious concern for public health. Of the various bacterial mechanisms for antimicrobial resistance, active efflux is a well-known system that extrudes clinically relevant antimicrobial agents, rendering specific pathogens recalcitrant to the growth-inhibitory effects of multiple drugs. In particular, multidrug efflux pump members of the major facilitator superfamily constitute central resistance systems in bacterial pathogens. This review article addresses the recent efforts to modulate these antimicrobial efflux transporters from a molecular perspective. Such investigations can potentially restore the clinical efficacy of infectious disease chemotherapy.

Tackling multidrug-resistant Staphylococcus aureus by natural products and their analogues acting as NorA efflux pump inhibitors

Staphylococcus aureus (S. aureus) is a pathogen responsible for various community and hospital-acquired infections with life-threatening complications like bacteraemia, endocarditis, meningitis, liver abscess, and spinal cord epidural abscess. Antibiotics have been used to treat microbial infections since the introduction of penicillin in 1940. In recent decades, the abuse and misuse of antibiotics in humans, animals, plants, and fungi, including the treatment of non-microbial diseases, have led to the rapid emergence of multidrug-resistant pathogens with increased virulence. Bacteria have developed several complementary mechanisms to avoid the effects of antibiotics. These mechanisms include chemical transformations and enzymatic inactivation of antibiotics, modification of antibiotics' target site, and reduction of intracellular antibiotics concentration by changes in membrane permeability or by the overexpression of efflux pumps (EPs). The strategy to check antibiotic resistance includes synthesis of the antibiotic analogues, or antibiotics are given in combination with the adjuvant. The inhibitors of multidrug EPs are considered promising alternative therapeutic options with the potential to revive the effects of antibiotics and reduce bacterial virulence. Natural products played a vital role in drug discovery and significantly contributed to the area of infectious diseases. Also, natural products provide lead compounds that sometimes need modification based on structural and biological properties to meet the drug criteria. This review discusses natural products and their derived compounds as NorA efflux pump inhibitors (EPIs).

3-indoleacetonitrile attenuates biofilm formation and enhances sensitivity to imipenem in Acinetobacter baumannii

Acinetobacter baumannii poses a global danger due to its ability to resist most of the currently available antimicrobial agents. Furthermore, the rise of carbapenem-resistant A. baumannii isolates has limited the treatment options available. In the present study, plant auxin 3-indoleacetonitrile was found to inhibit biofilm formation and motility of A. baumannii at sub-lethal concentration. Mechanistically, 3-indoleacetonitrile inhibited the synthesis of the quorum sensing signal 3-OH-C12-HSL by downregulating the expression of the abaI autoinducer synthase gene. 3-indoleacetonitrile was found to reduce MIC of A. baumannii ATCC 17 978 against imipenem, ofloxacin, ciprofloxacin, tobramycin, and levofloxacin, and significantly decreased persistence against imipenem. Inhibition of efflux pumps by down-regulating genes expression may be responsible for enhanced sensitivity and low persistence. 3-indoleacetonitrile reduced the resistance to imipenem in carbapenem-resistant A. baumannii isolates by down-regulating the expression of OXA β-lactamases (blaoxa-51 and blaoxa-23), outer membrane protein carO and transporter protein adeB. These findings demonstrate the therapeutic potential of 3-indoleacetonitrile which could be explored as an adjuvant with antibiotics for controlling A. baumannii infections.

Tackling Multiple-Drug-Resistant Bacteria With Conventional and Complex Phytochemicals

Emerging antibiotic resistance in bacteria endorses the failure of existing drugs with chronic illness, complicated treatment, and ever-increasing expenditures. Bacteria acquire the nature to adapt to starving conditions, abiotic stress, antibiotics, and our immune defense mechanism due to its swift evolution. The intense and inappropriate use of antibiotics has led to the development of multidrug-resistant (MDR) strains of bacteria. Phytochemicals can be used as an alternative for complementing antibiotics due to their variation in metabolic, genetic, and physiological fronts as well as the rapid evolution of resistant microbes and lack of tactile management. Several phytochemicals from diverse groups, including alkaloids, phenols, coumarins, and terpenes, have effectively proved their inhibitory potential against MDR pathogens through their counter-action towards bacterial membrane proteins, efflux pumps, biofilms, and bacterial cell-to-cell communications, which are important factors in promoting the emergence of drug resistance. Plant extracts consist of a complex assortment of phytochemical elements, against which the development of bacterial resistance is quite deliberate. This review emphasizes the antibiotic resistance mechanisms of bacteria, the reversal mechanism of antibiotic resistance by phytochemicals, the bioactive potential of phytochemicals against MDR, and the scientific evidence on molecular, biochemical, and clinical aspects to treat bacterial pathogenesis in humans. Moreover, clinical efficacy, trial, safety, toxicity, and affordability investigations, current status and developments, related demands, and future prospects are also highlighted.

Phenolic Compound Ethyl 3,4-Dihydroxybenzoate Retards Drug Efflux and Potentiates Antibiotic Activity

The World Health Organization indicated that antibiotic resistance is one of the greatest threats to health, food security, and development in the world. Drug resistance efflux pumps are essential for antibiotic resistance in bacteria. Here, we evaluated the plant phenolic compound ethyl 3,4-dihydroxybenzoate (EDHB) for its efflux pump inhibitory (EPI) activity against drug-resistant Escherichia coli. The half-maximal inhibitory concentration, modulation assays, and time-kill studies indicated that EDHB has limited antibacterial activity but can potentiate the activity of antibiotics for drug-resistant E. coli. Dye accumulation/efflux and MALDI-TOF studies showed that EDHB not only significantly increases dye accumulation and reduces dye efflux but also increases the extracellular amount of antibiotics in the drug-resistant E. coli, indicating its interference with substrate translocation via a bacterial efflux pump. Molecular docking analysis using AutoDock Vina indicated that EDHB putatively posed within the distal binding pocket of AcrB and in close interaction with the residues by H-bonds and hydrophobic contacts. Additionally, EDHB showed an elevated postantibiotic effect on drug-resistant E. coli. Our toxicity assays showed that EDHB did not change the bacterial membrane permeability and exhibited mild human cell toxicity. In summary, these findings indicate that EDHB could serve as a potential EPI for drug-resistant E. coli.

Antibacterial and antibiofilm activity of Lagotis brachystachya extract against extended-spectrum β-lactamases-producing Escherichia coli from broiler chickens

Lagotis brachystachya Maxim (L. brachystachya) is an herb widely used in traditional Tibetan medicine. In the present study, the antibacterial activity of L. brachystachya extract to extended-spectrum-lactamases (ESBLs)-producing E. coli was determined by Kirby-Bauer disc diffusion, minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) methods as well as time-kill curve assay. Meanwhile, the biofilm inhibition and eradication effects of L. brachystachya extract on the ESBLs-producing E. coli were evaluated by crystal violet staining, and further confirmed by confocal laser scanning microscope (CLSM) and scanning electron microscopy (SEM). The results indicated that L. brachystachya extract exhibited moderate antibacterial activity, with diameter of inhibition zones varying from 15.4 to 20.3 mm, and the MIC and MBC values were 6.25 to 25 mg/mL and 12.5 to 100 mg/mL, respectively. Time-kill curve showed that 4 × MIC level of L. brachystachya extract concentration of was able to kill 99.9% of ESBLs-producing E. coli after 16 h treatment. The biofilm inhibition rate and eradication rate for the ESBLs-producing E. coli were 35.66 to 79.91% and 22.18 to 56.21% at MIC level of extract concentration, respectively. CLSM images showed that the biofilm became thinner as the ESBLs-producing E. coli isolate exposed to L. brachystachya extract with a concentration-dependent manner from 1/4 × MIC to MIC compared with the control isolate. SEM images indicated that L. brachystachya extract at 1/2 × MIC and MIC levels could evidently inhibit the biofilm formation or eradicate the mature biofilms. The effect of L. brachystachya highlights its potential of antibacterial and antibiofilm activities against the ESBLs-producing E. coli.

Exploring Phytochemicals for Combating Antibiotic Resistance in Microbial Pathogens

Antibiotic resistance or microbial drug resistance is emerging as a serious threat to human healthcare globally, and the multidrug-resistant (MDR) strains are imposing major hurdles to the progression of drug discovery programs. Newer antibiotic-resistance mechanisms in microbes contribute to the inefficacy of the existing drugs along with the prolonged illness and escalating expenditures. The injudicious usage of the conventional and commonly available antibiotics in human health, hygiene, veterinary and agricultural practices is proving to be a major driver for evolution, persistence and spread of antibiotic-resistance at a frightening rate. The drying pipeline of new and potent antibiotics is adding to the severity. Therefore, novel and effective new drugs and innovative therapies to treat MDR infections are urgently needed. Apart from the different natural and synthetic drugs being tested, plant secondary metabolites or phytochemicals are proving efficient in combating the drug-resistant strains. Various phytochemicals from classes including alkaloids, phenols, coumarins, terpenes have been successfully demonstrated their inhibitory potential against the drug-resistant pathogens. Several phytochemicals have proved effective against the molecular determinants responsible for attaining the drug resistance in pathogens like membrane proteins, biofilms, efflux pumps and bacterial cell communications. However, translational success rate needs to be improved, but the trends are encouraging. This review highlights current knowledge and developments associated challenges and future prospects for the successful application of phytochemicals in combating antibiotic resistance and the resistant microbial pathogens.

Natural Compounds as Therapeutic Agents: The Case of Human Topoisomerase IB

Natural products are widely used as source for drugs development. An interesting example is represented by natural drugs developed against human topoisomerase IB, a ubiquitous enzyme involved in many cellular processes where several topological problems occur due the formation of supercoiled DNA. Human topoisomerase IB, involved in the solution of such problems relaxing the DNA cleaving and religating a single DNA strand, represents an important target in anticancer therapy. Several natural compounds inhibiting or poisoning this enzyme are under investigation as possible new drugs. This review summarizes the natural products that target human topoisomerase IB that may be used as the lead compounds to develop new anticancer drugs. Moreover, the natural compounds and their derivatives that are in clinical trial are also commented on.

Boesenbergia rotunda extract inhibits Candida albicans biofilm formation by pinostrobin and pinocembrin

ETHNOPHARMACOLOGICAL RELEVANCE

Boesenbergia rotunda (L.) Mansf. (Zingiberaceae) is an indigenous plant of Southeast Asia. Based on ethnopharmacological use, the rhizome is recommended in the treatment of stomachache, leukoplakia, abscesses, and leukorrhea in Thailand primary health care system. Candida albicans often causes leukorrhea, and infection of many mucosal sites. Its infection leads to serious illness.

AIM OF THE STUDY

This study aimed to investigate the effects of the ethanolic extract of the B. rotunda rhizome on C. albicans ATCC10231 in the stages of planktonic and biofilm formation and to explore the underlying mechanisms.

MATERIALS AND METHODS

The chemical composition of the extract was determined using ultra-performance liquid chromatography (UPLC). The planktonic growth of C. albicans was evaluated by the microdilution method, following EUCAST guidelines. For each stage of biofilm formation, the biofilm was assessed by the MTT assay. The biofilm structure was examined under a light microscope. The degree of cell surface hydrophobicity was measured. The mRNA levels of ALS1, ALS3, and ACT1 were determined by RT-qPCR.

RESULTS

The extract of B. rotunda consisted of 25% (w/w) pinostrobin and 12% (w/w) pinocembrin. All stages of C. albicans biofilm formation were significantly inhibited by the extract, whereas the planktonic growth did not change. Biofilm development greatly decreased due to the extract in a concentration-dependent manner, with an IC₅₀ value of 17.7 μg/mL. Pinostrobin and pinocembrin demonstrated inhibitory effects during this stage. These results were in accordance with the microscopic evaluation. The filamentous form decreased with pinocembrin rather than pinostrobin. Moreover, the cell surface hydrophobicity was significantly decreased by 6.25 and 12.5 μg/mL of the extract and 100 μM of pinocembrin. The ALS3 mRNA level was noticeably decreased by 12.5 μg/mL of the extract, 100 μM of pinostrobin, and 100 μM of pinocembrin. The ACT1 mRNA level decreased significantly with pinocembrin. However, the ALS1 mRNA level was not altered following all treatments.

CONCLUSION

The ethanolic extract of B. rotunda could inhibit biofilm formation of C. albicans, especially during the biofilm development stage, by means of reducing the cell surface hydrophobicity and suppressing the ALS3 mRNA expression. Pinocembrin had a stronger effect on ALS3 mRNA expression than pinostrobin. Only pinocembrin significantly decreased the ACT1 mRNA level.

Efficacy and Mechanism of Traditional Medicinal Plants and Bioactive Compounds against Clinically Important Pathogens

Traditional medicinal plants have been cultivated to treat various human illnesses and avert numerous infectious diseases. They display an extensive range of beneficial pharmacological and health effects for humans. These plants generally synthesize a diverse range of bioactive compounds which have been established to be potent antimicrobial agents against a wide range of pathogenic organisms. Various research studies have demonstrated the antimicrobial activity of traditional plants scientifically or experimentally measured with reports on pathogenic microorganisms resistant to antimicrobials. The antimicrobial activity of medicinal plants or their bioactive compounds arising from several functional activities may be capable of inhibiting virulence factors as well as targeting microbial cells. Some bioactive compounds derived from traditional plants manifest the ability to reverse antibiotic resistance and improve synergetic action with current antibiotic agents. Therefore, the advancement of bioactive-based pharmacological agents can be an auspicious method for treating antibiotic-resistant infections. This review considers the functional and molecular roles of medicinal plants and their bioactive compounds, focusing typically on their antimicrobial activities against clinically important pathogens.

Tackling drug resistance with efflux pump inhibitors: from bacteria to cancerous cells

Drug resistance is a serious concern in a clinical setting jeopardizing treatment for both infectious agents and cancers alike. The wide-spread emergence of multi-drug resistant (MDR) phenotypes from bacteria to cancerous cells necessitates the need to target resistance mechanisms and prevent the emergence of resistant mutants. Drug efflux seems to be one of the preferred approaches embraced by both microbial and mammalian cells alike, to thwart the action of chemotherapeutic agents thereby leading to a drug resistant phenotype. Relative to microbes, which predominantly employs proton motive force (PMF) powered, Major Facilitator Superfamily (MFS)/Resistance Nodulation and Division (RND) classes of efflux pumps to efflux drugs, cancerous cells preferentially use ATP fuelled ATP binding cassette (ABC) transporters to extrude chemotherapeutic agents. The prevalence, evolutionary characteristics and overlapping functions of ABC transporters have been highlighted in this review. Additionally, we outline the role of ABC pumps in conferring MDR phenotype to both bacteria and cancerous cells and underscore the importance of efflux pump inhibitors (EPI) to mitigate drug resistance. Based on the literature reports and analysis, we reason out feasibility of employing bacteria as a tool to screen for EPI's targeting ABC pumps of cancerous cells.

Brown and Red Seaweeds Serve as Potential Efflux Pump Inhibitors for Drug-Resistant Escherichia coli

Multidrug-resistant pathogens are a significant clinical problem. Efflux pump inhibitors (EPIs) can restore the activities of existing antibiotics by interfering with drug efflux pumps located in bacterial cell membranes. Seaweeds are important sources of biologically active metabolites of natural origin; however, their potential as EPIs remains uninvestigated. Here, functional extracts from the brown seaweeds Laminaria japonica and Sargassum horneri and the red seaweeds Gracilaria sp. and Porphyra dentata were evaluated as potential EPIs against drug-resistant Escherichia coli. All these extracts were found to potentiate the activities of drugs in modulation tests, although not to the same extent. Synergistic effects of the extracts and the drug clarithromycin were observed from the onset of Time-kill assays, with no evidence of bacterial regrowth. Ethidium bromide accumulation studies revealed that the efflux decreased in the presence of each extract, as indicated by the presence of EPIs. Most identified EPIs that have been discovered to date have aromatic structures, and the seaweed extracts were found to contain various terpenes, terpenoids, phenolic compounds, indoles, pyrrole derivatives, alkaloids, and halogenated aromatic compounds. Our study highlights the potential of these compounds of the seaweeds as drug EPIs.

Novel antibacterial modalities against methicillin resistant Staphylococcus aureus derived from plants

Methicillin-resistant Staphylococcus aureus (MRSA) is a notorious bacterial pathogen that induces high mortality and morbidity. Due to the emergence of multiple resistance, antibiotic treatments are rapidly becoming ineffective for the related infections. Natural products, especially those derived from plants, have been proven to be effective agents with unique antibacterial properties through different mechanisms. This review interprets the resistance mechanisms of MRSA with the aim to conquer public health threat. Further, recent researches about plant antimicrobials that showed remarkable antibacterial activity against MRSA are recorded, including the crude plant extracts and purified plant-derived bioactive compounds. Novel anti-MRSA modalities of plant antimicrobials such as alteration in efflux pump, inhibition of pyruvate kinase, and disturbance of quorum sensing in MRSA are also summarized which may be promising alternatives to antibacterial drug development in future.

Antibacterial and antifungal properties of crude extracts and isolated compounds from Lychnophora markgravii

Antimicrobial activity of dichloromethane and ethanol extracts and five compounds: pinostrobin (I), pinocembrin (II), tectochrysin (III), galangin 3-methyl ether (IV) and tiliroside (V) isolated from Lychnophora markgravii aerial parts against fifteen microorganisms was determined. The structures of these compounds were elucidated based on ESI-MS and NMR spectroscopic data. Both extracts showed antimicrobial activity against several tested microorganisms. Pinostrobin, tectochrysin and galangin 3-methyl ether showed the strongest antibacterial and antifungal effects.

Ferulic acid derivative inhibits NorA efflux and in combination with ciprofloxacin curtails growth of MRSA in vitro and in vivo

A series of ferulic acid (FA) derivatives were synthesized and evaluated for its ability to inhibit NorA efflux in methicillin resistant Staphylococcus aureus (MRSA), by in silico docking analysis. Based on prediction from glide scores and ability to reduce EtBr MIC, two of the ten derivatives S3- [4-((E)-2-(diethylcarbamoyl)vinyl)-2-methoxyphenyl acetate] and S6- [(E)-methyl 3-(4-((p-tolylcarbamoyl)methoxy)-3-methoxyphenyl)acrylate] were chosen as putative efflux pump inhibitors (EPI's). Time dependent accumulation studies revealed that S6 caused enhanced EtBr accumulation relative to standard NorA efflux inhibitor reserpine, in clinical isolate of MRSA (CIMRSA) and in NorA overexpressed strain of S. aureus (SA1199B). S6 also exhibited synergy with Ciprofloxacin (CPX) against NorA overexpressed strain (SA1199B) of S. aureus but not in NorA knock out strain (K1758). MIC reversal studies showed that S3 in CIMRSA and S6 in NorA overexpressed strain of S. aureus (SA1199B), caused a 4 fold reduction in CPX MIC. In vitro time kill studies revealed that both S3 and S6 with sub MIC of CPX caused a significant 4 log CFU decline in CIMRSA. A decline of >3 log fold CFU by time kill assay implies synergy between FA derivatives and CPX. When tested in vivo in infected muscle tissue of zebrafish both S3 and S6 with CPX caused >3.2 log decline in CIMRSA cell counts relative to CPX treatment alone. Of the two potent derivatives, S6 probably acts through NorA whereas S3 might exert its effect through pump other than NorA. Greater in vitro and in vivo efficiency of FA derivatives implies its potential to be used as an adjuvant along with CPX to curtail MRSA infection in higher animal models.

Curcumin alleviates persistence of Acinetobacter baumannii against colistin

Persisters are phenotypic variants of normal susceptible bacterial populations that survive prolonged exposure to high doses of antibiotics and are responsible for pertinacious infections and post-treatment relapses. Out of the three antibiotics, Acinetobacter baumannii formed the highest percentage of persister cells against rifampicin followed by amikacin and the least against colistin. Colistin-treated cells formed the high levels of reactive oxygen species (ROS) whose quenching with bipyridyl and thiourea led to an increased persister population. Curcumin, a polyphenolic pro-oxidant, significantly decreased persistence against colistin. The quenching of ROS generated by curcumin-colistin combination and the use of resveratrol, an anti-oxidant, with colistin increased the persister population, supporting the significance of ROS in decreased persistence against this combination. The down-regulation of repair genes by this combination in comparison to colistin alone supported the modulation of gene expression in response to ROS and their importance in decreased persistence. Increased membrane permeability by colistin, facilitating the penetration of curcumin into cells and resulting in increased ROS and compromised repair compounded by the decreased efflux of colistin by the inhibition of efflux pumps, may be responsible for enhanced lethality and low persistence. Hence, the curcumin-colistin combination can be another option with anti-persister potential for the control of chronic A. baumannii infections.

Nanoparticles as Efflux Pump and Biofilm Inhibitor to Rejuvenate Bactericidal Effect of Conventional Antibiotics

The universal problem of bacterial resistance to antibiotic reflects a serious threat for physicians to control infections. Evolution in bacteria results in the development of various complex resistance mechanisms to neutralize the bactericidal effect of antibiotics, like drug amelioration, target modification, membrane permeability reduction, and drug extrusion through efflux pumps. Efflux pumps acquire a wide range of substrate specificity and also the tremendous efficacy for drug molecule extrusion outside bacterial cells. Hindrance in the functioning of efflux pumps may rejuvenate the bactericidal effect of conventional antibiotics. Efflux pumps also play an important role in the exclusion or inclusion of quorum-sensing biomolecules responsible for biofilm formation in bacterial cells. This transit movement of quorum-sensing biomolecules inside or outside the bacterial cells may get interrupted by impeding the functioning of efflux pumps. Metallic nanoparticles represent a potential candidate to block efflux pumps of bacterial cells. The application of nanoparticles as efflux pump inhibitors will not only help to revive the bactericidal effect of conventional antibiotics but will also assist to reduce biofilm-forming capacity of microbes. This review focuses on a novel and fascinating application of metallic nanoparticles in synergy with conventional antibiotics for efflux pump inhibition.

Dithiazole thione derivative as competitive NorA efflux pump inhibitor to curtail multi drug resistant clinical isolate of MRSA in a zebrafish infection model

Multi drug resistant (MDR) pathogens pose a serious threat to public health since they can easily render most potent drugs ineffective. Efflux pump inhibitors (EPI) can be used to counter the MDR phenotypes arising due to increased efflux. In the present study, a series of dithiazole thione derivatives were synthesized and checked for its antibacterial and efflux pump inhibitory (EPI) activity. Among 10 dithiazole thione derivatives, real-time efflux studies revealed that seven compounds were potent EPIs relative to CCCP. Zebrafish toxicity studies identified four non-toxic putative EPIs. Both DTT3 and DTT9 perturbed membrane potential and DTT6 was haemolytic. Among DTT6 and DTT10, the latter was less toxic as evidenced by histopathology studies. Since DTT10 was non-haemolytic, did not affect the membrane potential, and was least toxic, it was chosen further for in vivo study, wherein DTT10 potentiated effect of ciprofloxacin against clinical strain of MRSA and reduced bacterial burden in muscle and skin tissue of infected zebrafish by ~ 1.7 and 2.5 log fold respectively. Gene expression profiling of major efflux transport proteins by qPCR revealed that clinical isolate of MRSA, in the absence of antibiotic, upregulated NorA, NorB and MepA pump, whereas it downregulates NorC and MgrA relative to wild-type strain of Staphylococcus aureus. In vitro studies with NorA mutant strains and substrate profiling revealed that at higher concentrations DTT10 is likely to function as a competitive inhibitor of NorA efflux protein in S. aureus, whereas at lower concentrations it might inhibit ciprofloxacin efflux through NorB and MepA as implied by docking studies. A novel non-toxic, non-haemolytic dithiazole thione derivative (DTT10) was identified as a potent competitive inhibitor of NorA efflux pump in S. aureus using in silico, in vitro and in vivo studies. This study also underscores the importance of using zebrafish infection model to screen and evaluate putative EPI for mitigating MDR strains of S. aureus.

L-Methionine based phenolic compound mediates unusual assembly of AgNPs and exerts efficient anti-biofilm effect

A methionine based phenolic chelating ligand together with PSS, PVA, PVP and SDS capping agents produced an unusual self-assembly of AgNPs and strong anti-biofilm effect.