Modulation of antimicrobial efflux pumps of the major facilitator superfamily in Staphylococcus aureus

Evaluation of the Efflux Pump Inhibition Activity of Thiadiazine-Derived Compounds Against the Staphylococcus aureus 1199B Strain

Background: Substances with antibacterial properties have become crucial in light of the continuous increase in infections caused by multidrug-resistant bacteria. In this context, thiadiazines have emerged as heterocyclic compounds already known for their pharmacological activities. However, their potential as antibacterial agents and inhibitors of the efflux system found in resistant bacteria remains poorly understood. From this perspective, the present study highlights the synthesis of thiadiazine-derived compounds and evaluates their antibacterial activity and efflux pump inhibition against the Staphylococcus aureus 1199B strain. Methods: To this end, Minimum Inhibitory Concentration (MIC) tests were conducted, along with the analysis of antibacterial activity through the inhibition of the NorA efflux system using 96-well microdilution assays. Additionally, to assess efflux system inhibition, ethidium bromide (EtBr) fluorescence emission tests were performed, alongside in silico molecular docking studies. Results: Based on the results obtained, it was observed that compound IJ28 exhibited direct activity against the tested SA 1199B strains, with an MIC of 512 µg/mL. It also demonstrated antibacterial activity through efflux pump inhibition, resulting in increased fluorescence rates emitted by EtBr. Compound IJ28 showed a more significant reduction in the Minimum Inhibitory Concentration (MIC) of ethidium bromide, decreasing from 26.6 µg/mL to 0.5 µg/mL, compared to the other compounds. Conclusions: Therefore, it is essential to conduct further studies to investigate the mechanism of action and clarify the feasibility and effects of compound IJ28 as a potential antibacterial agent.

Evaluation of phyto-gallic acid as a potential inhibitor of Staphylococcus aureus efflux pump mediated tetracycline resistance: an in-vitro and in-silico study

Plants contain many bioactive compounds with potent antibacterial and efflux pump inhibitory activity (EPI). In this study, gallic acid extracted from pomegranate molasses by analytical HPLC holds promise as an EPI drug for Staphylococcus aureus mediated tetracycline resistance, it lowered the bacterial resistance and reversed the mechanism via tet family efflux pump, using molecular technique and in-silico molecular docking analysis. Extracted gallic acid combined with tetracycline demonstrated a significant decrease in the minimal inhibitory concentration MIC compared to its single activity. Similarly, little growth and lower fluorescence of S. aureus were observed on ethidium bromide (2.5 mg/mL) agar plates, indicating a reversible efflux pump mechanism and a potent EPI activity. Molecular docking demonstrated a promising affinity binding energy between gallic acid and tet efflux genes, opening a new baseline in bacterial infection treatment. PCR for tetK and Qac A/B genes failed to show any relation between tet genes and gallic acid.

Novel antibiotic resistance profiles in bacteria isolated from oil fly larvae Helaeomyia petrolei living in the La Brea Tar Pits

Larvae from the petroleum oil fly, Helaeomyia petrolei, live in the asphaltene and polyaromatic hydrocarbon rich asphalt seeps of Rancho La Brea, Los Angeles, California. These larvae pass high amounts of viscous asphalt through their digestive system, and their gut microbiota is exposed to these extreme conditions. Environmental stress response mechanisms can co-select for antibiotic resistance, and in the current study we used 16S rRNA and genomic sequencing along with the Comprehensive Antibiotic Resistance Database (CARD) tools to characterize antibiotic resistance profiles from six bacteria previously isolated from the oil fly larval intestinal tract, linking phenotypic and genotypic resistance profiles. The isolates contain a core set of antibiotic resistance determinants along with determinants that are rarely found in these species. Comparing these oil fly isolates to the phenotypic prevalence data generated by the CARD Resistance Gene Identifier revealed sixteen instances where the oil fly bacteria appeared to carry a resistance not seen in related taxa in the database, suggesting a novel suite of resistance families in the oil fly isolates compared to other members of the same taxa. Results highlight the functional duality of genes that simultaneously code for antibiotic resistance and survival under extreme conditions, and expand our understanding of the ecological and evolutionary role of antibiotic resistance genes in environmental habitats.

Evaluation of Antibiotic Resistance Mechanisms in Gram-Positive Bacteria

The prevalence of resistance in Gram-positive bacterial infections is rapidly rising, presenting a pressing global challenge for both healthcare systems and economies. The WHO categorizes these bacteria into critical, high, and medium priority groups based on the urgency for developing new antibiotics. While the first priority pathogen list was issued in 2017, the 2024 list remains largely unchanged. Despite six years having passed, the progress that has been made in developing novel treatment approaches remains insufficient, allowing antimicrobial resistance to persist and worsen on a global scale. Various strategies have been implemented to address this growing threat by targeting specific resistance mechanisms. This review evaluates antimicrobial resistance (AMR) in Gram-positive bacteria, highlighting its critical impact on global health due to the rise of multidrug-resistant pathogens. It focuses on the unique cell wall structure of Gram-positive bacteria, which influences their identification and susceptibility to antibiotics. The review explores the mechanisms of AMR, including enzymatic inactivation, modification of drug targets, limiting drug uptake, and increased drug efflux. It also examines the resistance strategies employed by high-priority Gram-positive pathogens such as Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus faecium, as identified in the WHO's 2024 priority list.

Mechanism of staphylococcal resistance to clinically relevant antibiotics

Staphylococcus aureus, a notorious pathogen with versatile virulence, poses a significant challenge to current antibiotic treatments due to its ability to develop resistance mechanisms against a variety of clinically relevant antibiotics. In this comprehensive review, we carefully dissect the resistance mechanisms employed by S. aureus against various antibiotics commonly used in clinical settings. The article navigates through intricate molecular pathways, elucidating the mechanisms by which S. aureus evades the therapeutic efficacy of antibiotics, such as β-lactams, vancomycin, daptomycin, linezolid, etc. Each antibiotic is scrutinised for its mechanism of action, impact on bacterial physiology, and the corresponding resistance strategies adopted by S. aureus. By synthesising the knowledge surrounding these resistance mechanisms, this review aims to serve as a comprehensive resource that provides a foundation for the development of innovative therapeutic strategies and alternative treatments for S. aureus infections. Understanding the evolving landscape of antibiotic resistance is imperative for devising effective countermeasures in the battle against this formidable pathogen.

Metagenomic analysis demonstrates distinct changes in the gut microbiome of Kawasaki diseases children

Background

Kawasaki disease (KD) has been considered as the most common required pediatric cardiovascular diseases among the world. However, the molecular mechanisms of KD were not fully underlined, leading to a confused situation in disease management and providing precious prognosis prediction. The disorders of gut microbiome had been identified among several cardiovascular diseases and inflammation conditions. Therefore, it is urgent to elucidate the characteristics of gut microbiome in KD and demonstrate its potential role in regulating intravenous immunoglobulin (IVIG) resistance and coronary artery injuries.

Methods

A total of 96 KD children and 62 controls were enrolled in the study. One hundred forty fecal samples had been harvested from KD patients, including individuals before or after IVIG treatment, with or without early coronary artery lesions and IVIG resistance. Fecal samples had been collected before and after IVIG administration and stored at -80°C. Then, metagenomic analysis had been done using Illumina NovaSeq 6000 platform. After that, the different strains and functional differences among comparisons were identified.

Results

First, significant changes had been observed between KD and their controls. We found that the decrease of Akkermansia muciniphila, Faecalibacterium prausnitzii, Bacteroides uniformis, and Bacteroides ovatus and the increase of pathogenic bacteria Finegoldia magna, Abiotrophia defectiva, and Anaerococcus prevotii perhaps closely related to the incidence of KD. Then, metagenomic and responding functional analysis demonstrated that short-chain fatty acid pathways and related strains were associated with different outcomes of therapeutic efficacies. Among them, the reduction of Bacteroides thetaiotaomicron, the enrichment of Enterococcus faecalis and antibiotic resistance genes had been found to be involved in IVIG resistance of KD. Moreover, our data also revealed several potential pathogenetic microbiome of that KD patients with coronary artery lesions.

Conclusion

These results strongly proved that distinct changes in the gut microbiome of KD and the dysfunction of gut microbiomes should be responsible for the pathogenesis of KD and significantly impact the prognosis of KD.

Major facilitator superfamily efflux pumps in human pathogens: Role in multidrug resistance and beyond

The major facilitator superfamily (MFS) of proteins constitutes a large group of related solute transporters found across all known living taxa of organisms. The transporters of the MFS contain an extremely diverse array of substrates, including ions, molecules of intermediary metabolism, and structurally different antimicrobial agents. First discovered over 30 years ago, the MFS represents an important collection of integral membrane transporters. Bacterial microorganisms expressing multidrug efflux pumps belonging to the MFS are considered serious pathogens, accounting for alarming morbidity and mortality numbers annually. This review article considers recent advances in the structure-function relationships, the transport mechanism, and modulation of MFS multidrug efflux pumps within the context of drug resistance mechanisms of bacterial pathogens of public health concerns.

Enhanced Efficacy of Ciprofloxacin and Tobramycin against Staphylococcus aureus When Combined with Corydalis Tuber and Berberine through Efflux Pump Inhibition

One way that bacteria develop antibiotic resistance is by reducing intracellular antibiotic concentrations through efflux pumps. Therefore, enhancing the efficacy of antibiotics using efflux pump inhibitors provides a way to overcome this type of resistance. Notably, an increasing number of pathogenic Staphylococcus aureus strains have efflux pump genes. In this study, the extract from Corydalis ternata Nakai tuber (Corydalis Tuber) at 512 mg/L was demonstrated to have an antibiotic synergistic effect with ciprofloxacin at 2 mg/L and tobramycin at 1024 mg/L against methicillin-resistant S. aureus (MRSA). Berberine, an isoquinoline alkaloid identified in Corydalis Tuber, was identified as contributing to this effect. Ethidium bromide efflux pump activity assays showed that Corydalis Tuber extract and berberine inhibited efflux, suggesting that they are efflux pump inhibitors. Molecular docking simulations suggested that berberine binds to S. aureus efflux pump proteins MepA, NorA, NorB, and SdrM. Additionally, berberine and Corydalis Tuber extract inhibit biofilm formation, which can confer antibiotic resistance. This study's findings suggest that Corydalis Tuber, a traditional herbal medicine, and berberine, a medicinal supplement, act as S. aureus efflux pump inhibitors, synergistically increasing the efficacy of ciprofloxacin and tobramycin and showing promise as a treatment for antibiotic-resistant S. aureus infections, including MRSA.

Berberine disrupts staphylococcal proton motive force to cause potent anti-staphylococcal effects in vitro

The presence of antibiotic resistance has increased the urgency for more effective treatments of bacterial infections. Biofilm formation has complicated this issue as biofilm bacteria become tolerant to antibiotics due to environmental factors such as nutrient deprivation and adhesion. In septic arthritis, a disease with an 11% mortality rate, bacteria in synovial fluid organize into floating, protein-rich, bacterial aggregates (mm-cm) that display depressed metabolism and antibiotic tolerance. In this study, Staphylococcus aureus (S. aureus), which is the most common pathogen in septic arthritis, was tested against different inhibitors that modulate bacterial surface protein availability and that should decrease bacterial aggregation. One of these, berberine, a quaternary ammonium compound, was found to reduce bacterial counts by 3-7 logs in human synovial fluid (aggregating medium) with no effect in tryptic soy broth (TSB, non-aggregating). Unlike traditional antibiotics, the bactericidal activity of berberine appeared to be independent of bacterial metabolism. To elucidate the mechanism, we used synovial fluid fractionation, targeted MRSA transposon insertion mutants, dyes to assess changes in membrane potential (DiSC3(5)) and membrane permeability (propidium iodide (PI)), colony counting, and fluorescence spectroscopy. We showed that berberine's activity was dependent on an alkaline pH and berberine killed both methicillin-sensitive S. aureus and MRSA in alkaline media (pH 8.5-9.0; p < 0.0001 vs. same pH controls). Under these alkaline conditions, berberine localized to S. aureus where berberine was isolated in cytoplasmic (∼95%) and DNA (∼5%) fractions. Importantly, berberine increased bacterial cell membrane permeability, and disrupted the proton motive force, suggesting a mechanism whereby it may be able to synergize with other antibacterial compounds under less harsh conditions. We suggest that berberine, which is cheap and readily available, can be made into an effective treatment.

Impact of clonal lineages on susceptibility of Staphylococcus lugdunensis to chlorhexidine digluconate and chloride benzalkonium

BACKGROUND

Little is known about susceptibility of Staphylococcus lugdunensis to antiseptics. The objective of this study was to evaluate, at the molecular and phenotypic level, the susceptibility of 49 clinical S. lugdunensis strains (belonging to the seven clonal complexes [CCs] defined by multilocus sequence typing) to two antiseptics frequently used in healthcare settings (chlorhexidine digluconate [CHX] and chloride benzalkonium [BAC]).

RESULTS

The minimum inhibitory concentrations (MICs), by broth microdilution method, varied for BAC from 0.25 mg/L to 8 mg/L (MIC50 = 1 mg/L, MIC90 = 2 mg/L) and for CHX from 0.5 mg/L to 2 mg/L (MIC50 = 1 mg/L, MIC90 = 2 mg/L). The BAC and CHX minimum bactericidal concentrations (MBCs) varied from 2 mg/L to 8 mg/L (MBC50 = 4 mg/L, MBC90 = 8 mg/L) and from 2 mg/L to 4 mg/L (MBC50 and MBC90 = 4 mg/L), respectively. A reduced susceptibility to CHX (MIC = 2 mg/L) was observed for 12.2% of the strains and that to BAC (MIC ≥ 4 mg/L) for 4.1%. The norA resistance gene was detected in all the 49 isolates, whereas the qacA gene was rarely encountered (two strains; 4.1%). The qacC, qacG, qacH, and qacJ genes were not detected. The two strains harboring the qacA gene had reduced susceptibility to both antiseptics and belonged to CC3.

CONCLUSION

The norA gene was detected in all the strains, suggesting that it could belong to the core genome of S. lugdunensis. S. lugdunensis is highly susceptible to both antiseptics tested. Reduced susceptibility to BAC and CHX was a rare phenomenon. Of note, a tendency to higher MICs of BAC was detected for CC3 isolates. These results should be confirmed on a larger collection of strains.

Evaluation of the antibacterial and inhibitory activity of the MepA efflux pump of Staphylococcus aureus by riparins I, II, III, and IV

The efflux pump mechanism contributes to the antibiotic resistance of widely distributed strains of Staphylococcus aureus. Therefore, in the present work, the ability of the riparins N-(4-methoxyphenethyl)benzamide (I), 2-hydroxy-N-[2-(4-methoxyphenyl)ethyl]benzamide (II), 2, 6-dihydroxy-N-[ 2-(4-methoxyphenyl)ethyl]benzamide (III), and 3,4,5-trimethoxy-N-[2-(4-methoxyphenethyl)benzamide (IV) as potential inhibitors of the MepA efflux pump in S. aureus K2068 (fluoroquinolone-resistant). In addition, we performed checkerboard assays to obtain more information about the activity of riparins as potential inhibitors of MepA efflux and also analyzed the ability of riparins to act on the permeability of the bacterial membrane of S. aureus by the fluorescence method with SYTOX Green. A molecular coupling assay was performed to characterize the interaction between riparins and MepA, and ADMET (absorption, distribution, metabolism, and excretion) properties were analyzed. We observed that I-IV riparins did not show direct antibacterial activity against S. aureus. However, combination assays with substrates of MepA, ciprofloxacin, and ethidium bromide (EtBr) revealed a potentiation of the efficacy of these substrates by reducing the minimum inhibitory concentration (MIC). Furthermore, increased EtBr fluorescence emission was observed for all riparins. The checkerboard assay showed synergism between riparins I, II, and III, ciprofloxacin, and EtBr. Furthermore, riparins III and IV exhibited permeability in the S. aureus membrane at a concentration of 200 μg/mL. Molecular docking showed that riparins I, II, and III bound in a different region from the binding site of chlorpromazine (standard pump inhibitor), indicating a possible synergistic effect with the reference inhibitor. In contrast, riparin IV binds in the same region as the chlorpromazine binding site. From the in silico ADMET prediction based on MPO, it could be concluded that the molecules of riparin I-IV present their physicochemical properties within the ideal pharmacological spectrum allowing their preparation as an oral drug. Furthermore, the prediction of cytotoxicity in liver cell lines showed a low cytotoxic effect for riparins I-IV.

Genomic characterization of Staphylococcus aureus from Canastra Minas Artisanal Cheeses

Canastra Minas Artisanal Cheese is produced in the Brazilian State of Minas Gerais using raw milk, rennet, and pingo, a natural endogenous starter culture (fermented whey) collected from the previous day's production. Due to the use of raw milk, the product can carry microorganisms that may cause foodborne diseases (FBD), including Staphylococcus aureus. Genomic characterization of S. aureus is an important tool to assess diversity, virulence, antimicrobial resistance, and the potential for causing food poisoning due to enterotoxin production. This study is aimed at exploring the genomic features of S. aureus strains isolated from Canastra Minas Artisanal Cheeses. Multilocus sequence typing (MLST) classified these strains as ST1, ST5, and a new profile ST7849 (assigned to the clonal complex CC97). These strains belonged to four spa types: t008, t127, t359, and t992. We identified antimicrobial resistance genes with phenotypic correlation against methicillin (MRSA) and tetracycline. Virulome analysis revealed genes associated with iron uptake, immune evasion, and potential capacity for adherence and biofilm formation. The toxigenic potential included cyto- and exotoxins genes, and all strains presented the genes that encode for Panton-Valentine toxin and hemolysin, and two strains encoded 4 and 8 Staphylococcal enterotoxin (SE) genes. The results revealed the pathogenic potential of the evaluated S. aureus strains circulating in the Canastra region, representing a potential risk to public health. This study also provides useful information to monitor and guide the application of control measures to the artisanal dairy food production chain.

Understanding mechanisms of virulence in MRSA: implications for antivirulence treatment strategies

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is a widespread pathogen, often causing recurrent and deadly infections in the hospital and community. Many S. aureus virulence factors have been suggested as potential targets for antivirulence therapy to decrease the threat of diminishing antibiotic availability. Antivirulence methods hold promise due to their adjunctive and prophylactic potential and decreased risk for selective pressure.

AREAS COVERED

This review describes the dominant virulence mechanisms exerted by MRSA and antivirulence therapeutics that are currently undergoing testing in clinical or preclinical stages. We also discuss the advantages and downsides of several investigational antivirulence approaches, including the targeting of bacterial transporters, host-directed therapy, and quorum-sensing inhibitors. For this review, a systematic search of literature on PubMed, Google Scholar, and Web of Science for relevant search terms was performed in April and May 2023.

EXPERT OPINION

Vaccine and antibody strategies have failed in clinical trials and could benefit from more basic science-informed approaches. Antivirulence-targeting approaches need to be set up better to meet the requirements of drug development, rather than only providing limited results to provide 'proof-of-principle' translational value of pathogenesis research. Nevertheless, there is great potential of such strategies and potential particular promise for novel probiotic approaches.

Efflux pump gene amplifications bypass necessity of multiple target mutations for resistance against dual-targeting antibiotic

Antibiotics that have multiple cellular targets theoretically reduce the frequency of resistance evolution, but adaptive trajectories and resistance mechanisms against such antibiotics are understudied. Here we investigate these in methicillin resistant Staphylococcus aureus (MRSA) using experimental evolution upon exposure to delafloxacin (DLX), a novel fluoroquinolone that targets both DNA gyrase and topoisomerase IV. We show that selection for coding sequence mutations and genomic amplifications of the gene encoding a poorly characterized efflux pump, SdrM, leads to high DLX resistance, circumventing the requirement for mutations in both target enzymes. In the evolved populations, sdrM overexpression due to genomic amplifications containing sdrM and two adjacent genes encoding efflux pumps results in high DLX resistance, while the adjacent hitchhiking efflux pumps contribute to streptomycin cross-resistance. Further, lack of sdrM necessitates mutations in both target enzymes to evolve DLX resistance, and sdrM thus increases the frequency of resistance evolution. Finally, sdrM mutations and amplifications are similarly selected in two diverse clinical isolates, indicating the generality of this DLX resistance mechanism. Our study highlights that instead of reduced rates of resistance, evolution of resistance to multi-targeting antibiotics can involve alternate high-frequency evolutionary paths, that may cause unexpected alterations of the fitness landscape, including antibiotic cross-resistance.

Progress in the Prevalence, Classification and Drug Resistance Mechanisms of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus is a common human pathogen with a variety of virulence factors, which can cause multiple infectious diseases. In recent decades, due to the constant evolution and the abuse of antibiotics, Staphylococcus aureus was becoming more resistant, the infection rate of MRSA remained high, and clinical treatment of MRSA became more difficult. The genetic diversity of MRSA was mainly represented by the continuous emergence of epidemic strains, resulting in the constant changes of epidemic clones. Different classes of MRSA resulted in different epidemics and resistance characteristics, which could affect the clinical symptoms and treatments. MRSA had also spread from traditional hospitals to community and livestock environments, and the new clones established a relationship between animals and humans, promoting further evolution of MRSA. Since the resistance mechanism of MRSA is very complex, it is important to clarify these resistance mechanisms at the molecular level for the treatment of infectious diseases. We firstly described the diversity of SCCmec elements, and discussed the types of SCCmec, its drug resistance mechanisms and expression regulations. Then, we described how the vanA operon makes Staphylococcus aureus resistant to vancomycin and its expression regulation. Finally, a brief introduction was given to the drug resistance mechanisms of biofilms and efflux pump systems. Analyzing the resistance mechanism of MRSA can help study new anti-infective drugs and alleviate the evolution of MRSA. At the end of the review, we summarized the treatment strategies for MRSA infection, including antibiotics, anti-biofilm agents and efflux pump inhibitors. To sum up, here we reviewed the epidemic characteristics of Staphylococcus aureus, summarized its classifications, drug resistance mechanisms of MRSA (SCCmec element, vanA operon, biofilm and active efflux pump system) and novel therapy strategies, so as to provide a theoretical basis for the treatment of MRSA infection.

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.

Exploring Efflux as a Mechanism of Reduced Susceptibility towards Biocides and Fluoroquinolones in Staphylococcus pseudintermedius

Staphylococcus pseudintermedius is the main bacterial cause of skin and soft tissue infections (SSTIs) in companion animals, particularly dogs. The emergence of methicillin-resistant S. pseudintermedius (MRSP) strains, frequently with multidrug resistance phenotypes is a public health concern. This study aimed to evaluate efflux, a resistance mechanism still poorly characterized in S. pseudintermedius, as a contributor to biocide and fluoroquinolone resistance. Susceptibility to the efflux pump substrates ethidium bromide (EtBr), tetraphenylphosphonium bromide (TPP) and ciprofloxacin (CIP) was evaluated by minimum inhibitory concentration (MIC) determination for 155 SSTIs-related S. pseudintermedius in companion animals. EtBr and TPP MIC distributions were analyzed to estimate cut-off (COWT) values. The effect of the efflux inhibitors (EIs) thioridazine and verapamil was assessed upon MICs and fluorometric EtBr accumulation assays, performed with/without glucose and/or EIs. This approach detected a non-wild type population towards TPP with increased efflux, showed to be strain-specific and glucose-dependent. Resistance to fluoroquinolones was mainly linked to target gene mutations, yet a contribution of efflux on CIP resistance levels could not be ruled out. In sum, this study highlights the relevance of efflux-mediated resistance in clinical S. pseudintermedius, particularly to biocides, and provides a methodological basis for further studies on the efflux activity on this important pathogen of companion animals.

Efflux Pump (QacA, QacB, and QacC) and β-Lactamase Inhibitors? An Evaluation of 1,8-Naphthyridines against Staphylococcus aureus Strains

The bacterial species Staphylococcus aureus presents a variety of resistance mechanisms, among which the expression of β-lactamases and efflux pumps stand out for providing a significant degree of resistance to clinically relevant antibiotics. The 1,8-naphthyridines are nitrogen heterocycles with a broad spectrum of biological activities and, as such, are promising research targets. However, the potential roles of these compounds on bacterial resistance management remain to be better investigated. Therefore, the present study evaluated the antibacterial activity of 1,8-naphthyridine sulfonamides, addressing their ability to act as inhibitors of β-lactamases and efflux pump (QacA/B and QacC) against the strains SA-K4414 and SA-K4100 of S. aureus. All substances were prepared at an initial concentration of 1024 μg/mL, and their minimum inhibitory concentrations (MIC) were determined by the broth microdilution method. Subsequently, their effects on β-lactamase- and efflux pump-mediated antibiotic resistance was evaluated from the reduction of the MIC of ethidium bromide (EtBr) and β-lactam antibiotics, respectively. The 1,8-naphthyridines did not present direct antibacterial activity against the strains SA-K4414 and SA-K4100 of S. aureus. On the other hand, when associated with antibiotics against both strains, the compounds reduced the MIC of EtBr and β-lactam antibiotics, suggesting that they may act by inhibiting β-lactamases and efflux pumps such as QacC and QacA/B. However, further research is required to elucidate the molecular mechanisms underlying these observed effects.

The Major Facilitator Superfamily and Antimicrobial Resistance Efflux Pumps of the ESKAPEE Pathogen Staphylococcus aureus

The ESKAPEE bacterial pathogen Staphylococcus aureus has posed a serious public health concern for centuries. Throughout its evolutionary course, S. aureus has developed strains with resistance to antimicrobial agents. The bacterial pathogen has acquired multidrug resistance, causing, in many cases, untreatable infectious diseases and raising serious public safety and healthcare concerns. Amongst the various mechanisms for antimicrobial resistance, integral membrane proteins that serve as secondary active transporters from the major facilitator superfamily constitute a chief system of multidrug resistance. These MFS transporters actively export structurally different antimicrobial agents from the cells of S. aureus. This review article discusses the S. aureus-specific MFS multidrug efflux pump systems from a molecular mechanistic perspective, paying particular attention to structure-function relationships, modulation of antimicrobial resistance mediated by MFS drug efflux pumps, and direction for future investigation.

Skin-to-blood pH shift triggers metabolome and proteome global remodelling in Staphylococcus epidermidis

Staphylococcus epidermidis is one of the most common bacteria of the human skin microbiota. Despite its role as a commensal, S. epidermidis has emerged as an opportunistic pathogen, associated with 80% of medical devices related infections. Moreover, these bacteria are extremely difficult to treat due to their ability to form biofilms and accumulate resistance to almost all classes of antimicrobials. Thus new preventive and therapeutic strategies are urgently needed. However, the molecular mechanisms associated with S. epidermidis colonisation and disease are still poorly understood. A deeper understanding of the metabolic and cellular processes associated with response to environmental factors characteristic of SE ecological niches in health and disease might provide new clues on colonisation and disease processes. Here we studied the impact of pH conditions, mimicking the skin pH (5.5) and blood pH (7.4), in a S. epidermidis commensal strain by means of next-generation proteomics and 1H NMR-based metabolomics. Moreover, we evaluated the metabolic changes occurring during a sudden pH change, simulating the skin barrier break produced by a catheter. We found that exposure of S. epidermidis to skin pH induced oxidative phosphorylation and biosynthesis of peptidoglycan, lipoteichoic acids and betaine. In contrast, at blood pH, the bacterial assimilation of monosaccharides and its oxidation by glycolysis and fermentation was promoted. Additionally, several proteins related to virulence and immune evasion, namely extracellular proteases and membrane iron transporters were more abundant at blood pH. In the situation of an abrupt skin-to-blood pH shift we observed the decrease in the osmolyte betaine and changes in the levels of several metabolites and proteins involved in cellular redoxl homeostasis. Our results suggest that at the skin pH S. epidermidis cells are metabolically more active and adhesion is promoted, while at blood pH, metabolism is tuned down and cells have a more virulent profile. pH increase during commensal-to-pathogen conversion appears to be a critical environmental signal to the remodelling of the S. epidermidis metabolism toward a more pathogenic state. Targeting S. epidermidis proteins induced by pH 7.4 and promoting the acidification of the medical device surface or surrounding environment might be new strategies to treat and prevent S. epidermidis infections.

Promising FDA-approved drugs with efflux pump inhibitory activities against clinical isolates of Staphylococcus aureus

Background and objectives

Staphylococcus aureus is an opportunistic pathogen that causes wide range of nosocomial and community-acquired infections which have spread worldwide leading to an urgent need for developing effective anti-staphylococcal agents. Efflux is an important resistance mechanism that bacteria used to fight the antimicrobial action. This study aimed to investigate the efflux mechanism in S. aureus and assess diclofenac, domperidone, glyceryl trinitrate and metformin as potential efflux pump inhibitors that can be used in combination with antibiotics for treating topical infections caused by S. aureus.

Materials and methods

Efflux was detected qualitatively by the ethidium bromide Cart-Wheel method followed by investigating the presence of efflux genes by polymerase chain reaction. Twenty-six isolates were selected for further investigation of efflux by Cart-Wheel method in absence and presence of tested compounds followed by quantitative efflux assay. Furthermore, antibiotics minimum inhibitory concentrations in absence and presence of tested compounds were determined. The effects of tested drugs on expression levels of efflux genes norA, fexA and tetK were determined by quantitative real time-polymerase chain reaction.

Results

Efflux was found in 65.3% of isolates, the prevalence of norA, tetK, fexA and msrA genes were 91.7%, 77.8%, 27.8% and 6.9%. Efflux assay revealed that tested drugs had potential efflux inhibitory activities, reduced the antibiotic’s MICs and significantly decreased the relative expression of efflux genes.

Conclusion

Diclofenac sodium, domperidone and glyceryl trinitrate showed higher efflux inhibitory activities than verapamil and metformin. To our knowledge, this is the first report that shows that diclofenac sodium, glyceryl trinitrate and domperidone have efflux pump inhibitory activities against S. aureus.

Targeting the Achilles' Heel of Multidrug-Resistant Staphylococcus aureus by the Endocannabinoid Anandamide

Antibiotic-resistant Staphylococcus aureus is a major health issue that requires new therapeutic approaches. Accumulating data suggest that it is possible to sensitize these bacteria to antibiotics by combining them with inhibitors targeting efflux pumps, the low-affinity penicillin-binding protein PBP2a, cell wall teichoic acid, or the cell division protein FtsZ. We have previously shown that the endocannabinoid Anandamide (N-arachidonoylethanolamine; AEA) could sensitize drug-resistant S. aureus to a variety of antibiotics, among others, through growth arrest and inhibition of drug efflux. Here, we looked at biochemical alterations caused by AEA. We observed that AEA increased the intracellular drug concentration of a fluorescent penicillin and augmented its binding to membrane proteins with concomitant altered membrane distribution of these proteins. AEA also prevented the secretion of exopolysaccharides (EPS) and reduced the cell wall teichoic acid content, both processes known to require transporter proteins. Notably, AEA was found to inhibit membrane ATPase activity that is necessary for transmembrane transport. AEA did not affect the membrane GTPase activity, and the GTPase cell division protein FtsZ formed the Z-ring of the divisome normally in the presence of AEA. Rather, AEA caused a reduction in murein hydrolase activities involved in daughter cell separation. Altogether, this study shows that AEA affects several biochemical processes that culminate in the sensitization of the drug-resistant bacteria to antibiotics.

Flavonolignans from silymarin modulate antibiotic resistance and virulence in Staphylococcus aureus

Antibiotic resistance is currently a serious health problem. Since the discovery of new antibiotics no longer seems to be a sufficient tool in the fight against multidrug-resistant infections, adjuvant (combination) therapy is gaining in importance as well as reducing bacterial virulence. Silymarin is a complex of flavonoids and flavonolignans known for its broad spectrum of biological activities, including its ability to modulate drug resistance in cancer. This work aimed to test eleven, optically pure silymarin flavonolignans for their ability to reverse the multidrug resistance phenotype of Staphylococcus aureus and reduce its virulence. Silybin A, 2,3-dehydrosilybin B, and 2,3-dehydrosilybin AB completely reversed antibiotic resistance at concentrations of 20 µM or less. Both 2,3-dehydrosilybin B and AB decreased the antibiotic-induced gene expression of representative efflux pumps belonging to the major facilitator (MFS), multidrug and toxic compound extrusion (MATE), and ATP-binding cassette (ABC) families. 2,3-Dehydrosilybin B also inhibited ethidium bromide accumulation and efflux in a clinical isolate whose NorA and MdeA overproduction was induced by antibiotics. Most of the tested flavonolignans reduced cell-to-cell communication on a tetrahydrofuran-borate (autoinducer-2) basis, with isosilychristin leading the way followed by 2,3-dehydrosilybin A and AB, which halved communication at 10 µM. Anhydrosilychristin was the only compound that reduced communication based on acyl-homoserine lactone (autoinducer 1), with an IC₅₀ of 4.8 µM. Except for isosilychristin and anhydrosilychristin, all of the flavonolignans inhibited S. aureus surface colonization, with 2,3-dehydrosilybin A being the most active (IC₅₀ 10.6 µM). In conclusion, the selected flavonolignans, particularly derivatives of 2,3-dehydrosilybin B, 2,3-dehydrosilybin AB, and silybin A are non-toxic modulators of S. aureus multidrug resistance and can decrease the virulence of the bacterium, which deserves further detailed research.

AgNPs Targeting the Drug Resistance Problem of Staphylococcus aureus: Susceptibility to Antibiotics and Efflux Effect

The present work presents translational research with application of AgNPs targeting the global drug resistance problem. In vivo fieldwork was carried out with 400 breeding farm cows sick with a serous mastitis. Ex vivo results revealed that after cow treatment with LactobayTM (a mixture of antibiotic drugs) the susceptibility to 31 antibiotics of S. aureus isolates from cow breast secretion decreased by 25%, while after treatment with Argovit–CTM silver nanoparticles S. aureus susceptibility increased by 11%. The portion of isolates with an efflux effect leading to elimination of antibiotics from S. aureus after Lactobay-treatment resulted in a 15% increase, while Argovit-C-treatment led to a 17.5% decrease. The obtained results showed that mastitis treatments with Argovit-CTM AgNPs can partially restore the activity of antibiotics towards S. aureus and shorten the duration of mastitis treatment by 33%.

Evolutionary conservative analysis revealed novel functional sites in the efflux pump NorA of Staphylococcus aureus

OBJECTIVES

The NorA antiporter of Staphylococcus aureus belongs to the major facilitator superfamily (MFS) and extrudes various kinds of drugs. With no structure available for this drug efflux pump, the aim of this study was to explore its important structural elements that contribute to substrate binding and drug transport.

METHODS

Evolutionary conservative analyses were conducted on different compilations of NorA homologues to identify conservative motifs and residues. Site-directed mutations were constructed to verify the functional changes in NorA efflux capacities and the conformational changes were further measured by fluorescence resonance energy transfer (FRET) and microscale thermophoresis (MST) analysis.

RESULTS

Besides Motif-A, Motif-B and Motif-C that were reported previously in MFS proteins, two other motifs, Motif-1 and Motif-2, were identified in NorA. Site-directed mutations of Motif-1 and Motif-2 as well as 11 predicted binding sites all caused remarkable reductions in drug resistance and efflux activity. Among these, mutant F16A/E222A/F303A/D307A showed an altered binding affinity for tetraphenylphosphonium chloride when measured by MST and Motif-1 mutant G114D/A117E/D118G/V119I and Motif-2 mutant Q325E/G326E/A328E/G330E displayed obvious conformational alterations when compared with the wild-type NorA in the FRET signal spectra.

CONCLUSIONS

The NorA structure agrees well with the typical structures of MFS proteins, with two newly identified motifs (Motif-1 and Motif-2) that are critical to the structural stability of NorA, and sites F16, E222, F303 and D307 are involved in substrate binding.

Efflux Pump Mediated Antimicrobial Resistance by Staphylococci in Health-Related Environments: Challenges and the Quest for Inhibition

The increasing emergence of antimicrobial resistance in staphylococcal bacteria is a major health threat worldwide due to significant morbidity and mortality resulting from their associated hospital- or community-acquired infections. Dramatic decrease in the discovery of new antibiotics from the pharmaceutical industry coupled with increased use of sanitisers and disinfectants due to the ongoing COVID-19 pandemic can further aggravate the problem of antimicrobial resistance. Staphylococci utilise multiple mechanisms to circumvent the effects of antimicrobials. One of these resistance mechanisms is the export of antimicrobial agents through the activity of membrane-embedded multidrug efflux pump proteins. The use of efflux pump inhibitors in combination with currently approved antimicrobials is a promising strategy to potentiate their clinical efficacy against resistant strains of staphylococci, and simultaneously reduce the selection of resistant mutants. This review presents an overview of the current knowledge of staphylococcal efflux pumps, discusses their clinical impact, and summarises compounds found in the last decade from plant and synthetic origin that have the potential to be used as adjuvants to antibiotic therapy against multidrug resistant staphylococci. Critically, future high-resolution structures of staphylococcal efflux pumps could aid in design and development of safer, more target-specific and highly potent efflux pump inhibitors to progress into clinical use.

Development of an Antibiotic Resistance Breaker to Resensitize Drug-Resistant Staphylococcus aureus: In Silico and In Vitro Approach

Efflux pumps are one of the predominant microbial resistant mechanisms leading to the development of multidrug resistance. In Staphylococcus aureus, overexpression of NorA protein enables the efflux of antibiotics belonging to the class of fluoroquinolones and, thus, makes S. aureus resistant. Hence, NorA efflux pumps are being extensively exploited as the potential drug target to evade bacterial resistance and resensitize bacteria to the existing antibiotics. Although several molecules are reported to inhibit NorA efflux pump effectively, boronic acid derivatives were shown to have promising NorA efflux pump inhibition. In this regard, the current study exploits 6-(3-phenylpropoxy)pyridine-3-boronic acid to further improve the activity and reduce cytotoxicity using the bioisostere approach, a classical medicinal chemistry concept. Using the SWISS-Bioisostere online tool, from the parent compound, 42 compounds were obtained upon the replacement of the boronic acid. The 42 compounds were docked with modeled NorA protein, and key molecular interactions of the prominent compounds were assessed. The top hit compounds were further analyzed for their drug-like properties using ADMET studies. The identified potent lead, 5-nitro-2-(3-phenylpropoxy)pyridine (5-NPPP), was synthesized, and in vitro efficacy studies have been proven to show enhanced efflux inhibition, thus acting as a potent antibiotic breaker to resensitize S. aureus without elucidating any cytotoxic effect to the host Hep-G2 cell lines.

Impact of spent engine oil contamination on the antibiotic resistome of a tropical agricultural soil

Profiling of hydrocarbon-contaminated soils for antibiotic resistance genes (ARGs) is becoming increasingly important due to emerging realities of their preponderance in hydrocarbon-inundated matrices. In this study, the antibiotic resistome of an agricultural soil (1S) and agricultural soil contaminated with spent engine oil (AB1) were evaluated via functional annotation of the open reading frames (ORFs) of their metagenomes using the comprehensive antibiotic database (CARD) and KEGG KofamKOALA. CARD analysis of AB1 metagenome revealed the detection of 24 AMR (antimicrobial resistance) gene families, 66 ARGs, and the preponderance (69.7%) of ARGs responsible for antibiotic efflux in AB1 metagenome. CARD analysis of 1S metagenome revealed four AMR gene families and five ARGs. Functional annotation of the two metagenomes using KofamKOALA showed 171 ARGs in AB1 and 29 ARGs in 1S, respectively. Majority of the detected ARGs in AB1 (121; 70.8%) and 1S (16; 55.2%) using KofamKOALA are responsible for antibiotic efflux while ARGs for other resistance mechanisms were also detected. All the five major antibiotic efflux pump systems were detected in AB1 metagenome, though majority of the ARGs for antibiotic efflux belong to the RND (resistance-nodulation-cell division) and MFS (major facilitator superfamily) efflux systems. Significant differences observed in the ARGs recovered from 1S and AB1 metagenomes were statistically validated (P < 0.05). SEO contamination is believed to be responsible for ARGs increase in AB1 metagenome via mechanisms of cross-resistance especially with efflux pumps. The detection of these ARGs is of great public health concern in this era of multidrug resistant isolates resurgence.

Inhibition of Bacterial Efflux Pumps by Crude Extracts and Essential Oil from Myristica fragrans Houtt. (Nutmeg) Seeds against Methicillin-Resistant Staphylococcus aureus

Myristicafragrans Houtt. (Nutmeg) is a widely known folk medicine across several parts of Asia, particularly used in antimicrobial treatment. Bacterial resistance involves the expression of efflux pump systems (chromosomal norA and mepA) in methicillin-resistant Staphylococcus aureus (MRSA). Crude extract (CE) and essential oil (EO) obtained from nutmeg were applied as efflux pump inhibitors (EPIs), thereby enhancing the antimicrobial activity of the drugs they were used in. The major substances in CE and EO, which function as EPIs, in a descending order of % peak area include elemicin, myristicin, methoxyeugenol, myristicin, and asarone. Here, we investigated whether the low amount of CE and EO used as EPIs was sufficient to sensitize MRSA killing using the antibiotic ciprofloxacin, which acts as an efflux system. Interestingly, synergy between ciprofloxacin and CE or EO revealed the most significant viability of MRSA, depending on norA and mepA, the latter being responsible for EPI function of EO. Therefore, CE and EO obtained from nutmeg can act as EPIs in combination with substances that act as efflux systems, thereby ensuring that the MRSA strain is susceptible to antibiotic treatment.

Effect of Carvacrol and Thymol on NorA efflux pump inhibition in multidrug-resistant (MDR) Staphylococcus aureus strains

Undue exposure to antimicrobials has led to the acquisition and development of sophisticated bacterial resistance mechanisms, such as efflux pumps, which are able to expel or reduce the intracellular concentration of various antibiotics, making them ineffective. Therefore, inhibiting this mechanism is a promising way to minimize the phenomenon of resistance in bacteria. In this sense, the present study sought to evaluate the activity of the Carvacrol (CAR) and Thymol (THY) terpenes as possible Efflux Pump Inhibitors (EPIs), by determining the Minimum Inhibitory Concentration (MIC) and the association of these compounds in subinhibitory concentrations with the antibiotic Norfloxacin and with Ethidium Bromide (EtBr) against strains SA-1199 (wild-type) and SA-1199B (overexpresses NorA) of Staphylococcus aureus. In order to verify the interaction of the terpenes with the NorA efflux protein, an in silico molecular modeling study was carried out. The assays used to obtain the MIC of CAR and THY were performed by broth microdilution, while the Efflux Pump inhibitory test was performed by the MIC modification method of the antibiotic Norfloxacin and EtBr. docking was performed using the Molegro Virtual Docker (MVD) program. The results of the study revealed that CAR and THY have moderate bacterial activity and are capable of reducing the MIC of Norfloxacin antibiotic and EtBr in strains of S. aureus carrying the NorA efflux pump. The docking results showed that these terpenes act as possible competitive NorA inhibitors and can be investigated as adjuvants in combined therapies aimed at reducing antibiotic resistance.

Bacterial Resistance to Antimicrobial Agents

Bacterial pathogens as causative agents of infection constitute an alarming concern in the public health sector. In particular, bacteria with resistance to multiple antimicrobial agents can confound chemotherapeutic efficacy towards infectious diseases. Multidrug-resistant bacteria harbor various molecular and cellular mechanisms for antimicrobial resistance. These antimicrobial resistance mechanisms include active antimicrobial efflux, reduced drug entry into cells of pathogens, enzymatic metabolism of antimicrobial agents to inactive products, biofilm formation, altered drug targets, and protection of antimicrobial targets. These microbial systems represent suitable focuses for investigation to establish the means for their circumvention and to reestablish therapeutic effectiveness. This review briefly summarizes the various antimicrobial resistance mechanisms that are harbored within infectious bacteria.

Anandamide alters the membrane properties, halts the cell division and prevents drug efflux in multidrug resistant Staphylococcus aureus

Antibiotic resistance is a serious public health problem throughout the world. Overcoming methicillin and multidrug-resistant Staphylococcus aureus (MRSA/MDRSA) infections has become a challenge and there is an urgent need for new therapeutic approaches. We have previously demonstrated that the endocannabinoid Anandamide (AEA) can sensitize MRSA to antibiotics. Here we have studied the mechanism of action using a MDRSA clinical isolate that are sensitized by AEA to methicillin and norfloxacin. We found that AEA treatment halts the growth of both antibiotic-sensitive and antibiotic-resistant S. aureus. The AEA-treated bacteria become elongated and the membranes become ruffled with many protrusions. AEA treatment also leads to an increase in the percentage of bacteria having a complete septum, suggesting that the cell division is halted at this stage. The latter is supported by cell cycle analysis that shows an accumulation of bacteria in the G2/M phase after AEA treatment. We further observed that AEA causes a dose-dependent membrane depolarization that is partly relieved upon time. Nile red staining of the bacterial membranes indicates that AEA alters the membrane structures. Importantly, 4'-6-diamidino-2-phenylindole (DAPI) accumulation assay and ethidium bromide efflux (EtBr) assay unveiled that AEA leads to a dose-dependent drug accumulation by inhibiting drug efflux. In conclusion, our study demonstrates that AEA interferes with cell division, alters the membrane properties of MDRSA, and leads to increased intracellular drug retention, which can contribute to the sensitization of MDRSA to antibiotics.

Prevalence and Therapies of Antibiotic-Resistance in Staphylococcus aureus

Infectious diseases are the second most important cause of human death worldwide; Staphylococcus aureus (S. aureus) is a very common human pathogenic microorganism that can trigger a variety of infectious diseases, such as skin and soft tissue infections, endocarditis, osteomyelitis, bacteremia, and lethal pneumonia. Moreover, according to the sensitivity to antibiotic drugs, S. aureus can be divided into methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA). In recent decades, due to the evolution of bacteria and the abuse of antibiotics, the drug resistance of S. aureus has gradually increased, the infection rate of MRSA has increased worldwide, and the clinical anti-infective treatment for MRSA has become more difficult. Accumulating evidence has demonstrated that the resistance mechanisms of S. aureus are very complex, especially for MRSA, which is resistant to many kinds of antibiotics. Therefore, understanding the drug resistance of MRSA in a timely manner and elucidating its drug resistance mechanism at the molecular level are of great significance for the treatment of S. aureus infection. A large number of researchers believe that analyzing the molecular characteristics of S. aureus can help provide a basis for designing effective prevention and treatment measures against hospital infections caused by S. aureus and further monitor the evolution of S. aureus. This paper reviews the research status of MSSA and MRSA, the detailed mechanisms of the intrinsic antibiotic resistance and the acquired antibiotic resistance, the advanced research on anti-MRSA antibiotics and novel therapeutic strategies for MRSA treatment.

Functional and Structural Roles of the Major Facilitator Superfamily Bacterial Multidrug Efflux Pumps

Pathogenic microorganisms that are multidrug-resistant can pose severe clinical and public health concerns. In particular, bacterial multidrug efflux transporters of the major facilitator superfamily constitute a notable group of drug resistance mechanisms primarily because multidrug-resistant pathogens can become refractory to antimicrobial agents, thus resulting in potentially untreatable bacterial infections. The major facilitator superfamily is composed of thousands of solute transporters that are related in terms of their phylogenetic relationships, primary amino acid sequences, two- and three-dimensional structures, modes of energization (passive and secondary active), and in their mechanisms of solute and ion translocation across the membrane. The major facilitator superfamily is also composed of numerous families and sub-families of homologous transporters that are conserved across all living taxa, from bacteria to humans. Members of this superfamily share several classes of highly conserved amino acid sequence motifs that play essential mechanistic roles during transport. The structural and functional importance of multidrug efflux pumps that belong to the major facilitator family and that are harbored by Gram-negative and -positive bacterial pathogens are considered here.

Prevalence and Therapies of Antibiotic-Resistance in Staphylococcus aureus

Infectious diseases are the second most important cause of human death worldwide; Staphylococcus aureus (S. aureus) is a very common human pathogenic microorganism that can trigger a variety of infectious diseases, such as skin and soft tissue infections, endocarditis, osteomyelitis, bacteremia, and lethal pneumonia. Moreover, according to the sensitivity to antibiotic drugs, S. aureus can be divided into methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA). In recent decades, due to the evolution of bacteria and the abuse of antibiotics, the drug resistance of S. aureus has gradually increased, the infection rate of MRSA has increased worldwide, and the clinical anti-infective treatment for MRSA has become more difficult. Accumulating evidence has demonstrated that the resistance mechanisms of S. aureus are very complex, especially for MRSA, which is resistant to many kinds of antibiotics. Therefore, understanding the drug resistance of MRSA in a timely manner and elucidating its drug resistance mechanism at the molecular level are of great significance for the treatment of S. aureus infection. A large number of researchers believe that analyzing the molecular characteristics of S. aureus can help provide a basis for designing effective prevention and treatment measures against hospital infections caused by S. aureus and further monitor the evolution of S. aureus. This paper reviews the research status of MSSA and MRSA, the detailed mechanisms of the intrinsic antibiotic resistance and the acquired antibiotic resistance, the advanced research on anti-MRSA antibiotics and novel therapeutic strategies for MRSA treatment.

Epidemiology of efflux pumps genes mediating resistance among Staphylococcus aureus; A systematic review

BACKGROUND

Efflux of antibiotics is an effective resistance mechanism among antibiotic-resistant Staphylococcus aureus. This systematic review aims to evaluate the frequency and expression of efflux pump genes in S.aureus around the world.

METHOD

A comprehensive literature search of several databases (Medline Pub Med, ISI, Scopus, Google Scholar, ISC, Science direct and Persian Journals Online, and citation lists) was performed. We considered published studies from 2001 to 2018. Articles reporting the prevalence and expression of efflux pump genes were selected.

RESULT

Among 183 articles, 36 studies were selected. Of the 36, 23 articles were conducted in Asia.6 in Europe, 5 in America and 2 in African countries. In most of these studies norA, norB, qacA/B genes were commonly evaluated by molecular methods. The presence of efflux pump genes such as norA, norB, norC, mepA, mdeA, qacA/B was detected by PCR in 21 studies and over-expression of genes were reported in 13 studies. The most frequently reported genes in Asia were norA (75%), norB (60%), mepA (35%), mdeA (33%) and qacA/B (20.8%). In European studies, the prevalence of norB was mostly reported among S.aureus isolates and norA and qacA/B were commonly found in similar studies in America. The investigation of gene expression patterns showed that norA was most frequent single-pattern in Asia and America, norB or mdeA in Europe.

CONCLUSION

According to this study MDR efflux pumps not only cause high-level resistance but also it considerably associated with over-expression of these genes. Due to the selective pressure on MRSA isolate, the enormous diversity of plasmid-encoded genes had been recorded in different regions, owing to the various numbers and types of isolates in each study or types of disinfectants for general use.

Strategies for discovery of new molecular targets for anti-infective drugs

Multidrug resistant bacterial pathogens as causative agents of infectious disease are a primary public health concern. Clinical efficacy of antimicrobial chemotherapy toward bacterial infection has been compromised in cases where causative agents are resistant to multiple structurally distinct antimicrobial agents. Modification of extant antimicrobial agents that exploit conventional bacterial targets have been developed since the advent of the antimicrobial era. This approach, while successful in certain cases, nonetheless suffers overall from the costs of development and rapid emergence of bacterial variants with confounding resistances to modified agents. Thus, additional strategies toward discovery of new molecular targets have been developed based on bioinformatics analyses and comparative genomics. These and other strategies meant to identify new molecular targets represent promising avenues for reducing emergence of bacterial infections. This short review considers these strategies for discovery of new molecular targets within bacterial pathogens.