Structural Insights into the Inhibition of Undecaprenyl Pyrophosphate Synthase from Gram-Positive Bacteria.

The polyprenyl lipid undecaprenyl phosphate (C55P) is the universal carrier lipid for the biosynthesis of bacterial cell wall polymers. C55P is synthesized in its pyrophosphate form by undecaprenyl pyrophosphate synthase (UppS), an essential cis-prenyltransferase that is an attractive target for antibiotic development. We previously identified a compound (MAC-0547630) that showed promise as a novel class of inhibitor and an ability to potentiate ß-lactam antibiotics. Here, we provide a structural model for MAC-0547630's inhibition of UppS and a structural rationale for its enhanced effect on UppS from Bacillus subtilis versus Staphylococcus aureus. We also describe the synthesis of a MAC-0547630 derivative (JPD447), show that it too can potentiate ß-lactam antibiotics, and provide a structural rationale for its improved potentiation. Finally, we present an improved structural model of clomiphene's inhibition of UppS. Taken together, our data provide a foundation for structure-guided drug design of more potent UppS inhibitors in the future.

Design, synthesis and evaluation of carbazole derivatives as potential antimicrobial agents.

Five series of novel carbazole derivatives containing an aminoguanidine, dihydrotriazine, thiosemicarbazide, semicarbazide or isonicotinic moiety were designed, synthesised and evaluated for their antimicrobial activities. Most of the compounds exhibited potent inhibitory activities towards different bacterial strains (including one multidrug-resistant clinical isolate) and one fungal strain with minimum inhibitory concentrations (MICs) between 0.5 and 16 µg/ml. Compounds 8f and 9d showed the most potent inhibitory activities (MICs of 0.5-2 µg/ml). Furthermore, compounds 8b, 8d, 8f, 8k, 9b and 9e with antimicrobial activities were not cytotoxic to human gastric cancer cell lines (SGC-7901 and AGS) or a normal human liver cell line (L-02). Structure-activity relationship analyses and docking studies implicated the dihydrotriazine group in increasing the antimicrobial potency and reducing the toxicity of the carbazole compounds. In vitro enzyme activity assays suggested that compound 8f binding to dihydrofolate reductase might account for the antimicrobial effect.

Lead optimization of 8-(methylamino)-2-oxo-1,2-dihydroquinolines as bacterial type II topoisomerase inhibitors.

The global increase in multidrug-resistant pathogens has caused severe problems in the treatment of infections. To overcome these difficulties, the advent of a new chemical class of antibacterial drug is eagerly desired. We aimed at creating novel antibacterial agents against bacterial type II topoisomerases, which are well-validated targets. TP0480066 (compound 32) has been identified by using structure-based optimization originated from lead compound 1, which was obtained as a result of our previous lead identification studies. The MIC90 values of TP0480066 against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococci (VRE), and genotype penicillin-resistant Streptococcus pneumoniae (gPRSP) were 0.25, 0.015, and 0.06 µg/mL, respectively. Hence, TP0480066 can be regarded as a promising antibacterial drug candidate of this chemical class.

Highly Sensitive Bacteria-Responsive Membranes Consisting of Core-Shell Polyurethane Polyvinylpyrrolidone Electrospun Nanofibers for In Situ Detection of Bacterial Infections.

Bacteria responsive color-changing wound dressings offer a valuable platform for continuous monitoring of the wound bed facilitating early detection of bacterial infections. In this study, we present a highly sensitive electrospun nanofibrous polyurethane wound dressing incorporating a hemicyanine-based chromogenic probe with a labile ester linkage that can be enzymatically cleaved by bacterial lipase released from clinically relevant strains, such as Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA). A rapid chromogenic response was achieved by localizing the dye at the surface of core-shell fibers, resulting in a 5x faster response relative to conventional nanofibers. By incorporating polyvinylpyrrolidone (PVP) dopant in the shell, the sensitivity was boosted to enable detection of bacteria at clinically relevant concentrations after 2 h exposure: 2.5 × 105 CFU/cm2 P. aeruginosa and 1.0 × 106 CFU/cm2 MRSA. Introduction of PVP in the shell also boosted the degree of hydrolysis of the chromogenic probe by a factor of 1.2× after a 3 h exposure to a low concentration of P. aeruginosa (105 CFU/cm2). PVP was also found to improve the discernibility of the color change at high bacterial concentrations. The co-operativity between the chromogenic probe, fiber structure, and polymer composition is well-suited for timely in situ detection of wound infection.

Venturicidin A, A Membrane-active Natural Product Inhibitor of ATP synthase Potentiates Aminoglycoside Antibiotics.

Despite the remarkable advances due to the discovery and development of antimicrobials agents, infectious diseases remain the second leading cause of death worldwide. This fact underlines the importance of developing new therapeutic strategies to address the widespread antibiotic resistance, which is the major contributing factor for clinical failures of the current therapeutics. In a screen for antibiotic adjuvants, we identified a natural product from actinomycetes, venturicidin A (VentA), that potentiates the aminoglycoside antibiotic gentamicin against multidrug-resistant clinical isolates of Staphylococcus, Enterococcus, and Pseudomonas aeruginosa. Furthermore, the combination of gentamicin and VentA was bactericidal and rapidly eradicated methicillin-resistant S. aureus (MRSA). The molecular mechanism of gentamicin potentiation activity is attributed to uncoupling of ATP synthesis by VentA from electron transport presumably by blocking the proton flow through ATP synthase, which results in an elevated concentration of extracellular protons and subsequent anticipated raise in gentamicin uptake. The disruption of the proton flux was characterized by perturbed membrane potential in MRSA. These results demonstrate that inhibition of ATP synthase along with the subsequent membrane dysregulation, as shown here with VentA, complements aminoglycoside antibiotics against MDR bacteria, and that this approach may be employed to combat bacterial resistance.

The combination of salvianolic acid A with latamoxef completely protects mice against lethal pneumonia caused by methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus (S. aureus), especially methicillin-resistant Staphylococcus aureus (MRSA), is a major cause of pneumonia, resulting in severe morbidity and mortality in adults and children. Sortase A (SrtA), which mediates the anchoring of cell surface proteins in the cell wall, is an important virulence factor of S. aureus. Here, we found that salvianolic acid A (Sal A), which is a natural product that does not affect the growth of S. aureus, could inhibit SrtA activity (IC50 = 5.75 µg/ml) and repress the adhesion of bacteria to fibrinogen, the anchoring of protein A to cell wall, the biofilm formation, and the ability of S. aureus to invade A549 cells. Furthermore, in vivo studies demonstrated that Sal A treatment reduced inflammation and protected mice against lethal pneumonia caused by MRSA. More significantly, full protection (a survival rate of 100%) was achieved when Sal A was administered in combination with latamoxef. Together, these results indicate that Sal A could be developed into a promising therapeutic drug to combat MRSA infections while limiting resistance development.

N-thiadiazole-4-hydroxy-2-quinolone-3-carboxamides bearing heteroaromatic rings as novel antibacterial agents: Design, synthesis, biological evaluation and target identification.

Due to the occurrence of antibiotic resistance, bacterial infectious diseases have become a serious threat to public health. To overcome antibiotic resistance, novel antibiotics are urgently needed. N-thiadiazole-4-hydroxy-2-quinolone-3-carboxamides are a potential new class of antibacterial agents, as one of its derivatives was identified as an antibacterial agent against S. aureus. However, no potency-directed structural optimization has been performed. In this study, we designed and synthesized 37 derivatives, and evaluated their antibacterial activity against S. aureus ATCC29213, which led to the identification of ten potent antibacterial agents with minimum inhibitory concentration (MIC) values below 1 µg/mL. Next, we performed bacterial growth inhibition assays against a panel of drug-resistant clinical isolates, including methicillin-resistant S. aureus, and cytotoxicity assays with HepG2 and HUVEC cells. One of the tested compounds named 1-ethyl-4-hydroxy-2-oxo-N-(5-(thiazol-2-yl)-1,3,4-thiadiazol-2-yl)-1,2-dihydroquinoline-3-carboxamide (g37) showed 2 to 128-times improvement compared with vancomycin in term of antibacterial potency against the tested strains (MICs: 0.25-1 µg/mL vs. 1-64 µg/mL) and an optimal selective toxicity (HepG2/MRSA, 110.6 to 221.2; HUVEC/MRSA, 77.6-155.2). Further, comprehensive evaluation indicated that g37 did not induce resistance development of MRSA over 20 passages, and it has been confirmed as a bactericidal, metabolically stable, orally active antibacterial agent. More importantly, we have identified the S. aureus DNA gyrase B as its potential target and proposed a potential binding mode by molecular docking. Taken together, the present work reports the most potent derivative of this chemical series (g37) and uncovers its potential target, which lays a solid foundation for further lead optimization facilitated by the structure-based drug design technique.

Structures of lipoprotein signal peptidase II from Staphylococcus aureus complexed with antibiotics globomycin and myxovirescin.

Antimicrobial resistance is a major global threat that calls for new antibiotics. Globomycin and myxovirescin are two natural antibiotics that target the lipoprotein-processing enzyme, LspA, thereby compromising the integrity of the bacterial cell envelope. As part of a project aimed at understanding their mechanism of action and for drug development, we provide high-resolution crystal structures of the enzyme from the human pathogen methicillin-resistant Staphylococcus aureus (MRSA) complexed with globomycin and with myxovirescin. Our results reveal an instance of convergent evolution. The two antibiotics possess different molecular structures. Yet, they appear to inhibit identically as non-cleavable tetrahedral intermediate analogs. Remarkably, the two antibiotics superpose along nineteen contiguous atoms that interact similarly with LspA. This 19-atom motif recapitulates a part of the substrate lipoprotein in its proposed binding mode. Incorporating this motif into a scaffold with suitable pharmacokinetic properties should enable the development of effective antibiotics with built-in resistance hardiness.

Targeting Mannitol Metabolism as an Alternative Antimicrobial Strategy Based on the Structure-Function Study of Mannitol-1-Phosphate Dehydrogenase in Staphylococcus aureus.

Mannitol-1-phosphate dehydrogenase (M1PDH) is a key enzyme in Staphylococcus aureus mannitol metabolism, but its roles in pathophysiological settings have not been established. We performed comprehensive structure-function analysis of M1PDH from S. aureus USA300, a strain of community-associated methicillin-resistant S. aureus, to evaluate its roles in cell viability and virulence under pathophysiological conditions. On the basis of our results, we propose M1PDH as a potential antibacterial target. In vitro cell viability assessment of ΔmtlD knockout and complemented strains confirmed that M1PDH is essential to endure pH, high-salt, and oxidative stress and thus that M1PDH is required for preventing osmotic burst by regulating pressure potential imposed by mannitol. The mouse infection model also verified that M1PDH is essential for bacterial survival during infection. To further support the use of M1PDH as an antibacterial target, we identified dihydrocelastrol (DHCL) as a competitive inhibitor of S. aureus M1PDH (SaM1PDH) and confirmed that DHCL effectively reduces bacterial cell viability during host infection. To explain physiological functions of SaM1PDH at the atomic level, the crystal structure of SaM1PDH was determined at 1.7-Å resolution. Structure-based mutation analyses and DHCL molecular docking to the SaM1PDH active site followed by functional assay identified key residues in the active site and provided the action mechanism of DHCL. Collectively, we propose SaM1PDH as a target for antibiotic development based on its physiological roles with the goals of expanding the repertory of antibiotic targets to fight antimicrobial resistance and providing essential knowledge for developing potent inhibitors of SaM1PDH based on structure-function studies.IMPORTANCE Due to the shortage of effective antibiotics against drug-resistant Staphylococcus aureus, new targets are urgently required to develop next-generation antibiotics. We investigated mannitol-1-phosphate dehydrogenase of S. aureus USA300 (SaM1PDH), a key enzyme regulating intracellular mannitol levels, and explored the possibility of using SaM1PDH as a target for developing antibiotic. Since mannitol is necessary for maintaining the cellular redox and osmotic potential, the homeostatic imbalance caused by treatment with a SaM1PDH inhibitor or knockout of the gene encoding SaM1PDH results in bacterial cell death through oxidative and/or mannitol-dependent cytolysis. We elucidated the molecular mechanism of SaM1PDH and the structural basis of substrate and inhibitor recognition by enzymatic and structural analyses of SaM1PDH. Our results strongly support the concept that targeting of SaM1PDH represents an alternative strategy for developing a new class of antibiotics that cause bacterial cell death not by blocking key cellular machinery but by inducing cytolysis and reducing stress tolerance through inhibition of the mannitol pathway.

Characterization of serine acetyltransferase (CysE) from methicillin-resistant Staphylococcus aureus and inhibitory effect of two natural products on CysE.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major hospital-acquired infective pathogen that has developed resistance to many antibiotics. It is imperious to develop novel anti-MRSA drugs to control the emergence of drug resistance. The biosynthesis of cysteine in bacteria is catalyzed by CysE and CysK. CysE was predicted to be important for bacterial viability, it could be a potential drug target. The serine acetyltransferase activity of CysE was detected and its catalytic properties were also determined. CysE homology model was built to investigate interaction sites between CysE and substrate L-Ser or inhibitors by molecular docking. Docking data showed that residues Asp94 and His95 were essential for serine acetyltransferase activity of CysE, which were confirmed by site-directed mutagenesis. Colorimetric assay was used to screen natural products and six compounds which inhibited CysE activity (IC50 ranging from 29.83 µM to 203.13 µM) were found. Inhibition types of two compounds 4 (11-oxo-ebracteolatanolide B) and 30 ((4R,4aR)-dihydroxy-3-hydroxymethyl-7,7,10a-trimethyl-2,4,4a,5,6,6a,7,8,9,10,10a,l0b-dodecahydrophenanthro[3,2-b]furan-2-one) on CysE were determined. Compounds 4 and 30 showed inhibitory effect on MRSA growth (MIC at 12.5 µg/ml and 25 µg/ml) and mature biofilm. The established colorimetric assay will facilitate further high-throughput screening of CysE inhibitors from different compound libraries. The compounds 4 and 30 may offer structural basis for developing new anti-MRSA drugs.

Antibacterial Activity and Mode of Action of a Sulfonamide-Based Class of Oxaborole Leucyl-tRNA-Synthetase Inhibitors.

Benzoxaboroles are a class of boron-containing compounds with a broad range of biological activities. A subset of benzoxaboroles have antimicrobial activity due primarily to their ability to inhibit leucyl-tRNA synthetase (LeuRS) via the oxaborole tRNA-trapping mechanism, which involves the formation of a stable tRNALeu-benzoxaborole adduct in which the boron atom interacts with the 2'- and 3'-oxygen atoms of the terminal 3' tRNA adenosine. We sought to identify other antibacterial targets for this promising class of compounds by means of mode-of-action studies, and we selected a nitrophenyl sulfonamide based oxaborole (PT638) as a probe molecule because it had potent antibacterial activity (MIC of 0.4 µg/mL against methicillin-resistant Staphylococcus aureus) but did not inhibit LeuRS (IC50 > 100 µM). Analogues of PT638 were synthesized to explore the importance of the sulfonamide linker and the impact of altering the functionalization of the phenyl ring. These structure-activity-relationship studies revealed that the nitro substituent was essential for activity. To identify the target for PT638, we raised resistant strains of S. aureus, and whole-genome sequencing revealed mutations in leuRS, suggesting that the target for this compound was indeed LeuRS, despite the lack of enzyme inhibition. Subsequent analysis of PT638 metabolism demonstrated that bacterial nitroreductases readily converted this compound into the amino analogue, which inhibited LeuRS with an IC50 of 3.0 ± 1.2 µM, demonstrating that PT638 is thus a prodrug.

Biochemical, Kinetic, and Computational Structural Characterization of Shikimate Kinase from Methicillin-Resistant Staphylococcus aureus.

One of the most widespread pathogens worldwide is methicillin-resistant Staphylococcus aureus, a bacterium that provokes severe life-threatening illnesses both in hospitals and in the community. The principal challenge lies in the resistance of MRSA to current treatments, which encourages the study of different molecular targets that could be used to develop new drugs against this infectious agent. With this goal, a detailed characterization of shikimate kinase from this microorganism (SaSK) is described. The results showed that SaSK has a Km of 0.153 and 224 µM for shikimate and ATP, respectively, and a global reaction rate of 13.4 µmol/min/mg; it is suggested that SaSK utilizes the Bi-Bi Ping Pong reaction mechanism. Furthermore, the physicochemical data indicated that SaSK is an unstable, hydrophilic, and acidic protein. Finally, structural information showed that SaSK presented folding that is typical of its homologous counterparts and contains the typical domains of this family of proteins. Amino acids that have been shown to be important for SaSK protein function are conserved. Therefore, this study provides fundamental information that may aid in the design of inhibitors that could be used to develop new antibacterial agents.

Synthesis and anti-staphylococcal activity of novel bacterial topoisomerase inhibitors with a 5-amino-1,3-dioxane linker moiety.

Novel bacterial type II topoisomerase inhibitors (NBTIs) constitute a promising new class of antibacterial agents. We report a series of NBTIs with potent anti-staphylococcal activity and diminished hERG inhibition. Dioxane-linked compound 9 demonstrated MICs ≤1 µg/mL against both methicillin-susceptible (MSSA) and -resistant Staphylococcus aureus (MRSA), accompanied by reduced hERG inhibition as compared to cyclohexane- or piperidine-linked analogs.

A novel STK1-targeted small-molecule as an "antibiotic resistance breaker" against multidrug-resistant Staphylococcus aureus.

Ser/Thr protein kinase (STK1) plays a critical role in cell wall biosynthesis of and drug resistance in methicillin-resistant Staphylococcus aureus (MRSA). MRSA strains lacking STK1 become susceptible to failing cephalosporins, such as Ceftriaxone and Cefotaxime. STK1, despite being nonessential protein for MRSA survival, it can serve as an important therapeutic agent for combination therapy. Here, we report a novel small molecule quinazoline compound, Inh2-B1, which specifically inhibits STK1 activity by directly binding to its ATP-binding catalytic domain. Functional analyses encompassing in vitro growth inhibition of MRSA, and in vivo protection studies in mice against the lethal MRSA challenge indicated that at high concentration neither Inh2-B1 nor Ceftriaxone or Cefotaxime alone was able to inhibit the growth of bacteria or protect the challenged mice. However, the growth of MRSA was inhibited, and a significant protection in mice against the bacterial challenge was observed at a micromolar concentration of Ceftriaxone or Cefotaxime in the presence of Inh2-B1. Cell-dependent minimal to no toxicity of Inh2-B1, and its abilities to down-regulate cell wall hydrolase genes and disrupt the biofilm formation of MRSA clearly indicated that Inh2-B1 serves as a therapeutically important "antibiotic-resistance-breaker," which enhances the bactericidal activity of Ceftriaxone/Cefotaxime against highly pathogenic MRSA infection.

Rapid and low-cost biosensor for the detection of Staphylococcus aureus.

Staphylococcus aureus (S. aureus) is one of the most common etiological agents in hospital-acquired infections and food-borne illness. S. aureus toxins and virulence proteases often circulate in host blood vessels leading to life-threatening diseases. Standard identification approaches include bacterial culturing method, which takes several days. Other nucleic acid-based methods were expensive and required trained personnel. To surmount these limitations, a paper-based biosensor was developed. The sensing mechanism was based on the proteolytic activity of S. aureus proteases on a specific peptide substrate, sandwiched between magnetic nanobeads and gold surface on top of a paper support. An external magnet was fixed on the back of the sensor to accelerate the cleavage of the magnetic nanobeads-peptide moieties away from the sensor surface upon test sample dropping. The colour change resulting from the dissociation of the magnetic nanobeads moieties was detected by the naked eye and analysed using ImageJ analysis software for the purpose of quantitative measurement. Experimental results showed detection limits as low as 7, 40 and 100 CFU/mL for S. aureus in pure broth culture, and inoculated in food produces and environmental samples, respectively upon visual observation. The specificity of the sensor was examined by blind testing a panel of food-contaminating pathogens (Listeria monocytogenesis 19115 and E. coli O157:H7), clinical isolates (methicillin-resistant S. aureus (MRSA) and Candida albicans) and standard (Pseudomonas aeruginosa 15692) pathogens. Negative read-out was observed by the naked eye for all tested isolates except for MRSA. Moreover, this sensing tool requires minute's time to obtain the results. In conclusion, this sensing platform is a powerful tool for the detection of S. aureus as a potential point-of-care diagnostic platform in hospitals and for use by regulatory agencies for better control of health-risks associated with contaminated food consumption.

Distribution of methicillin-resistant coagulase-positive staphylococci (MRCoPS) in a surgical unit and cystotomy operation sites in a veterinary teaching hospital.

This study aimed to investigate the spread of methicillin-resistant coagulase-positive staphylococci (MRCoPS) among veterinary staff, hand-touch sites and surgical tissue during cystotomy operations on cats and dogs that were patients, and to analyze the genetic relatedness and antimicrobial resistance profiles of the isolates. Human and environmental samples were obtained from the nasal passageways of 12 surgeons and veterinary assistants and from 29 hand-touch sites of instruments in operative units and subjected to bacterial isolation and enumeration. Swab samples were collected in triplicate from 29 dogs and three cats at the site of incision, from the incision area, from the peritoneum during surgery and from the peritoneum before suture. MRCoPS were identified by mecA gene detection and characterized by their antibiogram profile, SCCmec type and pulsed-field gel electrophoresis. Twenty-four staphylococci were isolated, derived from one veterinary assistant, 12 operating room floor areas and hand-touch sites, three dogs and one cat. Methicillin-resistant S. pseudintermedius (MRSP) was found on an electric clipper and rebreathing circuits in the operating room. Three dogs were positive for MRSP during surgery, and one methicillin-resistant S. aureus (MRSA) was detected in a cat. All MRCoPS were resistant to doxycycline, erythromycin, clindamycin and enrofloxacin, but no patients developed surgical site infections. According to their genotypic patterns, the clones obtained from the environment and human sources differed from the animal clones. Despite intensive hygienic management, a variety of MRCoPS clones were present within the surgical unit and during surgery.

Design, Synthesis and Evaluation of Triazole-Pyrimidine Analogues as SecA Inhibitors.

SecA, a key component of the bacterial Sec-dependent secretion pathway, is an attractive target for the development of new antimicrobial agents. Through a combination of virtual screening and experimental exploration of the surrounding chemical space, we identified a hit bistriazole SecA inhibitor, SCA-21, and studied a series of analogues by systematic dissections of the core scaffold. Evaluation of these analogues allowed us to establish an initial structure-activity relationship in SecA inhibition. The best compounds in this group are potent inhibitors of SecA-dependent protein-conducting channel activity and protein translocation activity at low- to sub-micromolar concentrations. They also have minimal inhibitory concentration (MIC) values against various strains of bacteria that correlate well with the SecA and protein translocation inhibition data. These compounds are effective against methicillin-resistant Staphylococcus aureus strains with various levels of efflux pump activity, indicating the capacity of SecA inhibitors to null the effect of multidrug resistance. Results from studies of drug-affinity-responsive target stability and protein pull-down assays are consistent with SecA as a target for these compounds.

Evaluation of small molecule SecA inhibitors against methicillin-resistant Staphylococcus aureus.

Due to the emergence and rapid spread of drug resistance in bacteria, there is an urgent need for the development of novel antimicrobials. SecA, a key component of the general bacterial secretion system required for viability and virulence, is an attractive antimicrobial target. Earlier we reported that systematical dissection of a SecA inhibitor, Rose Bengal (RB), led to the development of novel small molecule SecA inhibitors active against Escherichia coli and Bacillus subtilis. In this study, two potent RB analogs were further evaluated for activities against methicillin-resistant Staphylococcus aureus (MRSA) strains and for their mechanism of actions. These analogs showed inhibition on the ATPase activities of S. aureus SecA1 (SaSecA1) and SecA2 (SaSecA2), and inhibition of SaSecA1-dependent protein-conducting channel. Moreover, these inhibitors reduce the secretion of three toxins from S. aureus and exert potent bacteriostatic effects against three MRSA strains. Our best inhibitor SCA-50 showed potent concentration-dependent bactericidal activity against MRSA Mu50 strain and very importantly, 2-60 fold more potent inhibitory effect on MRSA Mu50 than all the commonly used antibiotics including vancomycin, which is considered the last resort option in treating MRSA-related infections. Protein pull down experiments further confirmed SaSecA1 as a target. Deletion or overexpression of NorA and MepA efflux pumps had minimal effect on the antimicrobial activities against S. aureus, indicating that the effects of SecA inhibitors were not affected by the presence of these efflux pumps. Our studies show that these small molecule analogs target SecA functions, have potent antimicrobial activities, reduce the secretion of toxins, and have the ability to overcome the effect efflux pumps, which are responsible for multi-drug resistance. Thus, targeting SecA is an attractive antimicrobial strategy against MRSA.

An exhaustive yet simple virtual screening campaign against Sortase A from multiple drug resistant Staphylococcus aureus.

Methicillin resistant Staphylococcus aureus (MRSA) is one of the challenging bacterial pathogen due to its acquired resistance to the ß lactam antibiotics. The Sortase A is an enzyme of Gram-positive bacteria including S. aureus to anchor surface proteins to the cell wall. Sortase A is well studied enzyme and considered as the drug target against MRSA. Sortase A plays active role in anchoring the virulence proteins on the cell wall of the Gram-positive bacteria. The inhibition of Sortase A activity results in the separation of S. aureus from the host cells and ultimately alleviation of the infection. Here, we adapted a structure-based virtual screening protocol which helped in identification of novel potential inhibitors of Sortase A. The protocol involved the docking of a chemical library of druglike compounds with the Sortase A binding site represented by multiple crystal structures. The compounds were ranked by multiple scoring functions and shortlisted for future experimental screening. The method resulted in shortlisting of three compounds as potential novel inhibitors of Sortase A out of a large chemical library. The high rankings of shortlisted compounds estimated by multiple scoring functions showed their binding potential with Sortase A. The results are proved to be a simple yet efficient choice of structure-based virtual screening. The identified compounds are druglike and show high rankings among all set protocols of the virtual screening. We hope that the study would eventually help to expedite the discovery of novel drug candidates against MRSA.