Recent advances in studies on FtsZ inhibitors

With the abuse of antibiotics, multidrug resistant strains continue to emerge and spread rapidly. Therefore, there is an urgent need to develop new antimicrobial drugs. As a highly conserved cell division protein in bacteria, filamenting temperature-sensitive mutant Z (FtsZ) has been identified as a potential antimicrobial target. This paper reviews the structure, function, and action mechanism of FtsZ and a variety of natural and synthetic compounds targeting FtsZ, including 3-MBA derivatives, taxane derivatives, cinnamaldehyde, curcumin, quinoline and quinazoline derivatives, aromatic compounds, purpurin, and totarol. From these studies, FtsZ has a clear supporting role in the field of antimicrobial drug discovery. The urgent need and interest of antibacterial drugs will contribute to the discovery of new clinical drugs targeting FtsZ.

In Vitro Activities of Oxazolidinone Antibiotics Alone and in Combination with C-TEMPO against Methicillin-Resistant Staphylococcus aureus Biofilms

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a global health concern. The propensity of MRSA to form biofilms is a significant contributor to its pathogenicity. Strategies to treat biofilms often involve small molecules that disperse the biofilm into planktonic cells. Linezolid and, by extension, theoxazolidinones have been developed to treat infections caused by Gram-positive bacteria such as MRSA. However, the clinical development of these antibiotics has mainly assessed the susceptibility of planktonic cells to the drug. Previous studies evaluating the anti-biofilm activity of theoxazolidinones have mainly focused on the biofilm inhibition of Enterococcus faecalis and methicillin-sensitive Staphylococcus aureus, with only a few studies investigating the activity of oxazolidinones for eradicating established biofilms for these species. Very little is known about the ability of oxazolidinones to eradicate MRSA biofilms. In this work, five oxazolidinones were assessed against MRSA biofilms using a minimum biofilm eradication concentration (MBEC) assay. All oxazolidinones had inherent antibiofilm activity. However, only ranbezolid could completely eradicate MRSA biofilms at clinically relevant concentrations. The susceptibility of the MRSA biofilms to ranbezolid was synergistically enhanced by coadministration with the nitroxide biofilm dispersal agent C-TEMPO. We presume that ranbezolid acts as a dual warhead drug, which combines the mechanism of action of the oxazolidinones with a nitric oxide donor or cytotoxic drug.

Anthraquinones as Potential Antibiofilm Agents Against Methicillin-Resistant Staphylococcus aureus

Biofilms formed by methicillin-resistant Staphylococcus aureus (MRSA) are one of the contributing factors to recurrent nosocomial infection in humans. There is currently no specific treatment targeting on biofilms in clinical trials approved by FDA, and antibiotics remain the primary therapeutic strategy. In this study, two anthraquinone compounds isolated from a rare actinobacterial strain Kitasatospora albolonga R62, 3,8-dihydroxy-l-methylanthraquinon-2-carboxylic acid (1) and 3,6,8-trihydroxy-1-methylanthraquinone-2-carboxylic acid (2), together with their 10 commercial analogs 3-12 were evaluated for antibacterial and antibiofilm activities against MRSA, which led to the discovery of two potential antibiofilm anthraquinone compounds anthraquinone-2-carboxlic acid (6) and rhein (12). The structure-activity relationship analysis of these anthraquinones indicated that the hydroxyl group at the C-2 position of the anthraquinone skeleton played an important role in inhibiting biofilm formation at high concentrations, while the carboxyl group at the same C-2 position had a great influence on the antibacterial activity and biofilm eradication activity. The results of crystal violet and methyl thiazolyl tetrazolium staining assays, as well as scanning electron microscope and confocal scanning laser microscopy imaging of compounds 6 and 12 treatment groups showed that both compounds could disrupt preformed MRSA biofilms possibly by killing or dispersing biofilm cells. RNA-Seq was subsequently used for the preliminary elucidation of the mechanism of biofilm eradication, and the results showed upregulation of phosphate transport-related genes in the overlapping differentially expressed genes of both compound treatment groups. Herein, we propose that anthraquinone compounds 6 and 12 could be considered promising candidates for the development of antibiofilm agents.

Physicochemical properties of antibiotics: A review with an emphasis on detection in the aquatic environment

Antibiotics have extensively been applied to rescue a great number of lives through prevention and treatment of contagious diseases and infections. They are either natural or human-made substances, which are broadly employed for promoting the health condition of human, plant, and animal. However, antibiotics are known to exert detrimental impacts on useful and nontarget microbiota of the biological system due to the overuse, continuous discharge into the environment, and subsequently aggregation in various environmental matrices. Physical and chemical properties help to evaluate whether a substance is more likely to concentrate on the terrestrial, aquatic, or atmospheric environmental matrix as well as its fate. Therefore, appropriate characterization and proper understanding of physicochemical attributes of antibiotics are indispensable to protect ecosystem health. In this paper, the antibiotic classifications and their physicochemical properties were reviewed with emphasis on detection in the aqueous environment. PRACTITIONER POINTS: Antibiotic compounds were classified in main classes, groups, and their main use. Tetracyclines, sulfonamides, aminoglycosides, macrolides, β-lactams, quinolones, polyether ionophores, and glycopeptides are the most commonly detected antibiotics in the aquatic environment. Physical-chemical properties of the main antimicrobial classes were mentioned. Physicochemical properties can change under different environmental conditions such as pH and temperature.

An experiment-informed signal transduction model for the role of the Staphylococcus aureus MecR1 protein in β-lactam resistance

The treatment of hospital- and community-associated infections by methicillin-resistant Staphylococcus aureus (MRSA) is a perpetual challenge. This Gram-positive bacterium is resistant specifically to β-lactam antibiotics, and generally to many other antibacterial agents. Its resistance mechanisms to β-lactam antibiotics are activated only when the bacterium encounters a β-lactam. This activation is regulated by the transmembrane sensor/signal transducer proteins BlaR1 and MecR1. Neither the transmembrane/metalloprotease domain, nor the complete MecR1 and BlaR1 proteins, are isolatable for mechanistic study. Here we propose a model for full-length MecR1 based on homology modeling, residue coevolution data, a new extensive experimental mapping of transmembrane topology, partial structures, molecular simulations, and available NMR data. Our model defines the metalloprotease domain as a hydrophilic transmembrane chamber effectively sealed by the apo-sensor domain. It proposes that the amphipathic helices inserted into the gluzincin domain constitute the route for transmission of the β-lactam-binding event in the extracellular sensor domain, to the intracellular and membrane-embedded zinc-containing active site. From here, we discuss possible routes for subsequent activation of proteolytic action. This study provides the first coherent model of the structure of MecR1, opening routes for future functional investigations on how β-lactam binding culminates in the proteolytic degradation of MecI.

Evaluation of Telavancin Alone and Combined with Ceftaroline or Rifampin against Methicillin-Resistant Staphylococcus aureus in an In Vitro Biofilm Model

Infections caused by biofilm-producing methicillin-resistant Staphylococcus aureus (MRSA) bacteria are challenging due to increasing antibiotic resistance. Synergistic activities of lipopeptides and lipoglycopeptides with β-lactams have been demonstrated for MRSA, but little is known about biofilm-embedded organisms. Our objective was to evaluate two telavancin (TLV) dosage regimens (7.5 mg/kg of body weight and 10 mg/kg every 24 h [q24h]) alone and in combination with ceftaroline (CPT) (600 mg every 8 h [q8h]) or rifampin (RIF) (450 mg every 12 h [q12h]) against two biofilm-producing MRSA strains (494 and N315). Pharmacokinetic/pharmacodynamic CDC biofilm reactor models with polyurethane coupons were used to evaluate the efficacies of the antibiotic combinations over 72 h. Overall, there were no significant differences observed between the two TLV dosing regimens either alone or in combination with RIF or CPT against these strains. Both TLV dosing regimens and CPT alone demonstrated killing but did not reach bactericidal reduction at 72 h. However, both TLV regimens in combination with RIF demonstrated enhanced activity against both strains, with a rapid decrease in CFU/ml at 4 h that was bactericidal and maintained over the 72-h experiment (-Δ3.75 log10 CFU/ml from baseline; P < 0.0001). Of interest, no enhanced activity was observed for TLV combined with CPT. No development of resistance was observed in any of the combination models. However, resistance to RIF developed as early as 24 h, with MIC values exceeding 32 mg/liter. Our results show that TLV plus RIF displayed therapeutic improvement against biofilm-producing MRSA. These results suggest that TLV at 7.5 and 10 mg/kg q24h are equally effective in eradicating biofilm-associated MRSA strains in vitro.

Antimicrobial resistance in healthcare, agriculture and the environment: the biochemistry behind the headlines

The crisis of antimicrobial resistance (AMR) is one of the most serious issues facing us today. The scale of the problem is illustrated by the recent commitment of Heads of State at the UN to coordinate efforts to curb the spread of AMR infections. In this review, we explore the biochemistry behind the headlines of a few stories that were recently published in the public media. We focus on examples from three different issues related to AMR: (i) hospital-acquired infections, (ii) the spread of resistance through animals and/or the environment and (iii) the role of antimicrobial soaps and other products containing disinfectants in the dissemination of AMR. Although these stories stem from three very different settings, the underlying message in all of them is the same: there is a direct relationship between the use of antimicrobials and the development of resistance. In addition, one type of antimicrobial could select for cross-resistance to another type and/or for multidrug resistance. Therefore, we argue the case for increased stewardship to not only cover clinical use of antibiotics, but also the use of antimicrobials in agriculture and stewardship of our crucially important biocides such as chlorhexidine.

In Vitro and In Vivo Activities of a Bi-Aryl Oxazolidinone, RBx 11760, against Gram-Positive Bacteria

RBx 11760, a bi-aryl oxazolidinone, was investigated for antibacterial activity against Gram-positive bacteria. The MIC₉₀s of RBx 11760 and linezolid against Staphylococcus aureus were 2 and 4 mg/liter, against Staphylococcus epidermidis were 0.5 and 2 mg/liter, and against Enterococcus were 1 and 4 mg/liter, respectively. Similarly, against Streptococcus pneumoniae the MIC₉₀s of RBx 11760 and linezolid were 0.5 and 2 mg/liter, respectively. In time-kill studies, RBx 11760, tedizolid, and linezolid exhibited bacteriostatic effect against all tested strains except S. pneumoniae RBx 11760 showed 2-log₁₀ kill at 4× MIC while tedizolid and linezolid showed 2-log₁₀ and 1.4-log₁₀ kill at 16× MIC, respectively, against methicillin-resistant S. aureus (MRSA) H-29. Against S. pneumoniae 5051, RBx 11760 showed bactericidal activity, with 4.6-log₁₀ kill at 4× MIC compared to 2.42-log₁₀ and 1.95-log₁₀ kill for tedizolid and linezolid, respectively, at 16× MIC. RBx 11760 showed postantibiotic effects (PAE) at 3 h at 4 mg/liter against MRSA H-29, and linezolid showed the same effect at 16 mg/liter. RBx 11760 inhibited biofilm production against methicillin-resistant S. epidermidis (MRSE) ATCC 35984 in a concentration-dependent manner. In a foreign-body model, linezolid and rifampin resulted in no advantage over stasis, while the same dose of RBx 11760 demonstrated a significant killing compared to the initial control against S. aureus (P < 0.05) and MRSE (P < 0.01). The difference in killing was statistically significant for the lower dose of RBx 11760 (P < 0.05) versus the higher dose of linezolid (P > 0.05 [not significant]) in a groin abscess model. In neutropenic mouse thigh infection, RBx 11760 showed stasis at 20 mg/kg of body weight, whereas tedizolid showed the same effect at 40 mg/kg. These data support RBx 11760 as a promising investigational candidate.

Successful infection control for a vancomycin-intermediate Staphylococcus aureus outbreak in an advanced emergency medical service centre

BACKGROUND

A vancomycin-intermediate Staphylococcus aureus (VISA) (vancomycin minimum inhibitory concentration: 4mg/L) outbreak occurred in an advanced emergency medical service centre [hereafter referred to as the intensive care unit (ICU)] between 2013 and 2014.

AIM

Our objective was to evaluate the infection control measures that were successful.

METHODS

Seventeen VISA strains were isolated from the sputum of 15 inpatients and the skin of two inpatients. Fourteen VISA strains were recognized as colonization. However, three VISA strains were isolated from the sputum of three inpatients with pneumonia. Environmental cultures were performed and VISA strains were detected in five of 65 sites. Pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) was performed on 21 VISA strains.

FINDINGS

Molecular typing including PFGE and MLST showed that the patterns of 19 VISA strains were identical and those of the other two VISA strains were possibly related. This meant that a horizontal transmission of VISA strains had occurred in the ICU. In August 2013, the infection control team began interventions. However, new inpatients with VISA strains continued to appear. Therefore, in October 2013, the ICU was partially closed in order to try to prevent further horizontal transmission, and existing inpatients with the VISA strain were isolated. Although new cases quickly dissipated after the partial closure, it took approximately five months to eradicate the VISA outbreak.

CONCLUSION

Our data suggest that despite the employment of various other infection control measures, partial closure of the ICU was essential in terminating this VISA outbreak.

Prevalence of vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA among methicillin-resistant S. aureus with high vancomycin minimal inhibitory concentrations in Taiwan: A multicenter surveillance study, 2012-2013

BACKGROUND/PURPOSE

Intermediate-resistance and heteroresistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) is reported worldwide. A surveillance study in 2003 showed that the prevalence rates of vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) in Taiwan were 0.2% and 0.7%, respectively. This study aimed to investigate the updated prevalence of VISA and hVISA in Taiwan.

METHODS

MRSA isolates from sterile sites with minimal inhibitory concentrations (MICs) of 1 μg/mL or more to vancomycin were collected from 15 participating hospitals in Taiwan. Enrolled MRSA isolates were submitted to antimicrobial susceptibility testing, staphylococcal cassette chromosome mec (SCCmec) element typing, and multilocus sequence typing. Isolates with vancomycin MIC of 1 μg/mL or 2 μg/mL were screened for vancomycin heterogeneous resistance by Etest glycopeptide-resistance detection (GRD). Those with positive GRD screening results were then analyzed by modified population analysis profiling-area under the curve method for confirmation of vancomycin heteroresistance.

RESULTS

Between 2012 and 2013, a total of 622 MRSA isolates from sterile sites with vancomycin MIC of 1 μg/mL or more were studied. The prevalence rates of hVISA and VISA among these isolates were 10.0% and 2.7%, respectively. The hVISA prevalence increased significantly compared to that in 2003. Compared with vancomycin-susceptible S. aureus, hVISA and VISA isolates were less susceptible to ciprofloxacin, clindamycin, daptomycin, gentamicin, rifampin, and trimethoprim/sulfamethoxazole, and are thus, more likely to have SCCmec II or III element. A twofold increase in either vancomycin or teicoplanin MIC doubled the probability of being hVISA.

CONCLUSION

Growing hVISA prevalence was highly suspected. Longitudinal surveillance of this phenomenon and monitoring of its clinical impact are necessary.

Antibiotics and bacterial resistance in the 21st century

Dangerous, antibiotic resistant bacteria have been observed with increasing frequency over the past several decades. In this review the factors that have been linked to this phenomenon are addressed. Profiles of bacterial species that are deemed to be particularly concerning at the present time are illustrated. Factors including economic impact, intrinsic and acquired drug resistance, morbidity and mortality rates, and means of infection are taken into account. Synchronously with the waxing of bacterial resistance there has been waning antibiotic development. The approaches that scientists are employing in the pursuit of new antibacterial agents are briefly described. The standings of established antibiotic classes as well as potentially emerging classes are assessed with an emphasis on molecules that have been clinically approved or are in advanced stages of development. Historical perspectives, mechanisms of action and resistance, spectrum of activity, and preeminent members of each class are discussed.

Development of a PCR-free electrochemical point of care test for clinical detection of methicillin resistant Staphylococcus aureus (MRSA)

An MRSA assay requiring neither labeling nor amplification of target DNA has been developed. Sequence specific binding of fragments of bacterial genomic DNA is detected at femtomolar concentrations using electrochemical impedance spectroscopy (EIS). This has been achieved using systematic optimisation of probe chemistry (PNA self-assembled monolayer film on gold electrode), electrode film structure (the size and nature of the chemical spacer) and DNA fragmentation, as these are found to play an important role in assay performance. These sensitivity improvements allow the elimination of the PCR step and DNA labeling and facilitate the development of a simple and rapid point of care test for MRSA. Assay performance is then evaluated and specific direct detection of the MRSA diagnostic mecA gene from genomic DNA, extracted directly from bacteria without further treatment is demonstrated for bacteria spiked into saline (10(6) cells per mL) on gold macrodisc electrodes and into human wound fluid (10(4) cells per mL) on screen printed gold electrodes. The latter detection level is particularly relevant to clinical requirements and point of care testing where the general threshold for considering a wound to be infected is 10(5) cells per mL. By eliminating the PCR step typically employed in nucleic acid assays, using screen printed electrodes and achieving sequence specific discrimination under ambient conditions, the test is extremely simple to design and engineer. In combination with a time to result of a few minutes this means the assay is well placed for use in point of care testing.

Antibiotic susceptibility survey of blood-borne MRSA isolates in Japan from 2008 through 2011

We conducted an antibiotic susceptibility survey of 830 blood-borne methicillin resistant Staphylococcus aureus collected from nationwide hospitals in Japan over a three-year period from January 2008 through May 2011. Antibiotic susceptibility was judged according to the criteria recommended by the Clinical Laboratory Standard Institute. Over 99% of the MRSA showed to be susceptible to teicoplanin, linezolid, sulfamethoxazole/trimethoprim and vancomycin, and over 97% of them were susceptible to daptomycin, arbekacin and rifampin. The majority of the MRSA strains showed resistant to minocycline, meropenem, imipenem, clindamycin, ciprofloxacin, cefoxitin, and oxacillin in the rates of 56.6, 72.9, 73.7, 78.7, 89.0, 99.5, and 99.9%, respectively. Among the MRSA strains, 72 showed reduced susceptibility to vancomycin, including 8 strains (0.96%) of vancomycin-intermediate S. aureus (VISA), 54 (6.51%) of heterogeneous vancomycin-intermediate S. aureus (hVISA), and 55 (5.63%) of β-lactam antibiotics-induced vancomycin resistant S. aureus (BIVR). Unexpectedly, among the 54 hVISA and 55 BIVR, 45 isolates (83.3% and 81.8%, respectively) showed both hVISA and BIVR phenotypes. A new trend of vancomycin resistance found in this study was that VISA strains were still prevalent among the bacteremic specimens. The high rates of the hVISA/BIVR two-phenotypic vancomycin resistance, and the prevalence of VISA in the bloodborne MRSA call attention in the MRSA epidemiology in Japan.

Advances in MRSA drug discovery: where are we and where do we need to be?

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) have been on the increase during the past decade, due to the steady growth of the elderly and immunocompromised patients, and the emergence of multidrug-resistant (MDR) bacterial strains. Although there are a limited number of anti-MRSA drugs available, a number of different combination antimicrobial drug regimens have been used to treat serious MRSA infections. Thus, the addition of several new antistaphylococcal drugs into clinical practice should broaden clinician's therapeutic options. As MRSA is one of the most common and problematic bacteria associated with increasing antimicrobial resistance, continuous efforts for the discovery of lead compounds as well as development of alternative therapies and faster diagnostics are required.

AREAS COVERED

This article summarizes the FDA-approved drugs to treat MRSA infections, the drugs in clinical trials, and the drug leads for MRSA and related Gram-positive bacterial infections. In addition, the article discusses the mode of action of antistaphylococcal molecules and the resistant mechanisms of some molecules.

EXPERT OPINION

The number of pipeline drugs presently undergoing clinical trials is not particularly encouraging. There are limited and rather expensive therapeutic options for MRSA infections in the critically ill. Further research efforts are required for effective phage therapy on MRSA infections in clinical use, which seem to be attractive therapeutic options for the future.

Hyaluronidase expression and biofilm involvement in Staphylococcus aureus UAMS-1 and its sarA, agr and sarA agr regulatory mutants

In a previous study, two proteins identified as hyaluronidases were detected in spent media by MS and found to be in greater quantity in the sarA and sarA agr mutant strains when compared with the parent and agr mutant strains of Staphylococcus aureus UAMS-1. In the present study, spent media and total RNA were isolated from UAMS-1 and its regulatory mutants and analysed for hyaluronidase activity and steady-state hyaluronidase (hysA) RNA message levels. Hyaluronidase activity was observed throughout all time points examined regardless of the regulatory effects of sarA and agr but activity was always substantially higher in the sarA and sarA agr mutant strains than in the UAMS-1 parent and agr mutant strains. Northern analysis did not detect hysA message for either the UAMS-1 parent or the agr mutant strains at any time point examined, while steady-state hysA message levels were detected throughout growth for the sarA mutant strain, but only at exponential and early post-exponential growth for the sarA agr mutant strain. An in vitro biofilm plate assay, pre-coated with human plasma as a source of hyaluronic acid, demonstrated no significant increase in biofilm for a sarA mutant strain of S. aureus UAMS-1 defective in hyaluronidase activity when compared with the sarA mutant strain. These data indicate that, while hysA message levels and hyaluronidase activity are elevated in the sarA mutant strains of S. aureus UAMS-1, the increase in activity did not contribute to the biofilm-negative phenotype observed in the sarA mutant strain of S. aureus UAMS-1.

Dissection of events in the resistance to β-lactam antibiotics mediated by the protein BlaR1 from Staphylococcus aureus

A heterologous expression system was used to evaluate activation of BlaR1, a sensor/signal transducer protein of Staphylococcus aureus with a central role in resistance to β-lactam antibiotics. In the absence of other S. aureus proteins that might respond to antibiotics and participate in signal transduction events, we documented that BlaR1 fragmentation is autolytic, that it occurs in the absence of antibiotics, and that BlaR1 directly degrades BlaI, the gene repressor of the system. Furthermore, we disclosed that this proteolytic activity is metal ion-dependent and that it is not modulated directly by acylation of the sensor domain by β-lactam antibiotics.

Therapeutic potential of FtsZ inhibition: a patent perspective

INTRODUCTION

Filamentous temperature sensitive mutant Z (FtsZ), an essential protein for bacterial cell division, has emerged as an attractive therapeutic target for the development of efficacious antibacterial agents active against drug-sensitive and drug-resistant bacterial strains. Recently, FtsZ has garnered special attention in the antibacterial research field, which is evident by the amount of research papers and patents disclosed in the public domain. Because of the significance of FtsZ as a highly promising target for the development of novel antibacterial agents, it is timely to review the patents on this subject so far published to date.

AREAS COVERED

This review article covers the patent literature on FtsZ-targeting potential antibacterial agents up to November 2010, including their pharmacological findings.

EXPERT OPINION

Since FtsZ is well preserved in various bacteria, the FtsZ-targeting agents would act as novel broad-spectrum antibacterial drugs in addition to their use against particular bacteria, especially drug-resistant strains. Based on the increasing interest and advancement in this field of research, it looks almost certain that a good number of clinical candidates targeting FtsZ will emerge in the near future.

Binding of the gene repressor BlaI to the bla operon in methicillin-resistant Staphylococcus aureus

The expression of the gene products in many methicillin-resistant Staphylococcus aureus (MRSA) strains is regulated by the gene repressor BlaI. Here we show that BlaI is a mixture of monomer and dimer at in vivo concentrations, binds to the operator regions preferentially as a monomeric protein, and the measured dissociation constants and in vivo concentrations account for the basal level transcription of the resistance genes. These observations for the first time provide a quantitative picture of the processes that take place in the cytoplasm that lead to the induction of antibiotic resistance factors to counter the challenge by β-lactams.

Design, synthesis, and biological evaluation of a novel series of quercetin diacylglucosides as potent anti-MRSA and anti-VRE agents

A series of novel quercetin diacylglucosides were designed and first synthesized by Steglich esterification on the basis of MRSA strains inhibiting natural compound A. The in vitro inhibition of different multi-drug resistant bacterial strains and Escherichia coli DNA gyrase B was investigated. In the series, compound 10h was up to 128-fold more potent against vancomycin-resistant enterococci and more effective than A, which represents a promising new candidate as a potent anti-MRSA and anti-VRE agent.