Current Pharmaceutical Design - Volume 21, Issue 16, 2015

As MRSA are considered Staphylococcus aureus isolates with oxacillin minimum inhibitory concentration (MIC) of ≥4 mg/L or harboring the mecA gene. However, the presence of mecA does not necessarily lead to oxacillin resistance and mecA gene-carrying isolates may have oxacillin MIC within the susceptible range (≥2 mg/L). During the last few years it has become apparent that oxacillin-susceptible (OS) mecA-positive S. aureus isolates (commonly called OS-MRSA) are rather commonly detected worldwide and may remain undiagnosed using phenotypic susceptibility testing methods. This review will summarize the current reports on OS-MRSA isolations and the underlying mechanisms regulating the expression of oxacillin resistance and also oxacillin susceptibility in mecA-positive S. aureus isolates. As MRSA commonly cause severe infections against which effective therapies are limited, understanding of these mechanisms could enable the identification of new targets for the treatment or reversion of the MRSA phenotype.

There is a growing concern by regulatory authorities for the selection of antibiotic resistance caused by the use of biocidal products. We aimed to complete the detailed information on large surveys by investigating the relationship between biocide and antibiotic susceptibility profiles of a large number of Staphylococcus aureus isolates using four biocides and antibiotics commonly used in clinical practice. The minimal inhibitory concentration (MIC) for most clinically-relevant antibiotics was determined according to the standardized methodology for over 1600 clinical S. aureus isolates and compared to susceptibility profiles of benzalkonium chloride, chlorhexidine, triclosan, and sodium hypochlorite. The relationship between antibiotic and biocide susceptibility profiles was evaluated using non-linear correlations. The main outcome evidenced was an absence of any strong or moderate statistically significant correlation when susceptibilities of either triclosan or sodium hypochlorite were compared for any of the tested antibiotics. On the other hand, correlation coefficients for MICs of benzalkonium chloride and chlorhexidine were calculated above 0.4 for susceptibility to quinolones, beta-lactams, and also macrolides. Our data do not support any selective pressure for association between biocides and antibiotics resistance and furthermore do not allow for a defined risk evaluation for some of the compounds. Importantly, our data clearly indicate that there does not involve any risk of selection for antibiotic resistance for the compounds triclosan and sodium hypochlorite. These data hence infer that biocide selection for antibiotic resistance has had so far a less significant impact than feared.

Methicillin-resistant Staphylococcus aureus (MRSA) remains the single biggest challenge in infectious disease in the civilized world. Moreover, vancomycin resistance is also spreading, leading to fears of untreatable infections as were common in ancient times. Molecular microbiology and bioinformatics have revealed many of the mechanisms involved in resistance development. Mobile genetic elements, up-regulated virulence factors and multi-drug efflux pumps have been implicated. A range of approved antibiotics from the glycopeptide, lipopeptide, pleuromutilin, macrolide, oxazolidinone, lincosamide, aminoglycoside, tetracycline, steptogramin, and cephalosporin classes has been employed to treat MRSA infections. The upcoming pipeline of drugs for MRSA includes some new compounds from the above classes, together with fluoroquinolones, antibacterial peptide mimetics, aminomethylciclines, porphyrins, peptide deformylase inhibitors, oxadiazoles, and diaminopyrimidines. A range of non-drug alternative approaches has emerged for MRSA treatment. Bacteriophage-therapy including purified lysins has made a comeback after being discovered in the 1930s. Quorum-sensing inhibitors are under investigation. Small molecule inhibitors of multi-drug efflux pumps may potentiate existing antibiotics. The relative failure of staphylococcal vaccines is being revisited by efforts with multi-valent vaccines and improved adjuvants. Photodynamic therapy uses non-toxic photosensitizers and harmless visible light to produce reactive oxygen species that can nonspecifically destroy bacteria while preserving host cells. Preparation of nanoparticles can kill bacteria themselves, as well as improve the delivery of anti-bacterial drugs. Anti-MRSA drug discovery remains an exciting field with great promise for the future.

The pervasiveness of bacterial resistance to conventional antibiotics, particularly those associated with staphylococcal infections, has become a global epidemic. However, research involving antimicrobial peptides (AMPs) and their synthetic analogues has unearthed a potentially novel class of antibacterials for the treatment of an array of diseases caused by pathogenic bacteria, such as staphylococci. AMPs have several unique advantages over traditional antibiotics such as the projected slow emergence of bacterial resistance to these agents and their capability to modulate the host immune response to infection. Unfortunately, their susceptibility to proteolytic degradation, loss of antimicrobial activity due to serum binding or physiological concentration of salts, and toxicity to host tissues has limited their use as systemic agents thus far. Additionally, the presence of economic and regulatory obstacles has hindered the translation of AMPs, as antimicrobials, from the bench to the clinic. The present review delves further into the benefits and challenges of utilizing AMPs as antibacterial agents (particularly for staphylococcal infections), the methods which have been utilized to overcome their limitations, their successes and failures in clinical trials, and future avenues for researchers to pursue to develop AMPs as novel therapeutic allies in the treatment of bacterial infections.

The development and approval of new antimicrobials capable of being used to treat infections caused by multidrug-resistant pathogens has not kept pace with the rapid emergence of bacterial resistance. Without a doubt, there is a critical unmet need for the identification of novel strategies to develop antimicrobials to deal with this new scourge. One strategy, which warrants special attention as a unique method for identifying new antimicrobials, is drug repurposing. Several approved drugs have been successfully repurposed for different ailments giving hope that this strategy can also be utilized to uncover new antibacterials. To aid in this process, the present review presents non-antimicrobial approved drugs and clinical molecules, which have been shown to possess antimicrobial activity against Staphylococcus aureus and their potential clinical applications. Additionally, approved drugs with novel applications such as interference in staphylococcal pathogenesis and host immunomodulators are also explained. The current review also discusses the challenges associated with repurposing already approved non-antimicrobial drugs as antibacterials and potential uses of these drugs that can be further explored in order to develop novel therapeutics for the treatment of multidrug- resistant staphylococcal infections. Collectively, the information presented demonstrates that repurposing approved drugs and clinical molecules as antimicrobials may help to speed up the drug development process and save years of expensive research invested in antimicrobial drug development.

The Gram-positive, facultative anaerobic coccus-shaped bacteria of the genus Staphylococcus are among the most important causative agents of acute and chronic bacterial infections in humans as well as in animals. Treatment of Staphylococcus infections has become increasingly challenging due to the growing problem of antibiotic resistance. For this reason innovative antimicrobials with novel targets and modes of action are needed. Since the discovery that QS is used by Staphylococcus spp. to coordinate the expression of several genes involved in virulence, biofilm formation and pathogenicity, QS inhibition has gained increasing attention as an alternative anti-pathogenic strategy. A major advantage compared with antibiotic therapy is that QSIs are used in concentrations that do not affect bacterial growth. For this reason, it is expected that these compounds would exert less pressure towards the development of resistance. However, some important points still need to be addressed. Although several inhibitors have proven to be active antipathogenic agents in vitro and in several in vivo models, it is still unknown whether these compounds will also be useful in humans. Furthermore, several fundamental mechanisms by which the different QS systems in Staphylococcus spp. exert their regulatory functions and how they are inhibited by QSIs are still poorly understood. In order to achieve real-life applications with QSIs, these challenges should be addressed and more research will be needed. In this article, we will discuss the different QS systems present in Staphylococcus spp., how they are used to control virulence and biofilm formation and how they can be blocked.

Methicillin-resistant Staphylococcus aureus (MRSA) has become the most important drug-resistant microbial pathogen in countries throughout the world. Morbidity and mortality due to MRSA infections continue to increase despite efforts to improve infection control measures and to develop new antibiotics. Therefore alternative antimicrobial strategies that do not give rise to development of resistance are urgently required. A group of therapeutic interventions has been developed in the field of photomedicine with the common theme that they rely on electromagnetic radiation with wavelengths between 200 and 1000 nm broadly called “light”. These techniques all use simple absorption of photons by specific chromophores to deliver the killing blow to microbial cells while leaving the surrounding host mammalian cells relatively unharmed. Photodynamic inactivation uses dyes called photosensitizers (PS) that bind specifically to MRSA cells and not host cells, and generate reactive oxygen species including singlet oxygen and singlet oxygen upon illumination. Sophisticated molecular strategies to target the PS to MRSA cells have been designed. Ultraviolet C radiation can damage microbial DNA without unduly harming host DNA. Blue light can excite endogenous porphyrins and flavins in MRSA cells that are not present in host cells. Near-infrared lasers can interfere with microbial membrane potentials without raising the temperature of the tissue. Taken together these innovative approaches towards harnessing the power of light suggest that the ongoing threat of MRSA may eventually be defeated.

To evaluate new drugs, the immune system should be considered. Here we evaluated a proof-of-concept that uncovers bacterial-leukocyte interactions. Analyzing longitudinal leukocyte data from bovines infected with either methicillin-resistant (MRSA) or methicillin-susceptible (MSSA) Staphylococcus aureus, two methods were investigated: (i) an approach that assesses lymphocytes, monocytes, or neutrophils, separately, and (ii) a method that, using dimensionless indicators (products, ratios, or combinations derived from leukocyte data), explores the dynamics of leukocyte relationships in three-dimensional (3D) space and identifies data subsets of informative value. The classic approach not always distinguished infected from non-infected cows. In contrast, the alternative approach differentiated noninfected from infected animals and distinguished early MRSA from early MSSA and late MRSA infections. Discrimination was associated with the use of dimensionless indicators. When measured in 3D space, such indicators generated a very large number of combinations, which helped detect data subsets usually unobserved, such as non-overlapping infection-negative and -positive subsets, and several disease stages. The validity of such data subsets was determined with biologically interpretable data. This graphic, pattern recognition-based information system included but did not depend on any one number or variable. Because it can detect functions (relationships that involve two or more elements), in real time, if shown reproducible, the analysis of complex hostmicrobial dynamics could be used to evaluate antimicrobials.

Staphylococcus aureus is a fastidious pathogen of global concern. S. aureus can not only cause a wide range of serious infections, but can also colonize healthy individuals. Nosocomial- associated S. aureus infection is a major concern for healthcare facilities. Recent increases in antibiotic resistance and community-acquired infection highlight the need for improved understanding for prevention and treatment of this pathogen. This minireview addresses the current state of S. aureus prevalence, correlates of immunity, and vaccine development.

Molecular imaging enables noninvasive characterization, quantification and visualization of biological and pathological processes in vivo at cellular and molecular level. It plays an important role in drug discovery and development. The skillful use of molecular imaging can provide unique insights into disease processes, which greatly aid in identifications of target. Importantly, molecular imaging is widely applied in the pharmacodynamics study to provide earlier endpoints during the preclinical drug development process, since it can be applied to monitor the effects of treatment in vivo with the use of biomarkers. Herein, we reviewed the application of molecular imaging technologies in antitumor drug development process ranging from identification of targets to evaluation of therapeutic effect.

Phenylbutyrate (PBA) is an aromatic short-chain fatty acid which is a chemical derivative of butyric acid naturally produced by colonic bacteria fermentation. At the intestinal level butyrate exerts a multitude of activities including amelioration of mucosal inflammation, regulation of transepithelial fluid transport, improvement in oxidative status and colon cancer prevention. Moreover, increasing number of studies report the beneficial role of butyric acid in prevention or inhibition of other types of malignancies, leading to cancer cell growth arrest and apoptosis. Similarly, phenylbutyrate displays potentially favorable effects on many pathologies including cancer, genetic metabolic syndromes, neuropathies, diabetes, hemoglobinopathies, and urea cycle disorders. The mechanisms by which PBA exerts these effects are different. Some of them are connected with the regulation of gene expression, playing the role of a histone deacetylase inhibitor, while others contribute to the ability of rescuing conformational abnormalities of proteins, serving as chemical chaperone, and some are dedicated to its metabolic characteristic enabling excretion of toxic ammonia, thus acting as ammonia scavenger. Phenylbutyrate may exert variable effects depending on the cell type, thus the term “butyrate paradox” has been proposed. These data indicate a broad spectrum of beneficial effects evoked by PBA with a high potential in therapy. In this review, we focus on cellular and systemic effects of PBA treatment with special attention to the three main branches of its molecular activity: ammonia scavenging, chaperoning and histone deacetylase inhibiting, and describe its particular role in various human diseases.