New and emerging treatment of Staphylococcus aureus infections in the hospital setting

From garden to lab: C-3 chemical modifications of tomatidine unveil broad-spectrum ATP synthase inhibitors to combat bacterial resistance

Antibiotic resistance is escalating alarmingly worldwide. Bacterial resistance mechanisms are surfacing and proliferating across the globe, jeopardizing our capacity to manage prevalent infectious illnesses. Without drastic measures, we risk entering a post-antibiotic era, where even trivial infections and injuries can cause death again. In this context, we have developed a new class of antibiotics based on tomatidine (TO), a natural product derived from tomato plants, with a novel mode of action by targeting bacterial ATP synthases. The first generation of compounds proved highly specific for small-colony variants (SCVs) of Staphylococcus aureus. However, optimization of this scaffold through extensive structure-activity relationship studies has enabled us to broaden its effectiveness to include both Gram-positive and Gram-negative bacteria. Notably, the results showed that specific C3-modification of TO could improve ATP synthase inhibition and also bypass the outer membrane barrier of Gram-negative bacteria to gain substantial growth inhibition including against multi-resistant strains.

Cloning, Purification, and Biophysical Characterization of FemB Protein from Methicillin-Resistant Staphylococcus aureus and Inhibitors Screening

Methicillin-resistant Staphylococcus aureus has emerged as a leading cause of nosocomial, community acquired infections worldwide. Earlier investigations revealed that mecA-encoded FEM proteins play a role in antimicrobial resistance by developing unique peptidoglycan cross-linking which helps in the formation of protective cell membrane. In view to this, present study focused on expression, purification FEM proteins, and FemB biophysical characterization with the aid of in silico and in vitro approaches. Furthermore, we carried out biological screening assays and identified the novel potent 1,2,3-triazole conjugated 1,3,4-oxadiazole hybrid molecule which could inhibit the MRSA than the proven oxacillin.

Epidemiology of Antimicrobial Resistance Genes in Staphyloccocus aureus Isolates from a Public Database in a One Health Perspective-Sample Characteristics and Isolates' Sources

Staphylococcus aureus is considered one of the most widespread bacterial pathogens for both animals and humans, being the causative agent of various diseases like food poisoning, respiratory tract infections, nosocomial bacteremia, and surgical site and cardiovascular infections in humans, as well as clinical and subclinical mastitis, dermatitis, and suppurative infections in animals. Thanks to their genetic flexibility, several virulent and drug-resistant strains have evolved mainly due to horizontal gene transfer and insurgence of point mutations. Infections caused by the colonization of such strains are particularly problematic due to frequently occurring antibiotic resistance, particulary methicillin-resistant S. aureus (MRSA), and are characterized by increased mortality, morbidity, and hospitalization rates compared to those caused by methicillin-sensitive S. aureus (MSSA). S. aureus infections in humans and animals are a prime example of a disease that may be managed by a One Health strategy. In fact, S. aureus is a significant target for control efforts due to its zoonotic potential, the frequency of its illnesses in both humans and animals, and the threat posed by S. aureus antibiotic resistance globally. The results of an epidemiological analysis on a worldwide public database (NCBI Pathogen Detection Isolate Browser; NPDIB) of 35,026 S. aureus isolates were described. We considered the diffusion of antibiotic resistance genes (ARGs), in both human and animal setting, and the results may be considered alarming. The result of this study allowed us to identify the presence of clusters with specific ARG patterns, and that these clusters are associated with different sources of isolation (e.g., human, non-human).

Design, synthesis of pyridine coupled pyrimidinone/pyrimidinthione as anti-MRSA agent: Validation by molecular docking and dynamics simulation

Methicillin Resistant Staphylococcus aureus (MRSA) is a major cause of severe hospital and infections acquired by the population and related morbidity and mortality. In this unique situation, there is a need of dynamic strong drug candidates to control MRSA diseases. Thus, the present work focuses on the synthesis and characterization of pyrimidinones and pyrimidinthiones coupled pyridine derivatives as anti-MRSA agent. The synthesized compounds were characterized by different spectroscopic techniques and evaluated against MRSA strain. Among them, 4e and 4 g possessed better antibacterial activity with MIC values of 10 μg and 8 μg respectively. The key determinant of the wide range beta-lactam resistance in MRSA strains is the Penicillin-Binding Protein 2a (PBP2a) but the gene encodes PBP2a which has a low affinity towards β-lactam antibiotics. Because of this, the present investigation focused on the mechanism of PBP2a protein binding studies by in-silico studies. The synthesized compounds showed very good interactions with PBP2A compared with standard drug Vancomycin, among them compound 4 g showed better interaction with the binding score of -9.8 kcal/mol. Antibacterial activity was validated with molecular docking and molecular dynamic simulation. Simulation results revealed that protein-ligand interactions of 4 g compound stably sustained up to 20,000ps.Communicated by Ramaswamy H. Sarma.

Molecular Mechanisms of Drug Resistance in Staphylococcus aureus

This paper discusses the mechanisms of S. aureus drug resistance including: (1) introduction. (2) resistance to beta-lactam antibiotics, with particular emphasis on the mec genes found in the Staphylococcaceae family, the structure and occurrence of SCCmec cassettes, as well as differences in the presence of some virulence genes and its expression in major epidemiological types and clones of HA-MRSA, CA-MRSA, and LA-MRSA strains. Other mechanisms of resistance to beta-lactam antibiotics will also be discussed, such as mutations in the gdpP gene, BORSA or MODSA phenotypes, as well as resistance to ceftobiprole and ceftaroline. (3) Resistance to glycopeptides (VRSA, VISA, hVISA strains, vancomycin tolerance). (4) Resistance to oxazolidinones (mutational and enzymatic resistance to linezolid). (5) Resistance to MLS-B (macrolides, lincosamides, ketolides, and streptogramin B). (6) Aminoglycosides and spectinomicin, including resistance genes, their regulation and localization (plasmids, transposons, class I integrons, SCCmec), and types and spectrum of enzymes that inactivate aminoglycosides. (7). Fluoroquinolones (8) Tetracyclines, including the mechanisms of active protection of the drug target site and active efflux of the drug from the bacterial cell. (9) Mupirocin. (10) Fusidic acid. (11) Daptomycin. (12) Resistance to other antibiotics and chemioterapeutics (e.g., streptogramins A, quinupristin/dalfopristin, chloramphenicol, rifampicin, fosfomycin, trimethoprim) (13) Molecular epidemiology of MRSA.

Efficiency of Antimicrobial Photodynamic Therapy with Photodithazine® on MSSA and MRSA Strains

Staphylococccus aureus is a ubiquitous and opportunistic bacteria associated with high mortality rates. Antimicrobial photodynamic therapy (aPDT) is based on the application of a light source and a photosensitizer that can interact with molecular oxygen, forming Reactive Oxygen Species (ROS) that result in bacterial inactivation. This study aimed to analyze, in vitro, the action of aPDT with Photodithazine^® (PDZ) in methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) strains. The strains were incubated with PDZ at 25, 50, 75, and 100 mg/L for 15 min and irradiated with fluences of 25, 50, and 100 J/cm². The internalization of PDZ was evaluated by confocal microscopy, the bacterial growth by counting the number of colony-forming units, as well as the bacterial metabolic activity post-aPDT and the production of ROS. In both strains, the photosensitizer was internalized; the production of ROS increased when the aPDT was applied; there was a bacterial reduction compared to the control at all the evaluated fluences and concentrations; and, in most parameters, it was obtained complete inactivation with significant difference (p < 0.05). The implementation of aPDT with PDZ in clinical strains of S. aureus has resulted in its complete inactivation, including the MRSA strains.

In Vitro Selection of High-Level Beta-Lactam Resistance in Methicillin-Susceptible Staphylococcus aureus

Selective pressure of beta-lactams is thought to be responsible for mutation selection in methicillin-susceptible Staphylococcus aureus (MSSA). We used next-generation sequencing to compare the genomes of beta-lactamase-positive (SA0707) and -negative (SA0937) MSSA isolates with their derivatives obtained after selection with oxacillin, ceftaroline, or meropenem. Selection with oxacillin and ceftaroline caused a rapid and significant (6–8 times) increase in the minimum inhibitory concentration (MICs) of oxacillin, penicillin, amoxicillin/clavulanate, and ceftaroline against the derivatives of both isolates, associated with growth impairment. Selection with meropenem caused a limited increase in the MICs of all beta-lactams against both isolates. During the initial stages of selection (after 5–15 passages), mutations were detected only in some reads, which indicated the heterogeneity of the population; however, during the later stages, either the population reversed to the wild type or fixation of the mutation was observed in the entire population. Selection with different beta-lactams caused diverse mutational events, but common mutations were detected in gdpP, all penicillin-binding proteins, cell wall regulators (vraST, graR), and deletions in the promoter region of pbp4. Therefore, the disk diffusion test with cefoxitin does not reveal resistance associated with these mechanisms in some cases, which can lead to the failure of beta-lactam therapy.

Baicalin Weakens Staphylococcus aureus Pathogenicity by Targeting Sortase B

Staphylococcus aureus (S. aureus) is a human and other animal pathogen that contributes to the primary etiology of nosocomial pneumonia, a disease with high mortality rates and costs. Treatment of multidrug-resistant S. aureus infection is extremely challenging, and new therapeutic strategies beyond antibiotic treatment are needed. Anti-virulence agents that specifically target the molecular determinants of virulence may be a novel method for treating drug-resistant nosocomial infections. Sortase B (SrtB) is a crucial virulence factor in S. aureus and plays an important role during infection. In this study, we find that baicalin suppresses the activity of SrtB. Minimum inhibitory concentration and growth curve assays confirmed that baicalin has no anti-S. aureus properties. We performed live/dead, lactate dehydrogenase (LDH), adherence, and enzyme-linked immunosorbent assays to confirm that baicalin reduced human alveolar epithelial A549 cell injury caused by S. aureus, reduced the adherence of S. aureus to A549 cells, and significantly attenuated the inflammatory response of mouse macrophage J774 cells to S. aureus. Additionally, we were able to elucidate the binding mechanics and identify the interacting sites of baicalin and SrtB via a molecular dynamics simulation, site-directed mutagenesis, and fluorescence spectroscopy quenching. Finally, we confirmed that baicalin directly binds to the active center of SrtB, and the residues Asn⁹² and Tyr¹²⁸ perform an important function in the interaction of SrtB and baicalin. Taken together, these data indicate that baicalin is a promising candidate to combat S. aureus infections.

Novel Inhibitor Discovery of Staphylococcus aureus Sortase B and the Mechanism Confirmation via Molecular Modeling

SortaseB (SrtB) plays a critical role in Staphylococcus aureus (S. aureus) infections. According to the reports in the literature, SrtB can anchor the IsdC to the cell wall to capture iron from the host to achieve a successful invasion. On the other hand, SrtB could also affect the adhesion of S. aureus to host cells based on previous studies. Here, we report about a novel SrtB inhibitor, coptisine, a natural compound that does not exhibit antibacterial activity but can inhibit the SrtB activity in vitro. A cytotoxicity test indicated that coptisine protects human lung epithelial cells from S. aureus. In addition, coptisine can reduce the adhesion of S. aureus to human lung epithelial cells based on the result of plate colony counting assay. Molecular dynamics simulation revealed that coptisine can bind to the active pocket of SrtB, leading to its activity loss. Through the calculation of binding free energy between ligand and protein, site-directed mutagenesis and fluorescence spectroscopy quenching methods, it was confirmed that residues of Arg115, Asn116, and Ile182 played a vital role in the interaction of SrtB with coptisine. These data provide the theoretical basis for the therapy option to the infections caused by S. aureus.

Antimicrobial susceptibility pattern of Staphylococcus aureus isolates from clinical specimens at Kenyatta National Hospital

Objective

To determine antibiotic susceptibility pattern of S. aureus isolates from clinical specimens collected from patients at Kenyatta National Hospital from March 2014–February 2016, and to determine the prevalence and quarterly trends of MRSA throughout the study period.

Results

A total of 944 S. aureus isolates were analyzed. High sensitivity of S. aureus was observed for quinupristin/dalfopristin (100%), tigecycline (98.2), imipenem (98%), nitrofurantoin (97.6%), linezolid (97.3%), teicoplanin (97.1%) and vancomycin (95.1%). High resistance was recorded against penicillin G (91.9%), trimethoprim/sulfamethoxazole (56.9%) and tetracycline (33.2%). MRSA prevalence among the patients at KNH was 27.8%. Highest proportion (80%) of MRSA was in burns unit. Both MRSA and MSSA were highly susceptible to quinupristin/dalfopristin, tigecycline, linezolid, nitrofurantoin, ampicillin/sulbactam and vancomycin and showed high resistance to commonly used antibiotics such as gentamycin, erythromycin, levofloxacin and tetracycline. A majority of isolates were from pus specimen (68%).

Efficacy of ampicillin against methicillin-resistant Staphylococcus aureus restored through synergy with branched poly(ethylenimine)

Beta-lactam antibiotics kill Staphylococcus aureus bacteria by inhibiting the function of cell-wall penicillin binding proteins (PBPs) 1 and 3. However, β-lactams are ineffective against PBP2a, used by methicillin-resistant Staphylococcus aureus (MRSA) to perform essential cell wall crosslinking functions. PBP2a requires teichoic acid to properly locate and orient the enzyme, and thus MRSA is susceptible to antibiotics that prevent teichoic acid synthesis in the bacterial cytoplasm. As an alternative, we have used branched poly(ethylenimine), BPEI, to target teichoic acid in the bacterial cell wall. The result is restoration of MRSA susceptibility to the β-lactam antibiotic ampicillin with a MIC of 1 μg/mL, superior to that of vancomycin (MIC = 3.7 μg/mL). A checkerboard assay shows synergy of BPEI and ampicillin. Nuclear magnetic resonance (NMR) data show that BPEI alters the teichoic acid chemical environment. Laser scanning confocal microscopy (LSCM) images show BPEI residing on the bacterial cell wall where teichoic acids and PBPs are located.

Unraveling the structure-activity relationship of tomatidine, a steroid alkaloid with unique antibiotic properties against persistent forms of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is responsible for difficult-to-treat and relapsing infections and constitutes one of the most problematic pathogens due to its multiple resistances to clinically available antibiotics. Additionally, the ability of S. aureus to develop small-colony variants is associated with a reduced susceptibility to aminoglycoside antibiotics and in vivo persistence. We have recently demonstrated that tomatidine, a steroid alkaloid isolated from tomato plants, possesses anti-virulence activity against normal strains of S. aureus as well as the ability to potentiate the effect of aminoglycoside antibiotics. In addition, tomatidine has shown antibiotic activity against small-colony variants of S. aureus. We herein report the first study of the structure-activity relationship of tomatidine against S. aureus.

A positive interaction between inhibitors of protein synthesis and cefepime in the fight against methicillin-resistant Staphylococcus aureus

Quinupristin-dalfopristin (Q-D) synergizes with cefepime for the treatment of methicillin-resistant Staphylococcus aureus (MRSA). Here, we studied whether the synergism was restricted to MRSA and if it extended to non-beta-lactam cell wall inhibitors or to other inhibitors of protein synthesis. Three MRSA and two methicillin-susceptible S. aureus (MSSA) strains were tested, including an isogenic pair of mecA (-)/mecA (+) S. aureus Newman. The drug interactions were determined by fractional inhibitory concentration (FIC) indices and population analysis profiles. The antibacterial drugs that we used included beta-lactam (cefepime) and non-beta-lactam cell wall inhibitors (D-cycloserine, fosfomycin, vancomycin, teicoplanin), inhibitors of protein synthesis (Q-D, erythromycin, chloramphenicol, tetracycline, linezolid, fusidic acid), and polynucleotide inhibitors (cotrimoxazole, ciprofloxacin). The addition of each protein inhibitor to cefepime was synergistic (FIC ≤ 0.5) or additive (FIC > 0.5 but < 1) against MRSA, but mostly indifferent against MSSA (FIC ≥ 1 but ≤ 4). This segregation was not observed after adding cotrimoxazole or ciprofloxacin to cefepime. Population analysis profiles were performed on plates in the presence of increasing concentrations of the cell wall inhibitors plus 0.25 × minimum inhibitory concentration (MIC) of Q-D. Cefepime combined with Q-D was synergistic against MRSA, but D-cycloserine and glycopeptides were not. Thus, the synergism was specific to beta-lactam antibiotics. Moreover, the synergism was not lost against fem mutants, indicating that it acted at another level. The restriction of the beneficial effect to MRSA suggests that the functionality of penicillin-binding protein 2A (PBP2A) was affected, either directly or indirectly. Further studies are necessary in order to provide a mechanism for this positive interaction.

Unprecedented inhibition of resistant penicillin bindingproteins by bis-2-oxoazetidinylmacrocycles

Bis-2-oxoazetidinyl macrocycles, obtained as unexpected products of RCM cyclizations, exhibit good activities against d,d-peptidase from Actinomadura R39 and revealed very promising activities against PBP2a from methicillin-resistant Staphylococcus aureus.

Antibacterial activity of chalcones, hydrazones and oxadiazoles against methicillin-resistant Staphylococcus aureus

The increase in antibiotic resistance due to multiple factors has encouraged the search for new compounds which are active against multidrug-resistant pathogens. In this context, chalcones, dihydrochalcones, hydrazones and oxadiazoles were tested against Staphylococcus aureus ATCC 25923 and methicillin-resistant S. aureus (MRSA) isolates, which were obtained from clinical laboratories and were characterized as MRSA using traditional and molecular methods. Among 65 tested compounds, two chalcones, one dihydrochalcone and two hydrazones were active against MRSA. Based on the minimal inhibitory concentration and cytotoxicity, hydrazones provided a better selectivity index than chalcones. Active hydrazones are promising antibiotic-like substances and they should be the subject of further microbiological studies.

Linezolid interaction with serotonin reuptake inhibitors: report of two cases and incidence assessment

BACKGROUND

Prompted by the advent of potentially life-threatening neuromuscular symptoms following initiation of linezolid therapy in two patients receiving treatment with a serotonin reuptake inhibitor antidepressant, an evaluation was conducted to determine the incidence and characteristics of symptomatic serotonin toxicity among hospitalized patients receiving combined treatment with these medications.

METHODS

Patients admitted between January 1, 2006 and August 30, 2008 who received linezolid concurrently with citalopram or escitalopram were identified and their medical records were examined. Patients were judged to have serotonin toxicity if their records contained documentation of clinical evidence adequate to fulfill requisites of the Hunter Serotonin Toxicity Criteria. Severity of serotonin-related symptoms was graded according to previously established criteria.

RESULTS

During the period of observation, 24 patients received concurrent treatment with linezolid and citalopram or escitalopram. Of these, one patient (4%) treated with citalopram met evidentiary requirements for diagnosis of serotonin toxicity. The severity of symptoms in this patient was graded as mild. No evidence of serious harm related to a possible drug interaction was identified.

CONCLUSIONS

Severe symptoms associated with serotonin toxicity were shown to be uncommon in patients receiving linezolid and selected serotonin reuptake inhibitors. Nonetheless, serious interaction-related toxicity has been observed at our institution and reported in detail by others. Accordingly, concurrent use of these medications is categorized as contraindicated. Alternative antimicrobial therapy should be instituted in most cases. If no suitable alternative is available, recipient patients should be hospitalized for expectant observation and rigorous monitoring.

Critical shortage of new antibiotics in development against multidrug-resistant bacteria-Time to react is now

Two commercial databases (Pharmaprojects and Adis Insight R&D) were queried for antibacterial agents in clinical development. Particular attention was given to antibacterial agents for systemic administration. For each agent, reviewers were requested to indicate whether its spectrum of activity covered a set of selected multidrug-resistant bacteria, and whether it had a new mechanism of action or a new target. In addition, PubMed was searched for antibacterial agents in development that appeared in review articles. Out of 90 agents that were considered to fulfil the inclusion criteria for the analysis, 66 were new active substances. Fifteen of these could be systemically administered and were assessed as acting via a new or possibly new mechanism of action or on a new or possibly new target. Out of these, 12 agents were assessed as having documented in vitro activity against antibiotic-resistant Gram-positive bacteria and only four had documented in vitro activity against antibiotic-resistant Gram-negative bacteria. Of these four, two acted on new or possibly new targets and, crucially, none acted via new mechanisms of action. There is an urgent need to address the lack of effective treatments to meet the increasing public health burden caused by multidrug-resistant bacteria, in particular against Gram-negative bacteria.

Reflection paper on MRSA in food-producing and companion animals: epidemiology and control options for human and animal health

The scope of this reflection paper was to review the latest research on the risk of MRSA infection and colonization in animals. Attention focused on occurrence, risk factors for colonization and infection, and human contact hazard for livestock, horses, and companion animals. Whereas the clonal relationship between MRSA strains of CC398 is straightforward in livestock this is less obvious in horses. Small companion animals typically share MRSA strains that seem to exchange with a human reservoir. Management and therapeutic options have been suggested for livestock, horses, companion animals, as well as instructions on safety measures for persons in contact with animals. Conclusions were drawn with emphasis on future research activities, especially to confirm the apparent evolution of the organism and to demonstrate efficiency of control strategies.

Epidemiology and susceptibilities of methicillin-resistant Staphylococcus aureus in Northeastern Ohio

A retrospective survey was performed on all staphylococcal infections diagnosed by the Ashtabula County Medical Center (Ashtabula, OH) during 2006 and 2007. Of the 1,612 Staphylococcus aureus isolates evaluated for their antibiotic resistances, 947 were methicillin-resistant S aureus (MRSA). In 2007, MRSA infections reached 589 cases per 100,000 inhabitants, a 77% increase compared with 2006. The increase in MRSA infections was noticeable among youth (6-25 years old), middle-aged people (45-50 years old), and elderly people (86-90 years old). MRSA infections increased among inpatients by 58%, among outpatients by 43%, and among nursing home residents by 183%. More than 66% of MRSA infections were found among healthy people in the community with no apparent risk factors. More than 88.7% of the infections belong to only 9 profiles of antibiotic resistance indiscriminately distributed among inpatients, outpatients, and nursing home residents. This report sheds further light on the rapid spread of MRSA across Northeastern Ohio, stressing the need for better education in preventive measures and infection control at the level of community and health care settings.

Impact of sarA on antibiotic susceptibility of Staphylococcus aureus in a catheter-associated in vitro model of biofilm formation

Mutation of the staphylococcal accessory regulator (sarA) in Staphylococcus aureus limits but does not abolish the capacity of the organism to form a biofilm. As a first step toward determining whether this limitation is therapeutically relevant, we carried out in vitro studies comparing the relative susceptibility of an S. aureus clinical isolate (UAMS-1) and its isogenic sarA mutant (UAMS-929) in the specific context of a catheter-associated biofilm. The antibiotics tested were daptomycin, linezolid, and vancomycin, all of which were evaluated by using concentrations based on the MIC defined as the breakpoint for a susceptible strain of S. aureus (< or = 1.0, < or = 2.0, and < or = 4.0 microg/ml for daptomycin, vancomycin, and linezolid, respectively). Mutation of sarA had no significant impact on the MIC of UAMS-1 for any of the targeted antibiotics, as defined by Etest antimicrobial susceptibility testing. However, mutation of sarA did result in a significant increase in antimicrobial susceptibility to all targeted antibiotics when they were tested in the specific context of a biofilm. Additionally, whether susceptibility was assessed by using UAMS-1 or its sarA mutant, daptomycin was found to be more effective against established S. aureus biofilms than either linezolid or vancomycin.