Treatment of infections caused by antimicrobial-resistant gram-positive bacteria

Multi-resistant organisms in burn patients: an end or a new beginning

Infections are a major cause of morbidity and mortality in burn patients, and the rise of multidrug-resistant organisms (MDROs) has made it more challenging to manage and prevent infections. This review examines the available treatment options for MDROs in burn patients and anticipates the future challenges posed by their increasing prevalence. The review covers new antibiotics, such as Eravacycline and Plazomicin, as well as non-antibiotic therapies, such as bacteriophages and nanoparticles. Future research should focus on examining the long-term efficacy, cost-effectiveness, and in vivo efficacy of different treatment modalities. The potential of alternative therapies, such as probiotics and low-frequency magnetic fields, should also be explored. Accurate and rapid diagnostic and monitoring tools for detecting MDROs in burn patients should be developed. The emergence of MDROs in burn care is a challenge and a new beginning in infection innovation and novel treatments.

Phytochemicals with activity against methicillin-resistant Staphylococcus aureus

BACKGROUND

The evolution of resistance to antimicrobials is a ubiquitous phenomenon. The evolution of antibiotic resistance in Staphylococcus aureus suggests that there is no remedy with sustaining effectiveness against this pathogen. The limited number of antibacterial drug classes and the common occurrence of cross-resistant bacteria reinforce the urgent need to discover new compounds targeting novel cellular functions. Natural products are a potential source of novel antibacterial agents. Anti-MRSA (methicillin-resistant S. aureus) bioactive compounds from Streptomyces and the anti-MRSA activity of a series of plant extracts have been reviewed respectively. However, there has been no detailed review of the precise bioactive components from plants.

PURPOSE

The present review aimed to summarize the phytochemicals that have been reported with anti-MRSA activities, analyze their structure-activity relationship and novel anti-MRSA mechanisms.

METHODS

Data contained in this review article are compiled from the authoritative databases PubMed, Web of Science, Google Scholar, and so on.

RESULTS

This review summarizes 100 phytochemicals (27 flavonoids, 23 alkaloids, 17 terpenes and 33 others) that have been tested for their anti-MRSA activity. Among these phytochemicals, 39 compounds showed remarkable anti-MRSA activity with MIC values less than 10 μg/ml, 14 compounds with MIC ranges including values < 10 μg/ml, 5 compounds with MIC values less than 5 μM; 11 phytochemicals show synergism anti-MRSA effects in combination with antibiotics. Phytochemicals exerted anti-MRSA activities mainly by destroying the membrane structure and inhibiting the efflux pump.

CONCLUSIONS

The 58 compounds with excellent anti-MRSA activity the 11 compounds with synergistic anti-MRSA effect, especially cannabinoids, xanthones and fatty acids should be further studied in vitro. Novel targets, such as cell membrane and efflux pump could be promising alternatives to develop antibacterial drugs in the future in order to prevent drug resistance.

Effect of Vancomycin on Cellular Fatty Acid Profiles of Vancomycin-Susceptible and Nonsusceptible Staphylococcus aureus

Vancomycin is widely used for treatment of infection caused by methicillin-resistant Staphylococcus aureus (MRSA) leading to an increasing appearance of low-level vancomycin-resistant isolates called heterogeneous vancomycin-intermediate S. aureus (hVISA). The mechanism of vancomycin tolerance in hVISA is still unclear. This study aimed to investigate the fatty acid compositions of S. aureus isolates under the stress environment with vancomycin. The different responses of hVISA and vancomycin-susceptible S. aureus (VSSA) may lead to more understanding the mechanism. The bacterial lipid profiles were tested three times from three extractions of each isolate cultured on tryptic soy agar (TSA) and TSA with vancomycin. Of the 30 MRSA isolates studied, 13, 12, and 5 isolates were VSSA, hVISA, and VISA, respectively. The analysis of bacterial lipid profiles showed that under vancomycin stress, there was a reduction of straight chain fatty acids (SCFAs) in VSSA isolates but an increase in branched chain fatty acids (BCFAs). In contrast, the hVISA group exhibited an increase only in the BCFAs but not in SCFAs. Of interest, vancomycin had no effect on either BCFAs or SCFAs of the VISA cells. This study provided information of bacterial adaptation during stress with vancomycin that may be helpful to overcome the resistant bacteria.

Discovery, Synthesis, and Optimization of Peptide-Based Antibiotics

The rise of multidrug resistant bacteria has significantly compromised our supply of antibiotics and poses an alarming medical and economic threat to society. To combat this problem, it is imperative that new antibiotics and treatment modalities be developed, especially those toward which bacteria are less capable of developing resistance. Peptide natural products stand as promising candidates to meet this need as bacterial resistance is typically slow in response to their unique modes of action. They also have additional benefits including favorable modulation of host immune responses and often possess broad-spectrum activity against notoriously treatment resistant bacterial biofilms. Moreover, nature has provided a wealth of peptide-based natural products from a range of sources, including bacteria and fungi, which can be hijacked in order to combat more dangerous clinically relevant infections.This Account highlights recent advances in the total synthesis and development of a range of peptide-based natural product antibiotics and details the medicinal chemistry approaches used to optimize their activity.In the context of antibiotics with potential to treat Gram-positive bacterial infections, this Account covers the synthesis and optimization of the natural products daptomycin, glycocin F, and alamethicin. In particular, the reported synthesis of daptomycin highlights the utility of on-resin ozonolysis for accessing a key kynurenine residue from the canonical amino acid tryptophan. Furthermore, the investigation into glycocin F analogues uncovered a potent lead compound against Lactobacillus plantarum that bears a non-native thioacetal linkage to a N-acetyl-d-glucosamine (GlcNAc) sugar, which is otherwise O-linked in its native form.For mycobacterial infections, this Account covers the synthesis and optimization of teixobactin, callyaerin A, lassomycin, and trichoderin A. The synthesis of callyaerin A, in particular, highlighted the importance of a (Z)-2,3-diaminoacrylamide motif for antimicrobial activity against Mycobacterium tuberculosis, while the synthesis of trichoderin A highlighted the importance of (R)-stereoconfiguration in a key 2-amino-6-hydroxy-4-methyl-8-oxodecanoic acid (AHMOD) residue.Lastly, this Account covers lipopeptide antibiotics bearing activity toward Gram-negative bacterial infections, namely, battacin and paenipeptin C. In both cases, optimization of the N-terminal lipid tails led to the identification of analogues with potent activity toward Escherichia coli and Pseudomonas aeruginosa.

Advances in engineering of low molecular weight hydrogels for chemotherapeutic applications

Chemotherapy is the primary option for the treatment of cancer, inflammation, and infectious diseases. Conventional drug delivery poses solubility and bioavailability challenges, systemic toxicity, non-specific targeting, and poor accumulation of chemotherapeutic drugs at the desired site. Nanotechnology has led to the development of various nanomaterials that have decreased the toxicity and increased the accumulation of drugs at the target site. Systemic administration of nanomaterials causes burst release and non-specific targeting of chemotherapeutics, leading to off-target organ toxicity. Drug delivery based on low molecular weight hydrogels (LMWHs) provides a suitable alternative for drug delivery due to their ability to entrap chemotherapeutic drugs. Injectable and biodegradable LMWHs allow the administration of chemotherapeutics with minimal invasion, allow the sustained release of chemotherapeutic drugs for long periods, and reduce the challenges of immunogenicity and low drug entrapment efficiency. Herein, we summarize the advances in the engineering of LMWHs for controlled and prolonged delivery of chemotherapeutics for cancer, infectious diseases, and inflammatory disorders.

Resistance of Gram-Positive Bacteria to Current Antibacterial Agents and Overcoming Approaches

The discovery of antibiotics has created a turning point in medical interventions to pathogenic infections, but unfortunately, each discovery was consistently followed by the emergence of resistance. The rise of multidrug-resistant bacteria has generated a great challenge to treat infections caused by bacteria with the available antibiotics. Today, research is active in finding new treatments for multidrug-resistant pathogens. In a step to guide the efforts, the WHO has published a list of the most dangerous bacteria that are resistant to current treatments and requires the development of new antibiotics for combating the resistance. Among the list are various Gram-positive bacteria that are responsible for serious healthcare and community-associated infections. Methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and drug-resistant Streptococcus pneumoniae are of particular concern. The resistance of bacteria is an evolving phenomenon that arises from genetic mutations and/or acquired genomes. Thus, antimicrobial resistance demands continuous efforts to create strategies to combat this problem and optimize the use of antibiotics. This article aims to provide a review of the most critical resistant Gram-positive bacterial pathogens, their mechanisms of resistance, and the new treatments and approaches reported to circumvent this problem.

Comparative evaluation of VITEK® 2 and three commercial gradient strip assays for daptomycin susceptibility testing of Staphylococcus aureus

Objectives

MRSA remains a major cause of severe nosocomial infections and the increased use of vancomycin and daptomycin for MRSA treatment over the last decade has led to the isolation of MRSA strains with decreased daptomycin susceptibility. In addition, a growing number of MSSA isolates with reduced susceptibility to daptomycin have been described lately. Surveillance of the emergence of such a daptomycin-non-susceptible MSSA population requires prompt and reliable daptomycin susceptibility testing. Therefore, this work aimed to evaluate the ability of commonly used methods to detect daptomycin resistance in clinical microbiological laboratories.

Methods

We used commercially available manual and automated test systems, including VITEK® 2 and three gradient strip assays, in comparison with broth microdilution, to detect daptomycin resistance in a representative Staphylococcus aureus strain collection.

Results

We found high inter-assay concordance as well as congruence with the reference method. This is demonstrated by essential agreement between commercial test systems and reference broth microdilution ranging from 98.1% to 100% and by categorical agreement from 98.2% to 99.1%. Thus, all systems used were able to detect daptomycin non-susceptibility in MRSA and MSSA isolates.

Conclusions

Our data indicate that routine laboratories are at limited risk of overlooking further daptomycin resistance development, as long as commercially available test systems are used according to the manufacturer's recommendations. However, laboratories must be aware of an increasing number of daptomycin-non-susceptible MSSA isolates, including those exhibiting elevated MICs of glycopeptides.

Pharmacokinetics and Tolerance of the Phage Endolysin-Based Candidate Drug SAL200 after a Single Intravenous Administration among Healthy Volunteers

This study was a phase 1, single-center, randomized, double-blind, placebo-controlled, single-dosing, and dose-escalating study of intravenous SAL200. It is a new candidate drug for the treatment of antibiotic-resistant staphylococcal infections based on a recombinant form of the phage endolysin SAL-1. The study evaluated the pharmacokinetics, pharmacodynamics, and tolerance among healthy male volunteers after the intravenous infusion of single ascending doses of SAL200 (0.1, 0.3, 1, 3, and 10 mg/kg of body weight). SAL200 was well tolerated, and no serious adverse events (AEs) were observed in this clinical study. Most AEs were mild, self-limiting, and transient. The AEs reported in more than three participants were fatigue, rigors, headache, and myalgia. No clinically significant values with respect to the findings of clinical chemistry, hematology, and coagulation analyses, urinalysis, vital signs, and physical examinations were observed, and no notable trends in our electrocardiogram (ECG) results for any tested dose were noticed. A greater-than-dose-proportional increase with regard to systemic exposure and the maximum serum concentration was observed when the SAL200 dose was increased from 0.1 mg/kg to 10 mg/kg. This investigation constitutes the first-in-human phase 1 study of an intravenously administered, phage endolysin-based drug. (This study has been registered at ClinicalTrials.gov under identifier NCT01855048 and at the Clinical Research Information Service [https://cris.nih.go.kr/cris/] under identifier KCT0000968.).

Virulence Factors in Staphylococci Isolated From Nasal Cavities of Footballers

AIM

This study aimed to investigate the rate of Panton-Valentine Leukocidin producing Staphylococcus aureus and methicillin (mecA) and slime (icaA/icaD) genes in staphylococcal strains isolated from nasal cavities of footballers.

MATERIALS AND METHODS

Nasal swab samples were taken from each footballers and a healthy control group for the isolation of staphylococcal strains. The polymerase chain reaction technique was used to determine Panton-Valentine Leukocidin, mecA and icaA/icaD genes in staphylococcal isolates.

RESULTS

Among 91 S. aureus strains, the presence of mecA gene was detected as 9.9%. This ratio was 17.9% (27 of 151) among the coagulase-negative staphylococci. A significant difference was found between coagulase-negative staphylococci and S. aureus isolates regarding the presence of mecA gene (P < 0.001). As for the genes of the slime, icaA/icaD genes were detected in 198 of 242 (81.8%) strains. The occurrence of slime genes was 91.2% and 89.4% among the S. aureus coagulase and negative staphylococci, respectively (P > 0.05). There was a statistically significant difference between the frequency of the mecA and slime genes when compared with the healthy control group and the football players (P < 0.01). Of 91 isolates, 22 were found to be methicillin resistant by the oxacillin disc diffusion method, whereas the remaining (220) were methicillin susceptible. Methicillin resistance was detected as 14.9% by the polymerase chain reaction method, whereas it was found as 9.1% by phenotypic methods.

CONCLUSIONS

Early and accurate diagnosis of virulent staphylococcal strains is crucial because the virulent coagulase-negative and coagulase-positive staphylococcal strains in the nasal floras of footballers may be major potential sources of superficial and deep tissue infections.

Daptomycin experience in patients with human immunodeficiency virus and resistant gram-positive infections

OBJECTIVES

This study was conducted to evaluate the clinical experience with daptomycin in the treatment of resistant gram-positive infections (GPIs) in patients with HIV infection.

METHODS

Using a retrospective, multicenter, and observational registry study, investigators assessed outcomes following daptomycin therapy in 78 patients (62 efficacy evaluable) infected with HIV and with resistant GPIs.

RESULTS

Overall, success rates by infection type were bacteremia 91% (20 of 22), endocarditis 91% (10 of 11), and bone/joint 100% (9 of 9). Success by pathogen was 93% (39 of 42), 93% (14 of 15), and 100% (5 of 5) for methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and methicillin-resistant coagulase-negative staphylococci, respectively. Daptomycin appeared to be well tolerated, with 9% having an adverse event possibly related to daptomycin and 4% discontinuing daptomycin.

CONCLUSIONS

In HIV-infected patients, daptomycin appears to be a useful agent for treating resistant GPIs.

Effect of vancomycin on the cytoplasmic membrane fatty acid profile of vancomycin-resistant and -susceptible isolates of Staphylococcus aureus

This study was designed to analyze the effect of vancomycin on the cytoplasmic membrane fatty acid (FA) composition of vancomycin-resistant Staphylococcus aureus (VRSA), vancomycin-intermediate resistant S. aureus (VISA), and vancomycin-susceptible S. aureus. One low-level vancomycin-resistant isolate (LLR-VRSA) termed CP2, along with two vancomycin intermediate-resistant S. aureus isolates (VISA-CP1) and Mu50 (ATCC #700699), were studied. The LLR-VRSA isolate CP2, recovered from the blood sample of a postoperative cardiac patient, exhibited vanA type vancomycin resistance [minimum inhibitory concentration (MIC) 16 μg/ml], and the vanA cassette was located on a plasmid. CP1, isolated from the pus sample of the same patient, exhibited vancomycin intermediate resistance (MIC 8 μg/ml) in the absence of the vanA, vanB, or vanC gene. As susceptible controls, we used PSA (vancomycin MIC 2 μg/ml), which was isolated from the pus sample of a neonate, and S. aureus (ATCC# 29213). Membrane FA analysis was carried out using gas chromatography coupled with mass spectrometry. For this purpose, CP1, CP2, Mu50, and the susceptible control isolates were grown in the presence and absence of vancomycin. Comparative analysis showed an increase in the relative proportion of unsaturated FAs during growth under vancomycin stress. The isolate CP2 (LLR-VRSA) exhibited a higher MIC to vancomycin than the other isolates used in present study (16 μg/ml) and under vancomycin stress conditions, quantitatively, it showed a high rate of conversion of saturated to unsaturated membrane FAs than CP1, Mu50 (VISA isolate) and the susceptible control PSA. The rate of saturated-to-unsaturated FA conversion increased as the concentration of vancomycin in the growth media was increased. Therefore, it is concluded that S. aureus tend to modify their membrane lipid chemistry from saturated to unsaturated in order to survive in a vancomycin stress environment.

Clinical pharmacokinetic/pharmacodynamic profile of linezolid in severely ill intensive care unit patients

Severely ill Intensive Care Unit (ICU) patients have an increased risk of developing multiresistant Gram-positive infections, largely due to the inappropriate use of antimicrobials. In this study, the pharmacokinetic/pharmacodynamic (PK/PD) profile of linezolid, an antibiotic against Gram-positive infections, was characterised in eight critically ill patients admitted to the ICU. Remarkable variation amongst patients in the PK parameters of linezolid was observed, including a 5-7-fold difference in peak serum concentration (C(max)) (mean±standard deviation 15.70±6.58 mg/L) and 12-h area under the serum concentration-time curve (AUC(0-12)) (96.73±56.45 mg h/L), although the minimum inhibitory concentration (MIC) was similar amongst patients. In particular, variation amongst patients was found in the ratio of AUC(0-24)/MIC (range 31.66-216.82, mean 96.73) and the percentage of time that the serum concentration exceeded the MIC (T>MIC) (range 53.4-100%), two parameters used to predict linezolid efficacy. These variations highlight the importance of individual monitoring of linezolid PK/PD properties in critically ill patients. Furthermore, it was observed that regardless of AUC(0-24)/MIC and T>MIC values, the clinical and microbiological responses of patients were primarily affected by the individual's pathophysiological condition. In summary, these findings point to highly variable PK/PD properties of linezolid in severely ill patients, providing the rationale for targeting linezolid dosage to each individual patient's specific properties. An optimal dosage regimen based on individual PK/PD properties and pathophysiological conditions will help reduce the occurrence of resistance in Gram-positive bacteria.

Complicated skin and soft tissue infections: literature review of evidence for and experience with daptomycin

Skin and soft tissue infections (SSTIs) are the second most common infection encountered in hospitals. Management decisions have become increasingly complex due to the prevalence of resistant pathogens, the wide array of licensed antimicrobials and the availability of potent oral agents and of out-patient parenteral antibiotic therapy. Daptomycin is one of the newer therapeutic agents licensed for complex SSTI management. Rapid cidality, good soft tissue penetration, once daily IV bolus administration and activity against resistant Gram-positive infections make daptomycin an attractive option both in hospitalized and community treated patients. A comprehensive review of the evidence for and experience with daptomycin and its use in SSTIs is presented.

Lack of the delta subunit of RNA polymerase increases virulence related traits of Streptococcus mutans

The delta subunit of the RNA polymerase, RpoE, maintains the transcriptional specificity in Gram-positive bacteria. Lack of RpoE results in massive changes in the transcriptome of the human dental caries pathogen Streptococcus mutans. In this study, we analyzed traits of the ΔrpoE mutant which are important for biofilm formation and interaction with oral microorganisms and human cells and performed a global phenotypic analysis of its physiological functions. The ΔrpoE mutant showed higher self-aggregation compared to the wild type and coaggregated with other oral bacteria and Candida albicans. It formed a biofilm with a different matrix structure and an altered surface attachment. The amount of the cell surface antigens I/II SpaP and the glucosyltransferase GtfB was reduced. The ΔrpoE mutant displayed significantly stronger adhesion to human extracellular matrix components, especially to fibronectin, than the wild type. Its adhesion to human epithelial cells HEp-2 was reduced, probably due to the highly aggregated cell mass. The analysis of 1248 physiological traits using phenotype microarrays showed that the ΔrpoE mutant metabolized a wider spectrum of carbon sources than the wild type and had acquired resistance to antibiotics and inhibitory compounds with various modes of action. The reduced antigenicity, increased aggregation, adherence to fibronection, broader substrate spectrum and increased resistance to antibiotics of the ΔrpoE mutant reveal the physiological potential of S. mutans and show that some of its virulence related traits are increased.

Antimicrobial photodynamic therapy in the non-surgical treatment of aggressive periodontitis: microbiological profile

The aim of this trial was to investigate changes occurring in the subgingival microbiological composition of subjects with aggressive periodontitis, treated with antimicrobial photodynamic therapy (aPDT), in a single episode, or scaling and root planing (SRP), in a split-mouth design on -7, 0, and +90 days. Ten patients were randomly assigned to either aPDT using a laser source in conjunction with a photosensitizer or SRP with hand instruments. Subgingival plaque samples were collected and the counts of 40 subgingival species were determined using checkerboard DNA-DNA hybridization. The data were analyzed using the method of generalized estimating equations (GEE) to test the associations between treatments, evaluated parameters, and experimental times (α = .05). The results indicated that aPDT and SRP affects different bacterial species, with aPDT being effective in reducing numbers of A. actinomycetemcomitans than SRP. On the other hand, SRP was more efficient than aPDT in reducing the presence of periodontal pathogens of the Red Complex. Additionally, a recolonization in the sites treated by aPDT was observed, especially for T. forsythia and P. gingivalis. Under our experimental conditions, this trial demonstrates that aPDT and SRP affected different groups of bacteria, suggesting that their association may be beneficial for the non-surgical treatment of aggressive periodontitis.