Resistant MRSA Research Articles

Resilience Against Resistance: Exploring Cutting-edge Therapies for Methicillin-resistant Staphylococcus aureus (MRSA).

Methicillin-resistant Staphylococcus aureus [MRSA] stands as an enduring threat within healthcare landscapes, characterized by its ability to rapidly evolve and develop resistance to conventional antibiotics. This comprehensive review embarks on a journey through the historical landscape of MRSA, elucidating its initial emergence and subsequent evolution of resistance mechanisms over time. The narrative unfolds to underscore the profound impact of MRSA on patient outcomes and healthcare systems globally. Current trends in MRSA therapies come under meticulous scrutiny, spotlighting the limitations and challenges associated with existing treatment modalities. This analysis underscores the critical need for transformative and innovative therapeutic strategies to effectively combat the ever-growing spectre of drug resistance in MRSA from the exploration of novel antibiotics designed to overcome resistance mechanisms to the promising potential of phage therapy and immunotherapies. Amidst the exploration of innovative therapies, the review identifies and discusses emerging issues and challenges in MRSA management. Insights are provided into the intricate web of obstacles hindering the adoption and implementation of new therapeutic strategies. Furthermore, the socio-economic implications of MRSA and drug resistance are brought to the forefront, emphasizing the broader impact on public health and healthcare systems. In parallel, historical perspectives on MRSA research illuminate key milestones in scientific understanding and technological advancements. The evolution of research strategies and their impact on our ability to comprehend and combat MRSA is examined, providing context for the current state of the field. In conclusion, this review summarizes major findings and drawing implications for the future of MRSA treatment. Recommendations for further research and clinical practice are outlined, encapsulating a holistic overview of the resilient efforts against resistance in the ongoing battle against MRSA.

Green synthesis of cerium oxide nanoparticles usingTribulus terrestris: characterization and evaluation of antioxidant, anti-inflammatory and antibacterial efficacy against wound isolates.

Multi-drug resistance (MDR) infections are a significant global challenge, necessitating innovative and eco-friendly approaches for developing effective antimicrobial agents. This study focuses on the synthesis, characterization, and evaluation of cerium oxide nanoparticles (CeO2NPs) for their antioxidant, anti-inflammatory, and antibacterial properties. The CeO2NPs were synthesized using aTribulus terrestrisaqueous extract through an environmentally friendly process. Characterization techniques included UV-visible spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), x-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive x-ray (EDX) analysis. The UV-vis spectroscopy shows the presence of peak at 320 nm which confirms the formation of CeO2NPs. The FT-IR analysis of the CeO2NPs revealed several distinct functional groups, with peak values at 3287, 2920, 2340, 1640, 1538, 1066, 714, and 574 cm-1. These peaks correspond to specific functional groups, including C-H stretching in alkynes and alkanes, C=C=O, C=C, alkanes, C-O-C, C-Cl, and C-Br, indicating the presence of diverse chemical bonds within the CeO2NPs. XRD revealed that the nanoparticles were highly crystalline with a face-centered cubic structure, and SEM images showed irregularly shaped, agglomerated particles ranging from 100-150 nm. In terms of biological activity, the synthesized CeO2NPs demonstrated significant antioxidant and anti-inflammatory properties. The nanoparticles exhibited 82.54% antioxidant activity at 100 μg ml-1, closely matching the 83.1% activity of ascorbic acid. Additionally, the CeO2NPs showed 65.2% anti-inflammatory activity at the same concentration, compared to 70.1% for a standard drug. Antibacterial testing revealed that the CeO2NPs were particularly effective against multi-drug resistant strains, includingPseudomonas aeruginosa,Enterococcus faecalis, and MRSA, with moderate activity againstKlebsiella pneumoniae. These findings suggest that CeO2NPs synthesized viaT. terrestrishave strong potential as antimicrobial agents in addressing MDR infections.

Phytoconstituent and In silico Screening of Active Compounds from Red Ginger (Zingiber officinale var. rubrum Theilade) Rhizome and Avocado (Persea americana Mill.) Leaves Extracts as Novel Inhibitors of MRSA

Red ginger rhizome (Zingiber officinale var. Rubrum) and avocado leaves (Persea americana Mill.) are empirically known as one of the medicinal plants used in Taro Village, Gianyar Regency, Bali which have great potential in treating infectious diseases caused by antibiotic resistance, such as MRSA. This study aims to analyze the phytoconstituents and anti-MRSA potential contained in red ginger rhizome and avocado leaves extracts by assessing their inhibitory effects on three proteins related to MRSA resistance and virulence (PBAP2a, transglycosylase, and glycosyltransferase). Phytoconstituents of avocado leaf and red ginger extracts were analyzed using GC-MS. Molecular docking was performed in silico to determine the similarity properties of predicted drugs, bioactivity, toxicity, identification of active sites and validation of protein structures, and docking simulations were performed between compounds found in the extract and their target proteins. Phytoconstituent analysis revealed that avocado leaves and red ginger extracts as a whole have 43 types of compounds and 10 bioactive compounds each with beneficial drug-like properties. The compound 6,11-hexadecadien-1-ol from avocado leaves extracts was predicted to have hepatotoxic properties. There were at least 3 compounds, namely beta-bisabolene from avocado leaves extract, zingiberenol and gamma-curcumene from red ginger rhizome extract, showing the lowest binding affinity for the target protein. Red ginger rhizome and avocado leaves extracts showed valuable potential as anti-MRSA agents through the mechanism of inhibition of three resistance-related proteins, as predicted by in silico analysis.

Unveiling the Potential of Bergenia Phenolics: Vitexin's Role in Allosteric Modulation of PBP2a as a Strategy against MRSA Resistance.

For cell wall biosynthesis, drug-resistant S. aureus uses a special protein called PBP2a, even when antibiotics are present and stop its natural processes from working. To combat this, novel therapies are required to specifically target PBP2a with greater efficacy. Using computational approaches, we screened nine phenolic compounds from other Bergenia species, including Bergenia ciliata, Begenia ligulata, Bergenia purpurascens, and Ber-genia stracheyi, against the PBP2a allosteric site to explore the potential interaction between phe-nolic compounds and a specific region of PBP2a known as the allosteric site. Based on interaction patterns and estimated affinity, vitexin has been found to be the most prominent phenolic compound. We performed MD simulations on vitexin and ceftazidime as control molecules based on the docking results. The binding free energy estimates of vitexin (-94.48 +/- 17.92 kJ/mol) using MM/PBSA were lower than those of the control (-67.61 +/- 12.29 kJ/mol), which suggests that vitexin may be able to inhibit PBP2a activity in MRSA. It has been intriguing to observe a correlation between the affinity of the lead com-pounds at the allosteric site and the modification of Tyr446, the active site gatekeeper residue in PBP2a. Our findings have implied that lead compounds can either directly or indirectly decrease PBP2a activity by inducing allosteric site change in conventional medicine.

High Prevalence and Antibiotic Resistance of MRSA and Acinetobacter spp. among Healthcare Personnel and Neonatal Units: Implications for Infection Control and Hygiene Protocols

High Prevalence and Antibiotic Resistance of MRSA and Acinetobacter spp. among Healthcare Personnel and Neonatal Units: Implications for Infection Control and Hygiene Protocols

ConsensusPrime—A Bioinformatic Pipeline for Efficient Consensus Primer Design—Detection of Various Resistance and Virulence Factors in MRSA—A Case Study

Background: The effectiveness and reliability of diagnostic tests that detect DNA sequences largely hinge on the quality of the used primers and probes. This importance is especially evident when considering the specific sample being analyzed, as it affects the molecular background and potential for cross-reactivity, ultimately determining the test’s performance. Methods: Predicting primers based on the consensus sequence of the target has multiple advantages, including high specificity, diagnostic reliability, broad applicability, and long-term validity. Automated curation of the input sequences ensures high-quality primers and probes. Results: Here, we present a use case for developing a set of consensus primers and probes to identify antibiotic resistance and virulence genes in Staphylococcus (S.) aureus using the ConsensusPrime pipeline. Extensive qPCR experiments with several S. aureus strains confirm the exceptional quality of the primers designed using the pipeline. Conclusions: By improving the quality of the input sequences and using the consensus sequence as a basis, the ConsensusPrime pipeline pipeline ensures high-quality primers and probes, which should be the basis of molecular assays.

Increasing Antibiotic-Resistant Infections With Inpatient Endoscopic Retrograde Cholangioscopies (ERCP) Is Associated With Higher Mortality in the United States: A Cross-sectional Cohort Study.

This study aims to investigate associated mortality with inpatient endoscopic retrograde cholangiopancreatography (ERCP) with and without resistant infections. The co-primary objective compares frequencies of inpatient ERCP with resistant infections to overall hospitalizations with resistant infections. The risks of inpatient antibiotic-resistant organisms are known, but the associated mortality for inpatient ERCP is unknown. We aim to use a national database of hospitalizations and procedures to understand trends and mortality for patients with antibiotic-resistant infections during inpatient ERCP. The largest publicly available all-payer inpatient database in the United States (National Inpatient Sample) was used to identify hospitalizations associated with ERCPs and antibiotic-resistant infections for MRSA, VRE, ESBL, and MDRO. National estimates were generated, frequencies were compared across years, and multivariate regression for mortality was performed. From 2017 to 2020, national weighted estimates of 835,540 inpatient ERCPs were generated, and 11,440 ERCPs had coincident resistant infections. Overall resistant infection, MRSA, VRE, and MDRO identified at the same hospitalization of inpatient ERCPs were associated with higher mortality (OR CI(95%): Overall: 2.2(1.77-2.88), MRSA: 1.90 (1.34-2.69), VRE: 3.53 (2.16-5.76), and MDRO: 2.52 (1.39-4.55)). While overall hospitalizations with resistant infections have been decreasing annually, there has been a yearly increase in admissions requiring ERCPs with simultaneous resistant infections ( P =0.001-0.013), as well as infections with VRE, ESBL, and MDRO ( P =0.001-0.016). Required Research Practices for Studies Using the NIS scoring was 0, or the most optimal. Inpatient ERCPs have increasing coincident resistant infections and are associated with higher mortality. These rising infections during ERCP highlight the importance of endoscopy suite protocols and endoscopic infection control devices.

Identification of CH2-linked quinolone-aminopyrimidine hybrids as potent anti-MRSA agents: Low resistance potential and lack of cross-resistance with fluoroquinolone antibiotics

The structural optimization of B14, an antibacterial agent we previously obtained, has led to the discovery of a new class of CH2-linked quinolone-aminopyrimidine hybrids with potent anti-MRSA activities. Surprisingly, the hybrids lacking a C-6 fluoro atom at the quinolone nucleus showed equal or even stronger anti-MRSA activities than their corresponding 6-fluoro counterparts, despite the well-established structure-activity relationships (SARs) indicating that the 6-fluoro substituent enhances the antibacterial activity in conventional fluoroquinolone antibiotics. Moreover, these new hybrids, albeit structurally related to conventional fluoroquinolones, showed no cross-resistance with fluoroquinolone drugs. The most active compound, 15m, exhibited excellent activities with a MIC value of 0.39 μg/mL against both fluoroquinolone-sensitive strain USA500 and -resistant MRSA isolate Mu50. Further resistance development studies indicated MRSA is unlikely to acquire resistance against 15m. Moreover, 15m displayed favorable in vivo half-life and safety profiles. These findings suggest a rationale for further evolution of quinolone antibiotics with a high barrier to resistance.

Charge adaptive phytochemical-based nanoparticles for eradication of methicillin-resistant staphylococcus aureus biofilms

The intrinsic resistance of MRSA coupled with biofilm antibiotic tolerance challenges the antibiotic treatment of MRSA biofilm infections. Phytochemical-based nanoplatform is a promising emerging approach for treatment of biofilm infection. However, their therapeutic efficacy was restricted by the low drug loading capacity and lack of selectivity. Herein, we constructed a surface charge adaptive phytochemical-based nanoparticle with high isoliquiritigenin (ISL) loading content for effective treatment of MRSA biofilm. A dimeric ISL prodrug (ISL-G2) bearing a lipase responsive ester bond was synthesized, and then encapsulated into the amphiphilic quaternized oligochitosan. The obtained ISL-G2 loaded NPs possessed positively charged surface, which allowed cis-aconityl-d-tyrosine (CA-Tyr) binding via electrostatic interaction to obtain ISL-G2@TMDCOS-Tyr NPs. The NPs maintained their negatively charged surface, thus prolonging the blood circulation time. In response to low pH in the biofilms, the fast removal of CA-Tyr led to a shift in their surface charge from negative to positive, which enhanced the accumulation and penetration of NPs in the biofilms. Sequentially, the pH-triggered release of d-tyrosine dispersed the biofilm and lipase-triggered released of ISL effectively kill biofilm MRSA. An in vivo study was performed on a MRSA biofilm infected wound model. This phytochemical-based system led to ∼2 log CFU (>99 %) reduction of biofilm MRSA as compared to untreated wound (P < 0.001) with negligible biotoxicity in mice. This phytochemical dimer nanoplatform shows great potential for long-term treatment of resistant bacterial infections.

Study on antimicrobial resistance and detection of MRSA of Staphylococcus aureus isolated from carcass in Daegu slaughterhouses

Study on antimicrobial resistance and detection of MRSA of <i>Staphylococcus aureus</i> isolated from carcass in Daegu slaughterhouses

Comparative structural analysis of MecA encoded beta-lactam resistance in MRSA

As the level of antibiotic resistance in bacteria rises, the threat of patients facing fatal consequences from a simple cut or infection grows dramatically. One example of an emerging antibiotic-resistant threat is MRSA, methicillin-resistant staphylococcus aureus, which is a growing cause of hospital-acquired pneumonia, skin infections, and even sepsis through cross-contamination in health care settings. However, methicillin resistance like that exploited by MRSA is also highly conserved with that of another species of staphylococcus bacteria, Staphylococcus sciuri which is the ancestral bacterium of S. aureus. S. sciuri is a typically animal-associated bacterium with increasing clinical relevance as the amount of human infections from it has grown. Both these bacteria share the commonality of having the mecA gene that determines methicillin resistance transported through the mobile Staphylococcal cassette chromosome. This study focuses on the relationship between the mecA mobile element in S. sciuri compared to S. aureus and explores the specific role of S. sciuri in the creation of the mecA cassette. Understanding the cassette evolution and similarities and differences between S. sciuri and S. aureus will enable the continued tracking of S. sciuri as an emerging clinical threat. To answer all these questions, BLAST analysis, InterProScan, and additional computational analysis were used to characterize differences in homology, structure, function, and effect on infectivity, robustness of antibiotic resistance, and morbidity. The overall goal of this analysis is to characterize the differences between mecA and methicillin-resistant genes in clinically relevant MRSA as well as environmental samples such as S. sciuri.

Identification of isothiazolones analogues as potent bactericidal agents against antibiotic resistant CRE and MRSA strains

Carbapenem-resistant Enterobacterales (CRE) has emerged as a worldwide spread nosocomial superbug exhibiting antimicrobial resistance (AMR) to all current antibiotics, leaving limited options for treating its infection. To discovery novel antibiotics against CRE, we designed and synthesized a series of 14 isothiazol-3(2H)-one analogues subjected to antibacterial activity evaluation against Escherichia coli (E. coli) BL21 (NDM-1) and clinical strain E. coli HN88 for investigating their structure–activity relationships (SAR). The results suggested that 5-chloroisothiazolone core with an N-(4-chlorophenyl) substitution 5a was the most potent antibacterial activity against the E. coli BL21 (NDM-1) with MIC value of less than 0.032 μg/mL, which was at least 8000-fold higher than the positive control Meropenem (MRM). It also displayed 2048-fold potent than the positive control MRM against E. coli HN88. Additionally, SAR analysis supported the conclusion that compounds with a chloro-group substituted on the 5-position of the heterocyclic ring was much more potent than other positions. The board spectrum analysis suggested that compound 5a showed a promising antimicrobial activity on MRSA and CRE pathogens. Meanwhile, cytotoxicity study of compound 5a suggested that it had a therapeutic index value of 875, suggesting future therapeutic potential. In vivo efficacy study declared that compound 5a could also protect the BALB/c mice against American type culture collection (ATCC) 43,300. Further screening of our compounds against a collection of CRE strains isolated from patients indicated that compound 5 g displayed much stronger antibacterial activity compared with MRM. In conclusion, our studies indicated that isothiazolones analogues could be potent bactericidal agents against CRE and MRSA pathogens.

Recombination-mediated dissemination of Methicillin-resistant S. aureus clonal complex 1 in the Egyptian health care settings

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) is a rapidly evolving pathogen that is frequently associated with outbreaks and sustained epidemics. This study investigated the population structure, resistome, virulome, and the correlation between antimicrobial resistance determinants with phenotypic resistance profiles of 36 representative hospital-acquired MRSA isolates recovered from hospital settings in Egypt.ResultsThe community-acquired MRSA lineage, clonal complex 1 (CC1) was the most frequently detected clone, followed by three other globally disseminated clones, CC121, CC8, and CC22. Most isolates carried SCCmec type V and more than half of isolates demonstrated multi-drug resistant phenotypes. Resistance to linezolid, a last resort antibiotic for treating multidrug resistant MRSA, was observed in 11.11% of the isolates belonging to different genetic backgrounds. Virulome analysis indicated that most isolates harboured a large pool of virulence factors and toxins. Genes encoding aureolysin, gamma hemolysins, and serine proteases were the most frequently detected virulence encoding genes. CC1 was observed to have a high pool of AMR resistance determinants including cfr, qacA, and qacB genes, which are involved in linezolid and quaternary ammonium compounds resistance, as well as high content of virulence-related genes, including both of the PVL toxin genes. Molecular clock analysis revealed that CC1 had the greatest frequency of recombination (compared to mutation) among the four major clones, supporting the role of horizontal gene transfer in modulating AMR and hypervirulence in this clone.ConclusionsThis pilot study provided evidence on the dissemination success of CA-MRSA clone CC1 among Egyptian hospitals. Co-detection of multiple AMR and virulence genes in this lineage pose a broad public health risk, with implications for successful treatment. The results of this study, together with other surveillance studies in Egypt, should be used to develop strategies for controlling MRSA infections in Egyptian health-care settings.

Deriving Novel Quaternary Ammonium Compound Disinfectant Scaffolds from a Natural Product: Mechanistic Insights of the Quaternization of Ianthelliformisamine C.

In the search for novel quaternary ammonium compound (QAC) disinfectants that can evade bacterial resistance, we turned to natural products as a source of inspiration. Herein we used natural product ianthelliformisamine C as a scaffold to design a small library of QACs. We first synthesized ianthelliformisamine C via an amide coupling that allowed for facile purification without the need for protecting groups. We then alkylated and quaternized the internal amines to yield four novel QACs, but all but one demonstrated no antibacterial activity against the tested strains. Using a combination of membrane depolarization and permeabilization assays, we were able to demonstrate that ianthelliformisamine C and the active QAC analog enact cell death via membrane permeabilization, contrary to prior reports on ianthelliformisamine C's mechanism of action.

Biosynthesis Strategy of Gold Nanoparticles and Biofabrication of a Novel Amoxicillin Gold Nanodrug to Overcome the Resistance of Multidrug-Resistant Bacterial Pathogens MRSA and E. coli.

The prevalence of multidrug-resistant (MDR) bacteria has recently increased dramatically, seriously endangering human health. Herein, amoxicillin (Amoxi)-conjugated gold nanoparticles (AuNPs) were created as a novel drug delivery system to overcome MDR bacteria. MDR bacteria were isolated from a variety of infection sources. Phenotype, biotype, and 16S rRNA gene analyses were used for isolate identification. Additionally, Juniperus excelsa was used for the production of AuNPs. The conjugation of AuNPs with Amoxi using sodium tri-polyphosphate (TPP) as a linker to produce Amoxi-TPP-AuNPs was studied. The AuNP and Amoxi-TPP-AuNP diameters ranged from 15.99 to 24.71 nm, with spherical and hexagonal shapes. A total of 83% of amoxicillin was released from Amoxi-TPP-AuNPs after 12 h, and after 3 days, 90% of the medication was released. The Amoxi-TPP-AuNPs exhibited superior antibacterial effectiveness against MRSA and MDR E. coli strains. Amoxi-TPP-AuNPs had MICs of 3.6-8 µg mL-1 against the tested bacteria. This is 37.5-83 fold higher compared to values reported in the literature. Amoxi-TPP-AuNPs exhibit a remarkable ability against MRSA and E. coli strains. These results demonstrate the applicability of Amoxi-TPP-AuNPs as a drug delivery system to improve therapeutic action.

Metabolic reprogramming and altered cell envelope characteristics in a pentose phosphate pathway mutant increases MRSA resistance to β-lactam antibiotics.

Central metabolic pathways control virulence and antibiotic resistance, and constitute potential targets for antibacterial drugs. In Staphylococcus aureus the role of the pentose phosphate pathway (PPP) remains largely unexplored. Mutation of the 6-phosphogluconolactonase gene pgl, which encodes the only non-essential enzyme in the oxidative phase of the PPP, significantly increased MRSA resistance to β-lactam antibiotics, particularly in chemically defined media with physiologically-relevant concentrations of glucose, and reduced oxacillin (OX)-induced lysis. Expression of the methicillin-resistance penicillin binding protein 2a and peptidoglycan architecture were unaffected. Carbon tracing and metabolomics revealed extensive metabolic reprogramming in the pgl mutant including increased flux to glycolysis, the TCA cycle, and several cell envelope precursors, which was consistent with increased β-lactam resistance. Morphologically, pgl mutant cells were smaller than wild-type with a thicker cell wall and ruffled surface when grown in OX. The pgl mutation reduced resistance to Congo Red, sulfamethoxazole and oxidative stress, and increased resistance to targocil, fosfomycin and vancomycin. Levels of lipoteichoic acids (LTAs) were significantly reduced in pgl, which may limit cell lysis, while the surface charge of pgl cells was significantly more positive. A vraG mutation in pgl reversed the increased OX resistance phenotype, and partially restored wild-type surface charge, but not LTA levels. Mutations in vraF or graRS from the VraFG/GraRS complex that regulates DltABCD-mediated d-alanylation of teichoic acids (which in turn controls β-lactam resistance and surface charge), also restored wild-type OX susceptibility. Collectively these data show that reduced levels of LTAs and OX-induced lysis combined with a VraFG/GraRS-dependent increase in cell surface positive charge are accompanied by significantly increased OX resistance in an MRSA pgl mutant.

Antibiotic susceptibility of staphylococcus aureus strains isolated from various clinical specimens in a tertiary hospital

Aims: Staphylococcus aureus infection rates, which are the cause of infections, have rapidly risen in both hospitals and society, constituting a concern. In this study, it was aimed to examine the antibiotic susceptibility of S. aureus strains isolated from patients treated in a tertiary state hospital for four years. Methods: A retrospective analysis was performed on S. aureus strains (n=584) identified from clinical samples delivered to the medical microbiology laboratory of Niğde Ömer Halisdemir University Training and Research Hospital for bacterial culture between 2016 and 2019. The isolates were identified by standard laboratory procedure. VITEK 2 automated system (bioMerieux, France) was used to identification and antibiotic susceptibilities of evaluate the strains. Results: Strains were most commonly isolated from wound swab (n=173) and blood culture (n=107). While the highest resistance rate was observed against Erythromycin (n=232), the least amikacin (n=16) resistant strain was determined. Vancomycin and teicoplanin resistance was not observed. Conclusion: Multi-drug resistance and MRSA resistance still exist today. The absence of vancomycin and teicoplanin resistance, in addition to the low level of trimethoprim-sulfamethoxazole resistance, is encouraging. This information about S. aureus's susceptibility may be helpful in determining how to administer antibiotics.

Novel Thiazolylketenyl Quinazolinones as Potential Anti-MRSA Agents and Allosteric Modulator for PBP2a.

Bacterial infections caused by methicillin-resistant Staphylococcus aureus have seriously threatened public health. There is an urgent need to propose an existing regimen to overcome multidrug resistance of MRSA. A unique class of novel anti-MRSA thiazolylketenyl quinazolinones (TQs) and their analogs were developed. Some synthesized compounds showed good bacteriostatic potency. Especially TQ 4 was found to exhibit excellent inhibition against MRSA with a low MIC of 0.5 μg/mL, which was 8-fold more effective than norfloxacin. The combination of TQ 4 with cefdinir showed stronger antibacterial potency. Further investigation revealed that TQ 4, with low hemolytic toxicity and low drug resistance, was not only able to inhibit biofilm formation but also could reduce MRSA metabolic activity and showed good drug-likeness. Mechanistic explorations revealed that TQ 4 could cause leakage of proteins by disrupting membrane integrity and block DNA replication by intercalated DNA. Furthermore, the synergistic antibacterial effect with cefdinir might be attributed to TQ 4 with the ability to induce PBP2a allosteric regulation of MRSA and further trigger the opening of the active site to promote the binding of cefdinir to the active site, thus inhibiting the expression of PBP2a, thereby overcoming MRSA resistance and significantly enhancing the anti-MRSA activity of cefdinir. A new strategy provided by these findings was that TQ 4, possessing both excellent anti-MRSA activity and allosteric effect of PBP2a, merited further development as a novel class of antibacterial agents to overcome increasingly severe MRSA infections.

Up-regulation of resident chromosomal fosB gene expression: a novel mechanism of acquired fosfomycin resistance in MRSA.

This study investigated fosfomycin susceptibility and mechanisms of resistance in a collection of 99 Staphylococcus aureus isolated from cases of hospital-acquired pneumonia, previously collected from a multicentre survey carried out in Italy. Fosfomycin susceptibility was tested by reference agar dilution. Bioinformatic and gene expression analysis, mutant selection experiments and WGS were executed to characterize fosfomycin resistance mechanisms. Fosfomycin resistance rates were 0% (0 of 35) among MSSA and 22% (14 of 64) among MRSA, with no evidence of clonal expansion. Resistance mechanisms were putatively identified in 8 of the 14 resistant strains, including: (i) chromosomal mutations causing loss of function of the UhpT transporter; (ii) overexpression of the gene encoding the Tet38 efflux pump; and (iii) overexpression of a fosB gene encoding a fosfomycin-inactivating enzyme, which was found to be resident in the chromosome of several S. aureus lineages but not always associated with fosfomycin resistance. The latter mechanism, which had not been previously described and was confirmed by results of in vitro mutant selection experiments, was associated in two cases with transposition of an IS1182 element upstream of the chromosomal fosB gene, apparently providing an additional promoter. This study showed that some S. aureus clonal lineages carry a resident chromosomal fosB gene and can evolve to fosfomycin resistance by overexpression of this gene.

Increased copy number of 23S ribosomal RNA gene with point mutation in MRSA associated with linezolid resistance in a patient treated with long-term linezolid

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) infection is one of the most difficult infections we have to treat. Linezolid is one of the effective treatment options for refractory MRSA infections. There are cases where we are forced to use long-term linezolid treatment for refractory MRSA infections. ObjectiveTo discuss the evolution of Linezolid resistance factors in clinical isolates of MRSA. MethodsWe investigated 16 MRSA isolated from a patient treated with linezolid for a long period of 75 days. We performed antibiotic susceptibility test, 23S rRNA genes sequencing analysis, Pulsed-field gel electrophoresis. ResultsMRSA isolates were susceptible to linezolid before the start of treatment, but became less susceptible by prolonged treatment. The 23S rRNA sequencing analysis of linezolid-resistant strains that appeared 17 days after the start of treatment with linezolid revealed that all resistant MRSA had the G2576T substitution (Escherichia coli 23S rRNA gene number). The number of copies of this mutation increased with the use of linezolid. ConclusionLong-term use of linezolid in a patient or reuse of linezolid in a patient who has been previously treated with linezolid can lead to the emerging of linezolid-resistant MRSA in the host.