Persistent Methicillin-resistant Staphylococcus Aureus Research Articles

Short versus long duration of ceftaroline combination therapy and outcomes in persistent or high-grade MRSA bacteremia: A retrospective single-center study.

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with high mortality rates. Despite antibiotic therapy, persistent bacteremia is challenging to treat. Combination therapy with ceftaroline has emerged as a potential treatment option; however, the optimal duration and clinical implications after bacteremia clearance are unknown. This retrospective cohort study examined patients with high-grade or persistent MRSA bacteremia who were treated with ceftaroline combination therapy at the University of New Mexico Hospital between January 2014 and June 2021. Patients were categorized into short- (<7 days) or long-duration (≥7 days) groups based on the duration of combination therapy after bacteremia clearance. Outcomes included 30-day all-cause mortality, bacteremia recurrence, post-bacteremia clearance length of stay, and adverse events. A total of 32 patients were included in this study. The most common sources of bacteremia were bone/joint and endovascular (28.1%, 9/32 each). The median duration of combination therapy after clearance was seven days (IQR 2.8, 11). Patients in the long-duration group had a lower Charlson comorbidity index (1.0 vs 5.5, p = 0.017) than those in the short-duration group. After adjusting for confounders, there was no significant difference in the 30-day all-cause mortality between the groups (AOR 0.17, 95% CI 0.007-1.85, p = 0.18). No association was found between combination therapy duration and recurrence (OR 2.53, 95% CI 0.19-inf, p = 0.24) or adverse drug events (OR 3.46, 95% CI 0.39-74.86, p = 0.31). After controlling for total hospital length of stay, there was no significant difference in the post-bacteremia clearance length of stay between the two groups (p = 0.37). Prolonging ceftaroline combination therapy after bacteremia clearance did not significantly improve outcomes in patients with persistent or high-grade MRSA bacteremia. The limitations of this study warrant cautious interpretation of its results. Larger studies are needed to determine the optimal duration and role of combination therapy for this difficult-to-treat infection.

Daptomycin and Ceftaroline Combination Therapy in Complicated Endovascular Infections Caused by Methicillin-Resistant Staphylococcus epidermidis.

Background In complicated endovascular infections by methicillin-resistant Staphylococcus aureus (MRSA) or Staphylococcus epidermidis (MRSE), when first-line therapy with vancomycin (VAN) or daptomycin (DAP) fails, combination therapy with ceftaroline (CFT) and DAP has been shown to be a useful approach as salvage therapy for persistent MRSA bacteremia. Objectives This study aimed to describe experience with daptomycin and ceftaroline combination therapy in MRSE-complicated endovascular infections. Methods A single-center retrospective review of consecutive patients with MRSE-complicated endovascular infections treated with ≥72 hours of DAP+CFT at any time during the course of treatment, from January 1, 2016 to December 31, 2020, at Centro Hospitalar Universitário São João (CHUSJ), Porto, Portugal, was conducted. The exclusion criteria were known resistance to daptomycin or ceftaroline, total time of combination therapy <72 hours and loss to follow-up. Results We identified seven cases that matched our criteria: five endocarditis and two central venous catheter infections. Six patients switched to combination therapy due to treatment failure with first-line agents - three due to persistent bacteremiaand three due to progression of infection despite negative blood cultures. Effective surgical source control took one to four weeks to occur. Three patients died during the treatment, one from progression of the disease and two due to another infection. Conclusions We consider the DAP+CFT combination therapy to be a valid and safe therapeutic choice in complicated patients, such as those with severe infection, poor functional status, and impossibility or delay of surgical source control. However, conclusions on the role of combination therapy should be careful due to the low number of patients and the several confounding factors.

A Retrospective Cohort Study Comparing Dual Therapy With Ceftaroline With Vancomycin or Daptomycin Monotherapy for High-Grade or Persistent MRSA Bacteremia.

Background: Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is a serious clinical infection associated with a high risk of mortality. Dual therapy is often used in patients with persistent bacteremia. Objective: This study aimed to compare the outcomes of vancomycin or daptomycin monotherapy with those of dual therapy with ceftaroline in high-grade or persistent MRSA bacteremia. Methods: We conducted a retrospective cohort study at a university teaching hospital between January 2014 and June 2021, involving adults initially treated with vancomycin or daptomycin. Patients were categorized into monotherapy and dual therapy groups. The primary outcome was 30-day mortality. Secondary outcomes included microbiological relapse and antibiotic-related adverse events. Results: In a group of 155 patients, 30-day mortality rates were similar between the monotherapy (23.4%) and dual therapy (22.6%) groups, with comparable microbiological relapse rates (6.5%). In inverse probability of treatment weighting analysis, we found no significant association between dual therapy and mortality (adjusted risk ratio [ARR] 1.38, 95% CI 0.64-2.41, P = 0.38) or microbiological relapse (ARR 0.95, 95% CI 0.31-2.73, P = 0.93). Dual therapy was associated with a lower risk of antibiotic-related adverse events (ARR 0.45, 95% CI 0.21-0.89, P = 0.02). Infectious diseases (ID) consultation was associated with a reduced mortality risk (ARR 0.27, 95% CI 0.07-0.95, P = 0.04). Conclusions: Dual therapy with ceftaroline did not reduce mortality risk compared with monotherapy in patients with MRSA bacteremia. However, patients with ID consultations showed a 73% reduction in mortality rates. Large-scale, prospective, and randomized controlled trials are needed to provide conclusive evidence regarding the potential benefits of dual therapy with ceftaroline for MRSA bacteremia.

In Vivo-Acquired Resistance to Daptomycin during Methicillin-Resistant Staphylococcus aureus Bacteremia.

Daptomycin (DAP) represents an interesting alternative to treat methicillin-resistant Staphylococcus aureus (MRSA) infections. Different mechanisms of DAP resistance have been described; however, in vivo-acquired resistance is uncharacterized. This study described the phenotypic and genotypic evolution of MRSA strains that became resistant to DAP in two unrelated patients with bacteremia under DAP treatment, in two hospitals in the South of France. DAP MICs were determined using broth microdilution method on the pairs of isogenic (DAP-S/DAP-R) S. aureus isolated from bloodstream cultures. Whole genome sequencing was carried out using Illumina MiSeq Sequencing system. The two cases revealed DAP-R acquisition by MRSA strains within three weeks in patients treated by DAP. The isolates belonged to the widespread ST5 (patient A) and ST8 (patient B) lineages and were of spa-type t777 and t622, respectively. SNP analysis comparing each DAP-S/DAP-R pair confirmed that the isolates were isogenic. The causative mutations were identified in MprF (Multiple peptide resistance Factor) protein: L826F (Patient A) and S295L (Patient B), and in Cls protein: R228H (Patient B). These proteins encoded both proteins of the lipid biosynthetic enzymes. The resistance to DAP is particularly poorly described whereas DAP is highly prescribed to treat MRSA. Our study highlights the non-systematic cross-resistance between DAP and glycopeptides and the importance of monitoring DAP MIC in persistent MRSA bacteremia.

Molecular characterization of MRSA collected during national surveillance between 2008 and 2019 in the Netherlands

Background.Although the Netherlands is a country with a low endemic level, methicillin-resistant Staphylococcus aureus (MRSA) poses a significant health care problem. Therefore, high coverage national MRSA surveillance has been in place since 1989. To monitor possible changes in the type-distribution and emergence of resistance and virulence, MRSA isolates are molecularly characterized.Methods.All 43,321 isolates from 36,520 persons, collected 2008–2019, were typed by multiple-locus variable number tandem repeats analysis (MLVA) with simultaneous PCR detection of the mecA, mecC and lukF-PV genes, indicative for PVL. Next-generation sequencing data of 4991 isolates from 4798 persons were used for whole genome multi-locus sequence typing (wgMLST) and identification of resistance and virulence genes.Results.We show temporal change in the molecular characteristics of the MRSA population with the proportion of PVL-positive isolates increasing from 15% in 2008–2010 to 25% in 2017–2019. In livestock-associated MRSA obtained from humans, PVL-positivity increases to 6% in 2017–2019 with isolates predominantly from regions with few pig farms. wgMLST reveals the presence of 35 genogroups with distinct resistance, virulence gene profiles and specimen origin. Typing shows prolonged persistent MRSA carriage with a mean carriage period of 407 days. There is a clear spatial and a weak temporal relationship between isolates that clustered in wgMLST, indicative for regional spread of MRSA strains.Conclusions.Using molecular characterization, this exceptionally large study shows genomic changes in the MRSA population at the national level. It reveals waxing and waning of types and genogroups and an increasing proportion of PVL-positive MRSA.

Clinical Outcomes of Ceftaroline Fosamil in the Treatment of Persistent Methicillin-Resistant Staphylococcus aureus Bacteremia

Abstract Background Limited evidence exists in the management of persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia with ceftaroline as salvage therapy. This retrospective study aims to evaluate the use of ceftaroline as salvage therapy in the treatment of persistent MRSA bacteremia (MRSAB). Methods Electronic medical charts of patients who received ceftaroline for the treatment of persistent MRSAB at an academic, quaternary care medical center from January 1, 2015, to December 31, 2021, were reviewed for clinical cure, reinfection, prior antibiotic use, source of infection, microbiological culture clearance, patient mortality, and adverse effects. Primary endpoints included clinical and microbiological success, and secondary endpoints were recurrence of infection and 60-day all-cause mortality. Results Nineteen patient charts were identified, and 9 patients met the inclusion criteria for this analysis. Vancomycin or daptomycin was given for a median of 7 ± 2.3 days, respectively, before the initiation of ceftaroline. The total daily dose of ceftaroline ranged from 400 to 1800 mg depending on the patients' kidney function. Five patients achieved clinical cure and 4 patients died. No patients experienced a recurrence. Three patients (33%) experienced adverse effects while on ceftaroline therapy. Conclusions The use of ceftaroline in persistent MRSAB demonstrated microbiological cure, clinical cure, and minimal reinfection in the reviewed patient population. Ceftaroline may be a potential treatment option for patients with persistent MRSAB as salvage therapy.

Gp05, a Prophage-Encoded Virulence Factor, Contributes to Persistent Methicillin-Resistant Staphylococcus aureus Endovascular Infection.

Persistent methicillin-resistant Staphylococcus aureus (MRSA) endovascular infections represent a serious public health threat. We recently demonstrated that the presence of a novel prophage ϕSA169 was associated with vancomycin (VAN) treatment failure in experimental MRSA endocarditis. In this study, we assessed the role of a ϕSA169 gene, ϕ80α_gp05 (gp05), in VAN-persistent outcome using gp05 isogenic MRSA strain sets. Of note, Gp05 significantly influences the intersection of MRSA virulence factors, host immune responses, and antibiotic treatment efficacy, including the following: (i) activity of the significant energy-yielding metabolic pathway (e.g., tricarboxylic acid cycle); (ii) carotenoid pigment production; (iii) (p)ppGpp (guanosine tetra- and pentaphosphate) production, which activates the stringent response and subsequent downstream functional factors (e.g., phenol-soluble modulins and polymorphonuclear neutrophil bactericidal activity); and (iv) persistence to VAN treatment in an experimental infective endocarditis model. These data suggest that Gp05 is a significant virulence factor which contributes to the persistent outcomes in MRSA endovascular infection by multiple pathways. IMPORTANCE Persistent endovascular infections are often caused by MRSA strains that are susceptible to anti-MRSA antibiotics in vitro by CLSI breakpoints. Thus, the persistent outcome represents a unique variant of traditional antibiotic resistance mechanisms and a significant therapeutic challenge. Prophage, a critical mobile genetic element carried by most MRSA isolates, provides their bacterial host with metabolic advantages and resistance mechanisms. However, how prophage-encoded virulence factors interact with the host defense system and antibiotics, driving the persistent outcome, is not well known. In the current study, we demonstrated that a novel prophage gene, gp05, significantly impacts tricarboxylic acid cycle activity, stringent response, and pigmentation, as well as vancomycin treatment outcome in an experimental endocarditis model using isogenic gp05 overexpression and chromosomal deletion mutant MRSA strain sets. The findings significantly advance our understanding of the role of Gp05 in persistent MRSA endovascular infection and provide a potential target for development of novel drugs against these life-threatening infections.

Effectiveness and Safety of Linezolid Versus Vancomycin, Teicoplanin, or Daptomycin against Methicillin-Resistant Staphylococcus aureus Bacteremia: A Systematic Review and Meta-Analysis.

Vancomycin (VCM) and daptomycin (DAP) are standard therapies for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, despite concerns regarding clinical utility and growing resistance. Linezolid (LZD) affords superior tissue penetration to VCM or DAP and has been successfully used as salvage therapy for persistent MRSA bacteremia, indicating its utility as a first-choice drug against MRSA bacteremia. In a systematic review and meta-analysis, we compared the effectiveness and safety of LZD with VCM, teicoplanin (TEIC), or DAP in patients with MRSA bacteremia. We evaluated all-cause mortality as the primary effectiveness outcome, clinical and microbiological cure, hospital length of stay, recurrence, and 90-day readmission rates as secondary effectiveness outcomes, and drug-related adverse effects as primary safety outcomes. We identified 5328 patients across 2 randomized controlled trials (RCTs), 1 pooled analysis of 5 RCTs, 1 subgroup analysis (1 RCT), and 5 case-control and cohort studies (CSs). Primary and secondary effectiveness outcomes were comparable between patients treated with LZD versus VCM, TEIC, or DAP in RCT-based studies and CSs. There was no difference in adverse event incidence between LZD and comparators. These findings suggest that LZD could be a potential first-line drug against MRSA bacteremia as well as VCM or DAP.

Persistent Methicillin-Resistant Staphylococcus aureus Bacteremia: Host, Pathogen, and Treatment.

Methicillin-resistant Staphylococcus aureus (MRSA) is a devastating pathogen responsible for a variety of life-threatening infections. A distinctive characteristic of this pathogen is its ability to persist in the bloodstream for several days despite seemingly appropriate antibiotics. Persistent MRSA bacteremia is common and is associated with poor clinical outcomes. The etiology of persistent MRSA bacteremia is a result of the complex interplay between the host, the pathogen, and the antibiotic used to treat the infection. In this review, we explore the factors related to each component of the host-pathogen interaction and discuss the clinical relevance of each element. Next, we discuss the treatment options and diagnostic approaches for the management of persistent MRSA bacteremia.

Transmission and microevolution of methicillin-resistant Staphylococcus aureus ST88 strain among patients, healthcare workers, and household contacts at a trauma and orthopedic ward.

Surgical sites infections (SSIs) caused by Methicillin-resistant Staphylococcus aureus (MRSA) constitute a major clinical problem. Understanding the transmission mode of MRSA is important for its prevention and control. We investigated the transmission mode of a MRSA outbreak in a trauma and orthopedic hospital ward. Clinical data were collected from patients (n = 9) with MRSA infection in a trauma and orthopedic ward from January 1, 2015 to December 31, 2019. The wards (n = 18), patients (n = 48), medical staff (n = 23), and their households (n = 5) were screened for MRSA. The transmission mode of MRSA isolates was investigated using next-generation sequencing and phylogenetic analyses. The resistance genes, plasmids, and single-nucleotide variants of the isolates were analyzed to evaluate microevolution of MRSA isolates causing SSIs. The MRSA colonization-positive doctor was asked to suspend his medical activities to stop MRSA spread. Nine MRSA infected patients were investigated, of which three patients were diagnosed with SSI and had prolonged hospitalization due to the persistent MRSA infection. After screening, MRSA isolates were not detected in environmental samples. The surgeon in charge of the patients with SSI caused by MRSA and his son were positive for MRSA colonization. The MRSA from the son was closely related to the isolates detected in MRSA-induced SSIs patients with 8-9 single-nucleotide variants, while ST88-MRSA isolates with three different spa types were detected in the surgeon's nasal cavity. Comparative genomic analysis showed that ST88-MRSA isolates acquired mutations in genes related to cell wall synthesis, colonization, metabolism, and virulence during their transmission. Suspending the medical activity of this surgeon interrupted the spread of MRSA infection in this ward. Community-associated MRSA clones can invade hospitals and cause severe postoperative nosocomial infections. Further MRSA surveillance in the households of health workers may prevent the transition of MRSA from colonization to infection.

Transcriptome Analyses of Prophage in Mediating Persistent Methicillin-Resistant Staphylococcus aureus Endovascular Infection.

Persistent methicillin-resistant Staphylococcus aureus (MRSA) endovascular infections represent a significant subset of S. aureus infections and correlate with exceptionally high mortality. We have recently demonstrated that the lysogenization of prophage ϕSA169 from a clinical persistent MRSA bacteremia isolate (300-169) into a clinical resolving bacteremia MRSA isolate (301-188) resulted in the acquisition of well-defined in vitro and in vivo phenotypic and genotypic profiles related to persistent outcome. However, the underlying mechanism(s) of this impact is unknown. In the current study, we explored the genetic mechanism that may contribute to the ϕSA169-correlated persistence using RNA sequencing. Transcriptomic analyses revealed that the most significant impacts of ϕSA169 were: (i) the enhancement of fatty acid biosynthesis and purine and pyrimidine metabolic pathways; (ii) the repression of galactose metabolism and phosphotransferase system (PTS); and (iii) the down-regulation of the mutual prophage genes in both 300-169 and 301-188 strains. In addition, the influence of different genetic backgrounds between 300-169 and 301-188 might also be involved in the persistent outcome. These findings may provide targets for future studies on the persistence of MRSA.

Persistent Methicilin-Resistant Staphylococcus aureus Bacteremia: Resetting the Clock for Optimal Management.

A positive follow-up blood culture for methicillin-resistant Staphylococcus aureus (MRSA) while on seemingly appropriate therapy is a common and ominous development. However, the definition and management of persistent MRSA bacteremia is unstandardized. In this Opinion Paper, we identify the presence of bacteremia for > 1 calendar day as a "worry point" that should trigger an intensive diagnostic evaluation to identify metastatic infection sites. Next, we define the duration of MRSA bacteremia that likely constitutes antibiotic failure and outline a potential management algorithm for such patients. Finally, we propose pragmatic clinical trial designs to test treatment strategies for persistent MRSA bacteremia.

The Host CYP1A1-Microbiota Metabolic Axis Promotes Gut Barrier Disruption in Methicillin-Resistant Staphylococcus aureus-Induced Abdominal Sepsis.

BackgroundHost-microbiota crosstalk has been implicated in multiple host metabolic pathway axes that regulate intestinal barrier function. Although constitutive cytochrome P4501A1 (CYP1A1) expression perturbs the microbiome-derived autoregulatory loop following enteric infection, little is known about the role of host CYP1A1 in modulating gut microbiome-mediated signaling during methicillin-resistant Staphylococcus aureus (MRSA)-induced abdominal sepsis and its effects on intestinal barrier integrity.MethodsAbdominal sepsis was induced by the intraperitoneal injection of MRSA in mice. The effect of CYP1A1 deficiency on gut barrier integrity was investigated using RNA sequencing, microbiome analyses, and targeted metabolomics. The microbiota-produced metabolites were validated in patients with sepsis and persistent MRSA infection.ResultsMice lacking CYP1A1 exhibited an altered gut microbiome, a reduced metabolic shift from lysine to cadaverine in the caecal contents and antimicrobial molecule production (Retnlb, Gbp7, and Gbp3), and they were protected against gut barrier disruption when subjected to MRSA challenge. These beneficial effects were validated in aryl hydrocarbon receptor (AHR) knockout (KO) mice by cohousing with CYP1A1 KO mice and abrogated after supplementation with cadaverine or Enterococcus faecalis, the primary microbiota genus for cadaverine synthesis. Antibiotic-driven gut dysbacteriosis impaired the survival benefit and disrupted the intestinal barrier integrity in CYP1A1 KO mice after MRSA infection. Furthermore, increased cadaverine levels in feces and serum were detected in critically ill patients with gut leakiness during persistent MRSA infection, whereas cadaverine was not detected in healthy controls. Additionally, microbiota-derived cadaverine induced enterocyte junction disruption by activating the histamine H4 receptor/nuclear factor-κB/myosin light-chain kinase signaling pathway.ConclusionThis study revealed the unexpected function of host CYP1A1 in microbiota-mediated cadaverine metabolism, with crucial consequences for dysbacteriosis following MRSA-induced abdominal sepsis, indicating that inhibiting CYP1A1 or blocking cadaverine-histamine H4 receptor signaling could be a potential therapeutic target against abdominal sepsis.Clinical Trial Registration[http://www.chictr.org.cn/index.aspx], identifier [ChiCTR1800018646].

New Mechanistic Insights into Purine Biosynthesis with Second Messenger c-di-AMP in Relation to Biofilm-Related Persistent Methicillin-Resistant Staphylococcus aureus Infections.

ABSTRACTPersistent methicillin-resistant Staphylococcus aureus (MRSA) endovascular infections represent a significant clinically challenging subset of invasive, life-threatening S. aureus infections. We have recently demonstrated that purine biosynthesis plays an important role in such persistent infections. Cyclic di-AMP (c-di-AMP) is an essential and ubiquitous second messenger that regulates many cellular pathways in bacteria. However, whether there is a regulatory connection between the purine biosynthesis pathway and c-di-AMP impacting persistent outcomes was not known. Here, we demonstrated that the purine biosynthesis mutant MRSA strain, the ΔpurF strain (compared to its isogenic parental strain), exhibited the following significant differences in vitro: (i) lower ADP, ATP, and c-di-AMP levels; (ii) less biofilm formation with decreased extracellular DNA (eDNA) levels and Triton X-100-induced autolysis paralleling enhanced expressions of the biofilm formation-related two-component regulatory system lytSR and its downstream gene lrgB; (iii) increased vancomycin (VAN)-binding and VAN-induced lysis; and (iv) decreased wall teichoic acid (WTA) levels and expression of the WTA biosynthesis-related gene, tarH. Substantiating these data, the dacA (encoding diadenylate cyclase enzyme required for c-di-AMP synthesis) mutant strain (dacAG206S strain versus its isogenic wild-type MRSA and dacA-complemented strains) showed significantly decreased c-di-AMP levels, similar in vitro effects as seen above for the purF mutant and hypersusceptible to VAN treatment in an experimental biofilm-related MRSA endovascular infection model. These results reveal an important intersection between purine biosynthesis and c-di-AMP that contributes to biofilm-associated persistence in MRSA endovascular infections. This signaling pathway represents a logical therapeutic target against persistent MRSA infections.

Impact of initial vancomycin pharmacokinetic/pharmacodynamic parameters on the clinical and microbiological outcomes of methicillin-resistant Staphylococcus aureus bacteremia in children.

Optimal vancomycin exposure is important to minimize treatment failure of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. We aimed to analyze the impact of initial vancomycin pharmacokinetic/pharmacodynamic (PK/PD) parameters, including the initial vancomycin C trough and the area under the curve (AUC)/minimal inhibitory concentration (MIC) on the outcomes of pediatric MRSA bacteremia. The study population consisted of hospitalized children aged between 2 months and 18 years with MRSA bacteremia, in whom C trough was measured at least one time within the time period of January 2010 to March 2018. Demographic profiles, underlying diseases, and clinical/microbiological outcomes were abstracted retrospectively. During the study period, 73 cases of MRSA bacteremia occurred in children with a median age of 12.4 months. Severe clinical outcomes leading to intensive care unit stay and/or use of mechanical ventilation occurred in 47.5% (35/73); all-cause 30-day mortality was 9.7% (7/72). The median dosage of vancomycin was 40.0 mg/kg/day. There was a weak linear relationship between C trough and the corresponding AUC/MIC (r = 0.235). ROC curves for achieving an AUC/MIC of 300 suggested that the initial C trough at 10 μg/mL could be used as a cut-off value with a sensitivity of 90.5% and a specificity of 44%. Although persistent bacteremia at 48-72 hours after vancomycin administration was observed more frequently when the initial C trough was < 10 μg/mL and initial AUC/MIC was < 300, initial AUC/MIC < 300 was the only risk factor associated with persistent bacteremia at 48-72 hours (adjusted OR 3.05; 95% CI, 1.07-8.68). Initial C trough and AUC/MIC were not associated with 30-day mortality. Although there was a weak relationship between C trough and AUC/MIC, initial AUC/MIC < 300 could be used as a predictor of persistent MRSA bacteremia at 48-72 hours. Further prospective data on optimal vancomycin dosing are necessary to improve clinical and microbiological outcomes in pediatric MRSA bacteremia.

SarA-Dependent Antibiofilm Activity of Thymol Enhances the Antibacterial Efficacy of Rifampicin Against Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious human pathogen which has been listed as a high-priority multi-drug resistance pathogen by the World Health Organization (WHO). Persistent MRSA infections are often associated with biofilm formation and resistance to conventional antimicrobial therapy. Inhibiting the surface adherence and the virulence of the bacterium is the current alternative approach without affecting growth to reduce the possibility of resistance development. Although numerous antibiofilm agents have been identified, their mode of action remains unclear. Combining two drugs with different modes of action will improve the efficiency of the treatment strategy against MRSA. The present study was aimed to decipher the molecular mechanism underlying the antibiofilm activity of thymol against MRSA and assess the ability of thymol to improve the antibacterial activity of rifampicin. Thymol significantly inhibited 88% of MRSA biofilm formation at 100 μg/ml and reduced the surface adherence of MRSA on glass, stainless steel, and titanium surface coated with human plasma as evidenced by microscopic analyses. qPCR analysis of global virulence regulatory genes and biofilm assay with S. aureus wild type, ΔsarA, and Δagr strains revealed the sarA-mediated antibiofilm activity of thymol and inhibition of sarA-controlled virulence factors. Congo red assay and erythrocyte lysis assay further confirmed the reduction in polysaccharide intracellular adhesin and hemolysin. Importantly, thymol enhanced the antibacterial and the biofilm eradication efficiency of rifampicin against MRSA and also reduced the formation of persisters. Thus, the present study reveals the sarA-dependent antibiofilm efficacy of MRSA and suggests thymol as the promising combinatorial candidate in potentiating the antibacterial activity of rifampicin against persistent MRSA infections.

Focusing the Lens on the CAMERA Concepts: Early Combination β-Lactam and Vancomycin Therapy in Methicillin-Resistant Staphylococcus aureus Bacteremia.

Methicillin-resistant Staphylococcus aureus (MRSA) has grown to become a major burden on health care systems. The cumulation of limited therapeutic options and worsened patient outcomes with persistent MRSA bacteremia has driven research in optimizing its initial management. The guidelines published by the Infectious Diseases Society of America currently recommend combination therapy for refractory MRSA bacteremia, but the utility of combining antibiotics from the start of therapy is under investigation. The alternative strategy of early use of β-lactam antibiotics in combination with vancomycin upon initial MRSA bacteremia detection has shown promise. While this concept has gained international attention, providers should give this strategy serious consideration prior to implementation. The objective of this review is to examine retrospective and prospective evidence for early combination with vancomycin and β-lactam antibiotics, as well as explore potential consequences of combination therapy.

The Stringent Response Contributes to Persistent Methicillin-Resistant Staphylococcus aureus Endovascular Infection Through the Purine Biosynthetic Pathway.

Persistent methicillin-resistant Staphylococcus aureus (MRSA) endovascular infections represent a significant clinical-therapeutic challenge. Of particular concern is antibiotic treatment failure in infections caused by MRSA that are "susceptible" to antibiotic in vitro. In the current study, we investigate specific purine biosynthetic pathways and stringent response mechanism(s) related to this life-threatening syndrome using genetic matched persistent and resolving MRSA clinical bacteremia isolates (PB and RB, respectively), and isogenic MRSA strain sets. We demonstrate that PB isolates (vs RB isolates) have significantly higher (p)ppGpp production, phenol-soluble-modulin expression, polymorphonuclear leukocyte lysis and survival, fibronectin/endothelial cell (EC) adherence, and EC damage. Importantly, an isogenic strain set, including JE2 parental, relP-mutant and relP-complemented strains, translated the above findings into significant outcome differences in an experimental endocarditis model. These observations indicate a significant regulation of purine biosynthesis on stringent response, and suggest the existence of a previously unknown adaptive genetic mechanism in persistent MRSA infection.

Unidirectional animal-to-human transmission of methicillin-resistant Staphylococcus aureus ST398 in pig farming; evidence from a surveillance study in southern Italy

BackgroundLivestock-associated methicillin-resistant Staphylococcus aureus (MRSA) belonging to clonal complex 398 is recognized as an occupational hazard for workers employed in intensive animal husbandry, especially in the swine-breeding chain. In this study, we compared the prevalence and epidemiological type of MRSA isolates from swine and farm workers in a large area of southern Italy.MethodsBetween January and March 2018, 88 workers from 32 farms where we had previously performed a survey for MRSA colonization of farmed pigs, were sampled by nasal swabbing. A follow-up investigation was conducted on seven workers 1 year after primary screening. MRSA isolates were characterized by MLST, spa and SCCmec typing, and tested for susceptibility to 15 antimicrobials. Epidemiological correlations between human and swine MRSA isolates were supported by Rep-MP3 and RAPD PCR fingerprinting, and whole-genome sequencing.ResultsThe overall colonization rate of MRSA in swine farm workers was 21.6%, being significantly higher in intensive farms and in workers with direct animal contact. All human MRSA isolates were multi-drug resistant, belonged to the ST398 livestock clade, and did not carry Panton-Valentine leukocidin and enterotoxin genes. Notably, 94.1% of human MRSA isolates belonged to the same epidemiological type as swine MRSA isolates from the corresponding farm. Persistent MRSA carriage was documented in some workers 1 year after primary sampling.ConclusionsWe report a high prevalence of MRSA among swine farm workers, with higher colonization rates associated with intensive breeding and animal exposure. Our findings suggest unidirectional animal-to-human transmission of LA-MRSA and denote the high zoonotic transmissibility of the ST398 livestock clade.

The first report of Methicillin-resistant Staphylococcus aureus (MRSA) in cystic fibrosis (CF) patients in Saudi Arabia.

IntroductionMethicillin-resistant Staphylococcus aureus infections have been increasingly reported in patients with cystic fibrosis (CF) who have progressive deterioration in their pulmonary function.ObjectivesTo determine the prevalence of MRSA infections in CF in a tertiary care center in Saudi Arabia.MethodologyThis is a retrospective chart review conducted as part of the CF registry data from 1 January 2002 to 1 June 2016. All patients with confirmed CF of all age groups who had a respiratory culture positive for MRSA were included in the study.ResultsAmong 385 patients with CF who had respiratory samples, 43 (11%) were positive for MRSA at a mean age of 10.4 ± 7.2 years. Twenty-two patients out of the 43 (51%) were treated with different regimens: nasal Bactroban in 13/22 (59%); a combination of nasal Bactroban, oral vancomycin, and rifampicin for 2 weeks in 5 patients (23%); Bactroban and linezolid in one patient (5%); and oral vancomycin and rifampicin in 3 patients (14%). Eight out of the 22 treated patients (36%) achieved MRSA eradication. Six out of the 22 treated (27%) had experienced MRSA recurrence within 3–6 months, and another 5/22 (23%) continued to have MRSA colonization up to 2–4 years of follow-up despite using a proper eradication protocol. Twelve out of the 43 (28%) patients with MRSA infection died.ConclusionMRSA infection in our population with CF is common. Therefore, an eradication protocol should be instituted at an early stage to prevent chronic colonization. Children with persistent MRSA colonization have high morbidity and mortality rate.