Staphylococcus aureus bacteraemia and endocarditis - epidemiology and outcome: a review

Impeding Biofilm-Forming Mediated Methicillin-Resistant Staphylococcus aureus and Virulence Genes Using a Biosynthesized Silver Nanoparticles-Antibiotic Combination

Methicillin-resistant Staphylococcus aureus (MRSA) continues to represent a significant clinical challenge, characterized by consistently elevated rates of morbidity and mortality. Care regimen success is still difficult and necessitates assessing new antibiotics as well as supplemental services, including source control and searching for alternative approaches to combating it. Hence, we propose to synthesize silver nanoparticles (Ag-NPs) by employing a cell-free filter (CFF) of Streptomyces sp. to augment antibiotic activity and combat biofilm-forming MRSA. Seven bacterial isolates from clinical samples were identified, antibiotics were profiled with Vitek-2, and the phenotypic detecting of biofilm with Congo red medium and microplate assay was carried out. The PCR technique was used for detecting genes (icaA and icaD) coded in biofilm forming. The characterization of Ag-NPs was performed using several analytical methods, such as UV spectroscopy, dynamic light scattering (DLS), zeta potential measurement, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The antibacterial properties of Ag-NPs and oxacillin-Ag-NPs were assessed against standard strains and clinical isolates by employing the agar well diffusion technique and the microdilution assay. The biogenic synthesis Ag-NPs resulted in uniformly spherical particles, with an average size of 20 nm. These Ag-NPs demonstrated significant activity against biofilm-forming MRSA, with minimum inhibitory concentrations (MICs) ranging from 12 to 15 μg/mL. Additionally, Ag-NPs completely impede biofilm formation by MRSA at sublethal doses of 0.75 MICs. The expression levels of the icaA and icaD genes were reduced by 1.9- to 2.2- and 2.4- to 2.8-fold, respectively. A significant synergistic effect was noted when Ag-NPs were used in combination with oxacillin, leading to reduced MICs of 1.87 μg/mL for oxacillin and 4.0 μg/mL for Ag-NPs against MRSA. The FICi of 0.375 further validated the synergistic relationship between oxacillin and Ag-NPs at the concentrations of 1.87 and 4 μg/mL. Findings from the time-kill test demonstrated the highest reduction in log10 (CFU)/mL of the initial MRSA inoculum after 12-hour exposure. The cytotoxicity analysis of Ag-NPs revealed no significant cytotoxic effects on the human skin cell line HFB-4 at low concentrations, with IC50 values of 61.40 µg/mL for HFB-4 and 34.2 µg/mL for HepG-2. Comparable with oxacillin-Ag-NPs, Ag-NPs showed no cytotoxic effects on HFB-4 at different concentrations and exhibited an IC50 value of 31.2 against HepG-2-cells. In conclusion, the biosynthesis of Ag-NPs has demonstrated effective antibacterial activity against MRSA and has completely hindered biofilm formation, suggesting a valuable alternative for clinical applications.

Antibiotic susceptibility and molecular characterization based on whole-genome sequencing of Staphylococcus aureus causing invasive infection in children and women living in Southwest China during 2018-2023

BACKGROUND

Staphylococcus aureus is one of the most common pathogens that colonizes human skin/mucous membranes, where it causes local infection that can progress to invasive infection, resulting in high morbidity and mortality worldwide. This study aimed to investigate the antibiotic susceptibility and molecular characteristics of invasive S. aureus in children and women in Southwest China from 2018 to 2023 to provide novel insights helpful in preventing and treating S. aureus infections.

METHODS

The demographic and clinical characteristics of patients with invasive S. aureus infection were collected and analyzed. Next-generation sequencing (NGS) and sequence analysis techniques were used to determine the molecular epidemiological characteristics of the S. aureus isolates, and the microdilution broth method was used for antimicrobial susceptibility testing.

RESULTS

A total of 108 invasive S. aureus isolates, 29 methicillin-resistant S. aureus (MRSA) isolates and 79 methicillin- susceptible S. aureus (MSSA) isolates, were included. The isolates had the highest rate of resistance to PEN, at 91.67%, with all the MRSA isolates being resistant; the next highest resistance was to ERY and CLI, both at 65.74%. A total of 32 STs (including 8 novel STs) were detected and divided into 10 CCs. Moreover, 45 spa types were also detected. The main STs were ST22 (17.59%) and ST59 (15.74%), and the main CCs were CC59 (21.30%) and CC22 (19.44%). The most prevalent spa types were t309 and t437, both at 14.81%, and the SCCmec type could be assigned to two categories: IV (62.07%) and V (34.48%). Among the 29 MRSA isolates tested, CC59-IV-t437 (34.48%) and CC59-V-t437 (13.79%) were the main lineages, and among the 79 MSSA isolates, CC22-t309 (18.99%), CC1-t189 (10.13%), and CC5-t002 (7.60%) were the main lineages. Except for SXT, the resistance rates of the 29 MRSA isolates were greater than those of the MSSA isolates. Most isolates carried common virulence genes, among which the carriage rate of pvl reached 33.33%.

CONCLUSIONS

This study provides valuable information, including the prevalence, molecular characteristics and antimicrobial resistance of S. aureus isolates that cause invasive infectious diseases in Southwest China, and the findings may advance the prevention and treatment of S. aureus infections.

Sequential Therapy of Linezolid and Contezolid to Treat Hematogenous Lung Abscess Caused by Staphylococcus aureus in a Congenital Cerebral Hypoplasia Patient: A Case Report

Staphylococcus aureus is a common pathogen of hematogenous lung abscesses. The increased resistance of S. aureus to antibiotics makes infections difficult to treat, often resulting in a poor prognosis. Therefore, it is important to identify S. aureus infections as early as possible and evaluate its sensitivity and resistance to antibiotics, to formulate an appropriate treatment plan. Oxazolidinone antibiotics exhibit potent antibacterial activity against multidrug-resistant (MDR) S. aureus; however, the adverse effects of linezolid, particularly thrombocytopenia, limit its application. Contezolid may ameliorate the hematologic toxicity associated with linezolid. Here, we report the case of a patient with congenital cerebral hypoplasia who was hospitalized due to fever and multiple abscesses in both lungs. In the context of negative blood culture results, the final diagnosis of MDR S. aureus as the causative agent of hematogenous lung abscess was confirmed using macrogenomic next-generation sequencing (mNGS) and targeted next-generation sequencing (tNGS). The patient was treated with linezolid but developed significant thrombocytopenia, so switching to sequential therapy with contezolid, the patient's platelet counts returned to normal and his condition improved significantly.

99mTc-DTPA-Collagen Radiotracer for the Noninvasive Detection of Infective Endocarditis

Infective endocarditis (IE) represents a significant concern among hospital-acquired infections, frequently caused by the Gram-positive bacterium Staphylococcus aureus. Nuclear imaging is emerging as a noninvasive and precise diagnostic tool. However, the gold standard radiotracer [18F]-FDG cannot distinguish between infection and inflammation, resulting in false positives. Based on the presence of collagen-binding proteins in the cell wall of S. aureus, we propose the radiolabeling of collagen for its evaluation in IE animal models by single-photon emission computed tomography (SPECT) imaging. We radiolabeled rat tail collagen I using DTPA chelator and [99mTc]NaTcO4. Selectivity was evaluated in vitro using 3 Gram-positive bacteria, 1 Gram-negative bacteria and 1 yeast. In vivo SPECT/computed tomography (CT) imaging was conducted on 8 SD rat models of IE and 8 sterile sham model as controls. Ex vivo biodistribution and autoradiography were performed following imaging. Diagnosis of IE was confirmed through microbiological studies and H&E histopathology. [99mTc]-DTPA-Collagen was synthesized successfully with a yield of 42.86 ± 6.35%, a purity of 95.84 ± 1.85% and a stability higher than 90% after 50 h postincubation. In vitro uptake demonstrated the selectivity for Gram-positive bacteria (63.85 ± 15.15%). Ex vivo analysis confirmed hepato-splenic excretion. In vivo SPECT/CT imaging revealed highly localized uptake within the aortic valve with a sensitivity of 62.5% and specificity of 87.5%. We successfully synthesized and characterized a new SPECT radiotracer based on [99mTc]Tc-radiolabeled collagen. In vitro studies demonstrated the selectivity of the radiotracer for Gram-positive bacteria. In vivo SPECT/CT-based assessment in an IE model confirmed the potential of this approach to detect active IE.

Reshaping the battlefield: A decade of clonal wars among Staphylococcus aureus in China

BACKGROUND

Long-term comprehensive studies on the genomic epidemiology of both methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolates are limited in China. Here, we aimed to assess the genomic epidemiological characteristics and population dynamics of S. aureus in China.

METHODS

We performed whole-genome sequencing and resistance phenotyping on 3848 S. aureus isolates from bloodstream infections across 72 hospitals in 22 provinces, from 2011 to 2020 in China. We explored the dynamic trends in the resistance/virulence genes and mobile genetic element profiles across lineages, and conducted time-scaled phylogenetic investigation for prevalent lineages.

FINDINGS

The results revealed 315 different sequence types (STs) among all strains, 205 of which were novel. Significant shifts in MRSA population structure were observed, with ST59 replacing ST239 as the dominant lineage, exhibiting widespread inter-hospital transmission and increasing lineage diversity. In contrast, the composition of predominant MSSA lineages, ST188 (11.21 %), ST7 (9.79 %), ST22 (9.10 %), ST5 (8.56 %) and ST398 (7.91 %), remained relatively stable over time, with the diversity among MSSA strains consistently preserved at the population level. Phylogenetic reconstruction showed that ST59, ST398, ST22 and ST188 MSSA could evolve into corresponding MRSA lineages through the acquisition of staphylococcal cassette chromosome mec (SCCmec) elements. Moreover, the distribution patterns of resistance and virulence genes closely correlated with different lineages, where the proportion of PVL+ isolates in MRSA is rising. Concurrently, changes in the MRSA population structure led to an overall decrease in the number of resistance and virulence genes, significantly increased antimicrobial sensitivity.

INTERPRETATION

The shifting genomic landscape of S. aureus in China underscores the need for tailored antimicrobial stewardship and enhances understanding of its epidemiological trends over the past decade.

Essential oils of Eugenia spp. (myrtaceae) show in vitro antibacterial activity against Staphylococcus aureus isolates from bovine mastitis

Bovine mastitis, an inflammation of the mammary glands, is mainly caused by bacteria such as Staphylococcus aureus. While antibiotics are the primary treatment for this disease, their effectiveness is often diminished due to resistant strains and biofilm formation, creating the need for safer and more efficient therapies. Plant-based oil therapies, particularly those derived from the genus Eugenia, are gaining popularity due to their pharmacological potential and historical use. In this study, we evaluated the antibacterial, antibiofilm, and synergistic potential of essential oils (EOs) from four species of the genus Eugenia (E. brejoensis, E. gracillima, E. pohliana, and E. stictopetala) against S. aureus isolates from bovine mastitis. The EO of E. stictopetala was obtained by hydrodistillation, and its composition was analyzed using gas chromatography coupled with mass spectrometry. The experiment employed seven clinical isolates from mastitis and two control strains: ATCC 33591 (methicillin-resistant S. aureus - MRSA) and ATCC 25923 (methicillin-susceptible and biofilm producer). A broth microdilution assay was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the EOs and oxacillin. The EO of E. stictopetala contained (E)-caryophyllene (18.01%), β-pinene (8.84%), (E)-nerolidol (8.24%), and α-humulene (6.14%) as major compounds. In the MIC assay, all essential oils showed bactericidal and bacteriostatic effects, especially the species E. brejoensis and E. pohliana, which had MICs ranging from 64 to 256 µg/mL. Regarding the antibiofilm effect, all essential oils were capable of interfering with biofilm formation at subinhibitory concentrations of ½ and ¼ of the MIC. However, they did not significantly affect pre-established biofilms. Additionally, a synergistic interaction was detected between the EOs and oxacillin, with a reduction of 75-93.75% in the antimicrobial MIC. Molecular docking studies indicated that the phytochemicals β-(E)-caryophyllene, (E)-nerolidol, Δ-elemene, and α-cadinol present in the EOs formed more stable complexes with penicillin-binding proteins, indicating a possible mechanism of antibacterial action. Therefore, these results show that the essential oils of Eugenia spp. are promising sources for the development of new therapeutic methods, opening new perspectives for a more effective treatment of bovine mastitis.

Heartfelt Impact: A Descriptive Analysis of Ceftaroline-Containing Regimens in Endocarditis due to Methicillin-Resistant Staphylococcus aureus

INTRODUCTION

Infective endocarditis (IE) due to methicillin-resistant Staphylococcus aureus (MRSA) is characterized by frequent treatment failure to first-line agents and high mortality, necessitating use of alternative management strategies. Ceftaroline fosamil (CPT) is a cephalosporin antibiotic with activity against MRSA but without regulatory approval for the indication of IE. This study describes clinical experience with CPT-based regimens utilized in MRSA-IE.

METHODS

This is a retrospective, observational, descriptive analysis of patients from two major urban medical centers in Detroit, Michigan from 2011 to 2023. Included adult patients (≥ 18 years) had ≥ 1 positive blood culture for MRSA, met definitive clinical criteria for IE, and received CPT for ≥ 72 h. The primary outcome was treatment failure, defined as a composite of 30-day all-cause mortality from index culture or failure to improve or resolve infectious signs/symptoms after CPT initiation.

RESULTS

Seventy patients were included. The median (interquartile range [IQR]) age was 51 (34-63) years and 45.7% were male. Persons with injection drug use (PWID) made up 55.7% of the cohort and right-sided IE was the most prevalent subtype (50.0%). CPT was frequently employed second-line or later, often in combination with vancomycin (10.0%) or daptomycin (72.9%). Overall, 31.4% experienced treatment failure and 30-day all-cause mortality occurred in 15.7%.

CONCLUSIONS

These findings illustrate the challenges posed by MRSA-IE, including frequent treatment failures, and highlight the utilization of CPT as salvage therapy. Comparative studies are needed to more clearly define its role in MRSA-IE.

Identification and validation of diagnostic biomarkers and immune cell abundance characteristics in Staphylococcus aureus bloodstream infection by integrative bioinformatics analysis

Staphylococcus aureus (S. aureus) is an opportunistic pathogen that could cause life-threatening bloodstream infections. The objective of this study was to identify potential diagnostic biomarkers of S. aureus bloodstream infection. Gene expression dataset GSE33341 was optimized as the discovery dataset, which contained samples from human and mice. GSE65088 dataset was utilized as a validation dataset. First, after overlapping the differentially expressed genes (DEGs) in S. aureus infection samples from GSE33341-human and GSE33341-mice samples, we detected 63 overlapping genes. Subsequently, the hub genes including DRAM1, PSTPIP2, and UPP1 were identified via three machine-learning algorithms: random forest, support vector machine-recursive feature elimination, and least absolute shrinkage and selection operator. Additionally, the receiver operating characteristic curve was leveraged to verify the efficacy of the hub genes. DRAM1 (AUC=1), PSTPIP2 (AUC=1), and UPP1 (AUC=1) were investigated and demonstrated significant expression differences (all P < 0.05) and diagnostic efficacy in the training and validation datasets. Furthermore, the relationship between the diagnostic markers and the abundance of immune cells was assessed using cell-type identification by estimating relative subsets of RNA transcripts (CIBERSORT). These three diagnostic indicators also correlated with multiple immune cells to varying degrees. The expression of DRAM1 was significantly positively correlated with B cell naive and mast cell activation, and negatively correlated with NK cells and CD4/CD8+ T cells. The expression of PSTPIP2 was significantly positively correlated with macrophage M0, macrophage M1, B cell naive, and dendritic cell activation, while the expression of PSTPIP2 was negatively correlated with NK cells and CD4/CD8+ T cells. Significant negative correlations between UPP1 expression and T cell CD4 memory rest and neutrophils were also observed. Finally, we established a mouse model of S. aureus bloodstream infection and collected the blood samples for RNA-Seq analysis and RT-qPCR experiments. The analysis results in RNA-Seq and RT-qPCR experiments further confirmed the significant expression differences (all P < 0.05) of these three genes. Overall, three candidate hub genes (DRAM1, PSTPIP2, and UPP1) were identified initially for S. aureus bloodstream infection diagnosis. Our study could provide potential diagnostic biomarkers for S. aureus bloodstream infection patients.

Staphylococcus aureus bacteraemia for the general physician: A narrative review of a metastatic infection with malignant complications

Staphylococcus aureus bacteraemia (SAB) is a multi-system disease associated with a 20-25% mortality in the UK setting. Many patients with SAB are admitted acutely unwell and are treated by the general physician. This review summarises the key management steps that a general physician needs to be aware of when treating patients with SAB. Successful management relies on appropriate empirical and definitive antimicrobial therapy, effective source control, accurate risk stratification and timely identification of metastatic foci of infection, as well as exclusion of infective endocarditis, which can be present in up to 10% of patients with SAB.

Enhancement of Fluoride's Antibacterial and Antibiofilm Effects against Oral Staphylococcus aureus by the Urea Derivative BPU

Background: The oral cavity is an important but often overlooked reservoir for Staphylococcus aureus. The effective control and prevention of S. aureus colonization and infection in the oral and maxillofacial regions are crucial for public health. Fluoride is widely used in dental care for its remineralization and antibacterial properties. However, its effectiveness against S. aureus has not been thoroughly investigated. Objectives: This study aimed to evaluate the potential of combining sodium fluoride (NaF) with compounds to enhance its antibacterial and antibiofilm effects against S. aureus. Method: We found that a urea derivative significantly enhances the efficacy of fluoride by promoting the retention of fluoride ions within the cells. The synergistic antibacterial and antibiofilm effects of BPU with NaF were confirmed through various assays, including checkerboard assays, time-kill assays, and growth curve analysis. These findings were further supported by additional methods, including transmission electron microscopy (TEM), in silico simulations, and gene overexpression studies. Results: These findings suggest that targeting fluoride ion membrane exporters could enhance antibacterial efficacy. When combined with fluoride, 1,3-Bis [3,5-bis(trifluoromethyl)phenyl]urea (BPU) showed increased effectiveness in inhibiting S. aureus growth and reducing established biofilms. Conclusions: This novel combination represents a promising therapeutic strategy for treating biofilm-associated S. aureus infections, offering a new strategy in oral healthcare. To fully evaluate the clinical potential of this synergistic therapy, further in vivo studies are essential.

Incidence and predictive factors of mortality of infective endocarditis in adults with congenital heart disease: A systematic review and meta-analysis

INTRODUCTION

Congenital heart diseases (CHD) with abnormal turbulent blood flow are associated with the highest risk of infective endocarditis (IE). Despite advancement in diagnostics and treatment, the mortality rate of IE remains high due the life-threatening complications. Our study aims to assess the incidence and mortality rates of IE and predictive factors for mortality among adults CHD (ACHD).

METHODS

A systematic literature search was conducted on PubMed, SCOPUS, and Ovid SP to retrieve relevant studies. The pooled estimates and predictors of mortality were calculated using the random-effects generic inverse variance method using R programming.

RESULTS

12 studies involving 3738 ACHD patients were included in this meta-analysis. The overall incidence of IE in ACHD was 1.26 per 1000 patient-years (95% CI 0.55-1.96). 60% (95% CI 46-72%) of patients had surgical management for IE. The mortality rate of IE was 9% (95% CI 7-12%). The predictors of mortality were conservative management (OR: 5.07, 95% CI: 4.63-5.57), renal dysfunction (OR: 4.15, 95% CI: 2.92-5.88), cerebral complications (OR: 3.59, 95% CI: 1.78-7.23), abscesses/valve complications (OR: 2.67, 95% CI: 1.71-4.16), Staphylococcus aureus infection (OR: 2.32, 95% CI: 1.33-4.06), emboli (OR: 2.03, 95% CI: 1.47-2.79), body mass index (OR: 1.10, 95% CI: 1.01-1.21), age (OR: 1.02, 95% CI: 1.00-1.04), and previous IE (OR: 1.02, 95% CI: 1.00-1.04).

CONCLUSION

The mortality rate of IE in ACHD is low. However, conservative management is associated with the highest risk of mortality.

Prevalence of Selected Immune Evasion Genes and Clonal Diversity in Methicillin-Susceptible Staphylococcus aureus Isolated from Nasal Carriers and Outpatients with Cut Wound Infections

Staphylococcus aureus, being one of the most common human pathogens, is responsible for infections in both hospital and community settings. Its virulence is attributed to its ability to evade the immune system by producing immune evasion (IE) proteins. The aim of this study was to detect the frequency of selected IE genes (spin, sbi, sea, sak, chp, scin, sep, ecb), belonging to the immune evasion cluster (IEC), and IEC types in 86 methicillin-susceptible S. aureus (MSSA) strains isolated from unrelated outpatients. In order to determine the diversity of analyzed strains, the phylogenetic relatedness was also determined. All strains were examined for the presence of IE genes using polymerase chain reaction assay. To analyze the clonal relatedness of S. aureus, pulsed-field gel electrophoresis (PFGE) was performed. All analyzed strains harbored the scn gene, followed by sbi (95.4%), ecb (91.7%), spin (89.5%), sak (83.7%), chp (67.4%), sep (67.4%) and sea (5.8%). Seventy-three (84.9%) S. aureus strains were classified into IEC types, of which, IEC type F was most commonly observed. IEC type A was not detected. PFGE results showed no association between clonal relatedness and the presence of IE genes/IEC types. In conclusion, the abundant and so diverse repertoire of genes determining invasion in analyzed strains may prove the fact that these strains are highly advanced and adapted to evade the host immune response.

The Oral Cavity-Another Reservoir of Antimicrobial-Resistant Staphylococcus aureus?

Staphylococcus aureus is one of the most common potentially pathogenic bacteria that may asymptomatically colonize many sites of healthy carriers. Non-nasal carriage, especially in the oral cavity, and its role in transmitting antimicrobial-resistant S. aureus strains in the healthcare community, is poorly understood. This study aimed to assess the prevalence and antimicrobial susceptibility of S. aureus in both oral and nasal cavities among preclinical dentistry students. A total of 264 oral and nasal swabs were taken from 132 participants, and all specimens were cultured using standard diagnostic procedures and antimicrobial susceptibility testing (EUCAST). The prevalence of S. aureus exclusively in the nasal (11.4%) or oral (9.1%) cavity was comparable, while concurrent oral and nasal carriage was present in 27.3% of participants. Although antibiotic resistance rates observed in both oral and nasal isolates were similar (ranging from 2.7% to 95.5%), 16.7% of carriers exhibited distinct antibiotic resistance profiles between oral and nasal isolates. Three (2.7%) methicillin-resistant S. aureus (MRSA) were isolated from the mouth and nose but multidrug resistance (27.3%) was more frequent in the oral than in the nasal isolates: 34% and 21.1%, respectively. This study demonstrated that preclinical dentistry students have a similar rate of oral S. aureus carriage as the nasal carriage rate, and that the oral cavity can be colonized by antimicrobial-resistant strains that do not originate from the nose. Consequently, the oral cavity seems to be an unjustly overlooked body site in screening for S. aureus carriage.

Risk of infective endocarditis and complicated infection in Staphylococcus aureus bacteremia - a retrospective cohort study on the role of bacteriuria

PURPOSE

S. aureus bacteremia (SAB) is a common and severe infection with high mortality and morbidity. The clinical relevance of the finding of concurrent S. aureus bacteriuria (SABU) is debated. The goal of this study was to analyze whether a concurrent SABU is associated with complicated SAB, infective endocarditis (IE) and mortality.

METHODS

We conducted a retrospective cohort study, reviewing medical charts of all episodes of SAB in patients > 18 years in the region of Skåne, Sweden, between 1st of January and 31st of June 2020. Episodes where a concurrent urine culture was performed were included for analysis. An episode was considered as complicated SAB if there was either attributable mortality, recurrent infection, embolic stroke, or occurrence of a complicated focus of infection.

RESULTS

During the study period, there were 279 episodes of SAB. 154 episodes met the eligibility criteria, of whom 37 (24%) had concurrent SABU. In 78 episodes (51%), the patients had a complicated SAB. There was a significantly lower proportion of complicated SAB for episodes with concurrent SABU (32%), compared to episodes without concurrent SABU (56%), p-value 0.014. Moreover, in the cohort there were 11 episodes (7.1%) of IE and a 30 days mortality rate of 16%, with no difference between the groups with or without SABU.

CONCLUSIONS

There is an association between concurrent SABU and a decreased risk for complicated SAB among patients with SAB. This study found no significant association between SABU and neither IE nor mortality for patients with SAB.

Polyclonal but not monoclonal circulating memory CD4+ T cells attenuate the severity of Staphylococcus aureus bacteremia

Staphylococcus aureus bacteremia causes significant morbidity and mortality. Treatment of staphylococcal infections is hindered by widespread antibiotic resistance, and attempts to develop an S. aureus vaccine have failed. Improved S. aureus treatment and infection prevention options require a deeper understanding of the correlates of protective immunity. CD4+ T cells have been identified as key orchestrators in the defense against S. aureus, but uncertainties persist regarding the subset, polarity, and breadth of the memory CD4+ T-cell pool required for protection. Here, using a mouse model of systemic S. aureus infection, we discovered that the breadth of bacterium-specific memory CD4+ T-cell pool is a critical factor for protective immunity against invasive S. aureus infections. Seeding mice with a monoclonal bacterium-specific circulating memory CD4+ T-cell population failed to protect against systemic S. aureus infection; however, the introduction of a polyclonal and polyfunctional memory CD4+ T-cell pool significantly reduced the bacterial burden. Our findings support the development of a multi-epitope T-cell-based S. aureus vaccine, as a strategy to mitigate the severity of S. aureus bacteremia.

Performance of Risk Scores in Predicting Infective Endocarditis in Patients with Staphylococcus aureus Bacteraemia in a Prospective Asian Cohort

Background: Several risk scores have been derived to predict the risk of infective endocarditis (IE) amongst patients with Staphylococcus aureus bacteraemia (SAB), which helps to guide clinical management. Methods: We prospectively studied 634 patients admitted with SAB. The cohort was stratified into those with or without IE, and the PREDICT Day 1, Day 5 and VIRSTA scores were tabulated. Area under the receiver operating characteristic (AUC) curves were constructed to compare the performance of each score. Results: Of the 634 patients examined, 36 (5.7%) had IE. These patients were younger (51.6 ± 20.1 vs. 59.2 ± 18.0 years, p = 0.015), tended to have community acquisition of bacteraemia (41.7% vs. 17.9%, p < 0.001), and had persistent bacteraemia beyond 72 h (19.4% vs. 6.0%, p = 0.002). The VIRSTA score had the best performance in predicting IE (AUC 0.76, 95%CI 0.66-0.86) compared with PREDICT Day 1 and Day 5. A VIRSTA score of <3 had the best negative predictive value (97.5%), compared with PREDICT Day 1 (<4) and Day 5 (<2) (94.3% and 96.6%, respectively). Conclusions: Overall, the risk scores performed well in our Asian cohort. If applied, 23.5% of the cohort with a VIRSTA ≥ 3 would require TEE, and a score of <3 had an excellent negative predictive value.

Staphylococcus aureus Infections and Human Intestinal Microbiota

Staphylococcus aureus (S. aureus) is a common pathogen that can cause many human diseases, such as skin infection, food poisoning, endocarditis, and sepsis. These diseases can be minor infections or life-threatening, requiring complex medical management resulting in substantial healthcare costs. Meanwhile, as the critically ignored "organ," the intestinal microbiome greatly impacts physiological health, not only in gastrointestinal diseases but also in disorders beyond the gut. However, the correlation between S. aureus infection and intestinal microbial homeostasis is largely unknown. Here, we summarized the recent progress in understanding S. aureus infections and their interactions with the microbiome in the intestine. These summarizations will help us understand the mechanisms behind these infections and crosstalk and the challenges we are facing now, which could contribute to preventing S. aureus infections, effective treatment investigation, and vaccine development.

The effect and mechanism of volatile oil emulsion from leaves of Clausena lansium (Lour.) Skeels on Staphylococcus aureus in vitro

This study aimed to develop a suitable dosage form of volatile oil from wampee leaves and to explore its antibacterial mechanism in vitro. The chemical composition of the volatile oil from wampee leaves was determined by gas chromatography-mass spectrometry (GC-MS). Different microemulsion ratios were tested and their stabilities were investigated to determine the optimal ratio. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the wampee leaves volatile oil emulsion (WVOE) against Salmonella typhimurium (S. typhimurium) and Staphylococcus aureus (S. aureus) were determined using double-dilution and plate-counting methods, respectively. Morphological changes in these two bacteria were observed using scanning electron microscopy. Death, ultrastructural morphology, and biofilm formation were also assessed for S. aureus. Finally, we established an S. aureus-infected Lewis lung carcinoma (LLC) cell model to evaluate the protective effects of the volatile oil emulsion and the associated mechanisms. The volatile oil extracted from wampee leaves contained 37 compounds, of which 96.49% were aromatic hydrocarbons, terpenoids, and their oxygen-containing derivatives. The emulsion was most stable at 1:1 in the oil phase and 1:9 in the water phase. WVOE had poor antibacterial activity against S. typhimurium, but the MIC and MBC against S. aureus were 312.5 and 2,500 μg/mL, respectively. S. aureus survival rates were 84.6%, 14.5%, and 12.8% in the 1/2, 1, and 4 × MIC groups, respectively, compared with 97.2% in the control group. S. typhimurium survival was not affected by WVOE treatment. WVOE administration induced cavity formation and abnormal binary fission, and significantly inhibited biofilm formation in S. aureus cells. The WVOE notably reduced the number of S. aureus and inhibited TLR4, NLRP3, NF-κB, IL-6, IL-18, and TNF-α gene expression in S. aureus-infected LLC cells. The WVOE had a significant inhibitory effect on S. aureus and altered its cell membrane permeability. Moreover, it alleviated inflammation by inhibiting the NF-κB-NLRP3 pathway in S. aureus-infected LLC cells.

Bacteraemia with gram-positive bacteria-when and how do I need to look for endocarditis?

BACKGROUND

Patients with bacteraemia caused by gram-positive bacteria are at risk for infective endocarditis (IE). Because IE needs long antibiotic treatment and sometimes heart valve surgery, it is very important to identify patients with IE.

OBJECTIVES

In this narrative review we present and discuss how to determine which investigations to detect IE that are needed in individual patients with gram-positive bacteraemia.

SOURCES

Published original studies and previous reviews in English, within the relevant field are used.

CONTENT

First, the different qualities of the bacteraemia in relation to IE risk are discussed. The risk for IE in bacteraemia is related to the species of the bacterium but also to monomicrobial bacteraemia and the number of positive cultures. Second, patient-related factors for IE risk in bacteraemia are presented. Next, the risk stratification systems to determine the risk for IE in gram-positive bacteraemia caused by Staphylococcus aureus, viridans streptococci, and Enterococcus faecalis are presented and their use is discussed. In the last part of the review, an account for the different modalities of IE-investigations is given. The main focus is on echocardiography, which is the cornerstone of IE-investigations. Furthermore, 18F-fluorodesoxyglucose positron emission tomography/computed tomography and cardiac computed tomography are presented and their use is also discussed. A brief account for investigations used to identify embolic phenomena in IE is also given. Finally, we present a flowchart suggesting which investigations to perform in relation to IE in patients with gram-positive bacteraemia.

IMPLICATIONS

For the individual patient as well as the healthcare system, it is important both to diagnose IE and to decide when to stop looking for IE. This review might be helpful in finding that balance.

Infective endocarditis after isolated aortic valve replacement: comparison between catheter-interventional and surgical valve replacement

BACKGROUND AND AIMS

Prosthetic valve endocarditis (PVE) is the prognostically most unfavourable complication after aortic valve replacement. This study aims to contribute to a better understanding of the different pathological and therapeutical aspects between PVE following surgical (SAVR) and transcatheter aortic valve replacement (TAVI).

METHODS

All patients who had undergone primary isolated SAVR (n = 3447) or TAVI (n = 2269) at our Centre between 01/2012 and 12/2018 were analysed. Diagnosis of PVE was based on Duke criteria modified in 2015. Incidence, risk factors, pathogens, impact of complications or therapy on mortality were analysed and compared between SAVR- and TAVI-PVE.

RESULTS

PVE incidence did not differ significantly after SAVR with 4.9/100 patient-years and TAVI with 2.4/100 patient-years (p = 0.49), although TAVI patients were older (mean 80 vs. 67 years) and had more comorbidities (STS score mean 5.9 vs. 1.6) (p < 0.001). TAVI prostheses with polymer showed a 4.3-fold higher risk to develop PVE than without polymer (HR 4.3; p = 0.004). Most common pathogens were staphylococci and enterococci (p > 0.05). Propensity-score matching analysis showed that the type of aortic valve replacement had no effect on the development of post-procedural PVE (p = 0.997). One-year survival was higher in TAVI-PVE patients treated with antibiotics only compared to additional surgical therapy (90.9% vs. 33.3%; p = 0.005). In SAVR-PVE patients, both therapies were comparable in terms of survival (p = 0.861). However, SAVR-PVE patients who were not operated, despite ESC-guideline recommendation, had significantly poorer one-year survival (p = 0.004).

CONCLUSION

TAVI patients did not have a significantly higher risk to develop PVE. Our data suggest that TAVI-PVE patients in contrast to SAVR-PVE patients can more often be treated with antibiotics only, presumably due to the lack of a polymeric suture ring.

Biofilm Producing Methicillin-Resistant Staphylococcus aureus (MRSA) Infections in Humans: Clinical Implications and Management

Since its initial description in the 1960s, methicillin-resistant Staphylococcus aureus (MRSA) has developed multiple mechanisms for antimicrobial resistance and evading the immune system, including biofilm production. MRSA is now a widespread pathogen, causing a spectrum of infections ranging from superficial skin issues to severe conditions like osteoarticular infections and endocarditis, leading to high morbidity and mortality. Biofilm production is a key aspect of MRSA's ability to invade, spread, and resist antimicrobial treatments. Environmental factors, such as suboptimal antibiotics, pH, temperature, and tissue oxygen levels, enhance biofilm formation. Biofilms are intricate bacterial structures with dense organisms embedded in polysaccharides, promoting their resilience. The process involves stages of attachment, expansion, maturation, and eventually disassembly or dispersion. MRSA's biofilm formation has a complex molecular foundation, involving genes like icaADBC, fnbA, fnbB, clfA, clfB, atl, agr, sarA, sarZ, sigB, sarX, psm, icaR, and srtA. Recognizing pivotal genes for biofilm formation has led to potential therapeutic strategies targeting elemental and enzymatic properties to combat MRSA biofilms. This review provides a practical approach for healthcare practitioners, addressing biofilm pathogenesis, disease spectrum, and management guidelines, including advances in treatment. Effective management involves appropriate antimicrobial therapy, surgical interventions, foreign body removal, and robust infection control practices to curtail spread within healthcare environments.

The role of human extracellular matrix proteins in defining Staphylococcus aureus biofilm infections

Twenty to forty one percent of the world's population is either transiently or permanently colonized by the Gram-positive bacterium, Staphylococcus aureus. In 2017, the CDC designated methicillin-resistant S. aureus (MRSA) as a serious threat, reporting ∼300 000 cases of MRSA-associated hospitalizations annually, resulting in over 19 000 deaths, surpassing that of HIV in the USA. S. aureus is a proficient biofilm-forming organism that rapidly acquires resistance to antibiotics, most commonly methicillin (MRSA). This review focuses on a large group of (>30) S. aureus adhesins, either surface-associated or secreted that are designed to specifically bind to 15 or more of the proteins that form key components of the human extracellular matrix (hECM). Importantly, this includes hECM proteins that are pivotal to the homeostasis of almost every tissue environment [collagen (skin), proteoglycans (lung), hemoglobin (blood), elastin, laminin, fibrinogen, fibronectin, and fibrin (multiple organs)]. These adhesins offer S. aureus the potential to establish an infection in every sterile tissue niche. These infections often endure repeated immune onslaught, developing into chronic, biofilm-associated conditions that are tolerant to ∼1000 times the clinically prescribed dose of antibiotics. Depending on the infection and the immune response, this allows S. aureus to seamlessly transition from colonizer to pathogen by subtly manipulating the host against itself while providing the time and stealth that it requires to establish and persist as a biofilm. This is a comprehensive discussion of the interaction between S. aureus biofilms and the hECM. We provide particular focus on the role of these interactions in pathogenesis and, consequently, the clinical implications for the prevention and treatment of S. aureus biofilm infections.

Safety and effectiveness of fifth generation cephalosporins for the treatment of methicillin-resistant staphylococcus aureus bloodstream infections: a narrative review exploring past, present, and future

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) is a major issue in healthcare, since it is often associated with endocarditis or deep site foci. Relevant morbidity and mortality associated with MRSA-BSIs forced the development of new antibiotic strategies; in particular, this review will focus the attention on fifth-generation cephalosporins (ceftaroline/ceftobiprole), that are the only ß-lactams active against MRSA.

AREAS COVERED

The review discusses the available randomized controlled trials and real-world observational studies conducted on safety and effectiveness of ceftaroline/ceftobiprole for the treatment of MRSA-BSIs. Finally, a proposal of MRSA-BSI treatment flowchart, based on fifth-generation cephalosporins, is described.

EXPERT OPINION

The use of anti-MRSA cephalosporins is an acceptable choice either in monotherapy or combination therapy for the treatment of MRSA-BSIs due to their relevant effectiveness and safety. Particularly, their use may be advisable in combination therapy in case of severe infections (including endocarditis or persistent bacteriemia) or in monotherapy in subjects at higher risk of drugs-induced toxicity with older regimens. On the contrary, caution should be taken in case of suspected/ascertained central nervous system infections due to inconsistent data regarding penetration of these drugs in cerebrospinal fluid and brain tissues.

Dynamics of Staphylococcus aureus in patients and the hospital environment in a tertiary care hospital in the Netherlands

BACKGROUND

The dynamics of Staphylococcus aureus in patients and the hospital environment are relatively unknown. We studied these dynamics in a tertiary care hospital in the Netherlands.

METHODS

Nasal samples were taken from adult patients at admission and discharge. Isolates cultured from clinical samples taken before and during hospitalization from these patients were included. Environmental samples of patient rooms were taken over a three-year period. Finally, isolates from clinical samples from patients with an epidemiological link to S. aureus positive rooms were included. Staphylococcal protein A (spa) typing was performed.

RESULTS

Nasal samples were taken from 673 patients. One hundred eighteen (17.5%) were positive at admission and discharge, 15 (2.2%) patients acquired S. aureus during hospitalization. Nineteen patients had a positive clinical sample during hospitalization, 15.9% of the S. aureus were considered as from an exogenous source. One hundred and forty (2.8%) environmental samples were S. aureus positive. No persistent contamination of surfaces was observed. Isolates were highly diverse: spa typing was performed for 893 isolates, identifying 278 different spa types, 161 of these spa types were observed only once.

CONCLUSION

Limited transmission could be identified between patients and the hospital environment, and from patient-to-patient. Exogenous acquisition was assumed to occur in 15% of clinical samples. Environmental contamination was infrequent, temporarily, and coincided with the strain from the patient admitted to the room at that time. MRSA was rare and not found in the environment.

Eluding the immune system's frontline defense: Secreted complement evasion factors of pathogenic Gram-positive cocci

The human complement system is an important part of the innate immune response in the fight against invasive bacteria. Complement responses can be activated independently by the classical pathway, the lectin pathway, or the alternative pathway, each resulting in the formation of a C3 convertase that produces the anaphylatoxin C3a and the opsonin C3b by specifically cutting C3. Other important features of complement are the production of the chemotactic C5a peptide and the generation of the membrane attack complex to lyse intruding pathogens. Invasive pathogens like Staphylococcus aureus and several species of the genus Streptococcus have developed a variety of complement evasion strategies to resist complement activity thereby increasing their virulence and potential to cause disease. In this review, we focus on secreted complement evasion factors that assist the bacteria to avoid opsonization and terminal pathway lysis. We also briefly discuss the potential role of complement evasion factors for the development of vaccines and therapeutic interventions.

Phage Therapy, a Salvage Treatment for Multidrug-Resistant Bacteria Causing Infective Endocarditis

Infective endocarditis (IE) is defined as an infection of the endocardium, or inner surface of the heart, most frequently affecting the heart valves or implanted cardiac devices. Despite its rarity, it has a high rate of morbidity and mortality. IE generally occurs when bacteria, fungi, or other germs from another part of the body, such as the mouth, spread through the bloodstream and attach to damaged areas in the heart. The epidemiology of IE has changed as a consequence of aging and the usage of implantable cardiac devices and heart valves. The right therapeutic routes must be assessed to lower complication and fatality rates, so this requires early clinical suspicion and a fast diagnosis. It is urgently necessary to create new and efficient medicines to combat multidrug-resistant bacterial (MDR) infections because of the increasing threat of antibiotic resistance on a worldwide scale. MDR bacteria that cause IE can be treated using phages rather than antibiotics to combat MDR bacterial strains. This review will illustrate how phage therapy began and how it is considered a powerful potential candidate for the treatment of MDR bacteria that cause IE. Furthermore, it gives a brief about all reported clinical trials that demonstrated the promising effect of phage therapy in combating resistant bacterial strains that cause IE and how it will become a hope in future medicine.

Microbiologic Analysis of Hand Infections: A Prospective Study

Background: Hand infections are a common problem in emergency departments. Staphylococcus aureus is the main pathogen of both hand and blood stream infections. Therefore, the aim of the present study was to evaluate the frequency and impact of bacteremia in patients with hand infections to improve the microbiologic diagnostics. Patients and Methods: A prospective study of 90 patients with acute hand infections without antimicrobial pre-treatment was performed. Blood cultures were taken pre-operatively. If positive, transesophageal echocardiography was performed to rule out infectious endocarditis. Tissue samples were microbiologically processed using standardized culture media. If negative, a broad-spectrum bacterial 16S ribosomal RNA (rRNA) gene polymerase chain reaction (PCR) was applied. The etiology and location of the infection, the length of hospital stay, the number of surgical interventions, and the inflammatory parameters were obtained. Results: Six patients with bacteremia (6.6%) were diagnosed, after animal bites (n = 3) and intra-articular empyema (n = 3). Pathogens included Staphylococcus pettenkoferi, Pasteurella multocida, Staphylococcus epidermidis, Staphylococcus aureus, and Bacteroides pyogenes. No case of infective endocarditis was detected. Patients with bacteremia required more surgical interventions (p = 0.002), had a longer hospital stay (p < 0.001), higher plasma C-reactive protein (CRP; p = 0.016), and a higher age (p = 0.002) compared with those without bacteremia. In 14 cases (15.6%) no pathogen was detected by culture, whereas the subsequent broad-spectrum PCR diagnosed three cases (21.4%). Conclusions: Pre-operative blood cultures in patients with hand infections are important to detect bacteremia as an essential marker of clinical severity. Those blood cultures are indicated after deep animal bites and joint empyema. A precise identification of pathogens is fundamental for an effective treatment of hand infections, for which a 16S rRNA gene PCR can contribute in culture-negative tissue samples.

Increasing numbers and complexity of Staphylococcus aureus bloodstream infection-14 years of prospective evaluation at a German tertiary care centre with multi-centre validation of findings

OBJECTIVES

Staphylococcus aureus bloodstream infection (SAB) is a common and severe infection. This study aims to describe temporal trends in numbers, epidemiological characteristics, clinical manifestations, and outcomes of SAB.

METHODS

We performed a post-hoc analysis of three prospective SAB cohorts at the University Medical Centre Freiburg between 2006 and 2019. We validated our findings in a large German multi-centre cohort of five tertiary care centres (R-Net consortium, 2017-2019). Time-dependent trends were estimated using Poisson or beta regression models.

RESULTS

We included 1797 patients in the mono-centric and 2336 patients in the multi-centric analysis. Overall, we observed an increasing number of SAB cases over 14 years (6.4%/year and 1000 patient days, 95% CI: 5.1% to 7.7%), paralleled by an increase in the proportion of community-acquired SAB (4.9%/year [95% CI: 2.1% to 7.8%]) and a decrease in the rate of methicillin-resistant-SAB (-8.5%/year [95% CI: -11.2% to -5.6%]). All of these findings were confirmed in the multi-centre validation cohort (6.2% cases per 1000 patient cases/year [95% CI: -0.6% to 12.6%], community-acquired-SAB 8.7% [95% CI: -1.2% to 19.6%], methicillin-resistant S. aureus-SAB -18.6% [95% CI: -30.6 to -5.8%]). Moreover, we found an increasing proportion of patients with multiple risk factors for complicated/difficult-to-treat SAB (8.5%/year, 95% CI: 3.6% to 13.5%, p < 0.001), alongside an overall higher level of comorbidities (Charlson comorbidity score 0.23 points/year, 95% CI: 0.09 to 0.37, p 0.005). At the same time, the rate of deep-seated foci such as osteomyelitis or deep-seated abscesses significantly increased (6.7%, 95% CI: 3.9% to 9.6%, p < 0.001). A reduction of in-hospital mortality by 0.6% per year (95% CI: 0.08% to 1%) was observed in the subgroup of patients with infectious diseases consultations.

DISCUSSION

We found an increasing number of SAB combined with a significant increase in comorbidities and complicating factors in tertiary care centres. The resulting challenges in securing adequate SAB management in the face of high patient turnover will become an important task for physicians.

Phages for treatment of Staphylococcus aureus infection

Combating multi-drug resistant bacterial infections should be a universal urgency. The gram- positive Staphylococcus aureus (S. aureus) bacteria are generally harmless; healthy people frequently have them on their skin and nose. These bacteria, for the most part, produce no difficulties or only minor skin diseases. Antibiotics and cleansing of the affected region are usually the treatments of choice. S. aureus can become virulent causing serious infections that may lead to pustules to sepsis or death. Normally, it is thought that antibiotics may solve problems concerning bacterial infection; but unfortunately, Staphylococci have evolved mechanisms to resist drugs. Methicillin-Resistant Staphylococcus aureus (MRSA); both in hospitals and in the community, infections are evolving into dangerous pathogens. Health care practitioners may need to use antibiotics with more adverse effects to treat antibiotic-resistant S. aureus infections. Amid existing efforts to resolve this problem, phage therapy proposes a hopeful alternate to face Staphylococcal infections. When the majority of antibiotics have failed to treat infections caused by multidrug-resistant bacteria, such as methicillin- and vancomycin-resistant S. aureus, phage therapy may be an option. Here, we appraise the potential efficacy, current knowledge on bacteriophages for S. aureus, experimental research and information on their clinical application, and limitations of phage therapy for S. aureus infections.

Synthesis and biological evaluation of ruthenium complexes containing phenylseleny against Gram-positive bacterial infection by damage membrane integrity and avoid drug-resistance

Compounds modified with selenium atom as potential antibacterial agents have been exploited to combat the nondrug-resistant bacterial infection. In this study, we designed and synthesized four ruthenium complexes retouching of selenium-ether. Fortunately, those four ruthenium complexes shown excellent antibacterial bioactive (MIC: 1.56-6.25 μg/mL) against Staphylococcus aureus (S. aureus), and the most active complex Ru(II)-4 could kill S. aureus by targeting the membrane integrity and avoid the bacteria to evolve drug resistance. Moreover, Ru(II)-4 was found to significantly inhibit the formation of biofilms and biofilm eradicate capacity. In toxicity experiments, Ru(II)-4 exhibited poor hemolysis and low mammalian toxicity. To illustrate the antibacterial mechanism: we conducted scanning electron microscope (SEM), fluorescent staining, membrane rupture and DNA leakage assays. Those results demonstrated that Ru(II)-4 could destroy the integrity of bacterial cell membrane. Furthermore, both G. mellonella wax worms infection model and mouse skin infection model were established to evaluate the antibacterial activity of Ru(II)-4 in vivo, the results indicated that Ru(II)-4 was a potential candidate for combating S. aureus infections, and almost non-toxic to mouse tissue. Thus, all the results indicated that introducing selenium-atom into ruthenium compounds were a promising strategy for developing interesting antibacterial agents.

Staphylococcus aureus Host Spectrum Correlates with Methicillin Resistance in a Multi-Species Ecosystem

Although antibiotic resistance is a major issue for both human and animal health, very few studies have investigated the role of the bacterial host spectrum in its dissemination within natural ecosystems. Here, we assessed the prevalence of methicillin resistance among Staphylococcus aureus (MRSA) isolates from humans, non-human primates (NHPs), micromammals and bats in a primatology center located in southeast Gabon, and evaluated the plausibility of four main predictions regarding the acquisition of antibiotic resistance in this ecosystem. MRSA strain prevalence was much higher in exposed species (i.e., humans and NHPs which receive antibiotic treatment) than in unexposed species (micromammals and bats), and in NHP species living in enclosures than those in captivity-supporting the assumption that antibiotic pressure is a risk factor in the acquisition of MRSA that is reinforced by the irregularity of drug treatment. In the two unexposed groups of species, resistance prevalence was high in the generalist strains that infect humans or NHPs, supporting the hypothesis that MRSA strains diffuse to wild species through interspecific transmission of a generalist strain. Strikingly, the generalist strains that were not found in humans showed a higher proportion of MRSA strains than specialist strains, suggesting that generalist strains present a greater potential for the acquisition of antibiotic resistance than specialist strains. The host spectrum is thus a major component of the issue of antibiotic resistance in ecosystems where humans apply strong antibiotic pressure.

Epidemiology and risk factors for mortality among methicillin-resistant Staphylococcus aureus bacteremic patients in Southern Brazil

This study aimed to evaluate the epidemiology and 30-day mortality of adult patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. We retrospectively reviewed the demographic and clinical data of adult patients with S. aureus bloodstream infections (BSI), admitted to a tertiary public teaching medical center in Porto Alegre, Southern Brazil, from January 2014 to December 2019. A total of 928 patients with S. aureus BSI were identified in the study period (68.5 per 100,000 patient-years), and the proportion of MRSA isolates was 22% (19-27%). Thus, 199 patients were included in the analyses. The median age was 62 (IQR: 51-74) years, Charlson Comorbidity Index (CCI) median was 5 (IQR: 3-6), the Pitt bacteremia score (PBS) median was 1 (IQR: 1-4), and the most common site of infection was skin and soft tissue (26%). Most infections were hospital-acquired (54%), empirical anti-MRSA treatment was initiated in 34% of the cases, and in 44% vancomycin minimum inhibitory concentration was 1.5mg/L or above. Sixty-two (31.2%) patients died up to 30 days after the bacteremia episode. Patients with more comorbid conditions (higher CCI; aOR 1.222, p = 0.006) and a more severe presentation (higher PBS; aOR 1.726, p<0.001) were independently associated with mortality. Empiric antimicrobial therapy with an anti-MRSA regimen was associated with reduced mortality (aOR 0.319, p = 0.016). Our study identified significant risk factors for 30-day mortality in patients with MRSA BSI in a population with a high incidence of S. aureus bacteremia. Empiric treatment with an anti-MRSA drug was a protective factor. No significant variation in the incidence of S. aureus BSI was recorded throughout the period.

Prevalence and Mortality of Infective Endocarditis in Community-Acquired and Healthcare-Associated Staphylococcus aureus Bacteremia: A Danish Nationwide Registry-Based Cohort Study

BACKGROUND

Staphylococcus aureus bacteremia (SAB) can be community-acquired or healthcare-associated, and prior small studies have suggested that this mode of acquisition impacts the subsequent prevalence of infective endocarditis (IE) and patient outcomes.

METHODS

First-time SAB was identified from 2010 to 2018 using Danish nationwide registries and categorized into community-acquired (no healthcare contact within 30 days) or healthcare-associated (SAB >48 hours of hospital admission, hospitalization within 30 days, or outpatient hemodialysis). Prevalence of IE (defined from hospital codes) was compared between groups using multivariable adjusted logistic regression analysis. One-year mortality of S aureus IE (SAIE) was compared between groups using multivariable adjusted Cox proportional hazard analysis.

RESULTS

We identified 5549 patients with community-acquired SAB and 7491 with healthcare-associated SAB. The prevalence of IE was 12.1% for community-acquired and 6.6% for healthcare-associated SAB. Community-acquired SAB was associated with a higher odds of IE as compared with healthcare-associated SAB (odds ratio, 2.12 [95% confidence interval {CI}, 1.86-2.41]). No difference in mortality was observed with 0-40 days of follow-up for community-acquired SAIE as compared with healthcare-associated SAIE (HR, 1.07 [95% CI, .83-1.37]), while with 41-365 days of follow-up, community-acquired SAIE was associated with a lower mortality (HR, 0.71 [95% CI, .53-.95]).

CONCLUSIONS

Community-acquired SAB was associated with twice the odds for IE, as compared with healthcare-associated SAB. We identified no significant difference in short-term mortality between community-acquired and healthcare-associated SAIE. Beyond 40 days of survival, community-acquired SAIE was associated with a lower mortality.

Rapid and Simple Approaches for Diagnosis of Staphylococcus aureus in Bloodstream Infections

Staphylococcus aureus is an important causative pathogen of bloodstream infections. An amplification assay such as real-time PCR is a sensitive, specific technique to detect S. aureus. However, it needs well-trained personnel, and costs are high. A literature review focusing on rapid and simple methods for diagnosing S. aureus was performed. The following methods were included: (a) Hybrisep in situ hybridization test, (b) T2Dx system, (c) BinaxNow Staphylococcus aureus and PBP2a, (d) Gram staining, (e) PNA FISH and QuickFISH, (f) Accelerate Pheno^TM system, (g) MALDI-TOF MS, (h) BioFire FilmArray, (i) Xpert MRSA/SA. These rapid and simple methods can rapidly identify S. aureus in positive blood cultures or direct blood samples. Furthermore, BioFire FilmArray and Xpert MRSA/SA identify methicillin-resistant S. aureus (MRSA), and the Accelerate Pheno^TM system can also provide antimicrobial susceptibility testing (AST) results. The rapidity and simplicity of results generated by these methods have the potential to improve patient outcomes and aid in the prevention of the emergence and transmission of MRSA.

Staphylococcus aureus Causes the Arrest of Neutrophils in the Bloodstream in a Septicemia Model

Staphylococcus aureus induces the expression of VCAM-1, P- and E-selectins on the endothelial cells of the EA.hy926 cell line but, at the same time, causes the significant suppression of the force and work of adhesion between these receptors of endotheliocytes and the receptors of neutrophils in an experimental septicemia model. Adhesion contacts between the receptors of neutrophils and endotheliocytes are statistically significantly suppressed under non-opsonized and opsonized S. aureus treatment, which disrupts the initial stage of transendothelial migration of neutrophils—adhesion. Thus, S. aureus causes the arrest of neutrophils in the bloodstream in an experimental septicemia model.

Bacteriophage Therapy for Staphylococcus Aureus Infections: A Review of Animal Models, Treatments, and Clinical Trials

Staphylococcus aureus (S. aureus) is a common and virulent human pathogen causing several serious illnesses including skin abscesses, wound infections, endocarditis, osteomyelitis, pneumonia, and toxic shock syndrome. Antibiotics were first introduced in the 1940s, leading to the belief that bacterial illnesses would be eradicated. However, microorganisms, including S. aureus, began to develop antibiotic resistance from the increased use and abuse of antibiotics. Antibiotic resistance is now one of the most serious threats to global public health. Bacteria like methicillin-resistant Staphylococcus aureus (MRSA) remain a major problem despite several efforts to find new antibiotics. New treatment approaches are required, with bacteriophage treatment, a non-antibiotic strategy to treat bacterial infections, showing particular promise. The ability of S. aureus to resist a wide range of antibiotics makes it an ideal candidate for phage therapy studies. Bacteriophages have a relatively restricted range of action, enabling them to target pathogenic bacteria. Their usage, usually in the form of a cocktail of bacteriophages, allows for more focused treatment while also overcoming the emergence of resistance. However, many obstacles remain, particularly in terms of their effects in vivo, necessitating the development of animal models to assess the bacteriophage efficiency. Here, we provide a review of the animal models, the various clinical case treatments, and clinical trials for S. aureus phage therapy.

An animal derivative-free medium enhances Lactobacillus johnsonii LJO02 supernatant selective efficacy against the methicillin (oxacillin)-resistant Staphylococcus aureus virulence through key-metabolites

The spread of multidrug-resistant bacteria, such as the skin commensal Staphylococcus aureus, is a worldwide health challenge; new methods to counteract opportunistic pathogen growth and virulence are urgent. We compared the activity of Lacticaseibacillus rhamnosus LR06 (DSM 21981) and Lactobacillus johnsonii LJO02 (DSM 33828) cell-free supernatants (CFSs) produced in the conventional animal derivative-based MRS medium and an innovative animal derivative-free broth (TIL) versus the MDR S. aureus (ATCC 43300). CFS influence was assessed towards the viability, metabolic activity, and ability to form biofilm of the MDR strain through optical density, alamarBlue assay, and crystal violet staining; their content in short-chain fatty acids, lactic acid, and proteins was analysed via high-resolution mass spectrometry and gas chromatography. All CFSs reduce viable and metabolically active S. aureus, being TIL more efficient compared to MRS in stimulating lactic acid bacteria metabolism and decreasing S. aureus biofilm formation. Particularly, the CFS from LJO02 grown in TIL has the best efficacy, revealing a high amount of lactic acid and 59 peculiar proteins; its effectiveness is partially maintained upon trypsin and proteinase K treatments, but not by pepsin and pH basification. Therefore, antagonistic CFSs may represent a strategic prevention approach, with bacteriotherapeutic and bio-repair potential.

A Severe Systemic Infection in a 14-Year-Old Boy That Took Place during the COVID-19 Pandemic

Introduction: Since March 2020, the COVID-19 pandemic has been a global talking point. Access to health care has become more difficult, and such an obstacle increase the risk of inadequate medical care, especially among paediatric patients. Case: This report describes the case of a previously healthy teenager who was staying home for 2 months due to a strict lockdown period in the COVID-19 pandemic and was admitted to hospital for fever, nausea and lumbar pain. He was diagnosed consecutively with meningitis, sepsis, paraspinal abscesses and endocarditis. Further investigation did not reveal any risk factors or immunodeficiency in the patient. Discussion: Sepsis is defined as the presence of systemic inflammatory response syndrome (SIRS) associated with a probable or documented infection. It is the leading cause of death from infection, especially if not recognized and treated quickly. Sepsis may lead to various complications, such as infective endocarditis, meningitis and abscesses. Although such complications may initially be latent, they can promote internal organ dysfunction and the possibility of their presence should be considered in any patient with systemic infection. Any child with a fever should be treated as one with the possibility of developing a severe infection. Conclusion: The presented case shows that even a previously healthy child staying in long-term home isolation can develop a severe infection with multiorgan complications, and the COVID-19 pandemic should not extend the diagnostic process in patients with symptoms of infection.

Evidence of clinical impact supports a new petition for Medicare coverage of 18F-FDG-PET/CT in the evaluation of Staphylococcus aureus bacteremia: a focused literature review and call to action

Staphylococcus aureus bacteremia (SAB) causes considerable morbidity and mortality and requires comprehensive assessment for metastatic infection. The roles of routine imaging beyond echocardiography in SAB, including 18F-FDG-PET/CT, remain contentious. We performed a literature review of studies reporting impact of 18F-FDG-PET/CT on the clinical management or outcomes of SAB published through 3/1/2022. We identified seven observational studies, in which 18F-FDG-PET/CT frequently identified metastatic foci of infection, revealed foci undetected by prior investigations, led to additional source control procedures, and was associated with fewer infection relapses and lower mortality. Calculated numbers needed to treat (NNTs) for receipt of 18F-FDG-PET/CT were 7-9 to change antimicrobial therapy, 10-27 to lead to an additional source control procedure, and 4-8 to prevent death. These data are comparable to the evidence for clinical impact of other diagnostic modalities accepted as standard of care in SAB, and form a compelling basis for advocacy to expand access to 18F-FDG-PET/CT.

Comparable Effectiveness of Cefuroxime and Piperacillin-Tazobactam as Empirical Therapy for Methicillin-Susceptible Staphylococcus aureus Bacteremia

Our objective was to examine whether empirical antimicrobial therapy (EAT) against methicillin-susceptible Staphylococcus aureus bacteremia (MS-SAB) with piperacillin-tazobactam (TZP), cefuroxime or combination therapy with one of these was differentially associated with 7-, 30-, and 90- day all-cause mortality or MS-SAB relapse. A multicenter retrospective cohort study of adults with MS-SAB from 2009 through 2018 was used, and 7-, 30-, 90-day mortality and relapse within 90 days were assessed and expressed as hazard ratio (HR) with a 95% confidence interval (95% CI) using Cox proportional hazard regression analysis. Matching of the two monotherapy groups was performed using propensity score matching. In total, 1158 MS-SAB cases were included and received one of three EAT regimens: TZP (n = 429), cefuroxime (n = 337), or TZP or cefuroxime with one or more additional effective antimicrobial (n = 392). The overall 30-day mortality was 28.0% (25.5 to 30.3%). After adjustment and matching, there was no significant difference in 7-, 30-, or 90-day mortality between the therapy groups. The matched HR of death was 0.81 (95% CI, 0.38 to 1.76) at 7 days, 0.82 (95% CI, 0.47 to 1.46) at 30 days, and 0.81 (95% CI, 0.50 to 1.32) at 90 days for TZP compared with cefuroxime. Adjusted HR of 90-day relapse was insignificant between the three therapy groups: TZP: 1.55 (95% CI, 0.54 to 4.43); combination therapy: 1.73 (95% CI, 0.62 to 4.80) compared to cefuroxime. There was no significant difference in 7-, 30-, or 90-day mortality or relapse between MS-SAB patients treated with empirical TZP or cefuroxime after adjustment and matching of covariables.

IMPORTANCE This multicenter retrospective matched cohort study evaluated the effect of empirical antimicrobial therapy on the clinical outcome of methicillin-susceptible Staphylococcus aureus bacteremia (MS-SAB) in >1100 adult patients. To the best of our knowledge, this is the largest study to date evaluating the effect of empirical treatment on the MS-SAB outcome. Importantly, the study found no significant difference in either short- or long-term mortality nor relapse between patients with MS-SAB receiving empirical treatment with cefuroxime or piperacillin-tazobactam. As such, this study provides crucial contemporary data supporting the widespread clinical practice of initiating empirical antimicrobial therapy of sepsis with β-lactam-β-lactamase-inhibitor.

Th17 cell plasticity towards a T-bet-dependent Th1 phenotype is required for bacterial control in Staphylococcus aureus infection

Staphylococcus aureus is frequently detected in patients with sepsis and thus represents a major health burden worldwide. CD4⁺ T helper cells are involved in the immune response to S. aureus by supporting antibody production and phagocytosis. In particular, Th1 and Th17 cells secreting IFN-γ and IL-17A, are involved in the control of systemic S. aureus infections in humans and mice.

To investigate the role of T cells in severe S. aureus infections, we established a mouse sepsis model in which the kidney was identified to be the organ with the highest bacterial load and abundance of Th17 cells. In this model, IL-17A but not IFN-γ was required for bacterial control. Using Il17aCre × R26YFP mice we could show that Th17 fate cells produce Th17 and Th1 cytokines, indicating a high degree of Th17 cell plasticity. Single cell RNA-sequencing of renal Th17 fate cells uncovered their heterogeneity and identified a cluster with a Th1 expression profile within the Th17 cell population, which was absent in mice with T-bet/Tbx21-deficiency in Th17 cells (Il17aCre x R26eYFP x Tbx21-flox). Blocking Th17 to Th1 transdifferentiation in Th17 fate cells in these mice resulted in increased S. aureus tissue loads.

In summary, we highlight the impact of Th17 cells in controlling systemic S. aureus infections and show that T-bet expression by Th17 cells is required for bacterial clearance. While targeting the Th17 cell immune response is an important therapeutic option in autoimmunity, silencing Th17 cells might have detrimental effects in bacterial infections.

Staphylococcus aureus is a commensal and opportunistic pathogen that is involved in a variety of diseases such as skin infection, food poisoning, endocarditis or pneumonia and sepsis. In particular, in patients with bacterial sepsis, S. aureus causes a high mortality. Despite progress in medical treatment in general, the survival rates of S. aureus sepsis did not improve in the last decades. The interaction between adaptive immune system and this pathogen is a topic of great interest. Infection of mice with S. aureus revealed the highest bacterial load and abundance of Th17 cells in the kidney. We could show prominent T-bet-dependent transdifferentiation of Th17 cells to highly effective anti-bacterial Th1 phenotypes in the kidney. Thus, T-bet is essential for the Th17 to Th1 transdifferentiation which is required for the control of bacterial infections. Targeting the plasticity of pro-inflammatory T cell subset is a promising therapeutic strategy to silence detrimental T cells in autoimmunity while augmenting anti-bacterial T cells in infection.

HPLC-DAD analysis and antimicrobial activities of Spondias mombin L. (Anacardiaceae)

Spondias mombin is used in the folk medicine for the treatment of diarrhea and dysentery, indicating that extracts obtained from this species may present pharmacological activities against pathogenic microorganisms. The purpose of this work was to investigate the chemical composition and evaluate the antimicrobial activity of extracts obtained from the leaves (aqueous) and bark (hydroethanolic) of S. mombin both as single treatments and in combination with conventional drugs. Following a qualitative chemical prospection, the extracts were analyzed by HPLC-DAD. The antimicrobial activities were evaluated by microdilution. The combined activity of drugs and extracts was verified by adding a subinhibitory concentration of the extract in the presence of variable drug concentrations. The Minimum Fungicidal Concentration (MFC) was determined by a subculture of the microdilution test, while the effect of the in vitro treatments on morphological transition was analyzed by subculture in moist chambers. While the qualitative analysis detected the presence of phenols and flavonoids, the HPLC analysis identified quercetin, caffeic acid, and catechin as major components in the leaf extract, whereas kaempferol and quercetin were found as major compounds in the bark extract. The extracts showed effective antibacterial activities only against the Gram-negative strains. With regard to the combined activity, the leaf extract potentiated the action of gentamicin and imipenem (against Staphylococcus aureus), while the bark extract potentiated the effect of norfloxacin (against S. aureus), imipenem (against Escherichia coli), and norfloxacin (against Pseudomonas aeruginosa). A more significant antifungal (fungistatic) effect was achieved with the bark extract (even though at high concentrations), which further enhanced the activity of fluconazole. The extracts also inhibited the emission of filaments by Candida albicans and Candida tropicalis. Together, these findings suggest that that the extract constituents may act by favoring the permeability of microbial cells to conventional drugs, as well as by affecting virulence mechanisms in Candida strains.

Human MAIT Cells Respond to Staphylococcus aureus with Enhanced Anti-Bacterial Activity

Mucosal-Associated Invariant T (MAIT) cells have been shown to play protective roles during infection with diverse pathogens through their propensity for rapid innate-like cytokine production and cytotoxicity. Among the potential applications for MAIT cells is to defend against Staphylococcus aureus, a pathogen of serious clinical significance. However, it is unknown how MAIT cell responses to S. aureus are elicited, nor has it been investigated whether MAIT cell cytotoxicity is mobilized against intracellular S. aureus. In this study, we investigate the capacity of human MAIT cells to respond directly to S. aureus. MAIT cells co-cultured with dendritic cells (DCs) infected with S. aureus rapidly upregulate CD69, express IFNγ and Granzyme B and degranulate. DC secretion of IL-12, but not IL-18, was implicated in this immune response, while TCR binding of MR1 is required to commence cytokine production. MAIT cell cytotoxicity resulted in apoptosis of S. aureus-infected cells, and reduced intracellular persistence of S. aureus. These findings implicate these unconventional T cells in important, rapid anti-S. aureus responses that may be of great relevance to the ongoing development of novel anti-S. aureus treatments.

Reassessment of vegetation size as a sole indication for surgery in left-sided infective endocarditis

BACKGROUND

Guidelines recommend surgery in left-sided infective endocarditis (LSIE) associated with large vegetations. Given that most patients who undergo surgery also have other indications (heart failure and/or uncontrolled infection), it is not settled whether surgery should be routinely recommended in patients with large vegetations but no other predictors of poor outcome.

METHODS

A total of 726 patients with definitive LSIE were included in our analysis. Mean age was 64.9 years, 61% were male. Multivariate analysis of all patients was performed to determine if vegetation size is related to death in LSIE. Then, patients were divided in two groups according to vegetation size: Group A (>10 mm, n=420) and group B (≤10 mm, n=306). Univariate and multivariate analyses of group A patients were carried out to identify the variables related to death in this group. Impact of surgery on mortality of group A patients without heart failure or uncontrolled local infection (n=139) was assessed.

RESULTS

Age, Staphylococcus aureus, perivalvular complications, heart failure, kidney failure and septic shock, but not vegetation size, were associated with death. Patients with large vegetations showed increased mortality (31.7% in group A vs 24.8% in group B, p=0.045). Group A had more valve rupture and valve regurgitation than group B, but heart failure (55% vs 53%, p=0.678), stroke (22% vs 17.0%, p=0.091), systemic embolism (39% vs 32%, p=0.074), perivalvular complication (28% vs 28%, p=0.865) or septic shock (15% vs 13%, p=0.288) were similar in both groups. In patients from group A without heart failure or uncontrolled infection mortality was similar with and without surgery (n=139; n=70 with surgery, n=69 without surgery; mortality 18.6% vs 11.6% respectively, p=0.251).

CONCLUSIONS

large vegetations identify patients with poor outcome in LSIE. However, surgery is not associated with a better prognosis in patients with large vegetations if they do not present with another predictor of poor outcome such as heart failure or uncontrolled infection. These findings challenge whether vegetation size alone should be an indication for surgery in LSIE.

Synthesis and biological evaluation of ruthenium polypyridine complexes with 18β-glycyrrhetinic acid as antibacterial agents against Staphylococcus aureus

Four new ruthenium(II) polypyridine complexes bearing 18β-glycyrrhetinic acid derivatives, [Ru(bpy)₂L](PF₆)₂ (Ru1), [Ru(dmb)₂L](PF₆)₂ (Ru2), [Ru(dtb)₂L](PF₆)₂ (Ru3) and [Ru(phen)₂L](PF₆)₂ (Ru4) (bpy = 2,2-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine, dtb = 4,4'-di-tert-butyl-2,2'-bipyridine, phen = 1,10-phenanthroline and L is the GA modified new ligand) were designed and synthesized. Their antimicrobial activities against Staphylococcus aureus (S. aureus) were evaluated and all complexes showed an obvious inhibitory effect, especially, the minimum inhibitory concentration (MIC) value of Ru2 was 3.9 μg mL^-1. Moreover, Ru2 was found to significantly inhibit the formation of biofilms. The membrane-compromising action mode was suggested to be their potential antibactericidal mechanism. In hemolysis experiments, Ru2 hardly showed cytotoxicity to mammalian erythrocytes. Furthermore, the synergism between Ru2 and common antibiotics, such as ampicillin, chloramphenicol, tetracyclines and ofloxacin, against S. aureus was also detected using the checkerboard method. Finally, a mouse skin infection model was established to evaluate the antibacterial activity of Ru2in vivo, and the results showed that Ru2 could effectively promote wound healing in mice infected with S. aureus. Moreover, the results of histopathological research were consistent with the results of the hemolysis test, indicating that the Ru2 complex was almost non-toxic. Thus, it was demonstrated that the polypyridine ruthenium complexes modified with glycyrrhetinic acid (GA) are a promising strategy for developing interesting antibacterial agents.