A Prognostic Model of Persistent Bacteremia and Mortality in Complicated Staphylococcus aureus Bloodstream Infection

Integrated transcriptomic analysis reveals immune signatures distinguishing persistent versus resolving outcomes in MRSA bacteremia

Introduction

Staphylococcus aureus bacteremia (SAB) is a life-threatening infection particularly involving methicillin-resistant S. aureus (MRSA). In contrast to resolving MRSA bacteremia (RB), persistent MRSA bacteremia (PB) blood cultures remain positive despite appropriate antibiotic treatment. Host immune responses distinguishing PB vs. RB outcomes are poorly understood. Here, integrated transcriptomic, IL-10 cytokine levels, and genomic analyses sought to identify signatures differentiating PB vs. RB outcomes.

Methods

Whole-blood transcriptomes of propensity-matched PB (n=28) versus RB (n=30) patients treated with vancomycin were compared in one independent training patient cohort. Gene expression (GE) modules were analyzed and prioritized relative to host IL-10 cytokine levels and DNA methyltransferase-3A (DNMT3A) genotype.

Results

Differential expression of T and B lymphocyte gene expression early in MRSA bacteremia discriminated RB from PB outcomes. Significant increases in effector T and B cell signaling pathways correlated with RB, lower IL-10 cytokine levels and DNMT3A heterozygous A/C genotype. Importantly, a second PB and RB patient cohort analyzed in a masked manner demonstrated high predictive accuracy of differential signatures.

Discussion

Collectively, the present findings indicate that human PB involves dysregulated immunity characterized by impaired T and B cell responses associated with excessive IL-10 expression in context of the DNMT3A A/A genotype. These findings reveal distinct immunologic programs in PB vs. RB outcomes, enable future studies to define mechanisms by which host and/or pathogen drive differential signatures and may accelerate prediction of PB outcomes. Such prognostic assessment of host risk could significantly enhance early anti-infective interventions to avert PB and improve patient outcomes.

Tensor modeling of MRSA bacteremia cytokine and transcriptional patterns reveals coordinated, outcome-associated immunological programs

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is a common and life-threatening infection that imposes up to 30% mortality even when appropriate therapy is used. Despite in vitro efficacy determined by minimum inhibitory concentration breakpoints, antibiotics often fail to resolve these infections in vivo, resulting in persistent MRSA bacteremia. Recently, several genetic, epigenetic, and proteomic correlates of persistent outcomes have been identified. However, the extent to which single variables or their composite patterns operate as independent predictors of outcome or reflect shared underlying mechanisms of persistence is unknown. To explore this question, we employed a tensor-based integration of host transcriptional and cytokine datasets across a well-characterized cohort of patients with persistent or resolving MRSA bacteremia outcomes. This method yielded high correlative accuracy with outcomes and immunologic signatures united by transcriptomic and cytokine datasets. Results reveal that patients with persistent MRSA bacteremia (PB) exhibit signals of granulocyte dysfunction, suppressed antigen presentation, and deviated lymphocyte polarization. In contrast, patients with resolving bacteremia (RB) heterogeneously exhibit correlates of robust antigen-presenting cell trafficking and enhanced neutrophil maturation corresponding to appropriate T lymphocyte polarization and B lymphocyte response. These results suggest that transcriptional and cytokine correlates of PB vs. RB outcomes are complex and may not be disclosed by conventional modeling. In this respect, a tensor-based integration approach may help to reveal consensus molecular and cellular mechanisms and their biological interpretation.

Antimicrobial effect of pimozide by targeting ROS-mediated killing in Staphylococcus aureus

In spite of the higher nosocomial and community-acquired infections caused by Staphylococcus aureus, emerging drug resistance is a leading cause of increased mortality and morbidity associated with the overuse of antimicrobials. It is an emergent need to find out new molecules to combat such infections. In the present study, we analyzed the antibacterial effect of pimozide (PMZ) against gram-positive and gram-negative bacterial strains, including methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) S. aureus. The growth of MSSA and MRSA was completely inhibited at concentrations of 12.5 and 100 μg/mL, respectively, which is referred to as 1× minimum inhibitory concentration (MIC). The cell viability was completely eliminated within 90 min of PMZ treatment (2× MIC) through reactive oxygen species (ROS)-mediated killing without affecting cell membrane permeability. It suppressed α-hemolysin production and biofilm formation of different S. aureus strains by almost 50% at 1× MIC concentration, and was found to detach matured biofilm. PMZ treatment effectively eliminates S. aureus infection in Caenorhabditis elegans and improves its survival by 90% and is found safe to use with no hemolytic effect on human and chicken blood tissues. Taken together, it is concluded that PMZ may turn out to be an effective antibacterial for treating bacterial infections including MSSA and MRSA.

Next-generation humanized NSG-SGM3 mice are highly susceptible to Staphylococcus aureus infection

Humanized hemato-lymphoid system mice, or humanized mice, emerged in recent years as a promising model to study the course of infection of human-adapted or human-specific pathogens. Though Staphylococcus aureus infects and colonizes a variety of species, it has nonetheless become one of the most successful human pathogens of our time with a wide armory of human-adapted virulence factors. Humanized mice showed increased vulnerability to S. aureus compared to wild type mice in a variety of clinically relevant disease models. Most of these studies employed humanized NSG (NOD-scid IL2Rgnull) mice which are widely used in the scientific community, but show poor human myeloid cell reconstitution. Since this immune cell compartment plays a decisive role in the defense of the human immune system against S. aureus, we asked whether next-generation humanized mice, like NSG-SGM3 (NOD-scid IL2Rgnull-3/GM/SF) with improved myeloid reconstitution, would prove to be more resistant to infection. To our surprise, we found the contrary when we infected humanized NSG-SGM3 (huSGM3) mice with S. aureus: although they had stronger human immune cell engraftment than humanized NSG mice, particularly in the myeloid compartment, they displayed even more pronounced vulnerability to S. aureus infection. HuSGM3 mice had overall higher numbers of human T cells, B cells, neutrophils and monocytes in the blood and the spleen. This was accompanied by elevated levels of pro-inflammatory human cytokines in the blood of huSGM3 mice. We further identified that the impaired survival of huSGM3 mice was not linked to higher bacterial burden nor to differences in the murine immune cell repertoire. Conversely, we could demonstrate a correlation of the rate of humanization and the severity of infection. Collectively, this study suggests a detrimental effect of the human immune system in humanized mice upon encounter with S. aureus which might help to guide future therapy approaches and analysis of virulence mechanisms.

Clinical Characteristics and Outcomes of Persistent Staphylococcal Bacteremia in a Tertiary Care Hospital

Clinical outcomes of persistent staphylococcal bacteremia vary depending on the causative organism. This secondary data analysis study compared the clinical characteristics of persistent Staphylococcus aureus (S. aureus)- and coagulase-negative staphylococci (CoNS)-caused bacteremia, focusing on the methicillin-resistant status. This study used data collected from patients who underwent blood cultures between January 2012 and December 2021 at Tohoku University Hospital, Japan. Patients with persistent staphylococcal bacteremia were divided into groups based on the pathogen and methicillin-resistant status, and their characteristics were analyzed. The primary outcomes were early (30-day), late (30–90 days), and 90-day mortality rates. The early, late, and 90-day mortality rates were similar between the persistent CoNS and S. aureus bacteremia groups. Patients with persistent methicillin-resistant S. aureus (MRSA) bacteremia tended to have higher early, late, and 90-day mortality rates than those with persistent methicillin-susceptible S. aureus bacteremia (not statistically significant). No differences were observed between the methicillin-resistant and-susceptible CoNS groups. In patients with persistent CoNS bacteremia, mortality tended to increase, especially in debilitated or immunocompromised patients with distant metastases, underscoring the importance of infection source control. Mortality tended to be high in patients with persistent MRSA bacteremia, especially when persistent bacteremia clearance was not confirmed, illustrating the need for careful therapeutic management.

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.

Inappropriate empirical antibiotic therapy was an independent risk factor of pediatric persistent S. aureus bloodstream infection

Persistent S. aureus bloodstream infection (PSBSI) increased the incidence of metastatic infection and mortality. We aimed to clarify its risk factors and correlation with metastatic infection and septic shock in children. This retrospective and observational study enrolled children with S. aureus bloodstream infection who admitted to Children's Hospital of Chongqing Medical University between January 2016 and December 2021. The logistic regression model was used for multivariable analyses to determine independent factors associated with PSBSI and clarify the effect of persistent S. aureus bloodstream infection and other factors on metastatic infection and septic shock. One hundred and twenty-seven children were included in this study retrospectively. There were thirty-two cases in the persistent S. aureus bloodstream infection group and ninety-five children in the non-persistent infection group. Multivariate logistic regression analysis indicated that inappropriate empirical antibiotic therapy (OR, 7.26; 95%CI, 2.48-21.30; P<0.01) was an independent risk factor of persistent S. aureus bloodstream infection. Persistent S. aureus bloodstream infection (OR, 6.40; 95%CI, 2.08-19.70; P<0.01) and community-acquired S. aureus bloodstream infection (OR, 4.75; 95%CI, 1.34-16.89; P=0.02) were independent predictors of metastatic infection. Pittsburgh bacteremia scores ≥ 2 (OR, 28.81; 95%CI, 5.26-157.99; P<0.01), hypoalbuminemia (OR, 13.34; 95%CI, 2.43-73.28; P<0.01) and persistent S. aureus bloodstream infection (OR, 5.48; 95%CI, 1.13-26.54; P=0.04) were independent risk factors of septic shock.

CONCLUSION

Inappropriate empirical antibiotic therapy was an independent risk factor of pediatric persistent S. aureus bloodstream infection. Pediatric persistent S. aureus bloodstream infection was associated with metastatic infection and septic shock.

WHAT IS KNOWN

• Pathogenic features such as Methicillin-resistant S. aureus and sources of infection such as central venous catheter related infection were risk factors of PSBSI in adults. • PSBSI increased the incidence of metastatic infection and mortality in adults.

WHAT IS NEW

• Inappropriate empirical antibiotic therapy was an independent risk factor of pediatric persistent S. aureus bloodstream infection. • Pediatric persistent S. aureus bloodstream infection was associated with metastatic infection and septic shock.

Redefining Staphylococcus aureus bacteremia: A structured approach guiding diagnostic and therapeutic management

The current duration of therapy in patients with Staphylococcus aureus bacteremia (SAB) is based on differentiating complicated from uncomplicated disease. While this approach allows clinicians and investigators to group SAB patients into broadly similar clinical categories, it fails to account for the intrinsic heterogeneity of SAB. This is due in part to the fact that risk factors for metastatic infection and confirmed metastatic infection are considered as equivalent in most scoring systems. In this viewpoint, we propose a two-step system of categorizing patients with SAB. Initially, patients with SAB would be categorized as 'high risk' or 'low risk' for metastatic infection based upon an initial set of diagnostic procedures. In the second step, patients identified as 'high-risk' would undergo additional diagnostic evaluation. The results of this stepwise diagnostic evaluation would define a 'final clinical diagnosis' to inform an individualized final treatment plan.

In vitro antimicrobial activity and resistance mechanisms of the new generation tetracycline agents, eravacycline, omadacycline, and tigecycline against clinical Staphylococcus aureus isolates

In this study, we investigated the in vitro activity and resistance mechanisms of the new generation tetracycline agents, namely eravacycline, omadacycline, and tigecycline, against Staphylococcus aureus isolates. A total of 1,017 non-duplicate S. aureus isolates were collected and subjected to susceptibility testing against eravacycline, omadacycline, and tigecycline using the broth microdilution method. Tetracyclines-resistant (eravacycline/omadacycline/tigecycline-resistant) isolates were selected to elucidate the resistance mechanisms using polymerase chain reaction (PCR), cloning experiment, efflux pump inhibition, and quantitative real-time PCR. The results of the antibacterial susceptibility testing showed that compared with omadacycline, eravacycline and tigecycline had superior antibacterial activity against S. aureus isolates. Among 1,017 S. aureus, 41 tetracyclines-resistant isolates were identified. These resistant isolates possessed at least one tetracycline resistance gene and genetic mutation in the MepRAB efflux pump and 30S ribosome units. A frameshift mutation in mepB was detected in most tetracyclines-resistant strains (except for JP3349) compared with tetracyclines-susceptible (eravacycline/omadacycline/tigecycline-susceptible) strains. This was first shown to decrease susceptibility to omadacycline, but not to eravacycline and tigecycline. After treatment with eravacycline, omadacycline or tigecycline, overexpression of mepA, tet38, tet(K) and tet(L) was detected. Moreover, multi-locus sequence typing showed a major clonal dissemination type, ST5, and its variant ST764 were seen in most tetracyclines-resistant strains. To conclude, eravacycline and tigecycline exhibited better activity against S. aureus including tetracycline-resistant isolates than omadacycline. The resistance to these new generation tetracyclines due to an accumulation of many resistance mechanisms.

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.

Modern vaccine development via reverse vaccinology to combat antimicrobial resistance

With the continuous evolution of bacteria, the global antimicrobial resistance health threat is causing millions of deaths yearly. While depending on antibiotics as a primary treatment has its merits, there are no effective alternatives thus far in the pharmaceutical market against some drug-resistant bacteria. In recent years, vaccinology has become a key topic in scientific research. Combining with the growth of technology, vaccine research is seeing a new light where the process is made faster and more efficient. Although less discussed, bacterial vaccine is a feasible strategy to combat antimicrobial resistance. Some vaccines have shown promising results with good efficacy against numerous multidrug-resistant strains of bacteria. In this review, we aim to discuss the findings from studies utilizing reverse vaccinology for vaccine development against some multidrug-resistant bacteria, as well as provide a summary of multi-year bacterial vaccine studies in clinical trials. The advantages of reverse vaccinology in the generation of new bacterial vaccines are also highlighted. Meanwhile, the limitations and future prospects of bacterial vaccine concludes this review.

Identification of Prognostic Factors in Patients With Streptococcus Bloodstream Infection

Aim

The purpose of this study was to explore prognostic factors of bloodstream infections (BSIs), a common severe infection and a major cause of mortality worldwide, so as to construct a prognosis model of patients with BSI.

Materials and Methods

Clinical and biochemical test data were obtained retrospectively from the medical records of 562 patients with BSI who had been treated at a single center; the end point was 60 days of all-cause death. The chi-square test was used to compare the mortality of patients grouped by the types of antibiotic treatment. The logistic regression analysis was adopted to identify prognostic factors; the Kaplan–Meier survival curve and log-rank test were conducted to compare the survival rate of patients with different prognostic factors; the receiver operating characteristic (ROC) curve was used to estimate the predictive value of different prognostic factors.

Results

Of the 562 patients, 455 survived (80.96%), and 107 died (19.04%). The mortality rate of patients treated with a combination of antibiotics (25.40%) was higher than that treated with a single antibiotic (15.82%). Univariate analysis identified 19 prognostic factors for patients with BSI, including gender, age, diabetes, malignant tumor (non-blood system), total hospitalization time, alanine aminotransferase, aspartate aminotransferase, total protein, albumin, total bilirubin, direct bilirubin, creatinine, ratio of granulocytes, fibrinogen, D-dimer, platelet, C-reactive protein, shock, and respiratory failure (P < 0.05). Multivariate analysis indicated that albumin (odds ratio [OR] = 0.94, 95% confidence interval [CI]: 0.89–0.99), fibrinogen (OR = 0.61, 95%CI: 0.46–0.82), shock (OR = 16.61, 95%CI: 7.00–39.41), and respiratory failure (OR = 47.53, 95%CI: 19.93–133.64) were independent factors. The combination of four indicators demonstrated a favorable predictive value for the 60-day outcome of patients with BSI, with an area under the ROC of 0.96 (95%CI: 0.94–0.99), sensitivity of 90.65%, specificity of 94.95%, and accuracy of 94.13%.

Conclusions

Shock, respiratory failure, albumin, and fibrinogen are potential independent prognostic factors for 60-day mortality.

Clindamycin Efficacy in Patients With Methicillin-Sensitive Staphylococcus aureus in a Fourth-Level Hospital in the City of Medellín

Background: The antibiotic of choice for methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia is antistaphylococcal penicillins, such as oxacillin, but cefazolin has also risen as an equally effective alternative. Murine models have suggested that clindamycin is a therapeutic alternative for Staphylococcus aureus bacteremia (SAB).

Methods: In this retrospective cohort study, patients from the Hospital Universitario San Vicente Fundación (HUSVF) in Medellín, Colombia, were recruited from January 2013 and December 2019. Patients with positive blood culture for MSSA, with at least one follow-up blood culture, and those with more than 72 hours of parenteral antibiotic therapy for SAB were selected. The main objective was to determine the efficacy of clindamycin compared to other antibiotics to achieve a microbiologic cure. Secondary results included in-hospital mortality and hospital stay.

Results: A total of 486 patients were included (clindamycin = 50 and other anti-MSSA = 436). The patients in the clindamycin group had a lower rate of microbiological cure (n = 41 [84%]) compared to other antibiotics (n = 367 [84%]) (OR 1.08 IC 95% 0.74-1.58). In secondary outcomes, no statistically significant differences were observed in the in-hospital mortality. The main source of SAB was a central or peripheral catheter (58%).

Conclusions: Our study found no differences in the rate of microbiological cure, in-hospital mortality, and hospital stay on the clindamycin group compared to other anti-MSSA antibiotics. However, in patients with metastatic complications, the rate of microbiological cure is reduced, and the in-hospital mortality is higher in patients with more severe disease.

Bacterial genotype and clinical outcomes in solid organ transplant recipients with Staphylococcus aureus bacteremia

INTRODUCTION

Outcomes from Staphylococcus aureus bacteremia (SAB) in solid organ transplant (SOT) recipients are poorly understood.

METHODS

This is a prospective cohort study comparing the bacterial genotype and clinical outcomes of SAB among SOT and non-transplant (non-SOT) recipients from 2005 to 2019. Each subject's initial S. aureus bloodstream isolate was genotyped using spa typing and assigned to a clonal complex.

RESULTS

A total of 103 SOT and 1783 non-SOT recipients with SAB were included. Bacterial genotype did not differ significantly between SOT and non-SOT recipients (p = .4673), including the proportion of SAB caused by USA300 (13.2% vs. 16.0%, p = .2680). Transplant status was not significantly associated with 90-day mortality (18.4% vs. 29.5%; adjusted odds ratio [aOR] 0.74; 95% confidence interval [CI]: 0.44, 1.25), but was associated with increased risk for septic shock (50.0% vs. 21.8%; aOR 2.31; 95% CI: 1.48, 3.61) and acute respiratory distress syndrome (21.4% vs. 13.7%; aOR 2.03; 95% CI: 1.22, 3.37), and a significantly lower risk of metastatic complications (33.0% vs. 45.5%; aOR 0.49; 95% CI: 0.32, 0.76). No association was found between bacterial genotype and 90-day mortality (p = .6222) or septic shock (p = .5080) in SOT recipients with SAB.

CONCLUSIONS

SOT recipients with SAB do not experience greater mortality than non-SOT recipients. The genotype of S. aureus bloodstream isolates in SOT recipients is similar to that of non-SOT recipients, and does not appear to be an important determinant of outcome in SOT recipients with SAB.

Dissecting the Human Response to Staphylococcus aureus Systemic Infections

Staphylococcus aureus is a common human commensal and the leading cause of diverse infections. To identify distinctive parameters associated with infection and colonization, we compared the immune and inflammatory responses of patients with a diagnosis of invasive S. aureus disease to healthy donors. We analyzed the inflammatory responses founding a pattern of distinctive cytokines significantly higher in the patients with invasive disease. The measure of antibody levels revealed a wide antibody responsiveness from all subjects to most of the antigens, with significantly higher response for some antigens in the invasive patients compared to control. Moreover, functional antibodies against toxins distinctively associated with the invasive disease. Finally, we examined the genomic variability of isolates, showing no major differences in genetic distribution compared to a panel of representative strains. Overall, our study shows specific signatures of cytokines and functional antibodies in patients with different primary invasive diseases caused by S. aureus. These data provide insight into human responses towards invasive staphylococcal infections and are important for guiding the identification of novel preventive and therapeutic interventions against S. aureus.

Pharmacokinetics, Tissue Distribution, and Efficacy of VIO-001 (Meropenem/Piperacillin/Tazobactam) for Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia in Immunocompetent Rabbits with Chronic Indwelling Vascular Catheters

Methicillin-resistant Staphylococcus aureus (MRSA) infections of surgically implanted subcutaneous vascular catheters (SISVCs) cause serious morbidity in patients with chronic illnesses. Previous in vitro and murine models demonstrated the synergistic interaction of equimolar concentrations of meropenem/piperacillin/tazobactam (MPT) (VIO-001) against MRSA infection. We investigated the pharmacokinetics (PK) and efficacy of VIO-001 for the treatment of MRSA bacteremia in immunocompetent rabbits with SISVCs. In PK studies, we determined that optimal dosing to achieve a time above 4× MIC (T_>4×MIC) of a duration of 3 to 3.30 h required a 1-h infusion with every-4-h (Q4h) dosing. Study groups in efficacy experiments consisted of MPT combinations of 100/150/100 mg/kg of body weight (MPT100), 200/300/200 mg/kg (MPT200), and 400/600/400 mg/kg (MPT400); vancomycin (VAN) at 15 mg/kg; and untreated controls (UC). The inoculum of MRSA isolate USA300-TCH1516 (1 × 10³ organisms) was administered via the SISCV on day 1 and locked for 24 h. The 8-day therapy started at 24 h postinoculation. There was a significant reduction of MRSA in blood cultures from the SISVCs in all treatment groups, with full clearance on day 4, versus UCs (P < 0.05). Consistent with the clearance of SISVC-related infection, full eradication of MRSA was achieved in lungs, heart, liver, spleen, and kidneys at the end of the study versus UC (P < 0.01). These results strongly correlated with time-kill data, where MPT in the range of 4/6/4 μg/ml to 32/48/32 μg/ml demonstrated a significant 6-log decrease in the bacterial burden versus UC (P < 0.01). In summary, VIO-001 demonstrated a favorable PK/pharmacodynamic (PD) profile and activity against SISCV MRSA infection, bacteremia, and disseminated infection. This rabbit model provides a new system for understanding new antimicrobial agents against MRSA SISVC-related infection, and these data provide a basis for future clinical investigation.

Abiotrophia defectiva DnaK Promotes Fibronectin-Mediated Adherence to HUVECs and Induces a Proinflammatory Response

Abiotrophia defectiva is a nutritionally variant streptococci that is found in the oral cavity, and it is an etiologic agent of infective endocarditis. We have previously reported the binding activity of A. defectiva to fibronectin and to human umbilical vein endothelial cells (HUVECs). However, the contribution of some adhesion factors on the binding properties has not been well delineated. In this study, we identified DnaK, a chaperon protein, as being one of the binding molecules of A. defectiva to fibronectin. Recombinant DnaK (rDnaK) bound immobilized fibronectin in a concentration-dependent manner, and anti-DnaK antiserum reduced the binding activity of A. defectiva with both fibronectin and HUVECs. Furthermore, DnaK were observed on the cell surfaces via immune-electroscopic analysis with anti-DnaK antiserum. Expression of IL-8, CCL2, ICAM-1, and VCAM-1 was upregulated with the A. defectiva rDnaK treatment in HUVECs. Furthermore, TNF-α secretion of THP-1 macrophages was also upregulated with the rDnaK. We observed these upregulations in rDnaK treated with polymyxin B, but not in the heat-treated rDnaK. The findings show that A. defectiva DnaK functions not only as an adhesin to HUVECs via the binding to fibronectin but also as a proinflammatory agent in the pathogenicity to cause infective endocarditis.

Staphylococcal trafficking and infection - from 'nose to gut' and back

Staphylococcus aureus is an opportunistic human pathogen, which is a leading cause of infections worldwide. The challenge in treating S. aureus infection is linked to the development of multidrug-resistant strains and the mechanisms employed by this pathogen to evade the human immune defenses. In addition, S. aureus can hide asymptomatically in particular ‘protective’ niches of the human body for prolonged periods of time. In the present review, we highlight recently gained insights in the role of the human gut as an endogenous S. aureus reservoir next to the nasopharynx and oral cavity. In addition, we address the contribution of these ecological niches to staphylococcal transmission, including the roles of particular triggers as modulators of the bacterial dissemination. In this context, we present recent advances concerning the interactions between S. aureus and immune cells to understand their possible roles as vehicles of dissemination from the gut to other body sites. Lastly, we discuss the factors that contribute to the switch from colonization to infection. Altogether, we conclude that an important key to uncovering the pathogenesis of S. aureus infection lies hidden in the endogenous staphylococcal reservoirs, the trafficking of this bacterium through the human body and the subsequent immune responses.

Bacteremia in solid organ transplant recipients as compared to immunocompetent patients: Acute phase cytokines and outcomes in a prospective, matched cohort study

We undertook a prospective, matched cohort study of patients with Staphylococcus aureus bacteremia (SAB) and gram-negative bacteremia (GNB) to compare the characteristics, outcomes, and chemokine and cytokine response in transplant recipients to immunocompetent, nontransplant recipients. Fifty-five transplant recipients (GNB n = 29; SAB n = 26) and 225 nontransplant recipients (GNB n = 114; SAB n = 111) were included for clinical analysis. Transplant GNB had a significantly lower incidence of septic shock than nontransplant GNB (10.3% vs 30.7%, p = .03). Thirty-day mortality did not differ significantly between transplant and nontransplant recipients with GNB (10.3% vs 15.8%, p = .57) or SAB (0.0% vs 11.7%, p = .13). Next, transplant patients were matched 1:1 with nontransplant patients for the chemokine and cytokine analysis. Five cytokines and chemokines were significantly lower in transplant GNB vs nontransplant GNB: IL-2 (median [IQR]: 7.1 pg/ml [7.1, 7.1] vs 32.6 pg/ml [7.1, 88.0]; p = .001), MIP-1β (30.7 pg/ml [30.7, 30.7] vs 243.3 pg/ml [30.7, 344.4]; p = .001), IL-8 (32.0 pg/ml [5.6, 53.1] vs 59.1 pg/ml [39.2, 119.4]; p = .003), IL-15 (12.0 pg/ml [12.0, 12.0] vs 12.0 pg/ml [12.0, 126.7]; p = .03), and IFN-α (5.1 pg/mL [5.1, 5.1] vs 5.1 pg/ml [5.1, 26.3]; p = .04). Regulated upon Activation, Normal T Cell Expressed and Secreted (RANTES) was higher in transplant SAB vs nontransplant SAB (mean [SD]: 750.2 pg/ml [194.6] vs 656.5 pg/ml [147.6]; p = .046).

Current Paradigms of Combination therapy in Methicillin-Resistant Staphylococcus aureus (MRSA) Bacteremia: Does it Work, Which Combination and For Which Patients?

The last several years have seen an emergence of literature documenting the utility of combination antimicrobial therapy, particularly in the salvage of refractory MRSA bacteremia. Recent clinical data are shaping conundrums of which regimens may be more beneficial, which can be potentially harmful, and which subset of patients stand to benefit from more aggressive treatment regimens than called for by current standards. In addition, the incorporation of combination therapy for MRSA bacteremia should be accompanied by the reminder that antimicrobial therapy does not need to be uniform for the entire duration, with an early intensive phase in high inoculum infections (e.g. with combination therapy), followed by a consolidation phase (i.e. monotherapy). This review and perspective consolidates the recent data on this subject and directs future goals in filling the knowledge gaps to methodically move forward towards improving patient outcomes.

Cell Membrane Adaptations Mediate β-Lactam-Induced Resensitization of Daptomycin-Resistant (DAP-R) Staphylococcus aureus In Vitro

The reversal of daptomycin resistance in MRSA to a daptomycin-susceptible phenotype following prolonged passage in selected β-lactams occurs coincident with the accumulation of multiple point mutations in the mprF gene. MprF regulates surface charge by modulating the content and translocation of the positively charged cell membrane phospholipid, lysyl-phosphatidylglycerol (LPG). The precise cell membrane adaptations accompanying such β-lactam-induced mprF perturbations are unknown. This study examined key cell membrane metrics relevant to antimicrobial resistance among three daptomycin-resistant MRSA clinical strains, which became daptomycin-susceptible following prolonged exposure to cloxacillin ('daptomycin-resensitized'). The causal role of such secondary mprF mutations in mediating daptomycin resensitization was confirmed through allelic exchange strategies. The daptomycin-resensitized strains derived either post-cloxacillin passage or via allelic exchange (vs. their respective daptomycin-resistant strains) showed the following cell membrane changes: (i) enhanced BODIPY-DAP binding; (ii) significant reductions in LPG content, accompanied by significant increases in phosphatidylglycerol content (p < 0.05); (iii) no significant changes in positive cell surface charge; (iv) decreased cell membrane fluidity (p < 0.05); (v) enhanced carotenoid content (p < 0.05); and (vi) lower branched chain fatty acid profiles (antiso- vs. iso-), resulting in increases in saturated fatty acid composition (p < 0.05). Overall, the cell membrane characteristics of the daptomycin-resensitized strains resembled those of parental daptomycin-susceptible strains. Daptomycin resensitization with selected β-lactams results in both definable genetic changes (i.e., mprF mutations) and a number of key cell membrane phenotype modifications, which likely facilitate daptomycin activity.

Cytokine measurements add value to clinical variables in predicting outcomes for Staphylococcus aureus bacteremia

Background

We demonstrated that an early dysregulated cytokine response [high interleukin-10 to tissue necrosis factor (IL-10/TNF) ratio] predicted poor outcomes in patients with Staphylococcus aureus bacteremia (SAB). However, high interpatient variability in cytokine levels were observed. We grouped cytokine measurements in quartiles and assessed their additive value to clinical variables for predicting bacterial persistence and 30-day mortality in patients with SAB.

Methods

A multicenter observational study was conducted in hospitalized patients with SAB. Medical charts were reviewed for relevant information. Blood samples were obtained for cytokine measurements by ELISA: interferon-gamma (IFNγ), interleukin (IL-1β, IL-6, IL-8, IL-10, IL-17) and tissue necrosis factor (TNF). Cytokine measurements were grouped into quartiles. Significant predictors for bacterial persistence and 30-day mortality were determined by multivariable logistic regression analysis. Area under the ROC curve (AUC) analysis was performed and predictive performance was compared between models with and without cytokine quartiles.

Results

Among 606 patients with SAB, a subset of patients (n = 239) had Day 1 cytokine measurements and clinical data collected; of those, 53 (22%) had persistent bacteremia. Accounting for septic shock, the addition of either IL-10 (AUC 0.708) or TNF (AUC 0.714) quartiles measured on Day 1 improved model performance for predicting bacterial persistence. All patients had Day 4 cytokine measurements; 52 patients (8.5%) died within 30-days of SAB onset. Inclusion of either IL-10 (AUC 0.873) or TNF (AUC 0.879) quartiles, but not both, measured on Day 4 to the significant clinical predictors (coronary artery disease, Pitt bacteremia score ≥ 4, and septic shock) improved model performance for mortality.

Conclusions

IL-10 or TNF levels falling within the range in the upper quartiles, when combined with clinical variables, improved model performance for predicting outcomes, and may potentially be used to support aggressive management and biomarker-guided studies to evaluate the benefit of adjunctive immunotherapy for SAB in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06010-0.

Variable Release of Lipoteichoic Acid From Staphylococcus aureus Bloodstream Isolates Relates to Distinct Clinical Phenotypes, Strain Background, and Antibiotic Exposure

Background

Staphylococcus aureus is a leading cause of bacterial bloodstream infections. The heterogeneity in patient outcomes in S. aureus bacteremia (SAB) can be attributed in part to strain characteristics, which may influence host response to infection. We specifically examined the relationship between lipoteichoic acid (LTA) release from S. aureus and disease phenotype, strain background, and antibiotic exposure.

Methods

Seven strains of S. aureus causing different clinical phenotypes of bacteremia and two reference strains (LAC USA 300 and Mu3) were analyzed for LTA release at baseline and following exposure to antibiotics from different pharmacologic classes (vancomycin, ceftaroline, and tedizolid). LTA release was quantified by LTA-specific ELISA. Whole genome sequencing was performed on the clinical strains and analyzed using open-source bioinformatics tools.

Results

Lipoteichoic acid release varied by 4-fold amongst the clinical strains and appeared to be related to duration of bacteremia, independent of MLST type. Low LTA releasing strains were isolated from patients who had prolonged duration of bacteremia and died. Antibiotic-mediated differences in LTA release appeared to be associated with MLST type, as ST8 strains released maximal LTA in response to tedizolid while other non-ST8 strains demonstrated high LTA release with vancomycin. Genetic variations related to the LTA biosynthesis pathway were detected in all non-ST8 strains, though ST8 strains showed no variations despite demonstrating differential LTA release.

Conclusion

Our findings provide the basis for future studies to evaluate the relationship between LTA release-mediated host immune response and clinical outcomes as well as the potential for antibiotic modulation of LTA release as a therapeutic strategy and deserve confirmation with larger number of strains with known clinical phenotypes.

Interleukin (IL)-1β and IL-10 Host Responses in Patients With Staphylococcus aureus Bacteremia Determined by Antimicrobial Therapy

BACKGROUND

Patient interleukin (IL)-1β and IL-10 responses early in Staphylococcus aureus bacteremia (SaB) are associated with bacteremia duration and mortality. We hypothesized that these responses vary depending on antimicrobial therapy, with particular interest in whether the superiority of β-lactams links to key cytokine pathways.

METHODS

Three medical centers included 59 patients with SaB (47 methicillin-resistant S. aureus [MRSA], 12 methicillin-sensitive S. aureus [MSSA]) from 2015-2017. In the first 48 hours, patients were treated with either a β-lactam (n = 24), including oxacillin, cefazolin, or ceftaroline, or a glyco-/lipopeptide (n = 35), that is, vancomycin or daptomycin. Patient sera from days 1, 3, and 7 were assayed for IL-1β and IL-10 by enzyme-linked immunosorbent assay and compared using the Mann-Whitney U test.

RESULTS

On presentation, IL-10 was elevated in mortality (P = .008) and persistent bacteremia (P = .034), while no difference occurred in IL-1β. Regarding treatment groups, IL-1β and IL-10 were similar prior to receiving antibiotic. Patients treated with β-lactam had higher IL-1β on days 3 (median +5.6 pg/mL; P = .007) and 7 (+10.9 pg/mL; P = .016). Ex vivo, addition of the IL-1 receptor antagonist anakinra to whole blood reduced staphylococcal killing, supporting an IL-1β functional significance in SaB clearance. β-lactam-treated patients had sharper declines in IL-10 than vancomycin or daptomycin -treated patients over 7 days.

CONCLUSIONS

These data underscore the importance of β-lactams for SaB, including consideration that the adjunctive role of β-lactams for MRSA in select patients helps elicit favorable host cytokine responses.

Antimicrobial susceptibility patterns of bacteria that commonly cause bacteremia at a tertiary hospital in Zambia

Background: Bloodstream infections and antimicrobial resistance cause global increases in morbidity and mortality. Aim: We evaluated the antimicrobial susceptibility patterns of bacteria that commonly cause bacteremia in humans. Materials & methods: We conducted a retrospective cross-sectional study at the University Teaching Hospitals in Lusaka, Zambia, using Laboratory Information Systems. Results: The commonest isolated bacteria associated with sepsis were Klebsiella pneumoniae. The distribution of bacteria associated with bacteremia in different wards and departments pneumonia. The distribution of bacteria associated with bacteremia in different wards and departments at University Teaching Hospitals was were statistically significant (χ2 = 1211.518; p < 0.001). Conclusion: K. pneumoniae, Escherichia coli, Pantoea agglomerans and Enterococcus species have developed high resistance levels against ampicillin, cefotaxime, ciprofloxacin, gentamicin and trimethoprim/sulfamethoxazole and a very low resistance levels against imipenem and Amikacin.

Development of a vaccine against Staphylococcus aureus invasive infections: Evidence based on human immunity, genetics and bacterial evasion mechanisms

Invasive Staphylococcus aureus infections are a leading cause of morbidity and mortality in both hospital and community settings, especially with the widespread emergence of virulent and multi-drug resistant methicillin-resistant S. aureus strains. There is an urgent and unmet clinical need for non-antibiotic immune-based approaches to treat these infections as the increasing antibiotic resistance is creating a serious threat to public health. However, all vaccination attempts aimed at preventing S. aureus invasive infections have failed in human trials, especially all vaccines aimed at generating high titers of opsonic antibodies against S. aureus surface antigens to facilitate antibody-mediated bacterial clearance. In this review, we summarize the data from humans regarding the immune responses that protect against invasive S. aureus infections as well as host genetic factors and bacterial evasion mechanisms, which are important to consider for the future development of effective and successful vaccines and immunotherapies against invasive S. aureus infections in humans. The evidence presented form the basis for a hypothesis that staphylococcal toxins (including superantigens and pore-forming toxins) are important virulence factors, and targeting the neutralization of these toxins are more likely to provide a therapeutic benefit in contrast to prior vaccine attempts to generate antibodies to facilitate opsonophagocytosis.

Mortality Risk Profiling of Staphylococcus aureus Bacteremia by Multi-omic Serum Analysis Reveals Early Predictive and Pathogenic Signatures

Staphylococcus aureus bacteremia (SaB) causes significant disease in humans, carrying mortality rates of ∼25%. The ability to rapidly predict SaB patient responses and guide personalized treatment regimens could reduce mortality. Here, we present a resource of SaB prognostic biomarkers. Integrating proteomic and metabolomic techniques enabled the identification of >10,000 features from >200 serum samples collected upon clinical presentation. We interrogated the complexity of serum using multiple computational strategies, which provided a comprehensive view of the early host response to infection. Our biomarkers exceed the predictive capabilities of those previously reported, particularly when used in combination. Last, we validated the biological contribution of mortality-associated pathways using a murine model of SaB. Our findings represent a starting point for the development of a prognostic test for identifying high-risk patients at a time early enough to trigger intensive monitoring and interventions.

Defining persistent Staphylococcus aureus bacteraemia: secondary analysis of a prospective cohort study

BACKGROUND

Staphylococcus aureus persistent bacteraemia is only vaguely defined and the effect of different durations of bacteraemia on mortality is not well established. Our primary aim was to analyse mortality according to duration of bacteraemia and to derive a clinically relevant definition for persistent bacteraemia.

METHODS

We did a secondary analysis of a prospective observational cohort study at 17 European centres (nine in the UK, six in Spain, and two in Germany), with recruitment between Jan 1, 2013, and April 30, 2015. Adult patients who were consecutively hospitalised with monomicrobial S aureus bacteraemia were included. Patients were excluded if no follow-up blood culture was taken, if the first follow-up blood-culture was after 7 days, or if active antibiotic therapy was started more than 3 days after first blood culture. The primary outcome was 90-day mortality. Univariable and time-dependent multivariable Cox regression analysis were used to assess predictors of mortality. Duration of bacteraemia was defined as bacteraemic days under active antibiotic therapy counting the first day as day 1.

FINDINGS

Of 1588 individuals assessed for eligibility, 987 were included (median age 65 years [IQR 51-75]; 625 [63%] male). Death within 90 days occurred in 273 (28%) patients. Patients with more than 1 day of bacteraemia (315 [32%]) had higher Charlson comorbidity index and sequential organ failure assessment scores and a longer interval from first symptom to first blood culture. Crude 90-day mortality increased from 22% (148 of 672) with 1 day of bacteraemia, to 39% (85 of 218) with 2-4 days, 43% (30 of 69) with 5-7 days, and 36% (10 of 28) with more than 7 days of bacteraemia. Metastatic infections developed in 39 (6%) of 672 patients with 1 day of bacteraemia versus 40 (13%) of 315 patients if bacteraemia lasted for at least 2 days. The second day of bacteraemia had the highest HR and earliest cutoff significantly associated with mortality (adjusted hazard ratio 1·93, 95% CI 1·51-2·46; p<0·0001).

INTERPRETATION

We suggest redefining the cutoff duration for persistent bacteraemia as 2 days or more despite active antibiotic therapy. Our results favour follow-up blood cultures after 24 h for early identification of all patients with increased risk of death and metastatic infection.

FUNDING

None.

A Bioinformatic Approach to Utilize a Patient's Antibody-Secreting Cells against Staphylococcus aureus to Detect Challenging Musculoskeletal Infections

Noninvasive diagnostics for Staphylococcus aureus musculoskeletal infections (MSKI) remain challenging. Abs from newly activated, pathogen-specific plasmablasts in human blood, which emerge during an ongoing infection, can be used for diagnosing and tracking treatment response in diabetic foot infections. Using multianalyte immunoassays on medium enriched for newly synthesized Abs (MENSA) from Ab-secreting cells, we assessed anti-S. aureus IgG responses in 101 MSKI patients (63 culture-confirmed S. aureus, 38 S. aureus-negative) and 52 healthy controls. MENSA IgG levels were assessed for their ability to identify the presence and type of S. aureus MSKI using machine learning and multivariate receiver operating characteristic curves. Eleven S. aureus-infected patients were presented with prosthetic joint infections, 15 with fracture-related infections, 5 with native joint septic arthritis, 15 with diabetic foot infections, and 17 with suspected orthopedic infections in the soft tissue. Anti-S. aureus MENSA IgG levels in patients with non-S. aureus infections and healthy controls were 4-fold (***p = 0.0002) and 8-fold (****p < 0.0001) lower, respectively, compared with those with culture-confirmed S. aureus infections. Comparison of MENSA IgG responses among S. aureus culture-positive patients revealed Ags predictive of active MSKI (IsdB, SCIN, Gmd) and Ags predictive of MSKI type (IsdB, IsdH, Amd, Hla). When combined, IsdB, IsdH, Gmd, Amd, SCIN, and Hla were highly discriminatory of S. aureus MSKI (area under the ROC curve = 0.89 [95% confidence interval 0.82-0.93, p < 0.01]). Collectively, these results demonstrate the feasibility of a bioinformatic approach to use a patient's active immune proteome against S. aureus to diagnose challenging MSKI.

Antimicrobial Resistance and Molecular Epidemiology of Staphylococcus aureus Causing Bloodstream Infections at Ruijin Hospital in Shanghai from 2013 to 2018

Staphylococcus aureus or methicillin-resistant Staphylococcus aureus (MRSA) is an important issue associated with significant morbidity and mortality and well known as a predominant pathogen causing bloodstream infection (BSIs) globally. To estimate the antibiotic resistance and molecular characteristics of S. aureus causing BSIs in Shanghai, 120 S. aureus isolates (20 isolates each year) from the patients with S. aureus BSIs from 2013 to 2018 were randomly selected and enrolled in this study. Fifty-three (44.2%) MRSA isolates were determined, and no isolate was found resistant to vancomycin, daptomycin, synercid, linezolid and ceftaroline. The toxin genes tst, sec, seg and sei were found more frequently among MRSA isolates compared with MSSA isolates (all P < 0.0001). Twenty-nine sequence types (STs) were identified, and ST5 (23.3%) was the most common ST, followed by ST398 (11.7%) and ST764 (10.0%). SCCmec II (73.6%) was the most frequent SCCmec type among MRSA isolates. The dominant clonal complexes (CCs) were CC5 (ST5, ST764, ST965 and ST3066; 36.7%) and the livestock-associated clone CC398 (ST398, 11.7%). MRSA-CC5 was the predominant CC among MRSA isolates (37/53, 69.8%), and CC5-II MRSA was found in 34 isolates accounting for 91.9% (34/37) among CC5 MRSA isolates. In addition, all 29 tst-positive MRSA isolates were CC5-MRSA as well. Our study provided the properties and genotypes of S. aureus causing BSIs at Ruijin Hospital in Shanghai from 2013 to 2018, and might suggest of value clues for the further study insights into pathogenic mechanisms intrinsically referring to the development of human-adapted S. aureus clones and their diffusions.

Peripheral Merozoite Surface Proteins Are Targets of Naturally Acquired Immunity against Malaria in both India and Ghana

Development of a successful blood-stage vaccine against Plasmodium falciparum malaria remains a high priority. Immune-epidemiological studies are effective tools for the identification of antigenic targets of naturally acquired immunity (NAI) against malaria. However, differences in study design and methodology may compromise interstudy comparisons. Here, we assessed antibody responses against intact merozoites and a panel of 24 recombinant merozoite antigens in longitudinal cohort studies of Ghanaian (n = 115) and Indian (n = 121) populations using the same reagents and statistical methods. Anti-merozoite antibodies were associated with NAI in both the Indian (hazard ratio [HR] = 0.41, P = 0.020) and the Ghanaian (HR = 0.17, P < 0.001) participants. Of the 24 antigen-specific antibodies quantified, 12 and 8 were found to be protective in India and Ghana, respectively. Using least absolute shrinkage and selection operator (LASSO) regression, a powerful variable subselection technique, we identified subsets of four (MSP6, MSP3.7, MSPDBL2, and Pf12) and five (cMSP3^3D7, MSP3.3, MSPDBL1, GLURP-R2, and RALP-1) antigens that explained NAI better than the individual antibodies in India (HR = 0.18, P < 0.001) and Ghana (HR = 0.31, P < 0.001), respectively. IgG1 and/or IgG3 subclasses against five antigens from these subsets were associated with protection. Through this comparative study, maintaining uniformity of reagents and methodology, we demonstrate that NAI across diverse geographic regions may result from antibodies to multiple antigenic targets that constitute the peripheral merozoite surface protein complexes.

Therapy of Staphylococcus aureus bacteremia: Evidences and challenges

Staphylococcus aureus bacteremia (SAB) is still a daily challenge for clinicians. Despite all efforts, the associated mortality and morbidity has not significantly improved in the last 20 years. The available evidence suggests that adherence to some quality-of-care indicators with regard to clinical management is important in improving the outcome of patients, but it is lower than desired in many hospitals; as such, management of patients with SAB by infectious diseases specialists has been demonstrated to contribute in the reduction of the mortality rate of these patients. In this article, the most relevant clinical studies published over the last few years evaluating the efficacy and safety of alternative drugs for the treatment of SAB are reviewed. However, classic drugs are still used in a high proportion of patients because the promising results obtained from in vivo and in vivo studies with these alternative drugs have not translated as frequently as expected into evident superiority in clinical studies. Nevertheless, some data suggest that certain alternatives may offer advantages in specific situations. Overall, an individualised and expert approach is needed in order to decide the best treatment according to the source, severity, complications, patients' features and microbiological data.

Risk stratification biomarkers for Staphylococcus aureus bacteraemia

Objectives

To identify risk stratification biomarkers to enrich for the subset of Staphylococcus aureus bacteraemia patients who develop deep‐seated tissue infections with high morbidity and mortality to guide clinical trial enrolment and clinical management.

Methods

We evaluated the prognostic value of eight biomarkers for persistent bacteraemia, mortality and endovascular infection foci in a validation cohort of 160 patients with S. aureus bacteraemia enrolled consecutively over 3 years.

Results

High levels of IL‐17A, IL‐10 or soluble E‐selectin at bacteraemia diagnosis correlated with the duration of positive blood cultures. When thresholds defined in an independent cohort were applied, these biomarkers were robust predictors of persistent bacteraemia or endovascular infection. High serum levels of IL‐17A and IL‐10 often preceded the radiographic diagnosis of infective endocarditis, suggesting potential utility for prioritising diagnostic radiographic imaging. High IL‐8 was prognostic for all‐cause mortality, while IL‐17A and IL‐10 were superior to clinical metrics in discriminating between attributable mortality and non‐attributable mortality. High IL‐17A and IL‐10 identified more patients who developed microbiological failure or mortality than were identified by infective endocarditis diagnosis.

Conclusion

These biomarkers offer potential utility to identify patients at risk of persistent bacteraemia to guide diagnostic imaging and clinical management. Low biomarker levels could be used to rule out the need for more invasive TEE imaging in patients at lower risk of infective endocarditis. These biomarkers could enable clinical trials by enriching for patients with the greatest need for novel therapies.

Burden of bacterial bloodstream infection-a brief update on epidemiology and significance of multidrug-resistant pathogens

BACKGROUND

Bloodstream infections comprise a wide variety of pathogens and clinical syndromes with considerable overlap with similar syndromes of non-bacteraemic infections and diverse risk factors, therapeutic implications and outcomes. Yet, this heterogeneous 'entity' has the advantage to be pathogen-defined compared with the broad and even more heterogeneous entity 'sepsis', and so has become helpful for clinicians and epidemiologists for research and surveillance purposes. The increasing availability of population-based and large multicentre well-defined cohort studies should allow us to assess with much confidence and in detail its burden, the significance of antimicrobial resistance, and areas of uncertainty regarding further epidemiological evolution and optimized treatment regimens.

AIM

To review key aspects of bloodstream infection epidemiology and burden, and summarize recent news and questions concerning critical developments.

SOURCES

Peer-reviewed articles based on the search terms 'bloodstream infection' and 'bacteremia' combined with the terms 'epidemiology' and 'burden'. The emphasis was on new information from studies in adult patients and on the added burden due to pathogen resistance to first- and second-line antimicrobial agents.

CONTENT

Topics covered include recent developments in the epidemiology of bloodstream infection due to key pathogens and published information about the relevance of resistance for patient outcomes.

IMPLICATIONS

Despite the availability of population-based studies and an increasing number of large well-defined multicentre cohort studies, more surveillance and systematic data on bloodstream infection epidemiology at regional level and in resource-limited settings may be needed to better design new methods for prevention and define the need for and further develop optimized therapeutic strategies.

Genetic variation of DNA methyltransferase-3A contributes to protection against persistent MRSA bacteremia in patients

The severity and duration of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia varies widely between individuals. Host factors predisposing to persistent MRSA bacteremia are poorly understood, although genetic association studies are beginning to identify potentially influential variants. We found an association between the A/C heterozygous genotype in the DNMT3A correlating with shorter time to resolution of MRSA bacteremia. Using in vitro macrophage assays and murine sepsis models, we demonstrated that DNMT3A variants may alter host response to infection through increased methylation of key regulatory genes, resulting in reduced interleukin-10 production and in turn, allowing for a more protective immune response that clears infection. An improved understanding of the factors predisposing to persistent MRSA bacteremia may help to discover better treatment options.

The role of the host in development of persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is not well understood. A cohort of prospectively enrolled patients with persistent methicillin-resistant S. aureus bacteremia (PB) and resolving methicillin-resistant S. aureus bacteremia (RB) matched by sex, age, race, hemodialysis status, diabetes mellitus, and presence of implantable medical device was studied to gain insights into this question. One heterozygous g.25498283A > C polymorphism located in the DNMT3A intronic region of chromosome 2p with no impact in messenger RNA (mRNA) expression was more common in RB (21 of 34, 61.8%) than PB (3 of 34, 8.8%) patients (P = 7.8 × 10⁻⁶). Patients with MRSA bacteremia and g.25498283A > C genotype exhibited significantly higher levels of methylation in gene-regulatory CpG island regions (Δmethylation = 4.1%, P < 0.0001) and significantly lower serum levels of interleukin-10 (IL-10) than patients with MRSA bacteremia without DNMT3A mutation (A/C: 9.7038 pg/mL vs. A/A: 52.9898 pg/mL; P = 0.0042). Expression of DNMT3A was significantly suppressed in patients with S. aureus bacteremia and in S. aureus-challenged primary human macrophages. Small interfering RNA (siRNA) silencing of DNMT3A expression in human macrophages caused increased IL-10 response upon S. aureus stimulation. Treating macrophages with methylation inhibitor 5-Aza-2′-deoxycytidine resulted in increased levels of IL-10 when challenged with S. aureus. In the murine sepsis model, methylation inhibition increased susceptibility to S. aureus. These findings indicate that g.25498283A > C genotype within DNMT3A contributes to increased capacity to resolve MRSA bacteremia, potentially through a mechanism involving increased methylation of gene-regulatory regions and reduced levels of antiinflammatory cytokine IL-10.

Prognostic Power of Pathogen Cell-Free DNA in Staphylococcus aureus Bacteremia

BACKGROUND

Staphylococcus aureus is a leading global cause of bacteremia that can cause invasive tissue infections with high morbidity and mortality despite appropriate antibiotic therapy. Clinicians lack sufficient tools to rapidly identify patients with a poor prognosis to guide diagnostic workup and treatment decisions. Host cell-free DNA provides prognostic value across a spectrum of critical illnesses, including S. aureus bacteremia and sepsis. Metrics of high bacterial load are associated with disease severity in S. aureus bacteremia, and the objective of this study was to evaluate whether incorporating quantitation of cell-free bacterial DNA would provide additive prognostic value when combined with biomarkers of the inflammatory response.

METHODS

S. aureus cell-free DNA was measured by quantitative polymerase chain reaction (PCR) in baseline serum samples from an observational cohort of 111 patients with complicated S. aureus bacteremia and correlated with host inflammatory markers and clinical outcomes.

RESULTS

High levels of S. aureus cell-free DNA at the time of positive index blood culture were prognostic for all-cause and attributable mortality and persistent bacteremia and were associated with infective endocarditis. However, they did not provide additive value to biomarkers of the host response to infection in multivariate analysis.

CONCLUSIONS

Measurements of bacterial load by PCR are a clinically feasible candidate biomarker for stratifying patients at higher risk for complications and poor outcomes. Their diagnostic and prognostic value for identifying foci of infection and influencing treatment remain to be evaluated in additional cohorts.