Predictors of mortality in Staphylococcus aureus Bacteremia

Differences in oxazolidinone resistance mechanisms and small colony variants emergence of Staphylococcus aureus induced in an in vitro resistance development model

Invasive Staphylococcus aureus infections are associated with a high burden of disease, case fatality rate and healthcare costs. Oxazolidinones such as linezolid and tedizolid are considered potential treatment choices for conditions involving methicillin resistance or penicillin allergies. Additionally, they are being investigated as potential inhibitors of toxins in toxin-mediated diseases. In this study, linezolid and tedizolid were evaluated in an in vitro resistance development model for induction of resistance in S. aureus. Whole genome sequencing was conducted to elucidate resistance mechanisms through the identification of causal mutations. After inducing resistance to both linezolid and tedizolid, several partially novel single nucleotide variants (SNVs) were detected in the rplC gene, which encodes the 50S ribosome protein L3 in S. aureus. These SNVs were found to decrease the binding affinity, potentially serving as the underlying cause for oxazolidinone resistance. Furthermore, in opposite to linezolid we were able to induce phenotypically small colony variants of S. aureus after induction of resistance with tedizolid for the first time in literature. In summary, even if different antibiotic concentrations were required and SNVs were detected, the principal capacity of S. aureus to develop resistance to oxazolidinones seems to differ between linezolid and tedizolid in-vivo but not in vitro. Stepwise induction of resistance seems to be a time and cost-effective tool for assessing resistance evolution. Inducted-resistant strains should be examined and documented for epidemiological reasons, if MICs start to rise or oxazolidinone-resistant S. aureus outbreaks become more frequent.

Community-Acquired Staphylococcus aureus Bacteremia Among People Who Inject Drugs: A National Cohort Study in England, 2017-2020

BACKGROUND

People who inject drugs (PWID) are at increased risk of community-acquired Staphylococcus aureus bacteremia (CA-SAB), but little is known about clinical outcomes of CA-SAB in PWID compared with the wider population of patients with CA-SAB.

METHODS

Three national datasets were linked to provide clinical and mortality data on patients hospitalized with CA-SAB in England between 1 January 2017 and 31 December 2020. PWID were identified using the International Classification of Diseases, Tenth Revision code for "mental health and behavioral disorder due to opioid use" (F11). Multivariable logistic regression was used to estimate adjusted odds ratios (aORs) for associations of PWID with 30-day all-cause mortality and 90-day hospital readmission.

RESULTS

In 10 045 cases of CA-SAB, 1612 (16.0%) were PWID. Overall, 796 (7.9%) patients died within 30 days of CA-SAB admission and 1189 (11.8%) patients were readmitted to hospital within 90 days of CA-SAB. In those without infective endocarditis, there was strong evidence of lower odds of mortality among PWID compared with non-PWID (aOR, 0.47 [95% confidence interval {CI}: .33-.68]; P < .001), whereas there was no association in CA-SAB case fatality with endocarditis (aOR, 1.40 [95% CI: .87-2.25]; P = .163). PWID were less likely to be readmitted within 90 days of CA-SAB (aOR, 0.79 [95% CI: .65-.95]; P = .011).

CONCLUSIONS

In this large cohort study of patients with CA-SAB in England, PWID had lower odds of death in the absence of endocarditis and lower odds of readmission within 90 days compared to non-PWID patients. This study highlights the overrepresentation of PWID among patients with CA-SAB nationally.

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

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

Staphylococcus aureus bacteremia in alcoholics

BACKGROUND

Alcoholism associates with increased Staphylococcus aureus bacteremia incidence and mortality. The objective was to compare disease progression, treatment and prognosis of Staphylococcus aureus bacteremia in alcoholics versus non-alcoholics.

METHODS

The study design was a multicenter retrospective analysis of methicillin-sensitive Staphylococcus aureus bacteremia with 90-day follow-up. Patients were stratified as alcoholics or non-alcoholics based on electronic health record data. Altogether 617 Staphylococcus aureus bacteremia patients were included of which 83 (13%) were alcoholics.

RESULTS

Alcoholics, versus non-alcoholics, were younger, typically male and more commonly had community-acquired Staphylococcus aureus bacteremia. No differences in McCabe´s classification of underlying conditions was observed. Higher illness severity at blood culture sampling, including severe sepsis (25% vs. 7%) and intensive care unit admission (39% vs. 17%), was seen in alcoholics versus non-alcoholics. Clinical management, including infectious disease specialist (IDS) consultations and radiology, were provided equally. Alcoholics, versus non-alcoholics, had more pneumonia (49% vs. 35%) and fewer cases of endocarditis (7% vs. 16%). Mortality in alcoholics versus non-alcoholics was significantly higher at 14, 28 and 90 days (14% vs. 7%, 24% vs. 11% and 31% vs. 17%), respectively. Considering all prognostic parameters, male sex (OR 0.19, p = 0.021) and formal IDS consultation (OR 0.19, p = 0.029) were independent predictors of reduced mortality, whereas ultimately or rapidly fatal comorbidity in McCabe´s classification (OR 12.34, p < 0.001) was an independent predictor of mortality in alcoholics.

CONCLUSIONS

Alcoholism deteriorates Staphylococcus aureus bacteremia prognosis, and our results suggests that this is predominantly through illness severity at bacteremia onset. Three quarters of Staphylococcus aureus bacteremia patients we studied had identified deep infection foci, and of them alcoholics had significantly less endocarditis but nearly half of them had pneumonia.

Assessing antibacterial efficacy of a polyhexanide hydrogel versus alginate-based wound dressing in burns

OBJECTIVE

Burn injuries pose a heightened risk of infection, which is primarily responsible for increased morbidity and mortality. Factors such as extensive skin damage and compromised immunity exacerbate this vulnerability. Pseudomonas aeruginosa and Staphylococcus aureus are frequently identified in burns, with Gram-negative Pseudomonas aeruginosa often resistant to antibacterial agents. While Flaminal, an alginate-based wound dressing (Flen Health, Belgium), aids wound healing, its antibacterial effects are limited compared with 1% silver sulfadiazine (1% SSD). In contrast, Prontosan Wound Gel X, a betaine and polyhexanide-based hydrogel (B. Braun Medical AG, Switzerland), has been shown to effectively combat various microbes and promotes wound healing.

METHOD

In this study, two research cohorts were retrospectively established (control group: patients receiving standard of care with the alginate-based wound dressing; intervention group: patients receiving the polyhexanide hydrogel wound dressing), comprising patients admitted to a burn centre between 2019 and 2022. Patients were eligible when continuous wound treatment with either of the two wound dressings was performed. Laser Doppler imaging (LDI) scans were conducted. Regions of interest (ROIs) were selected based on LDI scans and divided into healing time categories. Wound swabs were collected and the presence of Pseudomonas aeruginosa and Staphylococcus aureus was documented. Bacterial load was evaluated using a semiquantitative scale. Wound healing was recorded.

RESULTS

The control group consisted of 31 patients with 93 ROIs, while the intervention group had 67 ROIs involving 29 patients. Both groups exhibited similar proportions of healing time categories (p>0.05). The polyhexanide hydrogel dressing outperformed the alginate-based dressing in antiseptic efficacy by significantly reducing the incidence of Pseudomonas aeruginosa- and Staphylococcus aureus-positive cultures in patients' wounds. Wound healing time for conservative treatment was comparable between groups.

CONCLUSION

In this study, the polyhexanide hydrogel dressing minimised Pseudomonas aeruginosa and Staphylococcus aureus colonisation in burn wounds, demonstrating strong antibacterial properties, emphasising its potential to minimise infections in burn injuries.

Validation of a new risk stratification system-based management for methicillin-resistant Staphylococcus aureus bacteraemia: analysis of a multicentre prospective study

PURPOSE

Distinguishing between complicated and uncomplicated Staphylococcus aureus bacteraemia (SAB) is therapeutically essential. However, this distinction has limitations in reflecting the heterogeneity of SAB and encouraging targeted diagnostics. Recently, a new risk stratification system for SAB metastatic infection, involving stepwise approaches to diagnosis and treatment, has been suggested. We assessed its applicability in methicillin-resistant SAB (MRSAB) patients.

METHODS

We retrospectively analysed data of a 3-year multicentre, prospective cohort of hospitalised patients with MRSAB. We classified the patients into three risk groups: low, indeterminate, and high, based on the new system and compared between-group management and outcomes.

RESULTS

Of 380 patients with MRSAB, 6.3% were classified as low-, 7.6% as indeterminate-, and 86.1% as high-risk for metastatic infection. No metastatic infection occurred in the low-, 6.9% in the indeterminate-, and 19.6% in the high-risk groups (P < 0.001). After an in-depth diagnostic work-up, patients were finally diagnosed as 'without metastatic infection (6.3%)', 'with metastatic infection (17.4%)', and 'uncertain for metastatic infection (76.3%)'. 30-day mortality increased as the severity of diagnosis shifted from 'without metastatic infection' to 'uncertain for metastatic infection' and 'with metastatic infection' (P = 0.09). In multivariable analysis, independent factors associated with metastatic complications were suspicion of endocarditis in transthoracic echocardiography, clinical signs of metastatic infection, Pitt bacteraemia score ≥ 4, and persistent bacteraemia.

CONCLUSIONS

The new risk stratification system shows promise in predicting metastatic complications and guiding work-up and management of MRSAB. However, reducing the number of cases labelled as 'high-risk' and 'uncertain for metastatic infection' remains an area for improvement.

Developing an intervention package to optimise the management of vancomycin therapy using theory informed co-design

BACKGROUND

Optimising the management of vancomycin by achieving target therapeutic concentrations early during therapy has been associated with reduced mortality and morbidity. Despite the availability of guidelines and training, the management of vancomycin remains suboptimal.

OBJECTIVES

The primary outcome was the development of interventions and associated implementation strategies to optimise the management of vancomycin therapy. This paper describes how co-design process was used to build a theory informed intervention package, which was implemented across a wide range of in-patient hospital settings in Queensland, Australia.

METHODS

This multiple methods study was conducted in four phases: 1) a baseline audit to identify the nature of the problem and associated determinants informed by stakeholder interviews 2) mapping these findings to the Theoretical Domains Framework (TDF) to identify behavioural correlates and modifiers 3) prioritising the behavioural modifiers and associated implementation strategies to inform a protype of the intervention in a series of co-design sessions and 4) implementing and evaluating the intervention package. The study was conducted across the four teaching hospitals in a large Queensland Hospital and Health Service across multiple healthcare disciplines namely nurses, doctors, and pharmacists. This intervention package was subsequently implemented across Queensland Health with the support of the local champions under the guidance of the steering group.

RESULTS

Clinicians identified that a multifaceted intervention package and training which can be tailored to the health-care professional disciplines, would be best suited to shift clinician behaviour to align with guidelines. The findings from the co-design process aligned with theory-informed intervention package. Each of the intervention strategies varied in their frequency and popularity of use.

CONCLUSIONS

The use of theory-informed and participatory approach assisted with the intervention development process and aligned the intervention content with the priorities of stakeholders. The TDF provided a structured process for developing intervention content which is both acceptable and useful to stakeholders and may improve the management of vancomycin.

Sorbent functionalization with vancomycin enhances bacteria killing in extracorporeal hemoadsorption

BACKGROUND

The level of bacteremia in patients with sepsis and septic shock is a predictor of complications and mortality, regardless of the type of bacteria. Devices for bacteria, endotoxin and cytokines removal by adsorption have been recently developed. Thus, extracorporeal blood purification therapies have been proposed as adjunctive therapy in sepsis in combination with drugs. Some potentially useful drugs, however, are precluded due to their organ or metabolic toxicity. The present study represents a preliminary report on the in vitro effect of a sorbent device (minimodule with HA380 beads, Jafron medical, Zhuhai, China) in which the particles have been functionalized with vancomycin on the surface. The impact of the surface-modified beads on circulating bacteria (Staphylococcus aureus) has been tested in a simulated in vitro circulation.

METHODS

In vitro experiments were carried out with 800 mL of blood enriched with S. aureus species. Blood was circulated in the vancomycin-functionalized and non-functionalized mini-module cartridges in hemoadsorption setup (300 mL each) and the bactericidal effect was assessed. Also, 200 mL of blood was used as a control.

RESULTS

A significant increase in the time to positivity of blood cultures was observed after 60 min and also after 120 min of therapy with the mini-module functionalized with vancomycin as opposed to the non-functionalized cartridge.

CONCLUSIONS

These results suggest a possible way of treating sepsis by using drug- or antibiotic-functionalized cartridges without worrying about pharmacological toxicity. The prolongation of the time to bacterial culture positivity to S. aureus after a passage through a column packed with beads functionalized with vancomycin represents a proof of concept.

Impact of the implementation of the Intelligent Antimicrobial System (iAMS) on clinical outcomes among patients with bacteraemia caused by methicillin-resistant Staphylococcus aureus

OBJECTIVES

This study aimed to investigate the clinical impact of the Intelligent Antimicrobial System (iAMS) on patients with bacteraemia due to methicillin-resistant (MRSA) and methicillin-susceptible Staphylococcus aureus (MSSA).

METHODS

A total of 1008 patients with suspected SA infection were enrolled before and after the implementation of iAMS. Among them, 252 with bacteraemia caused by SA, including 118 in the iAMS and 134 in the non-iAMS groups, were evaluated.

RESULTS

The iAMS group exhibited a 5.2% (from 55.2% to 50.0%; P = 0.96) increase in the 1-year survival rate. For patients with MRSA and MSSA compared to the non-iAMS group, the 1-year survival rate increased by 17.6% (from 70.9% to 53.3%; P = 0.41) and 7.0% (from 52.3% to 45.3%; P = 0.57), respectively, both surpassing the rate of the non-iAMS group. The iAMS intervention resulted in a higher long-term survival rate (from 70.9% to 52.3%; P = 0.984) for MRSA patients than for MSSA patients. MRSA patients experienced a reduced length of hospital stay (from 23.3% to 35.6%; P = 0.038), and the 45-day discharge rate increased by 20.4% (P = 0.064). Furthermore, the intervention resulted in a significant 97.3% relative decrease in near miss medication incidents reported by pharmacists (P = 0.013).

CONCLUSIONS

Implementation of iAMS platform improved long-term survival rates, discharge rates, hospitalization days, and medical cost (although no significant differences were observed) among patients with MRSA bacteraemia. Additionally, it demonstrated significant benefits in ensuring drug safety.

Liposomal Rifabutin-A Promising Antibiotic Repurposing Strategy against Methicillin-Resistant Staphylococcus aureus Infections

Methicillin-resistant Staphylococcus aureus (M RSA) infections, in particular biofilm-organized bacteria, remain a clinical challenge and a serious health problem. Rifabutin (RFB), an antibiotic of the rifamycins class, has shown in previous work excellent anti-staphylococcal activity. Here, we proposed to load RFB in liposomes aiming to promote the accumulation of RFB at infected sites and consequently enhance the therapeutic potency. Two clinical isolates of MRSA, MRSA-C1 and MRSA-C2, were used to test the developed formulations, as well as the positive control, vancomycin (VCM). RFB in free and liposomal forms displayed high antibacterial activity, with similar potency between tested formulations. In MRSA-C1, minimal inhibitory concentrations (MIC) for Free RFB and liposomal RFB were 0.009 and 0.013 μg/mL, respectively. Minimum biofilm inhibitory concentrations able to inhibit 50% biofilm growth (MBIC50) for Free RFB and liposomal RFB against MRSA-C1 were 0.012 and 0.008 μg/mL, respectively. Confocal microscopy studies demonstrated the rapid internalization of unloaded and RFB-loaded liposomes in the bacterial biofilm matrix. In murine models of systemic MRSA-C1 infection, Balb/c mice were treated with RFB formulations and VCM at 20 and 40 mg/kg of body weight, respectively. The in vivo results demonstrated a significant reduction in bacterial burden and growth index in major organs of mice treated with RFB formulations, as compared to Control and VCM (positive control) groups. Furthermore, the VCM therapeutic dose was two fold higher than the one used for RFB formulations, reinforcing the therapeutic potency of the proposed strategy. In addition, RFB formulations were the only formulations associated with 100% survival. Globally, this study emphasizes the potential of RFB nanoformulations as an effective and safe approach against MRSA infections.

Phage-antibiotic synergy against daptomycin-nonsusceptible MRSA in an ex vivo simulated endocardial pharmacokinetic/pharmacodynamic model

Phage-antibiotic combinations (PAC) offer a potential solution for treating refractory daptomycin-nonsusceptible (DNS) methicillin-resistant Staphylococcus aureus (MRSA) infections. We examined PAC activity against two well-characterized DNS MRSA strains (C4 and C37) in vitro and ex vivo. PACs comprising daptomycin (DAP) ± ceftaroline (CPT) and a two-phage cocktail (Intesti13 + Sb-1) were evaluated for phage-antibiotic synergy (PAS) against high MRSA inoculum (109 CFU/mL) using (i) modified checkerboards (CB), (ii) 24-h time-kill assays (TKA), and (iii) 168-h ex vivo simulated endocardial vegetation (SEV) models. PAS was defined as a fractional inhibitory concentration ≤0.5 in CB minimum inhibitory concentration (MIC) or a ≥2 log10 CFU/mL reduction compared to the next best regimen in time-kill assays and SEV models. Significant differences between regimens were assessed by analysis of variance with Tukey's post hoc modification (α = 0.05). CB assays revealed PAS with Intesti13 + Sb-1 + DAP ± CPT. In 24-h time-kill assays against C4, Intesti13 + Sb-1 + DAP ± CPT demonstrated synergistic activity (-Δ7.21 and -Δ7.39 log10 CFU/mL, respectively) (P < 0.05 each). Against C37, Intesti13 + Sb-1 + CPT ± DAP was equally effective (-Δ7.14 log10 CFU/mL each) and not significantly different from DAP + Intesti13 + Sb-1 (-Δ6.65 log10 CFU/mL). In 168-h SEV models against C4 and C37, DAP ± CPT + the phage cocktail exerted synergistic activities, significantly reducing bio-burdens to the detection limit [2 log10 CFU/g (-Δ7.07 and -Δ7.11 log10 CFU/g, respectively)] (P < 0.001). At 168 h, both models maintained stable MICs, and no treatment-emergent phage resistance occurred with DAP or DAP + CPT regimens. The two-phage cocktail demonstrated synergistic activity against two DNS MRSA isolates in combination with DAP + CPT in vitro and ex vivo. Further in vivo PAC investigations are needed.

Sequential Time to Positivity as a Prognostic Indicator in Staphylococcus aureus Bacteremia

Background

We aimed to determine the factors associated with sequential blood culture time to positivity (STTP) and validate the previously defined time to positivity (TTP) ratio threshold of 1.5 in predicting adverse disease outcomes and mortality of Staphylococcus aureus bacteremia (SAB).

Methods

We conducted an observational study of adult patients with SAB. The TTP ratio was calculated by dividing the TTP of the second blood culture by that of the first.

Results

Of 186 patients, 69 (37%) were female, with a mean age of 63.6 years. Median TTP was 12 hours (interquartile range [IQR], 10-15 hours) from the initial and 21 hours (17-29) from sequential blood cultures. Methicillin-resistant S aureus (MRSA)-infected patients had significantly shorter STTPs (P < .001) and lower TTP ratios (P < .001) compared to patients with methicillin-susceptible S aureus (MSSA). A significant correlation between initial and STTP was observed in patients with MRSA (r = 0.42, P = .002) but not in those with MSSA. A higher rate of native valve endocarditis (NVE) significantly correlated with a TTP ratio of ≤1.5 (odds ratio, 2.65 [95% confidence interval, 1.3-5.6]; P = .01). The subgroup having an initial TTP <12 hours combined with a TTP ratio ≤1.5 showed the highest prevalence of NVE.

Conclusions

The STTP varies based on methicillin susceptibility of S aureus isolate. This study suggests a potential clinical utility of the STTP to identify patients at a higher risk of NVE. However, prospective studies are required to validate these findings.

A retrospective study on the effect of statins on mortality and antimicrobial resistance among patients with Staphylococcus aureus bloodstream infection

Introduction

There is insufficient evidence in statin on the treatment of Staphylococcus aureus (SA) infection, we observe and analyze the clinical outcomes and antibiotic resistance of SA bloodstream infections in patients who received statins.

Methods

A retrospective study was carried out in SA bloodstream infection of hospitalized patients from January 2018 to August 2023. The 30-day attributable mortality, 30-day all-cause mortality and clinical data of patients who received statins and non-statins were compared.

Results

A total of 74 patients with SA bloodstream infection were included, 32 (43.2%) patients received treatment with statins and 42 (56.8%) with non-statins. The incidence of methicillin-resistant SA (MRSA) was significantly lower in the statins group (15.6% vs. 38.1%, p = 0.034), however, no significant differences were observed in the mortality rate (p = 0.410).

Conclusions

This study revealed the superiority of statins in reducing incidence of MRSA among SA bloodstream infection patients, but statins do not improve the 30-day mortality rate.

Early Initiation of Ceftaroline-Based Combination Therapy for Methicillin-resistant Staphylococcus aureus Bacteremia

Purpose

Monotherapy with vancomycin or daptomycin remains guideline-based care for methicillin-resistant Staphylococcus aureus bacteremia (MRSA-B) despite concerns regarding efficacy. Limited data support potential benefit of combination therapy with ceftaroline as initial therapy. We present an assessment of outcomes of patients initiated on early combination therapy for MRSA-B.

Methods

This was a single-center, retrospective study of adult patients admitted with MRSA-B between July 1, 2017 and April 31, 2023. During this period, there was a change in institutional practice from routine administration of monotherapy to initial combination therapy for most patients with MRSA-B. Combination therapy included vancomycin or daptomycin plus ceftaroline within 72 hours of index blood culture and monotherapy was vancomycin or daptomycin alone. The primary outcome was a composite of persistent bacteremia, 30-day all-cause mortality, and 30-day bacteremia recurrence. Time to microbiological cure and safety outcomes were assessed. All outcomes were assessed using propensity score-weighted logistic regression.

Results

Of 213 patients included, 118 received monotherapy (115 vancomycin, 3 daptomycin) and 95 received combination therapy with ceftaroline (76 vancomycin, 19 daptomycin). The mean time from MRSA-positive molecular diagnostic blood culture result to combination therapy was 12.1 hours. There was no difference between groups for the primary composite outcome (OR 1.58, 95% CI 0.60, 4.18). Time to microbiological cure was longer with combination therapy (mean difference 1.50 days, 95% CI 0.60, 2.41). Adverse event rates were similar in both groups.

Conclusions

Early initiation of ceftaroline-based combination therapy did not improve outcomes for patients with MRSA-B in comparison to monotherapy therapy.

Relationship between blood culture time to positivity, mortality rate, and severity of bacteremia

OBJECTIVES

We investigated the association between patient severity or mortality and time to positivity in bacteremia caused by various pathogens.

PATIENTS AND METHODS

This single-center retrospective study included patients with positive blood culture results.

RESULTS

Longer time to positivity was associated with 30-day mortality for Staphylococcus aureus (221 cases, time to positivity: 17.4 h in the 30-day mortality group vs. 14.1 h in the survival group). Age, chronic kidney disease, cerebrovascular disease, hypertensive drug use, consciousness disorder, and minimal systolic blood pressure were significant predictors of 30-day mortality. For S. aureus, mortality within 30 days was significantly higher when time to positivity was > 24 h (p = 0.04). The time to positivity of Streptococcus pneumoniae, α, β-hemolytic Streptococcus, Enterococcus sp., Enterobacteriaceae, glucose-nonfermenting Gram-negative rods, Candida sp., and anaerobe was not significantly associated with 30-day mortality.

CONCLUSIONS

Among various pathogens, time to positivity > 24 h was associated with 30-day mortality for S. aureus.

The Changing Epidemiology and Antimicrobial Susceptibility of Staphylococcus aureus Isolated from Blood Cultures in a University Hospital from Argentina

Staphylococcus aureus bacteremia (SAB) is one of the most common serious bacterial infections worldwide. In this study, we demonstrated changes in SAB epidemiology in an Argentinean University Hospital during an 8-year period (2009-2016). A total of 326 S. aureus clinical isolates were recovered in three periods: P1: 2009-2010, P2: 2012-2014, and P3: 2015-2016. Among these, 127 were methicillin-resistant S. aureus (MRSA) and were characterized by phenotypic and molecular methods. We hereby report a significant decline in multiple drug resistance among MRSA isolates associated with an increase in SCCmec IV between the three periods. A diversity of MRSA-IV clones (mainly ST30-MRSA-IV, ST5-MRSA-IV, and ST8-MRSA-IV) replaced between 2009 and 2016 the previous prevalent MRSA clone causing bloodstream infections at this hospital (ST5-MRSA-I). MRSA population structure continued to diversify between P2 and P3. Notably, ST8-MRSA-IV-t008 related to USA300 was first detected during P2, and ST8-MRSA-IV together with ST30-MRSA-IV related to the Southwest Pacific clone were the more prevalent MRSA genotypes circulating during P3.

Cephalotin Versus Dicloxacillin for the Treatment of Methicillin-Susceptible Staphylococcus aureus Bacteraemia: A Retrospective Cohort Study

BACKGROUND

First-line treatments for methicillin-susceptible S. aureus (MSSA) bacteraemia are nafcillin, oxacillin, or cefazolin. Regional shortages of these antibiotics force clinicians to use other options like dicloxacillin and cephalotin. This study aims to describe and compare the safety and efficacy of cephalotin and dicloxacillin for the treatment of MSSA bacteraemia.

METHODS

This retrospective study was conducted in a referral centre in Mexico City. We identified MSSA isolates in blood cultures from 1 January 2012 to 31 December 2022. Patients ≥ 18 years of age, with a first episode of MSSA bacteraemia, who received cephalotin or dicloxacillin as the definitive antibiotic treatment, were included. The primary outcome was in-hospital all-cause mortality.

RESULTS

We included 202 patients, of which 48% (97/202) received cephalotin as the definitive therapy and 52% (105/202) received dicloxacillin. In-hospital all-cause mortality was 20.7% (42/202). There were no differences in all-cause in-hospital mortality between patients receiving cephalotin or dicloxacillin (20% vs. 21%, p = 0.43), nor in 30-day all-cause mortality (14% vs. 18%, p = 0.57) or 90-day all-cause mortality (24% vs. 22%, p = 0.82). No severe adverse reactions were associated with either antibiotic.

CONCLUSIONS

Cephalotin and dicloxacillin were equally effective for treating MSSA bacteraemia, and both showed an adequate safety profile.

Female Sex and Mortality in Patients with Staphylococcus aureus Bacteremia: A Systematic Review and Meta-analysis

Importance

Staphylococcus aureus is the leading cause of death due to bacterial bloodstream infection. Female sex has been identified as a risk factor for mortality in S aureus bacteremia (SAB) in some studies, but not in others.

Objective

To determine whether female sex is associated with increased mortality risk in SAB.

Data Sources

MEDLINE, Embase, and Web of Science were searched from inception to April 26, 2023.

Study Selection

Included studies met the following criteria: (1) randomized or observational studies evaluating adults with SAB, (2) included 200 or more patients, (3) reported mortality at or before 90 days following SAB, and (4) reported mortality stratified by sex. Studies on specific subpopulations (eg, dialysis, intensive care units, cancer patients) and studies that included patients with bacteremia by various microorganisms that did not report SAB-specific data were excluded.

Data Extraction and Synthesis

Data extraction and quality assessment were performed by 1 reviewer and verified by a second reviewer. Risk of bias and quality were assessed with the Newcastle-Ottawa Quality Assessment Scale. Mortality data were combined as odds ratios (ORs).

Main Outcome and Measures

Mortality at or before 90-day following SAB, stratified by sex.

Results

From 5339 studies retrieved, 89 were included (132 582 patients; 50 258 female [37.9%], 82 324 male [62.1%]). Unadjusted mortality data were available from 81 studies (109 828 patients) and showed increased mortality in female patients compared with male patients (pooled OR, 1.12; 95% CI, 1.06-1.18). Adjusted mortality data accounting for additional patient characteristics and treatment variables were available from 32 studies (95 469 patients) and revealed a similarly increased mortality risk in female relative to male patients (pooled adjusted OR, 1.18; 95% CI, 1.11-1.27). No evidence of publication bias was encountered.

Conclusions and Relevance

In this systematic review and meta-analysis, female patients with SAB had higher mortality risk than males in both unadjusted and adjusted analyses. Further research is needed to study the potential underlying mechanisms.

Significant Publications on Infectious Diseases Pharmacotherapy in 2021

Purpose: To summarize the most noteworthy infectious diseases (ID) pharmacotherapy articles published in peer-reviewed literature in 2021. Summary: Members of the Houston Infectious Diseases Network (HIDN) nominated articles that were deemed to have significant contributions to ID pharmacotherapy in 2021. These nominations included articles pertaining to both general ID, including coronavirus disease 2019 (COVID-19), and human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) pharmacotherapy. A total of 35 articles were nominated by HIDN: 30 articles pertaining to general ID pharmacotherapy and 5 articles with HIV/AIDS focus. To select the most influential articles of 2021, a survey was created and distributed to members of the Society of Infectious Diseases Pharmacists (SIDP). Of the 239 SIDP members who responded to the survey, there were 192 recorded votes for the top 10 general ID pharmacotherapy articles and 47 recorded votes for the top HIV/AIDS article, respectively. The top publications are summarized. Conclusion: Antimicrobial stewardship and the optimal management of infectious disease states continues to be a priority in the midst of the ongoing coronavirus disease 2019 (COVID-19) global pandemic. In light of the sheer volume of ID-related articles published in the past year, this review aims to aid clinicians in remaining up-to-date on key practice-changing ID pharmacotherapy publications from 2021.

Mortality patterns in patients with Staphylococcus aureus bacteremia during the COVID-19 pandemic: Predictors and insights

Objectives

This paper aims to determine the Staphylococcus aureus bacteremia (SAB) in-hospital mortality rate and its associated risk factors during the COVID-19 pandemic.

Methods

A total of 167 SAB samples were collected between March 2020 and March 2022 at a teaching hospital in Tehran, Iran. The patient's baseline data and antibiograms were collected. The outcome of the study was in-hospital mortality.

Results

The overall in-hospital mortality rate was 41.9 %, with higher mortality observed in patients over 60 years old (P = 0.032), those with community-acquired Staphylococcus aureus bacteremia (P = 0.010), and those admitted to the ICU (P = 0.016). Antibiotic resistance profiles indicated a higher mortality in resistant S.aureus strains but only significant for ciprofloxacin (P = 0.001), methicillin (P = 0.047), and sulfamethoxazole (P = 0.023). Multivariate analysis identified age, sex, ICU admission, and the source of bacteremia as independent predictors of mortality, while COVID-19 coinfection and resistance to antibiotics were not found to be significant predictors.

Conclusion

SAB remains a challenging infection that is amplified by the pandemic. Older age and ICU admission are significant mortality predictors. In settings with a high prevalence of MRSA, factors like age, sex, and quality of care outweigh pathogen-related factors such as antibiotic resistance.

Measuring beta-lactam minimum inhibitory concentrations in Staphylococcus aureus in the clinical microbiology laboratory: pinning the tail on the donkey

Significant shortcomings have been identified in standard methods of susceptibility testing in bacteriological media, not only because the media fails to recapitulate the in vivo environment, but susceptibility testing itself fails to capture sub-MIC effects that significantly attenuate bacterial virulence properties. Until susceptibility testing conditions better recapitulate the in vivo environment, attempts to establish the quantitative relevance of beta-lactam MIC using current clinical microbiology standards in Staphylococcus aureus infections will likely prove unsuccessful.

Evaluation of Antibacterial and Antibiofilm Activity of Rice Husk Extract against Staphylococcus aureus

Infections caused by Staphylococcus aureus are particularly difficult to treat due to the high rate of antibiotic resistance. S. aureus also forms biofilms that reduce the effects of antibiotics and disinfectants. Therefore, new therapeutic approaches are increasingly required. In this scenario, plant waste products represent a source of bioactive molecules. In this study, we evaluated the antimicrobial and antibiofilm activity of the rice husk extract (RHE) on S. aureus clinical isolates. In a biofilm inhibition assay, high concentrations of RHE counteracted the formation of biofilm by S. aureus isolates, both methicillin-resistant (MRSA) and -sensitive (MSSA). The observation of the MRSA biofilm by confocal laser scanning microscopy using live/dead cell viability staining confirmed that the bacterial viability in the RHE-treated biofilm was reduced. However, the extract showed no or little biofilm disaggregation ability. An additive effect was observed when treating S. aureus with a combination of RHE and oxacillin/cefoxitin. In Galleria mellonella larvae treated with RHE, the extract showed no toxicity even at high concentrations. Our results support that the rice husk has antimicrobial and antibiofilm properties and could potentially be used in the future in topical solutions or on medical devices to prevent biofilm formation.

Characterization of Prescribing Practices for Uncomplicated Streptococcal and Enterococcal Bacteremias: The NARRATE Study

Background

Bloodstream infections (BSIs) rank among the top causes of death in North America. Despite the prevalence of these infections, there remain significant practice variations in the prescribing of antibiotics.

Objective

To investigate current prescribing practices for management of uncomplicated streptococcal and enterococcal BSIs.

Methods

A retrospective cohort study was conducted using charts for patients admitted to an acute care centre in British Columbia between November 16, 2019, and October 20, 2020. Adult patients (≥ 18 years of age) with a diagnosis of uncomplicated streptococcal or enterococcal BSI were included. Patients were excluded if they had polymicrobial bacteremia or deep-seated infection or had been admitted for no more than 48 hours. The primary outcomes were duration of antibiotic therapy (IV and oral) and time to appropriate oral therapy for treatment of BSI. The secondary outcomes were observed rates of re-initiation of antibiotics and readmission with recurrent BSI. Descriptive statistics were calculated and regression analysis was performed for the primary and secondary outcomes.

Results

A total of 96 patients met the inclusion criteria. The median total duration of therapy for uncomplicated streptococcal and enterococcal BSI was about 2 weeks. Streptococcus pneumoniae BSIs were associated with a significantly shorter duration of IV therapy and were more likely to be associated with transition to oral antibiotics. No recurrent BSIs were observed in patients for whom therapy was transitioned to oral antibiotics.

Conclusions

Further study is warranted to explore shorter duration of antibiotic therapy and transition to oral therapy as treatment approaches for uncomplicated streptococcal and enterococcal BSI. Other outcomes of interest for future research include determining the optimal time for transition to oral therapy.

Evaluating indwelling devices and other risk factors for mortality in invasive Carbapenem-resistant Enterobacterales infections in Georgia, 2012-2019

Objective

Carbapenem-resistant Enterobacterales (CRE) infections are a public health threat due to the risk of transmission between patients and high associated mortality. We sought to identify risk factors for mortality in patients with invasive CRE infections and to specifically evaluate whether there was an association between indwelling medical devices and 90-day mortality.

Design

Retrospective observational cohort study of patients infected with CRE in the eight-county metropolitan Atlanta area between 2012 and 2019.

Methods

Patients with invasive CRE infections were identified via the Georgia Emerging Infections Program's active, population- and laboratory-based surveillance system and linked with the Georgia Vital Statistics database. We used bivariate analysis to identify risk factors for mortality and completed log binomial multivariable regression to estimate risk ratios (RR) for the association between indwelling devices and mortality.

Results

In total, 154 invasive CRE infections were identified, with indwelling devices present in most patients (87.7%) around the time of infection. Admission to an intensive care unit was found to be associated with 90-day mortality (adjusted RR [aRR] 1.55, 95% CI 1.07, 2.24); however, the presence of any indwelling device was not associated with increased risk of 90-day mortality in multivariable analysis (aRR 1.22, 95% CI 0.55, 2.73). Having at least two indwelling devices was associated with increased mortality (aRR 1.79, 95% CI 1.05, 3.05).

Conclusions

Indwelling devices were prevalent in our cohort but were not consistently associated with an increased risk of mortality. Further studies are needed to examine this relationship and the role of device removal.

Preventing healthcare-associated MRSA bacteremia: getting to the root of the problem

Introduction

Bloodstream infections caused by methicillin-resistant Staphylococcus aureus (MRSA) remain a major challenge in most countries worldwide.

Setting

We describe a quasi-experimental sequential intervention at Mater Dei Hospital, Malta, to reduce hyper-prevalence of healthcare-associated MRSA bacteremia (HA-MRSA-B).

Interventions

The hospital initiated a hand hygiene (HH) campaign in 2008 to improve alcohol hand rub (AHR) use. In 2011, this was followed by root cause analysis (RCA) of all HA-MRSA-B cases and finally universal MRSA admission screening in 2014. Change-point analysis was used to evaluate the impact of the interventions.

Results

The effect of the HH campaign became evident when AHR consumption reached 40 L/1000 occupied bed days (BD). RCAs identified intravascular devices as the likely risk factor in 83% of all HA-MRSA-B; specifically non-tunneled double-lumen hemodialysis catheters (36%), peripheral venous cannulas (25%), and central venous catheters (22%). Interventions to improve their management resulted in the greatest reduction of HA-MRSA-B rates. They were informed by the RCA findings and targeted behavior change through education, motivation, and system change. Universal MRSA admission screening provided the final decline in incidence. Each intervention affected HA-MRSA-B rates after a lag period of approximately 18-24 months. Overall, HA-MRSA-B incidence decreased from 1.72 cases/10000BD in 2008 to 0.18/10000BD in 2019; a reduction of almost 90%. Intravenous device interventions were also associated with a reduction of methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia rates.

Conclusions

Significant improvement in HA-MRSA-B is possible, even in highly endemic regions. It requires well-planned behavior change interventions which are compatible with local context and culture.

Healing wounds, defeating biofilms: Lactiplantibacillus plantarum in tackling MRSA infections

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) infections are well-known hospital-borne infections and are a major contributing factor to global health concerns of antimicrobial resistance due to the formation of biofilms. Probiotics are known to assist in the healing of wounds through immunomodulation and also possess anti-pathogen properties via competitive inhibition. The probiotic bacterium, Lactiplantibacillus plantarum MTCC 2621 and its cell-free supernatant (Lp2621) have previously been reported to have antibacterial, excellent antioxidant, and wound healing activity in in vitro conditions and wounds contaminated with S. aureus in mice.

Methods

In the current study, we evaluated its anti-MRSA, biofilm inhibition and eradication efficacy, immunomodulatory activity in THP-1 cells, and wound healing potential in wounds contaminated with MRSA infection in mice.

Results

In agar well diffusion assay, Lp2621 showed anti-MRSA activity and revealed dose-dependent inhibition and eradication of biofilm by crystal violet assay as well as by Confocal Scanning Laser Microscopy (CLSM) analysis. Further, Lp2621 showed immunomodulatory activity at varied concentrations as measured by IL-6 and IL-10 gene expression in THP-1 cells. Similar findings were observed in serum samples of mice after treatment of excision wound contaminated with MRSA infection by Lp2621 gel, as evident by expression of IL-6 (pro-inflammatory) and IL-10 (anti-inflammatory) cytokines.

Conclusions

Overall, our results show that Lp2621 has potent anti-MRSA and antioxidant properties and can prevent and eliminate biofilm formation. It also showed promise when applied to mice with MRSA-infected wounds.

Estimating the Burden of Clinically Significant Staphylococcus aureus Infections and Predictors for Hospitalization for Skin and Soft Tissue Infections, Fulton County, Georgia, 2017

Background

Incidence estimates of Staphylococcus aureus infections rarely include the full spectrum of clinically relevant disease from both community and healthcare settings.

Methods

We conducted a prospective study capturing all S aureus infections in Fulton County, Georgia, during 2017. Medical records of patients with any incident infection (clinical cultures growing S aureus from any site, without prior positive culture in previous 14 days) were reviewed. Estimates of disease incidence were calculated using age-, race-, and sex-specific population denominators accounting for weighted sampling methods. Multivariable logistic regression models were used to identify risk factors for hospitalization among patients with skin and soft tissue infections (SSTIs).

Results

The overall incidence of clinically relevant S aureus infection was 405.7 cases per 100 000 people (standard error [SE], 5.62 [range, 400.1-411.3]). Overall incidence for those of Black race was 500.84 cases per 100 000 people (SE, 14.55), whereas White patients had overall incidence of 363.67 cases per 100 000 people (SE, 13.8). SSTIs were the most common infection (2351; 225.8 cases per 100 000 people [SE, 7.1]), and 30% required hospitalization. Among SSTIs, after adjusting for invasive disease, cellulitis, diabetes, and demographics, independent predictors of hospitalization included methicillin-resistant S aureus (adjusted odds ratio [aOR], 1.6 [95% confidence interval {CI}, 1.0-2.7]) and homelessness (aOR, 4.9 [95% CI, 1.1-22]).

Conclusions

The burden of clinically relevant S aureus infections is high, particularly among the Black population, and risks for hospitalization among SSTIs include isolate factors and factors related to patients' vulnerability.

Rapamycin Exacerbates Staphylococcus aureus Pneumonia by Inhibiting mTOR-RPS6 in Macrophages

Purpose

This study aimed to explore the effect of Rapamycin (Rapa) in Staphylococcus aureus (S. aureus) pneumonia and clarify its possible mechanism.

Methods

We investigated the effects of Rapa on S. aureus pneumonia in mouse models and in macrophages cultured in vitro. Two possible mechanisms were investigated: the mTOR-RPS6 pathway phosphorylation and phagocytosis. Furthermore, for the mechanism verification in vivo, mice with specific Mtor knockout in myeloid cells were constructed for pneumonia models.

Results

Rapa exacerbated S. aureus pneumonia in mouse models, promoting chemokines secretion and inflammatory cells infiltration in lung. In vitro, Rapa upregulated the secretion of chemokines and cytokines in macrophages induced by S. aureus. Mechanistically, the mTOR-ribosomal protein S6 (RPS6) pathway in macrophages was phosphorylated in response to S. aureus infection, and the inhibition of RPS6 phosphorylation upregulated the inflammation level. However, Rapa did not increase the phagocytic activity. Accordingly, mice with specific Mtor knockout in myeloid cells experienced more severe S. aureus pneumonia.

Conclusion

Rapa exacerbates S. aureus pneumonia by increasing the inflammatory levels of macrophages. Inhibition of mTOR-RPS6 pathway upregulates the expression of cytokines and chemokines in macrophages, thus increases inflammatory cells infiltration and exacerbates tissue damage.

Staphylococcus aureus epidemiology, pathophysiology, clinical manifestations and application of nano-therapeutics as a promising approach to combat methicillin resistant Staphylococcus aureus

Staphylococcus aureus is a Gram-positive bacterium and one of the most prevalent infectious disease-related causes of morbidity and mortality in adults. This pathogen can trigger a broad spectrum of diseases, from sepsis and pneumonia to severe skin infections that can be fatal. In this review, we will provide an overview of S. aureus and discuss the extensive literature on epidemiology, transmission, genetic diversity, evolution and antibiotic resistance strains, particularly methicillin resistant S. aureus (MRSA). While many different virulence factors that S. aureus produces have been investigated as therapeutic targets, this review examines recent nanotechnology approaches, which employ materials with atomic or molecular dimensions and are being used to diagnose, treat, or eliminate the activity of S. aureus. Finally, having a deeper understanding and clearer grasp of the roles and contributions of S. aureus determinants, antibiotic resistance, and nanotechnology will aid us in developing anti-virulence strategies to combat the growing scarcity of effective antibiotics against S. aureus.

Evaluating the use of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography in the workup of Staphylococcus aureus bacteraemia: a cost-utility analysis

OBJECTIVES

The use of positron emission tomography/computed tomography (PET/CT) in the evaluation of patients with Staphylococcus aureus bacteraemia can improve the diagnosis of infectious foci and guide clinical management. We aimed to evaluate the cost-utility of PET/CT among adults hospitalized with Staphylococcus aureus bacteraemia.

METHODS

A cost-utility analysis was conducted from the healthcare payer perspective using a probabilistic Markov cohort model assessing three diagnostic strategies: (a) PET/CT in all patients, (b) PET/CT in high-risk patients only, and (c) routine diagnostic workup. Primary outcomes were quality-adjusted life years (QALYs), costs in Canadian dollars, and an incremental cost-effectiveness ratio. Deterministic and probabilistic sensitivity analyses were conducted to evaluate parameter uncertainty.

RESULTS

Routine workup resulted in an average of 16.64 QALYs from the time of diagnosis at a lifetime cost of $209 060/patient. This was dominated by PET/CT in high-risk patients (i.e. greater effectiveness at lower costs) with average 16.88 QALYs at a cost of $199 552. Compared with PET/CT in high-risk patients only, PET/CT for all patients cost on average $11 960 more but resulted in 0.14 more QALYs, giving an incremental cost-effectiveness ratio of $83 500 (cost per additional QALY gained); however, there was a high degree of uncertainty comparing these two strategies. At a willingness-to-pay threshold of $50 000/QALY, PET/CT in high-risk patients was the most cost-effective strategy in 58.6% of simulations vs. 37.9% for PET/CT in all patients.

DISCUSSION

Our findings suggest that a strategy of using PET/CT in high-risk patients is more cost-effective than no PET/CT. Randomized controlled trials should be conducted to evaluate the use of PET/CT in different patient groups.

Fast detection of Staphylococcus aureus using thiol-functionalized WS2 quantum dots and Bi2O2Se nanosheets hybrid through a fluorescence recovery mechanism

Ultrafast and sensitive detection of Staphylococcus aureus (S. aureus), a harmful Gram-positive human pathogenic bacterium, by two-dimensional layered materials continues to be a challenge. Herein, we have studied the sensing of S. aureus using a tungsten disulfide (WS2) quantum dot (QD) and bismuth oxyselenide (Bi2O2Se) nanosheet (NS) hybrid through their unique optical functionalities. The WS2 QDs of a mean diameter of 2.5 nm were synthesized by liquid exfoliation. Due to the quantum confinement and functional groups, the WS2 QDs exhibit high fluorescence (FL) yield under UV excitation. The addition of Bi2O2Se NSs resulted in the adsorption of WS2 QDs on their surface, resulting in quenching of the FL emission due to nonfluorescent complex formation between the WS2 QDs and Bi2O2Se NSs. A specific sequencing single-standard DNA (ssDNA) aptamer, which identifies and explicitly binds with S. aureus, was attached to the defect sites of the WS2 QDs for selective detection. The thiol-modified ssDNA aptamers attach covalently to the WS2 QD defect sites, which was confirmed by Raman and X-ray photoelectron spectroscopy (XPS). The interaction of S. aureus with the aptamer functionalized WS2 QDs weakens the van der Waals interaction between the WS2 QDs and Bi2O2Se NSs, which results in the detachment of the WS2 QDs from the Bi2O2Se NS surface and restores the FL intensity of the WS2 QDs, thus allowing the efficient detection of S. aureus. Similar measurements with non-targeted bacteria show that the system is quite selective towards S. aureus. Our FL-based biosensor has a linear response in the range of 103-107 CFU mL-1 (colony formation unit mL-1) with a detection limit of 580 CFU mL-1. We have observed a fast response time of 15 minutes for sensing, which is superior to the previous reports. The proposed system was tested in human urine and can detect S. aureus in human urine samples selectively, proving its potential in real-life applications. The reported approach is versatile enough for sensing other biomolecules and metal ions by choosing suitable receptors.

Priorities and Progress in Gram-positive Bacterial Infection Research by the Antibacterial Resistance Leadership Group: A Narrative Review

The Antibacterial Resistance Leadership Group (ARLG) has prioritized infections caused by gram-positive bacteria as one of its core areas of emphasis. The ARLG Gram-positive Committee has focused on studies responding to 3 main identified research priorities: (1) investigation of strategies or therapies for infections predominantly caused by gram-positive bacteria, (2) evaluation of the efficacy of novel agents for infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci, and (3) optimization of dosing and duration of antimicrobial agents for gram-positive infections. Herein, we summarize ARLG accomplishments in gram-positive bacterial infection research, including studies aiming to (1) inform optimal vancomycin dosing, (2) determine the role of dalbavancin in MRSA bloodstream infection, (3) characterize enterococcal bloodstream infections, (4) demonstrate the benefits of short-course therapy for pediatric community-acquired pneumonia, (5) develop quality of life measures for use in clinical trials, and (6) advance understanding of the microbiome. Future studies will incorporate innovative methodologies with a focus on interventional clinical trials that have the potential to change clinical practice for difficult-to-treat infections, such as MRSA bloodstream infections.

Nuclease activity and protein A release of Staphylococcus aureus clinical isolates determine the virulence in a murine model of acute lung infection

Staphylococcus aureus is a common cause of hospital-acquired pneumonia associated with high mortality. Adequate clinical treatment is impeded by increasing occurrence of antibiotic resistances. Understanding the underlying mechanisms of its virulence during infections is a prerequisite to finding alternative treatments. Here, we demonstrated that an increased nuclease activity of a S. aureus isolate from a person with cystic fibrosis confers a growth advantage in a model of acute lung infection compared to the isogenic strain with low nuclease activity. Comparing these CF-isolates with a common MRSA-USA300 strain with similarly high nuclease activity but significantly elevated levels of Staphylococcal Protein A (SpA) revealed that infection with USA300 resulted in a significantly increased bacterial burden in a model of murine lung infection. Replenishment with the cell wall-bound SpA of S. aureus, which can also be secreted into the environment and binds to tumor necrosis factor receptor -1 (TNFR-1) to the CF-isolates abrogated these differences. In vitro experiments confirmed significant differences in spa-expression between USA300 compared to CF-isolates, thereby influencing TNFR-1 shedding, L-selectin shedding, and production of reactive oxygen species through activation of ADAM17.

Predictive models for sepsis in children with Staphylococcus aureus bloodstream infections: a retrospective cohort study

BACKGROUND

The presence of Staphylococcus aureus in the bloodstream can lead to the development of sepsis; however, the severity and risk factors of the systemic inflammatory response to Staphylococcus aureus bloodstream infections were unclear. This study is aimed to build a model to predict the risk of sepsis in children with Staphylococcus aureus bloodstream infections.

METHODS

A retrospective analysis of hospitalized pediatric patients diagnosed with Staphylococcus aureus bloodstream infections was performed between January 2013 and December 2019. Each patient was assessed using the pediatric version of the Sequential Organ Failure Assessment score (pSOFA) within 24 h of blood culture collection. A nomogram based on logistic regression models was constructed to predict the risk factors for sepsis in children with Staphylococcus aureus bloodstream infections. It was validated using the area under the receiver-operating characteristic curve (AUC).

RESULTS

Of the 94 patients included in the study, 35 cases (37.2%) developed sepsis. The pSOFA scores ranged from 0 to 8, with 35 patients having a pSOFA score of ≥ 2. Six children (6.4%) died within 30 days, who were all from the sepsis group and had different pSOFA scores. The most common organs involved in sepsis in children with staphylococcal bloodstream infections were the neurologic system (68.6%), respiratory system (48.6%), and coagulation system (45.7%). Hospital-acquired infections (adjusted odds ratio [aOR], 3.0; 95% confidence interval [CI], 1.3-7.2), implanted catheters (aOR, 10.4; 95% CI, 3.8-28.4), procalcitonin level ≥ 1.7 ng/mL (aOR, 15.4; 95% CI, 2.7-87.1), and underlying diseases, especially gastrointestinal malformations (aOR, 14.0; 95% CI, 2.9-66.7) were associated with Staphylococcus aureus sepsis. However, methicillin-resistant Staphylococcus aureus infection was not a risk factor for sepsis. The nomogram had high predictive accuracy for the estimation of sepsis risk, with an AUC of 0.85.

CONCLUSIONS

We developed a predictive model for sepsis in children with Staphylococcus aureus infection.

Clinical outcomes and epidemiological characteristics of bacteremia in the older Japanese population

BACKGROUND

The characteristics and clinical consequences of bacteremia in older people, who are highly susceptible to infections, need to be clarified. This study aimed to determine the epidemiological characteristics, prognosis, and predictors of 7-day mortality in patients with community-acquired (CA), healthcare-associated (HCA), and hospital-onset (HO) bacteremia in older adults aged ≥65 years.

METHODS

Patients aged ≥65 years with positive blood cultures between April 1, 2015, and March 31, 2018, were divided into three groups: pre-old (65-74 years), old (75-89 years), and super-old (≥90 years). Characteristics based on medical exposure, including CA, HCA, and HO, were also compared and factors related to mortality were identified.

RESULTS

Overall, 1716 episodes of bacteremia were identified in 1415 patients. Of the 1211 episodes without contamination, 32.8%, 54.3%, and 12.9% occurred in pre-old, old, and super-old patients. Central line-associated bloodstream infections were more common in pre-old patients and urinary tract infections in the old and super-old. The 7-day mortality rates in the pre-old, old, and super-old groups were 7.4%, 5.8%, and 14.2% (P = 0.002), respectively. Multivariable logistic regression showed that super-old age (adjusted odds ratio, aOR: 2.09 [1.13-3.88], P = 0.019) and HO bacteremia (aOR: 1.97 [1.18-3.28], P = 0.010) were independent risk factors for 7-day mortality. Infectious disease consultation had a protective effect on 7-day mortality (aOR: 0.59 [0.35-0.99], P = 0.047).

CONCLUSIONS

The epidemiology of bacteremia differs among older people; thus, they should not be treated as a single entity. A careful approach is needed for the optimal management of bacteremia in these vulnerable patients.

Factors for mortality in patients with persistent Staphylococcus aureus bacteremia: The importance of treatment response rather than bacteremia duration

BACKGROUND

The criteria for antibiotic failure in persistent Staphylococcus aureus bacteremia (SAB) are unclear, but treatment response and bacteremia duration are commonly used indicators of antibiotic failure. We evaluated the effects of treatment response and bacteremia duration on mortality in persistent SAB.

METHODS

We retrospectively identified patients with persistent SAB in four university-affiliated hospitals between 2017 and 2021. Bacteremia duration was calculated from the first day of active antibiotic therapy, and persistent SAB was defined as bacteremia lasting for 2 or more days. Defervescence and Pitt bacteremia score (PBS) were used to evaluate treatment response at treatment day 4. The primary outcome was 30-day in-hospital mortality. Time-dependent multivariable Cox regression analysis and subgroup analysis according to methicillin resistance were performed.

RESULTS

A total of 221 patients was included in the study, and the 30-day in-hospital mortality was 28.5%. There was no significant difference in bacteremia duration between survived and deceased patients. Independent factors for mortality included age, Charlson comorbidity index, initial PBS, pneumonia, and removal of the eradicable focus. PBS at treatment day 4 ≥ 3 was the strongest risk factor (adjusted hazard ratio [HR] = 4.260), but defervescence was not. Bacteremia duration was not an independent factor except for 13 days or more of methicillin-resistant SAB (adjusted HR = 1.064).

CONCLUSIONS

In patients with persistent SAB, PBS at treatment day 4 was associated with 30-day in-hospital mortality rather than defervescence and bacteremia duration. The results of this study could help determine early intensified treatment strategies in persistent SAB patients.

Efficacy and safety of vancomycin for the treatment of Staphylococcus aureus bacteraemia: a systematic review and meta-analysis

OBJECTIVES

To evaluate the safety and efficacy of vancomycin with the other anti-Gram-positive bacteria antibiotics in the treatment of Staphylococcus aureus bacteraemia.

METHODS

We searched the PubMed, MEDLINE, Embase and Cochrane Library databases until August 2022 for studies that compared vancomycin with other antibiotic regimens for treating Staphylococcus aureus bacteraemia. Clinical and microbiological responses, adverse events, relapse rate and mortality were considered.

RESULTS

Fifteen randomized controlled trials and nine retrospective studies were included. The efficacy and safety data of vancomycin differed from those of the comparators group. After subgroup analysis, the differences came mainly from the trials compared with daptomycin. Compared to daptomycin, vancomycin showed a lower microbiological cure rate (OR = 0.58, 95% CI = 0.41∼0.82, I2 = 0%, P = 0.002) and clinical cure rate (OR = 0.53, 95% CI = 0.42∼0.68, I2 = 3%, P < 0.00001), as well as more adverse events (OR = 3.21, 95% CI = 1.43∼7.19, I2 = 59%, P = 0.005).

CONCLUSION

The efficacy of vancomycin in treating Staphylococcus aureus bacteraemia is still excellent but slightly inferior in adverse events. However, this does not affect its use as a first-line drug. Daptomycin is expected to be a better antimicrobial drug.

A statistical genomics framework to trace bacterial genomic predictors of clinical outcomes in Staphylococcus aureus bacteremia

Outcomes of severe bacterial infections are determined by the interplay between host, pathogen, and treatments. While human genomics has provided insights into host factors impacting Staphylococcus aureus infections, comparatively little is known about S. aureus genotypes and disease severity. Building on the hypothesis that bacterial pathoadaptation is a key outcome driver, we developed a genome-wide association study (GWAS) framework to identify adaptive mutations associated with treatment failure and mortality in S. aureus bacteremia (1,358 episodes). Our research highlights the potential of vancomycin-selected mutations and vancomycin minimum inhibitory concentration (MIC) as key explanatory variables to predict infection severity. The contribution of bacterial variation was much lower for clinical outcomes (heritability <5%); however, GWASs allowed us to identify additional, MIC-independent candidate pathogenesis loci. Using supervised machine learning, we were able to quantify the predictive potential of these adaptive signatures. Our statistical genomics framework provides a powerful means to capture adaptive mutations impacting severe bacterial infections.

Monoclonal antibodies neutralizing alpha-hemolysin, bicomponent leukocidins, and clumping factor A protected against Staphylococcus aureus-induced acute circulatory failure in a mechanically ventilated rabbit model of hyperdynamic septic shock

Background

Patients with septic shock caused by Staphylococcus aureus have mortality rates exceeding 50%, despite appropriate antibiotic therapy. Our objectives were to establish a rabbit model of S. aureus septic shock and to determine whether a novel immunotherapy can prevent or halt its natural disease progression.

Methods

Anesthetized rabbits were ventilated with lung-protective low-tidal volume, instrumented for advanced hemodynamic monitoring, and characterized for longitudinal changes in acute myocardial dysfunction by echocardiography and sepsis-associated biomarkers after S. aureus intravenous challenge. To demonstrate the potential utility of this hyperdynamic septic shock model for preclinical drug development, rabbits were randomized for prophylaxis with anti-Hla/Luk/ClfA monoclonal antibody combination that neutralizes alpha-hemolysin (Hla), the bicomponent pore-forming leukocidins (Luk) including Panton-Valentine leukocidin, leukocidin ED, and gamma-hemolysin, and clumping factor A (ClfA), or an irrelevant isotype-matched control IgG (c-IgG), and then challenged with S. aureus.

Results

Rabbits challenged with S. aureus, but not those with saline, developed a hyperdynamic state of septic shock characterized by elevated cardiac output (CO), increased stroke volume (SV) and reduced systemic vascular resistance (SVR), which was followed by a lethal hypodynamic state characterized by rapid decline in mean arterial pressure (MAP), increased central venous pressure, reduced CO, reduced SV, elevated SVR, and reduced left-ventricular ejection fraction, thereby reproducing the hallmark clinical features of human staphylococcal septic shock. In this model, rabbits pretreated with anti-Hla/Luk/ClfA mAb combination had 69% reduction in mortality when compared to those pretreated with c-IgG (P<0.001). USA300-induced acute circulatory failure-defined as >70% decreased in MAP from pre-infection baseline-occurred in only 20% (2/10) of rabbits pretreated with anti-Hla/Luk/ClfA mAb combination compared to 100% (9/9) of those pretreated with c-IgG. Prophylaxis with anti-Hla/Luk/ClfA mAb combination halted progression to lethal hypodynamic shock, as evidenced by significant protection against the development of hyperlactatemia, hypocapnia, hyperkalemia, leukopenia, neutropenia, monocytopenia, lymphopenia, as well as biomarkers associated with acute myocardial injury.

Conclusion

These results demonstrate the potential utility of a mechanically ventilated rabbit model that reproduced hallmark clinical features of hyperdynamic septic shock and the translational potential of immunotherapy targeting S. aureus virulence factors for the prevention of staphylococcal septic shock.

The association of female sex with management and mortality in patients with Staphylococcus aureus bacteraemia

OBJECTIVES

The association of biological female sex with outcome in patients with Staphylococcus aureus bacteraemia remains unresolved. The aim of this study was to determine the independent association of female sex with management and mortality in patients with S. aureus bacteraemia.

METHODS

This is a post hoc analysis of prospectively collected data from the S. aureus Bacteraemia Group Prospective Cohort Study. Adult patients with monomicrobial S. aureus bacteraemia at Duke University Medical Center were enrolled from 1994 to 2020. Univariable and multivariable Cox regression analyses were performed to assess differences in management and mortality between females and males.

RESULTS

Among 3384 patients with S. aureus bacteraemia, 1431 (42%) were women. Women were, as compared with men, more often Black (581/1431 [41%] vs. 620/1953 [32%], p < 0.001), haemodialysis dependent (309/1424 [22%] vs. 334/1940 [17%], p 0.001) and more likely to be infected with methicillin-resistant S. aureus (MRSA) (697/1410 [49%] MRSA in women vs. 840/1925 [44%] MRSA in men, p 0.001). Women received shorter durations of antimicrobial treatment (median 24 [interquartile range 14-42] vs. 28 [interquartile range 14-45] days, p 0.005), and were less likely to undergo transesophageal echocardiography as compared with men (495/1430 [35%] vs. 802/1952 [41%], p < 0.001). Despite these differences, female sex was not associated with 90-day mortality in either univariable (388/1431 [27%] in women vs. 491/1953 [25%] in men, p 0.204) or multivariable analysis (adjusted hazard ratio for women 0.98 [95% CI, 0.85-1.13]).

DISCUSSION

Despite significant differences in patient characteristics, disease characteristics, and management, women and men with S. aureus bacteraemia have a similar mortality risk.

Going Beyond Host Defence Peptides: Horizons of Chemically Engineered Peptides for Multidrug-Resistant Bacteria

Multidrug-resistant (MDR) bacteria are considered a health threat worldwide, and this problem is set to increase over the decades. The ESKAPE, a group of six pathogens including Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp. is the major source of concern due to their high death incidence and nosocomial acquired infection. Host defence peptides (HDPs) are a class of ribosomally synthesised peptides that have shown promising results in combating MDR, including the ESKAPE group, in- and outside bacterial biofilms. However, their poor pharmacokinetics in physiological mediums may impede HDPs from becoming viable clinical candidates. To circumvent this problem, chemical engineering of HDPs has been seen as an emergent approach to not only improve their pharmacokinetics but also their efficacy against pathogens. In this review, we explore several chemical modifications of HDPs that have shown promising results, especially against ESKAPE pathogens, and provide an overview of the current findings with respect to each modification.

The emergence of multidrug-resistant Gram-positive bloodstream infections in India - a single center prospective cohort study

Introduction

Gram-positive bloodstream infections (BSIs) are an emerging health concern, especially in resource-limited settings. There is a paucity of data regarding the antimicrobial resistance (AMR) pattern of Gram-positive BSIs. The rise in multidrug-resistant infections further convoluted antibiotic selection. We aimed to assess the incidence, clinical and microbiological profile, antimicrobial resistance (AMR) and outcome in Gram-positive BSIs.

Methods

This was a single-center prospective study conducted at a tertiary care hospital in Western India. All patients (age ≥18 years) with culture-proven Gram-positive BSIs were included. Data were collected on all patients' demography, risk factors, AMR and clinical outcome.

Results

A total of 210 clinically significant isolates were grown from July 2020 to December 2021. The incidence of Gram-positive BSIs was 29% (n=61); 55.9% of cases were healthcare-associated, while 44.1% were community-acquired. Coagulase-negative staphylococci (CoNS) were the major isolates (36.1%), followed by Enterococcus spp. (27.9%), methicillin-susceptible Staphylococcus aureus (MSSA) (18%) and methicillin-resistant Staphylococcus aureus (MRSA) (14.7%). The proportion of vancomycin and teicoplanin-resistant CoNS isolates was 13.6% and 19%. Among Enterococcus isolates, the proportion of vancomycin-resistant enterococci (VRE) and linezolid-resistant enterococci (LRE) were 11.8% and 5.9%. The overall mortality in Gram-positive BSIs was 42.6%. Older age, MRSA infection, septic shock, and high NLR were significantly associated with mortality. On the Cox regression model, age ≥65 years (HR: 2.5; 95%CI: 1.1-5.8; p=0.024) and MRSA infection (HR: 3.6; 95%CI: 1.5-8.5; p=0.021) were found as independent predictors of 30-day mortality.

Conclusions

This study found substantial mortality with Gram-positive BSIs, especially MRSA infections. Moreover, the emergence of VRE and LRE is also alarming. Active surveillance of AMR and evaluation of mortality predictors may help overcome the therapeutic challenges in managing BSIs.

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.

Epinephrine Affects Ribosomes, Cell Division, and Catabolic Processes in Micrococcus luteus Skin Strain C01: Revelation of the Conditionally Extensive Hormone Effect Using Orbitrap Mass Spectrometry and Proteomic Analysis

In the current study, extensive Orbitrap mass spectrometry analysis was conducted for skin strain Micrococcus luteus C01 planktonic cultures and biofilms after 24 h and 72 h of incubation either in the presence of epinephrine or without any implementations. The investigation revealed the complex and conditionally extensive effect of epinephrine at concentrations closer to normal blood plasma concentrations on both planktonic cultures and biofilms of skin strain M. luteus C01. The concentrations of hundreds of proteins changed during the shift from planktonic growth mode to biofilm and hundreds of proteins were downregulated or upregulated in the presence of epinephrine. Ribosomal, TCA, and cell division proteins appear to be the most altered in their amounts in the presence of the hormone. Potentially, the regulatory mechanism of this process is connected with c-di-GMP and histidine kinases, which were affected by epinephrine in different samples. The phenomenon of epinephrine-based biofilm regulation in M. luteus C01 has wide implications for microbial endocrinology and other research areas.

The Impact of Aging and Toll-like Receptor 2 Deficiency on the Clinical Outcomes of Staphylococcus aureus Bacteremia

Staphylococcus aureus (S. aureus) causes a broad range of infections. Toll-like receptor (TLR) 2 senses the S. aureus lipoproteins in S. aureus infections. Aging raises the risk of infection. Our aim was to understand how aging and TLR2 affect the clinical outcomes of S. aureus bacteremia. Four groups of mice (wild type/young, wild type/old, TLR2-/-/young, and TLR2-/-/old) were intravenously infected with S. aureus, and the infection course was followed. Both TLR2 deficiency and aging enhanced the susceptibility to disease. Increased age was the main contributing factor for increased mortality rates and changes in spleen weight, whereas other clinical parameters, such as weight loss and kidney abscess formation, were more TLR2 dependent. Importantly, aging increased mortality rates without relying on TLR2. In vitro, both aging and TLR2 deficiency down-regulated cytokine/chemokine production of immune cells with distinct patterns. In summary, we demonstrate that aging and TLR2 deficiency impair the immune response to S. aureus bacteremia in distinct ways.

In vitro efficacy of different PEGylation designs on cathelicidin-like peptide with high antibacterial and antifungal activity

Recent reports on antibiotic resistance have highlighted the need to reduce the impact of this global health issue through urgent prevention and control. The World Health Organization currently considers antibiotic resistance as one of the most dangerous threats to global health. Therefore, Antimicrobial peptides (AMPs) are promising for the development of novel antibiotic molecules due to their high antimicrobial effects, non-inducing antimicrobial resistance (AMR) properties, and broad spectrum. Hence, in this study, we developed novel antimicrobial peptide/polymer conjugates to reduce the adverse effects of TN6 (RLLRLLLRLLR) peptide. We demonstrate how our constructs function in vitro in terms of antimicrobial activity, hemolytic activity, cytotoxicity, and protease resistance. Our findings show that our molecules are effective against different types of microorganisms such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, methicillin-resistant S. aureus, vancomycin-resistant Enteroccus faecium, and Candida albicans, which are known to be pathogenic and antibiotic-resistant. Our constructs generally showed low cytotoxicity relative to the peptide in HaCaT and 3T3 cells. Especially these structures are very successful in terms of hemotoxicity. In the bacteremia model with S. aureus, the naked peptide (TN6) was hemotoxic even at 1 µg/mL, while the hemotoxicity of the conjugates was considerably lower than the peptide. Remarkably in this model, the hemolytic activity of PepC-PEG-pepC conjugate decreased 15-fold from 2.36 to 31.12 µg/mL compared to the bacteria-free 60-min treatment. This is proof that in the case of bacteremia and sepsis, the conjugates specifically direct to bacterial cell membranes rather than red blood cells. In addition, the PepC-PEG-pepC conjugate is resistant to plasma proteases. Moreover, morphological and intracellular damage of the peptide/conjugates to Escherichia coli are demonstrated in SEM and TEM images. These results suggest our molecules can be considered potential next-generation broad-spectrum antibiotic molecule/drug candidates that might be used in clinical cases such as bacteremia and sepsis.

Contemporary pharmacologic treatments of MRSA for hospitalized adults: rationale for vancomycin versus non-vancomycin therapies as first line agents

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) remains an important pathogen in the hospital setting and causes significant morbidity and mortality each year. Since the initial discovery over 60 years ago, vancomycin has remained a first-line treatment for many different types of MRSA infections. However, significant concerns related to target attainment and nephrotoxicity have spurred efforts to develop more effective agents in the last two decades.

AREAS COVERED

Newer anti-MRSA antibiotics that have been approved since 2000 include linezolid, daptomycin, and ceftaroline. As clinical evidence has accumulated, these newer agents have become more frequently used, and some are now recommended as co-first-line options (along with vancomycin) in clinical practice guidelines. For this review, a scoping review of the literature was conducted to support our findings and recommendations.

EXPERT OPINION

Vancomycin remains an important standard of care for MRSA infections but is limited with respect to nephrotoxicity and rapid target attainment. Newer agents such as linezolid, daptomycin, and ceftaroline have specific indications for treating different types of MRSA infections; however, newer agents also have unique attributes which require consideration during therapy.

Antimicrobial Peptides and Small Molecules Targeting the Cell Membrane of Staphylococcus aureus

Clinical management of Staphylococcus aureus infections presents a challenge due to the high incidence, considerable virulence, and emergence of drug resistance mechanisms. The treatment of drug-resistant strains, such as methicillin-resistant S. aureus (MRSA), is further complicated by the development of tolerance and persistence to antimicrobial agents in clinical use. To address these challenges, membrane disruptors, that are not generally considered during drug discovery for agents against S. aureus, should be explored. The cell membrane protects S. aureus from external stresses and antimicrobial agents, but membrane-targeting antimicrobial agents are probably less likely to promote bacterial resistance. Nontypical linear cationic antimicrobial peptides (AMPs), highly modified AMPs such as daptomycin (lipopeptide), bacitracin (cyclic peptide), and gramicidin S (cyclic peptide), are currently in clinical use. Recent studies have demonstrated that AMPs and small molecules can penetrate the cell membrane of S. aureus, inhibit phospholipid biosynthesis, or block the passage of solutes between the periplasm and the exterior of the cell. In addition to their primary mechanism of action (MOA) that targets the bacterial membrane, AMPs and small molecules may also impact bacteria through secondary mechanisms such as targeting the biofilm, and downregulating virulence genes of S. aureus. In this review, we discuss the current state of research into cell membrane-targeting AMPs and small molecules and their potential mechanisms of action against drug-resistant physiological forms of S. aureus, including persister cells and biofilms.

Efflux pump gene amplifications bypass necessity of multiple target mutations for resistance against dual-targeting antibiotic

Antibiotics that have multiple cellular targets theoretically reduce the frequency of resistance evolution, but adaptive trajectories and resistance mechanisms against such antibiotics are understudied. Here we investigate these in methicillin resistant Staphylococcus aureus (MRSA) using experimental evolution upon exposure to delafloxacin (DLX), a novel fluoroquinolone that targets both DNA gyrase and topoisomerase IV. We show that selection for coding sequence mutations and genomic amplifications of the gene encoding a poorly characterized efflux pump, SdrM, leads to high DLX resistance, circumventing the requirement for mutations in both target enzymes. In the evolved populations, sdrM overexpression due to genomic amplifications containing sdrM and two adjacent genes encoding efflux pumps results in high DLX resistance, while the adjacent hitchhiking efflux pumps contribute to streptomycin cross-resistance. Further, lack of sdrM necessitates mutations in both target enzymes to evolve DLX resistance, and sdrM thus increases the frequency of resistance evolution. Finally, sdrM mutations and amplifications are similarly selected in two diverse clinical isolates, indicating the generality of this DLX resistance mechanism. Our study highlights that instead of reduced rates of resistance, evolution of resistance to multi-targeting antibiotics can involve alternate high-frequency evolutionary paths, that may cause unexpected alterations of the fitness landscape, including antibiotic cross-resistance.