Clinical management of Staphylococcus aureus bacteraemia

Photodynamic inactivation of antibiotic-resistant bacteria in whole blood using riboflavin photodynamic method

Treating bacteremia caused by antibiotic-resistant bacteria is a global concern. Antibacterial photodynamic inactivation is a promising strategy to combat it. However, it's challenging to achieve the inactivation of antibiotic-resistant bacteria in whole blood because of its opacity and complexity. We investigated a riboflavin photodynamic method to effectively inactivate antibiotic-resistant bacteria in whole blood. Four strains of antibiotic-resistant bacteria were isolated, identified, and cultured in this research: methicillin-resistant Staphylococcus aureus (MRSA), pan-drug-resistant Acinetobacter baumannii (PDRAB), ESBLs-producing Escherichia coli (EPEC) and pan-drug-resistant Klebsiella pneumoniae (PDRKP). To simulate bacteremia, antibiotic-resistant bacteria was added into whole blood. Whole blood was treated using riboflavin photodynamic method with ultraviolet irradiation (308 nm and 365 nm). The ultraviolet irradiation dose was divided into 18 J/cm2, 36 J/cm2, and 54 J/cm2. Microbial count of antibiotic-resistant bacteria in whole blood was used for evaluating inactivation effectiveness. The roles of red blood cells, lymphocytes, coagulation factors, and platelets in whole blood were assessed. In results, inactivation effectiveness increased as the ultraviolet dose increased from 18 J/cm2 to 54 J/cm2. At the dose of 18 J/cm2, inactivation effectiveness of four antibiotic-resistant bacteria were more than 80%, while only 67% of MRSA. The antibacterial effect was enhanced by the combination of riboflavin photodynamic treatment and antibiotic. The red blood cell function was susceptible to ultraviolet dose. At the dose of 18 J/cm2, hemolysis rate was less than 0.8% and there was no change in levels of ATP and 2,3-DPG. At the same dose, the proliferation, cell killing, and cytokine secretion activities of lymphocytes decreased 20-70%; Factor V and Factor VIII activities decreased 50%; Fibrinogen and platelet function loss significantly but reparable. Consequently, we speculated that riboflavin photodynamic method with a ultraviolet dose of 18 J/cm2 was effective in inactivating four antibiotic-resistant bacteria in whole blood while whole blood function was preserved. We also provided a novel extracorporeal circulation phototherapy mode for treating bacteremia caused by antibiotic-resistant bacteria.

Evolution of polyamine resistance in Staphylococcus aureus through modulation of potassium transport

Microbes must adapt to diverse biotic and abiotic factors encountered in host environments. Polyamines are an abundant class of aliphatic molecules that play essential roles in fundamental cellular processes across the tree of life. Surprisingly, the bacterial pathogen Staphylococcus aureus is highly sensitive to polyamines encountered during infection, and acquisition of a polyamine resistance locus has been implicated in spread of the prominent USA300 methicillin-resistant S. aureus lineage. At present, alternative pathways of polyamine resistance in staphylococci are largely unknown. Here we applied experimental evolution to identify novel mechanisms and consequences of S. aureus adaption when exposed to increasing concentrations of the polyamine spermine. Evolved populations of S. aureus exhibited striking evidence of parallel adaptation, accumulating independent mutations in the potassium transporter genes ktrA and ktrD. Mutations in either ktrA or ktrD are sufficient to confer polyamine resistance and function in an additive manner. Moreover, we find that ktr mutations provide increased resistance to multiple classes of unrelated cationic antibiotics, suggesting a common mechanism of resistance. Consistent with this hypothesis, ktr mutants exhibit alterations in cell surface charge indicative of reduced affinity and uptake of cationic molecules. Finally, we observe that laboratory-evolved ktr mutations are also present in diverse natural S. aureus isolates, suggesting these mutations may contribute to antimicrobial resistance during human infections. Collectively this study identifies a new role for potassium transport in S. aureus polyamine resistance with consequences for susceptibility to both host-derived and clinically-used antimicrobials.

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.

Invasive Community-Acquired Methicillin-Resistant Staphylococcus aureus With Aortic Aneurysm in a 10-Year-Old Patient: A Case Report

The clinical presentation of disseminated community-acquired Methicillin-resistant Staphylococcus aureus (MRSA) in young pediatric patients without a known predisposing risk factor poses a diagnostic dilemma due to its non-specific clinical symptoms. This can lead to delayed initiation of appropriate antibiotics and surgical interventions to achieve a favorable outcome and prevent mortality. Appropriate imaging with good clinical judgment is required in the management of this infection. Outpatient surveillance for subacute and chronic complications is required for a good long-term prognosis. Few reported cases of disseminated infections with aortic aneurysm exist in the literature. We report a case of a child without predisposing risk factors managed for community-acquired MRSA sepsis, acute respiratory distress syndrome (ARDS), multiple abscesses, osteomyelitis, and necrotizing pneumonia with a post-discharge unruptured aortic aneurysm. This case emphasizes the importance of post-discharge monitoring even in patients with favorable outcomes.

Molecular detection of virulence genes in Staphylococcus aureus isolated from wild pigeons (Columba domestica livia) in KwaZulu-Natal in South Africa

The current study aimed to determine virulence determinants among S. aureus isolated from wild pigeons and houseflies around hospital areas in the Greater Durban area, South Africa. Following enrichment and bacterial growth, DNA extraction using the boiling method was performed. Overall, 57 out of 252 samples (22.6%) were positive for S. aureus. Six known virulence genes were tested, where five known virulence determinants were positive and none of the S. aureus isolates were positive to coagulase (coa) gene. The highest prevalence rates were found in the genes encoding haemolysins, with the hla and hld genes having 8 (14%) and 9 (15.8%) positive isolates respectively. The sea, LukS/F-PV, and spa genes had 5 (8.8%), 4 (7%), and 2 (3.5%) positive isolates respectively. These results demonstrated the detection of pathogenic S. aureus from hospital environment in Durban, South Africa which may account for the emergence staphylococcal infections. The findings of the present study highlights the significant role of wild pigeons and houseflies as potenital infectious disease vectors in a One Health context.

Differential survival of Staphylococcal species in macrophages

Staphylococcus aureus is considered an extracellular pathogen, yet the bacterium is able to survive within and escape from host cells. An agr/sae mutant of strain USA300 is unable to escape from macrophages but can replicate and survive within. We questioned whether such "non-toxic" S. aureus resembles the less pathogenic coagulase-negative Staphylococcal (CoNS) species like S. epidermidis, S. carnosus, S. lugdunensis, S. capitis, S. warneri, or S. pettenkoferi. We show that the CoNS are more efficiently killed in macrophage-like THP-1 cells or in human primary macrophages. Mutations in katA, copL, the regulatory system graRS, or sigB did not impact bacterial survival in THP-1 cells. Deletion of the superoxide dismutases impaired S. aureus survival in primary macrophages but not in THP-1 cells. However, expression of the S. aureus-specific sodM in S. epidermidis was not sufficient to protect this species from being killed. Thus, at least in those cells, better bacterial survival of S. aureus could not be linked to higher protection from ROS. However, "non-toxic" S. aureus was found to be insensitive to pH, whereas most CoNS were protected when phagosomal acidification was inhibited. Thus, species differences are at least partially linked to differences in sensitivity to acidification.

Effectiveness of adjunctive rifampicin for treatment of Staphylococcus aureus bacteraemia: a systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To assess whether the addition of rifampicin to conventional treatment of Staphylococcus aureus bacteraemia (SAB) reduces bacteriological or clinical failure or death.

DATA SOURCES

PubMed, Embase and Cochrane CENTRAL databases were searched from inception to 31 December 2022. Reference lists and PubMed citations of eligible studies were checked.

REVIEW METHODS

Two study authors independently identified randomized controlled trials (RCTs) involving adult participants with SAB, in which an intervention group received adjunctive rifampicin and the control group received usual care with or without a placebo. Dichotomous data (bacteriological and clinical failure and deaths) were analysed and pooled across studies using risk ratio (RR) with 95% confidence intervals (CI) using a Mantel-Haenszel random-effect model. The key variable of interest being whether rifampicin was used.

RESULTS

Six RCTs including 894 participants-of which 758 (85%) were from one trial-met the inclusion criteria. The addition of rifampicin to conventional treatment of SAB significantly reduced bacteriological failure by 59% (RR 0.41, 95% CI 0.21-0.81, I2 = 0%, number need to treat 27). However, it did not reduce clinical failure (RR 0.70, 95% CI 0.47-1.03, I2 = 0%) or deaths (RR 0.96, 95% CI 0.70-1.32, I2 = 0%). Further, it did not reduce the duration of bacteraemia, or the length of hospital stay. Adjunctive rifampicin reduced SAB recurrences (1% versus 4%, P = 0.01). Emergence of rifampicin resistance during treatment was uncommon (<1%).

CONCLUSION

Although adjunctive rifampicin reduced the risk of bacteriological failure and recurrences, we found no mortality benefit to support its use in SAB.

[Antibiotic allergies: targeted approach in suspected β‑lactam allergy]

Allergic reactions to antibiotics belong to hypersensitivity drug reactions and can trigger both immunoglobulin E-mediated symptoms and T cell-mediated symptoms. Skin manifestations are the most common symptoms. Although reporting a penicillin allergy results in considerable restrictions in the treatment of acute infections, which may be associated with poor treatment outcomes, in most cases the label 'penicillin allergy' is not called into question or critically reviewed. However, in 85-90% of patients, 'penicillin allergy' constitutes a mislabeling of a non-specific intolerance reaction that does not pose a risk to the patient when re-exposed to penicillins. Careful history taking, an evaluation of manifestations in the past, and easy-to-perform initial diagnostic steps are crucial in differentiating non-specific intolerance reactions from penicillin allergy sensu stricto. Thus, a penicillin de-labeling strategy allows for optimized antibiotic therapy in the event of a future infection. Although allergic cross-reactivity between different β‑lactam antibiotics can occur, the risk for a severe cross-reactivity is dependent on chemical properties of the specific β‑lactam. Published cross-reactivity tables can help in risk stratification and choice of alternative β‑lactam agents.

Early switching from intravenous to oral antibiotic therapy in bone and joint infections associated with methicillin-susceptible Staphylococcus aureus bacteremia

OBJECTIVES

We aimed to evaluate the clinical outcomes of patients with bone and joint infection (BJI) associated with methicillin-susceptible Staphylococcus aureus bacteremia (MSSAB) treated with early oral switch to oral antibiotics (before day 14) versus later or no switch.

PATIENTS AND METHODS

We included all cases reported between January 2016 and December 2021 in the University Hospital of Reims.

RESULTS

Among 79 patients with BJI associated with MSSAB, 50.6% had an early switch to oral antibiotics, with median duration of intravenous antibiotics of 9 (IQR 6-11) days. The overall cure rate was 81% with follow-up of 6 months, and was 85.7% after excluding the 9 patients whose death was not related to BJI infection. Failure to control BJI did not differ between the two groups.

CONCLUSION

An early (before day 14) switch to oral antibiotics may be a safe therapeutic option in BJI associated with MSSAB.

TPST2-mediated receptor tyrosine sulfation enhances leukocidin cytotoxicity and S. aureus infection

Background

An essential fact underlying the severity of Staphylococcus aureus (S. aureus) infection is the bicomponent leukocidins released by the pathogen to target and lyse host phagocytes through specific binding cell membrane receptors. However, little is known about the impact of post-transcriptional modification of receptors on the leukocidin binding.

Method

In this study, we used small interfering RNA library (Horizon/Dharmacon) to screen potential genes that affect leukocidin binding on receptors. The cell permeability was investigated through flow cytometry measuring the internalization of 4',6-diamidino-2-phenylindole. Expression of C5a anaphylatoxin chemotactic receptor 1 (C5aR1), sulfated C5aR1 in, and binding of 6x-His-tagged Hemolysin C (HlgC) and Panton-Valentine leukocidin (PVL) slow-component to THP-1 cell lines was detected and analyzed via flow cytometry. Bacterial burden and Survival analysis experiment was conducted in WT and myeloid TPST-cko C57BL/6N mice.

Results

After short hairpin RNA (shRNA) knockdown of TPST2 gene in THP-1, HL-60, and RAW264.7, the cytotoxicity of HlgAB, HlgCB, and Panton-Valentine leukocidin on THP-1 or HL-60 cells was decreased significantly, and the cytotoxicity of HlgAB on RAW264.7 cells was also decreased significantly. Knockdown of TPST2 did not affect the C5aR1 expression but downregulated cell surface C5aR1 tyrosine sulfation on THP-1. In addition, we found that the binding of HlgC and LukS-PV on cell surface receptor C5aR1 was impaired in C5aR1+TPST2- and C5aR1-TPST2- cells. Phagocyte knockout of TPST2 protects mice from S. aureus infection and improves the survival of mice infected with S. aureus.

Conclusion

These results indicate that phagocyte TPST2 mediates the bicomponent leukocidin cytotoxicity by promoting cell membrane receptor sulfation modification that facilitates its binding to leukocidin S component.

FBXO11 governs macrophage cell death and inflammation in response to bacterial toxins

Staphylococcus aureus causes severe infections such as pneumonia and sepsis depending on the pore-forming toxin Panton-Valentine leukocidin (PVL). PVL kills and induces inflammation in macrophages and other myeloid cells by interacting with the human cell surface receptor, complement 5a receptor 1 (C5aR1). C5aR1 expression is tighly regulated and may thus modulate PVL activity, although the mechanisms involved remain incompletely understood. Here, we used a genome-wide CRISPR/Cas9 screen and identified F-box protein 11 (FBXO11), an E3 ubiquitin ligase complex member, to promote PVL toxicity. Genetic deletion of FBXO11 reduced the expression of C5aR1 at the mRNA level, whereas ectopic expression of C5aR1 in FBXO11-/- macrophages, or priming with LPS, restored C5aR1 expression and thereby PVL toxicity. In addition to promoting PVL-mediated killing, FBXO11 dampens secretion of IL-1β after NLRP3 activation in response to bacterial toxins by reducing mRNA levels in a BCL-6-dependent and BCL-6-independent manner. Overall, these findings highlight that FBXO11 regulates C5aR1 and IL-1β expression and controls macrophage cell death and inflammation following PVL exposure.

Safe shortening of antibiotic treatment duration for complicated Staphylococcus aureus bacteraemia (SAFE trial): protocol for a randomised, controlled, open-label, non-inferiority trial comparing 4 and 6 weeks of antibiotic treatment

INTRODUCTION

A major knowledge gap in the treatment of complicated Staphylococcus aureus bacteraemia (SAB) is the optimal duration of antibiotic therapy. Safe shortening of antibiotic therapy has the potential to reduce adverse drug events, length of hospital stay and costs. The objective of the SAFE trial is to evaluate whether 4 weeks of antibiotic therapy is non-inferior to 6 weeks in patients with complicated SAB.

METHODS AND ANALYSIS

The SAFE-trial is a multicentre, non-inferiority, open-label, parallel group, randomised controlled trial evaluating 4 versus 6 weeks of antibiotic therapy for complicated SAB. The study is performed in 15 university hospitals and general hospitals in the Netherlands. Eligible patients are adults with methicillin-susceptible SAB with evidence of deep-seated or metastatic infection and/or predictors of complicated SAB. Only patients with a satisfactory clinical response to initial antibiotic treatment are included. Patients with infected prosthetic material or an undrained abscess of 5 cm or more at day 14 of adequate antibiotic treatment are excluded. Primary outcome is success of therapy after 180 days, a combined endpoint of survival without evidence of microbiologically confirmed disease relapse. Assuming a primary endpoint occurrence of 90% in the 6 weeks group, a non-inferiority margin of 7.5% is used. Enrolment of 396 patients in total is required to demonstrate non-inferiority of shorter antibiotic therapy with a power of 80%. Currently, 152 patients are enrolled in the study.

ETHICS AND DISSEMINATION

This is the first randomised controlled trial evaluating duration of antibiotic therapy for complicated SAB. Non-inferiority of 4 weeks of treatment would allow shortening of treatment duration in selected patients with complicated SAB. This study is approved by the Medical Ethics Committee VUmc (Amsterdam, the Netherlands) and registered under NL8347 (the Netherlands Trial Register). Results of the study will be published in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NL8347 (the Netherlands Trial Register).

Impact of the COVID-19 Pandemic on the Management of Staphylococcus aureus Bloodstream Infections in a Tertiary Care Hospital

Staphylococcus aureus bacteremia (SAB) is associated with a high mortality rate. The clinical outcome of SAB patients highly depends on early diagnosis, adequate antibiotic therapy and source control. In the context of the COVID-19 pandemic, the health care system faced additional organizational challenges and the question arose whether structured screening and triaging for COVID-19 and shifting resources influence the management of SAB. Patients (n = 115) with SAB were enrolled in a retrospective comparative study with historical controls (March 2019-February 2021). The quality of SAB therapy was assessed with a point score, which included correct choice of antibiotic, adequate dosage of antibiotic, sufficient duration of therapy, early start of therapy after receipt of findings, focus search and taking control blood cultures 3-4 days after starting adequate antibiotic therapy. The quality of treatment before and after the onset of the COVID-19 pandemic were compared. No significant differences in the total score points were found between the pre-COVID-19 and COVID-19 cohort. All quality indicators, except the correct duration of antibiotic therapy, showed no significant differences in both cohorts. Furthermore, there were no significant differences in the outcome between both cohorts. The treatment quality of SAB therapy was comparable before and during the COVID-19 pandemic.

Invasive Community-Acquired Methicillin-Resistant Staphylococcus aureus (MRSA) Infection in Children: A Report of Five Cases and Literature Review

Staphylococcus aureus developed resistance against most antibiotics; the most known resistant form is methicillin-resistant Staphylococcus aureus (MRSA), which can be acquired either from healthcare facilities or the community. The prevalence of hospital-acquired MRSA is higher than community-acquired MRSA (CA-MRSA). CA-MRSA has become an emerging infection and has been increasingly reported recently. Usually, CA-MRSA presents with skin and soft tissue infection but can cause severe invasive infection with significant morbidity. Invasive CA-MRSA needs rapid and aggressive treatment to prevent complications. For MRSA bacteremia that is persistent despite appropriate treatment, the possibility of metastatic invasive infection should be thought of. In this case series, we describe five pediatric cases of different age groups that had different presentations for invasive CA-MRSA infection. This report aims to highlight that physicians should be aware of the growing role of CA-MRSA in pediatrics; they should be meticulous in treating patients with CA-MRSA, and be aware of the complications of this disease and the appropriate empiric and target antibiotics regimen for such infections.

[Antibiotic allergies: targeted approach in suspected β‑lactam allergy]

Allergic reactions to antibiotics belong to hypersensitivity drug reactions and can trigger both immunoglobulin E-mediated symptoms and T cell-mediated symptoms. Skin manifestations are the most common symptoms. Although reporting a penicillin allergy results in considerable restrictions in the treatment of acute infections, which may be associated with poor treatment outcomes, in most cases the label 'penicillin allergy' is not called into question or critically reviewed. However, in 85-90% of patients, 'penicillin allergy' constitutes a mislabeling of a non-specific intolerance reaction that does not pose a risk to the patient when re-exposed to penicillins. Careful history taking, an evaluation of manifestations in the past, and easy-to-perform initial diagnostic steps are crucial in differentiating non-specific intolerance reactions from penicillin allergy sensu stricto. Thus, a penicillin de-labeling strategy allows for optimized antibiotic therapy in the event of a future infection. Although allergic cross-reactivity between different β‑lactam antibiotics can occur, the risk for a severe cross-reactivity is dependent on chemical properties of the specific β‑lactam. Published cross-reactivity tables can help in risk stratification and choice of alternative β‑lactam agents.

Antibacterial and biofilm-inhibitory effects of vancomycin-loaded mesoporous silica nanoparticles on methicillin-resistant staphylococcus aureus and gram-negative bacteria

The present study aimed to prepare and characterize vancomycin-loaded mesoporous silica nanoparticles (Van-MSNs) to detect inhibitory effects on the planktonic and biofilm forms of methicillin-resistant Staphylococcus aureus (MRSA) isolates, and study the biocompatibility and toxicity of Van-MSNs in vitro as well as antibacterial activity of Van-MSNs against Gram-negative bacteria. The inhibitory effects of Van-MSNs were investigated on MRSA using the determination of minimum inhibitory (MIC) and minimum biofilm-inhibitory concentrations (MBIC) as well as the effect on bacterial attachment. Biocompatibility was studied by examining the effect of Van-MSNs on the lysis and sedimentation rate of red blood cells (RBC). The interaction of Van-MSNs with human blood plasma was detected by the SDS-PAGE approach. The cytotoxic effect of the Van-MSNs on human bone marrow mesenchymal stem cells (hBM-MSCs) was evaluated by the MTT assay. The antibacterial effects of vancomycin and Van-MSNs on Gram-negative bacteria were also investigated using MIC determination using the broth microdilution method. Furthermore, bacteria outer membrane (OM) permeabilization was determined. Van-MSNs showed inhibitory effects on planktonic and biofilm forms of bacteria on all isolates at levels lower than MICs and MBICs of free vancomycin, but the antibiofilm effect of Van-MSNs was not significant. However, Van-MSNs did not affect bacterial attachment to surfaces. Van-loaded MSNs did not show a considerable effect on the lysis and sedimentation of RBC. A low interaction of Van-MSNs was detected with albumin (66.5 kDa). The hBM-MSCs viability in exposure to different levels of Van-MSNs was 91-100%. MICs of ≥ 128 µg/mL were observed for vancomycin against all Gram-negative bacteria. In contrast, Van-MSNs exhibited modest antibacterial activity inhibiting the tested Gram-negative bacterial strains, at concentrations of ≤ 16 µg/mL. Van-MSNs increased the OM permeability of bacteria that can increase the antimicrobial effect of vancomycin. According to our findings, Van-loaded MSNs have low cytotoxicity, desirable biocompatibility, and antibacterial effects and can be an option for the battle against planktonic MRSA.

Risk Factors for Nephrotoxicity in Methicillin-Resistant Staphylococcus aureus Bacteraemia: A Post Hoc Analysis of the CAMERA2 Trial

BACKGROUND

Clinical risk factors for nephrotoxicity in Staphylococcus aureus bacteraemia remain largely undetermined, despite its common occurrence and clinical significance. In an international, multicentre, prospective clinical trial (CAMERA2), which compared standard therapy (vancomycin monotherapy) to combination therapy (adding an anti-staphylococcal beta-lactam) for methicillin-resistant S. aureus bacteraemia, significantly more people in the combination therapy arm experienced acute kidney injury compared with those in the monotherapy arm (23% vs 6%).

OBJECTIVE

The aim of this post hoc analysis was to explore in greater depth the risk factors for acute kidney injury from the CAMERA2 trial.

METHODS

Among participants of the CAMERA2 trial, demographic-related, infection-related and treatment-related risk factors were assessed for their relationship with acute kidney injury by univariable and multivariable logistic regression. Acute kidney injury was defined by a modified-KDIGO (Kidney Disease: Improving Global Outcomes) criteria (not including urinary output).

RESULTS

Of the 266 participants included, age (p = 0.04), randomisation to combination therapy (p = 0.002), vancomycin area under the concentration-time curve (p = 0.03) and receipt of (flu)cloxacillin as the companion beta-lactam (p < 0.001) were significantly associated with acute kidney injury. On a multivariable analysis, concurrent use of (flu)cloxacillin increased the risk of acute kidney injury over four times compared with the use of cefazolin or no beta-lactam. The association of vancomycin area under the concentration-time curve with acute kidney injury also persisted in the multivariable model.

CONCLUSIONS

For participants receiving vancomycin for S. aureus bacteraemia, use of (flu)cloxacillin and increased vancomycin area under the concentration-time curve were risk factors for acute kidney injury. These represent potentially modifiable risk factors for nephrotoxicity and highlight the importance of avoiding the use of concurrent nephrotoxins.

Bioactive metabolites of Streptomyces misakiensis display broad-spectrum antimicrobial activity against multidrug-resistant bacteria and fungi

Background

Antimicrobial resistance is a serious threat to public health globally. It is a slower-moving pandemic than COVID-19, so we are fast running out of treatment options.

Purpose

Thus, this study was designed to search for an alternative biomaterial with broad-spectrum activity for the treatment of multidrug-resistant (MDR) bacterial and fungal pathogen-related infections.

Methods

We isolated Streptomyces species from soil samples and identified the most active strains with antimicrobial activity. The culture filtrates of active species were purified, and the bioactive metabolite extracts were identified by thin-layer chromatography (TLC), preparative high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry (GC-MS). The minimum inhibitory concentrations (MICs) of the bioactive metabolites against MDR bacteria and fungi were determined using the broth microdilution method.

Results

Preliminary screening revealed that Streptomyces misakiensis and S. coeruleorubidus exhibited antimicrobial potential. The MIC₅₀ and MIC₉₀ of S. misakiensis antibacterial bioactive metabolite (ursolic acid methyl ester) and antifungal metabolite (tetradecamethylcycloheptasiloxane) against all tested bacteria and fungi were 0.5 μg/ml and 1 μg/mL, respectively, versus S. coeruleorubidus metabolites: thiocarbamic acid, N,N-dimethyl, S-1,3-diphenyl-2-butenyl ester against bacteria (MIC₅₀: 2 μg/ml and MIC₉₀: 4 μg/mL) and fungi (MIC₅₀: 4 μg/ml and MIC₉₀: 8 μg/mL). Ursolic acid methyl ester was active against ciprofloxacin-resistant strains of Streptococcus pyogenes, S. agalactiae, Escherichia coli, Klebsiella pneumoniae, and Salmonella enterica serovars, colistin-resistant Aeromonas hydrophila and K. pneumoniae, and vancomycin-resistant Staphylococcus aureus. Tetradecamethylcycloheptasiloxane was active against azole- and amphotericin B-resistant Candida albicans, Cryptococcus neoformans, C. gattii, Aspergillus flavus, A. niger, and A. fumigatus. Ursolic acid methyl ester was applied in vivo for treating S. aureus septicemia and K. pneumoniae pneumonia models in mice. In the septicemia model, the ursolic acid methyl ester-treated group had a significant 4.00 and 3.98 log CFU/g decrease (P < 0.05) in liver and spleen tissue compared to the infected, untreated control group. Lung tissue in the pneumonia model showed a 2.20 log CFU/g significant decrease in the ursolic acid methyl ester-treated group in comparison to the control group. The haematological and biochemical markers in the ursolic acid methyl ester-treated group did not change in a statistically significant way. Moreover, no abnormalities were found in the histopathology of the liver, kidneys, lungs, and spleen of ursolic acid methyl ester-treated mice in comparison with the control group.

Conclusion

S. misakiensis metabolite extracts are broad-spectrum antimicrobial biomaterials that can be further investigated for the potential against MDR pathogen infections. Hence, it opens up new horizons for exploring alternative drugs for current and reemerging diseases.

The Golden Grapes of Wrath - Staphylococcus aureus Bacteremia: A Clinical Review

Staphylococcus aureus bacteremia is common and associated with fatality rates approximating 25%. We provide a brief overview of S. aureus bacteremia from a clinical and microbiological lens and review the relevant evidence and literature gaps in its management. Using a case-based approach, evidence and clinical judgement are meshed to highlight and justify the 5 core interventions that ought to be performed for all cases of S. aureus bacteremia: 1) appropriate anti-staphylococcal therapy, 2) screening echocardiography, 3) assessment for metastatic phenomena and source control, 4) decision on duration of antimicrobial therapy, and 5) Infectious Diseases consultation.

Adherence to a care bundle for Staphylococcus aureus bacteraemia: A retrospective cohort study

BACKGROUND

Staphylococcus aureus bacteraemia is associated with high hospital mortality. Improvements in outcome have been described with standardised bundles of care.

OBJECTIVES

To study the adherence of a standardised bundle of care (BOC) recommendations using a consultation pro forma, for all patients admitted with S. aureus bacteraemia to Groote Schuur Hospital over a year. The study further aimed to describe the 90-day mortality in these patients and to assess for an association between adherence to the bundle of care and outcome.

METHOD

A retrospective audit of all unsolicited infectious disease consultations for patients with S. aureus bacteraemia admitted to Groote Schuur Hospital during 2018. Adherence to recommendations of a standard bundle of care was audited.

RESULTS

A total of 86 patients were included in the study: 61 (71%) with hospital-associated infection and 25 (29%) with community-associated infection. Over 80% of adherence to treatment recommendations was achieved regarding antibiotic (including vancomycin) usage, source control and use of echocardiography as required. In-hospital mortality was 16%, while the overall 90-day mortality was 18%, with only age as an independent predictor of mortality. No association between adherence to the bundle of care and outcome was found.

CONCLUSION

Adherence to a simple, structured bundle of care was good when using standardised pro forma as communication tools for advice and a structured antibiotic chart for vancomycin administration. Although adherence was not associated with outcome, the overall mortality for S. aureus bacteraemia was improving in the institution under study.

CONTRIBUTION

Our findings support feasibility and ongoing use of bundles of care for S. aureus bacteraemia in similar settings.

Emergence of infectious diseases and role of advanced nanomaterials in point-of-care diagnostics: a review

Infectious outbreaks are the foremost global public health concern, challenging the current healthcare system, which claims millions of lives annually. The most crucial way to control an infectious outbreak is by early detection through point-of-care (POC) diagnostics. POC diagnostics are highly advantageous owing to the prompt diagnosis, which is economical, simple and highly efficient with remote access capabilities. In particular, utilization of nanomaterials to architect POC devices has enabled highly integrated and portable (compact) devices with enhanced efficiency. As such, this review will detail the factors influencing the emergence of infectious diseases and methods for fast and accurate detection, thus elucidating the underlying factors of these infections. Furthermore, it comprehensively highlights the importance of different nanomaterials in POCs to detect nucleic acid, whole pathogens, proteins and antibody detection systems. Finally, we summarize findings reported on nanomaterials based on advanced POCs such as lab-on-chip, lab-on-disc-devices, point-of-action and hospital-on-chip. To this end, we discuss the challenges, potential solutions, prospects of integrating internet-of-things, artificial intelligence, 5G communications and data clouding to achieve intelligent POCs.

Staphylococcus aureus bacteremia mortality across country income groups: A secondary analysis of a systematic review

OBJECTIVES

Staphylococcus aureus bacteremia (SAB) is a common infection worldwide. We compared SAB mortality in low- and middle-income countries (LMIC) versus high-income countries (HIC) in a meta-analysis.

METHODS

We searched MEDLINE, Embase, and Cochrane Database of Systematic Reviews from 1991-2021 and included observational, single-country studies on patients with positive blood cultures for S. aureus. The main outcome was the proportion of patients with SAB who died in the hospital. A generalized linear mixed random-effects model was used to pool estimates, and a meta-regression was used to adjust for study-level characteristics.

RESULTS

A total of 332 studies involving 517,671 patients in 39 countries were included. No study was conducted in a low-income country. Only 33 (10%) studies were performed in middle-income countries (MIC), which described 6,216 patients. The pooled in-hospital mortality was 32.4% (95% confidence interval [CI] 27.2%-38.2%, T2 = 0.3063) in MIC and 22.3% (95% CI 20.1%-24.6%, T2 = 0.3257) in HIC. In a meta-regression model, MIC had higher in-hospital mortality (adjusted odds ratio 1.37, 95% CI 1.11-1.71; P = 0.0042) than HIC.

CONCLUSION

In SAB studies, LMIC are poorly represented. In-hospital mortality was significantly higher in MIC than in HIC. Research should be conducted in LMIC to characterize differences in care processes driving the mortality gap.

Successful management of a mediastinum abscess with sternum destruction caused by MSSA bloodstream infection

BACKGROUND

Multiple deep organ abscesses associated with Staphylococcus aureus bloodstream infection (SAB) have a high mortality rate, requiring rapid removal or drainage of infective foci with long-term appropriate antimicrobial therapy. Cases in which infective foci cannot be completely removed are challenging for their management.

CASE PRESENTATION

A 77-year-old man developed multiple deep organ abscesses associated with SAB. The left anterior chest subcutaneous abscess continued into the right anterior mediastinum and had extensively destroyed the sternum. Necrotizing fasciitis was observed in the bilateral feet. The anterior mediastinum abscess was drained percutaneously, and the chest wall abscess was incised cautiously without causing an external pneumothorax. On the next day, right-sided pyothorax had developed, requiring pleural drainage. On the third day, debridement of anterior chest wall abscess followed by concurrent thoracoscopic pleural curettage and debridement of bilateral feet were performed. Thorough sternal debridement was not performed, considering the risk of respiratory failure due to the sternal defects. On the 24th day, sternum debridement and incisional drainage of sciatic rectus fossa abscess, which had been present since the time of admission, were performed to control persistent infection. The caudal half of the sternal body was resected, leaving the costal cartilage attachments. The general condition further improved without postoperative respiratory failure after the second surgery, leading to a transfer to the general ward on the 43rd day.

CONCLUSIONS

We successfully treated the severe multiple deep organ abscesses, including a mediastinum abscess with sternum destruction, by repeated removal of the infective foci while avoiding respiratory failure due to excessive debridement of the anterior chest wall, including the sternum.

A Severe Case of Disseminated Multifocal Methicillin-Susceptible Staphylococcal Infection in a Diabetic Patient

Methicillin-susceptible Staphylococcus aureus (MSSA) is quite common in the environment. It can lead to a wide range of infections varying from simple boils to disseminated and metastatic infections. Disseminated multifocal MSSA infection without infective endocarditis is extremely rare. We report a case of a 48-year-old diabetic male who presented with complaints of back pain, lower limb weakness, urinary retention, and saddle sensation loss. His imaging showed an epidural abscess, spondylitis, multiple paraspinous abscess collections, iliopsoas and gluteal abscess formation, multiple abdominal abscesses, multiple cavitating lung nodules, left-sided empyema, and azygos venous thrombosis. He was managed with urgent laminectomy and evacuation of spinal epidural abscess. He was admitted under the medical team for further multidisciplinary patient care. Emergency physicians and internists should be able to recognize such cases early on to make appropriate management plans. Misdiagnosis and delay in treatment initiation can lead to high mortality and poor patient outcomes. Advanced imaging techniques should be utilized to avoid missed foci. Improved source control results in better patient outcomes.

Staphylococcus aureus bacteremia mortality: A systematic review and meta-analysis

BACKGROUND

Precise estimates of mortality in Staphylococcus aureus bacteremia (SAB) are important to convey prognosis and guide design of interventional studies.

OBJECTIVE

We performed a systematic review and meta-analysis to estimate the all-cause mortality in SAB and to explore how it changed with time.

DATA SOURCES

MEDLINE, Embase, and Cochrane Database of Systematic Reviews from January 1, 1991 to May 7, 2021.

STUDY ELIGIBILITY CRITERIA

Human observational studies on patients with S. aureus bloodstream infection.

PARTICIPANTS

Patients with a positive blood culture for S. aureus.

METHODS

Two independent reviewers extracted study data and assessed risk of bias using the Newcastle Ottawa Scale. A generalized linear mixed random effects model was used to pool estimates.

RESULTS

A total of 341 studies were included, which described 536,791 patients. From 2011 onwards, the estimated mortality was 10.4% (95% confidence interval (CI) 9.0%-12.1%) at 7 days, 13.3% (95% CI 11.1%-15.8%) at 2 weeks, 18.1% (95% CI 16.3%-20.0%) at 1 month, 27.0% (95% CI 21.5%-33.3%) at 3 months, and 30.2% (95% CI 22.4%-39.3%) at 1 year. In a meta-regression model of 1-month mortality, methicillin-resistant S. aureus (MRSA) had a higher mortality (adjusted odds ratio (aOR) 1.04 95% CI 1.02-1.06 per 10% increase in MRSA proportion), and compared to prior to 2001, more recent time periods had lower mortality (aORs 0.88 [95% CI 0.75-1.03] for 2001 to 2010; 0.82 [95% CI 0.69-0.97] for 2011 onwards).

CONCLUSIONS

SAB mortality has decreased over the last 3 decades. However, more than 1 in 4 patients will die within 3 months and continuous improvement in care remains necessary.

REGISTRATION

PROSPERO CRD42021253891.

Effectiveness and Safety of Ceftriaxone Compared to Standard of Care for Treatment of Bloodstream Infections Due to Methicillin-Susceptible Staphylococcus aureus: A Systematic Review and Meta-Analysis

(1) Background: Ceftriaxone is a potential alternative for the treatment of methicillin-susceptible Staphylococcus aureus (MSSA) bloodstream infections (BSIs) in acute care and outpatient parenteral antimicrobial therapy (OPAT) settings. We evaluated the effectiveness and safety of ceftriaxone for the treatment of MSSA BSIs. (2) Method: We searched PubMed, Embase, and Cochrane Library from their inception to October 30th 2021. Our outcomes included clinical cure, microbiological cure, 30- and 90-day mortality, 90-day hospital readmission, and adverse drug reactions (ADRs). We compared ceftriaxone against standard of care (SOC) therapy. We used the random-effects model for the meta-analysis, and our estimated effects were reported as odds ratios (ORs) with 95% confidence intervals (CI). (3) Results: Twelve retrospective cohort studies were included, comprising 1037 patients in the ceftriaxone arms and 2088 patients in the SOC arms. The clinical cure rate of the ceftriaxone regimen was not statistically different from SOC: OR 0.65 (95% CI: 0.29–1.45). Ceftriaxone was also not statistically different from SOC in microbiological cure: OR 1.48 (95% CI: 0.29–7.51); 30-day mortality: OR 0.79 (95% CI: 0.14–4.65); 90-day mortality: OR 0.82 (95% CI: 0.38–1.80); 90-day hospital readmission: OR 1.20 (95% CI: 0.92–1.56); and ADRs: OR 0.92 (95% CI: 0.39–2.18). (4) Conclusion: Ceftriaxone could provide an alternative for the treatment of MSSA BSIs in acute care and OPAT settings (except in patients whose BSIs were due to infective endocarditis).

Comparative Genomic Reveals Clonal Heterogeneity in Persistent Staphylococcus aureus Infection

Persistent infections caused by Staphylococcus aureus remain a clinical challenge. Adaptational mechanisms of the pathogen influencing infection persistence, treatment success, and clinical outcome in these types of infections by S. aureus have not been fully elucidated so far. We applied a whole-genome sequencing approach on fifteen isolates retrieved from a persistent S. aureus infection to determine their genetic relatedness, virulome, and resistome. The analysis of the genomic data indicates that all isolates shared a common clonal origin but displayed a heterogenous composition of virulence factors and antimicrobial resistance. This heterogeneity was reflected by different mutations in the rpoB gene that were related to the phenotypic antimicrobial resistance towards rifampicin and different minimal inhibitory concentrations of oxacillin. In addition, one group of isolates had acquired the genes encoding for staphylokinase (sak) and staphylococcal complement inhibitor (scn), leading to the truncation of the hemolysin b (hlb) gene. These features are characteristic for temperate phages of S. aureus that carry genes of the immune evasion cluster and confer triple conversion by integration into the hlb gene. Modulation of immune evasion mechanisms was demonstrated by significant differences in biofilm formation capacity, while invasion and intracellular survival in neutrophils were not uniformly altered by the presence of the immune evasion cluster. Virulence factors carried by temperate phages of S. aureus may contribute to the course of infection at different stages and affect immune evasion and pathogen persistence. In conclusion, the application of comparative genomic demonstrated clonal heterogeneity in persistent S. aureus infection.

Intravenous versus Oral Step-Down for the Treatment of Staphylococcus aureus Bacteremia in a Pediatric Population

Limited data are available regarding optimal antimicrobial therapy for Staphylococcus aureus bacteremia (SAB) in pediatric patients. The purpose of this study was to assess clinical characteristics and outcomes associated with intravenous (IV) versus oral step-down treatment of pediatric SAB. This study evaluated patients aged 3 months to 18 years that received at least 72 h of inpatient treatment for SAB. The primary endpoint was 30-day readmission. Secondary endpoints included hospital length of stay and inpatient mortality. One hundred and one patients were included in this study. The median age was 7.9 years. Patients who underwent oral step-down were less likely to be immunocompromised and more likely to have community-acquired SAB from osteomyelitis or skin and soft tissue infection (SSTI). More patients in the IV therapy group had a 30-day readmission (10 (25.6%) vs. 3 (5.3%), p = 0.006). Mortality was low (5 (5%)) and not statistically different between groups. Length of stay was greater in patients receiving IV therapy only (11 vs. 7 days, p = 0.001). In this study, over half of the patients received oral step-down therapy and 30-day readmission was low for this group. Oral therapy appears to be safe and effective for patients with SAB from osteomyelitis or SSTIs.

Individualizing the use of [18F]FDG-PET/CT in patients with complicated Staphylococcus aureus bacteremia: experiences from a tertiary care center

Purpose

[¹⁸F]FDG-PET/CT scanning can help detect metastatic infectious foci and reduce mortality in patients with Staphylococcus aureus bacteremia (SAB), but it is unknown if patients with SAB and an indication for prolonged treatment because of possible endovascular, orthopaedic implant, or other metastatic infection still need [¹⁸F]FDG-PET/CT.

Methods

In a retrospective single-center cohort study, we included all consecutive adult patients with SAB between 2013 and 2020 if an [¹⁸F]FDG-PET/CT scan was performed and antibiotic treatment was planned for ≥ 6 weeks prior to [¹⁸F]FDG-PET/CT. We aimed to identify patients for whom treatment was adjusted due to the results of [¹⁸F]FDG-PET/CT, and assessed concordance of [¹⁸F]FDG-PET/CT and clinical diagnosis for infected prosthetic material.

Results

Among 132 patients included, the original treatment plan was changed after [¹⁸F]FDG-PET/CT in 22 patients (16.7%), in the majority (n = 20) due to diagnosing or rejecting endovascular (graft) infection. Antibiotic treatment modifications were shortening in 2, iv-oral switch in 3, extension in 13, and addition of rifampicin in 4 patients. Ninety additional metastatic foci based on [¹⁸F]FDG-PET/CT results were found in 69/132 patients (52.3%). [¹⁸F]FDG-PET/CT suggested vascular graft infection in 7/14 patients who lacked clinical signs of infection, but showed no infection of prosthetic joints or osteosynthesis material in eight patients who lacked clinical signs of such an infection.

Conclusion

[¹⁸F]FDG-PET/CT can help refine treatment for SAB in patients with clinically suspected endovascular infection or vascular grafts, even if 6 weeks treatment is already indicated, but can be safely omitted in other patients who are clinically stable.

Supplementary Information

The online version contains supplementary material available at 10.1007/s15010-021-01740-4.

Ceftriaxone versus antistaphylococcal antibiotics for definitive treatment of methicillin-susceptible Staphylococcus aureus infections: a systematic review and meta-analysis

Optimal therapy for methicillin-susceptible Staphylococcus aureus (MSSA) infections is unclear. Current standard of care consists of antistaphylococcal antibiotics (ASAs) such as nafcillin, oxacillin and cefazolin. Ceftriaxone has been evaluated due to its advantage as a once-daily outpatient regimen. However, questions remain regarding its efficacy compared with ASAs. We aimed to conduct a review and synthesis of available literature for outcomes of patients treated with ceftriaxone or ASAs for MSSA infections. We searched Cochrane Central Register of Controlled Trials, Embase Ovid, MEDLINE Ovid, Scopus and Web of Science (1990 to June 2021). Risk of bias for cohort studies was assessed by the Newcastle-Ottawa scale. We pooled risk ratios (RRs) using the DerSimonian-Laird random-effects model for outcomes of those receiving ceftriaxone versus ASAs. Heterogeneity was assessed by the I² index. From 459 identified studies, 7 were included in the quantitative synthesis totalling 1640 patients. Definitive therapy with ceftriaxone was associated with a lower risk of toxicity requiring therapy alteration (RR 0.49, 95% CI 0.27-0.88; I² = 0%). There was no difference in terms of 90-day all-cause mortality (RR 0.93, 95% CI 0.46-1.88; I² = 9%), hospital readmission (RR 0.96, 95% CI 0.57-1.64; I² = 0%) or infection recurrence (RR 1.04, 95% CI 0.63-1.72; I² =0%). Current evidence suggests there is no difference in efficacy between ceftriaxone and ASAs for MSSA infection, with a lower risk of toxicity with ceftriaxone. Within the limitations of available retrospective studies, ceftriaxone is a consideration for definitive therapy of MSSA infection. [Trial registration: PROSPERO ID: CRD42021259086].

Therapeutic Drug Monitoring of Antibiotics in the Elderly: A Narrative Review

PURPOSE

Antibiotic dosing adaptation in elderly patients is frequently complicated by age-related changes affecting the processes of drug absorption, distribution, metabolism, and/or elimination. These events eventually result in treatment failure and/or development of drug-related toxicity. Therapeutic drug monitoring (TDM) can prevent suboptimal antibiotic exposure in adult patients regardless of age. However, little data are available concerning the specific role of TDM in the elderly.

METHODS

This review is based on a PubMed search of the literature published in the English language. The search involved TDM studies of antibiotics in the elderly performed between 1990 and 2021. Additional studies were identified from the reference lists of the retrieved articles. Studies dealing with population pharmacokinetic modeling were not considered.

RESULTS

Only a few studies, mainly retrospective and with observational design, have specifically dealt with appropriate antibiotic dosing in the elderly based on TDM. Nevertheless, some clinical situations in which the selection of optimal antibiotic dosing in the elderly was successfully guided by TDM were identified.

CONCLUSIONS

Elderly patients are at an increased risk of bacterial infections and inadequate drug dosing compared to younger patients. Therefore, the availability of TDM services can improve the appropriateness of antibiotic prescriptions in this population.

How to investigate and manage a patient with a Staphylococcus aureus bacteraemia

Staphylococcus aureus bacteraemia is common, and associated with significant morbidity and mortality as a result of its high relapse rate and the risk of complicated infection. A positive blood culture for S. aureus should prompt a thorough patient assessment to identify a potential focus of infection, and the risk factors for the development or presence of complicated infection. Clinical management depends on the patient's characteristics and presenting features. This article gives a systematic approach to the patient with S. aureus bacteraemia, including points to look for on history and examination, the markers of complicated infection, and when to request transoesophageal echocardiography and further imaging. Treatment principles outlined include the rationale for choice of antibiotic treatment and need to involve infection specialists.

Combination therapy with rifampicin or fosfomycin in patients with Staphylococcus aureus bloodstream infection at high risk for complications or relapse: results of a large prospective observational cohort

OBJECTIVES

To investigate whether Staphylococcus aureus bloodstream infection (SAB) patients at high risk for complications or relapse benefit from combination therapy with adjunctive rifampicin or fosfomycin.

METHODS

In this post hoc analysis, SAB patients with native valve infective endocarditis, osteoarticular infections or implanted foreign devices were included. The co-primary endpoints were all-cause 90 day mortality and death or SAB-related late complications within 180 days. To overcome treatment selection bias and account for its time dependence, inverse probability of treatment weights were calculated and included in marginal structural Cox proportional hazard models (MSCMs).

RESULTS

A total of 578 patients were included in the analysis, of which 313 (54%) received combination therapy with either rifampicin (n = 242) or fosfomycin (n = 58). In the multivariable MSCM, combination therapy was associated with a better outcome, that is, a lower rate of death or SAB-related late complications within 180 days (HR 0.65, 95% CI 0.46-0.92). This beneficial effect was primarily seen in patients with implanted foreign devices, in which combination therapy was associated with a lower rate of death or SAB-related late complications within 180 days (HR 0.53, 95% CI 0.35-0.79) and a lower 90 day mortality (HR 0.57, 95% CI 0.36-0.91). Upon agent-specific stratification, we found no significant differences in outcomes between combination therapy containing rifampicin and fosfomycin; however, the number of patients in most subgroups was not large enough to draw firm conclusions.

CONCLUSIONS

In patients with implanted foreign devices, combination therapy was associated with a better long-term outcome. Larger prospective studies are needed to validate these findings.

The autophagic response to Staphylococcus aureus provides an intracellular niche in neutrophils

Staphylococcus aureus is a major human pathogen causing multiple pathologies, from cutaneous lesions to life-threatening sepsis. Although neutrophils contribute to immunity against S. aureus, multiple lines of evidence suggest that these phagocytes can provide an intracellular niche for staphylococcal dissemination. However, the mechanism of neutrophil subversion by intracellular S. aureus remains unknown. Targeting of intracellular pathogens by macroautophagy/autophagy is recognized as an important component of host innate immunity, but whether autophagy is beneficial or detrimental to S. aureus-infected hosts remains controversial. Here, using larval zebrafish, we showed that the autophagy marker Lc3 rapidly decorates S. aureus following engulfment by macrophages and neutrophils. Upon phagocytosis by neutrophils, Lc3-positive, non-acidified spacious phagosomes are formed. This response is dependent on phagocyte NADPH oxidase as both cyba/p22phox knockdown and diphenyleneiodonium (DPI) treatment inhibited Lc3 decoration of phagosomes. Importantly, NADPH oxidase inhibition diverted neutrophil S. aureus processing into tight acidified vesicles, which resulted in increased host resistance to the infection. Some intracellular bacteria within neutrophils were also tagged by Sqstm1/p62-GFP fusion protein and loss of Sqstm1 impaired host defense. Together, we have shown that intracellular handling of S. aureus by neutrophils is best explained by Lc3-associated phagocytosis (LAP), which appears to provide an intracellular niche for bacterial pathogenesis, while the selective autophagy receptor Sqstm1 is host-protective. The antagonistic roles of LAP and Sqstm1-mediated pathways in S. aureus-infected neutrophils may explain the conflicting reports relating to anti-staphylococcal autophagy and provide new insights for therapeutic strategies against antimicrobial-resistant Staphylococci.Abbreviations: ATG: autophagy related; CFU: colony-forming units; CMV: cytomegalovirus; Cyba/P22phox: cytochrome b-245, alpha polypeptide; DMSO: dimethyl sulfoxide; DPI: diphenyleneiodonium; EGFP: enhanced green fluorescent protein; GFP: green fluorescent protein; hpf: hours post-fertilization; hpi: hours post-infection; Irf8: interferon regulatory factor 8; LAP: LC3-associated phagocytosis; lyz: lysozyme; LWT: london wild type; Map1lc3/Lc3: microtubule-associated protein 1 light chain 3; NADPH oxidase: nicotinamide adenine dinucleotide phosphate oxidase; RFP: red fluorescent protein; ROS: reactive oxygen species; RT-PCR: reverse transcriptase polymerase chain reaction; Sqstm1/p62: sequestosome 1; Tg: transgenic; TSA: tyramide signal amplification.

Daptomycin Plus β-Lactam Combination Therapy for Methicillin-resistant Staphylococcus aureus Bloodstream Infections: A Retrospective, Comparative Cohort Study

BACKGROUND

Mounting evidence suggests the addition of a β-lactam (BL) to daptomycin (DAP) results in synergistic in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA) and bolsters the innate immune response to infection. This study's objective was to provide clinical translation to these experimental data and determine if DAP+BL combination therapy results in improved clinical outcomes compared with treatment with DAP alone in patients with MRSA bloodstream infections (BSIs).

METHODS

This was a retrospective, comparative cohort study conducted at 2 academic medical centers between 2008 and 2018. Adults with MRSA BSI treated with DAP for ≥72 hours and initiated ≤5 days of culture collection were included. Patients who received a BL for ≥24 hours and initiated ≤24 hours of DAP comprised the DAP+BL group. The primary outcome was composite clinical failure (60-day all-cause mortality and/or 60-day recurrence). Analyses were adjusted for confounding using inverse probability of treatment weighting (IPTW).

RESULTS

A total of 229 patients were included (72 DAP+BL and 157 DAP). In unadjusted and IPTW-adjusted analyses, DAP+BL was associated with significantly reduced odds of clinical failure (odds ratio [OR], 0.362; 95% confidence interval [CI], .164-.801; adjusted OR, 0.386; 95% CI, .175-.853). Adjusted analyses restricted to prespecified subgroups based on infection complexity and baseline health status were consistent with the main analysis.

CONCLUSIONS

The addition of a BL to DAP was associated with improved clinical outcomes in patients with MRSA BSI. This study provides support to ongoing and future studies evaluating the impact of combination therapy for invasive MRSA infections.Patients treated with daptomycin plus a β-lactam for MRSA bloodstream infection had lower odds of composite clinical failure defined as 60-day all-cause mortality and/or 60-day recurrence compared with patients treated with daptomycin monotherapy after adjusting for confounding variables using inverse probability of treatment weighting.

Could simulation methods solve the curse of sparse data within clinical studies of antibiotic resistance?

Infectious disease (ID) physicians and ID pharmacists commonly confront therapeutic questions relating to antibiotic resistance. Randomized controlled trial data are few and meta-analytic-based approaches to develop the evidence-base from several small studies that might relate to an antibiotic resistance question are not simple. The overriding challenge is the sparsity of data which is problematic for traditional frequentist methods, being the paradigm underlying the derivation of ‘P value’ inferential statistics. In other sparse data contexts, simulation methods enable answers to key questions that are meaningful, quantitative and potentially relevant. How these simulation methods ‘work’ and how Bayesian-based methods, being not ‘P value based’, can facilitate simulation are reviewed. These methods are becoming increasingly accessible. This review highlights why sparse data is less of an issue within Bayesian versus frequentist paradigms. A fictional pharmacokinetic study with sparse data illustrates a simplistic application of Bayesian and simulation methods to antibiotic dosing. Whether within epidemiological projections or clinical studies, simulation methods are likely to play an increasing role in antimicrobial resistance research within both hospital and community studies of either rare infectious disease or infections within specific population groups.

CD11b Deficiency Exacerbates Methicillin-Resistant Staphylococcus aureus-Induced Sepsis by Upregulating Inflammatory Responses of Macrophages

Macrophages are important for the first line of defense against microbial pathogens. Integrin CD11b, which is encoded by Itgam, is expressed on the surface of macrophages and has been implicated in adhesion, migration, and cell-mediated cytotoxicity. However, the functional impact of CD11b on the inflammatory responses of macrophages upon microbial infection remains unclear. Here, we show that CD11b deficiency resulted in increased susceptibility to sepsis induced by methicillin-resistant Staphylococcus aureus (MRSA) infection by enhancing the pro-inflammatory activities of macrophages. Upon infection with MRSA, the mortality of Itgam knockout mice was significantly higher than that of control mice, which is associated with increased production of TNF-α and IL-6. In response to MRSA, both bone marrow-derived macrophages and peritoneal macrophages lacking CD11b produced elevated amounts of pro-inflammatory cytokines and nitric oxide. Moreover, CD11b deficiency upregulated IL-4-induced expression of anti-inflammatory mediators such as IL-10 and arginase-1, and an immunomodulatory function of macrophages to restrain T cell activation. Biochemical and confocal microscopy data revealed that CD11b deficiency augmented the activation of NF-κB signaling and phosphorylation of Akt, which promotes the functional activation of macrophages with pro-inflammatory and immunoregulatory phenotypes, respectively. Overall, our experimental evidence suggests that CD11b is a critical modulator of macrophages in response to microbial infection.

Intravenous to oral switch in complicated Staphylococcus aureus bacteremia without endovascular infection: a retrospective single-center cohort study

In this retrospective cohort study, selected patients with disseminated Staphylococcus aureus bacteremia, but without endovascular infection on echocardiography and ¹⁸F-FDG-PET/CT, were free of relapse after IV-oral switch. Mortality was low and similar to patients who received prolonged intravenous treatment. IV-oral switch was associated with a shorter length of hospital stay.

Recurrent Infective Endocarditis with Mycotic Aneurysm - Imaging Modalities for the Detection of an Infective Focus

Staphylococcus aureus bacteremia (SAB) and infective endocarditis (IE) are infections associated with considerable morbidity, requiring prompt accurate diagnosis and treatment. We present a case of a 58-year-old male patient with four episodes of recurrent symptomatic SAB treated for IE, but without positive findings on transthoracic echocardiography, transesophageal echocardiography, and fluorodeoxyglucose-positron emission tomography (FDG-PET). On the last admission, FDG-PET showed increased uptake in the right atrial appendage, and white blood cell single-photon emission computerized tomography (WBC-SPECT) was able to identify the infective focus as IE of the aortic valve. CT of the thorax also identified an associated mycotic aneurysm of the right coronary sinus. He was subsequently treated with mechanical aortic prosthesis and right coronary sinus plasty, and his symptoms did not recur till 2 years postcardiothoracic surgery. This case report demonstrates the emergence of nuclear cardiovascular imaging modalities in the diagnostic workup of IE and the utility of FDG-PET and WBC-SPECT in the identification of the infective focus. Patients with possible IE from the modified Duke criteria should be considered for FDG-PET or WBC-SPECT to enhance sensitivity. Peripheral mycotic aneurysms are a common complication of left-sided IE, which can present late into the disease process, and aortic imaging should be considered in patients with recurrent endocarditis to identify this.

Early differentiation between uncomplicated and complicated Staphylococcus aureus bacteraemia: Potential value and limitations of a clinical risk score

OBJECTIVE

A cornerstone in the management of Staphylococcus aureus bacteraemia (SAB) is the differentiation between a complicated and an uncomplicated SAB course. The ability to early and accurately identify patients with - and without - complicated bacteraemia may optimise the utility of diagnostics and prevent unnecessary prolonged antibiotic therapy.

METHODS

Development and validation of a prediction score in SAB using demographic, clinical, and laboratory data from two independent Dutch cohorts; estimating the risk of complicated disease at the time of the first positive blood culture. Models were developed using logistic regression and evaluated by c-statistics, ie area under the ROC-curve, and negative predictive values (NPV).

RESULTS

The development- and validation cohorts included 150 and 183 patients, respectively. The most optimal prediction model included: mean arterial pressure, signs of metastatic infection on physical examination, leucocyte count, urea level and time to positivity of blood cultures (c-statistic 0.82, 95% CI 0.74-0.89). In the validation cohort, the c-statistic of the prediction score was 0,77 (95% CI 0.69-0.84). The NPV for complicated disease for patients with a score of ≤2 was 0.83 (95% CI 0.68-0.92), with a negative likelihood ratio of 0.14 (95% CI 0.06-0.31).

CONCLUSION

The early SAB risk score helps to identify patients with high probability of uncomplicated SAB. However, the risk score's lacked absolute discriminative power to guide decisions on the management of all patients with SAB on its own. The heterogenicity of the disease and inconsistency in definitions of complicated SAB are important challenges in the development of clinical rules to guide the management of SAB.

Australian Group on Antimicrobial Resistance (AGAR) Australian Staphylococcus aureus Sepsis Outcome Programme (ASSOP) Annual Report 2019

From 1 January to 31 December 2019, 39 institutions around Australia participated in the Australian Staphylococcus aureus Sepsis Outcome Programme (ASSOP). The aim of ASSOP 2019 was to determine the proportion of Staphylococcus aureus bacteraemia (SAB) isolates in Australia that are antimicrobial resistant, with particular emphasis on susceptibility to methicillin and on characterising the molecular epidemiology of the methicillin-resistant isolates. A total of 3,157 S. aureus bacteraemia episodes were reported, of which 79.8% were community-onset. 18.5% of S. aureus were methicillin resistant. The 30-day all-cause mortality associated with methicillin-resistant SAB was 14.0%, which was not significantly different from the 14.3% mortality associated with methicillin-susceptible SAB (p = 0.9). With the exception of the β-lactams and erythromycin, antimicrobial resistance in methicillin-susceptible S. aureus was rare. However, in addition to the β-lactams, approximately 36% of methicillin-resistant S. aureus (MRSA) were resistant to ciprofloxacin, 34% to erythromycin, 13% to tetracycline, 9% to gentamicin and 4% to co-trimoxazole. When applying the EUCAST breakpoints, teicoplanin resistance was detected in two S. aureus isolates. Resistance was not detected for vancomycin and linezolid. Resistance to non-beta-lactam antimicrobials was largely attributable to two healthcare-associated MRSA clones: ST22-IV [2B] (EMRSA-15) and ST239-III [3A] (Aus-2/3 EMRSA). ST22-IV [2B] (EMRSA-15) is the predominant healthcare-associated clone in Australia. Eighty percent of methicillin-resistant SAB, however, were due to community-associated clones. Although polyclonal, approximately 71.4% of community-associated clones were variously characterised as ST93-IV [2B] (Queensland CA-MRSA), ST5-IV [2B], ST45-V_T [5C2&5], ST1-IV [2B], ST30-IV [2B], ST78-IV [2B] and ST8-IV [2B]. Community-associated MRSA (CA-MRSA), in particular the ST45-V_T [5C2&5] clone, have acquired multiple antimicrobial resistance determinants including ciprofloxacin, erythromycin, clindamycin, gentamicin and tetracycline. The multiresistant ST45-V_T [5C2&5] clone accounted for 12.7% of CA-MRSA. As CA-MRSA is well established in the Australian community, it is important that antimicrobial resistance patterns in community- and healthcare-associated SAB are monitored, as this information will guide therapeutic practices in treating S. aureus sepsis.

Molecular Detection of Panton Valentine Leukocidin Toxin in Clinical Isolates of Staphylococcus aureus from Kiambu County, Kenya

Panton-Valentine leukocidin gene is produced by Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus isolates as a pore-forming toxin is largely responsible for skin and soft tissue illnesses. MRSA produces PVL toxins through lukS and lukF proteins causing tissue necrosis by damaging membrane of the defense cells. Presence of PVL toxin was tested from the 54 S. aureus clinical isolates obtained from Thika and Kiambu Level 5 Hospitals, in Kiambu County, Kenya, by Geno Type® MRSA assay (Hain Life Science, Nehren, Germany). DNA was isolated from freshly harvested bacterial cultures by spin column using Geno Type DNA isolation kit. The detection of PVL toxins was performed by amplification of genomic DNA and by reverse hybridization that identifies PVL genes using Geno Type MRSA kit. Out of 138 samples that were collected from patients in Kiambu County, 54 S. aureus isolates were obtained, of which 14 (25.9%; 95% CI = 11.9-38.9) samples had PVL toxins. The isolates that were obtained from the female patients had a higher PVL toxin prevalence of 35.7%, while the isolates collected from the male patients had a lower prevalence of 15.4% (P = 0.09). The pediatrics department had the highest PVL gene prevalence compared to outpatient department and surgical units (P = 0.08). However, the age groups of patients and the hospital attended by patients showed no significant difference in terms of PVL gene prevalence (P = 0.26). Therefore, the patients' gender and hospital units were not significantly associated with PVL gene prevalence (P = 0.08). This study shows that PVL positive isolates occur in the sampled hospitals in the county and female as well as children must be taken into consideration among patients with wound infections when isolating S. aureus.

Outcomes of Outpatient Parenteral Antimicrobial Therapy With Ceftriaxone for Methicillin-Susceptible Staphylococcus aureus Bloodstream Infections-A Single-Center Observational Study

Background

Staphylococcus aureus bloodstream infections (BSIs) are associated with significant morbidity and mortality. Ceftriaxone is convenient for outpatient parenteral antimicrobial therapy (OPAT), but data for this indication are limited.

Methods

Adult patients with methicillin-susceptible Staphylococcus aureus (MSSA) BSI discharged on OPAT with cefazolin, oxacillin, or ceftriaxone for at least 7 days were included. We compared outcomes of ceftriaxone vs either oxacillin or cefazolin. Ninety-day all-cause mortality, readmission due to MSSA infection, and microbiological failure were examined as a composite outcome and compared among groups. Rates of antibiotic switches due to intolerance were assessed.

Results

Of 243 patients included, 148 (61%) were discharged on ceftriaxone and 95 (39%) were discharged on either oxacillin or cefazolin. The ceftriaxone group had lower rates of intensive care unit care, endocarditis, and shorter duration of bacteremia, but higher rates of cancer diagnoses. There was no significant difference in the composite adverse outcome in the oxacillin or cefazolin group vs the ceftriaxone group (18 [19%] vs 31 [21%]; P = .70), comprising microbiological failure (6 [6.3%] vs 9 [6.1%]; P = .94), 90-day all-cause mortality (7 [7.4%] vs 15 [10.1%]; P = .46), and readmission due to MSSA infection (10 [10.5%] vs 13 [8.8%]; P = .65). Antibiotic intolerance necessitating a change was similar between the 2 groups (4 [4.2%] vs 6 [4.1%]; P = .95).

Conclusions

For patients with MSSA BSI discharged on OPAT, within the limitations of the small numbers and retrospective design we did not find a significant difference in outcomes for ceftriaxone therapy when compared with oxacillin or cefazolin therapy.