Publisher Correction: SERPINB1-mediated checkpoint of inflammatory caspase activation.

In the version of this article initially published, the label (CASP4-C285A-HA) above the second and fifth lanes in the right blot in Fig. 1e is incorrect; the correct label is CASP4-C258A-HA. Also, the two labels at right above the plot in Fig. 6c were switched; the far right label should be 'Co-housed Serpinb1a-/-' (in red font) and the label just to its left (above the fourth column) should be 'Co-housed WT' (in black font). Finally, the bottom two symbols in the key to Fig. 7d were switched; the red circle should identify 1CARD-SUMO (TEV) and the blue triangle should identify 1CARD-SUMO + SERPINB1 (TEV). The errors have been corrected in the HTML and PDF versions of the article.

SERPINB1-mediated checkpoint of inflammatory caspase activation.

Inflammatory caspases (caspase-1, caspase-4, caspase-5 and caspase-11 (caspase-1/-4/-5/-11)) mediate host defense against microbial infections, processing pro-inflammatory cytokines and triggering pyroptosis. However, precise checkpoints are required to prevent their unsolicited activation. Here we report that serpin family B member 1 (SERPINB1) limited the activity of those caspases by suppressing their caspase-recruitment domain (CARD) oligomerization and enzymatic activation. While the reactive center loop of SERPINB1 inhibits neutrophil serine proteases, its carboxy-terminal CARD-binding motif restrained the activation of pro-caspase-1/-4/-5/-11. Consequently, knockdown or deletion of SERPINB1 prompted spontaneous activation of caspase-1/-4/-5/-11, release of the cytokine IL-1ß and pyroptosis, inducing elevated inflammation after non-hygienic co-housing with pet-store mice and enhanced sensitivity to lipopolysaccharide- or Acinetobacter baumannii-induced endotoxemia. Our results reveal that SERPINB1 acts as a vital gatekeeper of inflammation by restraining neutrophil serine proteases and inflammatory caspases in a genetically and functionally separable manner.

Population pharmacokinetics and humanized dosage regimens matching the peak, area, trough, and range of amikacin plasma concentrations in immune-competent murine bloodstream and lung infection models.

Amikacin is an FDA-approved aminoglycoside antibiotic that is commonly used. However, validated dosage regimens that achieve clinically relevant exposure profiles in mice are lacking. We aimed to design and validate humanized dosage regimens for amikacin in immune-competent murine bloodstream and lung infection models of Acinetobacter baumannii. Plasma and lung epithelial lining fluid (ELF) concentrations after single subcutaneous doses of 1.37, 13.7, and 137 mg/kg of body weight were simultaneously modeled via population pharmacokinetics. Then, humanized amikacin dosage regimens in mice were designed and prospectively validated to match the peak, area, trough, and range of plasma concentration profiles in critically ill patients (clinical dose: 25-30 mg/kg of body weight). The pharmacokinetics of amikacin were linear, with a clearance of 9.93 mL/h in both infection models after a single dose. However, the volume of distribution differed between models, resulting in an elimination half-life of 48 min for the bloodstream and 36 min for the lung model. The drug exposure in ELF was 72.7% compared to that in plasma. After multiple q6h dosing, clearance decreased by ~80% from the first (7.35 mL/h) to the last two dosing intervals (~1.50 mL/h) in the bloodstream model. Likewise, clearance decreased by 41% from 7.44 to 4.39 mL/h in the lung model. The humanized dosage regimens were 117 mg/kg of body weight/day in mice [administered in four fractions 6 h apart (q6h): 61.9%, 18.6%, 11.3%, and 8.21% of total dose] for the bloodstream and 96.7 mg/kg of body weight/day (given q6h as 65.1%, 16.9%, 10.5%, and 7.41%) for the lung model. These validated humanized dosage regimens and population pharmacokinetic models support translational studies with clinically relevant amikacin exposure profiles.

Development of a Bispecific Antibody Targeting Clinical Isolates of Acinetobacter baumannii.

BACKGROUND: We previously reported developing 2 anticapsular monoclonal antibodies (mAbs) as a novel therapy for Acinetobacter baumannii infections. We sought to determine whether a bispecific mAb (bsAb) could improve avidity and efficacy while maximizing strain coverage in one molecule. METHODS: Humanized mAb 65 was cloned into a single-chain variable fragment and attached to humanized mAb C8, combining their paratopes into a single bsAb (C73). We tested bsAb C73's strain coverage, binding affinity, ex vivo opsonic activity, and in vivo efficacy compared to each mAb alone and combined. RESULTS: The bsAb demonstrated strain coverage, binding affinity, opsonization, and in vivo efficacy superior to either original mAb alone or combined. CONCLUSIONS: A humanized bsAb targeting distinct A. baumannii capsule moieties enabled potent and effective coverage of disparate A. baumannii clinical isolates. The bsAb enhances feasibility of development by minimizing the number of components of a promising novel therapeutic for these difficult-to-treat infections.

Real-World Application of Oral Therapy for Infective Endocarditis: A Multicenter, Retrospective, Cohort Study.

BACKGROUND: We sought to compare the outcomes of patients treated with intravenous (IV)-only vs oral transitional antimicrobial therapy for infective endocarditis (IE) after implementing a new expected practice within the Los Angeles County Department of Health Services (LAC DHS). METHODS: We conducted a multicentered, retrospective cohort study of adults with definite or possible IE treated with IV-only vs oral therapy at the 3 acute care public hospitals in the LAC DHS system between December 2018 and June 2022. The primary outcome was clinical success at 90 days, defined as being alive and without recurrence of bacteremia or treatment-emergent infectious complications. RESULTS: We identified 257 patients with IE treated with IV-only (n = 211) or oral transitional (n = 46) therapy who met study inclusion criteria. Study arms were similar for many demographics; however, the IV cohort was older, had more aortic valve involvement, were hemodialysis patients, and had central venous catheters present. In contrast, the oral cohort had a higher percentage of IE caused by methicillin-resistant Staphylococcus aureus. There was no significant difference between the groups in clinical success at 90 days or last follow-up. There was no difference in recurrence of bacteremia or readmission rates. However, patients treated with oral therapy had significantly fewer adverse events. Multivariable regression adjustments did not find significant associations between any selected variables and clinical success across treatment groups. CONCLUSIONS: These results demonstrate similar outcomes of real-world use of oral vs IV-only therapy for IE, in accord with prior randomized, controlled trials and meta-analyses.

Antimicrobial Susceptibility Testing Performed in RPMI 1640 Reveals Azithromycin Efficacy against Carbapenem-Resistant Acinetobacter baumannii and Predicts In Vivo Outcomes in Galleria mellonella.

Antimicrobial susceptibility testing (AST) in RPMI 1640, a more physiologically relevant culture medium, revealed that a substantial proportion of carbapenem-resistant Acinetobacter baumannii isolates were susceptible to azithromycin, a macrolide antibiotic not currently considered effective against A. baumannii. Experiments using Galleria mellonella validated these in vitro data. Our finding that RPMI 1640's predictive accuracy for in vivo outcomes is superior to that of Mueller-Hinton II broth also supports the use of more physiologically relevant AST culturing conditions.

Therapeutic, Humanized Monoclonal Antibody Exhibits Broad Binding and Protective Efficacy against Acinetobacter baumannii.

Acinetobacter baumannii is an extremely drug-resistant pathogen necessitating the development of new therapies. We seek to generate a cocktail of monoclonal antibodies (MAbs) that can target the full diversity of A. baumannii isolates. We have newly identified the antibody MAb5. Here, we demonstrate that MAb5 has broad binding against U.S. (n = 300) and international (n = 250) isolates (72.24% and 28.76%, respectively), likely targets O-antigen capsular carbohydrates, and exhibits protective efficacy in vivo.

Individual Components of Polymyxin B Modeled via Population Pharmacokinetics to Design Humanized Dosage Regimens for a Bloodstream and Lung Infection Model in Immune-Competent Mice.

Polymyxin B is a "last-line-of-defense" antibiotic approved in the 1960s. However, the population pharmacokinetics (PK) of its four main components has not been reported in infected mice. We aimed to determine the PK of polymyxin B1, B1-Ile, B2, and B3 in a murine bloodstream and lung infection model of Acinetobacter baumannii and develop humanized dosage regimens. A linear 1-compartment model, plus an epithelial lining fluid (ELF) compartment for the lung model, best described the PK. Clearance and volume of distribution were similar among the four components. The bioavailability fractions were 72.6% for polymyxin B1, 12.0% for B1-Ile, 11.5% for B2, and 3.81% for B3 for the lung model and were similar for the bloodstream model. While the volume of distribution was comparable between both models (17.3 mL for the lung and ~27 mL for the bloodstream model), clearance was considerably smaller for the lung (2.85 mL/h) compared to that of the bloodstream model (5.59 mL/h). The total drug exposure (AUC) in ELF was high due to the saturable binding of polymyxin B presumably to bacterial lipopolysaccharides. However, the modeled unbound AUC in ELF was ~16.7% compared to the total drug AUC in plasma. The long elimination half-life (~4 h) of polymyxin B enabled humanized dosage regimens with every 12 h dosing in mice. Daily doses that optimally matched the range of drug concentrations observed in patients were 21 mg/kg for the bloodstream and 13 mg/kg for the lung model. These dosage regimens and population PK models support translational studies for polymyxin B at clinically relevant drug exposures.

Capsule carbohydrate structure determines virulence in Acinetobacter baumannii.

Acinetobacter baumannii is a highly antibiotic-resistant bacterial pathogen for which novel therapeutic approaches are needed. Unfortunately, the drivers of virulence in A. baumannii remain uncertain. By comparing genomes among a panel of A. baumannii strains we identified a specific gene variation in the capsule locus that correlated with altered virulence. While less virulent strains possessed the intact gene gtr6, a hypervirulent clinical isolate contained a spontaneous transposon insertion in the same gene, resulting in the loss of a branchpoint in capsular carbohydrate structure. By constructing isogenic gtr6 mutants, we confirmed that gtr6-disrupted strains were protected from phagocytosis in vitro and displayed higher bacterial burden and lethality in vivo. Gtr6+ strains were phagocytized more readily and caused lower bacterial burden and no clinical illness in vivo. We found that the CR3 receptor mediated phagocytosis of gtr6+, but not gtr6-, strains in a complement-dependent manner. Furthermore, hypovirulent gtr6+ strains demonstrated increased virulence in vivo when CR3 function was abrogated. In summary, loss-of-function in a single capsule assembly gene dramatically altered virulence by inhibiting complement deposition and recognition by phagocytes across multiple A. baumannii strains. Thus, capsular structure can determine virulence among A. baumannii strains by altering bacterial interactions with host complement-mediated opsonophagocytosis.

Characteristics and Outcomes of 360 Consecutive COVID-19 Patients Discharged From the Emergency Department With Supplemental Oxygen.

STUDY OBJECTIVE: To describe characteristics and outcomes of coronavirus disease (COVID-19) patients with new supplemental oxygen requirements discharged from a large public urban emergency department (ED) with supplemental oxygen. METHODS: This observational case series describes the characteristics and outcomes of 360 consecutive COVID-19 patients with new supplemental oxygen requirements discharged from a large urban public ED between April 2020 and March 2021 with supplemental oxygen. Primary outcomes included 30-day survival and 30-day survival without unscheduled inpatient admission. Demographic and clinical data were collected through a structured chart review. RESULTS: Among 360 patients with COVID-19 discharged from the ED with supplemental oxygen, 30-day survival was 97.5% (95% confidence interval (CI) 95.3 to 98.9%; n=351), and 30-day survival without unscheduled admission was 81.1% (95% CI 76.7 to 85.0%; n=292). A sensitivity analysis incorporating worst-case-scenario for 12 patients without complete follow-up 30 days after index visit yields 30-day survival of 95.5% (95% CI 92.5 to 97.2%; n=343), and 30-day survival without unscheduled admission of 78.9% (95% CI 74.3 to 83.0%; n=284). Among study patients, 32.2% (n=116) had a nadir ED oxygen saturation of <90%, among these 30-day survival was 97.4% (95% CI 92.6 to 99.4%; n=113), and 30-day survival without unscheduled admission was 76.7% (95% CI 68.8 to 84.1%; n=89). CONCLUSION: COVID-19 patients with new supplemental oxygen requirements discharged from the ED had survival comparable to COVID-19 ED patients with mild exertional hypoxia treated with supplemental oxygen in other settings, and this held true when the analysis was restricted to patients with nadir ED index visit oxygen saturations <90%. Discharge of select COVID-19 patients with supplemental oxygen from the ED may provide a viable alternative to hospitalization, particularly when inpatient capacity is limited.

Effect of mortality from COVID-19 on inpatient outcomes.

When hospitals first encountered coronavirus disease 2019 (COVID-19), there was a dearth of therapeutic options and nearly 1 in 3 patients died from the disease. By the summer of 2020, as deaths from the disease declined nationally, multiple single-center studies began to report declining mortality of patients with COVID-19. To evaluate the effect of COVID-19 on hospital-based mortality, we searched the Vizient Clinical Data Base for outcomes data from approximately 600 participating hospitals, including 130 academic medical centers, from January 2017 through December 2020. More than 32 million hospital admissions were included in the analysis. After an initial spike, mortality from COVID-19 declined in all regions of the country to under 10% by June 2020 and remained constant for the remainder of the year. Despite this, inpatient, all-cause mortality has increased since the beginning of the pandemic, even those without respiratory failure. Inpatient mortality has particularly increased in elderly patients and in those requiring intubation for respiratory failure. Since June 2020, COVID-19 kills one in every 10 patients admitted to the hospital with this diagnosis. The addition of this new disease has raised overall hospital mortality especially those who require intubation for respiratory failure.

Shorter is better: The case for short antibiotic courses for common infections in solid organ transplant recipients.

BACKGROUND: Prolonged antibiotics are associated with toxicity, selection for resistant organisms, and secondary infections such as Clostridioides difficile colitis. Emerging clinical data suggest that short courses of antibiotics can be used for common bacterial infections among immune competent patients, but for many randomized controlled trials (RCTs), immunocompromised patients, including solid organ transplant recipients (SOTRs), have been excluded. METHODS: Peer-reviewed publications were identified through PubMed and Embase searches. RESULTS: We review data examining shorter antibiotic courses among immunocompetent and immunocompromised patients and the rationale for use of short antibiotic courses in SOTRs. CONCLUSION: There are known harms associated with antibiotics and, when studied, existing data do not demonstrate harm associated with shorter courses of antibiotics among SOTRs. Furthermore, several RCTs did include some immune compromised patients and found shorter therapy to result in similar clinical efficacy with diminished adverse effects. Shorter antibiotic durations should be considered in SOTRs, and questions of antibiotic duration among SOTRs should be prioritized for study in clinical trials.

Monoclonal Antibody Requires Immunomodulation for Efficacy Against Acinetobacter baumannii Infection.

Monoclonal antibodies (mAbs) are gaining significant momentum as novel therapeutics for infections caused by antibiotic-resistant bacteria. We evaluated the mechanism by which antibacterial mAb therapy protects against Acinetobacter baumannii infections. Anticapsular mAb enhanced macrophage opsonophagocytosis and rescued mice from lethal infections by harnessing complement, macrophages, and neutrophils; however, the degree of bacterial burden did not correlate with survival. Furthermore, mAb therapy reduced proinflammatory (interleukin-1ß [IL-1ß], IL-6, tumor necrosis factor-α [TNF-α]) and anti-inflammatory (IL-10) cytokines, which correlated inversely with survival. Although disrupting IL-10 abrogated the survival advantage conferred by the mAb, IL-10-knockout mice treated with mAb could still survive if TNF-α production was suppressed directly (via anti-TNF-α neutralizing antibody) or indirectly (via macrophage depletion). Thus, even for a mAb that enhances microbial clearance via opsonophagocytosis, clinical efficacy required modulation of pro- and anti-inflammatory cytokines. These findings may inform future mAb development targeting bacteria that trigger the sepsis cascade.

Monoclonal Antibody Therapy against Acinetobacter baumannii.

Extremely drug-resistant (XDR) Acinetobacter baumannii is a notorious and frequently encountered pathogen demanding novel therapeutic interventions. An initial monoclonal antibody (MAb), C8, raised against A. baumannii capsule, proved a highly effective treatment against a minority of clinical isolates. To overcome this limitation, we broadened coverage by developing a second antibody for use in a combination regimen. We sought to develop an additional anti-A. baumannii MAb through hybridoma technology by immunizing mice with sublethal inocula of virulent, XDR clinical isolates not bound by MAb C8. We identified a new antibacterial MAb, 65, which bound to strains in a pattern distinct from and complementary to that of MAb C8. MAb 65 enhanced macrophage opsonophagocytosis of targeted strains and markedly improved survival in lethal bacteremic sepsis and aspiration pneumonia murine models of A. baumannii infection. MAb 65 was also synergistic with colistin, substantially enhancing protection compared to monotherapy. Treatment with MAb 65 significantly reduced blood bacterial density, ameliorated cytokine production (interleukin-1ß [IL-1ß], IL-6, IL-10, and tumor necrosis factor), and sepsis biomarkers. We describe a novel MAb targeting A. baumannii that broadens immunotherapeutic strain coverage, is highly potent and effective, and synergistically improves outcomes in combination with antibiotics.

Should Therapeutic Drug Monitoring Based on the Vancomycin Area Under the Concentration-Time Curve Be Standard for Serious Methicillin-Resistant Staphylococcus aureus Infections?-No.

In this counterpoint we critically appraise the evidence supporting therapeutic drug monitoring based on the vancomycin 24-hour area under the concentration-time curve (AUC24) for serious methicillin-resistant Staphylococcus aureus infections. We reveal methodologically weaknesses and inconsistencies in the data and suggest that, in the absence of clear and convincing evidence of benefit compared with modestly reducing trough targets, alternative strategies are more likely to result in superior safety and efficacy. These include focusing on fundamental antibiotic stewardship to limit vancomycin exposure overall, achieving earlier and more complete source control, and establishing alternative therapeutic options to vancomycin. Implementation of AUC24-based therapeutic drug monitoring will take resources away from these more promising, alternative solutions.

Reducing Catheter-associated Urinary Tract Infections via Cost-saving Diagnostic Stewardship.

We conducted a quality improvement project at our large, public, tertiary-care, academic hospital to reduce the standardized infection ratio (SIR) of hospital-acquired catheter-associated urinary tract infections (CAUTIs). Our diagnostic stewardship program, based on education and audit and feedback, significantly reduced inpatient urine culture orders and CAUTI SIR.

Synergistic Rifabutin and Colistin Reduce Emergence of Resistance When Treating Acinetobacter baumannii.

Recently, we reported rifabutin hyperactivity against Acinetobacter baumannii We sought to characterize potential interactions between rifabutin and colistin, the last-resort drug for carbapenem-resistant infections. Rifabutin and colistin were synergistic in vitro and in vivo, and low-dose colistin significantly suppressed emergence of resistance to rifabutin. Thus, this combination is a promising therapeutic option for highly resistant A. baumannii infections.

Defining the Breakpoint Duration of Staphylococcus aureus Bacteremia Predictive of Poor Outcomes.

BACKGROUND: Persistent Staphylococcus aureus bacteremia (SAB) is defined based on varying duration in literature. The primary objective was to determine the risk of poor outcomes in relation to bacteremia duration. METHODS: Multicenter, prospective, observational study of adult hospitalized patients with SAB. Medical records were reviewed for pertinent data. Patients were grouped by bacteremia duration: short (1-2 days), intermediate (3-6 days), and prolonged (≥7 days) and compared for risk factors and outcomes. RESULTS: Of 884 patients, 63% had short, 28% intermediate, and 9% prolonged bacteremia. Overall mean age was 57 years, and 70% were male. The prolonged group had the highest proportion of methicillin-resistant SAB (P < .0001). Choice of antibiotic therapy did not significantly affect bacteremia duration; however, time to source-control procedure was delayed in the prolonged and intermediate groups compared with the short group (3.5 vs 3 vs 1 day, P < .0001). Metastatic complications, length of stay, and 30-day mortality were progressively worse as bacteremia duration increased (P < .0001). Every continued day of bacteremia was associated with a relative risk of death of 1.16 (95% confidence interval, 1.10-1.22; P < .0001), with a significant increase in risk starting at 3 days as determined by receiver operating characteristic analysis. CONCLUSIONS: Optimal management of SAB should target bacterial clearance as soon as possible to minimize incremental risk of mortality with each day of positive blood culture. Delay in source control but not type of antistaphylococcal therapy was significantly associated with prolonged bacteremia and worse outcomes.

Osteomyelitis Complicating Sacral Pressure Ulcers: Whether or Not to Treat With Antibiotic Therapy.

The treatment of osteomyelitis in patients with stage IV sacral pressure ulcers is controversial. We conducted a systematic literature review and did not find evidence of benefit of antibacterial therapy in this setting without concomitant surgical debridement and wound coverage. Furthermore, many patients with chronically exposed bone do not have evidence of osteomyelitis when biopsied, and magnetic resonance imaging may not accurately distinguish osteomyelitis from bone remodeling. The goal of therapy should be local wound care and assessment for the potential of wound closure. If the wound can be closed and osteomyelitis is present on bone biopsy, appropriate antibiotic therapy is reasonable. We find no data to support antibiotic durations of >6 weeks in this setting, and some authors recommend 2 weeks of therapy if the osteomyelitis is limited to cortical bone. If the wound will not be closed, we find no clear evidence supporting a role for antibiotic therapy.

Rapid and Extensive Expansion in the United States of a New Multidrug-resistant Escherichia coli Clonal Group, Sequence Type 1193.

We describe the rapid and ongoing emergence across multiple US cities of a new multidrug-resistant Escherichia coli clone-sequence type (ST) 1193-resistant to fluoroquinolones (100%), trimethoprim-sulfamethoxazole (55%), and tetracycline (53%). ST1193 is associated with younger adults (age <40 years) and currently comprises a quarter of fluoroquinolone-resistant clinical E. coli urine isolates.