Staphylococcus Aureus Pneumonia

Complex Involvement of Interleukin-26 in Bacterial Lung Infection

Pneumonia is a global cause of mortality, and this provides a strong incentive to improve the mechanistic understanding of innate immune responses in the lungs. Here, we characterized the involvement of the cytokine interleukin (IL)-26 in bacterial lung infection. We observed markedly increased concentrations of IL-26 in lower airway samples from patients with bacterial pneumonia and these correlated with blood neutrophil concentrations. Moreover, pathogen-associated molecular patterns (PAMPs) from both Gram-negative and -positive bacteria increased extracellular IL-26 concentrations in conditioned media from human models of alveolar epithelial cells, macrophages, and neutrophils in vitro. Stimulation with IL-26 inhibited the inherent release of neutrophil elastase and myeloperoxidase in unexposed neutrophils. This stimulation also inhibited the expression of activity makers in neutrophils exposed to Klebsiella pneumoniae. In addition, priming of human lung tissue ex vivo with exogenous IL-26 potentiated the endotoxin-induced increase in mRNA for other cytokines involved in the innate immune response, including the master Th17-regulator IL-23 and the archetype inhibitory cytokine IL-10. Finally, neutralization of endogenous IL-26 clearly increased the growth of Klebsiella pneumoniae in the macrophage culture. These findings suggest that IL-26 is involved in bacterial lung infection in a complex manner, by modulating critical aspects of innate immune responses locally and systemically in a seemingly purposeful manner and by contributing to the killing of bacteria in a way that resembles an antimicrobial peptide. Thus, IL-26 displays both diagnostic and therapeutic potential in pneumonia and deserves to be further evaluated in these respects.

Exploring Virulence Factors and Alternative Therapies against Staphylococcus aureus Pneumonia

Pneumonia is an acute pulmonary infection associated with high mortality and an immense financial burden on healthcare systems. Staphylococcus aureus is an opportunistic pathogen capable of inducing S. aureus pneumonia (SAP), with some lineages also showing multidrug resistance. Given the high level of antibiotic resistance, much research has been focused on targeting S. aureus virulence factors, including toxins and biofilm-associated proteins, in an attempt to develop effective SAP therapeutics. Despite several promising leads, many hurdles still remain for S. aureus vaccine research. Here, we review the state-of-the-art SAP therapeutics, highlight their pitfalls, and discuss alternative approaches of potential significance and future perspectives.

A retrospective study (2001-2017) of acute and chronic morbidity and mortality associated with Staphylococcus aureus bacteraemia in a tertiary neonatal intensive care unit

BACKGROUND

Staphylococcus aureus bacteraemia (SAB) in NICU patients can cause significant morbidity and mortality.

AIMS

To review early and late neonatal SAB with regard to risk factors, treatment, acute complications and long-term outcomes.

METHODS

A retrospective study of laboratory confirmed SAB over a 16-year period (November 2001-January 2017) in a tertiary neonatal unit in Ireland.

FINDINGS

A total of 74 neonates (MSSA n = 72, MRSA n = 2) were identified; 8.1% (n = 6) early sepsis, 91.8% (n = 68) late sepsis. Low birth weight neonates (born weighing less than 2500 g) 80% (n = 59). Median age to bacteraemia 11 days post-delivery (range = 0-100 days); median onset early sepsis 1.5 days versus late sepsis 12 days. Complications of SAB; cellulitis n = 17, pneumonia n = 12, necrotising enterocolitis n = 7, thromobophlebitis n = 5, skin abscess formation n = 4, osteomyelitis n = 3, endocarditis n = 1. Late SAB mortality 6.4% (n = 3).

CONCLUSIONS

Preterm and low birth weight infants were at highest risk of SAB. Only a small proportion of affected children had long-term clinical sequelae on follow-up. The high rate of recurrence and breakthrough bacteraemia suggests that early implementation of a targeted anti-staphylococcal antimicrobial regimen may be of particular benefit.

Staphylococcus aureus Community-acquired Pneumonia: Prevalence, Clinical Characteristics, and Outcomes

BACKGROUND

Prevalence of Staphylococcus aureus community-acquired pneumonia (CAP) and its clinical features remain incompletely understood, complicating empirical selection of antibiotics.

METHODS

Using a multicenter, prospective surveillance study of adults hospitalized with CAP, we calculated the prevalence of methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) among all CAP episodes. We compared the epidemiologic, radiographic, and clinical characteristics of S. aureus CAP (per respiratory or blood culture) with those of pneumococcal (per respiratory or blood culture or urine antigen) and all-cause non-S. aureus CAP using descriptive statistics.

RESULTS

Among 2259 adults hospitalized for CAP, 37 (1.6%) had S. aureus identified, including 15 (0.7%) with MRSA and 22 (1.0%) with MSSA; 115 (5.1%) had Streptococcus pneumoniae Vancomycin or linezolid was administered to 674 (29.8%) patients within the first 3 days of hospitalization. Chronic hemodialysis use was more common among patients with MRSA (20.0%) than pneumococcal (2.6%) and all-cause non-S. aureus (3.7%) CAP. Otherwise, clinical features at admission were similar, including concurrent influenza infection, hemoptysis, multilobar infiltrates, and prehospital antibiotics. Patients with MRSA CAP had more severe clinical outcomes than those with pneumococcal CAP, including intensive care unit admission (86.7% vs 34.8%) and in-patient mortality (13.3% vs 4.4%).

CONCLUSIONS

Despite very low prevalence of S. aureus and, specifically, MRSA, nearly one-third of adults hospitalized with CAP received anti-MRSA antibiotics. The clinical presentation of MRSA CAP overlapped substantially with pneumococcal CAP, highlighting the challenge of accurately targeting empirical anti-MRSA antibiotics with currently available clinical tools and the need for new diagnostic strategies.

Staphylococcal enterotoxin A regulates bone marrow granulocyte trafficking during pulmonary inflammatory disease in mice

Pulmonary neutrophil infiltration produced by Staphylococcal enterotoxin A (SEA) airway exposure is accompanied by marked granulocyte accumulation in bone marrow (BM). Therefore, the aim of this study was to investigate the mechanisms of BM cell accumulation, and trafficking to circulating blood and lung tissue after SEA airway exposure. Male BALB/C mice were intranasally exposed to SEA (1μg), and at 4, 12 and 24h thereafter, BM, circulating blood, bronchoalveolar lavage (BAL) fluid and lung tissue were collected. Adhesion of BM granulocytes and flow cytometry for MAC-1, LFA1-α and VLA-4 and cytokine and/or chemokine levels were assayed after SEA-airway exposure. Prior exposure to SEA promoted a marked PMN influx to BAL and lung tissue, which was accompanied by increased counts of immature and/or mature neutrophils and eosinophils in BM, along with blood neutrophilia. Airway exposure to SEA enhanced BM neutrophil MAC-1 expression, and adhesion to VCAM-1 and/or ICAM-1-coated plates. Elevated levels of GM-CSF, G-CSF, INF-γ, TNF-α, KC/CXCL-1 and SDF-1α were detected in BM after SEA exposure. SEA exposure increased production of eosinopoietic cytokines (eotaxin and IL-5) and BM eosinophil VLA-4 expression, but it failed to affect eosinophil adhesion to VCAM-1 and ICAM-1. In conclusion, BM neutrophil accumulation after SEA exposure takes place by integrated action of cytokines and/or chemokines, enhancing the adhesive responses of BM neutrophils and its trafficking to lung tissues, leading to acute lung injury. BM eosinophil accumulation in SEA-induced acute lung injury may occur via increased eosinopoietic cytokines and VLA-4 expression.

Experimental phage therapy against lethal lung-derived septicemia caused by Staphylococcus aureus in mice

Nosocomial respiratory infections caused by methicillin-resistant Staphylococcus aureus (MRSA) can progress to lethal systemic infections. Bacteriophage (phage) therapy is expected to be effective against these critical infections. Previously, phage S13' was proposed as a potential therapeutic phage. We here examined phage treatment in a mouse model of lung-derived septicemia using phage S13'. Intraperitoneal phage administration at 6 h postinfection reduced the severity of infection and rescued the infected mice. Phage S13' can efficiently lyse hospital-acquired MRSA strains causing pneumonia-associated bacteremia in vitro. Thus, phage therapy may be a possible therapeutic intervention in staphylococcal lung-derived septicemia.

The changing microbiologic epidemiology of community-acquired pneumonia

Community-acquired pneumonia (CAP) is a common infectious disease in the United States and the incidence continues to grow as the aging population increases. Overall, in-hospital patient mortality rates have been reported to be as high as 18%. Management of patients with CAP has been challenged by the evolution of resistant pathogens (particularly Streptococcus pneumoniae and Staphylococcus aureus) that have reduced susceptibility to recommended standard antimicrobial agents. Streptococcus pneumoniae continues to be the most frequently identified pathogen in CAP and recently, S. aureus has been found to be the second most often identified pathogen. Data from the SENTRY Antimicrobial Surveillance Program has shown declining susceptibility of pneumococci to penicillin, amoxicillin/clavulanate, and ceftriaxone from 1998 through 2011. In the Assessing Worldwide Resistance Evaluation (AWARE) surveillance program, > 50% of all S. aureus isolates from patient bloodstream infections, skin and skin structure infections, and pneumonia were methicillin-resistant. Stratifying risk factors to identify patients at risk for community-acquired multidrug-resistant pathogens should be considered when selecting therapy. Differences in microbiology and outcomes have been noted in patients presenting from the community with recent exposure to the health care system (eg, nursing home residents, patients with a recent hospital admission). These patients are at an increased risk of an infection caused by a multidrug-resistant pathogen. Understanding a patient's risk for drug-resistant pathogens will allow the physician to choose an appropriate empiric treatment regimen to optimize clinical outcomes.

Treatment of infections due to resistant Staphylococcus aureus

This chapter reviews data on the treatment of infections caused by drug-resistant Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA). This review covers findings reported in the English language medical literature up to January of 2013. Despite the emergence of resistant and multidrug-resistant S. aureus, we have seven effective drugs in clinical use for which little resistance has been observed: vancomycin, quinupristin-dalfopristin, linezolid, tigecycline, telavancin, ceftaroline, and daptomycin. However, vancomycin is less effective for infections with MRSA isolates that have a higher MIC within the susceptible range. Linezolid is probably the drug of choice for the treatment of complicated MRSA skin and soft tissue infections (SSTIs); whether it is drug of choice in pneumonia remains debatable. Daptomycin has shown to be non-inferior to either vancomycin or β-lactams in the treatment of staphylococcal SSTIs, bacteremia, and right-sided endocarditis. Tigecycline was also non-inferior to comparator drugs in the treatment of SSTIs, but there is controversy about whether it is less effective than other therapeutic options in the treatment of more serious infections. Telavancin has been shown to be non-inferior to vancomycin in the treatment of SSTIs and pneumonia, but has greater nephrotoxicity. Ceftaroline is a broad-spectrum cephalosporin with activity against MRSA; it is non-inferior to vancomycin in the treatment of SSTIs. Clindamycin, trimethoprim-sulfamethoxazole, doxycycline, rifampin, moxifloxacin, and minocycline are oral anti-staphylococcal agents that may have utility in the treatment of SSTIs and osteomyelitis, but the clinical data for their efficacy is limited. There are also several drugs with broad-spectrum activity against Gm-positive organisms that have reached the phase II and III stages of clinical testing that will hopefully be approved for clinical use in the upcoming years: oritavancin, dalbavancin, omadacycline, tedizolid, delafloxacin, and JNJ-Q2. Thus, there are currently many effective drugs to treat resistant S. aureus infections and many promising agents in the pipeline. Nevertheless, S. aureus remains a formidable adversary, and despite our deep bullpen of potential therapies, there are still frequent treatment failures and unfortunate clinical outcomes. The following discussion summarizes the clinical challenges presented by MRSA, the clinical experience with our current anti-MRSA antibiotics, and the gaps in our knowledge on how to use these agents to most effectively combat MRSA infections.

Risk factors for methicillin-resistant Staphylococcus aureus in patients with community-onset and hospital-onset pneumonia

OBJECTIVES

The risk factors for methicillin-resistant Staphylococcus aureus (MRSA) pneumonia have not been fully characterized and are likely to be different depending on whether infection is acquired in the community or the hospital.

METHODS

We conducted a case-control study of 619 adults hospitalized between 2005 and 2010 with either MRSA or methicillin-sensitive S. aureus (MSSA) pneumonia. Patients with a respiratory culture within 48 h of hospitalization had community-onset pneumonia whereas patients with a culture collected after this time point had hospital-onset pneumonia.

RESULTS

Among patients with community-onset disease, the risk for MRSA was increased by tobacco use (OR 2.31, CI 1.23-4.31), chronic obstructive pulmonary disease (OR 3.76, CI 1.74-8.08), and recent antibiotic exposure (OR 4.87, CI 2.35-10.1) in multivariate analysis while patients with hospital-onset disease had an increased MRSA risk with tobacco use (OR 2.66, CI 1.38-5.14), illicit drug use (OR 3.52, CI 2.21-5.59), and recent antibiotic exposure (OR 2.04, CI 3.54-13.01). Hospitalization within the prior three months was associated with decreased risk (OR 0.64, CI 0.46-0.89) in multivariate analysis.

CONCLUSIONS

This study suggests there are common and distinct risk factors for MRSA pneumonia based on location of onset. The decreased risk for MRSA pneumonia associated with recent hospitalization is unexpected and warrants further investigation.

SUMMARY

This case-control study showed that there are common and distinct risk factors associated with MRSA pneumonia depending on whether the infection onset is in the hospital or in the community. Recent hospitalization was unexpectedly shown to be associated with decreased risk for MRSA pneumonia and warrants further investigation.

Identification of a hydrophobic cleft in the LytTR domain of AgrA as a locus for small molecule interactions that inhibit DNA binding

The AgrA transcription factor regulates the quorum-sensing response in Staphylococcus aureus, controlling the production of hemolysins and other virulence factors. AgrA binds to DNA via its C-terminal LytTR domain, a domain not found in humans but common in many pathogenic bacteria, making it a potential target for antimicrobial development. We have determined the crystal structure of the apo AgrA LytTR domain and screened a library of 500 fragment compounds to find inhibitors of AgrA DNA binding activity. Using nuclear magnetic resonance, the binding site for five compounds has been mapped to a common locus at the C-terminal end of the LytTR domain, a site known to be important for DNA binding activity. Three of these compounds inhibit AgrA DNA binding. These results provide the first evidence that LytTR domains can be targeted by small organic compounds.

Nrf2 promotes alveolar mitochondrial biogenesis and resolution of lung injury in Staphylococcus aureus pneumonia in mice

Acute lung injury (ALI) initiates protective responses involving genes downstream of the Nrf2 (Nfe2l2) transcription factor, including heme oxygenase-1 (HO-1), which stimulates mitochondrial biogenesis and related anti-inflammatory processes. We examined mitochondrial biogenesis during Staphylococcus aureus pneumonia in mice and the effect of Nrf2 deficiency on lung mitochondrial biogenesis and resolution of lung inflammation. S. aureus pneumonia established by nasal insufflation of live bacteria was studied in mitochondrial reporter (mt-COX8-GFP) mice, wild-type (WT) mice, and Nrf2⁻/⁻ mice. Bronchoalveolar lavage, wet/dry ratios, real-time RT-PCR and Western analysis, immunohistochemistry, and fluorescence microscopy were performed on the lung at 0, 6, 24, and 48 h. The mice survived S. aureus inoculations at 5×10⁸ CFU despite diffuse lung inflammation and edema, but the Nrf2⁻/⁻ lung showed increased ALI. In mt-COX8-GFP mice, mitochondrial fluorescence was enhanced in bronchial and alveolar type II (AT2) epithelial cells. WT mice displayed rapid HO-1 upregulation and lower proinflammatory TNF-α, IL-1β, and CCL2 and, especially in AT2 cells, higher anti-inflammatory IL-10 and suppressor of cytokine signaling-3 than Nrf2⁻/⁻ mice. In the alveolar region, WT but not Nrf2⁻/⁻ mice showed strongly induced nuclear respiratory factor-1, PGC-1α, mitochondrial transcription factor-A, SOD2, Bnip3, mtDNA copy number, and citrate synthase. These findings indicate that S. aureus pneumonia induces Nrf2-dependent mitochondrial biogenesis in the alveolar region, mainly in AT2 cells. Absence of Nrf2 suppresses the alveolar transcriptional network for mitochondrial biogenesis and anti-inflammation, which worsens ALI. The findings link redox activation of mitochondrial biogenesis to ALI resolution.

Staphylococcus aureus elicits marked alterations in the airway proteome during early pneumonia

Pneumonia caused by Staphylococcus aureus is a growing concern in the health care community. We hypothesized that characterization of the early innate immune response to bacteria in the lungs would provide insight into the mechanisms used by the host to protect itself from infection. An adult mouse model of Staphylococcus aureus pneumonia was utilized to define the early events in the innate immune response and to assess the changes in the airway proteome during the first 6 h of pneumonia. S. aureus actively replicated in the lungs of mice inoculated intranasally under anesthesia to cause significant morbidity and mortality. By 6 h postinoculation, the release of proinflammatory cytokines caused effective recruitment of neutrophils to the airway. Neutrophil influx, loss of alveolar architecture, and consolidated pneumonia were observed histologically 6 h postinoculation. Bronchoalveolar lavage fluids from mice inoculated with phosphate-buffered saline (PBS) or S. aureus were depleted of overabundant proteins and subjected to strong cation exchange fractionation followed by liquid chromatography and tandem mass spectrometry to identify the proteins present in the airway. No significant changes in response to PBS inoculation or 30 min following S. aureus inoculation were observed. However, a dramatic increase in extracellular proteins was observed 6 h postinoculation with S. aureus, with the increase dominated by inflammatory and coagulation proteins. The data presented here provide a comprehensive evaluation of the rapid and vigorous innate immune response mounted in the host airway during the earliest stages of S. aureus pneumonia.

Treatment of infections caused by resistant Staphylococcus aureus

We review data on the treatment of infections caused by drug-resistant Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA). In this review, we cover findings reported in the English language medical literature up to February 2006. Despite the emergence of resistant and multidrug resistant S. aureus, five effective drugs for which little resistance has been observed are in clinical use: vancomycin, quinupristin-dalfopristin, linezolid, tigecycline, and daptomycin. However, vancomycin is less effective for infections with MRSA isolates that have a high minimum inhibitory concentration in the susceptible range. Linezolid looks promising in the treatment of MRSA pneumonia and skin and soft-tissue infections (SSTIs). Daptomycin displays rapid bactericidal activity in vitro, and it has been shown to be noninferior to comparator agents in the treatment of SSTIs and bacteremia. Tigecycline was also noninferior to comparator drugs in the treatment of SSTIs. Clindamycin, trimethoprim-sulfamethoxazole, doxycycline, and minocycline are oral antistaphylococcal agents that may have utility in the treatment of SSTIs and osteomyelitis, but the clinical data for their efficacy is limited. There are four drugs with broad-spectrum activity against Gram-positive organisms at an advanced stage of clinical testing: ceptobiprole and three new glycopeptides with potent bactericidal activity, oritavancin, dalbavancin, and telavancin. Thus, there are currently many effective drugs to treat resistant S. aureus infections and many promising agents in the pipeline. Nevertheless, S. aureus remains a formidable adversary against which there are frequent treatment failures. The next goals are to determine the most appropriate indications and cost-effectiveness of each of these drugs in the treatment strategy against S. aureus.

Methicillin-resistant Staphylococcus aureus sterile-site infection: The importance of appropriate initial antimicrobial treatment*

OBJECTIVE

The first goal of this investigation was to determine the rate of appropriate initial antimicrobial administration to patients with methicillin-resistant Staphylococcus aureus (MRSA) sterile-site infections. Our second goal was to evaluate the influence of appropriate initial treatment of MRSA sterile-site infection on outcome.

DESIGN

A retrospective, single-center, observational cohort study.

SETTING

Barnes-Jewish Hospital, a 1200-bed urban teaching facility.

PATIENTS

Adult patients requiring hospitalization identified to have an MRSA sterile-site infection.

INTERVENTIONS

Retrospective data collection from automated hospital and pharmacy databases.

MEASUREMENTS AND MAIN RESULTS

Five hundred forty-nine patients with S. aureus sterile site infections were identified during a 3-yr period (January 2002 through December 2004). One hundred twenty-seven (23.1%) died during hospitalization. Hospital mortality was statistically greater for patients receiving inappropriate initial antimicrobial treatment (n = 380) within 24 hrs of a positive culture than for those receiving appropriate initial treatment (n = 169) (26.1% vs. 16.6%; p = .015). Multiple logistic regression analysis identified inappropriate initial antimicrobial treatment (adjusted odds ratio [AOR], 1.92; 95% confidence interval [CI], 1.48-2.50; p = .0134), vasopressor administration (AOR, 5.49; 95% CI, 4.08-7.38; p < .001), and increasing age (1-yr increments) (AOR, 1.03; 95% CI, 1.02-1.04; p < .001) as independent determinants of hospital mortality.

CONCLUSIONS

Inappropriate initial antimicrobial treatment of MRSA sterile-site infections is common and is associated with an increased risk of hospital mortality. Appropriate antimicrobial treatment of MRSA sterile-site infections may be maximized by increased use of initial empirical antimicrobial treatment regimens targeting MRSA in patients at risk for this infection until organism identification and susceptibility become known.

Pleuropulmonary complications of Panton-Valentine leukocidin-positive community-acquired methicillin-resistant Staphylococcus aureus: importance of treatment with antimicrobials inhibiting exotoxin production

Four patients with pleuropulmonary complications attributed to community-acquired methicillin-resistant Staphylococcus aureus (CAMRSA) positive for Panton-Valentine leukocidin (PVL) are described. These patients presented to Barnes-Jewish Hospital with severe necrotizing pneumonia, empyema, ARDS-complicating pneumonia, and ventilator-associated pneumonia-complicating acute pancreatitis, respectively. The first three patients had influenza-like illnesses preceding their PVL-positive CAMRSA infections. In all four cases, PVL-positive CAMRSA was isolated from respiratory secretions, and from blood cultures in three of the individuals. Antimicrobial therapy was inappropriate initially in all four patients. Three patients failed to respond to subsequent treatment with vancomycin, including two patients with persistent bacteremia despite at least 48 h of treatment with vancomycin. These patients were subsequently treated with antimicrobials inhibiting exotoxin production (linezolid or clindamycin) with good clinical results. Clinicians should be aware of PVL-positive CAMRSA due to the rapid and severe progression of pleuropulmonary complications associated with this infection. Additionally, specific antimicrobial therapy directed against CAMRSA differs from the traditional antimicrobial agents prescribed for community-acquired pneumonia. Antimicrobial agents that specifically inhibit exotoxin production appear to be the preferred treatment agents.