Release of extracellular superoxide dismutase into alveolar fluid protects against acute lung injury and inflammation in Staphylococcus aureus pneumonia

Acute respiratory distress syndrome (ARDS) remains a significant cause of morbidity and mortality in critically ill patients. Oxidative stress and inflammation play a crucial role in the pathogenesis of ARDS. Extracellular superoxide dismutase (EC-SOD) is abundant in the lung and is an important enzymatic defense against superoxide. Human single-nucleotide polymorphism in matrix binding region of EC-SOD leads to the substitution of arginine to glycine at position 213 (R213G) and results in release of EC-SOD into alveolar fluid, without affecting enzyme activity. We hypothesized that R213G EC-SOD variant protects against lung injury and inflammation via the blockade of neutrophil recruitment in infectious model of methicillin-resistant S. aureus (MRSA) pneumonia. After inoculation with MRSA, wild-type (WT) mice had impaired integrity of alveolar-capillary barrier and increased levels of IL-1β, IL-6, and TNF-α in the broncho-alveolar lavage fluid (BALF), while infected mice expressing R213G EC-SOD variant maintained the integrity of alveolar-capillary interface and had attenuated levels of proinflammatory cytokines. MRSA-infected mice expressing R213G EC-SOD variant also had attenuated neutrophil numbers in BALF and decreased expression of neutrophil chemoattractant CXCL1 by the alveolar epithelial ATII cells, compared with the infected WT group. The decreased neutrophil numbers in R213G mice were not due to increased rate of apoptosis. Mice expressing R213G variant had a differential effect on neutrophil functionality-the generation of neutrophil extracellular traps (NETs) but not myeloperoxidase (MPO) levels were attenuated in comparison with WT controls. Despite having the same bacterial load in the lung as WT controls, mice expressing R213G EC-SOD variant were protected from extrapulmonary dissemination of bacteria.

Dehydrocostus Lactone Attenuates Methicillin-Resistant Staphylococcus aureus-Induced Inflammation and Acute Lung Injury via Modulating Macrophage Polarization

Dehydrocostus lactone (DHL), a natural sesquiterpene lactone isolated from the traditional Chinese herbs Saussurea lappa and Inula helenium L., has important anti-inflammatory properties used for treating colitis, fibrosis, and Gram-negative bacteria-induced acute lung injury (ALI). However, the effects of DHL on Gram-positive bacteria-induced macrophage activation and ALI remains unclear. In this study, we found that DHL inhibited the phosphorylation of p38 MAPK, the degradation of IκBα, and the activation and nuclear translocation of NF-κB p65, but enhanced the phosphorylation of AMP-activated protein kinase (AMPK) and the expression of Nrf2 and HO-1 in lipoteichoic acid (LTA)-stimulated RAW264.7 cells and primary bone-marrow-derived macrophages (BMDMs). Given the critical role of the p38 MAPK/NF-κB and AMPK/Nrf2 signaling pathways in the balance of M1/M2 macrophage polarization and inflammation, we speculated that DHL would also have an effect on macrophage polarization. Further studies verified that DHL promoted M2 macrophage polarization and reduced M1 polarization, then resulted in a decreased inflammatory response. An in vivo study also revealed that DHL exhibited anti-inflammatory effects and ameliorated methicillin-resistant Staphylococcus aureus (MRSA)-induced ALI. In addition, DHL treatment significantly inhibited the p38 MAPK/NF-κB pathway and activated AMPK/Nrf2 signaling, leading to accelerated switching of macrophages from M1 to M2 in the MRSA-induced murine ALI model. Collectively, these data demonstrated that DHL can promote macrophage polarization to an anti-inflammatory M2 phenotype via interfering in p38 MAPK/NF-κB signaling, as well as activating the AMPK/Nrf2 pathway in vitro and in vivo. Our results suggested that DHL might be a novel candidate for treating inflammatory diseases caused by Gram-positive bacteria.

Salvinorin A protects against methicillin resistant staphylococcus aureus-induced acute lung injury via Nrf2 pathway

Salvinorin A (SA), a neoclerodane diterpene, is isolated from the dried leaves ofSalvia divinorum. SA has traditionally been used treatments for chronic pain diseases. Recent research has demonstrated that SA possesses the anti-inflammatory property. The present study aim to explore the effects and potentialmechanisms ofSA in protection against Methicillin Resistant Staphylococcus aureus (MRSA)-induced acute lung injury (ALI). Here, we firstly found that verylowdosesof SA (50 μg/kg) could markedly decrease the infiltration of pulmonary neutrophils, mRNA expression of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) and then attenuated ALI cause by MRSA infection in mice. In vitro findings revealed that SA attenuated lipoteichoicacid-induced apoptosis, inflammation and oxidative stress in RAW264.7 cells. Mechanism research revealed that SA increased both mRNA levels and protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and up-regulated mRNA expression of its downstream genes (HO-1, Gclm, Trx-1, SOD1 and SOD2). Additionally, Nrf2 knockout mice abolished the inhibitory effect of SA on neutrophil accumulation and oxidative stress in MRSA-induced ALI. In conclusion, SA attenuates MRSA-induced ALI via Nrf2 signaling pathways.

Oral administration of Lactobacillus acidophilus alleviates exacerbations in Pseudomonas aeruginosa and Staphylococcus aureus pulmonary infections

Staphylococcus aureus and Pseudomonas aeruginosa are largely the cause of morbidity and mortality in both hospital and community settings. These pathogens remain the important cause of pulmonary infections in patients with cystic fibrosis with a worldwide prevalence. Although, antibiotics are efficient measures of treating bacterial lung infections, the occurrence of antibiotic resistant bacteria has been encouraging the researchers to explore novel therapeutic approaches. It has been discovered that certain lactic acid bacteria possess protective effects against bacterial and viral respiratory infections. The aim of present study was to investigate the capability of orally administered L. acidophilus to ameliorate S. aureus and P. aeruginosa pulmonary infections. Animals were exposed to aerosol of pathogenic suspension. After 24 hours of infection, L. acidophilus treatment was administered orally for 7 consecutive days. Evaluation of tissue bacteriology, histopathology and serum cytokinomics were performed. In parallel, human alveolar A549 cells were utilized to determine possible role of probiotic on pulmonary infections. Oral administration of L. acidophilus significantly (P<0.05) alleviate lung bacterial load and severity of infection as depicted by our histopathological studies. Results obtained from cytokinomics revealed that pro-inflammatory cytokines induced due to lung infection were suppressed in oral probiotic treatment groups. In addition, treatment with L. acidophilus induced murine lung anti inflammatory, IL-10 cytokine level. Current work suggests that orally administered L. acidophilus in mice is able to attenuate S. aureus and P. aeruginosa induced lung cytotoxicity by modulation of host immune response.

Mechanical Ventilation Alters the Development of Staphylococcus aureus Pneumonia in Rabbit

Ventilator-associated pneumonia (VAP) is common during mechanical ventilation (MV). Beside obvious deleterious effects on muco-ciliary clearance, MV could adversely shift the host immune response towards a pro-inflammatory pattern through toll-like receptor (TLRs) up-regulation. We tested this hypothesis in a rabbit model of Staphylococcus aureus VAP. Pneumonia was caused by airway challenge with S. aureus, in either spontaneously breathing (SB) or MV rabbits (n = 13 and 17, respectively). Pneumonia assessment regarding pulmonary and systemic bacterial burden, as well as inflammatory response was done 8 and 24 hours after S. aureus challenge. In addition, ex vivo stimulations of whole blood taken from SB or MV rabbits (n = 7 and 5, respectively) with TLR2 agonist or heat-killed S. aureus were performed. Data were expressed as mean±standard deviation. After 8 hours of infection, lung injury was more severe in MV animals (1.40±0.33 versus [vs] 2.40±0.55, p = 0.007), along with greater bacterial concentrations (6.13±0.63 vs. 4.96±1.31 colony forming units/gram, p = 0.002). Interleukin (IL)-8 and tumor necrosis factor (TNF)-αserum concentrations reached higher levels in MV animals (p = 0.010). Whole blood obtained from MV animals released larger amounts of cytokines if stimulated with TLR2 agonist or heat-killed S. aureus (e.g., TNF-α: 1656±166 vs. 1005±89; p = 0.014). Moreover, MV induced TLR2 overexpression in both lung and spleen tissue. MV hastened tissue injury, impaired lung bacterial clearance, and promoted a systemic inflammatory response, maybe through TLR2 overexpression.

Toxin-induced necroptosis is a major mechanism of Staphylococcus aureus lung damage

Staphylococcus aureus USA300 strains cause a highly inflammatory necrotizing pneumonia. The virulence of this strain has been attributed to its expression of multiple toxins that have diverse targets including ADAM10, NLRP3 and CD11b. We demonstrate that induction of necroptosis through RIP1/RIP3/MLKL signaling is a major consequence of S. aureus toxin production. Cytotoxicity could be prevented by inhibiting either RIP1 or MLKL signaling and S. aureus mutants lacking agr, hla or Hla pore formation, lukAB or psms were deficient in inducing cell death in human and murine immune cells. Toxin-associated pore formation was essential, as cell death was blocked by exogenous K+ or dextran. MLKL inhibition also blocked caspase-1 and IL-1β production, suggesting a link to the inflammasome. Rip3^-/- mice exhibited significantly improved staphylococcal clearance and retained an alveolar macrophage population with CD200R and CD206 markers in the setting of acute infection, suggesting increased susceptibility of these leukocytes to necroptosis. The importance of this anti-inflammatory signaling was indicated by the correlation between improved outcome and significantly decreased expression of KC, IL-6, TNF, IL-1α and IL-1β in infected mice. These findings indicate that toxin-induced necroptosis is a major cause of lung pathology in S. aureus pneumonia and suggest the possibility of targeting components of this signaling pathway as a therapeutic strategy.

Staphylococcus aureus (SA) cause a highly inflammatory pneumonia associated with substantial morbidity and mortality. Much of this lung destruction is attributed to toxins that target specific receptors on human and murine cells. We demonstrate that the α-hemolysin (Hla) and other agr-regulated toxins activate RIP1/RIP3/MLKL-mediated necroptosis and IL-1β expression, through a mechanism that involves MLKL pore-formation and inflammasome activation. Cell death can be inhibited by osmoprotectants and K⁺ repletion. Necroptosis results in alveolar macrophage depletion and loss of anti-inflammatory signaling. Rip3^-/- mice maintain significantly greater numbers of alveolar macrophages with anti-inflammatory phenotypes, CD206⁺ and CD200R⁺; decreased proinflammatory cytokine production; and improved SA clearance. Necroptosis represents a common mechanism of pulmonary damage activated by multiple SA toxins.

Bacterial pathogens activate a common inflammatory pathway through IFNλ regulation of PDCD4

The type III interferon (IFNλ) receptor IL-28R is abundantly expressed in the respiratory tract and has been shown essential for host defense against some viral pathogens, however no data are available concerning its role in the innate immune response to bacterial pathogens. Staphylococcus aureus and Pseudomonas aeruginosa induced significant production of IFNλ in the lung, and clearance of these bacteria from the lung was significantly increased in IL-28R null mice compared to controls. Improved bacterial clearance correlated with reduced lung pathology and a reduced ratio of pro- vs anti-inflammatory cytokines in the airway. In human epithelial cells IFNλ inhibited miR-21 via STAT3 resulting in upregulation of PDCD4, a protein known to promote inflammatory signaling. In vivo 18 hours following infection with either pathogen, miR-21 was significantly reduced and PDCD4 increased in the lungs of wild type compared to IL-28R null mice. Infection of PDCD4 null mice with USA300 resulted in improved clearance, reduced pathology, and reduced inflammatory cytokine production. These data suggest that during bacterial pneumonia IFNλ promotes inflammation by inhibiting miR-21 regulation of PDCD4.

The role of interferons (types I, II, and III) in viral and bacterial infections has been a topic of intense research over the last decade. The contribution of the type I interferons during bacterial pneumonias particularly has been shown to be highly variable depending on the specific pathogen. Our data for the first time demonstrate that type III interferon plays a significant role in the pathogenesis of bacterial pneumonia, and its contribution is similar in both Gram positive and Gram negative infections. We show in epithelial cells that miR-21 and PDCD4 are downstream effectors of type III interferon that prolong production of inflammatory cytokines. Utilizing mice that lack the receptor for type III interferon or PDCD4, we show that inhibiting this pathway improves bacterial clearance from the airways and lung tissue. These data suggest novel targets for therapy in a variety of bacterial pneumonias.

Linezolid Exerts Greater Bacterial Clearance but No Modification of Host Lung Gene Expression Profiling: A Mouse MRSA Pneumonia Model

Background

Linezolid (LZD) is beneficial to patients with MRSA pneumonia, but whether and how LZD influences global host lung immune responses at the mRNA level during MRSA-mediated pneumonia is still unknown.

Methods

A lethal mouse model of MRSA pneumonia mediated by USA300 was employed to study the influence of LZD on survival, while the sublethal mouse model was used to examine the effect of LZD on bacterial clearance and lung gene expression during MRSA pneumonia. LZD (100mg/kg/day, IP) was given to C57Bl6 mice for three days. On Day 1 and Day 3 post infection, bronchoalveolar lavage fluid (BALF) protein concentration and levels of cytokines including IL6, TNFα, IL1β, Interferon-γ and IL17 were measured. In the sublethal model, left lungs were used to determine bacterial clearance and right lungs for whole-genome transcriptional profiling of lung immune responses.

Results

LZD therapy significantly improved survival and bacterial clearance. It also significantly decreased BALF protein concentration and levels of cytokines including IL6, IL1β, Interferon-γ and IL17. No significant gene expression changes in the mouse lungs were associated with LZD therapy.

Conclusion

LZD is beneficial to MRSA pneumonia, but it does not modulate host lung immune responses at the transcriptional level.

Silibinin in vitro protects A549 cells from Staphylococcus aureus-mediated injury and in vivo alleviates the lung injury of staphylococcal pneumonia

In this study, hemolysis, Western blot, and real-time RT-PCR assays were performed to evaluate silibinin's activity against S. aureus α-toxin secretion. In addition, live/dead cell staining and lactate dehydrogenase activity assays were introduced to examine the influence of silibinin on α-toxin-induced cell injury in human alveolar epithelial cells. Furthermore, we tested the influence of silibinin on S. aureus pneumonia in a mouse model. We show that silibinin inhibits the expression of α-toxin in a dose-dependent manner and alleviates α-toxin-induced lung cell injury. The IC50 of silibinin that inhibits the hemolytic activity of S. aureus was 14.33 µg/mL for strain 8325-4. Moreover, this compound provides effective protection on the lung injury of staphylococcal pneumonia.

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.

Necrotizing pneumonia caused by Panton-Valentine leukocidin-producing methicillin-susceptible Staphylococcus aureus (MSSA)

Staphylococcus aureus harboured by Panton-Valentine leukocidin (PVL) is emerging as a serious problem worldwide. There has been an increase in the incidence of necrotizing lung infections in otherwise healthy young people with very high mortality rate associated with these strains. This report documents a confirmed case of necrotizing pneumonia due to methicillin-susceptible S. aureus (MSSA) harbouring Panton-Valentine leukocidin genes. An apparently healthy 49-year old man was admitted to our hospital for dyspnea and he quickly developed acute respiratory distress syndrome. MSSA harbouring Panton-Valentine leukocidin genes were cultured from the abscess fluid and from multiple blood specimens. Aggressive antibiotic therapy was started and intensive supportive care led finally to a complete recovery. Rapid identification of Panton-Valentine leukocidin in MSSA samples should be supposed when a young, immunocompetent patient, develops a necrotizing pneumonia. Bactericidal antistaphylococcal antibiotics are recommended for the treatment as soon as possible to avoid the potentially devastating consequences of this kind of S. aureus.

Necrotizing pneumonia in the community

A 62-year-old man presented with general fatigue. He was diagnosed with septic shock and severe pneumonia. The sputum at admission yielded methicillin-sensitive Staphylococcus aureus (MSSA) strain and methicillin-resistant S. aureus (MRSA) strain. Despite antibiotic treatment, he did not improve. A chest computed tomography (CT) revealed multilobar cavity lesions. Only MRSA strain was confirmed at that time. We diagnosed him with necrotizing pneumonia. Despite treatment with vancomycin, his pneumonia worsened and he died. At autopsy, many gram-positive cocci were observed in the lungs. The clinical presentation of our patient was different from typical CA-MRSA-mediated necrotizing pneumonia.

Fatal necrotizing pneumonia caused by Panton-Valentine leukocidin-producing hospital-acquired Staphylococcus aureus: a case report

Panton-Valentine leukocidin (PVL) is a cytotoxin which causes leukocyte destruction and tissue necrosis. Although it is produced by fewer than 5% of Staphylococcus aureus strains, PVL-producing S. aureus is emerging as a serious problem worldwide. There has been a marked increase in the incidence of necrotizing lung infections with a very high mortality associated with these strains. This report describes a fatal case of hospital-acquired necrotizing pneumonia caused by PVL-positive methicillin-susceptible S. aureus in a patient with a brain tumor.

Murine models of acute and chronic lung infection with cystic fibrosis pathogens

Animal models of acute and chronic infection, along with mice genetically modified for the Cftr gene, are a key asset in cystic fibrosis (CF) research. Despite some limitations, these models provide valuable resources to mimic the initial and progressive bronchopulmonary infection typical of CF patients. The following review summarizes the strengths and weaknesses of different types of animal models with a major emphasis placed on the significant species differences between mice and humans. Murine models of acute and chronic lung infection with Pseudomonas aeruginosa, Burkholderia cenocepacia, Staphylococcus aureus, and Haemophilus influenzae have been used to study the molecular mechanisms underlying the pathogen virulence and host defense. In addition, they have provided insights in the potential of vaccination to restrict infectious exacerbations, the activity of antibiotics, and the effectiveness of anti-inflammatory therapy in reducing lung damage. Indeed, animal models of infection should allow the validation of future therapeutic interventions for lung infections in patients with CF.

[Fatal pneumonia with Panton Valentine leucocidin-producing Staphylococcus aureus]

We describe a case of fatal pneumonia in a previously healthy 14-year-old boy. The patient was severely affected at the time of admission with high fever, tachypnea, tachycardia and peripheral cyanosis. The condition worsened despite treatment with antibiotics as well as respiratory and pressure support. Acidosis and critical leucopenia supervened and the patient died just short of 24 hours after admission. Subsequent bacterial cultivation showed Panton-Valentine Leucocidin-producing Staphylococcus aureus.

[Community-associated MRSA and Panton-Valentine leukocidin (PVL): novel trends in epidemiology and forensic implications]

The propagation of multi-resistant bacteria, especially methicilline-resistant Staphylococcus aureus strains (MRSA), in hospitals and nursing homes is a well-known sanitary and therapeutic problem (Healthcare-associated MRSA, HA-MRSA). For some years, an increasing incidence of MRSA outside the hospital environment (Community-acquired or Community-Associated MRSA, CA-MRSA) has been observed all over the world, which, contrary to the hospital strains, produces the leukocytotoxic toxin PVL and causes purulent inflammations of the skin and necrotizing pneumonia. In previously healthy children and adolescents these pneumonias are fatal in most cases. The authors report a case of fatal necrotizing S. aureus pneumonia in a 16-year-old girl observed in 2001. The suspicion that the infection had been caused by a CA-MRSA strain following an influenza A infection was confirmed by the bacteriological investigation of a heart blood specimen stored for more than 2 years at 4 degrees C. In view of the bad prognosis and the fulminat course of these special pneumonias the attending physician could not be accused of having caused the death of the girl by omitting the indicated antibiotic treatment. This case of pneumonia caused by CA-MRSA was one of the first seen in Germany. The epidemiological situation suggests that a higher incidence has to be expected in the future.

A case of rapidly progressive necrotizing pneumonia caused by community-acquired methicillin-resistant Staphylococcus aureus

We present the case of a patient with a necrotizing multilobar pneumonia caused by community-acquired methicillin-resistant Staphylococcus aureus (MRSA). The patient presented with shortness of breath and a productive cough of 3 days duration. On arrival to the emergency department she was intubated for increased work of breathing and given vasopressors for hypotension refractory to fluid resuscitation. Blood cultures taken at admission, sputum cultures from the patient's endotracheal tube, and bronchoalveolar lavage cultures all grew S. aureus resistant to penicillinase-resistant penicillins. Over the following days the patient's respiratory function deteriorated as she grew progressively hypoxemic and hypercarbic despite aggressive mechanical ventilation and intravenous antibiotics. On day 4 of her hospitalization a computed tomogram revealed extensive pulmonary necrosis consistent with necrotizing pneumonia. The patient's family elected to withdraw support, and the patient rapidly died following cessation of mechanical ventilation.

[Two cases of severe necrotizing pneumonia caused by community-acquired methicillin-resistant Staphylococcus aureus]

We present 2 cases with severe necrotizing pneumonia due to community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection. The patients were a 89-year-old man and a male student of 15 years of age. Chest X-rays and CT scans demonstrated multiple consolidations with cavitary lesions showing necrotizing pneumonia. MRSA strains were isolated from the sputum cultures on admission in these patients who did not have any established risk factors for MRSA infections such as history of hospitalization, surgery, hemodialysis, the presence of a permanent indwelling catheter or percutaneous medical device, and residence in a long-term care facility. These patients thus satisfied the international criteria for CA-MRSA presented by the Centers for Disease Control and Prevention (CDC). Unfortunately, the first case died of CA-MRSA pneumonia in spite of intensive treatments including anti-MRSA antibiotics. Unlike the severe CA-MRSA cases in western countries, Panton-Valentine leukocidin (PVL) genes were not detected in the present cases, suggesting that factors other than PVL had a significant effect on the severity of necrotizing pneumonia. To the best of our knowledge, this is the first report of severe necrotizing pneumonia caused by CA-MRSA in Japan.

A rapidly fatal case of Panton-valentine leukocidin positive Staphylococcus aureus necrotizing pneumonia in an HIV-infected patient

This article reports a rare case of necrotizing pneumonia caused by Panton-Valentine leukocidin (PVL) positive Staphylococcus aureus in an HIV-infected patient presenting with severe back pain and rash. The back pain progressed to excruciating abdominal pain which was misleading, resulting in an investigation on intraabdominal conditions. He developed massive hemoptysis and died within 2 days of the first clinical symptoms. Recognizing the emergence of PVL-producing S. aureus is important in both immunocompetent and immunocompromised patients. This organism was transmitted from his wife.

Successful use of extracorporeal membrane oxygenation in severe necrotizing pneumonia caused by Staphylococcus aureus

OBJECTIVE

To report the successful use of extracorporeal membrane oxygenation (ECMO) as rescue therapy for severe necrotizing pneumonia secondary to infection by the Staphylococcus aureus species.

DESIGN

Case series.

SETTING

Pediatric intensive care unit at a freestanding tertiary care children's hospital.

PATIENTS

Two pediatric patients with severe S. aureus-induced necrotizing pneumonia requiring rescue with ECMO. Both patients survived with good neurologic outcomes. One patient required the use of activated factor VII for severe bleeding while on ECMO, with no thrombotic effect on the ECMO circuit.

CONCLUSION

ECMO as rescue support should be considered in a timely fashion for refractory hypoxemic respiratory failure resulting from S. aureus pneumonia, including patients with necrotizing pneumonia. Use of ECMO support in such cases, coupled with aggressive measures aimed at minimizing bleeding, such as the use of activated factor VII, may result in excellent short- and long-term outcomes for such patients.

[Panton-Valentine leukocidin-producing Staphylococcus aureus responsible for necrotizing pneumonia]

Panton-Valentine leukocidin-producing (PVL) Staphylococcus aureus is responsible for a highly lethal necrotizing pneumonia, which occurs predominantly in young immunocompetent patients. Hemoptysis and leucopenia often occur but are not always present. Detection of PVL gene on S. aureus strains responsible for pneumonia should help us to a better understanding of this disease, to improve its treatment with antibiotics capable of lower the toxin production and to prevent its diffusion to others persons by detection and elimination of a nasal S. aureus carriage.

Methicillin-Resistant Staphylococcus aureus Necrotizing Pneumonia Arising From an Infected Episiotomy Site

BACKGROUND

We report a case of methicillin-resistant Staphylococcus aureus (MRSA) sepsis and pneumonia in a postpartum patient.

CASE

A 21-year-old gravida 1 para 1 presented on postpartum day 9 with persistent elevated fever, dyspnea, cellulitis of the upper extremities, and an infected episiotomy site. Computed tomography of the chest revealed multiple widely distributed nodules and bilateral infiltrates with central cavitations. Sputum, blood, urine, and episiotomy site cultures grew MRSA, subsequently demonstrated by molecular fingerprinting and antibiotic susceptibility to be community acquired. A magnetic resonance imaging of the pelvis demonstrated pelvic thrombophlebitis.

CONCLUSION

Community-acquired MRSA is an emerging problem, which may present as skin and soft tissue infections or sepsis. Seeding from an infected episiotomy site seems to be a potential route of systemic infection. The use of empirical treatment with beta-lactam agents may fail. Appropriate cultures should be obtained and if MRSA is diagnosed, vancomycin should be employed.

Staphylococcus aureus Panton-Valentine leukocidin causes necrotizing pneumonia

The Staphylococcus aureus Panton-Valentine leukocidin (PVL) is a pore-forming toxin secreted by strains epidemiologically associated with the current outbreak of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and with the often-lethal necrotizing pneumonia. To investigate the role of PVL in pulmonary disease, we tested the pathogenicity of clinical isolates, isogenic PVL-negative and PVL-positive S. aureus strains, as well as purified PVL, in a mouse acute pneumonia model. Here we show that PVL is sufficient to cause pneumonia and that the expression of this leukotoxin induces global changes in transcriptional levels of genes encoding secreted and cell wall-anchored staphylococcal proteins, including the lung inflammatory factor staphylococcal protein A (Spa).

Potency of DX-619, a novel des-F(6)-quinolone, in haematogenous murine bronchopneumonia caused by methicillin-resistant and vancomycin-intermediate Staphylococcus aureus

In this study, the potency of DX-619, a novel des-fluoro(6)-quinolone agent, was compared with that of vancomycin (VCM) in a murine model of haematogenous bronchopneumonia infection caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate S. aureus (VISA). The minimum inhibitory concentrations (MICs) of DX-619 and VCM against MRSA were 0.03 microg/mL and 1.0 microg/mL, respectively, whilst the MICs against VISA were 0.125 microg/mL and 8.0 microg/mL, respectively. Treatment with DX-619 resulted in a significant decrease in the number of viable bacteria in the MRSA infection model (mean+/-standard error of the mean for control, VCM and DX-619 groups: 7.97+/-0.32, 7.19+/-0.33 and 2.91+/-0.60 log(10) colony-forming units/lung, respectively). For infection with VISA, mice were pre-treated with cyclophosphamide. The survival rate of mice treated with DX-619 (90% survival) was significantly higher than survival rates in the other two groups (45% both for VCM and control groups; P<0.05). Histopathological examination revealed that inflammatory changes in the DX-619-treated group were less marked than in the other two groups. The parameters in lung tissue for the area under the concentration-time curve/MIC ratio both for MRSA and VISA were higher in the DX-619 group than in the VCM group. Our results emphasise the potency of DX-619 against MRSA and VISA murine haematogenous pulmonary infection.

Pneumonia and new methicillin-resistant Staphylococcus aureus clone

Necrotizing pneumonia caused by Staphylococcus aureus strains carrying the Panton-Valentin leukocidin gene is a newly described disease entity. We report a new fatal case of necrotizing pneumonia. An S. aureus strain with an agr1 allele and of a new sequence type 377 was recovered, representing a new, emerging, community-acquired methicillin-resistant clone.

Post-MRSA infection glomerulonephritis with marked Staphylococcus aureus cell envelope antigen deposition in glomeruli

A 48-year-old male developed massive proteinuria and renal dysfunction after pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA) infection. Examination of a renal biopsy specimen by light microscopy showed severe mesangiocapillary proliferative glomerulonephritis with fibrocellular crescents. Immunofluorescence microscopy showed weak linear staining for immunoglobulin G (IgG), while both the peripheral and mesangial lesions stained for IgA and C3. Immunostaining for a possible antigen related to post-MRSA infection glomerulonephritis, using monoclonal antibody S1D6, revealed marked deposition of S.aureus cell envelope antigen in the glomeruli. Electron-dense deposits were observed in both the subendothelial and the mesangial areas. Focal subendothelial widening accompanied with monocytes or foam cell infiltration was also seen. The findings reflect a typical post-MRSA infection glomerulonephritis caused by S.aureus cell envelope antigen.

Staphylococcus aureus Panton-Valentine leukocidin directly targets mitochondria and induces Bax-independent apoptosis of human neutrophils

Panton-Valentine leukocidin (PVL) is a pore-forming toxin secreted by Staphylococcus aureus that has recently been associated with necrotizing pneumonia. In the present study, we report that in vitro, PVL induces polymorphonuclear cell death by necrosis or by apoptosis, depending on the PVL concentration. PVL-induced apoptosis was associated with a rapid disruption of mitochondrial homeostasis and activation of caspase-9 and caspase-3, suggesting that PVL-induced apoptosis is preferentially mediated by the mitochondrial pathway. Polymorphonuclear cell exposure to PVL leads to mitochondrial localization of the toxin, whereas Bax, 1 of the 2 essential proapoptotic members of the Bcl-2 family, was still localized in the cytosol. Addition of PVL to isolated mitochondria induced the release of the apoptogenic proteins cytochrome c and Smac/DIABLO. Therefore, we suggest that PVL, which belongs to the pore-forming toxin family, could act at the mitochondrion level by creating pores in the mitochondrial outer membrane. Furthermore, LukS-PV, 1 of the 2 components of PVL, was detected in lung sections of patients with necrotizing pneumonia together with DNA fragmentation, suggesting that PVL induces apoptosis in vivo and thereby is directly involved in the pathophysiology of necrotizing pneumonia.

[Staphylococcal pneumonia]

In January to December 2000, a total of 15 (8.8%) patients with staphylococcal community-acquired pneumonia (CAP), 13 (27.7%) patients with staphyloccocal nosocomial pneumonia (NP) that occurred at general units (GU), and 9 (50%) patients with GU that occurred under artificial ventilation (AV) at intensive care units (ICU) were followed up. Meticillin-resistant S. aureus strains were isolated in 6.7, 38.5, and 55.6% of cases, respectively. As compared with pneumococcal CAP, staphyloccocal CAP were more frequently characterized by the severe course of the disease (46.7% versus 15.4%), bilateral lesion (33.3% versus 5.1%), and the presence of complications (66.7% versus 30.8%). Staphyloccocal NP that had occurred at GU, as compared to that at ICU also showed the severe course of the disease (46.2% versus 2.9%), bilateral lesion (30.7% versus 0%), and developed complications (75% versus 25%). Staphylococcal NP developed under AV at ICU had no specific features as compared with NP of another etiology. Oxacillin and first-second-generation cephalosporins remain to be the drugs of choice when meticillin-sensitive S. aureus strains are isolated; lincomycin and erythromycin being alternative agents against these strains. Glycopeptides are the drugs of choice when meticillin-resistant S. aureus strains are isolated, its alernatives are linesolide or rifampicin. High mortality rates due to staphylococcal pneumonia are preserved. These are 7.1% in CAP, 7.7 and 66.7 in staphylococcal NP occurring at GU and under AV at ICU, respectively.

Lipoteichoic acid and peptidoglycan from Staphylococcus aureus synergistically induce neutrophil influx into the lungs of mice

Staphylococcus aureus is an important pathogen in nosocomial pneumonia. Lipoteichoic acid (LTA) and peptidoglycan (PepG) are part of the staphylococcal cell wall. Here we show that LTA and PepG act in synergy to cause polymorphonuclear cell recruitment in the pulmonary compartment during S. aureus pneumonia.

[Fatal pneumonia in an adolescent due to community-acquired methicillin-resistant Staphylococcus aureus positive for Panton-Valentine-leukocidin]

A 15-year-old girl developed a severe Staphylococcus aureus pneumonia following an influenza virus infection. The patient was admitted to a paediatric intensive-care facility because of respiratory and circulatory failure. Despite aggressive therapy, she died on the third day following admission to the intensive care unit due to secondary hypoxic-ischaemic encephalopathy. Blood and respiratory aspirate cultures showed community-acquired methicillin-resistant S. aureus (CA-MRSA) with a normal antibiotic sensitivity except for betalactam antibiotics. PCR-based methods demonstrated that the isolate possessed the Panton-Valentine-leukocidin (PVL) gene, encoding an S. aureus exotoxin that is associated with fulminant necrotising pneumonia. This case shows that clinicians in the Netherlands should also be aware of the possibility of CA-MRSA in patients without risk factors for MRSA carriage. Especially in children and adolescents with an influenza virus infection, pneumonia due to PVL-positive S. aureus strains may be life-threatening.

Intrafamilial spread of highly virulent staphylococcus aureus strains carrying the gene for Panton-Valentine leukocidin

Necrotizing pneumonia caused by Staphylococcus aureus carrying the gene for Panton-Valentine leukocidin is a newly described disease entity. We report 2 cases with intrafamilial spread.

Differential role of interleukin-6 in lung inflammation induced by lipoteichoic acid and peptidoglycan from Staphylococcus aureus

Lipoteichoic acids (LTA) and peptidoglycans (PepG) are major components of the cell walls of gram-positive bacteria that trigger inflammatory responses in vitro. To study the in vivo effects of LTA and PepG from Staphylococcus aureus in lungs and to determine the role of interleukin (IL)-6 herein, these compounds were intranasally administered to IL-6 gene deficient (IL-6(-/-)) and wild type (IL-6(+/+)) mice. In IL-6(+/+) mice, LTA and PepG induced acute pulmonary inflammation in a dose-dependent way, characterized by neutrophilic influx and IL-6 production in the bronchoalveolar lavage fluid. Endogenously produced IL-6 attenuated inflammation induced by 10 microg LTA, as reflected by enhanced neutrophil influx, and increased tumor necrosis factor-alpha, macrophage inflammatory protein-1-alpha, and cytokine-induced neutrophil chemoattractant (KC) release into bronchoalveolar lavage fluid of IL-6(-/-) mice, compared with IL-6(+/+) mice. By contrast, pulmonary inflammation induced by 100 microg LTA was similar (neutrophil influx) or even tended to be attenuated (cytokine and chemokine release) in IL-6(-/-) mice. Endogenous IL-6 increased inflammation induced by PepG, as reflected by decreased neutrophil influx into lungs of IL-6(-/-) mice, compared with IL-6(+/+) mice. These data suggest that IL-6 plays an anti-inflammatory role during LTA-induced pulmonary inflammation, which is dependent on the severity of the inflammatory challenge, and a proinflammatory role in peptidoglycan-induced acute lung inflammation. Thus, the contribution of IL-6 to lung inflammation may vary with the stimulus used.

Association between Staphylococcus aureus strains carrying gene for Panton-Valentine leukocidin and highly lethal necrotising pneumonia in young immunocompetent patients

BACKGROUND

Between 1986 and 1998, eight cases of community-acquired pneumonia due to Staphylococcus aureus strains carrying the gene for the Panton-Valentine leukocidin (PVL) were recorded in France, six of which were fatal. We aimed to assess the clinical features of these eight cases, and those of other cases identified prospectively, and to compare them with the characteristics of patients with pneumonia caused by PVL-negative strains.

METHODS

We compared eight retrospective and eight prospective cases of PVL-positive S aureus pneumonia with 36 cases of PVL-negative S aureus pneumonia. For all patients, we recorded age, length of hospital stay, risk factors for infection, signs and symptoms, laboratory findings, antibiotic treatment, and serial radiological findings.

FINDINGS

Median age was 14.8 years (IQR 5.4-24.0) for the PVL-positive patients and 70.1 years (59.2-81.4) for the others (p=0.001). Influenza-like illness had occurred during the 2 days before admission in 12 of the 16 PVL-positive patients, but in only three of 33 PVL-negative patients (p<0.001). PVL-positive infections were more often marked by: temperature greater than 39 degrees C (p=0.01), heart rate above 140 beats per min (p=0.02), haemoptysis (p=0.005), onset of pleural effusion during hospital stay (p=0.004), and leucopenia (p=0.001). The survival rate 48 h after admission was 63% for the PVL-positive patients and 94% for PVL-negative individuals (p=0.007). Histopathological examination of lungs at necropsy from three cases of necrotising pneumonia associated with PVL-positive S aureus showed extensive necrotic ulcerations of the tracheal and bronchial mucosa and massive haemorrhagic necrosis of interalveolar septa.

INTERPRETATION

PVL-producing S aureus strains cause rapidly progressive, haemorrhagic, necrotising pneumonia, mainly in otherwise healthy children and young adults. The pneumonia is often preceded by influenza-like symptoms and has a high lethality rate.

[Severe staphylococcal pneumonia in children]

Between 1986 and 1999, 8 cases of severe pneumonia due Staphylococcus aureus strains producing the Panton and Valentine leukotoxin (PVL) were referred to the French reference centre for staphylococcal toxaemia. All but one patient were children and to determine the clinical features of these pneumonia we conducted a prospective surveillance during 1999. Staphylococcal pneumonia was defined according to usual standards. All the strains were tested for the gene coding PVL, the cases associated with PVL positive strains were considered as study group. Nosocomial pneumonia were excluded. 52 cases were referred and 16 were PVL positive. These pneumonia occurred in younger patients (median age = 14.8 vs. 70.1) which were previously healthy (40% of underlying disease in control) Remarkable features were the presence of viral infection in the preceding day (75% vs. 9%), the frequency of shock (81% vs. 53%), respiratory distress (75% vs. 53%) and hemoptysia (38% vs. 3%). Leucopenia was present in 79% of cases. Mortality was higher in the PVL group (75% vs. 47%). Severe staphylococcal pneumonia with shock, leucopenia, hemoptysia and high mortality rate have been previously described in children and young adults. We established the relationship between this syndrome and the PVL production by S. aureus. We believe that viral infection constitute the prerequisite altering the respiratory epithelium which secondary allows S. aureus invasion. The necrotizing action of the PVL leads to the massive haemorrhagic necrotic pneumonia. Staphylococcal necrotizing pneumonia is a new entity which frequency is probably underestimated. Further studies are needed to determinate the prognosis factors, the role of S. aureus carriage and of viral infections. The description of this new syndrome could lead to changes in the management of staphylococcal pneumonia in children.

Bacterial superantigen staphylococcal enterotoxin B induces interstitial pneumonia in SCID mice reconstituted with peripheral blood mononuclear cells from collagen vascular disease patients

To investigate whether superantigens induce interstitial pneumonia associated with collagen vascular disease (CVD), staphylococcal enterotoxin B (SEB) was intratracheally administered to SCID mice reconstituted with peripheral blood mononuclear cells (PBMCs) from CVD patients that suffered lung complications. Although a slight accumulation of inflammatory cells into the perivascular area was seen in the lungs of SCID mice injected with PBMCs from CVD patients or healthy donors, SEB administration significantly increased the severity of inflammation in the lungs of SCID mice that received CVD patient PBMCs. Furthermore, human leukocytes were detected by immunohistochemistry in the lungs of SCID mice that received SEB after reconstitution with PBMCs from CVD patients but not in other groups of SCID mice. CD45RO(+) memory T cells comprised the majority of infiltrating human leukocytes. These results suggest the possibility that external superantigens may induce the development of interstitial pneumonia in patients that have a genetic background predisposition to autoimmune disease.

Factors affecting the course and severity of transnasally induced Staphylococcus aureus pneumonia in mice

In order to examine several factors that may affect the course and severity of transnasally induced Staphylococcus aureus pneumonia in mice, bacteria were prepared in a free suspension or bound to fetal mouse cells. Immunosuppression was induced in five strains of mice (ICR, C57BL/6, BALB/c, C3H/He and CBA/J) by injection of cyclophosphamide (200 mg/kg body weight), 2 days before infection. Impairment of mucociliary clearance was induced by intranasal instillation of formalin. Mice were then infected with various doses and strains of the organism. Although no significant differences were observed between either form of inoculum, pretreatment with formalin plus cyclophosphamide was associated with a significant increase in lung bacterial counts. In particular, cyclophosphamide treatment was associated with a high mortality in mice infected with several strains of S. aureus irrespective of their toxin production profiles. Histopathological examination demonstrated that in mice treated with formalin plus cyclophosphamide, clusters of bacteria were observed in lung parenchyma, associated with a mild accumulation of inflammatory cells at day 2 and extensive cell infiltration at day 7. CBA/J mice represented the most susceptible strain among those examined, with 10(4)- and 10(2)-fold higher bacterial counts in the lungs at days 3 and 5, respectively. These results indicate that neutropenia and impaired mucociliary clearance are major factors that influence the severity of S. aureus pneumonia in mice. Analysis of the role of genetic background in enhancement of vulnerability to infection is warranted in future studies.

Alpha-toxin damages the air-blood barrier of the lung in a rat model of Staphylococcus aureus-induced pneumonia

We have shown that injury to alveolar epithelial type I cells may account, in part, for damage to the air-blood barrier of the lung in a rat model of Staphylococcus aureus pneumonia. We have also shown that alpha-toxin is an important cause of damage to the air-blood barrier; however, our data suggest that the toxin is not acting directly on alveolar type I cells.

Spontaneous tension pneumopericardium complicating staphylococcal pneumonia

The authors describe a patient with spontaneous pneumopericardium complicating staphylococcal pneumonia and empyema that resulted in cardiac tamponade. Spontaneous pneumopericardium is an unusual disorder. The causes and clinical findings of pneumopericardium are reviewed, as are the radiographic features that differentiate this condition from pneumomediastinum. Early recognition of pneumopericardium is important, because emergent pericardiocentesis may be required if there is clinical evidence of tamponade.

Role of coagulase in a murine model of hematogenous pulmonary infection induced by intravenous injection of Staphylococcus aureus enmeshed in agar beads

We describe a novel mouse model of acute staphylococcal pneumonia induced by intravenous injection of Staphylococcus aureus enmeshed in agar beads. For comparison, we also used various strains of bacteria, including three strains of S. aureus, two strains of Staphylococcus epidermidis, one strain of Streptococcus pyogenes, three strains of Pseudomonas aeruginosa, and one strain of Klebsiella pneumoniae. All except two strains of S. aureus were cleared rapidly from the lungs. When S. aureus NUMR1 enmeshed in agar beads was injected intravenously, the organisms concentrated and remained in the lung for a period longer than several weeks. Multiple lung abscesses were evident macroscopically, and histological examination of the infected lung showed multiple lung abscesses around the pulmonary arterioles, consisting of bacterial colonies encircled with fibrin filaments and surrounded by inflammatory cells of neutrophils and macrophages. When 14 strains of clinically isolated S. aureus were injected intravenously, the number of bacteria recovered from the lung tissue 7 days after infection correlated with the titer of staphylocoagulase (P < 0.01) but not with the titer of clumping factor. Injection of coagulase-deficient mutant strain DU5843 was associated with a markedly reduced number of viable bacteria isolated from the lung, compared with its coagulase-positive parental strain DU5789. Our results suggest that coagulase may play a role in the development of blood-borne staphylococcal pneumonia in our model. Our animal model is simple and reproducible and resembles blood-borne staphylococcal pneumonia in humans, and it could be useful for investigating the pathogenicity or treatment of staphylococcal pulmonary infection, including infections with methicillin-resistant S. aureus.

Radiographic features of staphylococcal pneumonia in adults and children

BACKGROUND

Clinical and laboratory features do not accurately correlate with the cause of community acquired pneumonia. A study was performed to examine whether the radiographic features of staphylococcal pneumonia are sufficiently distinct to aid early diagnosis.

METHODS

The chest radiographs of 34 patients (including eight children) with proven staphylococcal pneumonia were reviewed by two experienced observers using methods described previously. Features on presentation and follow up were noted.

RESULTS

The most striking features were the presence of multilobar consolidation on presentation, cavitation, pneumatocoeles and spontaneous pneumothorax, together with a tendency to radiographic deterioration after admission in both adults and children. Some of these features are much less common with other causes of community acquired pneumonia. However, most of the cases did not have these classic features.

CONCLUSIONS

The presence of certain radiographic features, including multilobar shadowing, cavitation, pneumatocoeles, and spontaneous pneumothorax, are seen with staphylococcal pneumonia in adults and children, but their absence does not exclude the diagnosis.

Effect of pentoxifylline on changes in neutrophil sequestration and emigration in the lungs

The response of neutrophils to inflammatory stimuli includes sequestration, adhesion, and migration. Pentoxifylline protects against many neutrophil-mediated lung injuries. This study investigated whether pentoxifylline prevented changes in neutrophil kinetics induced by infusion of complement fragments or neutrophil emigration induced by Streptococcus pneumoniae. Complement fragments were infused in New Zealand White rabbits treated with pentoxifylline or saline, and the circulating neutrophil counts in the arterial and venous blood samples were measured. Neutrophil emigration was induced by intrabronchial instillation of S. pneumoniae and quantitated morphometrically. The results show that, at doses achievable in vivo, pentoxifylline did not prevent either the CD18-dependent or -independent phase of complement-mediated neutrophil sequestration within the pulmonary microvasculature or the release of neutrophils from the bone marrow. Pentoxifylline also did not alter either the deformability of unstimulated leukocytes or stimulus-induced decreases in deformability. Finally, neutrophil emigration into the alveolar space was neither attenuated nor accentuated by pentoxifylline. These data suggest that, in vivo, pentoxifylline does not protect against lung injury by inhibiting neutrophil sequestration or emigration and may act to alter the generation of mediators that affect neutrophil behavior, rather than acting directly on neutrophils.

Prospective study of the aetiology of adult community acquired bacterial pneumonia needing hospitalisation in Singapore

A prospective survey of 96 consecutive adult patients with community acquired pneumonia requiring hospitalisation was carried out at National University Hospital, Singapore. Causative pathogens were identified in 58% of patients. Mycobacterium tuberculosis was the most common pathogen (21%), followed by Streptococcus pneumoniae (12%), Haemophilus influenzae (5.2%), Mycoplasma pneumoniae (5.2%) and Staphylococcus aureus (4.2%). Gram-negative organisms (apart from Haemophilus influenzae) were found in 10% of pneumonia patients. More than half of the patients had pre-existing illness, the most common was diabetes mellitus (21%).