IFN-γ Drives TNF-α Hyperproduction and Lethal Lung Inflammation during Antibiotic Treatment of Postinfluenza Staphylococcus aureus Pneumonia.

Inflammatory cytokine storm is a known cause for acute respiratory distress syndrome. In this study, we have investigated the role of IFN-γ in lethal lung inflammation using a mouse model of postinfluenza methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. To mimic the clinical scenario, animals were treated with antibiotics for effective bacterial control following MRSA superinfection. However, antibiotic therapy alone is not sufficient to improve survival of wild-type animals in this lethal acute respiratory distress syndrome model. In contrast, antibiotics induce effective protection in mice deficient in IFN-γ response. Mechanistically, we show that rather than inhibiting bacterial clearance, IFN-γ promotes proinflammatory cytokine response to cause lethal lung damage. Neutralization of IFN-γ after influenza prevents hyperproduction of TNF-α, and thereby protects against inflammatory lung damage and animal mortality. Taken together, the current study demonstrates that influenza-induced IFN-γ drives a stepwise propagation of inflammatory cytokine response, which ultimately results in fatal lung damage during secondary MRSA pneumonia, despite of antibiotic therapy.

Serious life-threatening multifocal infection in a child, caused by Panton-Valentine leucocidin-producing Staphylococcus aureus (PVL-MSSA).

Groin pain is a frequently occurring complaint in presentations to the Emergency Department. Muscular sprain is often a differential diagnosis, however serious conditions such as pyomyositis should not be ignored. This case report presents a child with atraumatic right groin pain, which was initially diagnosed as a muscular sprain. The patient later re-presented out of hours to the Emergency Department with what was found to be extensive pelvic abscesses. He was subsequently found to have bilateral pneumonia and later developed a pericardial effusion and osteomyelitis of the right iliac bone, sacroiliac joint and sacrum. With multiple surgical interventions and appropriate antibiotics, he made a full recovery and was discharged home after a total admission time of 41 days. The causative organism was found to be Panton-Valentine leucocidin-positive methicillin-susceptible Staphylococcus aureus.

Successful percutaneous drainage of pneumatoceles in an extremely low-birthweight infant.

Pneumatoceles are thin-walled, air-filled cystic lesions developing within the lung parenchyma. It used to be a relatively common entity in the presurfactant era when preterm babies were ventilated at an unacceptably high positive pressure for respiratory distress syndrome. Pneumatocele formation is a very rare complication of pneumonia in neonates. We here report a case of extremely low-birthweight (ELBW) neonate who developed large bilateral pneumatoceles after staphylococcal pneumonia. Hereby, we present a case of an ELBW infant with bilateral massive pneumatoceles who underwent successful percutaneous catheter drainage to decompress these pneumatoceles.

Lack of Sphingosine Causes Susceptibility to Pulmonary Staphylococcus Aureus Infections in Cystic Fibrosis.

BACKGROUND: Pulmonary Staphylococcus aureus (S. aureus) infections occur early in a high percentage of cystic fibrosis (CF) patients and it is believed that these infections facilitate further colonization of CF lungs with Pseudomonas aeruginosa (P. aeruginosa). Previous studies demonstrated a marked reduction of sphingosine in tracheal and bronchial epithelial cells in CF compared to wild type mice, while ceramide is massively increased in CF mice. METHODS: We investigated the effect of C18-sphingosine and C16-ceramide on S. aureus in vitro. Based on our results we performed pulmonary infections with S. aureus and tested the influence of sphingosine inhalation. RESULTS: In vitro incubation of S. aureus with C18-sphingosine rapidly killed S. aureus, while C16-ceramide did not affect bacterial survival, but abrogated the effect of C18-sphingosine when applied together. The in vivo infection experiments revealed a high susceptibility of CF mice to pulmonary infection with S. aureus. Inhalation of C18-sphingosine rescued CF mice from pulmonary infections with different clinical S. aureus isolates, including a methicillin-resistant S. aureus (MRSA) strain. CONCLUSIONS: Our data indicate that the imbalance between ceramide and sphingosine in the CF respiratory tract prevents killing of S. aureus and causes the high susceptibility of CF mice to pulmonary S. aureus infections.

Adjunctive dexamethasone therapy improves lung injury by inhibiting inflammation and reducing RIP3 expression during Staphylococcus aureus pneumonia in mice.

Antibiotic-induced immunopathology associated with the release of bacterial cell wall components has been suggested to contribute to poor outcomes in bacterial pneumonia. Adjunctive systemic glucocorticoid steroid (GC) therapy for pneumonia has been a controversial issue. In the present study, we first found that dexamethasone (2.5 mg/kg/day) in combination with oxacillin was beneficial for improving lung injury in mice inoculated intratracheally with live Staphylococcus aureus, and did not interfere with bacterial clearance. Alleviation of lung injury was evidenced by attenuated lung pathology, reduced total protein levels, soluble receptor for advanced glycation end-products (sRAGE), tumor necrosis factor alpha (TNF-α), and keratinocyte chemoattractant (KC) and interleukin (IL)-6 in bronchoalveolar lavage fluid (BALF). It was further confirmed by inhibition of receptor interacting protein-3 (RIP3) expression in pulmonary tissues. As in the live S. aureus experiments, dexamethasone (2.5 mg/kg/day) improved lung injury in mice challenged with heat-killed S. aureus (HKSA). In conclusion, our results demonstrated that an appropriate dose of adjunctive dexamethasone (2.5 mg/kg/day) with oxacillin alleviated experimental S. aureus-induced lung injury via its inhibition of inflammatory cytokine release and RIP3 expression.

Diffuse cerebral petechial hemorrhage in an 8-year-old girl with MRSA pneumonia and sepsis.

An 8-year-old girl in septic shock due to necrotizing methicillin-resistant Staphylococcus aureus (MRSA) pneumonia developed signs of end-organ damage, new right hemiplegia, and left gaze preference. Susceptibility-weighted MRI demonstrated extensive multifocal petechial hemorrhage preferentially at the gray-white matter interface due to septic microemboli (figure). Mechanisms of hemorrhage include small-vessel occlusion leading to mycotic aneurysm formation with rupture or pyogenic arteritis without aneurysm formation.(1) Intracranial hemorrhage associated with metastatic staphylococcal infections is rarely described(2) and is especially noteworthy with diffuse cerebral petechial hemorrhage in the setting of metastatic MRSA.

Antimicrobial susceptibility and molecular typing of MRSA in cystic fibrosis.

OBJECTIVES: The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in cystic fibrosis (CF) patients in the United States is approximately 25%. Little is known about the relative proportion of hospital- versus community-associated strains or the antimicrobial susceptibility of MRSA in different CF centers. We hypothesized that the majority of MRSA isolates obtained from children with CF are those endemic in the hospital and that those associated with community acquisition (SCCmec IV) would be more resistant than typically seen in non-CF MRSA isolates. METHODS: We studied MRSA strains from seven pediatric CF centers to determine the clonal distribution based on DNA sequencing of the staphylococcal protein A gene (spa typing), the type of staphylococcal chromosomal cassette mec (SCCmec), and the proportion of strains with Panton-Valentine leukocidin (PVL). Antimicrobial susceptibility to systemic and topical antibiotics was compared between different MRSA types. RESULTS: We analyzed 277 MRSA isolates from unique patients (mean age 11.15 ± 4.77 years, 55% male). Seventy % of isolates were SCCmec II PVL negative and the remainder SCCmec IV. Overall 17% MRSA strains were PVL positive (all SCCmec IV). Spa typing of 118 isolates showed most of the SCCmec II strains being t002, while SCCmec IV PVL positive isolates were t008, and SCCmec IV PVL negative isolates represented a variety of spa-types. The proportions of SCCmec II strains and spa-types were similar among centers. Overall rates of resistance to trimethoprim-sulfamethoxazole (4%), tetracycline (7%), tigecycline (0.4%), linezolid (0.4%) as well as fosfomycin (0.4%), fusidic acid (3%), and mupirocin (1%) were low. No strains were resistant to vancomycin. SCCmec II strains had higher rates of resistance to ciprofloxacin and clindamycin (P < 0.001) than SCCmec IV strains. CONCLUSIONS: In this U.S. study, most MRSA isolates in the pediatric CF population were SCCmec II PVL negative. Rates of resistance were low, including to older and orally available antibiotics such as trimethoprim-sulfamethoxazole.

Community-associated methicillin-resistant Staphylococcus aureus necrotizing pneumonia in a healthy neonate.

The number of cases of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) pneumonia has increased since the late 1990s, with skin and soft tissue infections predominant among neonates. Herein, we present a rare case of CA-MRSA necrotizing pneumonia with empyema following respiratory syncytial virus (RSV) infection in a healthy neonate. Despite prompt vancomycin treatment, the disease worsened and finally we had to perform pneumonectomy. This case highlights the possibility of emerging CA-MRSA-related invasive disease among neonates.

Protecting against post-influenza bacterial pneumonia by increasing phagocyte recruitment and ROS production.

Seasonal and especially pandemic influenza predispose patients to secondary bacterial pneumonias, which are a major cause of deaths and morbidity. Staphylococcus aureus is a particularly common and deadly form of post-influenza pneumonia, and increasing staphylococcal drug resistance makes the development of new therapies urgent. We explored an innate immune-mediated model of the lung to define novel mechanisms by which the host can be protected against secondary staphylococcal pneumonia after sub-lethal influenza infection. We found that stimulating the innate immunity in the lung by overexpression of GM-CSF will result in resistance to S. aureus pneumonia after sublethal influenza infection. Resistance was mediated by alveolar macrophages and neutrophils, and was associated with increased production of reactive oxygen species (ROS) by alveolar macrophages. Resistance was abrogated by treatment with agents that scavenged ROS. We conclude that stimulating innate immunity in the lung markedly reduces susceptibility to post-influenza staphylococcal pneumonia and that this may represent a novel immunomodulatory strategy for prevention and treatment of secondary bacterial pneumonia after influenza.

Staphylococcus aureus in early cystic fibrosis lung disease.

Staphylococcus aureus: is a common bacterial organism infecting children with cystic fibrosis (CF). Emerging evidence suggests early lower airway infection with this organism in young children with CF results in the deterioration of lung function, poorer nutrition parameters and heightens the airway inflammatory response. Despite contributing significantly to the burden of early lung disease among this group, there are ongoing controversies in the management of S. aureus infection, and gaps in our understanding of exactly how this organism causes lung disease. To reduce the morbidity and mortality of early infection ongoing research is needed to: (i) understand the early host immune response that enables this pathogen to reside within the CF lung; (ii) determine if there are organism specific factors that are associated with CF lung disease; and (iii) clarify the utility of anti-staphylococcal antibiotic prophylaxis and/or eradication in the treatment of this patient population.

MRSA infected emphysematous bullae in an asymptomatic COPD patient.

This is a case of a 57-year-old gentleman with a history of chronic obstructive pulmonary disease (COPD) who presented with diarrhoea of more than 4 weeks in length. On chest x-ray, he was incidentally found to have a large cavitating lesion in his right lung. He denied having any respiratory distress at any stage and clinically he had been completely asymptomatic. The CT-guided biopsy confirmed a methicillin-resistant Staphylococcus aureus positive lung cavitation, most likely secondary to his poor dentition. A full dental clearance was performed, and he was treated with a course of intravenous vancomycin and oral clindamycin with good effect.

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-1ß, 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.

Selective V(1a) agonism attenuates vascular dysfunction and fluid accumulation in ovine severe sepsis.

Vasopressin analogs are used as a supplement to norepinephrine in septic shock. The isolated effects of vasopressin agonists on sepsis-induced vascular dysfunction, however, remain controversial. Because V(2)-receptor stimulation induces vasodilation and procoagulant effects, a higher V(1a)- versus V(2)-receptor selectivity might be advantageous. We therefore hypothesized that a sole, titrated infusion of the selective V(1a)-agonist Phe(2)-Orn(8)-Vasotocin (POV) is more effective than the mixed V(1a)-/V(2)-agonist AVP for the treatment of vascular and cardiopulmonary dysfunction in methicillin resistant staphylococcus aureus pneumonia-induced, ovine sepsis. After the onset of hemodynamic instability, awake, chronically instrumented, mechanically ventilated, and fluid resuscitated sheep were randomly assigned to receive continuous infusions of either POV, AVP, or saline solution (control; each n = 6). AVP and POV were titrated to maintain mean arterial pressure above baseline - 10 mmHg. When compared with that of control animals, AVP and POV reduced neutrophil migration (myeloperoxidase activity, alveolar neutrophils) and plasma levels of nitric oxide, resulting in higher mean arterial pressures and a reduced vascular leakage (net fluid balance, chest and abdominal fluid, pulmonary bloodless wet-to-dry-weight ratio, alveolar and septal edema). Notably, POV stabilized hemodynamics at lower doses than AVP. In addition, POV, but not AVP, reduced myocardial and pulmonary tissue concentrations of 3-nitrotyrosine, VEGF, and angiopoietin-2, thereby leading to an abolishment of cumulative fluid accumulation (POV, 9 ± 15 ml/kg vs. AVP, 110 ± 13 ml/kg vs. control, 213 ± 16 ml/kg; P < 0.001 each) and an attenuated cardiopulmonary dysfunction (left ventricular stroke work index, PaO(2)-to-FiO(2) ratio) versus control animals. Highly selective V(1a)-agonism appears to be superior to unselective vasopressin analogs for the treatment of sepsis-induced vascular dysfunction.

Pneumatocele in an adult.

We report a case of 25-year-old male who presented with high grade fever with cough and expectoration. Chest examination revealed amphoric breath sounds on the right interscapular region. Chest X ray revealed multiple air fluid levels with collapse lung at places. Staph pneumonia with pneumatoceles is common in children but uncommon to in adult population.