Staphylococcus aureus Pneumonia: Preceding Influenza Infection Paves the Way for Low-Virulent Strains.

Staphylococcus aureus is a facultative pathogenic bacterium that colonizes the nasopharyngeal area of healthy individuals, but can also induce severe infection, such as pneumonia. Pneumonia caused by mono- or superinfected S.aureus leads to high mortality rates. To establish an infection, S. aureus disposes of a wide variety of virulence factors, which can vary between clinical isolates. Our study aimed to characterize pneumonia isolates for their virulent capacity. For this, we analyzed isolates from colonization, pneumonia due to S. aureus, and pneumonia due to S. aureus/influenza virus co-infection. A total of 70 strains were analyzed for their virulence genes and the host-pathogen interaction was analyzed through functional assays in cell culture systems. Strains from pneumonia due to S. aureus mono-infection showed enhanced invasion and cytotoxicity against professional phagocytes than colonizing and co-infecting strains. This corresponded to the high presence of cytotoxic components in pneumonia strains. By contrast, strains obtained from co-infection did not exhibit these virulence characteristics and resembled strains from colonization, although they caused the highest mortality rate in patients. Taken together, our results underline the requirement of invasion and toxins to cause pneumonia due to S. aureus mono-infection, whereas in co-infection even low-virulent strains can severely aggravate pneumonia.

Combination of ECMO and cytokine adsorption therapy for severe sepsis with cardiogenic shock and ARDS due to Panton-Valentine leukocidin-positive Staphylococcus aureus pneumonia and H1N1.

Sepsis-induced cardiogenic shock in combination with severe acute respiratory failure represents a life-threatening combination that is often refractory to the conventional methods of treatment. We describe the case of a 33-year-old patient who developed acute cardiovascular collapse and ARDS secondary to superinfection of Panton-Valentine leukocidin-positive Staphylococcus aureus and H1N1 pneumonia who underwent successful combination therapy for severe sepsis-related cardiomyopathy and respiratory failure using extracorporeal membrane oxygenation and cytokine adsorption therapy.

Influenza A virus exacerbates Staphylococcus aureus pneumonia in mice by attenuating antimicrobial peptide production.

Influenza A represents a significant cause of morbidity and mortality worldwide. Bacterial complications of influenza A confer the greatest risk to patients. TH17 pathway inhibition has been implicated as a mechanism by which influenza A alters bacterial host defense. Here we show that preceding influenza causes persistent Staphylococcus aureus infection and suppression of TH17 pathway activation in mice. Influenza does not inhibit S. aureus binding and uptake by phagocytic cells but instead attenuates S. aureus induced TH17 related antimicrobial peptides necessary for bacterial clearance in the lung. Importantly, exogenous lipocalin 2 rescued viral exacerbation of S. aureus infection and decreased free iron levels in the bronchoalveolar lavage from mice coinfected with S. aureus and influenza. These findings indicate a novel mechanism by which influenza A inhibits TH17 immunity and increases susceptibility to secondary bacterial pneumonia. Identification of new mechanisms in the pathogenesis of bacterial pneumonia could lead to future therapeutic targets.

Respiratory syncytial virus and Staphylococcus aureus coinfection in children hospitalized with pneumonia.

Respiratory syncytial virus (RSV) infection might facilitate bacterial infection. We describe 5 patients with RSV among 30 children admitted to pediatric hospitals in Atlanta between October 1, 2006 and April 30, 2007 with community-onset Staphylococcus aureus pneumonia. RSV-S. aureus patients were younger and had less medical comorbidity than those without RSV.

A postinfluenza model of Staphylococcus aureus pneumonia.

BACKGROUND: Postinfluenza Staphylococcus aureus pneumonias are increasingly recognized as a major form of life-threatening infections. METHODS: A mouse model of postinfluenza S. aureus pneumonia was developed. Mice were intranasally infected with bacteria alone or bacteria plus virus. Infection was assessed by mouse survival, lung histopathology, bacterial density in the lungs, and cellular response to infection. RESULTS: Mice infected with both influenza virus and S. aureus showed higher mortality, greater lung parenchymal damage, and greater bacterial density at metastatic tissue sites than mice infected with only S. aureus. At 4 h, more polymorphonuclear leukocytes and fewer CD11c(+) cells were found in lung samples from mice infected with virus and bacteria than in those from mice infected with bacteria. alpha-Hemolysin and protein A were maximally expressed 4 h after infection, and Panton-Valentine leukocidin was maximally expressed 72 h after infection, with higher levels of alpha-hemolysin expression in mice infected with bacteria alone. Interferon gamma expression was higher in tissue collected from mice infected with virus plus bacteria than in those from bacteria-infected mice. CONCLUSIONS: The results from this model demonstrate diverse effects caused by antecedent influenza virus infection, which have a profound influence on the morbidity and mortality associated with S. aureus pneumonia.

[H3N2 subtype of human influenza pneumonia with staphylococcal sepsis and staphylococcal pneumonia: report of one case].

To investigate the clinical characteristics, diagnosis and therapy of influenza pneumonia with staphylococcal infection. One patient in our hospital was diagnosed and the literatures on the subject were reviewed. The patient presented with high fever and dyspnea. Arterial gas analysis indicated type 1 respiratory failure. Chest X ray photographs showed bilateral infiltrations and bilateral encapsulated pleural effusions. Viral separation and culture of pharyngeal swab indicated H(3)N(2) subtype of human influenza virus. Blood, sputum and bronchoalveolar lavage fluid (BALF) cultures showed Staphylococcus aureus. Pleural effusion was complex parapneumonic pleural effusion. After the administration of anti-virus, anti-staphylococcal antibiotics and pleural cavity drainage, the patient was cured. The infection of staphylococcus aureus is a typical characteristic of influenza pneumonia, and anti-staphylococcal antibiotic therapy (with MRSA activity in MRSA endemic regions) should be initiated in hospitalized cases of influenza pneumonia. If complex parapneumonic pleural effusion or empyema complicated, we should perform pleural cavity drainage in time. The oral neuraminidase inhibitor (oseltamivir) could significantly improve prognosis.