Phenol-Soluble Modulin Peptides Contribute to Influenza A Virus-Associated Staphylococcus aureus Pneumonia

Abstract

Influenza A virus (IAV) infection is often followed by secondary bacterial lung infection, which is a major reason for severe, often fatal pneumonia. Communityassociated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains such as USA300 cause particularly severe and difficult-to-treat cases of IAV-associated pneumonia. CA-MRSA strains are known to produce extraordinarily large amounts of phenol-soluble modulin (PSM) peptides, which are important cytotoxins and proinflammatory molecules that contribute to several types of S. aureus infection. However, their potential role in pneumonia has remained elusive. We determined the impact of PSMs on human lung epithelial cells and found that PSMs are cytotoxic and induce the secretion of the proinflammatory cytokine interleukin-8 (IL-8) in these cells. Both effects were boosted by previous infection with the 2009 swine flu pandemic IAV H1N1 strain, suggesting that PSMs may contribute to lung inflammation and damage in IAV-associated S. aureus pneumonia. Notably, the PSM-producing USA300 strain caused a higher mortality rate than did an isogenic PSM-deficient mutant in a mouse IAV-S. aureus pneumonia coinfection model, indicating that PSMs are major virulence factors in IAV-associated S. aureus pneumonia and may represent important targets for future anti-infective therapies.KEYWORDS influenza, pneumonia, Staphylococcus aureus, toxins B acterial pneumonia is a severe disease that can be caused by bacterial superinfection of virus-damaged mammalian lungs. Viruses commonly involved in the predisposition to bacterial pneumonia include influenza A virus (IAV), influenza B virus, respiratory syncytial virus, and human parainfluenza virus (1). Normally, the motility of cilia localized in the tracheal epithelium actively removes mucus, thereby eradicating entrapped foreign particles that would otherwise end up in the lungs. However, when a viral lung infection is already established, the function of the cilia is impaired, paving the way for further invaders (2, 3). Pandemic influenza virus infections such as those of the 2009 H1N1 swine flu pandemic correlated with bacterial superinfections with devastating consequences, such as high morbidity and mortality rates (4-6).Two forms of pneumonia have been distinguished: community-associated pneumonia (CAP) and hospital-associated pneumonia (HAP). In most cases of CAP, Streptococcus pneumoniae has been determined to be the cause of pneumonia (7). Staphylococcus aureus, another aggressive Gram-positive pathogen, causes a variety of diseases in humans, including HAP, especially in ventilated patients (8). CAP is less often caused by S. aureus, except for pneumonia following influenza virus infection, which constitutes a severe secondary infection often resulting in fatal outcomes (9, 10). Moreover, S. aureus iai.asm.org 1 Infection and Immunity causes influenza-associated CAP more frequently in children than in adults (11). Gramnegative bacteria, such as Escherichia coli (12), Haemophilus influenzae (13), Klebsiella ...

Staphylococcus aureus Phenol-Soluble Modulins α1–α3 Act as Novel Toll-Like Receptor (TLR) 4 Antagonists to Inhibit HMGB1/TLR4/NF-κB Signaling Pathway

“…PSMs were first isolated from Staphylococcus epidermidis culture filtrate by hot phenol extraction in 1999 with a description of “proinflammatory complex” ( 3 ). S. aureus PSMs were subsequently identified as a complex of seven PSMs, including PSMα1–α4, PSMβ1–β2, and δ-toxin, which have multiple roles in S. aureus infections ( 4 – 8 ). Ordered S. aureus PSMs aggregate into amyloid-like fibers can facilitate biofilm structuring, thereby protecting S. aureus from immune systems ( 9 – 13 ).…”

Synergistic Effects of Influenza and Staphylococcus aureus Toxins on Inflammation Activation and Cytotoxicity in Human Monocytic Cell Lines

“…In our present study, we tested a broad range of S. aureus virulence factors—including PVL, Hla, PSMs, protein A, and cell wall components which are involved in the pathophysiology of S. aureus lung infection [ 29 , 30 ]. We performed our initial screening in a standardized in vitro model of influenza virus-infected continuous human monocytic cell lines, and subsequent testing in an ex vivo model of influenza virus-infected human monocytes.…”

“…In contrast, we did not observe any additive effect in cells co-exposed to influenza virus and to the other tested toxins (Hla, PSMα1, and PSMα3). It appears that the contribution of PSM to post-influenza pneumonia is likely linked to epithelial cell damage rather than monocyte damage [ 30 ]. Under our experimental conditions, human monocytes were already highly sensitive to the utilized PVL concentrations, preventing us from observing any potential synergy between influenza virus and PVL on primary monocytes.…”

Staphylococcus aureus Lung Infection Results in Down-Regulation of Surfactant Protein-A Mainly Caused by Pro-Inflammatory Macrophages

“…Here, we were able to demonstrate that S. aureus USA300 disposes of a large number of virulence factors. For instance, S. aureus strain USA300 expresses leucocidins (lukS, lukF), phenol-soluble modulin (PSM) [22], and superantigens (ssl) that are mainly directed against immune cells and induce strong proinflammatory and cytotoxic effects [31]. During viral and/or bacterial infection, the cytokine profile, including the expression of TNF-α, of infected cells is altered depending on the host cell type and on the pathogens.…”