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)-alpha serum 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-alpha: 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

Mise au point d’un modèle de co-culture cellules entérocytes et d’un modèle de colonisation digestive stable chez la souris immuno-compétente permettant d’étudier les interactions cellulaires et moléculaires in vitro et in vivo de C. albicans avec la muqueuse digestive

National audienc

Kineret®/IL-1ra blocks the IL-1/IL-8 inflammatory cascade during recombinant Panton Valentine Leukocidin-triggered pneumonia but not during S. aureus infection.

OBJECTIVES: Community-acquired Staphylococcus aureus necrotizing pneumonia is a life-threatening disease. Panton Valentine Leukocidin (PVL) has been associated with necrotizing pneumonia. PVL triggers inflammasome activation in human macrophages leading to IL-1β release. IL-1β activates lung epithelial cells to release IL-8. This study aimed to assess the relevance of this inflammatory cascade in vivo and to test the potential of an IL-1 receptor antagonist (IL-1Ra/Kineret) to decrease inflammation-mediated lung injury. METHODS: We used the sequential instillation of Heat-killed S. aureus and PVL or S. aureus infection to trigger necrotizing pneumonia in rabbits. In these models, we investigated inflammation in the presence or absence of IL-1Ra/Kineret. RESULTS: We demonstrated that the presence of PVL was associated with IL-1β and IL-8 release in the lung. During PVL-mediated sterile pneumonia, Kineret/IL-1Ra reduced IL-8 production indicating the relevance of the PVL/IL-1/IL-8 cascade in vivo and the potential of Kineret/IL-1Ra to reduce lung inflammation. However, Kineret/IL-1Ra was ineffective in blocking IL-8 production during infection with S. aureus. Furthermore, treatment with Kineret increased the bacterial burden in the lung. CONCLUSIONS: Our data demonstrate PVL-dependent inflammasome activation during S.aureus pneumonia, indicate that IL-1 signaling controls bacterial burden in the lung and suggest that therapy aimed at targeting this pathway might be deleterious during pneumonia

Kineret®/IL-1ra blocks the IL-1/IL-8 inflammatory cascade during recombinant Panton Valentine Leukocidin-triggered pneumonia but not during S. aureus infection.

OBJECTIVES: Community-acquired Staphylococcus aureus necrotizing pneumonia is a life-threatening disease. Panton Valentine Leukocidin (PVL) has been associated with necrotizing pneumonia. PVL triggers inflammasome activation in human macrophages leading to IL-1β release. IL-1β activates lung epithelial cells to release IL-8. This study aimed to assess the relevance of this inflammatory cascade in vivo and to test the potential of an IL-1 receptor antagonist (IL-1Ra/Kineret) to decrease inflammation-mediated lung injury. METHODS: We used the sequential instillation of Heat-killed S. aureus and PVL or S. aureus infection to trigger necrotizing pneumonia in rabbits. In these models, we investigated inflammation in the presence or absence of IL-1Ra/Kineret. RESULTS: We demonstrated that the presence of PVL was associated with IL-1β and IL-8 release in the lung. During PVL-mediated sterile pneumonia, Kineret/IL-1Ra reduced IL-8 production indicating the relevance of the PVL/IL-1/IL-8 cascade in vivo and the potential of Kineret/IL-1Ra to reduce lung inflammation. However, Kineret/IL-1Ra was ineffective in blocking IL-8 production during infection with S. aureus. Furthermore, treatment with Kineret increased the bacterial burden in the lung. CONCLUSIONS: Our data demonstrate PVL-dependent inflammasome activation during S.aureus pneumonia, indicate that IL-1 signaling controls bacterial burden in the lung and suggest that therapy aimed at targeting this pathway might be deleterious during pneumonia

In Vivo Efficacy of Ceftaroline Fosamil in a Methicillin-Resistant Panton-Valentine Leukocidin-Producing Staphylococcus aureus Rabbit Pneumonia Model.

International audienceCeftaroline, the active metabolite of the prodrug ceftaroline fosamil, is a cephalosporin with broad-spectrum in vitro activity against Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Streptococcus pneumoniae (MDRSP), and common Gram-negative pathogens. This study investigated the in vivo activity of ceftaroline fosamil compared with clindamycin, linezolid, and vancomycin in a severe pneumonia model due to MRSA-producing Panton-Valentine leukocidin (PVL). A USA300 PVL-positive clone was used to induce pneumonia in rabbits. Infected rabbits were randomly assigned to no treatment or simulated human-equivalent dosing with ceftaroline fosamil, clindamycin, linezolid, or vancomycin. Residual bacterial concentrations in the lungs and spleen were assessed after 48 h of treatment. PVL expression was measured using a specific enzyme-linked immunosorbent assay (ELISA). Ceftaroline, clindamycin, and linezolid considerably reduced mortality rates compared with the control, whereas vancomycin did not. Pulmonary and splenic bacterial titers and PVL concentrations were greatly reduced by ceftaroline, clindamycin, and linezolid. Ceftaroline, clindamycin, and linezolid were associated with reduced pulmonary tissue damage based on significantly lower macroscopic scores. Ceftaroline fosamil, clindamycin, and, to a lesser extent, linezolid were efficient in reducing bacterial titers in both the lungs and spleen and decreasing macroscopic scores and PVL production compared with the control

Timeline representation of the experimental protocol.

<p>*denotes blood sample drawing.</p

Pulmonary and systemic bacterial burden of <i>Staphylococcus aureus</i>.

<p><b>(4A)</b><b><i>S</i></b>. <b><i>aureus</i></b><b>lung concentrations 8 and 24 hours after bacteria instillation.</b> Pulmonary bacterial burden according to the experimental group in either spontaneously breathing (SB + <i>S</i>. <i>aureus</i>) or mechanically ventilated (MV + <i>S</i>. <i>aureus</i>) animals with <i>Staphylococcus aureus</i> pneumonia 8 hours after inoculation (n = 5 and 6, respectively) and 24 hours after inoculation (n = 8 and 11 respectively). The bacterial burden was higher in the MV group both after 8 hours (5.00±1.03 versus [vs.] 5.87±0.38 log₁₀CFU/g, <i>p</i> = 0.028) and 24 hours of MV (4.96±1.31 vs. 6.13±0.63 log₁₀CFU/g, <i>p</i> = 0.002). *denotes <i>p</i>≤0.05. CFU: colony forming unit. (4B) <i>S</i>. <i>aureus</i> spleen concentrations 8 and 24 hours after bacteria instillation. Spleen bacterial burden according to the experimental group in either spontaneously breathing (SB + <i>S</i>. <i>aureus</i>) or mechanically ventilated (MV + <i>S</i>. <i>aureus</i>) animals with <i>Staphylococcus aureus</i> pneumonia (n = 4 and 5, respectively*). Interestingly, MV appears to promote early pulmonary-to-systemic translocation during <i>S</i>. <i>aureus</i> pneumonia, as indicated by the quantitative spleen cultures, as an indirect marker of bacteraemia, which were positive only in ventilated animals after 8 hours, even though there was no longer any difference after 24 hours. *spleen was lost in 1 animal from each group. Lung <i>S</i>. <i>aureus</i> concentrations SB versus (vs) MV 8 hours <i>p</i> = 0.050; Mann-Whitney U test, two-tailed. Lung <i>S</i>. <i>aureus</i> concentrations SB vs MV 24 hours <i>p</i> = 0.007; Mann-Whitney U test, two-tailed. Spleen <i>S</i>. <i>aureus</i> concentrations SB vs MV 8 hours <i>p</i> = 0.430; Mann-Whitney U test, two-tailed. Spleen <i>S</i>. <i>aureus</i> concentrations SB vs MV 24 hours <i>p</i> = 0.110; Mann-Whitney U test, two-tailed.</p

Histologic score according to the experimental condition.

<p>Histologic score ranging from 0 to 3, based on the degree of polymorphonuclear infiltration, haemorrhage, and oedema in the interstitial and alveolar spaces, following tracheal instillation of saline (controls) in either spontaneously breathing (SB, n = 5) rabbits or animals subjected to mechanical ventilation (MV, n = 5). Infected animals were challenged with 10⁹ CFU of <i>Staphylococcus aureus</i>. After bacterial challenge animals were kept SB or under MV for 8 hours (<i>n</i> = 5 and 6, respectively) and 24 hours (n = 8 and 11, respectively). The histologic score was higher under MV. ** denotes <i>p</i><0.05 between SB and MV animals; ns: not significant. CFU: colony forming unit. Controls SB versus (vs) MV p = 0.002; Mann-Whitney U test, two-tailed. <i>S</i>. <i>aureus</i> pneumonia SB vs MV 8 hours p = 0.011; Mann-Whitney U test, two-tailed. <i>S</i>. <i>aureus</i> pneumonia SB vs MV 24 hours p = 0.216; Mann-Whitney U test, two-tailed.</p

Mechanical Ventilation Alters the Development of <i>Staphylococcus aureus</i> Pneumonia in Rabbit

<div><p>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 <i>Staphylococcus aureus</i> VAP. Pneumonia was caused by airway challenge with <i>S</i>. <i>aureus</i>, 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 <i>S</i>. <i>aureus</i> challenge. In addition, <i>ex vivo</i> stimulations of whole blood taken from SB or MV rabbits (n = 7 and 5, respectively) with TLR2 agonist or heat-killed <i>S</i>. <i>aureus</i> 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 <i>versus [vs]</i> 2.40±0.55, <i>p</i> = 0.007), along with greater bacterial concentrations (6.13±0.63 vs. 4.96±1.31 colony forming units/gram, <i>p</i> = 0.002). Interleukin (IL)-8 and tumor necrosis factor (TNF)-αserum concentrations reached higher levels in MV animals (<i>p</i> = 0.010). Whole blood obtained from MV animals released larger amounts of cytokines if stimulated with TLR2 agonist or heat-killed <i>S</i>. <i>aureus</i> (e.g., TNF-α: 1656±166 vs. 1005±89; <i>p</i> = 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.</p></div

Inflammatory cytokine gene expression in the lung.

<p><b>(6A) IL-8 gene expression in the lung.</b> Inflammatory cytokine interleukin (IL)-8 gene expression in lung homogenates 8 hours after tracheal instillation of saline (controls) in either spontaneously breathing (SB, n = 5) rabbits or animals subjected to mechanical ventilation (MV, n = 5), or after challenge with 10⁹ CFU of <i>Staphylococcus aureus</i> (+<i>S</i>. <i>aureus</i>) (n = 5 in each group**). All values are reported as fold increase compared with SB rabbits. Results are expressed as mean±standard deviation. IL-8 gene expression was increased under MV in all groups. *denotes <i>p</i>≤0.05; ns: not significant; **PCR amplification failed in 1 MV rabbit. CFU: colony forming unit. Controls SB versus (vs) MV <i>p</i> = 0.008, Mann-Whitney U test, two-tailed. <i>S</i>. <i>aureus</i> SB vs MV p = 0.873, Mann-Whitney U test, two-tailed. (6B) TNF-α gene expression in the lung. Inflammatory cytokine tumor necrosis factor (TNF)-α gene expression in lung homogenates 8 hours after tracheal instillation of saline (controls) in either spontaneously breathing (SB, n = 5) rabbits or animals subjected to mechanical ventilation (MV, n = 5), or after challenge with 10⁹ CFU of <i>Staphylococcus aureus</i> (+<i>S</i>. <i>aureus</i>) (n = 5 in each group). All values are reported as fold increases compared with SB rabbits. Results are expressed as mean±standard deviation TNF-α gene expression was increased under MV only in control animals, *denotes <i>p</i>≤0.05; ns: not significant; **Polymerase chain reaction amplification failed in 1 MV rabbit. CFU: colony forming unit. Controls SB versus (vs) MV <i>p</i> = 0.076, Mann-Whitney U test, two-tailed. <i>S</i>. <i>aureus</i> SB vs MV p = 0.825, Mann-Whitney U test, two-tailed.</p