Sepsis-trained macrophages promote antitumoral tissue-resident T cells

Sepsis induces immune alterations, which last for months after the resolution of illness. The effect of this immunological reprogramming on the risk of developing cancer is unclear. Here we use a national claims database to show that sepsis survivors had a lower cumulative incidence of cancers than matched nonsevere infection survivors. We identify a chemokine network released from sepsis-trained resident macrophages that triggers tissue residency of T cells via CCR2 and CXCR6 stimulations as the immune mechanism responsible for this decreased risk of de novo tumor development after sepsis cure. While nonseptic inflammation does not provoke this network, laminarin injection could therapeutically reproduce the protective sepsis effect. This chemokine network and CXCR6 tissue-resident T cell accumulation were detected in humans with sepsis and were associated with prolonged survival in humans with cancer. These findings identify a therapeutically relevant antitumor consequence of sepsis-induced trained immunity.

RUFY3 regulates endolysosomes perinuclear positioning, antigen presentation and migration in activated phagocytes

Endo-lysosomes transport along microtubules and clustering in the perinuclear area are two necessary steps for microbes to activate specialized phagocyte functions. We report that RUN and FYVE domain-containing protein 3 (RUFY3) exists as two alternative isoforms distinguishable by the presence of a C-terminal FYVE domain and by their affinity for phosphatidylinositol 3-phosphate on endosomal membranes. The FYVE domain-bearing isoform (iRUFY3) is preferentially expressed in primary immune cells and up-regulated upon activation by microbes and Interferons. iRUFY3 is necessary for ARL8b + /LAMP1+ endo-lysosomes positioning in the pericentriolar organelles cloud of LPS-activated macrophages. We show that iRUFY3 controls macrophages migration, MHC II presentation and responses to Interferon-γ, while being important for intracellular Salmonella replication. Specific inactivation of rufy3 in phagocytes leads to aggravated pathologies in mouse upon LPS injection or bacterial pneumonia. This study highlights the role of iRUFY3 in controlling endo-lysosomal dynamics, which contributes to phagocyte activation and immune response regulation.

Monocyte Signature Associated with Herpes Simplex Virus Reactivation and Neurological Recovery After Brain Injury

RATIONALE

Brain injury induces systemic immunosuppression increasing the risk of viral reactivations and altering neurological recovery.

OBJECTIVES

To determine if systemic immune alterations and lung replication of Herpesviridae are associated and can help predict outcomes after brain injury.

METHODS

We collected peripheral blood mononuclear cells in severely brain-injured patients requiring invasive mechanical ventilation. We systematically searched for respiratory Herpes Simplex Virus (HSV) replications in tracheal aspirates. We also performed CHiP-sequencing, RNA-sequencing and in vitro functional assays of monocytes and CD4 T cells collected on day 1 to characterize immune response to severe acute brain injury. The primary outcome was the Glasgow outcome scale Extended (GOS-E) at 6 months.

MEASUREMENTS AND MAIN RESULTS

In 344 severe brain-injured patients, lung HSV reactivations were observed in 39% of patients seropositive for HSV, and independently associated with poor neurological recovery at six months (hazard ratio 1.90, 95%CI 1.08-3.57). WGNA analyses of the transcriptomic response of monocytes to brain injury defined a module of 721 genes, including PD-L1 and CD80, enriched for the binding DNA motif of the transcriptional factor Zeb2, and whose ontogenic analyses revealed decreased interferon--mediated and anti-viral response signaling pathways. This monocyte signature was preserved in a validation cohort and predicted the neurological outcome at 6 months with good accuracy (AUC 0.786, 95%CI 0.593-0.978).

CONCLUSIONS

A specific monocyte signature is associated with HSV reactivation and predicts recovery after brain injury. The alterations of the immune control of Herpesviridae replication are understudied and represent a novel therapeutic target.

Alveolar Macrophages: Adaptation to Their Anatomic Niche during and after Inflammation

At the early stages of life development, alveoli are colonized by embryonic macrophages, which become resident alveolar macrophages (ResAM) and self-sustain by local division. Genetic and epigenetic signatures and, to some extent, the functions of ResAM are dictated by the lung microenvironment, which uses cytokines, ligand-receptor interactions, and stroma cells to orchestrate lung homeostasis. In resting conditions, the lung microenvironment induces in ResAM a tolerogenic programming that prevents unnecessary and potentially harmful inflammation responses to the foreign bodies, which continuously challenge the airways. Throughout life, any episode of acute inflammation, pneumonia being likely the most frequent cause, depletes the pool of ResAM, leaving space for the recruitment of inflammatory monocytes that locally develop in monocyte-derived alveolar macrophages (InfAM). During lung infection, the local microenvironment induces a temporary inflammatory signature to the recruited InfAM to handle the tissue injury and eliminate the pathogens. After a few days, the recruited InfAM, which locally self-sustain and develop as new ResAM, gain profibrotic functions required for tissue healing. After the complete resolution of the infectious episode, the functional programming of both embryonic and monocyte-derived ResAM remains altered for months and possibly for the entire life. Adult lungs thus contain a wide diversity of ResAM since every infection brings new waves of InfAM which fill the room left open by the inflammatory process. The memory of these innate cells called trained immunity constitutes an immunologic scar left by inflammation, notably pneumonia. This memory of ResAM has advantages and drawbacks. In some cases, lung-trained immunity offers better defense capacities against autoimmune disorders and the long-term risk of infection. At the opposite, it can perpetuate a harmful process and lead to a pathological state, as is the case among critically ill patients who have immune paralysis and are highly susceptible to hospital-acquired pneumonia and acute respiratory distress syndrome. The progress in understanding the kinetics of response of alveolar macrophages (AM) to lung inflammation is paving the way to new treatments of pneumonia and lung inflammatory process.

Regulatory T Cells Expressing Tumor Necrosis Factor Receptor Type 2 Play a Major Role in CD4+ T-Cell Impairment During Sepsis

Sepsis causes inflammation-induced immunosuppression with lymphopenia and alterations of CD4+ T-cell functions that renders the host prone to secondary infections. Whether and how regulatory T cells (Treg) are involved in this postseptic immunosuppression is unknown. We observed in vivo that early activation of Treg during Staphylococcus aureus sepsis induces CD4+ T-cell impairment and increases susceptibility to secondary pneumonia. The tumor necrosis factor receptor 2 positive (TNFR2pos) Treg subset endorsed the majority of effector immunosuppressive functions, and TNRF2 was particularly associated with activation of genes involved in cell cycle and replication in Treg, probably explaining their maintenance. Blocking or deleting TNFR2 during sepsis decreased the susceptibility to secondary infection. In humans, our data paralleled those in mice; the expression of CTLA-4 was dramatically increased in TNFR2pos Treg after culture in vitro with S. aureus. Our findings describe in vivo mechanisms underlying sepsis-induced immunosuppression and identify TNFR2pos Treg as targets for therapeutic intervention.

Interleukin-22 regulates interferon lambda expression in a mice model of pseudomonas aeruginosa pneumonia

BACKGROUND

Interleukin (IL)-22 is a cytokine involved in tissue protection and repair following lung pathologies. Interferon (IFN)-λ cytokines displayed similar properties during viral infection and a synergy of action between these two players has been documented in the intestine. We hypothesize that during Pseudomonas aeruginosa challenge, IL-22 up-regulates IFN-λ and that IFN-λ exhibits protective functions during Pseudomonas aeruginosa acute pneumonia model in mice.

METHODS

Using an in vitro human alveolar epithelial cell line A549, we assessed the ability of IL-22 to enhance IFN-λ expression during infection. IFN-λ protective function was evaluated in an acute mouse pneumonia model.

RESULTS

We first demonstrated in murine lungs that only type-II alveolar cells express IL-22 receptor and that IL-22 treatment of A549 cell line up-regulates IFN-λ expression. In a murine acute pneumonia model, IL-22 administration maintained significant IFN-λ levels in the broncho-alveolar fluids whereas IL-22 neutralization abolished IFN-λ up-regulation. In vivo administration of IFN-λ during Pseudomonas aeruginosa pneumonia improves mice outcome by dampening neutrophil recruitment and decreasing epithelium damages.

DISCUSSION

We show here that IL-22 regulates IFN-λ levels during Pseudomonas aeruginosa pneumonia.

Interleukin-22 level is negatively correlated with neutrophil recruitment in the lungs in a Pseudomonas aeruginosa pneumonia model

Pseudomonas aeruginosa is a major threat for immune-compromised patients. Bacterial pneumonia can induce uncontrolled and massive neutrophil recruitment ultimately leading to acute respiratory distress syndrome and epithelium damage. Interleukin-22 plays a central role in the protection of the epithelium. In this study, we aimed to evaluate the role of interleukin-22 and its soluble receptor IL-22BP in an acute Pseudomonas aeruginosa pneumonia model in mice. In this model, we noted a transient increase of IL-22 during Pseudomonas aeruginosa challenge. Using an antibody-based approach, we demonstrated that IL-22 neutralisation led to increased susceptibility to infection and to lung damage correlated with an increase in neutrophil accumulation in the lungs. On the contrary, rIL-22 administration or IL-22BP neutralisation led to a decrease in mouse susceptibility and lung damage associated with a decrease in neutrophil accumulation. This study demonstrated that the IL-22/IL-22BP system plays a major role during Pseudomonas aeruginosa pneumonia by moderating neutrophil accumulation in the lungs that ultimately leads to epithelium protection.

Innate immune evasion of Escherichia coli clinical strains from orthopedic implant infections

Escherichia coli is one of the first causes of Gram-negative orthopedic implant infections (OII). Those infections, usually hematogenous, mostly originate from the urinary tract. We investigated the strategies developed by E. coli in this context to evade host innate immune responses, i.e. complement and polymorphonuclear neutrophils (PMN). Twenty strains from OII were compared with 20 strains from bacteremia in patients with non-infected orthopedic implant. In both groups, 6/20 (30 %) strains lysed PMNs, due to the production of the pore-forming toxin α-hemolysin (HlyA). For the others, resistance to phagocytic killing by PMN was not significantly different between both groups. In contrast, resistance to complement-mediated serum killing was significantly higher in OII strains than in the others (65 % vs 10 %; P <0.001). In E. coli, different mechanisms have been involved in complement resistance. Here, serum resistance was not linked to a group 2 capsule, or a loss of outer membrane permeability, or the recruitment of the complement inhibitor C4bp, but was significantly associated with the synthesis of long-chain LPS, regardless of the O-antigen. Thus, serum resistance could promote seeding of peri-implant tissues by helping E. coli to either persist in blood and reach the site of infection or overcome localized complement activation.

Adaptive processes of Staphylococcus aureus isolates during the progression from acute to chronic bone and joint infections in patients

Staphylococcus aureus bone and joint infection (BJI) is associated with significant rates of chronicity and relapse. In this study, we investigated how S. aureus is able to adapt to the human environment by comparing isolates from single patients with persisting or relapsing BJIs that were recovered during the initial and recurrent BJI episodes. In vitro and in vivo assays and whole-genome sequencing analyses revealed that the recurrent isolates induced a reduced inflammatory response, formed more biofilms, persisted longer in the intracellular compartments of host bone cells, were less cytotoxic and induced less mortality in a mouse infection model compared with the initial isolates despite the lack of significant changes at the genomic level. These findings suggest that S. aureus BJI chronicization is associated with an in vivo bacterial phenotypical adaptation that leads to decreased virulence and host immune escape, which is linked to increased intraosteoblastic persistence and biofilm formation.

IL-22BP is produced by eosinophils in human gut and blocks IL-22 protective actions during colitis

Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel diseases (IBDs), are characterized by high levels of IL-22 production. Rodent studies revealed that this cytokine is protective during colitis but whether this is true in IBDs is unclear. We show here that levels of the soluble inhibitor of IL-22, interleukin 22-binding protein (IL-22BP), are significantly enhanced during IBDs owing to increased numbers of IL-22BP-producing eosinophils, that we unexpectedly identify as the most abundant source of IL-22BP protein in human gut. In addition, using IL-22BP-deficient rats, we confirm that endogenous IL-22BP is effective at blocking protective actions of IL-22 during acute colitis. In conclusion, our study provides new important insights regarding the biology of IL-22 and IL-22BP in the gut and indicates that protective actions of IL-22 are likely to be suboptimal in IBDs thus making IL-22BP a new relevant therapeutic target.

New in vitro and in vivo models to evaluate antibiotic efficacy in Staphylococcus aureus prosthetic vascular graft infection

OBJECTIVE

Prosthetic vascular graft infection (PVGI) is an emerging disease, mostly caused by staphylococci, with limited data regarding efficacy of current antistaphylococcal agents. We aimed to assess the efficacy of different antibiotic regimens.

METHODS

Six different strains of MSSA and MRSA were used. We compared results of minimal biofilm inhibitory and eradicating concentrations (MBICs and MBECs) obtained with a Calgary Biofilm Pin Lid Device (CBPD) with those yielded by an original Dacron(®)-related minimal inhibitory and eradicating concentration measure model. We then used a murine model of Staphylococcus aureus vascular prosthetic material infection to evaluate efficacy of different antibiotic regimens: vancomycin and daptomycin combined or not with rifampicin for MRSA and the same groups with cloxacillin and cloxacillin combined with rifampicin for MSSA.

RESULTS

We demonstrated that classical measures of MBICs and MBECs obtained with a CPBD could overestimate the decrease in antibiotic susceptibility in material-related infections and that the nature of the support used might influence the measure of biofilm susceptibility, since results yielded by our Dacron(®)-related minimal eradicating assay were lower than those found with a plastic device. In our in vivo model, we showed that daptomycin was significantly more bactericidal than comparators for some strains of MRSA or MSSA but not for all. For the majority of strains, it was as efficient as comparators. The addition of rifampicin to daptomycin did not enhance daptomycin efficacy.

CONCLUSIONS

Despite the heterogeneity of results according to bacterial strains, these innovative models represent an option to better evaluate the in vitro efficacy of antibiotics on Dacron(®)-related biofilm S. aureus infections, and to screen different antibiotic regimens in a mouse model of PVGIs.

Pathogenic potential of Escherichia coli clinical strains from orthopedic implant infections towards human osteoblastic cells

Escherichia coli is one of the first causes of Gram-negative orthopedic implant infections (OII), but little is known about the pathogenicity of this species in such infections that are increasing due to the ageing of the population. We report how this pathogen interacts with human osteoblastic MG-63 cells in vitro, by comparing 20 OII E. coli strains to two Staphylococcus aureus and two Pseudomonas aeruginosa strains. LDH release assay revealed that 6/20 (30%) OII E. coli induced MG-63 cell lysis whereas none of the four control strains was cytotoxic after 4 h of coculture. This high cytotoxicity was associated with hemolytic properties and linked to hlyA gene expression. We further showed by gentamicin protection assay and confocal microscopy that the non-cytotoxic E. coli were not able to invade MG-63 cells unlike S. aureus strains (internalization rate <0.01% for the non-cytotoxic E. coli versus 8.88 ± 2.31% and 4.60 ± 0.42% for both S. aureus). The non-cytotoxic E. coli also demonstrated low adherence rates (<7%), the most adherent E. coli eliciting higher IL-6 and TNF-α mRNA expression in the osteoblastic cells. Either highly cytotoxic or slightly invasive OII E. coli do not show the same infection strategies as S. aureus towards osteoblasts.

Impact of bacterial biofilm on the treatment of prosthetic joint infections

Microbial biofilm contributes to chronic infection and is involved in the pathogenesis of prosthetic joint infections. Biofilms are structurally complex and should be considered a dynamic system able to protect the bacteria from host defence mechanisms and from antibacterial agents. Despite the use of antibiotics recognized as effective against acute infections, prosthetic joint infections require long-term suppressive treatment acting on adherent bacteria. Conventional in vitro susceptibility testing methods are not suitable for biofilm-associated infections given that these tests do not take into account the physiological parameters of bacterial cells in vivo. Most anti-staphylococcal drugs are able to inhibit in vitro the adhesion of bacteria to a surface, considered to be the first step in biofilm formation. Recent studies suggest that the lack of activity of antibiotics against biofilm-embedded bacteria seems to be more related to the decreased effect of the drug on the pathogen than to the poor penetration of the drug into the biofilm. Eradication of biofilm-embedded bacteria is a very difficult task and combination therapy is required in the treatment of persistent infections involving biofilm. Although several combinations demonstrate potent efficacy, rifampicin is the most common partner drug of effective combinations against staphylococcal biofilms. Considering the complexity of biofilm-related infections, further studies are needed to assess the activity of new therapeutic agents in combination with antibiotics (quorum-sensing inhibitors, biofilm disruptors and specific anti-biofilm molecules).

Analysis of autofluorescence in polymorphonuclear neutrophils: a new tool for early infection diagnosis

Diagnosing bacterial infection (BI) remains a challenge for the attending physician. An ex vivo infection model based on human fixed polymorphonuclear neutrophils (PMNs) gives an autofluorescence signal that differs significantly between stimulated and unstimulated cells. We took advantage of this property for use in an in vivo pneumonia mouse model and in patients hospitalized with bacterial pneumonia. A 2-fold decrease was observed in autofluorescence intensity for cytospined PMNs from broncho-alveolar lavage (BAL) in the pneumonia mouse model and a 2.7-fold decrease was observed in patients with pneumonia when compared with control mice or patients without pneumonia, respectively. This optical method provided an autofluorescence mean intensity cut-off, allowing for easy diagnosis of BI. Originally set up on a confocal microscope, the assay was also effective using a standard epifluorescence microscope. Assessing the autofluorescence of PMNs provides a fast, simple, cheap and reliable method optimizing the efficiency and the time needed for early diagnosis of severe infections. Rationalized therapeutic decisions supported by the results from this method can improve the outcome of patients suspected of having an infection.

Linezolid dampens neutrophil-mediated inflammation in methicillin-resistant Staphylococcus aureus-induced pneumonia and protects the lung of associated damages

BACKGROUND

Linezolid is considered as a therapeutic alternative to the use of glycopeptides for the treatment of pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA). Clinical studies reported a potent survival advantage conferred by the oxazolidinone and called into question the use of glycopeptides as first-line therapy.

METHODS

In a mouse model of MRSA-induced pneumonia, quantitative bacteriology, proinflammatory cytokine concentrations in lung, myeloperoxidase activity, Ly6G immunohistochemistry, and endothelial permeability were assessed to compare therapeutic efficacy and immunomodulative properties of linezolid and vancomycin administered subcutaneously every 12 hours.

RESULTS

Significant antibacterial activity was achieved after 48 hours of treatment for linezolid and vancomycin. Levels of interleukin 1β, a major proinflammatory cytokine, and macrophage inflammatory protein 2, a chemokine involved in the recruitment of neutrophils, were decreased by both antimicrobials. Only linezolid was able to dramatically reduce the production of tumor necrosis factor α. Analysis of myeloperoxidase activity and Ly6G immunostaining showed a dramatic decrease of neutrophil infiltration in infected lung tissues for linezolid-treated animals. A time-dependent increase of endothelial permeability was observed for the control and vancomycin regimens. Of interest, in the linezolid group, decreased endothelial permeability was detected 48 hours after infection.

CONCLUSIONS

Our results indicate that linezolid could be superior to vancomycin for the management of MRSA pneumonia by attenuating an excessive inflammatory reaction and protecting the lung from pathogen-associated damages.

Antenatal phosphodiesterase 4 inhibition restores postnatal growth and pulmonary development in a model of chorioamnionitis in rabbits

Chorioamnionitis is implicated in the pathophysiology of bronchopulmonary disease, and the associated inflammatory response is responsible for adverse effects on alveolar development. The aim of this work was to analyze the effects of a phosphodiesterase 4 (PDE4)-selective inhibitor, rolipram (a modulator of the inflammatory response), in an experimental model of chorioamnionitis on pulmonary development and on the processes of infection and inflammation. Rabbit mothers were assigned to four groups: 1) saline serum inoculation (controls); 2) Escherichia coli intrauterine inoculation (C+); 3) rolipram infusion (R+); and 4) E. coli inoculation + rolipram infusion (C+R+). High rates of morbility and mortality were noticed in mothers and pups (5 of 13 pregnant rabbits in groups with rolipram). Alveolar development, inflammation, and infection were analyzed in pups at day 0 and day 5. At day 0, in the context of chorioamnionitis, rolipram significantly decreased birth weight (p < 0.01) relative to that of controls (p < 0.05). At day 5, weight normalized in group C+R+ but not in group C+ relative to controls (p < 0.001); moreover, alveolar airspace volume was preserved in group C+R+ but not in group C+ (p < 0.05). Interstitial volume decreased in group C+ versus controls (p < 0.05) but was preserved in group C+R+. Specific alveolar area was not significantly modified by rolipram. No significant difference was found concerning bronchoalveolar lavage cellularity, and all blood cultures remained sterile. In this model of impaired alveologenesis, rolipram significantly preserved specific alveolar density. However, PDE4 inhibition induced antenatal fetal demise and growth retardation.

Diffusion of ofloxacin in the endocarditis vegetation assessed with synchrotron radiation UV fluorescence microspectroscopy

The diffusion of antibiotics in endocarditis vegetation bacterial masses has not been described, although it may influence the efficacy of antibiotic therapy in endocarditis. The objective of this work was to assess the diffusion of ofloxacin in experimental endocarditis vegetation bacterial masses using synchrotron-radiation UV fluorescence microspectroscopy. Streptococcal endocarditis was induced in 5 rabbits. Three animals received an unique IV injection of 150 mg/kg ofloxacin, and 2 control rabbits were left untreated. Two fluorescence microscopes were coupled to a synchrotron beam for excitation at 275 nm. A spectral microscope collected fluorescence spectra between 285 and 550 nm. A second, full field microscope was used with bandpass filters at 510–560 nm. Spectra of ofloxacin-treated vegetations presented higher fluorescence between 390 and 540 nm than control. Full field imaging showed that ofloxacin increased fluorescence between 510 and 560 nm. Ofloxacin diffused into vegetation bacterial masses, although it accumulated in their immediate neighborhood. Fluorescence images additionally suggested an ofloxacin concentration gradient between the vegetation peripheral and central areas. In conclusion, ofloxacin diffuses into vegetation bacterial masses, but it accumulates in their immediate neighborhood. Synchrotron radiation UV fluorescence microscopy is a new tool for assessment of antibiotic diffusion in the endocarditis vegetation bacterial masses.

Comparison of ceftaroline fosamil, daptomycin and tigecycline in an experimental rabbit endocarditis model caused by methicillin-susceptible, methicillin-resistant and glycopeptide-intermediate Staphylococcus aureus

OBJECTIVES

The aim of this study was to compare the in vivo activities of the new antistaphylococcal drugs ceftaroline fosamil, daptomycin and tigecycline at projected human therapeutic doses against methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA) and glycopeptide-intermediate S. aureus (GISA) strains in a rabbit model of endocarditis.

METHODS

The efficacy of therapeutic regimens in our model was evaluated following 4 days of treatment by determining colony counts of infected vegetations. Emergence of resistant variants during therapy was assessed.

RESULTS

Using this model of infective endocarditis, ceftaroline fosamil and daptomycin demonstrated high bactericidal in vivo activity (reduction of >5 log(10) cfu/g of vegetation) after a 4 day treatment against MSSA, MRSA and GISA strains. Both drugs were more efficacious than tigecycline, which showed moderate activity but failed to exhibit a bactericidal effect. Ceftaroline was superior to daptomycin in terms of sterilization of the vegetations. Emergence of resistant variants during daptomycin therapy was observed in two animals (one in the MSSA group and one in the MRSA group) but was not observed in ceftaroline- or tigecycline-treated animals.

CONCLUSIONS

The novel β-lactam agent ceftaroline fosamil was the most active bactericidal drug in this model and is a promising therapeutic option for the treatment of severe S. aureus infections, including those caused by MRSA and GISA strains.

Efficacy of doripenem in the treatment of Pseudomonas aeruginosa experimental pneumonia versus imipenem and meropenem

OBJECTIVES

The aim of this study was to compare doripenem with imipenem and meropenem in an experimental rabbit model of Pseudomonas aeruginosa pneumonia and then to compare different doripenem doses and methods of intravenous administration.

METHODS

Using a rabbit experimental model of pneumonia, efficacy was assessed following 2 days of treatment by colony counts of different tissues (lung, spleen and blood culture).

RESULTS

Mean pulmonary bacterial loads were 3.17 ± 0.53, 3.42 ± 0.61 and 2.75 ± 0.59 log(10) cfu/g for imipenem, doripenem (0.5 g three times daily) and meropenem, respectively, compared with 7.57 ± 0.99 cfu/g for control animals. At a higher dose (1 g three times daily), doripenem showed significantly better efficacy (2.70 ± 0.65 log(10) cfu/g) than the standard regimen of doripenem. Sterilization of spleen cultures was achieved with standard regimens of imipenem (1 g three times daily) and a higher dose of doripenem.

CONCLUSIONS

In this model of P. aeruginosa pneumonia, doripenem had an efficacy equivalent to that of meropenem and imipenem at a high dose of 1 g three times a day and lower efficacy at a standard dose (0.5 g three times daily) than the other two agents in terms of bacteria cultivated from spleens. Doripenem is a new drug that offers new therapeutic options, especially for difficult-to-treat infections such as pneumonia due to non-fermenting Gram-negative bacteria.

Efficacy of daptomycin combined with rifampicin for the treatment of experimental meticillin-resistant Staphylococcus aureus (MRSA) acute osteomyelitis

Daptomycin exhibits rapid bactericidal activity against Gram-positive organisms, including meticillin-resistant Staphylococcus aureus (MRSA). Daptomycin in combination with rifampicin needs to be assessed in bone infection. An MRSA acute osteomyelitis model was used. Daptomycin and vancomycin were compared, alone or in combination with rifampicin, over 4 days. Surviving bacteria were counted in bone, bone marrow and joint fluid. Vancomycin and daptomycin as single therapies were ineffective, but both combinations were significantly more effective than the corresponding monotherapy. Combination of daptomycin and rifampicin could prevent S. aureus from developing resistance. This combination could be a useful alternative to treat MRSA osteomyelitis at an early stage.

Fourier transform infrared microspectroscopy of endocarditis vegetation

The objectives of this work were to compare the infrared spectra of bacterial endocarditis vegetation with those of native valvular tissue and the infrared spectra of vegetation bacterial masses with those of surrounding vegetation tissue. Streptococcal aortic endocarditis was induced in three rabbits. Vegetation slices were cryo-sectioned for study by Fourier transform infrared (FT-IR) microspectroscopy. Valvular apparatus, vegetation, and bacterial masses within the vegetation were localized on hematoxylin and eosin (H&E) stained contiguous slices. Infrared images of whole vegetations and images of bacterial masses were acquired with apertures set to 80 x 80 and 20 x 20 microm, respectively. Valvular apparatus and vegetation showed different infrared spectra, mainly in the amide I and amide II bands (1674-1518 cm(-1)), and at about 1450, 1400, 1340, 1280, 1240, 1200, 1080, and 1030 cm(-1). Valvular collagen, elastin, and proteoglycans may explain these differences. Bacterial masses and surrounding vegetation showed different infrared patterns, mainly in the amide I and amide II bands and in the 1142-991 cm(-1) carbohydrate spectral range. Bacterial nucleic acids and polysaccharides may partly explain these differences. Study of experimental endocarditis vegetation using FT-IR microspectroscopy distinguishes (1) the vegetation from the valvular tissue, and (2) the bacterial masses from the surrounding tissue. This study demonstrates for the first time that FT-IR microspectroscopy is able to detect bacterial growth in infected tissue. FT-IR microspectroscopy appears to be a useful tool for investigation of the biochemical structure of endocarditis vegetation.

Efficacy of the new cephalosporin ceftaroline in the treatment of experimental methicillin-resistant Staphylococcus aureus acute osteomyelitis

OBJECTIVES

To evaluate the activity of a new cephalosporin, ceftaroline, in comparison with other antistaphylococcal drugs (linezolid and vancomycin) at projected human therapeutic doses against methicillin-resistant Staphylococcus aureus (MRSA) and glycopeptide-intermediate S. aureus (GISA) strains.

METHODS

Using a rabbit experimental model of acute osteomyelitis, efficacy was assessed following 4 days of treatment by colony counts of infected bone tissues (joint fluid, femoral bone marrow and bone).

RESULTS

Although vancomycin remains the standard treatment for MRSA osteomyelitis, it was ineffective against the MRSA strain and poorly active against GISA infections in this model. Ceftaroline and linezolid demonstrated significant activity in bone marrow and bone, and were significantly better than vancomycin treatment. However, ceftaroline was the only drug to exhibit significant activity against MRSA in infected joint fluid.

CONCLUSIONS

The present study supports ceftaroline as a promising therapeutic option for the treatment of severe MRSA infections, including osteomyelitis.

In vivo activity of a novel anti-methicillin-resistant Staphylococcus aureus cephalosporin, ceftaroline, against vancomycin-susceptible and -resistant Enterococcus faecalis strains in a rabbit endocarditis model: a comparative study with linezolid and vancomycin

We assessed the in vitro and in vivo efficacy of the novel parenteral broad-spectrum cephalosporin ceftaroline against Enterococcus faecalis in time-kill experiments and in a rabbit endocarditis model with simulated human dosing. Ceftaroline was more active than either vancomycin or linezolid against vancomycin-sensitive and -resistant isolates of E. faecalis.

Intermittent active motion versus immobilization in the treatment of Staphylococcus aureus-induced arthritis in a rabbit model

PURPOSE

This study has evaluated the effects of immobilization versus intermittent active motion on cartilage and on antibiotic efficacy in a rabbit septic arthritis model.

METHODS

Rabbits were infected and assigned to one of four groups: group 1, no treatment without immobilization (allowing intermittent active motion); group 2, cast; group 3, oxacillin without immobilization; group 4, oxacillin and cast. Animals were sacrificed 21 days later. Bacterial counts and lateral radiograms were performed. A radiological score was calculated.

RESULTS

Immobilization had no effect on oxacillin efficacy and a deleterious effect on the radiological score.

CONCLUSION

Intermittent active motion has allowed a better cartilage healing during the treatment of septic arthritis.

Internal device decreases antibiotic's efficacy on experimental osteomyelitis

PURPOSE

We have evaluated the effect of internal and external osteosynthesis devices on the efficacy of vancomycin treatment in a rabbit model of methicillin-resistant Staphylococcus aureus (MRSA)-induced post-traumatic osteomyelitis.

METHODS

Double tibial osteotomies in female New Zealand rabbits were performed, inoculated with a MRSA strain, then fixed with an intramedullary rod. A debridement was performed 4 days later for each rabbit, and a bacterial count in pus was determined (B1). In the first group (G1), the osteosynthesis material was removed and replaced by a new sterile nail. In the second group (G2), the intramedullary rod was removed and then replaced by an external fixator. Immediately after surgery, G1 and G2 rabbits were treated with vancomycin (60 mg/kg twice a day). The animals were sacrificed at the end of a 5-day period, and a bacterial count in pus was performed again (B2).

RESULTS

The difference of log(10) colony forming units per milliliter (CFU/ml) (B2-B1) was -1.2 +/- 0.5 and -2.9 +/- 1.1, respectively, for G1 and G2.

CONCLUSION

The efficacy of vancomycin treatment increased after removal of the internal osteosynthesis device.

In vivo efficacy of ceftaroline (PPI-0903), a new broad-spectrum cephalosporin, compared with linezolid and vancomycin against methicillin-resistant and vancomycin-intermediate Staphylococcus aureus in a rabbit endocarditis model

Using the rabbit endocarditis model, we compared the activity of a new broad-spectrum cephalosporin, ceftaroline, with those of linezolid and vancomycin against methicillin-resistant Staphylococcus aureus. After a 4-day treatment, ceftaroline exhibited superior bactericidal in vivo activity against resistant S. aureus strains and appeared to be the most effective drug against a heterogeneous glycopeptide-intermediate S. aureus strain.

In vitro and in vivo bactericidal activities of vancomycin dispersed in porous biodegradable poly(epsilon-caprolactone) microparticles

Treatment of methicillin-resistant Staphylococcus aureus osteomyelitis requires a prolonged antibiotic therapy with vancomycin. Because of its weak diffusion, the in situ implantation of vancomycin could be interesting. The activity of vancomycin encapsulated in microparticles was evaluated in vitro and in vivo on rabbit osteomyelitis and showed a good activity compared to intravenous administration.

The effects of milrinone on hemodynamics in an experimental septic shock model

OBJECTIVE

To investigate the specific hemodynamic effects of the phosphodiesterase inhibitor milrinone in a rabbit model of septic shock in the absence of any other treatment.

DESIGN

A prospective, controlled, interventional study. Animal Model: Fourteen sedated New Zealand rabbits.

SETTING

Research laboratory of a health sciences university.

INTERVENTIONS

Rabbits were anesthetized and vascular catheters inserted in femoral artery and jugular vein. After a stabilization period and the recording of baseline measurements (H0), all animals received a 10-mL infusion of Pseudomonas aeruginosa. Two hours later (H2rabbits were randomly assigned to receive 5% dextrose (control group) or milrinone (milrinone group).

MEASUREMENTS AND MAIN RESULTS

Mean arterial blood pressure (MAP) was monitored continuously, and a cardiac index (CI) was determined every 30 mins by a transpulmonary thermodilution technique using an integrated monitoring device (PICCO). No differences were detected between the two groups after stabilization (H0) or before the treatment (H2) for either CI (mL/min(-1)/kg(-1)) or MAP (mm Hg). CI decreased progressively in the control group during the following 4 hrs, but not in the treated group (at H6: 122 +/- 4 vs. 207 +/- 16 mL/min(-1)/kg(-1); p < .05). No drop of MAP occurred after milrinone infusion. A comparison of the treated and control group reveals that milrinone improved tissue perfusion as evidenced by measurements of central venous saturation (at H4: 0.59 +/- 0.05 vs. 0.71 +/- 0.03, p = .04), lactacidemia (at H6: 10.3 +/- 2.4 vs. 3.9 +/- 0.9 mmol/L, p = .03), creatinemia (at H6: 95 +/- 11 vs. 60 +/- 5 micromol/L, p = .02) and survival (at H6: 5 vs. 7, not significant).

CONCLUSION

Milrinone improves cardiac output and tissue perfusion in a rabbit model involving severe septic shock.

In vitro and in vivo synergistic activities of linezolid combined with subinhibitory concentrations of imipenem against methicillin-resistant Staphylococcus aureus

Indifference or moderate antagonism of linezolid combined with other antibiotics in vitro and in vivo have mainly been reported in the literature. We have assessed the in vitro activities of linezolid, alone or in combination with imipenem, against methicillin-resistant Staphylococcus aureus (MRSA) strains using the dynamic checkerboard and time-kill curve methods. Linezolid and low concentrations of imipenem had a synergistic effect, leading us to evaluate the in vivo antibacterial activity of the combination using the rabbit endocarditis experimental model. Two MRSA strains were used for in vivo experiments: one was a heterogeneous glycopeptide-intermediate clinical S. aureus strain isolated from blood cultures, and the other was the S. aureus COL reference strain. Animals infected with one of two MRSA strains were randomly assigned to one of the following treatments: no treatment (controls), linezolid (simulating a dose in humans of 10 mg/kg of body weight every 12 h), a constant intravenous infusion of imipenem (which allowed the steady-state concentration of about 1/32 the MIC of imipenem for each strain to be reached in serum), or the combination of both treatments. Linezolid and imipenem as monotherapies exhibited no bactericidal activity against either strain. The combination of linezolid plus imipenem showed in vivo bactericidal activity that corresponded to a decrease of at least 4.5 log CFU/g of vegetation compared to the counts for the controls. In conclusion, the combination exhibited synergistic and bactericidal activities against two MRSA strains after 5 days of treatment. The combination of linezolid plus imipenem appears to be promising for the treatment of severe MRSA infections and merits further investigations to explore the mechanism underlying the synergy between the two drugs.

Influence of carbon dioxide on the MIC of telithromycin for Streptococcus pneumoniae: an in vitro-in vivo study

Incubation in CO(2) resulted in higher (> or =3 doubling dilution) MICs of telithromycin than those found in ambient air for 31.2% of 346 Streptococcus pneumoniae ermB-positive strains. An increased telithromycin MIC in CO(2) was not correlated with loss of its activity in the murine sepsis/peritonitis model.

Comparison of in vivo intrinsic activity of cefepime and imipenem in a Pseudomonas aeruginosa rabbit endocarditis model: effect of combination with tobramycin simulating human serum pharmacokinetics

OBJECTIVES

The purpose of this experimental study was first to compare the in vivo intrinsic activity of imipenem and cefepime administered as a continuous infusion and to determine their lowest effective serum steady-state concentration (LESSC). Secondly, we studied the effect of combining therapy with tobramycin.

METHODS

In a Pseudomonas aeruginosa (ATCC 27853) rabbit endocarditis model, beta-lactam antibiotics were administered by continuous infusion over a 24 h treatment period at different doses until the LESSC was reached, i.e. able to achieve a 2-log drop of cfu/g of vegetations versus untreated animals. The effect of adding tobramycin (3 mg/kg once daily) was then studied.

RESULTS

The LESSC was between 3 x and 4 x MIC of cefepime for P. aeruginosa and about 0.2 5x MIC of imipenem. Combination of tobramycin with each of the two beta-lactams did not result in any further significant killing.

CONCLUSION

The optimal Css/MIC ratio might differ from one molecule to another. The LESSC of imipenem is lower than that of cefepime, giving a better intrinsic activity in vivo, despite a higher MIC in vitro.

Simulation of human gentamicin pharmacokinetics in an experimental Enterococcus faecalis endocarditis model

Significant differences between animal and human pharmacokinetics may be responsible for the conflicting results of experimental studies. This study determined the impact of human pharmacokinetic simulation (HPS) on gentamicin activity in an Enterococcus faecalis endocarditis model. The decrease in bacterial counts was greater with HPS than with a dose-equivalent regimen without HPS.

Persistent bacteremia in rabbit fetuses despite maternal antibiotic therapy in a novel intrauterine-infection model

The effect of optimized maternal therapy by bactericidal agents was evaluated in a reproducible rabbit model of Escherichia coli maternofetal infection simulating human pharmacokinetics. Intravenous antibiotic therapy was begun in the pregnant rabbit 12 h after bacterial intrauterine inoculation, using a computer-controlled pump to simulate human pharmacokinetics of ceftriaxone (1 g/day) associated or not with gentamicin (3 mg/kg of body weight/day). Data were compared for fetal survival, quantitative blood cultures, fetal histology in treated versus untreated groups, and maternal and fetal antibiotic concentrations in plasma in treated animals. Antibiotic therapy led to dramatic improvement in maternal outcome (100% survival versus 100% death in the untreated group in association with maternal septicemia). Fetal survival also improved, with the two-drug combination providing a more potent effect. After 3 days of treatment, 32% of fetuses survived with one-drug therapy and 62% with two-drug therapy (Yates corrected chi(2), P < 0.05). In untreated animals, bacterial counts in blood cultures increased rapidly during the first 24 h up to 8.1 +/- 0.5 log CFU/ml, but remained relatively constant at all times with antibiotic treatment: 4.5 +/- 0.7 log CFU/ml at the start of treatment and 6.2 +/- 0.4 and 5.2 +/- 0.9 log CFU/ml after 72 h for one- and two-drug therapy, respectively (data are means +/- standard deviations). The failure of animals to be cured after 3 days of treatment was not due to an inadequate concentration of ceftriaxone, as the residual level in fetal serum at sacrifice was more than 1000 times the MIC of the microbe. Unexpectedly, inflammation in fetal lung decreased in the treated group after as little as 24 h of antibiotic therapy, despite persistent bacteremia. Although maternal outcome improved and drug concentrations were above the MIC, the treatment did not achieve sterilization of fetuses in utero for this rabbit E. coli maternofetal infection. However, fetal survival showed some improvement, and the histologic features of lung inflammation were reduced.