Esmolol: immunomodulator in pyelonephritis by Pseudomonas aeruginosa.

BACKGROUND: Based on previous animal studies showing promising immunomodulatory efficacy esmolol, a selective ß1-blocker, it was assumed that administration of esmolol in experimental pyelonephritis by multidrug-resistant Pseudomonas aeruginosa would prolong survival and modulate immune response. METHODS: Acute pyelonephritis was induced in 80 rabbits and assigned to eight groups receiving normal saline (controls), esmolol, amikacin, or both agents as pretreatment and as treatment. Blood was sampled for measurement of malondialdehyde and tumor necrosis factor alpha. Animals were followed up for survival, and after death quantitative tissue cultures were performed. The in vitro effect of esmolol on bacterial growth and on the oxidative burst of neutrophils of healthy controls and of sepsis patients was studied. RESULTS: Survival of pretreatment groups administered single esmolol or esmolol and amikacin was prolonged compared with that of controls (P = 0.018 and P = 0.014, respectively); likewise, survival of treatment groups administered single esmolol or both agents was prolonged compared with that of controls (P = 0.007 and P = 0.014, respectively). Circulating malondialdehyde was significantly lower in pretreated animals administered esmolol or esmolol and amikacin compared with that in controls and in treated animals administered both agents compared with in controls (P = 0.020). In these groups, the bacterial load of the lung was significantly lower compared with controls. Serum tumor necrosis factor alpha did not change. Amikacin was increased in serum of esmolol-treated animals at levels which inhibited the in vitro growth of the studied isolate. Esmolol did not modify the in vitro growth of P aeruginosa and the oxidative burst of neutrophils. CONCLUSIONS: It is concluded that esmolol prolonged survival after experimental infection by multidrug-resistant P aeruginosa. Survival benefit may be related with pleiotropic actions connected with modulation of pharmacokinetics and attenuation of inflammation.

Comparative efficacy of tigecycline VERSUS vancomycin in an experimental model of soft tissue infection by methicillin-resistant Staphylococcus aureus producing Panton-Valentine leukocidin.

Methicillin-resistant Staphylococcus aureus (MRSA) producing Panton-Valentine leukocidin (PVL) is highly virulent. This study aimed to compare the efficacy of tigecycline versus vancomycin in experimental thigh abscess by a PVL-producing MRSA isolate. One hundred and ninety-six Wistar rats were divided into five groups: group A, controls; groups B and C, administered vancomycin starting 1 and 6 h after bacterial challenge respectively; groups D and E, administered tigecycline starting 1 and 6 h after bacterial challenge respectively. Treatment was continued every 12 hours for three consecutive days. Survival was recorded; separate animals were killed for quantitative cultures. Serum samples were collected for estimation of malondialdehyde (MDA). Survival of group D was prolonged compared to all other groups. The bacterial load of blood, liver, spleen and lung was significantly decreased within group D compared to group B at 36 hours. Treatment with tigecycline was accompanied by significant reduction of serum MDA at 24 hours. Tigecycline is comparable to vancomycin for the treatment of soft tissue infections by PVL-producing MRSA.

Gallbaldder perforation causing a subcutaneous abscess.

INTRODUCTION: This is a report of a rare case of an old woman with a large round mass in the right hypochondrium that was proven to be an abscess. PRESENTATION OF CASE: A 82-year old woman with a firm round mass in the right hypochondrium was admitted for evaluation. The abdominal CT showed an abscess produced by a gallbladder perforation, and a gallstone impacted at the Hartmann's pouch. DISCUSSION: The abscess was treated with a transcutaneous paracentesis, while the stone passed to the gastrointestinal tract through a cholecystoenteric fistula, without causing any further problems. CONCLUSION: Gallbaldder perforation can rarely create a subcutaneous abscess especially in thin, elder subjects. Abscess drainage is the first line of treatment.

Effect of clarithromycin in experimental empyema by multidrug-resistant Pseudomonas aeruginosa.

Evidence from a recent randomized study of our group suggests that intravenous clarithromycin resulted in earlier resolution of ventilator-associated pneumonia. The need to understand the mechanism of action of clarithromycin guided to the study of a model of experimental empyema by multidrug-resistant Pseudomonas aeruginosa in 40 rabbits. Animals were randomized into controls (group A); treatment with clarithromycin (group B); treatment with piperacillin/tazobactam (group C); and treatment with both agents (group D). Pleural fluid was collected at regular time intervals for quantitative culture, estimation of cell apoptosis and of concentrations of tumour necrosis factor-alpha (TNFα). After 7 days, animals were euthanized for estimation of tissue growth. Bacterial growth in the pleural fluid of group D was significantly decreased compared with the other groups on day 5. Lung growth of group D was lower than group A. That was also the case of cytokine stimulation by pleural fluid samples on U937 monocytes. It is concluded that administration of clarithromycin enhanced the antimicrobial efficacy of piperacillin/tazobactam and decreased bacterial growth in the pleural fluid and in tissues. It also attenuated the pro-inflammatory phenomena induced by the ß-lactam.

Dexamethasone Down-Regulates Expression of Triggering Receptor Expressed on Myeloid Cells-1: Evidence for a TNFα-Related Effect.

OBJECTIVES: To investigate the effect of dexamethasone on triggering receptor expressed on myeloid cells-1 (TREM-1). METHODS: Wild-type and tumor necrosis factor (TNF (-/-)) mice were pre-treated with saline, dexamethasone, or hydrocortisone and exposed to a lethal infection of Pseudomonas aeruginosa. Mortality and TREM-1 on neutrophil membranes was measured after sacrifice. U937 human monocytic cells were stimulated with lipopolysaccharide (LPS) or heat-killed P. aeruginosa without or with dexamethasone or hydrocortisone, and cell-surface TREM-1 and soluble TREM-1 (sTREM-1) were quantified. Expression of TREM-1 and sTREM-1 was also studied in LPS-stimulated U937 cells incubated in the absence or presence of TNFα or anti-TNFα antibody. RESULTS: Pre-treatment with dexamethasone, but not hydrocortisone, prolonged animal survival. Mice pre-treated with dexamethasone showed decreased expression of TREM-1 on neutrophils. In U937 cells, LPS or heat-killed P. aeruginosa induced the expression of TREM-1 and the release of sTREM-1. U937 TREM-1 and sTREM-1 were decreased upon addition of dexamethasone but not hydrocortisone. The suppressive effect of dexamethasone was enhanced in the presence of exogenous TNFα and lost in the presence of anti-TNFα antibody. In TNF (-/-) mice, dexamethasone suppression of mortality and TREM-1 neutrophil expression was lost. Gene expression of TREM-1 in U937 monocytes was decreased after treatment with dexamethasone. CONCLUSION: TREM-1/sTREM-1 is a novel site of action of dexamethasone. This action is associated with down-regulation of gene expression and is mediated by TNFα.

Pre-treatment with low-dose endotoxin prolongs survival from experimental lethal endotoxic shock: Benefit for lethal peritonitis by Escherichia coli.

Although LPS tolerance is well-characterized, it remains unknown if it is achieved even with single doses of lipopolysaccharide (LPS) and if it offers protection against lethal bacterial infections. To this end, C57B6 mice were assigned to groups A (sham); B (saline i.p followed after 24h by i.p 30mg/kg LPS); and C (3mg/kg LPS i.p followed after 24h by i.p 30mg/kg LPS). Survival was monitored and animals were sacrificed early after lethal challenge for measurement of tumour necrosis factor-alpha (TNFα) in serum; isolation of splenocytes and cytokine stimulation; and flow-cytometry for apoptosis and TREM-1. Experiments were repeated with mice infected i.p by Escherichia coli after challenging with saline or LPS. Mortality of group B was 72.2% compared with 38.9% of group C (p: 0.020). Serum TNFα of group C was lower than group B. Expression of TREM-1 of group C on monocytes/neutrophils was greater than group B. Release of TNFα, of IFNγ and of IL-17 from splenocytes of group C was lower than group B and the opposite happened for IL-10 showing evidence of cellular reprogramming. In parallel, apoptosis of circulating lymphocytes and of splenocytes of group C was greater compared with group B. Pre-treatment of mice challenged by E. coli with low dose LPS led to 0% mortality compared with 90% of saline pre-treated mice; in these mice, splenocytes improved over-time their capacity for release of IFNγ. It is concluded that single low doses of LPS lead to early reprogramming of the innate immune response and prolong survival after lethal E. coli challenge.

Efficacy of tigecycline alone and in combination with gentamicin in the treatment of experimental endocarditis due to linezolid-resistant Enterococcus faecium.

We evaluated the efficacy of tigecycline in a rabbit model of experimental endocarditis caused by a linezolid-resistant clinical strain of Enterococcus faecium. Tigecycline-treated animals had a 2.8-log10-CFU/g reduction in microbial counts in excised vegetations compared with controls. Addition of gentamicin caused a further arithmetical reduction in colony counts. The therapeutic effect was sustained 5 days after completion of treatment, as shown by relapse studies performed in treatment groups.

Angiopoietin-2 enhances survival in experimental sepsis induced by multidrug-resistant Pseudomonas aeruginosa.

Levels of circulating angiopoietin-2 (Ang-2) increase in sepsis, raising the possibility that Ang-2 acts as a modulator in the sepsis cascade. To investigate this, experimental sepsis was induced in male C57BL6 mice by a multidrug-resistant isolate of Pseudomonas aeruginosa; survival was determined along with neutrophil tissue infiltration and release of proinflammatory cytokines. Survival was significantly increased either by pretreatment with recombinant Ang-2 2 h before or treatment with recombinant Ang-2 30 min after bacterial challenge. Likewise, Ang-2 pretreatment protected against sepsis-related death elicited by Escherichia coli; however, Ang-2 failed to provide protection in lipopolysaccharide (LPS)-challenged mice. The survival advantage of Ang-2 in response to P. aeruginosa challenge was lost in tumor necrosis factor (TNF)-deficient mice or neutropenic mice. Infiltration of the liver by neutrophils was elevated in the Ang-2 group compared with saline-treated animals. Serum TNF-α levels were reduced by Ang-2, whereas those of interleukin (IL)-6 and IL-10 remained unchanged. This was accompanied by lower release of TNF-α by stimulated splenocytes. When applied to U937 cells in vitro, heat-killed P. aeruginosa induced the secretion of IL-6 and TNF-α; low levels of exogenous TNF-α synergized with P. aeruginosa. This synergistic effect was abolished after the addition of Ang-2. These results put in evidence a striking protective role of Ang-2 in experimental sepsis evoked by a multidrug-resistant isolate of P. aeruginosa attributed to modulation of TNF-α production and changes in neutrophil migration. The protective role of Ang-2 is shown when whole microorganisms are used and not LPS, suggesting complex interactions with the host immune response.

Impact of multidrug resistance on experimental empyema by Pseudomonas aeruginosa.

BACKGROUND: Pseudomonas aeruginosa is a cause of infections of the lower respiratory tract among patients with chronic lung disorders. It is questionable whether virulence of this species may be influenced by multidrug resistance (MDR). OBJECTIVES: To define the impact of MDR in experimental lung infection. METHODS: Experimental empyema was induced in rabbits by MDR (group A, n = 16) and by susceptible isolates (group B, n = 10). Pleural fluid was sampled for quantitative culture and estimation of cell apoptosis and of tumor necrosis factor-alpha (TNFα) and malondialdehyde (MDA). Survival was recorded. Cytokine production was stimulated in U937 monocytes by samples of pleural fluid. Whole blood of rabbits was incubated with the isolates; induction of apoptosis was assessed. RESULTS: Survival of group A was prolonged compared to group B. This was accompanied by lower bacterial counts of the inoculated pathogens in pleural fluid and in the lungs of group A compared with group B. Early apoptosis of neutrophils of pleural fluid of group A was lower compared with group B. Pleural fluid concentrations of TNFα and MDA did not differ between the groups. Cytokine production by U937 monocytes after stimulation with pleural fluid was greater in group B than in group A. The susceptible isolate induced apoptosis of neutrophils in vitro at a greater rate than the MDR isolate. CONCLUSIONS: Experimental empyema by susceptible P. aeruginosa is accompanied by greater mortality compared with MDR P. aeruginosa. This phenomenon may be attributed to the different growth pattern of the pathogens or to their interaction with the innate immune system.

Efficacy of carbapenems against a metallo-ß-lactamase-producing Escherichia coli clinical isolate in a rabbit intra-abdominal abscess model.

BACKGROUND: Although metallo-ß-lactamases (MBLs) hydrolyse most ß-lactams, including carbapenems, MBL-producing Enterobacteriaceae very often remain susceptible to carbapenems in vitro. We studied the in vivo efficacy of imipenem, meropenem, ertapenem and aztreonam against a carbapenem-susceptible MBL-producing clinical Escherichia coli strain in a rabbit intra-abdominal abscess model. METHODS: Rabbits were inoculated intraperitoneally with 10(8) cfu/mL of VIM-1-positive E. coli and were assigned to receive no treatment (controls) or intravenous imipenem/cilastatin (imipenem) 70 mg/kg/12 h or meropenem 125 mg/kg/12 h or ertapenem 60 mg/kg/12 h or aztreonam 70 mg/kg/12 h. Dosing regimens were chosen on the basis of preliminary pharmacokinetic studies so that T(>MIC) was achieved for ≥50% of the dosing interval for all tested antibiotics. A total of eight doses were administered before sacrifice and the abscesses were harvested and quantitatively cultured. RESULTS: MICs of imipenem, meropenem, ertapenem and aztreonam for the infecting isolate were 1, ≤0.25, 1.5 and ≤0.25 mg/L, respectively. The log(10) cfu/g (mean ±â€ŠSD) viable counts in pus were as follows: controls (n = 16), 8.71 ±â€Š1.34 (P < 0.001 versus all other groups); imipenem (n = 15), 4.89 ±â€Š2.42; meropenem (n = 15), 4.24 ±â€Š2.44; ertapenem (n = 16), 3.17 ±â€Š1.85 (P = 0.022 versus imipenem); and aztreonam (n = 15), 3.62 ±â€Š3.05. Mortality among treated rabbits was significantly reduced compared with controls. Four animals in the aztreonam group (26.7%) had culture-negative pus and no mortality was noted among aztreonam-treated animals. CONCLUSIONS: In the rabbit experimental model, carbapenems were shown to be effective in the treatment of intra-abdominal infection due to an extended-spectrum ß-lactamase-negative carbapenem-susceptible VIM-1-producing clinical E. coli strain, but treatment with aztreonam resulted in a more favourable outcome overall.

Pharmacokinetics of intravenously administered moxifloxacin in eye compartments: an experimental study.

The purpose of this study was to evaluate the pharmacokinetics of intravenously administered moxifloxacin, a fourth-generation fluoroquinolone, in different parts of the non-inflamed eye. Moxifloxacin was administered intravenously at a dose of 20mg/kg moxifloxacin over 30min. Sampling of peripheral blood, aqueous humour and vitreous was performed at standard time intervals post infusion once in each animal. Moxifloxacin levels were estimated by high-performance liquid chromatography with fluorescence detection. Mean serum concentrations were 3.43, 2.74, 1.48 and 1.12microg/mL at 0.5, 3, 6 and 24h after the end of drug infusion, respectively. Respective concentrations in aqueous humour were 2.44, 2.03, 1.30 and 1.09microg/mL and in vitreous body they were 1.68, 1.87, 1.78 and 1.15microg/mL. It is concluded that systemic administration of moxifloxacin in rabbits was accompanied by efficient penetration into both the aqueous humour and the vitreous body at concentrations well above the minimum inhibitory concentration for most causative pathogens of endophthalmitis. Further research is mandatory to clarify the clinical significance of these findings.

Efficacy and pharmacodynamics of linezolid, alone and in combination with rifampicin, in an experimental model of methicillin-resistant Staphylococcus aureus endocarditis.

OBJECTIVES: To evaluate the efficacy of oral linezolid, with or without rifampicin, on valve vegetations and secondary foci of infection compared with vancomycin, in the absence or presence of rifampicin, in experimental endocarditis caused by methicillin-resistant Staphylococcus aureus. METHODS: Treatment groups were controls (n = 16), linezolid (n = 15), vancomycin (n = 15), linezolid and rifampicin (n = 15), vancomycin and rifampicin (n = 13), linezolid relapse (n = 11) and vancomycin relapse (n = 9). Therapy lasted 5 days in all groups, with survival of animals in the linezolid relapse and vancomycin relapse groups being recorded for an additional 5 days. Blood was drawn to determine the linezolid concentration, and valve vegetations, and kidney, liver, lung and spleen segments were collected for culture. RESULTS: Survival in each individual group was higher than that in the control group; bacterial load in valve vegetations was reduced by all treatment regimens, with linezolid exhibiting bactericidal effects. Bactericidal activity of linezolid was noted in all secondary foci of infection except the lung, where only the combination of rifampicin with linezolid was bactericidal. CONCLUSIONS: Orally administered linezolid is effective in limiting bacterial growth in the secondary foci of endocarditis. Co-administration of rifampicin favoured the suppression of bacterial growth in the lung.

Early apoptosis of blood monocytes is a determinant of survival in experimental sepsis by multi-drug-resistant Pseudomonas aeruginosa.

Apoptosis of blood monocytes was studied in experimental sepsis by multi-drug-resistant Pseudomonas aeruginosa. Thirty-six rabbits were used, divided into the following groups: A (n = 6), sham; B (n = 6), administered anaesthetics; and C (n = 24), acute pyelonephritis induced after inoculation of the test isolate in the renal pelvis. Blood was sampled at standard time intervals for estimation of tumour necrosis factor (TNF)-alpha and isolation of monocytes. Half the monocytes were incubated and the other half was lysed for estimation of the cytoplasmic activity of caspase-3 by a kinetic chromogenic assay. No animal in groups A and B died; those in group C were divided into two subgroups, CI (n = 8) with present activity of caspase-3 of blood monocytes at 3.5 h and CII (n = 16) with absent activity. Their median survival was 2.0 and 3.5 days, respectively (P = 0.0089). Ex vivo secretion of TNF-alpha from monocytes was higher by monocytes of subgroup CII than subgroup CI at 3.5 h (P = 0.039) and of group A than CII at 48 h (P = 0.010). Median change of caspase-3 activity between 3.5 and 24 h of sampling was 56.1 and -5.8 pmol/min per 10(4) cells for subgroups CI and CII (P = 0.040), respectively. Respective changes between 3.5 and 48 h were 28 981.0 and 0 pmol/min per 10(4) cells (P = 0.036). Early induction of apoptosis in blood monocytes is of prime importance for the survival of the septic host and might be connected to changes of monocyte potential for the secretion of TNF-alpha.

Oleuropein: a novel immunomodulator conferring prolonged survival in experimental sepsis by Pseudomonas aeruginosa.

Oleuropein, a novel immunomodulator derived from olive tree, was assessed in vitro and in experimental sepsis by Pseudomonas aeruginosa. After addition in monocyte and neutrophil cultures, malondialdehyde, TNF-alpha, IL-6, and bacterial counts were estimated in supernatants. Acute pyelonephritis was induced in 70 rabbits after inoculation of pathogen in the renal pelvis. Intravenous therapy was administered in four groups postchallenge by one multidrug-resistant isolate (A, controls; B, oleuropein; C, amikacin; D, both agents) and in three groups postchallenge by one susceptible isolate (E, controls; F, oleuropein; G, amikacin). Survival was recorded; bacterial growth in blood and organs was counted; endotoxins (LPS), malondialdehyde, total antioxidant status, and TNF-alpha in serum were estimated. TNF-alpha and IL-6 of cell supernatants were not increased compared with controls when triggered by LPS and P. aeruginosa. Counts of multidrug-resistant P. aeruginosa were decreased in monocyte supernatants. Median survival of groups A, B, C, D, E, F, and G were 3.00, 6.00, 2.00, 10.00, 1.00, 5.00, and 1.00 days, respectively. Bacteria in blood were lower at 48 h in groups B and D compared with A and in groups F and G compared with E. Total antioxidant status decreased steadily over time in groups A, C, D, and G, but not in groups B and F. TNF-alpha of groups B, C, and D was lower than A at 48 h. Tissue bacteria decreased in group F compared with E. Oleuropein prolonged survival in experimental sepsis probably by promoting phagocytosis or inhibiting biosynthesis of proinflammatory cytokines.