Virulence potential and genomic mapping of the worldwide clone Escherichia coli ST131.

Recently, the worldwide propagation of clonal CTX-M-15-producing Escherichia coli isolates, namely ST131 and O25b:H4, has been reported. Like the majority of extra-intestinal pathogenic E. coli isolates, the pandemic clone ST131 belongs to phylogenetic group B2, and has recently been shown to be highly virulent in a mouse model, even though it lacks several genes encoding key virulence factors (Pap, Cnf1 and HlyA). Using two animal models, Caenorhabditis elegans and zebrafish embryos, we assessed the virulence of three E. coli ST131 strains (2 CTX-M-15- producing urine and 1 non-ESBL-producing faecal isolate), comparing them with five non-ST131 B2 and a group A uropathogenic E. coli (UPEC). In C. elegans, the three ST131 strains showed intermediate virulence between the non virulent group A isolate and the virulent non-ST131 B2 strains. In zebrafish, the CTX-M-15-producing ST131 UPEC isolates were also less virulent than the non-ST131 B2 strains, suggesting that the production of CTX-M-15 is not correlated with enhanced virulence. Amongst the non-ST131 B2 group isolates, variation in pathogenic potential in zebrafish embryos was observed ranging from intermediate to highly virulent. Interestingly, the ST131 strains were equally persistent in surviving embryos as the non-ST131-group B2 strains, suggesting similar mechanisms may account for development of persistent infection. Optical maps of the genome of the ST131 strains were compared with those of 24 reference E. coli strains. Although small differences were seen within the ST131 strains, the tree built on the optical maps showed that these strains belonged to a specific cluster (86% similarity) with only 45% similarity with the other group B2 strains and 25% with strains of group A and D. Thus, the ST131 clone has a genetic composition that differs from other group B2 strains, and appears to be less virulent than previously suspected.

Myostatin up-regulation is associated with the skeletal muscle response to hypoxic stimuli.

Myostatin and hypoxia signalling pathways are able to induce skeletal muscle atrophy, but whether a relationship between these two pathways exists is currently unknown. Here, we tested the hypothesis that a potential mechanism for hypoxia effect on skeletal muscle may be through regulation of myostatin. We reported an induction of myostatin expression in muscles of rats exposed to chronic hypoxia. Interestingly, we also demonstrated increased skeletal muscle myostatin protein expression in skeletal muscle of hypoxemic patients with severe chronic obstructive pulmonary disease (COPD). Parallel studies in human skeletal muscle cell cultures showed that induction of myostatin expression in myotubes treated with hypoxia-mimicking agent such as cobalt chloride (CoCl(2)) is associated with myotube atrophy. Furthermore, we demonstrated that inhibition of myostatin by means of genetic deletion of myostatin or treatment with blocking antimyostatin antibodies inhibits the CoCl(2)-induced atrophy in muscle cells. Finally, addition of recombinant myostatin restored the CoCl(2)-induced atrophy in myostatin deficient myotubes. These results strongly suggest that myostatin can play an essential role in the adaptation of skeletal muscle to hypoxic environment.

Reversal of bupivacaine-induced cardiac electrophysiologic changes by two lipid emulsions in anesthetized and mechanically ventilated piglets.

BACKGROUND: Accidental IV administration of bupivacaine can compromise cardiovascular function by inducing lethal arrhythmias whose hemodynamic consequences may be alleviated by lipid emulsions. However, little is known about the electrophysiologic effects of lipid emulsions. In this study, we assessed whether 2 different lipid emulsions can reverse cardiac electrophysiologic impairment induced by the IV administration of bupivacaine in anesthetized and mechanically ventilated piglets. METHODS: Bupivacaine (4 mg . kg(-1)) was injected over a 30-second period in 26 piglets. Thirty seconds after the end of bupivacaine injection, 1.5 mL . kg(-1) saline solution for the control group, and long-chain triglyceride emulsion (LCT group) or a mixture of long-chain and medium-chain triglyceride emulsion (LCT/MCT group) were infused over 1 minute. Cardiac conduction variables and hemodynamic variables were monitored for 30 minutes after injection. RESULTS: Bupivacaine induced similar electrophysiologic and hemodynamic changes. After 3 minutes, His ventricle intervals (median and interquartiles) were 100 (85-105), 45 (35-55), and 53 (48-73) milliseconds in the control, LCT, and LCT/MCT groups, respectively (P < 0.001 between control and both lipid emulsion groups). Lipid emulsions also reversed the effects on QRS duration, atrial-His, and PQ (the onset of the P wave to the Q wave of the QRS complex) intervals. LCT/MCT emulsion restored the decrease in maximal first derivative of left ventricular pressure (P < 0.01 after 3 minutes versus control group). CONCLUSIONS: LCT and LCT/MCT emulsions reversed the lengthening of His ventricle, QRS, atrial-His, and PQ intervals induced by the IV injection of 4 mg . kg(-1) bupivacaine.

Acute administration of l-arginine restores nitric oxide-mediated relaxation in isolated pulmonary arteries from pulmonary hypertensive exercise trained rats.

Hypoxia-induced pulmonary hypertension is associated with an impairment of nitric oxide-mediated vasorelaxation in the pulmonary circulation that is not prevented by exercise training. The present study was designed to test the hypothesis that a decrease in l-arginine bioavailability could be involved in this blunted response to exercise training. Male Wistar rats were randomly assigned to 4 groups: normotensive sedentary, normotensive trained, pulmonary hypertensive sedentary, pulmonary hypertensive trained. Pulmonary hypertension was induced by chronic exposure to hypobaric hypoxia (PIO(2) approximately 90 mmHg). Endothelium-dependent vasorelaxation to acetylcholine (10(-8)-10(-4) M) with or without l-arginine (10(-3) M) and/or nitro-l-arginine methyl ester (5.10(-6) M) was assessed on isolated pulmonary arterial rings. Maximal relaxation to acetylcholine was impaired in both pulmonary hypertensive groups. Acute l-arginine supplementation improved acetylcholine-induced vasorelaxation in the pulmonary hypertensive trained rats (P<0.01), to the level obtained in the normotensive sedentary ones, but not in the pulmonary hypertensive sedentary rats. This improvement was abolished when nitro-l-arginine methyl ester was added to the organ bath and was accounted for by an increase in eNOS protein content. These results confirm that the potential beneficial effect of exercise on nitric oxide-mediated pulmonary artery vasorelaxation is partly blunted by deleterious effects of hypoxia on l-arginine bioavailability. Further studies are needed to evaluate the benefit of the combination of exercise training and l-arginine supplementation for the treatment of pulmonary hypertension.

Training does not affect the alteration in pulmonary artery vasoreactivity in pulmonary hypertensive rats.

This study examined the effects of training on intrinsic vasorelaxation and vasoconstriction properties of pulmonary hypertensive rat arteries. Fifty seven male Wistar rats were randomly assigned to 4 groups: normotensive sedentary (n = 14), normotensive trained (n = 15), pulmonary hypertensive sedentary (n = 15) and pulmonary hypertensive trained (n = 13). Pulmonary hypertension was obtained using a chronic hypoxia exposure model. Endothelium-dependent vasorelaxation to acetylcholine (10(-8)-10(-4) M), endothelium-independent vasorelaxation to sodium nitro-prusside (10(-8)-10(-4) M), and vasoconstriction to epinephrine (10(-9)-10(-4) M) and endothelin-1 (10(-12)-10(-7) M) were assessed on isolated rings of large pulmonary arteries. Alterations in endothelium-dependent and -independent vasorelaxation properties as well as enhanced vasoconstrictor responses were obtained in pulmonary hypertensive rats. Chronic exercise did not affect those pulmonary vasoreactivity alterations. A predominant effect of chronic hypoxia over training seems to be partially responsible for this phenomenon, probably through impairment in nitric oxide bioavailability and vascular smooth muscle sensitivity.