Effect of linezolid alone and in Combination with other antibiotics, on methicillin-resistant staphylococcus aureus

The prevalence of methicillin-resistant Staphyloccoccus aureus [MRSA] strains has presented a new challenge in antimicrobial medication. Linezolid is a new drug with potent activity on Grampositive pathogens such as MRSA. The aim of the study was to investigate the in vitro activity of linezolid alone and in combination with imipenem, vancomycin or rifampicin to determine the most active therapy against MRSA strains. Twenty clinical MRSA strains were isolated from patients admitted to inpatient departments and outpatient clinics of Theodor Bilharz Research Institute. Standard strain MRSA ATCC 43300 was included as a control. The MICs of MRSA strains to linezolid, vancomycin, imipenem and rifampicin were evaluated using E test. Time-kill curve were used to assess the in vitro activity of linezolid [at 8x MIC] alone and in combination with imipenem [at 32x MIC], vancomycin or rifampicin [at 8x MIC]. Scanning and transmission electron microscopy were performed to compare bacterial morphological alterations owing to the different combinations. Time-kill studies showed synergistic effect when linezolid combined with imipenem was tested against all the MRSA strains. Linezolid plus vancomycin or rifampicin combinations did not display any synergism or antagonism. Scanning and transmission electron microscopy observations confirmed the interactions observed in time kill experiments. Linezolid in combination with subinhibitory concentrations of imipenem can be bactericidal against MRSA strains and appears to be a promising combination for the treatment of MRSA infections. No synergistic activity was seen when the linezolid and vancomycin or rifampicin were combined. Linezolid could prevent the emergence of mutants resistant to rifampicin

Angiogenic potential of human umbilical cord blood ex vivo expanded CD 133* stem cells in chronic hepatic fibrosis of murine schistosomiasis

As a source of hematopoietic stem cells [HSCs], umbilical cord blood [UCB] has the advantages of speed of availability, tolerance of more than one HLA mismatch, and a low incidence of severe graft-versus-host disease [GVHD]. Hence, it represents a promising, alternative non-costly and non-invasive source for prospective stem cell based therapy. In this study we investigated the angiogenic potential of ex vivo expanded human umbilical cord blood CD 133* stem cells transplanted into mice with chronic hepatic fibrosis induced by Schistosomiasis infection. Histopathological, ultrastructural and immunohistochemical analysis of mice liver sections were done to detect specific human angiogenic markers. Umbilical cord blood was obtained from healthy pregnant females after delivery and mononuclear cells were collected by density gradient using Ficoll Hypaque. Enrichment for the CD 133* stem cells was done by positive selection using the Magnetic Activated Cell Sorting system and magnetic microbeads. Cells were cultured in prirnaly ex vivo expansion medium for three weeks. Flowcytomeric analysis of the cultured cells was done in each step to identify the CD 133* cells. Schistosomiasis was induced in Swiss Albino mice by intradermal injection of schistosoma cercariae. Twenty two weeks post schistosoma infection a total of 0.3 x 106 human CD 133* stem cells were injected intrahepatically in mice. Accordingly, mice were divided into three groups: Group 1 [infected, transplanted]; Group 2 [infected controls] and Group 3 [healthy, transplanted]. All mice were sacrificed 3 wks after cell transplantation was done in groups I and 3. Histopathology and Electron microscopy showed an obvious increase in the capillary network and the small blood vessels and a decrease in the fibrosis known for this stage of the disease. By immunohistochemical analysis the cellular constituents of these newly formed blood vessels showed positive expression of the human-specific angiogenic markers CD31, CD34 and von Willebrand Factor [vWF]. Few hepatocyte like polygonal cells showed positive expression of human Vascular Endothelial Growth Factor [VEGF] and inducible Nitric Oxide Synthase [iNOS]. Ex vivo expanded CD 133* human stem cells incorporate into the liver of schistosoma infected mice enhancing local angiogenesis and hepatic neovascularization. These preliminary results obtained suggest a dual benefit of CD 133* cells in cell therapy in hepatic diseases based on its capability of hematopoietic and endothelial differentiation. We suggest that the CD 133* cells contribute to repair in a paracrine manner by creating a permissive environment that enables rapid proliferation and survival of damaged cells rather than through direct differentiation to hepatocytes

Soluble P-and E- selectins and ultrastructural evaluation of canine liver after reperfusion with methylprednisolone and prostaglandin E 1

Ischemia reperfusion injury [IRI] is a multifactorial process that may be the main underlying factor in critical phases faced during and after liver transplantation. This work evaluates the effect of methylprednisolone [MP] and prostaglandin El [PGE1] on IRI of the liver of dogs at the ultrastructural level together with the assessment of soluble P-and E- selectin levels. Three groups of dogs [9 each] were subjected to 60 min ischemia followed by 30 min reperfusion with the appropriate solution according to the group. Group I, the control untreated group was flushed with Ringer's solution, group II was administered 10 mg/kg MP 24 hours before the procedure and with induction of anaesthesia, and group III was flushed with PGE1 in Ringer's solution at a rate of 0.02 microg/kg/min. Liver specimens were collected before ischemia, after ischemia and after reperfusion and were processed for the preparation of ultrathin sections for electron microscopic examination. Corresponding venous blood samples were harvested, centrifuged and serum was processed for the estimation of soluble P-and E- selectins by enzyme immunoassay, together with alanine and aspartate aminotransferases. Electron microscopic [EM] examination of liver ultrathin sections revealed that the morphological structure of hepatocytes and endothelial lining of hepatic sinusoids were well preserved in the group treated with PGE1. Hepatic ultrastructure was much altered in MP treated group showing necrotic and degenerative changes. The control untreated group disclosed bleb formation of hepatocytic membrane with increased leukocyte infiltration. Soluble P-and E- selectin levels were significantly elevated in the control group, near to pre-ischemic level in PGE1 group and showed a persistent elevation in MP group. Serum transaminases [AST and ALT] were significantly elevated in both control and MP groups as compared to their corresponding pre-ischemic levels. Yet, in PGE1 group, their values were comparable to the pre-ischemic ones. This work confirms the hepatoprotective effect of PGE1 in IR injury. The PGE1 impact on preserving the subcellular structure of hepatic sinusoids is crucial and may be mainly attributed to its biological properties. We presume that P-and E- selectins are greatly implicated in the mechanism of IR and may be an important therapeutic target by specific monoclonal antibodies