Call plugin in third party extension of joomla

global $mainframe;
        include_once('components/com_content/models/article.php');
        include_once('components/com_content/helpers/query.php');
        $dispatcher =& JDispatcher::getInstance();
        $articleObject=new ContentModelArticle();
        $id= JRequest::getVar('content_id');
        $limitstart    = JRequest::getVar('limitstart', 0, '', 'int');
        $articleObject->setId($id);
        $item=new JObject;
        $item->text = $articleObject->getArticle(); 
        $item->params = clone($mainframe->getParams('com_content'));
        JPluginHelper::importPlugin('content');
        $results=$dispatcher->trigger('onBeforeDisplayContent', array (& $item->text, & $item->params, 0));
        echo $results[0];