Código PHP:
$resource = $this->getInvokeArg('bootstrap')->getPluginResource('multidb');
$resource->init();
$db = $resource->getDb();
$db->setFetchMode(Zend_Db::FETCH_OBJ);
$select = $db->select();
$select->from('usuarios');
$select->where('id = ?', $identity->id);
$select->limit(1);
$result = $db->fetchRow($select);
$namespace->email = $result->email;