Usando PDO com codeigniter

PDO_Codeigniter

<?php

    $pdo = new PDO('mysql:host=localhost;dbname=itlean',  $this->db->username, $this->db->password);

    $username = 'itlean';
    $consulta = $pdo->prepare("SELECT * FROM admin_users WHERE username = :username;");
    $consulta->bindParam(':username', $username, PDO::PARAM_STR);
    $consulta->execute();

    while ($linha = $consulta->fetch(PDO::FETCH_OBJ)) {
        print_r($linha);
    }
?>