MySQL server version for the right syntax to use near '= '15' OFFSET = '0''

Question

Getting error after changing from PHP to PDO. Previously I used following code to select from database after changing from PHP to PDO I receive following error can some one help me to sort error

PHP

$limit = (intval($_GET['limit']) != 0 ) ? $_GET['limit'] : 10;
$offset = (intval($_GET['offset']) != 0 ) ? $_GET['offset'] : 0;

$sql = "SELECT countries_name FROM countries WHERE 1 ORDER BY countries_name ASC LIMIT $limit OFFSET $offset";
try {
  $stmt = $DB->prepare($sql);
  $stmt->execute();
  $results = $stmt->fetchAll();
} catch (Exception $ex) {
  echo $ex->getMessage();
}
if (count($results) > 0) {
  foreach ($results as $res) {
    echo '<h3>' . $res['countries_name'] . '</h3>';
  }
}

PDO

$limit = (intval($_GET['limit']) != 0 ) ? $_GET['limit'] : 10;
$offset = (intval($_GET['offset']) != 0 ) ? $_GET['offset'] : 0;

try {
    $stmt = $db->prepare("SELECT countries_name FROM countries ORDER BY countries_id ASC LIMIT = :limit OFFSET = :offset");
    $stmt->bindParam(':limit', $limit);
    $stmt->bindParam(':offset', $offset);
    $stmt->execute();
    $results = $stmt->fetchAll();
} catch (Exception $ex) {
    echo $ex->getMessage();
}
if (count($results) > 0) {
    foreach ($results as $res) {
        echo '<h3>' . $res['countries_name'] . '</h3>';
    }
}