Function to filter item_citation to account for multiple creators.

multiple_creators.php

<?php

/**
 * Function to filter item_citation to account for multiple creators.
 */
function item_citation_multiple_creators($cite, $item) {

    $cite = '';

    if ($creators = item('Dublin Core', 'Creator', array('all' => true), $item)) {

        switch(count($creators)) {

            case 1:
              $cite .= $creators[0];
            break;

            case 2:
              $cite .= implode(' and ', $creators);
            break;

            case 3:
              $cite .= $creators[0] . ', ' . $creators[1] . ', and ' . $creators[2];
            break;

            default:
              $cite .= $creators[0] . ' et. al.';
            break;

        }

        $cite = $cite . ', ';

    }

    if ($title = item('Dublin Core', 'Title', array(), $item)) {
        $cite .= "&#8220;$title,&#8221; ";
    }

    if ($siteTitle = settings('site_title')) {
        $cite .= "<em>$siteTitle</em>, ";
    }

    $cite .= "accessed " . date('F j, Y') . ", ";

    $cite .= abs_item_uri($item);

    return strip_formatting($cite);

}

add_filter('item_citation', 'item_citation_multiple_creators');