As noted in the MLA Handbook, if a source lists two or more publishers, include each of them in the Publisher element, separating them with a forward slash (5.61). The following example shows a works-cited-list entry for a book copublished by Iberoamericana and Vervuert:  

Ortiz Wallner, Alexandra. El arte de ficcionar: La novela contemporánea en Centroamérica. Iberoamericana/Vervuert, 2012.

Add a space on either side of the slash when one or more of the publishers’ names consists of more than one word. In the above example, no space is needed around the slash because each of the publishers’ names is only one word. In the below example, however, a space is added on either side of the slash because each of the publishers’ names—“U of Massachusetts P” and “Library of Congress, Center for the Book”—consists of more than one word. In such instances, adding a space on either side of the slash lends readability.  

Dewar, James A., and Peng Hwa Ang. “The Cultural Consequences of Printing and the Internet.” Agent of Change: Print Culture Studies after Elizabeth L. Eisenstein, edited by Sabrina Alcorn Baron et al., U of Massachusetts P / Library of Congress, Center for the Book, 2007, pp. 365–77.

Work Cited

MLA Handbook. 9th ed., Modern Language Association of America, 2021. MLA Handbook Plus, 2021, mlahandbookplus.org/.