I think, unfortunately with a low confidence level, that “medio” is the abridged form of “medio de cultivo” in this context, which means “culture medium” in English being “culture media” just the plural form of it (= medios de cultivo).

“Growth medium” would be a possible alternative, both terms, “culture” and “growth medium” are possible.

So yes, I agree with your interpretation (but would certainly like to see more context to upgrade my confidence level).

https://www.oie.int/fileadmin/Home/esp/Health_standards/tahm...
PRUEBAS DE ESTERILIDAD Y AUSENCIA DE CONTAMINACIÓN EN LOS MATERIALES BIOLÓGICOS DE USO VETERINARIO
(…)
Si el material biológico que se está analizando tiene propiedades antimicrobianas, la membrana se lava tres veces tras aplicar la muestra con alrededor de 100 ml del diluyente apropiado (A o B). A continuación, la membrana se transfiere entera al medio de cultivo, se corta de forma aséptica en partes iguales y se pone en los medios, o bien los medios se transfieren a la membrana en el aparato del filtro.



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Note added at 6 hrs (2021-11-04 17:31:49 GMT)
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Hi, sebaspedlp, yes, we may be on the right track, but you are doing the right thing by resorting to your client to ask them for clarification. Let´s wait and see what they say.

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Note added at 11 hrs (2021-11-04 22:26:30 GMT)
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Glad to know! Thanks for your feedback, sebaspedlp.