The indexes for C and V only look at 1 row, but the index for M looks at ALL rows (but the PRIMARY is for ID_MEM). It says that PRIMARY is a possible key, but it isn't using it.
The main content that I am returning is from C, yet it looks like the query might be reading this in an inefficient way.
SELECT V.ti, V.vti, V.ad, C.* , M.av, M.me, M.ID_MEM
FROM c_n AS C
JOIN vis AS V ON V.ID = C.viid
JOIN mes AS M ON M.ID_MEM = C.uid
AND C.sil =1
C.oai LIKE '%;;word;;%'
AND C.silm NOT LIKE '%;;word2;;%'
AND C.uid !=74410
AND C.uid >0
ORDER BY C.ID DESC
LIMIT 0 , 25