The Italians have confirmed that they have acquired the two defenders as they look to continue their strong start to the season against Fiorentina this weekend
Mesto signed for Genoa in 2008 for €3 million and racked up around 100 appearances for the team. He completed a move to Napoli on Friday and has collected three Italian caps since 2005.
The 30-year-old joins fellow defender and teammate Bruno Uvini, who moved to the Italians from Brazilian club Sao Paulo. He has 13 Brazil under 20 caps and was in the London Olympic under 23 squad, who lost in the final to Mexico, this summer.
Napoli have had a strong start to their season, beating Palermo 3-0 last week with goals from Marek Hamsik, Christian Maggio and Edinson Cavani.
Napoli could showcase their new signings at home to Fiorentina on Sunday.