"It'll be cool to have USA on the front of my jersey," said Bell.
Bell will join Jake Peavy on the USA roster and will fly to Florida tonight to join the team. The United States opens in the WBC against Canada on Saturday.
Bell had a 6-6 record as a set-up man out of the Padres bullpen last season, with an earned run average of 3.58. He struck out 71 batters in 74 innings.
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Padres manager Bud Black told Bell "to be smart and have a good time" after learning of the assignment for his closer. Bell was added to the United States roster to replace Joe Nathan, who has a sore shoulder.