Silvio Berlusconi, who during the 17 years since he was first elected prime minister has been accused of tax fraud, mafia collusion, bribery of law-enforcement officials, and solicitation of an underage prostitute, stepped down after Italyâ??s parliament passed austerity measures seeking to contain the impact of the countryâ??s $2.6 trillion debt, which he had been denying was a problem.