The A- credit rating for Macquarie Bank derives from the prospect of public sector intervention to assist the bank in any future period of difficulty, ratings agency Standard & Poor's has made clear.the S&P assessment released last night leaves Macquarie Bank rated two notches higher than its owner, Macquarie Group, whose rating has fallen to BBB.S&P said that Macquarie Group, the holding company that earns half its income outside the banking business, operates in many markets that are "inherently complex and volatile", and said "this has a constraining effect on our view of Macquarie's stability".The rating agency noted, though, that "we view Macquarie's strategy as sound overall", given its shift in approach since the financial crisis hit three years ago. It said it expects this trend will continue.In its outlook summary, S&P mainly referred to factors that could drive a lowering in the ratings of Macquarie Group and Macquarie Bank (such as an increase in risk appetite for a poorly managed or poorly funded expansion in operations). It said that upward rating sentiment is not expected in the short term.