March 16 (Reuters) - S&P Global Ratings:
* S&P GLOBAL RATINGS - VIRGIN AUSTRALIA DOWNGRADED TO 'B-' ON DETERIORATING DOMESTIC MARKET CONDITIONS; PLACED ON CREDITWATCH NEGATIVE
* S&P GLOBAL RATINGS ON VIRGIN AUSTRALIA - LOWERED RELATED ISSUE RATINGS ON AIRLINE'S DEBT TO 'CCC+' FROM 'B'