Franklin-based medical transcription firm Spheris Inc. has hired Brian P. Callahan as its chief financial officer. The move marks the second change at that post in the past six months and comes three weeks after one of the major rating agencies cut the company's already junk-level credit score.

He replaces Chris Mack, who took the CFO post in December 2005. A company release indicates that Mack was serving in an interim capacity, although the company's website has not previously characterized his position as temporary. The statement says Mack will now "work closely with the Spheris operations team on a number of corporate initiatives."

Callahan is a former executive vice president and chief financial officer at Murray Inc., the Brentwood-based lawnmower maker  whose assets Briggs & Stratton Corp. purchased out of bankruptcy last year.

Last month, Standard & Poor's Ratings Services downgraded the company's corporate credit rating to B- from B and lowered an issue of its subordinated notes to CCC from CCC+. S&P analyst Alain Pelanne was quoted as citing Spheris' "reduced cushion under its financial covenants" and "significantly reduced" liquidity, as well as a shortage of qualified medical technologists, as factors in the rate cut.

Spheris has grown at a breakneck pace in the past several years, earning a place at #16 on the 2005 "Inc. 500" list of the nation's fastest-growing businesses. It posted revenue growth of 2,711 percent between 2001 and 2004.