Ann Arbor-based venture capital firm Arboretum Ventures is investing in University of Michigan spinoff Life Magnetics, which is developing a diagnostic product that helps hospitals determine a patient's bacterial response to antibiotics.

The size of the investment was not disclosed, but it was a Series A preferred stock financing deal, which is typically considered the first VC phase for a startup tech company.

“The technology being developed by Life Magnetics offers the opportunity to revolutionize the combined challenges of pathogen identification and antibiotic susceptibility testing," Arboretum managing director Jan Garfinkle said in a statement. "Instead of waiting for days while the most appropriate course of treatment is determined, clinicians will be able to quickly identify both the pathogen and the antibiotic best suited for treatment.”

Brandon McNaughton, founder and chief technical officer of Life Magnetics, said in a press release that mid-size hospitals spend up to $4 million a year because of long testing times associated with currently available technologies.

Arboretum focuses its investments on companies whose technology lowers the cost of health care. The firm -- whose successful investments include U-M spinoffs HealthMedia and HandyLab -- finished raising $73 million in fresh capital in early 2009 to continue making investments.

The firm's latest investments include Karmanos Cancer Institute spinoff Delphinus Medical Technologies, which moved into Ann Arbor SPARK's Michigan Life Science and Innovation Center in Plymouth Township.

Contact AnnArbor.com's Nathan Bomey at (734) 623-2587 or nathanbomey@annarbor.com. You can also follow him on Twitter or subscribe to AnnArbor.com's newsletters.