Exhibit 1

Joint Filing Agreement

The undersigned hereby agree that a single Schedule 13D (or any amendment thereto) relating to the Common Stock of OpGen, Inc. shall be filed on behalf of each of the undersigned and that this Agreement shall be filed as an exhibit to such Schedule 13D.

Dated: May 14, 2015

Versant Side Fund III, L.P.

By:  Versant Ventures III, LLC

Its:  General Partner

By:  /s/ Robin L. Praeger

        Authorized Representative

Versant Venture Capital III, L.P.

By:  Versant Ventures III, LLC

Its:  General Partner

By:  /s/ Robin L. Praeger

        Authorized Representative

Versant Ventures III, LLC

By:  /s/ Robin L. Praeger

        Authorized Representative

/s/ Robin L. Praeger as attorney in fact

Brian G. Atwood

/s/ Robin L. Praeger as attorney in fact

Samuel D. Colella

/s/ Robin L. Praeger as attorney in fact

Ross A. Jaffe

/s/ Robin L. Praeger as attorney in fact

William J. Link

/s/ Robin L. Praeger as attorney in fact

Donald B. Milder

/s/ Robin L. Praeger as attorney in fact

Rebecca B. Robertson

/s/ Robin L. Praeger as attorney in fact

Bradley J. Bolzon

/s/ Robin L. Praeger as attorney in fact

Charles M. Warden

/s/ Robin L. Praeger as attorney in fact

Barbara N. Lubash

/s/ Robin L. Praeger

Robin L. Praeger