The deal, for an undisclosed sum, sees Mmd absorb the three-strong Gulden team and the bulk of its client list, which includes healthcare giants such as Johnson & Johnson and Danone.
Gulden - thought to have had revenues of up to £600,000 last year - was part of the Burson-Marsteller PR network until ad agency Y&R bought the firm 18 months ago.
Y&R chairman and CEO Mark Bindloss Gibb said they wanted to refocus on the ad market: 'For Y&R, PR has not been a core area of business.'
Mmd GM Chris Dobson said the takeover gives the agency a headstart in the healthcare market.
Former Gulden head Katalin Molnar joins Mmd as an account director.