The invention provides a method to improve the efficacy of an antibiotic to inhibit the growth of Acinetobacter, said method comprising using said antibiotic together with an alginate oligomer. The Acinetobacter may be on an animate or inanimate surface and both medical and non-medical uses and methods are provided. In one aspect the invention provides an alginate oligomer for use together with at least one antibiotic in treating a subject infected, suspected to be infected, or at risk of infection, with Acinetobacter. In another aspect the method can be used to combat Acinetobacter contamination of a site e.g., for disinfection and cleaning purposes.