Abstract: A metal working fluid having increased resistance to bacterial growth. The metal working fluid includes a cross-linked polymeric ester emulsifier; and an amine represented by the formula (H2N)a-Q-(NH2)b, where a and b are each integers, and Q is at least one carbon atom. Q may also be represented by X—Y—Z, where a+b?2; X is a cyclic ring system including 3 to 24 carbon atoms; and Y and Z are groups that include at least one carbon atom directly attached to the cyclic ring system. The metal working fluid may also include a biocide, and may also include an amide that is formed by reacting the amine with a carboxylic acid.