A method for testing for the presence of bacteria in the field includes using a mixer and frother or a reagent to disrupt bacteria cells. A sample is collected from a source suspected to be contaminated by bacteria. A mixer and frother or similar mixer is used to mix the sample, or a reagent is added to the sample, to form an elute by disrupting bacteria cells present in the sample to expose bacteria enzymes. A reagent pad is immersed in the elute and then withdrawn from the elute, or a drop of the elute is deposited on a reagent pad. After a waiting period, the reagent pad is observed to determine if the bacteria is present in or on the source. The source may be a body of water, produce, prepared food, a food preparation area, or food processing equipment. The reagent is generally a lysis reagent.