Natural and acquired resistance of bacteria associated with food processing environments to disinfectant containing an extract from grapefruit seeds

Resistance to a new disinfectant amongst typical food spoilage organisms and factors influencing its activity have been studied. The results obtained reveal that a wide range of Gram-negative bacteria exhibit resistance to the disinfectant which is produced from grapefruit seed extract. Gram-positive bacteria were more sensitive. The minimum inhibitory concentration for nine out of 10 Gram-negative strains tested exceeded the lowest recommended concentration for use. Two of the four strains tested also exhibited resistance in a bactericidal suspension test. These two strains appeared to use components in the disinfectant as a carbon source for growth. Two other strains adapted easily to grow in Mueller Hinton broth containing increasingly higher concentrations of the disinfectant. Thus, regular use of this disinfectant could result in a build-up of Gram-negative resistant bacteria. However, adapted organisms slowly lost resistance during growth in the absence of the disinfectant, indicating alternation with other disinfectants could overcome this problem. Both protein and hard water had detrimental effects on the bactericidal efficacy.