Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 9, 2005
Publication Date: August 16, 2005
Citation: Niemira, B.A. 2005. Nalidixic acid resistance increases sensitivity of salmonella to ionizing radiation in solution and in orange juice. Annual Meeting of International Association of Food Protection (IAFP), August 14-17, 2005, Baltimore, MD. p. 1-33. Technical Abstract: Resistance to the antibiotic nalidixic acid has been used as a selective marker for studies of pathogen-inoculated fruits and vegetables. However, resistance to this antibiotic has been shown to influence the sensitivity of Escherichia coli O157:H7 to ionizing radiation. To determine the ubiquity of this phenomenon, a collection of 24 food-borne illness related isolates of Salmonella were screened for native resistance to nalidixic acid. The sensitivity to ionizing radiation was determined in a neutral buffer for three nalidixic acid sensitive (Nal-S) isolates and three nalidixic acid resistant (Nal-R) isolates. The radiation D10 values (the amount of ionizing radiation necessary to reduce the population by one log10, or 90%) were significantly (P<0.05) different among the isolates. As a group, Nal-R isolates of Salmonella were found to be significantly more sensitive to irradiation (D10=0.210kGy) than Nal-S isolates (D10=0.257kGy). Through selective reculturing in nalidixic acid-amended liquid media (up to 50 ug/ml), the Nal-S isolates were induced to become resistant (Nal-Ri). The radiation sensitivity of Nal-Ri isolates was significantly increased relative to the respective Nal-S parent for two of the three isolates tested. As a group, Nal-Ri isolates had D10 value of 0.234kGy, intermediate between Nal-S and Nal-R isoaltes. The study was repeated in reconstituted orange juice, using the same Nal-S, Nal-R and Nal-Ri isolates. Overall D10 values were higher than those observed in neutral buffer. The pattern of response was similar; as a group, Nal-R isolates were significantly more sensitive to ionizing radiation (D10=0.581kGy) than Nal-S isolates (D10=0.764kGy), with Nal-Ri intermediate between the two (D10=0.637kGy). Similarly, the radiation sensitivity of Nal-Ri isolates in orange juice was significantly increased relative to the respective Nal-S parent for two of the three isolates tested.