Assessment of impedance microbiological method for the detection of Escherichia coli in foods

This study was conducted to determine the sensitivity and specificity of th e impedance-based microbiological method for the detection of Escherichia c oli in foods within 24 h of testing. A Malthus Microbiological Analyzer sys tem (Malthus System V, Malthus Instruments Ltd., Bury, United Kingdom), and a modified Malthus Coliform Broth Medium (MCBM), and an incubation tempera ture of 44C were used. The sensitivity of the impedance method was determin ed by testing E. coli-negative food samples spiked with different concentra tions of E. coli. The specificity of the method was determined by testing E . coli-negative food samples spiked with Klebsiella pneumoniae, Enterobacte r cloacae and Pseudomonas aeruginosa. The test results were compared with t hose obtained by the Most Probable Number (MPN) method. Milk, milk products , raw and ready-to-eat meats, and vegetables were tested for the presence o f E. coli by both methods. The sensitivity of the impedance method and the MPN method for the detection of foods containing 10(1) CFU/g was 100% and 8 4.4% respectively. Both methods had a specificity of 100% for food samples spiked with 10(1) CFU/g E. coli. The specificity of the impedance and the M PN methods for the detection off. coli in naturally contaminated milk and m eat samples was 100% and 95.7% respectively. E. coli was detected in foods by the impedance method within 4-24 h of testing at a detection limit of 1 CFU/mL. These results demonstrate that the impedance method can be used as a rapid and sensitive method for the detection of coli in foods.