Modification of methods for detection of Escherichia coli O157:H7 on produce

To establish the best detection method for Escherichia coli O157:H7 on produce, the sensitivity, specificity, and recovery values of 3 selective media [sorbitol MacConkey agar containing cefixime and tellurite (CTSMAC), sorbitol MacConkey agar containing cefixime, tellurite, and 5-bromo-4-chloro-3-indoxyl-β-glucuronide (CTB-SMAC), and CHROMagar O157 were compared. Sample preparation methods (pummeling, sonication, and hand-shaking) were compared to determine the optimum procedure for qualitative analysis from cherry tomato. The selectivity and recovery rates of stressed cell of the 3 tested media were in the order of CHROMagar O157>CTBSMAC>CT-SMAC. The recovery rates of hand-shaken tomatoes (10/10) were higher than rates of sonicated (8/10) and pummeled tomatoes (6/10) for inoculated cherry tomatoes in modified E. coli (mEC) broth enriched with novobicin. CHROMagar O157 was the optimum agar medium for detection of E. coli O157:H7. Cherry tomatoes should be treated with hand-shaking to enhance recovery for qualitative analysis.