Purpose: To evaluate acid-resistance and storage conditions of potential surrogates for non-E. coli O157 STECs.
Methods: Non-O157 Shiga Toxin-producing E. coli (STECs) (ATCC # 2192, 2193, 2196, 2215, 2217 and 2219), E. coli biotype I surrogates (ATCC # BAA-1427, BAA-1428, BAA-1429, BAA-1430 and BAA-1431), and Rifampicin-resistant E. coli biotype I surrogates were cultured in tryptic soy broth (TSB) at 37°C for 18 h. Stationary and acid-adapted organisms were transferred into 10 ml of pre-warmed phosphate buffer saline (PBS) acidified with L-lactic acid at pH 2.5, 3.0 and 3.5. At pre-determined time intervals, enumeration was conducted to evaluate acid resistance. For freezing (-20 ± 0.5°C) and refrigerated (4 ± 0.5°C) storage, bacterial strains were enumerated on days 0, 7, 14, 21, 28, 60, and 90. Data were analyzed using GLM of SAS.
Results: For acid resistance, most E. coli biotype I microorganisms had similar (P > 0.05) reductions to the non-O157 STECs; however, there were some instances of greater (P < 0.05) reductions. Both refrigerated and frozen storage resulted in random differences between counts of E. coli biotype I microorganisms and non-O157 STECs; however, there were no notable trend or patterns observed. Findings for both acid resistance and storage conditions support previous research stating that surrogates may best be used as a cocktail rather than as single strains.
Significance: This research supports that E. coli biotype I microorganisms may serve as surrogates for acid resistance and storage conditions for these six non-O157 STECs.