Determination of strain variability and kinetics of food-associated microorganisms following ultrasound treatment

Abstract

Ultrasound is a promising emerging technology known for its antimicrobial efficacy. However, existing studies have not fully addressed the impact of strain variability and inactivation kinetics on US efficacy. Ten strains of Listeria monocytogenes, 𝘓𝘪𝘴𝘵𝘦𝘳𝘪𝘢 𝘮𝘰𝘯𝘰𝘤𝘺𝘵𝘰𝘨𝘦𝘯𝘦𝘴, 𝘓𝘢𝘤𝘵𝘪𝘱𝘭𝘢𝘯𝘵𝘪𝘣𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘱𝘭𝘢𝘯𝘵𝘢𝘳𝘶𝘮, 𝘚𝘢𝘤𝘤𝘩𝘢𝘳𝘰𝘮𝘺𝘤𝘦𝘴 𝘤𝘦𝘳𝘦𝘷𝘪𝘴𝘪𝘢𝘦 and 𝘌𝘴𝘤𝘩𝘦𝘳𝘪𝘤𝘩𝘪𝘢 𝘤𝘰𝘭𝘪 were exposed to US treatment (26 kHz, 200 mL, 100 % amplitude, 200 W, 65–71 W/cm²) under dynamic conditions to investigate their resistance profile. Furthermore, the inactivation kinetics of selected resistant/sensitive strains were assessed. The result showed significant intra-species variability in resistance (p < 0.05) for the four target microorganisms evaluated in this study. L6 and NCTC 10357 were the most resistant and sensitive 𝘓. 𝘮𝘰𝘯𝘰𝘤𝘺𝘵𝘰𝘨𝘦𝘯𝘦𝘴 strains respectively, having a reduction difference of ~3.4 log CFU/mL. Regarding 𝘓. 𝘱𝘭𝘢𝘯𝘵𝘢𝘳𝘶𝘮, FBR04 emerged as the most resistant strain (4.4 log reduction), while E. coli FAM21845, FAM21805 and FAM21843 (~2 log reduction) emerged as the most resistant strains. On the other hand, the most resistant strains of S. cerevisiae were CBS 1544, AD 1890 and 077.0001 (<1 log reduction) while S. cerevisiae AD 2913, 028.0404 and 028.0315 were the most sensitive (>5 log reduction). The survival curves of most of the strains exhibited an initial phase of insignificant microbial inactivation followed by a relatively fast log-linear inactivation period. The estimated 𝘋-value showed that 𝘓. 𝘮𝘰𝘯𝘰𝘤𝘺𝘵𝘰𝘨𝘦𝘯𝘦𝘴 strains exhibited higher resistance to US treatment than any other species, while other species displayed comparable resistance. The findings on strain variability resistance and inactivation kinetics following US treatment are essential for food safety and will pave the way for further research on microbial response to US stress, risk assessment and optimisation studies.