Poster O13 - Evaluating the efficacy of peracetic acid in removing dual-species biofilms formed by bacterial pathogens

Introduction: During food processing, bacterial pathogens can form biofilms on food contact surfaces which could contaminate food during processing. Biofilm attachment and detachment from the surfaces is governed by the surface topography of food contact surfaces, shear stresses, disinfectant contact time, type of disinfectant, among other factors. In this study, we investigated single- and dual- species E. coli O157:H7 and L. monocytogenes biofilm removal with peracetic acid (PAA) using a bioreactor.

Materials and

Methods: Biofilms were grown at shear stresses of 0.368 and 2.462 N/m2 on stainless steel (SS 316L), PTFE and EPDM coupons in a CDC bioreactor containing 10% TSB using E. coli O157:H7, L. monocytogenes alone or with R. insidiosa for 48 h. Coupons were retrieved from the CDC bioreactor and were plugged into the In-Line bioreactor. 160 ppm PAA was supplied to coupons in an In-line bioreactor at a flow rate of 1.2 liters/min for 1 and 4 minutes. Bacterial populations in biofilms from coupons pre- and post-PAA treatment were determined by spiral plating on selective agar media. Results from three individual replicates were analyzed to determine significant differences due to surface material and PAA treatment time. Surface topography of equipment surfaces were measured using profilometer and scanning electron microscopy.

Results, Conclusions, and Discussions:

Results: After 1-min PAA treatment, populations in single species E. coli O157:H7 biofilms were significantly reduced from SS 316L (3.77 log CFU/cm2 reduction) compared to EPDM (1.23 log CFU/cm2) surface. Similarly, after 4-minutes PAA treatment, the reductions from SS 316L (5.09 log CFU/cm2), PTFE (3.00 log CFU/cm2) and EPDM (0.81 log CFU/cm2) were significant (p < 0.05). The dual-species E. coli O157:H7 biofilms grown at a high shear stress were difficult to remove from EPDM material when treated with PAA for 1 min (p < 0.05) and 4 minutes. Single species L. monocytogenes biofilms grown at high shear stresses and treated with PAA for 1-minute exposure resulted in a significant reduction (p < 0.05) from SS 316L (2.53 log CFU/cm2) compared to EPDM (1.21 log CFU/cm2). Similar trend was observed when these biofilms were exposed to PAA for 4-minute wherein EPDM surface exhibited significantly lowest removal (1.63 log CFU/cm2) compared to PTFE (3.00 log CFU/cm2). Dual-species L. monocytogenes biofilms formed at low shear stress and treated with 1-and-4-minutes with PAA exhibited higher reductions from SS 316L compared to EPDM and PTFE. R. insidiosa populations in L. monocytogenes coenvironment biofilms formed at 0.368 N/m2 shear stress were significantly reduced from SS 316L (1.66 log CFU/cm2 reduction) compared to EPDM (0.92 log CFU/cm2 reduction) after 1-min PAA exposure.

Conclusion: Single and dual-species E. coli O157:H7 biofilms persisted in higher quantities on material with low surface roughness and high kurtosis. Surfaces with low roughness might be easier to disinfect for a dual-species L. monocytogenes contamination. In this study, EPDM was an unsuitable material compared to SS for food processing that involved high shear stresses.

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