Seminar: "Understanding Growth, Survival and Cross-Contamination of Bacteria from Stainless-Steel to Baby Spinach Leaves" - Anjama Dutta
Food Science Seminar:
"Understanding Growth, Survival and Cross-Contamination of Bacteria from Stainless-Steel to Baby Spinach Leaves"
Anjama Dutta
Ph.D. Student
Department of Food Science
Foodborne illnesses linked to fresh produce remain a significant public health concern, with leafy greens frequently implicated in outbreaks (Carstens et al., 2019). Stainless steel surfaces are widely used in the food industry and, if not properly cleaned, may be sources of pathogens such as Listeria monocytogenes (Pathirajah et al., 2022 ) and Escherichia coli O157 (Goulter-Thorsen et al., 2011). Understanding bacterial persistence and transfer under different environmental conditions is critical to managing cross-contamination risks.
Bacterial growth was quantified in three diluents (0.1% peptone, 1% PBS, and distilled water). Survival was also assessed after deposition onto stainless steel coupons held at 15% and 100% relative humidity (RH). Cross-contamination from stainless steel to real spinach leaves and synthetic spinach leaf surrogate made of polydimethylsiloxane (PDMS) was investigated to determine the effects of bacterial type, leaf type, RH, temperature, and contact time. Analysis of variance (ANOVA) was used to evaluate factor influence at 4 and 24 h post-inoculation. An additional 15% RH time-course study was performed to limit simultaneous parameter variation and better resolve time-dependent transfer, with sampling every 4 h over 24 h.
Results showed that 0.1% peptone supported the most robust bacterial growth. Both species concentrations declined significantly more rapidly at 15% RH than at 100% RH on stainless steel. RH was the most influential factor affecting cross-contamination at both 4 and 24 h post-inoculation across all transfer experiments. Leaf type and higher-order interactions involving leaf type, contact time, and RH became highly significant by 24 h, indicating that leaf properties increasingly governed transfer as time progressed. The 15% RH time-course further revealed that cross-contamination risk is not constant: transfer to real spinach remained low at early time points, spiked during an intermediate period (~4–8 h), and then dropped toward minimal/undetectable levels after extended drying (>12 h). Transfer to PDMS remained comparatively stable over the 24 h period.
These patterns support a “dynamic topography” mechanism differentiating biological and synthetic leaves. The PDMS surface represents a static snapshot of leaf topography and cannot wilt, shrivel, or change roughness, whereas real spinach at low RH undergoes loss of turgor pressure and progressive surface transformation. The real leaf remains relatively turgid and behaves similarly to the surrogate, producing low transfer from 0–4 h. From 4–8 h wilting in real leaves likely generates micro-ridges and altered contact geometry and/or changes in surface chemistry that increase bacterial availability for transfer, effects not seen in PDMS leaves. Further desiccation may deepen wrinkles and crevices or collapse tissue, physically trapping bacteria and reducing transfer after 12 h.
Cross-contamination risk is dynamic and strongly influenced by RH and time-dependent changes in leaf physical state. These findings suggest that studies using synthetic leaves at low humidity may underestimate risk by missing the transient wilting-associated transfer spike.
Selected References
Carstens, C. K., Salazar, J. K., & Darkoh, C. (2019). Multistate Outbreaks of Foodborne Illness in the United States Associated With Fresh Produce From 2010 to 2017. Frontiers in Microbiology, 10, 2667. https://doi.org/10.3389/fmicb.2019.02667
Goulter-Thorsen, R. M., Taran, E., Gentle, I. R., Gobius, K. S., & Dykes, G. A. (2011). Surface roughness of stainless steel influences attachment and detachment of Escherichia coli O157. Journal of Food Protection, 74(8), 1359–1363. https://doi.org/10.4315/0362-028X.JFP-11-006
Pathirajah, J. P., Balamurugan, S., Arvaj, L., Weiss, J., & Barbut, S. (2022). Influence of Different Stainless Steel Finishes on Biofilm Formation by Listeria monocytogenes. Journal of Food Protection, 85(11), 1584–1593. https://doi.org/10.4315/JFP-22-112