Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2014
Publication Date: 6/6/2014
Citation: Brandl, M., Huynh, S. 2014. Effect of the surfactant Tween 80 on the detachment and dispersal of Salmonella enterica Thompson single cells and aggregates from cilantro leaves as revealed by image analysis. Applied and Environmental Microbiology. 80(16):5037-5042. DOI: 10.1128/AEM.00795-14.
Interpretive Summary: Fresh vegetables have been recurrently associated with salmonellosis outbreaks. We observed that Salmonella enterica forms large aggregates on leaf surfaces, which may affect our ability to effectively decontaminate produce. Aggregates of the pathogen were indeed observed by confocal microscopy on the surface of washed cilantro leaves and in the leaf wash suspension. Addition of the surfactant Tween 80 increased the percentage of the S. enterica cells residing as single cells in the cell population recovered in the wash suspension and enhanced the dispersal of cells from large aggregates. Therefore, Tween 80 may have the potential to improve the efficacy of sanitizers during produce processing by dispersing aggregated cells of the human pathogen into single cells and smaller aggregates, which are more sensitive to the effect of antimicrobials.
Technical Abstract: Biofilms formed by human enteric pathogens on plants are a great concern to the produce industry. Salmonella enterica has the ability to form biofilms and large aggregates on leaf surfaces, including on cilantro leaves. Aggregates that remained attached after rigorous washing of cilantro leaves and that were present free or bound to dislodged leaf tissue in the wash suspension were observed by confocal microscopy. Measurement of population sizes of S. enterica in the leaf washes by bacterial plate counts failed to show an effect of 0.05% Tween 80(Polysorbate 80)on the removal of the pathogen from cilantro leaves two and six days after inoculation. On the contrary, digital image analysis of single cells and aggregates of GFP-labeled S. enterica in cilantro leaf washes observed by fluorescence microscopy revealed that single cells represented 13.7% of the cell assemblages in leaf washes containing 0.05% Tween 80(in 10 mM potassium phosphate buffer, pH 7)versus 9.3% in those without the surfactant. Moreover, Tween 80 decreased the percentage of the total S. enterica cell population located in aggregates equal of larger than 64 cells from 9.8% to 4.4%, indicating that the surfactant promoted the dispersal of cells from large aggregates into smaller ones or single cells. Given that a considerable portion of the S. enterica population in the leaf washes without surfactant was located in large aggregates, the addition of a compound capable of effectively dispersing these assemblages would enhance the efficacy of sanitizers used in the wash water and reduce the contamination of produce with enteric pathogens.