Optimization of a Microplate Assay for Generating Listeria Monocytogenes, E. Coli O157:H7, and Salmonella Biofilms and Enzymatic Recovery for Enumeration

Inactivation of Foodborne Pathogen Biofilm Cells Using a Combination Treatment with Gaseous Chlorine Dioxide and Aerosolized Sanitizers

A biofilm is a three-dimensional microbial community, which is difficult to completely control with a typical sanitizer owing to its complex structure. The aim of this study was to establish a system for the combined treatment of biofilms with 10 ppmv gaseous chlorine dioxide (ClO2) and antimicrobial agents (2% citric acid, 2% hydrogen peroxide [H2O2], and 100 ppm peracetic acid [PAA]), and to investigate the synergistic microbicidal efficacy of the combination treatments to inactivate Listeria monocytogenes, Salmonella Typhimurium, and Escherichia coli O157:H7 in biofilms. The antimicrobial agents were aerosolized using a humidifier on top of a chamber to achieve a relative humidity of 90% (within a range of ±2%). While biofilm treatment with the aerosolized antimicrobial agents for 20 min inactivated approximately 1 log CFU/cm2 (0.72-1.26 log CFU/cm2) of the pathogens and the gaseous ClO2 gas treatment for 20 min inactivated <3 log CFU/cm2 (2.19-2.77 log CFU/cm2), combination treatment with citric acid, H2O2, and PAA for 20 min achieved microbial reductions of 2.71-3.79, 4.56-5.12, and 4.45-4.67 log CFU/cm2, respectively. Our study demonstrates that foodborne pathogens in biofilms can be inactivated by combining gaseous ClO2 treatment with aerosolized antimicrobial agents. The results of this study provide baseline data for the food industry to help control foodborne pathogens in biofilms on inaccessible surfaces.

Efficacy of a Next Generation Quaternary Ammonium Chloride Sanitizer on Staphylococcus and Pseudomonas Biofilms and Practical Application in a Food Processing Environment

Foodborne pathogens are known to adhere strongly to surfaces and can form biofilms in food processing facilities; therefore, their potential to contaminate manufactured foods underscores the importance of sanitation. The objectives of this study were to (1) examine the efficacy of a new-generation sanitizer (Decon7) on Staphylococcus and Pseudomonas biofilms, (2) identify biofilm bacteria from workers’ boots in relation to previous sanitizer chemistry, (3) validate the efficacy of Decon7 on biofilm from workers’ boots from an abattoir/food processing environment, and (4) compare the sensitivity of isolated boot biofilm bacteria to new- and early (Bi-Quat)-generation QAC sanitizers. Decon7 was applied at two concentrations (5%, 10%) and was shown to be effective within 1 min of exposure against enhanced biofilms of Staphylococcus spp. and Pseudomonas spp. in 96-well microplates. Decon7 was also used to treat workers’ boots that had accumulated high levels of biofilm bacteria due to ineffective sanitization. Bacteria isolated before enzyme/sanitizer treatment were identified through 16S rRNA PCR and DNA sequencing. All treatments were carried out in triplicate and analyzed by one-way RM-ANOVA or ANOVA using the Holm–Sidak test for pairwise multiple comparisons to determine significant differences (p < 0.05). The data show a significant difference between Decon7 sanitizer treatment and untreated control groups. There was a ~4–5 log reduction in Staphylococcus spp. and Pseudomonas spp. (microplate assay) within the first 1 min of treatment and also a > 3-log reduction in the bacterial population observed in the biofilms from workers’ boots. The new next-generation QAC sanitizers are more effective than prior QAC sanitizers, and enzyme pre-treatment can facilitate biofilm sanitizer penetration on food contact surfaces. The rotation of sanitizer chemistries may prevent the selective retention of chemistry-tolerant microorganisms in processing facilities.

Advances in Foodborne Pathogen Analysis

As the world population has grown, new demands on the production of foods have been met by increased efficiencies in production, from planting and harvesting to processing, packaging and distribution to retail locations. These efficiencies enable rapid intranational and global dissemination of foods, providing longer “face time” for products on retail shelves and allowing consumers to make healthy dietary choices year-round. However, our food production capabilities have outpaced the capacity of traditional detection methods to ensure our foods are safe. Traditional methods for culture-based detection and characterization of microorganisms are time-, labor- and, in some instances, space- and infrastructure-intensive, and are therefore not compatible with current (or future) production and processing realities. New and versatile detection methods requiring fewer overall resources (time, labor, space, equipment, cost, etc.) are needed to transform the throughput and safety dimensions of the food industry. Access to new, user-friendly, and point-of-care testing technologies may help expand the use and ease of testing, allowing stakeholders to leverage the data obtained to reduce their operating risk and health risks to the public. The papers in this Special Issue on “Advances in Foodborne Pathogen Analysis” address critical issues in rapid pathogen analysis, including preanalytical sample preparation, portable and field-capable test methods, the prevalence of antibiotic resistance in zoonotic pathogens and non-bacterial pathogens, such as viruses and protozoa.

Efficacy of Commercial Sanitizers Used in Food Processing Facilities for Inactivation of Listeria Monocytogenes, E. Coli O157:H7, and Salmonella Biofilms

Bacteria entrapped in biofilms are a source of recurring problems in food processing environments. We recently developed a robust, 7-day biofilm microplate protocol for creating biofilms with strongly adherent strains of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella serovars that could be used to examine the effectiveness of various commercial sanitizers. Listeria monocytogenes 99-38, E.coli O157:H7 F4546, and Salmonella Montevideo FSIS 051 were determined from prior studies to be good biofilm formers and could be recovered and enumerated from biofilms following treatment with trypsin. Extended biofilms were generated by cycles of growth and washing daily, for 7 days, to remove planktonic cells. We examined five different sanitizers (three used at two different concentrations) for efficacy against the three pathogenic biofilms. Quaternary ammonium chloride (QAC) and chlorine-based sanitizers were the least effective, showing partial inhibition of the various biofilms within 2 h (1-2 log reduction). The best performing sanitizer across all three pathogens was a combination of modified QAC, hydrogen peroxide, and diacetin which resulted in ~6-7 log reduction, reaching levels below our limit of detection (LOD) within 1-2.5 min. All treatments were performed in triplicate replication and analyzed by one way repeated measures analysis of variance (RM-ANOVA) to determine significant differences (p < 0.05) in the response to sanitizer treatment over time. Analysis of 7-day biofilms by scanning electron microscopy (SEM) suggests the involvement of extracellular polysaccharides with Salmonella and E. coli, which may make their biofilms more impervious to sanitizers than L. monocytogenes.