No abstract

Listeria monocytogenes contaminated processing equipment and the general packing environment have been implicated in deadly foodborne listeriosis outbreaks, highlighting the significance of proper sanitization and disinfection of food contact surfaces. This study aims to comprehensively evaluate antimicrobial efficacy of commercially available, economical sanitizers at practical concentrations against L. monocytogenes biofilm formed on polystyrene surfaces under different conditions. Ozonated water 1-min treatment at 1.0, 2.0, and 4.0 ppm resulted in ∼0.9, 3.4, and 4.1 log reduction of L. monocytogenes single strain biofilm grown on polystyrene surfaces, respectively. However, its efficacy was dramatically diminished in multi-strain L. monocytogenes biofilm and was further compromised by aged biofilm and in the presence of organic matter. Quaternary ammonium compounds (QAC) at 100/400 ppm, chlorine at 100/200 ppm, chlorine dioxide at 2.5/5.0 ppm and peroxyacetic acid (PAA) at 80/160 ppm resulted in 2.4/3.6, 2.0/3.1, 2.4/3.8, and 3.6/4.8 log reduction of L. monocytogenes single strain biofilm, respectively. Antimicrobial efficacies of all tested sanitizers against 7-day-old biofilm were much lower when compared to 2-day-old biofilm, with PAA being the least influenced by the age of the biofilm. Organic matter conditioning with diluted milk or apple juice dramatically impacted the antimicrobial efficacy of all sanitizers. PAA treatment of 1 min at 160–200 ppm resulted in a 3.2–3.5 log reduction against 7-day-old biofilm in the presence of organic matter, thus showing its effectiveness in eradicating L. monocytogenes biofilm on polystyrene surface. Collectively, data highlight the importance of timely and thoroughly cleaning food contact surfaces before disinfection and provides practical information and guidance for the food industry in selecting the most effective sanitizer in their sanitizing regimes to eliminate L. monocytogenes biofilm.

The objectives of this study were to assess the microbiological quality of domiati cheese and to evaluate the capacity of Lactobacillus acidophilus La-5 and Bifidobacterium longum ATCC15707 to inhibit the growth of Staphylococcus aureus and Escherichia coli O157:H7 during manufacture and storage of domiati cheese. The results of the microbial investigation indicated poor microbiological quality of cheese samples, the microbiological parameters recorded higher values than admissible levels. Domiati cheese produced from milk artificially contaminated with S. aureus and E. coli O157:H7 was used as a model for studying the antibacterial activity of L. acidophilus La-5 and B. longum ATCC15707 against these pathogens. The results obtained in this study indicated the remarkable effect of L. acidophilus La-5 and B. longum ATCC15707 in preventing survival of S. aureus and E. coli O157:H7 during cheese storage. The inactivation rate was more pronounced with S. aureus than E. coli O157:H7 and it was dependent on probiotic strain. L. acidophilus inactivation was significantly higher (P value < 0.05) than that attained with B. longum. Survival of probiotic bacteria in domiati cheese was satisfactory. PRACTICAL APPLICATIONSThe microbial contamination of domiati cheese represents not only spoilage of the product but also constitutes a high risk to human health. The probiotic bacteria have the ability to improve the microbiological quality and safety of domiati cheese. Survival of both Lactobacillus acidophilus La-5 and Bifidobacterium longum ATCC15707 in domiati cheese was satisfactory, which indicate that the domiati cheese would be a suitable vehicle for the delivery of probiotic bacteria.

Contaminated food-contact surfaces are recognized as the primary reason for recent L. monocytogenes outbreaks in caramel apples and cantaloupes, highlighting the significance of cleaning and sanitizing food-contact surfaces to ensure microbial safety of fresh produce. This study evaluated efficacies of four commonly used chemical sanitizers at practical concentrations against L. monocytogenes biofilms on major food-contact surfaces including stainless steel, low-density polyethylene (LDPE), polyvinyl chloride (PVC), polyester (PET), and rubber. In general, efficacies against L. monocytogenes biofilms were enhanced by increasing concentrations of quaternary ammonium compound (QAC), chlorine, and chlorine dioxide, or extending treating time from 1 to 5 min. The 5-min treatments of 400 ppm QAC, 5.0 ppm chlorine dioxide, and 200 ppm chlorine reduced 3.0–3.7, 2.4–2.7, and 2.6–3.8 log10 CFU/coupon L. monocytogenes biofilms depending on surfaces. Peroxyacetic acid (PAA) at 160 and 200 ppm showed similar antimicrobial efficacies against biofilms either at 1- or 5-min contact. The 5-min treatment of 200 ppm PAA caused 4.0–4.5 log10 CFU/coupon reduction of L. monocytogenes biofilms on tested surfaces. Surface material had more impact on the efficacies of QAC and chlorine, less influence on those of PAA and chlorine dioxide, while organic matter soiling impaired sanitizer efficacies against L. monocytogenes biofilms independent of food-contact surfaces. Data from this study provide practical guidance for effective disinfection of food-contact surfaces in food processing/packing facilities.