Winter 2021

In this edition:

• Control of Campylobacter and Salmonella on meat and produce using a combination of organic acids and oxidizing reagents
• A New Method for Detection of Listeria
• Salmonella elimination from fruits intended for freeze-drying using antimicrobial dips

Control of Campylobacter and Salmonella on meat and produce using a combination of organic acids and oxidizing reagents

Nivin Nasser, Miranda Barr and Issmat I Kassem

Summary

Evaluating the impact of a selection of organic acids and oxidizing reagents on Campylobacter and Salmonella spp. in order to optimize the control of these important pathogens in different foods.

Situation

Campylobacter and Salmonella spp. are leading foodborne pathogens that can cause serious infections in consumers. These pathogens also exert a significant economic impact associated with hospitalization, product recall, and control efforts. Campylobacter infections have been linked primarily with the consumption of poultry products, while different serotypes of Salmonella can contaminate both meat and produce. Despite continuous control efforts, Campylobacter and Salmonella have remained problematic for the food industry and public health. Therefore, there is a need to devise and optimize antimicrobial interventions that can more effectively facilitate the control of pathogens in the food chain.

Response

We evaluated the effect of different concentrations of organic acids (fumarate, succinate and formate) and hydrogen peroxide on the survival of Campylobacter and Salmonella in culture and on poultry meat. We determined the growth kinetics of different Campylobacter spp. and Salmonella serotypes in the presence of the antimicrobials to determine the minimum inhibitory concentrations (MIC). We also artificially contaminated broiler chicken breasts to assess the effectiveness of the antimicrobials in reducing the contamination.

Impact

Based on the MICs and solubility of the organic acids, we were able to determine that formate was superior antimicrobial in comparison to fumarate and succinate. Growth kinetic analysis showed that 500 mM of formate was able to inhibit C. jejune, C. coli, S. Typhimurium, S. St. Paul, S. Tennessee, and S. Poona in culture. Additionally, we noted ~ 2 log reduction in CFU/ g (Campylobacter and Salmonella) on artificially contaminated chicken breasts after 15 min exposure to formate and hydrogen peroxide. Our findings highlight a relatively cheap and safe approach to effectively reduce contamination with important foodborne pathogens. Currently, we are optimizing the use of these antimicrobials to decontaminate produce.

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A New Method for Detection of Listeria

Ramaraja Ramasamy, Or Zolti, Baviththira Suganthan

Summary

A phage-based biosensing platform can serve as a rapid diagnostic tool for specific detection of Listeria monocytogenes in select food matrices.

Situation

Of the various food-borne bacterial pathogens, Listeria monocytogenes stands out due to its high mortality rate (15% U.S. and 24% worldwide). With a 94% rate of hospitalizations and 260 deaths each year in the U.S. alone from listeriosis, Listeria poses a great threat to public health. Listeria is present in a variety of food sources including dairy, meat and produce products. The organism is challenging to control because of its ability to grow even at refrigeration temperatures. At present, food pathogen screening tests are carried out in pathology labs, which use labor-intensive, time consuming, micro/molecular biology methods (e.g., PCR, ELISA, agar overlay) that typically take 24-72 hours depending on the nature of the sample. The agricultural, food and healthcare industries are interested in potent rapid diagnostic tools that are not only reliable (as the established molecular methods), but also cost less, do not require skilled experts, and can process large volumes of samples. Though some Listeria test kits are available in the market, to our knowledge, there is no Association of Analytical Collaboration International (AOAC) approved commercial food safety test kit for Listeria that could provide a result within a few hours in a point-of-service setting.

Response

We have developed and demonstrated a rapid testing method based on electrochemical biosensors for diagnosis of Listeria in liquid food samples that enables a positive detection within 20-30 minutes after sample preparation. The current development includes a new method for electrochemical detection of the pathogenic strains of Listeria monocytogenes in buffer solutions. The approach uses a bacteriophage bio-receptor that provides the necessary selectivity towards Listeria, with detection limits in the range of 100-1000 cells/mL, which is equal or better than conventional molecular methods. This new method is yet to be robustly tested in real-world conditions using contaminated food with multiple contaminants. More optimization tests will be conducted to ensure that key diagnostic parameters such as sensitivity, selectivity and detection limits are improved to enable minimal false positive and false negative detection.

Impact

Presently, food pathogen screening tests are carried out in pathology labs, which use labor-intensive, time consuming, micro/molecular biology methods (e.g., PCR, ELISA, agar overlay) that typically take 24-72 hours depending on the nature of the sample. Our rapid detection method offers additional advantages that some existing technologies do not offer: (1) quantitative detection (severity of contamination) as opposed to qualitative identification (e.g., only positive or negative answer); (2) detect only live Listeria cells as opposed to some DNA based tests that produce false positive results as they could not distinguish between live and dead Listeria cells. Providing a shorter time to results enables food processors and handlers to adopt in-house testing practices that will enable faster processing, minimize cost of production, and minimize safety recalls.
 

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Salmonella elimination from fruits intended for freeze-drying using antimicrobial dips

Summary

Freeze-drying is a commonly used method to increase both the shelf-life and the profitability of pre-cut fruits. The process is employed to rapidly reduce the water content of foods. The efficacy of a pre-treatment process to reduce the risk of foodborne pathogen contamination in freeze-dried fruits was evaluated.

Situation 

Fresh fruit and vegetables can be contaminated with foodborne pathogens such as Salmonella enterica, resulting in illnesses among consumers. Recalls of fresh fruit due to foodborne pathogen contamination results in negative public health outcomes as well as fiscal losses. Washing fruit with sanitizers such as chlorine might not be efficacious in presence of high organic loads. Processes such as freeze-drying to rapidly eliminate moisture from foods renders them shelf-stable but not free of contaminating bacterial pathogens. Several serotypes of Salmonella have marked tolerance to low moisture environments. Salmonella has been found on low moisture food matrices such as peanut butter and squid chips. Hence an antimicrobial dip was evaluated as a pre-treatment dip of fruits intended for freeze-drying. Further, the survival of Salmonella in fruits undergoing freeze-drying was also studied.

Response

Mango and pineapples were comminuted into 10 g chunks and slices and seeded with a cocktail of three Salmonella serotypes. The contaminated fruit chunks and slices were treated with two different concentrations (50 and 100 mM) pelargonic acid emulsions by dipping the contaminated fruit. After treatment, the fruit was held at conditions for temperature abuse that would facilitate the growth of bacteria for a duration of 18h. The fruit slices were then freeze-dried and evaluated for surviving Salmonella population.

Impact

The results of the study indicated that Salmonella present on fruit can survive the freeze-drying process necessitating the exploration of intervention measures. The freeze-drying process, fruit cut and concentration of antimicrobial used significantly affected the survival of Salmonella. Both 50- and 100-mM PA SAP treatments reduced the Salmonella cocktail by 2.20 log CFU/g. A reduction of 3.74 log CFU/g were observed in pineapple slices after optimizing the freeze-drying process.

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