Comparison of sampling procedures for recovery of Listeria monocytogenes from stainless steel food contact surfaces

Impact of different hand-drying methods on surrounding environment: aerosolization of virus and bacteria, and transfer to surfaces

BACKGROUND

In recent years, hand drying has been highlighted as a key step in appropriate hand hygiene, as moisture on hands can increase the transfer of micro-organisms from hands to surfaces and vice versa.

AIM

To understand bacterial and viral aerosolization following hand drying, and study the transfer of micro-organisms from hands to surfaces after drying using different methods.

METHODS

Groups of five volunteers had their hands pre-washed with soap, rinsed and dried, then inoculated with a concentrated mixture of Pseudomonas fluorescens and MS2 bacteriophage. Volunteers entered an empty washroom, one at a time, and rinsed their hands with water or washed their hands with soap prior to drying with a jet dryer or paper towels. Each volunteer applied one hand successively to various surfaces, while their other hand was sampled using the glove juice method. Both residual bacteria and viruses were quantified from the washroom air, surface swabs and hand samples.

FINDINGS

P. fluorescens and MS2 bacteriophages were rarely aerosolized while drying hands for any of the drying methods studied. Results also showed limited, and similar, transfer of both micro-organisms studied on to surfaces for all drying methods.

CONCLUSION

The use of jet dryers or paper towels produces low levels of aerosolization when drying hands in a washroom. Similarly, all drying methods result in low transfer to surfaces. While the coronavirus disease 2019 pandemic raised concerns regarding public washrooms, this study shows that all methods tested are hygienic solutions for dry washed hands.

Verification of a Rapid Analytical Method for the Qualitative Detection of Listeria spp. and Listeria monocytogenes by a Real-Time PCR Assay according to EN UNI ISO 16140-3:2021

Microbial contamination and foodborne infections are a significant global public health concern. For this reason, the detection, monitoring, and characterization of pathogens represent a significant challenge in quality control settings. Standard approaches, such as culture methods and biochemical tests, are known to be very time-consuming and intensive. Conversely, molecular technologies based on the genomic identification of bacteria are quick and low-cost. Listeria monocytogenes is an opportunistic pathogen and a major concern especially in food industries. It is important to understand and implement multiple quality control measures to control Listeria infection risk and prevent the contamination of products. Standardized detection and confirmation tests such as the API Listeria test, MALDI-TOF MS, and PCR analysis are available. The aim of our work is to provide a specific molecular method, designed according to the EN UNI ISO 16140-3:2021, for the specific detection, monitoring, and characterization of Listeria spp. and Listeria monocytogenes contamination. The verification of this new rapid approach by real-time PCR (qPCR) overcomes the limitations of culture-based techniques, meeting all the verification criteria required by ISO guidelines, including implementation and item confirmation. This system offers a powerful approach to the real-time assessment of food safety, useful for industry self-monitoring and regulatory inspection.

Temperature, Time, and Type, Oh My! Key Environmental Factors Impacting the Recovery of Salmonella Typhimurium, Listeria monocytogenes, and Tulane Virus from Surfaces

ABSTRACT

Environmental monitoring (EM) programs are designed to detect the presence of pathogens in food manufacturing environments, with the goal of preventing microbial contamination of food. Nevertheless, limited knowledge exists regarding the influence of environmental conditions on microbial recovery during EM. This study uses a commercially available polyurethane foam EM tool to determine the influence of environmental factors on the recovery of foodborne pathogens. The specific objectives of this study were to determine if environmental conditions and surface composition impact the recovery of sought-after microorganisms found in food processing environments. These data are compared across (i) microorganism type, (ii) surface type, (iii) environmental temperature and relative humidity (RH), and (iv) exposure time. Two bacteria (Listeria monocytogenes and Salmonella Typhimurium) and one human norovirus surrogate (Tulane virus) were inoculated onto three nonporous surfaces (polypropylene, stainless steel, and neoprene). Surfaces were held in an environmental chamber for 24 or 72 h at 30°C with 30% RH, 6°C with 85% RH, and 30°C with 85% RH. Data indicate that microbial recovery from environmental surfaces significantly (P ≤ 0.05) varies by microorganism type, environmental conditions, and exposure time. For instance, all microorganisms were significantly different from each other, with the greatest mean log reduction being Tulane virus and the lesser reduction being L. monocytogenes at 4.94 ± 1.75 log PFU per surface and 2.54 ± 0.91 log CFU per surface, respectively. Overall, these data can be used to improve the effectiveness of EM programs and underscores the need to better comprehend how EM test results are impacted by food manufacturing environmental conditions.

HIGHLIGHTS

Novel Approaches to Environmental Monitoring and Control of Listeria monocytogenes in Food Production Facilities

Listeria monocytogenes is a serious public health hazard responsible for the foodborne illness listeriosis. L. monocytogenes is ubiquitous in nature and can become established in food production facilities, resulting in the contamination of a variety of food products, especially ready-to-eat foods. Effective and risk-based environmental monitoring programs and control strategies are essential to eliminate L. monocytogenes in food production environments. Key elements of the environmental monitoring program include (i) identifying the sources and prevalence of L. monocytogenes in the production environment, (ii) verifying the effectiveness of control measures to eliminate L. monocytogenes, and (iii) identifying the areas and activities to improve control. The design and implementation of the environmental monitoring program are complex, and several different approaches have emerged for sampling and detecting Listeria monocytogenes in food facilities. Traditional detection methods involve culture methods, followed by confirmation methods based on phenotypic, biochemical, and immunological characterization. These methods are laborious and time-consuming as they require at least 2 to 3 days to obtain results. Consequently, several novel detection approaches are gaining importance due to their rapidness, sensitivity, specificity, and high throughput. This paper comprehensively reviews environmental monitoring programs and novel approaches for detection based on molecular methods, immunological methods, biosensors, spectroscopic methods, microfluidic systems, and phage-based methods. Consumers have now become more interested in buying food products that are minimally processed, free of additives, shelf-stable, and have a better nutritional and sensory value. As a result, several novel control strategies have received much attention for their less adverse impact on the organoleptic properties of food and improved consumer acceptability. This paper reviews recent developments in control strategies by categorizing them into thermal, non-thermal, biocontrol, natural, and chemical methods, emphasizing the hurdle concept that involves a combination of different strategies to show synergistic impact to control L. monocytogenes in food production environments.

Development and Evaluation of a Paper-Based Microfluidic Device for Detection of Listeria monocytogenes on Food Contact and Non-Food Contact Surfaces

Listeria monocytogenes is the third most deadly foodborne pathogen in the United States. The bacterium is found in soil and water, contaminating raw food products and the processing environment, where it can persist for an extended period. Currently, testing of food contact and non-food contact surfaces is performed using an array of sampling devices and endpoint technologies, offering various levels of sensitivity, cost, user skill, and time to detection. Paper-based microfluidic devices (µPADs) are a rapid detection platform amenable to low-cost, user-friendly, and portable diagnostics. In this study, we developed and evaluated a µPAD platform specific for the colorimetric detection of the Listeria genus following recovery from food contact and non-food contact surfaces. For detection, four colorimetric substrates specific for the detection of β-glucosidase, two broths selective for the detection of Listeria spp., and a nonselective broth were evaluated to facilitate detection of Listeria spp. The limit of detection and time to detection were determined by using pure bacterial cultures. After 8 h enrichment, L. monocytogenes (10² Colony Forming Units (CFU)/coupon) was detected on every surface. After 18 h enrichment, L. monocytogenes (10² CFU/coupon) was detected on all surfaces with all swabbing devices. This study demonstrated the ability of the µPAD-based method to detect potentially stressed cells at low levels of environmental contamination.

European survey and evaluation of sampling methods recommended by the standard EN ISO 18593 for the detection of Listeria monocytogenes and Pseudomonas fluorescens on industrial surfaces

The ready-to-eat products can be contaminated during processing by pathogen or spoilage bacteria, which persist in the industrial environment. Some bacterial species are able to form biofilms which protect them from environmental conditions. To check the bacterial contamination of the surfaces in the food industries, the professionals must regularly use surface sampling methods to detect the pathogen such as Listeria monocytogenes or the spoilage such as Pseudomonas fluorescens. In 2010, we designed and carried out a European survey to collect surface sampling information to detect or enumerate L. monocytogenes in food processing plants. A total of 137 questionnaires from 14 European Union Member States were returned. The outcome of this survey showed that the professionals preferred friction sampling methods with gauze pad, swab and sponges versus contact sampling methods. After this survey, we compared the effectiveness of these three friction sampling methods and the contact plates, as recommended in the standard EN ISO 18593 that was revised in 2018, on the recovery of L. monocytogenes and of P. fluorescens in mono-specie biofilms. This study showed no significant difference between the effectiveness of the four sampling methods to detach the viable and culturable bacterial population of theses mono-specie biofilms.

Improving the aseptic transfer procedures in hospital pharmacies part A: methods for the determination of the surface bioburden on ampoules and vials

OBJECTIVES

To develop methods for surface bioburden determination of ampoules and vials to be used in the validation of the disinfection procedures and in routine monitoring of ampoules and vials.

METHODS

The surface bioburdens of ampoules and vials are determined before and after disinfection by contact plates and total immersion.

RESULTS

The mean surface bioburdens of non-disinfected ampoules and vials taken straight from the original boxes are 2.4 and 5.01 cfu (total immersion; n = 20), and 0.97 and 0.94 cfu (contact plates; n = 60). The mean surface bioburdens of ampules and vials after disinfection by wiping are 1.15 and 7.50 cfu (total immersion; n = 20), and 0.12 and 0.10 cfu (contact plates; n = 60). The high number of cfu on vials (total immersion) indicate hidden cfu around the neck not removable by wiping and not detected by contact plates. Total immersion needs special laboratory facilities and is expensive (about €50 a sample). Therefore, it is less appropriate for use in routine monitoring. However, because of the high recovery, it is the method of choice for the validation of the disinfection procedure. Surface bioburden determination by contact plates is relatively simple. Non-flat surfaces cannot be reached, but the recovery from the touched flat part of the surface is high (around 50%). The recovery from swabs is low (around 10%). Another disadvantage of swabs is the laboratory work after sampling. We therefore advise contact plates for routine monitoring. To get a reliable value of the mean surface bioburden at least 30 samples need to be examined.

CONCLUSION

Total immersion is the method of choice for the determination of the effectiveness of a disinfection procedure for ampoules and vials. Contact plate is the method of choice for routine monitoring of the surfaces of ampoules and vials.

Application of Recombinase Polymerase Amplification with Lateral Flow for a Naked-Eye Detection of Listeria monocytogenes on Food Processing Surfaces

The continuous contamination of foods with L. monocytogenes, highlights the need for additional controls in the food industry. The verification of food processing plants is key to avoid cross-contaminations, and to assure the safety of the food products. In this study, a new methodology for the detection of L. monocytogenes on food contact surfaces was developed and evaluated. It combines Recombinase Polymerase Amplification (RPA) with the lateral flow (LF) naked-eye detection. Different approaches for the recovery of the bacteria from the surface, the enrichment step and downstream analysis by RPA-LF were tested and optimized. The results were compared with a standard culture-based technique and qPCR analysis. Sampling procedure with sponges was more efficient for the recovery of the bacteria than a regular swab. A 24 h enrichment in ONE broth was needed for the most sensitive detection of the pathogen. By RPA-LF, it was possible to detect 1.1 pg/µL of pure L. monocytogenes DNA, and the complete methodology reached a LoD₅₀ of 4.2 CFU/cm² and LoD₉₅ of 18.2 CFU/cm². These results are comparable with the culture-based methodology and qPCR. The developed approach allows for a next-day detection without complex equipment and a naked-eye visualization of the results.

Use of RODAC plates to measure containment of Mycobacterium tuberculosis in a Class IIB biosafety cabinet during routine operations

OBJECTIVE/BACKGROUND

Guidelines for the manipulation of Mycobacterium tuberculosis (MTB) cultures require a Biosafety Level 3 (BSL-3) infrastructure and accompanying code of conduct. In this study, we aimed to validate and apply detection methods for viable mycobacteria from surfaces in a BSL-3 MTB laboratory.

METHODS

We evaluated phenotypic (Replicate Organism Detection and Counting [RODAC] plates) and molecular (propidium monoazide [PMA]-based polymerase chain reaction [PCR]) approaches for the detection of viable mycobacteria, as well as the effect of 70% ethanol applied for 5min for disinfection against mycobacteria. For validation of the method, recovery of serial dilutions of Mycobacterium bovis bacillus Calmette-Guérin from glass slides was measured. Subsequently, we stamped surfaces in and around the biosafety cabinet (BSC) after different technicians had manipulated high bacterial load suspensions for routine drug-susceptibility testing in a Class II BSC.

RESULTS

RODAC stamping could detect as few as three bacteria on slides stamped either 5min or 60min after inoculation. PMA-based PCR, tested in parallel, did not pass validation. Mycobacteria were still detected after 5-min disinfection with ethanol 70%. In the BSL-3, from 201 RODAC-stamped surfaces, MTB was detected in four: three inside a BSC-on a tube cap and on an operator's gloves-and one outside, on an operator's gown.

CONCLUSION

RODAC plates detect mycobacteria at low numbers of microorganisms. In addition, this method allowed us to show that 70% ethanol does not reliably kill mycobacteria when applied for 5min to a dried surface, and that MTB bacilli may arrive outside a Class II BSC during routine practice, although the route could not be documented.

Occurrence of Listeria monocytogenes in Ready-to-Eat Meat Products and Meat Processing Plants in Spain

The aim of this work was to study the occurrence of Listeria monocytogenes in several types of ready-to-eat (RTE) meat products and in the environment of meat processing plants. A total of 129 samples of RTE meat products and 110 samples from work surfaces and equipment were analyzed. L. monocytogenes was detected in 6 out of 35 cooked products (17.14%), 21 out of 57 raw-cured products (36.84%), and 9 out of 37 dry-cured, salted products (24.32%). The number of sample units that exceeded the food safety limit of 100 cfu/g decreased from the manufacture date to half shelf life, and then it was further reduced at the end of shelf life. L. monocytogenes was detected in 25 out of 110 (22.72%) food contact surfaces. The number of positive and negative results from both food and environmental samples were cross-tabulated and the calculated Cohen's kappa coefficient (κ) was 0.3233, indicating a fair agreement in terms of Listeria contamination. L.monocytogenes was recovered after cleaning and disinfection procedures in four plants, highlighting the importance of thorough cleaning and disinfection.

Listeria monocytogenes-carrying consortia in food industry. Composition, subtyping and numerical characterisation of mono-species biofilm dynamics on stainless steel

In order to find out how real Listeria monocytogenes-carrying biofilms are in industrial settings, a total of 270 environmental samples belonging to work surfaces from fish (n = 123), meat (n = 75) and dairy industries (n = 72) were analysed in order to detect L. monocytogenes. 12 samples were positive for L. monocytogenes and a total of 18 different species were identified as accompanying microbiota in fish and meat industry. No L. monocytogenes was found in samples from dairy industry. Molecular characterisation combining results of AscI and ApaI macrorestriction PFGE assays yielded 7 different subtypes of L. monocytogenes sharing in 71.43% of cases the same serogroup (1/2a-3a). Results from dynamic numerical characterisation between L. monocytogenes monospecies biofilms on stainless steel (SS) using MATLAB-based tool BIOFILMDIVER demonstrated that except in isolate A1, in which a significant increase in the percentage of covered area (CA), average diffusion distance (ADD) and maximum diffusion distance (MDD) was observed after 120 h of culture, no significant differences were observed in the dynamics of the rest of the L. monocytogenes isolates. Quantitative dual-species biofilm association experiments performed on SS indicated that L. monocytogenes cell counts presented lower values in mixed-species cultures with certain species at 24 and 48 h compared with mono-species culture. However, they remained unaltered after 72 h except when co-cultured with Serratia fonticola which presented differences in all sampling times and was also the dominant species within the dual-species biofilm. When considering frequency of appearance of accompanying species, an ecological distribution was demonstrated as Escherichia coli appeared to be the most abundant in fish industry and Carnobacterium spp. in meat industry.

Improved recovery of Listeria monocytogenes from stainless steel and polytetrafluoroethylene surfaces using air/water ablation

AIMS

To develop a gentle ablation technique to recover Listeria monocytogenes biofilms from stainless steel (SS) and polytetrafluoroethylene (PTFE) surfaces by using compressed air and water injection.

METHODS AND RESULTS

Biofilms were grown for 4, 24 and 48 h or 7 days and a compressed air and water flow at 2, 3 and 4 bars was applied for cell removal. Collected cells were quantified for total/dead by staining with SYTO 9/PI double staining and cultivable populations were determined by plating onto brain heart infusion (BHI) agar, while coupon surfaces also were stained with DAPI to quantify in situ the remaining cells. The recovery efficiency was compared to that of conventional swabbing. Results showed that the air/water ablation is able to collect up to 98·6% of cells from SS surfaces while swabbing only recovered 11·2% of biofilm. Moreover, air/water ablation recovered 99·9% of cells from PTFE surfaces.

CONCLUSIONS

The high recovery rate achieved by this technique, along with the fact that cells were able to retain membrane integrity and cultivability, indicate that this device is suitable for the gentle recovery of viable L. monocytogenes biofilm cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work presents a highly efficient technique to remove, collect and quantify L. monocytogenes from surfaces commonly used in the food industry, which can thus serve as an important aid in verifying cleaning and sanitation as well as in reducing the likelihood of cross-contamination events.

Development of a fluorescent enzyme-linked DNA aptamer-magnetic bead sandwich assay and portable fluorometer for sensitive and rapid listeria detection

A fluorescent DNA aptamer-magnetic bead sandwich assay was developed to detect listeriolysin O (LLO) protein from pathogenic Listeria bacteria using a peroxidase-linked system, Amplex Ultra Red (AUR; derivatized resazurin) substrate, and a custom-designed handheld fluorometer. The assay is highly sensitive with demonstrated limits of detection (LODs) in the range of 4 to 61 L. monocytogenes cells or the equivalent LLO produced by 4 to 61 cells on average in separate titration trials. Total assay processing and analysis time was approximately 30 mins. The assay has demonstrated the ability to detect 6 species of Listeria as desired by the USDA's Food Safety Inspection Service (FSIS). The portable system was designed to be used primarily with surface swab samples from fomites, but it can also be used to assess enrichment cultures. The minimal time to detect a positive enrichment culture in our hands from an initial 10 cell inoculum in 200 ml of broth has been 8 h post-incubation at 37 °C in shaker flask cultures. An optional automated magnetic bead assay processing and wash device capable of simultaneously processing 6 samples with low and consistent fluorescence background for higher volume central laboratories is also described.

Evaluation of three swabbing devices for detection of Listeria monocytogenes on different types of food contact surfaces

Listeria monocytogenes can adhere to different types of food contact surfaces within a food processing environment. Therefore, environmental sampling devices should be capable of detecting unacceptable contamination. In this study, a sponge-stick, foam spatula and an environmental swab were evaluated on their ability to detect low concentrations of L. monocytogenes on different types of food contact surfaces. A cocktail of four L. monocytogenes serotypes was inoculated with a concentration of 100 CFU/250 cm2 onto stainless steel (SS), high density polyethylene (HDPE) and rubber surfaces in a 250 cm2 area. Immediately after inoculation and after 1 h exposure, the surfaces were swabbed with the different swabbing devices. The results of the study show only minor differences in the ability of the swabbing devices to detect L. monocytogenes. All devices were capable to detect the contamination immediately after inoculation. However, when the surfaces were allowed to air-dry for 1 h, L. monocytogenes was undetected in 11.1% of the samples (n = 27) with the sponge stick, in 7.4% of the samples (n = 27) with the foam spatula and in 3.7% of the samples (n = 27) with the environmental swab, especially on SS surfaces. The detection ability of the different devices for L. monocytogenes can be concluded to be rather high on different types of food contact surfaces.