Science-based guidance was used at eight small and very small state and federally inspected ready-to-eat meat and poultry processors across Michigan. Data were collected to determine the current level of sanitary control methods used for reducing Listeria in the processing environment and compared interactions with the facility microbial results. A checklist was created to assess the current recommended sanitary control methods from the U.S. Department of Agriculture, U.S. Food and Drug Administration, and the Michigan Department of Agriculture and Rural Development. The checklist, composed of 178 items divided into 10 general content domains, was used to assess which of the recommended controls were being used in the facilities to prevent postlethality contamination of ready-to-eat products. Effectiveness of preoperational and operational sanitation was assessed through sampling 12 nonfood contact surfaces by using an ATP reader and amplified nucleic single temperature reaction test for Listeria spp., including L. monocytogenes, at each facility. In total, 288 samples were taken collectively from the eight facilities (96 ATP, 96 preoperational Listeria spp., and 96 operational Listeria spp.). Microbial outcomes did not differ (P > 0.05) based on the overall number of recommended sanitary control methods used and the type of facility inspection. There was a greater content domain compliance overall in operational sanitation (P = 0.0005), sanitation (P = 0.0030), facility (P = 0.0397), and personal hygiene (P = 0.0033) than for segregation procedures regardless of the regulating body. Findings suggest that regardless of the regulating body, the quality of sanitary control measures used is more impactful for microbial control than simply the quantity implemented. Pathogen control may be obtained without implementing all of the sanitary control methods within the guidance documents.
Extent of guidance used was not statistically associated with microbial results.
Microbial results were not statistically associated with regulatory agency oversight.
Various methods were used to implement sanitation and prevent cross-contamination.
Controls are needed for areas of foot traffic and drains.
Scheduled cleaning is needed in outlying areas.
Inadequate sanitary controls are well known to result in cross-contamination of ready-to-eat (RTE) meat and poultry products with the foodborne pathogen Listeria monocytogenes. Using effective, robust methods to control Listeria in the environment is critical for a processor to produce a safe and wholesome product. L. monocytogenes is the agent for the foodborne illness listeriosis (7, 8, 31). The incidents of listeriosis in the United States are relatively low, but potentially fatal (3, 37), particularly to susceptible populations such as the immunocompromised, pregnant women, newborns, and the elderly (6, 8, 37). According to the Centers for Disease Control and Prevention, listeriosis is the third leading cause of death from foodborne illness and accounts for an estimated 1,600 cases of illness and 260 fatalities per year (7).
L. monocytogenes is a ubiquitous facultative gram-positive bacterium that inhabits soil, vegetation, water, and animal feces (3, 6, 37, 40). This bacterium is capable of surviving and growing in various environments for extended time frames under aerobic and anaerobic conditions (3, 8, 37, 40). It is particularly resilient and has the ability to survive a wide pH range (4.0 to 9.5) and in salty (up to 10% NaCl) environments (8, 15); at low and high (<1 to 45°C) temperatures (3); and in low moisture conditions (water activity >0.92) (34). L. monocytogenes also possess the ability to grow at refrigerated temperatures (4 to 10°C) (3, 41) and to survive at freezing temperatures (3).
The ubiquitous nature and resilience of Listeria allow it to remain in food processing facilities and multiply for many years. These characteristics create challenges, particularly for the RTE industry, whose products are consumed without further intervention, such as cooking (6, 9, 18, 24, 28, 29). Persistence in the food processing environment is the major source of postprocessing contamination (6, 9, 13, 18, 24, 29, 37) and has been reported in an extensive array of RTE foods. Listeria contamination has been found in raw fruits and vegetables, hard and soft cheeses, yogurt, milk, ice cream, unpasteurized milk and cheese, fish (crustaceans, shellfish, and mollusks), and fresh and frozen meats as well as RTE meats, such as deli meats (6, 8, 36, 37).
The resilience of Listeria supports that its elimination is unrealistic (18, 29); however, robust sanitation practices and environmental testing have been shown to be the most effective controls to prevent postprocessing product contamination (10, 12, 13, 16–18, 22–24, 29). The U.S. Department of Agriculture (USDA), Food Safety Inspection Service (FSIS) and U.S. Food and Drug Administration (FDA), Center for Food Safety and Applied Nutrition have provided expansive guidance on how to control L. monocytogenes in food processing facilities (34, 38). The guidance includes sanitation methods, testing practices, and large-scale segregation, such as completely separating raw and RTE equipment, processing rooms, and personnel. The FDA and FSIS have also implemented regulatory enforcement requiring facilities to use control measures and environmental testing via the Food Safety Modernization Act and 9 CFR part 430, the Listeria Rule, in an effort to prevent product adulteration (32, 39). Processors in Michigan that are not inspected by the FSIS or the FDA are subject to state regulations provided within the 2009 Michigan Modified Food Code and the Michigan Food Law, both enforced by the Michigan Department of Agriculture and Rural Development (MDARD) (19, 20). Currently, MDARD does not use regularly scheduled pathogen testing as a method to assess sanitary practices specific to controlling environmental Listeria in small and very small RTE facilities. Facilities are encouraged to conduct their own environmental tests because facility testing is not required (19–21).
Large processing operations often have the capital to execute many of the guidance's best sanitation practices, such as outsourcing sanitation, accessing the latest testing technology, consulting with technical food safety advisors, obtaining new equipment, operating under extensive equipment maintenance programs, and having large estates capable of physical separation of raw and RTE processes (5). By contrast, the regulatory guidance can present challenges to small and very small RTE processors with structural and financial limitations that can result in minimal implementation of current control measures as a result of limited specialized resources (33). In addition, many small and very small processors are not federally regulated, resulting in reduced verifications, such as testing. There are numerous studies detailing guidance on how to control Listeria in food processing plants; however, there is little research specific to small and very small RTE meat and poultry processors on the extent of sanitation practices necessary to control L. monocytogenes that aligns with their current abilities. This study aimed to compare current sanitary practices and use rapid method in-plant microbial testing to prevent postlethality cross-contamination in small and very small RTE facilities. The objective of this study was to determine the extent and effectiveness of sanitary control methods used by small and very small RTE processors in Michigan. It is hypothesized that environmental Listeria can be controlled without implementing all of the recommended methods within regulatory guidance documents. Findings will be used to provide recommendations to effectively prevent postlethality contamination in RTE products.
MATERIALS AND METHODS
Facilities eligible for the study included those operating within Michigan that are classified as a small or very small meat or poultry processor and subjected to the regulatory oversight of the FSIS, FDA, and/or MDARD and make RTE meat or poultry products. For the purposes of this study, a small or very small processor is defined as one that meets the USDA size classification for either small or very small. The USDA classifies facilities with 10 or more employees, but fewer than 500, as small, and facilities with fewer than 10 employees or annual sales of less than $2.5 million as very small (35). The study objective was communicated to small and very small processors throughout Michigan by using various outlets, such as processor meetings and e-mail communication. Selection to participate in the study was conducted by accepting the first eight Michigan facilities to volunteer for the study that met the aforementioned requirements. Participants were not provided testing locations or checklist information before the start of testing within their facility. The assessment included collecting a list of all the products produced at each facility.
Development of the sanitation checklist
Guidance on sanitary procedures to control L. monocytogenes in food processing environments provided by USDA-FSIS; FDA, Center for Food Safety and Applied Nutrition; and MDARD (21, 34, 38) were used to inform the creation of a facility sanitation checklist tool (26). All three guidance documents detailed expansive explanations of recommendations and divided the focus areas slightly differently. To standardize the checklist, the guidance was detailed in a succinct manner and divided into 10 broad content domains: pest control, facility, sanitation, operational sanitation, segregation, cold chain management, testing, retail, good manufacturing practices (GMP)–personal hygiene, and raw materials–receiving. All of the guidance detailed a multitude of different types of control measures, such as product formulations and other nonsanitation methods. For the purposes of this study, only guidance related to sanitation methods for controlling postlethality cross-contamination was incorporated into the checklist. Products produced by the facility and previous test results from the applicable regulating body were also included. The checklist included 178 items across 10 broad content domains.
Initially, the guidance provided by MDARD was compiled from the “Specialized Meat Processing at Retail Food Establishment Variance” (21). This guidance included the following: GMP for buildings and facilities, equipment and utensils, personnel, production and process controls, purchasing meat, operational sanitation standard operating procedures, and postcook pathogen control.
The checklist was further expanded by including controls recommended by FSIS from the “FSIS Compliance Guideline: Controlling Listeria monocytogenes in Post-lethality Exposed Ready-to-Eat Meat and Poultry Products” (34). Sanitary controls for preoperational sanitation procedures, operational sanitation, temperature, equipment design, foot traffic, employee hygiene, and cross-contamination were included into the checklist under the most relevant content domain.
Lastly, guidance provided in the FDA document, “Control of Listeria monocytogenes in Ready-to-Eat Foods: Guidance for Industry Draft Guidance,” was included (38). Controls for personnel, plant and grounds, maintenance equipment, sanitation, raw materials and ingredients, storage practices and time-temperature controls, and environmental monitoring to verify control of Listeria spp. or L. monocytogenes were incorporated into the checklist.
The compiled guidance was put into a succinct binary response choice of “yes” or “no” items with the option to select “not applicable” (NA) if the question did not apply to the facility being assessed. The checklist was completed through joint consensus of the first two authors of this article, who have extensive industry operational experience and auditing certifications through a combination of observations during processing and questioning the facility staff. Results were reported as follows: “yes,” following the guidance; “no,” not following the guidance; or “NA” if the guidance was not applicable for each question.
Sampling site and zone classification
Microbial sampling zones and site locations were chosen according to Simmons and Wiedmann (27). Sampling zones 2, 3, and 4 were selected for this study. Zone 2 is defined as nonfood contact, but closely next to food contact; zone 3 is nonfood contact in areas where food is processed, but not immediately adjacent to food contact surfaces; and zone 4 is nonfood contact in areas where food is not exposed (27). The ability for Listeria to surface during production from cracks and crevices known as niches highlights the importance of monitoring indicator sites (18). Indicator sites are nonfood contact surfaces exposed during operations that have the potential to harbor the pathogen that can then be transferred to food contact surfaces during production (18). The intent of this study was to evaluate the level of sanitation the facility retained by focusing on niches within indicator sites to obtain a more comprehensive measure of overall control and assess how far out the controls were effective by sampling throughout zones 2, 3, and 4. Specific sampling sites were chosen based on the ranking of Simmons and Wiedmann (27) that were deemed the most important for zones 2, 3, and 4. Simmons and Wiedmann (27) provide a numerical ranking for each of the respective zones: 1 as the least important location to 5 as the most important location. In this study, a total of 12 locations, four sites each from zones 2, 3, and 4, were sampled at every facility. The top four locations from each zone that were depicted by their numerical ranking were selected to capture the areas deemed most important for the respective zone. Zone 2 sites included conveyor systems, framework, and nonfood contact areas of food contact equipment; racks that are used for postlethality-exposed finished product; and maintenance tools. In the event one or more of the top four areas selected were not applicable, the two subsequent locations in order of importance were selected as an alternative. Alternative zone 2 sites selected were freezers and control switch–human-machine interface screens on equipment close to food contact surfaces. Zone 3 sites included drains, floor mats, floors, and carts. Zone 3 alternative sampling locations selected included a floor-wall junction and in-floor weighing equipment. Zone 4 included soap dispensers, break room or locker room area floors, loading dock doors, and windows. Limited zone 4 locations resulted in only one alternative location of electrical outlet covers to be selected.
Verification of clean surfaces
The AccuPoint advanced ATP reader (Neogen Corp., Lansing, MI) was used as a rapid method swab for organic material as an indicator of sanitation effectiveness (1). Use of ATP readers is a common practice within the food industry and is most widely used on zones 1 and 2. Extensive meat and poultry industry observation and experience confirm the use of ATP readers in zones 3 and 4 as a means to verify sanitation in outlying areas. Because of the mobility of L. monocytogenes, pathogen transfer from outlying areas to the production room is an important consideration for assessing sanitation practices used to control the organism within the environment (3, 13, 16, 18, 24, 29, 32, 38). In efforts to assess sanitation practices in their entirety, this study includes the use of ATP readers in zones 2, 3, and 4 to obtain facility-wide sanitation data rather than restricting the assessment solely to the production room. Swabbing followed AOAC International (AOAC) Method 091601, consisting of a collection area (10.16 by 10.16 cm) per sampling site in each zone, with the sample placed into the reader immediately after swabbing (1). When possible, all samples were collected from niches (e.g., cracks, crevices, hollow parts, wheel covers), because these areas are known to harbor organisms that can surface during production (18). In total, 12 ATP swab samples (4 per zone) per facility were taken to monitor cleaning effectiveness after preoperational sanitation before the start of production. Preoperational sanitation is defined as the cleaning and/or sanitizing activities conducted before the start of production. ATP readers are well known to reflect an amplified relative light unit (RLU) level in the presence of common sanitizers used by the food industry (1, 11). In efforts to avoid this interference, ATP readings were taken after cleaning activities (e.g., washing, scrubbing) were complete, but before the application of sanitizing agents or after sanitizing agents were given ample time to dry. Surfaces were determined to be passing, marginal, or failing by using previously determined thresholds provided by the manufacturer of the ATP reader. RLU readings of <150 were considered passing, readings between 150 and 299 RLUs were marginal, and RLU readings ≥300 were considered failing.
Detection of Listeria spp
An amplified nucleic single temperature reaction (ANSR) Listeria Right Now (Neogen Corp.) test was used to determine sanitation effectiveness for eliminating Listeria spp., including L. monocytogenes, from the processing environment (2). Sample collection incorporated an environmental swabbing area that measured 2.54 by 2.54 cm. Sample processing immediately followed swab collection by using AOAC Method 081802 for preparation and analysis (2). In total, 192 ANSR samples (24 per facility) were used to monitor the presence or absence of Listeria spp., including L. monocytogenes (12 after the preoperational cleaning process and 12 operational swabs within the first 5 h of RTE production). “Operational” is defined as any period during the time frame of when production began to when it concluded. ANSR swabs were collected in the same zones and sampling sites adjacent to the ATP test. ANSR results were reported as positive, negative, or inconclusive.
Data were analyzed using the generalized linear mixed model procedure with a binomial distribution and fixed effects of content domain and regulator, as well as the interactions, to assess compliance in SAS 9.4 (SAS Institute Inc., Cary, NC). Checklist items were assigned the numerical value of 1 for yes and 0 for no, and all NA responses were excluded. Scores were based on the percentage of yes and no responses to each item within each content domain. Means for the aggregated checklist data were compiled and are presented as a percentage of compliance to the guidance within that content domain. Initially, all items from the 10 content domains were aggregated to determine the effect of zone, compliance, content domain, and regulator as well as the following interactions: interactions between zone and compliance; zone and regulator; and zone, regulator, and content domain. Additional analysis on each content domain was performed in a similar manner, with content domain and any interactions with content domain removed from the model. Correlations for all items within the checklist together as well as separate content domains were assessed using the correlation procedure to determine the relationship among compliance in a given content domain and the different responses. All ATP results were aggregated for all eight facilities for each sampling site and per each zone to reflect the percentage of failures at each sampling site and zone as a whole. All Listeria spp. ANSR results were aggregated as a percentage of positives for each sampling site and zone, with the percentage of inconclusive tests reported per zone. ATP data were converted into scores: 1 for a fail, 2 for marginal, and a 3 for passing results as a response for analysis. Listeria ANSR data were also converted into scores: 1 for positives, 2 for inconclusives, and 3 for negative results as a response for analysis.
Assessment of checklist
The facility checklist collectively reflected various levels of adherence to the sanitary control guidance for the 10 different content domains. Collectively, the percentage of guidance used under each content domain ranged from 57 to 100% for all eight facilities (Table 1). Further analysis comparing the percentage of guidance implemented between the specific content domains found significant differences for greater compliance overall in operational sanitation (P = 0.0005), sanitation (P = 0.0030), facility (P = 0.0397), and GMP–personal hygiene (P = 0.0033) content domains than for segregation procedures regardless of the regulating body. Products produced at the selected facilities included RTE meat and poultry snack sticks, jerky, sausages, deli meats, whole-muscle meat products, summer sausage, bologna, salami, pulled pork, hot dogs, pizza, fish jerky, salmon pâte, smoked fish filets, and smoked fish spread.
ATP microbial results
Collectively the 96 preoperational ATP samples taken from all eight facilities resulted overall with 21% passing, 10% marginal, and 69% failing. Across all eight facilities, the percentage of failures for all 12 testing locations ranged from 50 to 88%. Sample locations with the highest percentage of fails included the following: conveyor system–freezer (88%; zone 2), drains (88%; zone 3), and break room–locker room floor (88%; zone 4; Table 2). Racks (zone 2), carts (zone 3), and soap dispensers (zone 4) yielded the lowest amount of ATP failures overall, with all three locations resulting in 50% failures (Table 2). Comparison of the percentage of ATP reader–failed samples across all three zones reflected fairly even numerical results; however, zone 3 (nonfood contact surfaces in areas where food is processed, but not immediately adjacent to food contact surfaces) had a slightly increased numerical percentage of positives over zones 2 and 4 (Table 3).
Preoperational Listeria spp., including L. monocytogenes results
In total, 96 samples for Listeria spp., including L. monocytogenes, were collected before the start of operations at the same sampling locations as the ATP swabs. Collectively, the eight facilities had an average of 22% positives, with the highest percentage of positives at the loading dock (57%; zone 4) and break–locker room floor (50%; zone 4), proceeded by the drains (33%; zone 3) and floors (33%; zone 3; Table 2). There were zero positives found at the framework (zone 2), soap dispensers (zone 4), and window (zone 4) sampling locations. Collectively, 9% of the ANSR tests resulted in an inconclusive reading for the preoperational results, with zone 3 showing a slightly higher numerical amount of inconclusives than zones 2 and 4 (Table 3).
Operational Listeria spp., including L. monocytogenes results
In total, 96 operational samples were collected for Listeria spp., including L. monocytogenes, within the first 5 h of RTE production, resulting overall in 10% positives for all eight facilities combined. Samples were collected in the same locations as the ATP and preoperational Listeria spp. tests. All eight facilities overall yielded the highest percentage of positives at the conveyor system–freezer (33%; zone 2), loading dock (29%; zone 4), and drain (20%; zone 3) sampling locations (Table 2). Testing locations with no positive findings at any of the facilities tested during the operational swabs included the framework (zone 2), floor (zone 3), cart (zone 3), soap dispenser (zone 4), and break–locker room floor and windows (zone 4; Table 2). These findings are consistent with the ATP and preoperational findings, with the exception of the floor and break–locker room floor. Overall, the percentage of operational positive Listeria spp. results was almost half that of the preoperational positives. The operational positives also decreased the farther away the test was taken from the RTE processing area (Table 3). Collectively, 10% of the ANSR samples resulted in an inconclusive reading for the operational swabs, with the majority occurring in zone 2 (Table 3).
Interactions between fixed effects and compliance to guidelines
Overall, the quantity of sanitary methods adhered to by the facilities did not result in a significant effect on the microbial outcomes (P = 0.2318). Further analysis of fixed effects preliminarily identified an interaction between the ATP and preoperational Listeria spp. results and the regulating body (P = 0.0452); however, after adjusting for the small sample size, the interaction was not statistically significant.
The various levels of adherence to the sanitary control measure guidance is common within small and very small meat and poultry processors. The identification of less compliance to segregation procedures in relationship to other content domains found within the checklist assessment highlights the reality of operating as a small or very small processor. These processors have limited employees and reduced equipment and structural restraints that result in overlapping use for raw and RTE applications. These limitations create a scenario in which all of the segregation methods described within the sanitary control guidance documents are not feasible; however, the importance of increased sanitation in the absence of extensive segregation should be prioritized.
Preoperational ATP and ANSR results reflected the highest percentage of failures within conveyor system–freezer, drains, loading docks, floors, and the break room–locker room floors. Visual observations made during sampling aligned with these findings, as these surfaces contained more debris overall compared with the other surfaces tested. These results also align with previous studies (17, 24) that found freezer doors and seals, drains, and floors to be a potential contamination source. Aside from conveyor systems and production floors, these locations are also areas that are not typically on a daily cleaning schedule, but are often cleaned on a rotational basis at a specified frequency. When asked, 50% of the facilities indicated that they do not clean their freezers at a minimum of semiannually, the recommended frequency within the evidence-based sanitary control guidance. The study results reflect a need to increase the frequency of cleaning within these areas. The incorporation of a “less than daily” facility cleaning schedule that ensures all areas of the plant (e.g., break rooms and locker rooms, freezers, maintenance tools, loading docks) receive a deep clean at some specified frequency is recommended. The ATP reader and ANSR results in these outlying areas also highlight the need for controlling the movement of pathogens into the production room.
When asked about cleaning drains, 63% of the participants stated that they do not have a drain cleaning program and that may have contributed to the higher percentage of failures in these areas. The prevalence of positive results found in drains suggests the need for the incorporation of a regular drain-cleaning program. Microbial data also indicate that locker areas are not a sanitary storage compartment for equipment; however, the results from the checklist reflected that 50% of the processors allowed lockers to be used for the storage of processing equipment, such as knives and scabbards. It is recommended that alternative storage within the RTE processing area be used as a more sanitary storage area.
In addition to ensuring outlying areas are cleaned, the daily sanitation practices should include a focus on areas easily missed, such as floor mats, barrels-totes, freezer doors and door seals, drip–catch pans, motor housings, cooling water pipes, floor-wall junctions, cleaning tools, equipment legs and feet, control panels, hoses, and ladders. The number of Listeria spp. positives found on the production floor before operations further highlights the need for greater sanitation controls to be implemented when segregation methods are not as feasible due to pathogen transfer from foot and equipment traffic. The impact on the mobility and capability of pathogen transfer by way of foot and equipment movement is well documented (3, 13, 16, 18, 24, 29, 32, 38). When asked, 75% of the facilities indicated that they do not sanitize footwear or the wheels of equipment before use in the RTE production area. The majority of these facilities included those that use a shared production area for raw and RTE activities. Increased sanitation practices and the use of dedicated RTE footwear or a sanitizer application to the bottom of footwear and equipment wheels will reduce the transfer of pathogens via employee and equipment traffic from raw (e.g., loading dock bumpers with floor contact, break–locker room floor, floor drains and floors) processes to RTE.
The facilities daily sanitation methods for processing equipment proved effective, with the results obtained from the interior of racks and cart wheel housings used within the processing room. Comparison of the preoperational data further supports this effectiveness; that is, the percentage of positives increased the farther away from the RTE production area that the sample was taken. This finding aligns with those of other studies (17, 24) that found a higher percentage of positives in outlying areas than in nonfood contact areas directly adjacent to food contact surfaces. This was not a surprise because 100% of the facilities indicated that they conduct thorough deep cleaning each day of production on all processing equipment that was used for or near food. It is recommended that this level of sanitation be carried out into the outlying areas of facilities. Findings of positive samples after the sanitation cycle may be indicative of a persistence of Listeria spp. within the environment (9, 13, 24, 29), supporting that microbial testing to identify potential persistence is an important part in the reduction of the pathogen (18, 24, 29).
The data reflected nearly a 50% reduction in positive operational Listeria spp. results and support that the sanitary methods implemented by the facility are effective in reducing the prevalence of Listeria spp. within the environment during operations. Unlike the preoperational Listeria spp. results, operational positives decreased the farther away from the RTE production area that the test was taken. Lower production volumes and decreased staff concentrate activities to the RTE area, decrease the amount of movement that would encourage pathogen mobility, and lower the prevalence of traffic to outlying parts of the facilities; however, further studies are needed to support these claims.
It is recommended that sanitation procedures be verified to ensure their adequacy. These verifications can be conducted at no cost via a visual inspection; or if financially possible, the facility can conduct environmental testing. Environmental testing was reported as being conducted via ATP reader and/or environmental Listeria spp. sampling at 63% of the facilities. Testing the environment is encouraged for all facilities and is highly recommended by the scientific community to aid in identifying and eradicating sanitary opportunities (17, 18, 21, 24, 29, 32, 34, 38, 39). ATP is not used as an indicator organism for L. monocytogenes; however, the overlap between the preoperational ATP and ANSR results indicate that ATP testing can be an indicator of poor sanitation that may lead to the presence of Listeria spp. The ANSR technology used in this study has the potential to benefit small and very small meat and poultry processors if the swabs could be made available through companies that own the equipment, because the cost per test would be faster and less expensive than other testing methods, such as PCR. The possible purchasing of individual ANSR swabs rather than the entire system would make this option more financially comparable with the ATP testing. In addition, ATP testing and ANSR swabbing can be conducted by the facility, making them viable options for some manufactures to use as a verification of their sanitation processes to further reduce the likelihood of Listeria spp. in the environment.
Interactions between current practices and microbial results infer that the quality of the methods implemented is more impactful than the quantity; however, further studies would need to be conducted for additional evaluation. Interactions identified between the ATP and preoperational Listeria spp. results and the regulating body support that small and very small state-licensed operations do not statistically differ from their federally inspected counterparts. This project offers small and very small RTE food processors an additional resource to aid in the development and implementation of scientifically supported postlethality Listeria controls. Findings and interactions within the study provide a scientific basis for effective methods and offer recommendations to further decrease the prevalence of postprocessing contamination in small and very small facilities, while staying within their financial and structural limitations.
We recognize that utilization of an ATP monitoring system presents limitations within the study. The surfaces throughout the sampling locations varied: stainless steel, plastic, rubber, metal, concrete, glass, and ceramic materials. Industry use of ATP-monitoring systems reflects that the technology is effective on any surface; however, the system used within this study was only validated by the manufacturer for stainless steel surfaces (1). Thresholds indicating a pass, marginal, or failing result were defined by the manufacturer based on their internal validation for use on stainless steel. The study used the same limits for other surfaces; however, there may be a more representative RLU limit for alternative surfaces to assess cleaning efficacy for each type of material tested. It is also well known that chemical residue and sanitizers can interfere with ATP-monitoring systems (4, 11, 30). Although testing was not conducted where visible residue or sanitizer was found, it is understood that surface chemicals could have interfered with the readings, thereby providing inaccurate results.
The ANSR technology used for the identification of Listeria spp., including L. monocytogenes, was validated for use on stainless steel, plastic, rubber, concrete, and ceramic tile surfaces (14, 25). The additional use during this study on metal and glass indicates that the technology is effective on any surface; however, the system was only validated by the manufacturer for the aforementioned surfaces. The manufacturers intended use of the technology also presents limitations as it is intended for use on visibly clean surfaces with an absence of excessive sanitizer. The validation for the technology was conducted with 100 times the background organism level above the target, which supports the use of the test on unclean surfaces; however, it is understood that debris or turbidity in the sample collected caused by not cleaning the surface may interfere with the detection sensor within the ANSR, which would provide an inconclusive result (14, 25). Understanding these limitations, we acknowledge that our results could have been impacted specifically with an increased incidence of inconclusive results; however, this does not seem to have occurred within this study due to the overall quantity of preoperational and operational inconclusive results only being numerically different by 1%.
This research was supported and funded by the Michigan Alliance for Animal Agriculture. Our gratitude goes to Abby Pritchard with the Michigan State University (MSU) Statistical Consulting Center. MSU does not endorse any specific products or companies: Reference to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned.