Comparison of adenosine triphosphate (ATP) bioluminescence and aerobic plate counts (APC) on plastic cutting boards*

A Comprehensive Analysis of ATP Tests: Practical Use and Recent Progress in the Total Adenylate Test for the Effective Monitoring of Hygiene

ABSTRACT

Rapid hygiene monitoring tests based on the presence of ATP have been widely used in the food industry to ensure that adequate cleanliness is maintained. In this study, the practical applications and limitations of these tests and recent technological progress for facilitating more accurate control were evaluated. The presence of ATP on a surface indicates improper cleaning and the presence of contaminants, including organic debris and bacteria. Food residues are indicators of insufficient cleaning and are direct hazards because they may provide safe harbors for bacteria, provide sources of nutrients for bacterial growth, interfere with the antimicrobial activity of disinfectants, and support the formation of biofilms. Residues of allergenic foods on a surface may increase the risk of allergen cross-contact. However, ATP tests cannot detect bacteria or allergenic proteins directly. To ensure efficient use of commercially available ATP tests, in-depth knowledge is needed regarding their practical applications, methods for determining pass-fail limits, and differences in performance. Conventional ATP tests have limitations due to possible hydrolysis of ATP to ADP and AMP, which further hinders the identification of food residues. To overcome this problem, a total adenylate test was developed that could detect ATP+ADP+AMP (A3 test). The A3 test is suitable for the detection of adenylates from food residues and useful for verification of hygiene levels. The A3 test in conjunction with other methods, such as microorganism culture and food allergen tests, may be a useful strategy for identifying contamination sources and facilitating effective hygiene management.

HIGHLIGHTS

Utility of rapid tests to assess the prevalence of indicator organisms (Aerobic plate count, Enterobacteriaceae, coliforms, Escherichia coli, and Listeria spp.) in apple packinghouses

The 2014 listeriosis outbreak caused by caramel-coated apples was linked to apples cross-contaminated within an apple packing facility. This outbreak has increased the focus on effective cleaning and sanitation methods that must be validated and monitored during apple packing. Thus, rapid and reliable testing methods are necessary for assessing cleanliness in the apple packing industry. The objectives of this study were to assess the prevalence of common indicator organisms [Aerobic plate count (APC), Enterobacteriaceae, coliforms, Escherichia coli, and Listeria spp.] on food contact surfaces (zone 1) in apple packinghouses and to evaluate the utility and accuracy of currently used rapid tests (ATP and glucose/lactose residue swabs). Food contact surfaces were sampled over a 100 cm² area in five commercial apple packinghouses to evaluate populations of indicator organisms APC, Enterobacteriaceae, coliforms, E. coli (n = 741), and rapid test readings (n = 659). Petrifilm plates were used for the quantification of APC, Enterobacteriaceae, and coliform/E. coli. Rapid tests [ATP swabs (UltraSnap) and glucose/lactose residue swabs (SpotCheck Plus)] were processed on-site. A larger area (0.93 m²) was sampled for the detection of Listeria spp. (n = 747), following a modified protocol of the FDA's Bacteriological Analytical Manual method, and confirmed with PCR and gel electrophoresis via the iap gene. No significant association was found between either rapid test and populations of APC, Enterobacteriaceae, coliforms, E. coli, and Listeria spp. detection. However, recovery of APC (log CFU/100 cm²) was higher with a failed glucose/lactose residue swab surface hygiene result (3.1) than a passed result (2.9) (p = 0.03). Populations of APC, Enterobacteriaceae, and coliforms were significantly different at each unit operation during the packing process (p ≤ 0.05). This study concluded that ATP and glucose/lactose residue rapid tests were poorly suited for determining microbial load since they were not related to populations of any common indicator organisms or the detection of Listeria spp. These findings emphasize the need to utilize a rapid test, which can be a good indicator of residual matter on a surface, along with traditional microbiological methods to assess cleaning and sanitation practices in apple packinghouses.

Efficacy of ATP Monitoring for Measuring Organic Matter on Postharvest Food Contact Surfaces

ABSTRACT

The Food Safety Modernization Act, specifically the Produce Safety Rule, requires growers to clean and sanitize food contact surfaces to protect against produce contamination. An ATP monitoring device is a potential sanitation tool to monitor the efficacy of an on-farm cleaning and sanitation program that could help growers meet regulatory expectations mandated by the Produce Safety Rule. This ATP monitoring device uses bioluminescence to detect all ATP (found in bacteria and produce matter cells) from a swabbed surface. Because little work has been done to test the efficacy of these tools under postharvest conditions, the present study evaluated ATP measurement for postharvest food contact surface cleanliness evaluation. Concentrations of leafy greens (spinach, romaine, and red cabbage, with or without Listeria innocua) were used as organic matter applied to stainless steel, high-density polyethylene plastic, and bamboo wood coupons to represent postharvest food contact surfaces. The ATP levels on the coupons were then measured by using swabs and an ATP monitoring device. Results showed that the concentration of L. innocua and leafy greens on a food contact surface had a highly significant effect on the ATP monitoring device reading (P < 0.0001). The ATP monitoring device had a lower limit of detection for L. innocua at 4.5 log CFU per coupon. The type of leafy green on a food contact surface did not affect the ATP reading (P = 0.88). Leafy greens with added L. innocua had a higher ATP reading when compared with saline and L. innocua, demonstrating the presence of leafy green matter contributes to ATP reading when combined with L. innocua. The different food contact surfaces had different ATP response readings (P = 0.03), resulting in no detectable levels of bacteria and/or leafy green material from bamboo wood surfaces (P = 0.16). On the basis of our results, the ATP measurement is an appropriate tool to measure produce or bacterial contamination on stainless steel or high-density polyethylene plastic surfaces; however, it is not recommended for wood surfaces.

HIGHLIGHTS

Implications of Adenylate Metabolism in Hygiene Assessment: A Review

The assessment of a hygienic state or cleanliness of contact surfaces has significant implications for food and medical industries seeking to monitor sanitation and exert improved control over a host of operations affecting human health. Methods used to make such assessments commonly involve visual inspections, standard microbial plating practices, and the application of ATP-based assays. Visual methods for inspection of hygienic states are inherently subjective and limited in efficacy by the accuracy of human senses, the degree of task-specific work experience, and various sources of human bias. Standard microbial swabbing and plating techniques are limited in that they require hours or even days of incubation to generate results, with such steps as enrichment and colony outgrowth resulting in delays that are often incompatible with manufacturing or usage schedules. Rapid in conduct and considered more objective in operation than visual or tactile inspection techniques, swabbing surfaces using ATP-based assessments are relied on as routine, even standard, methods of hygienic assessment alone or in complement with microbial and visual inspection methods. Still, current ATP methods remain indirect methods of total hygiene assessment and have limitations that must be understood and considered if such methods are to be applied judiciously, especially under increasingly strict demands for the verification of hygiene state. Here, we present current methods of ATP-based bioluminescence assays and describe the limitations of such methods when applied to general food manufacturing or health care facilities.

A systematic review of adenosine triphosphate as a surrogate for bacterial contamination of duodenoscopes used for endoscopic retrograde cholangiopancreatography

BACKGROUND

Bacterial culture is the accepted standard to measure the adequacy of high-level disinfection (HLD) of duodenoscopes. Adenosine triphosphate (ATP) bioluminescence assays have been suggested as an alternative method of evaluating the quality of reprocessing. We systematically reviewed published research describing the correlation between ATP and bacterial cultures.

METHODS

The primary outcome was the correlation or concordance between concomitantly sampled ATP and bacterial contamination obtained from the instrument channel and/or elevator mechanism of the duodenoscope. A secondary outcome included the reduction in ATP measurements between paired samples before and after stages of duodenoscope reprocessing.

RESULTS

Ten studies were included in the analysis. Four studies reported the relationship between concomitantly sampled ATP and cultures. Three studies reported receiver operating characteristic curves (1 study additionally reported a Wilcoxon rank sum test), and 1 study reported Spearman correlation coefficients and paired dichotomous measurements of ATP and bacterial contamination. All analyses suggested a poor relationship between the 2 measures. Studies measuring ATP before and after manual cleaning and before and after HLD reported a reduction in ATP after the reprocessing stage.

CONCLUSION

Current research does not support the direct substitution of ATP for bacterial culture surveillance of duodenoscopes. Serial ATP measurement may be a useful tool to evaluate the adequacy of manual cleaning and for training of endoscopic reprocessing staff.

Adenosine Triphosphate Quantification Correlates Poorly with Microbial Contamination of Duodenoscopes

OBJECTIVE The aim of this study was to quantify the correlation between adenosine triphosphate (ATP) measurements and bacterial cultures from duodenoscopes for evaluation of contamination following high-level disinfection. DESIGN Duodenoscopes used for any intended endoscopic retrograde cholangiopancreatography (ERCP) procedure were included. Microbiologic and ATP data were collected concomitantly and in the same manner from ERCP duodenoscopes. SETTING A high-volume endoscopy unit at a tertiary referral acute-care facility. METHODS Duodenoscopes were sampled for ATP and bacterial contamination in a contemporaneous and highly standardized fashion using a "flush-brush-flush" method for the working channel (WC) and a dry flocked swab for the elevator mechanism (EM). Specimens were processed for any aerobic bacterial growth (colony-forming units, CFU). Growth of CFU>0 and ATP relative light unit (RLU)>0 was considered a contaminated result. Frequency of discord between among WC and EM measurements were calculated using 2×2 contingency tables. The Spearman correlation coefficient was used to calculate the relatedness of bacterial contamination and ATP as continuous measurements. RESULTS The Spearman correlation coefficient did not demonstrate significant relatedness between ATP and CFU for either a WC or EM site. Among 390 duodenoscope sampling events, ATP and CFU assessments of contamination were discordant in 82 of 390 WC measurements (21%) and 331 of 390 of EM measurements (84.9%). The EM was frequently and markedly positive by ATP measurement. CONCLUSION ATP measurements correlate poorly with a microbiologic standard assessing duodenoscope contamination, particularly for EM sampling. ATP may reflect biological material other than nonviable aerobic bacteria and may not serve as an adequate marker of bacterial contamination. Infect Control Hosp Epidemiol 2017;38:678-684.

How reliable are ATP bioluminescence meters in assessing decontamination of environmental surfaces in healthcare settings?

BACKGROUND

Meters based on adenosine triphosphate (ATP) bioluminescence measurements in relative light units (RLU) are often used to rapidly assess the level of cleanliness of environmental surfaces in healthcare and other settings. Can such ATP measurements be adversely affected by factors such as soil and cleaner-disinfectant chemistry?

OBJECTIVE

This study tested a number of leading ATP meters for their sensitivity, linearity of the measurements, correlation of the readings to the actual microbial contamination, and the potential disinfectant chemicals' interference in their readings.

METHODS

First, solutions of pure ATP in various concentrations were used to construct a standard curve and determine linearity and sensitivity. Serial dilutions of a broth culture of Staphylococcus aureus, as a representative nosocomial pathogen, were then used to determine if a given meter's ATP readings correlated with the actual CFUs. Next, various types of disinfectant chemistries were tested for their potential to interfere with the standard ATP readings.

RESULTS

All four ATP meters tested herein demonstrated acceptable linearity and repeatability in their readings. However, there were significant differences in their sensitivity to detect the levels of viable microorganisms on experimentally contaminated surfaces. Further, most disinfectant chemistries tested here quenched the ATP readings variably in different ATP meters evaluated.

CONCLUSIONS

Apart from their limited sensitivity in detecting low levels of microbial contamination, the ATP meters tested were also prone to interference by different disinfectant chemistries.

Cleaning and decontamination efficacy of wiping cloths and silver dihydrogen citrate on food contact surfaces

AIMS

  To test the efficacy of four wipe cloth types (cotton bar towel, nonwoven, microfibre and blended cellulose/cotton) with either quaternary ammonia cleaning solution or silver dihydrogen citrate (SDC) in cleaning food contact surfaces.

METHODS

  Swab samples collected from untreated, cloth-treated and cloth disinfectant-treated surfaces were subjected to hygiene monitoring using adenosine triphosphate (ATP) bioluminescence and aerobic total plate counting (TPC) assays.

RESULTS

  Adenosine triphosphate measurements taken after wiping the surfaces showed poor cleaning by nonwoven cloths (2·89 RLU 100 cm(-2) ) than the microfibre (2·30 RLU 100 cm(-2) ), cotton terry bar (2·26 RLU 100 cm(-2) ) and blended cellulose/cotton cloth types (2·20 RLU 100 cm(-2) ). The cellulose/cotton cloth showed highest log reduction in ATP-B RLU values (95%) and CFU values (98·03%) when used in combination with SDC disinfectant.

CONCLUSIONS

  Cleaning effect of wiping cloths on food contact surfaces can be enhanced by dipping them in SDC disinfectant. ATP-B measurements can be used for real-time hygiene monitoring in public sector, and testing microbial contamination provides more reliable measure of cleanliness.

SIGNIFICANCE AND IMPACT OF THE STUDY

  Contaminated food contact surfaces need regular hygiene monitoring. This study could help to estimate and establish contamination thresholds for surfaces at public sector facilities and to base the effectiveness of cleaning methods.

Application of bacterial bioluminescence to assess the efficacy of fast-acting biocides

Traditional microbiological techniques are used to provide reliable data on the rate and extent of kill for a range of biocides. However, such techniques provide very limited data regarding the initial rate of kill of fast-acting biocides over very short time domains. This study describes the application of a recombinant strain of Escherichia coli expressing the Photorhabdus luminescens lux operon as a whole-cell biosensor. Light emission is linked directly to bacterial metabolism; therefore, by monitoring light output, the impact of fast-acting biocides can be assessed. Electrochemically activated solutions (ECASs), bleach, Virkon, and ethanol were assessed at three concentrations (1%, 10%, 80%) in the presence of organic soiling. Over a 2-s time course, 80% ECAS produced the greatest reduction in light output in the absence of organic load but was strongly inhibited by its presence. Eighty percent ethanol outperformed all tested biocides in the presence of organic soil. Bleach and Virkon produced similar reductions in bioluminescence at matched concentrations within the time course of the assay. It was also demonstrated that the assay can be used to rapidly assess the impact of organic soiling. The use of bioluminescent bacteria as whole-cell bioreporters allows assessment of the relative efficacies of fast-acting biocides within milliseconds of application. The assay can be used to investigate activity over short or extended time domains to confirm complete metabolic inhibition of the bioreporter. Moreover, the assay may enable further elucidation of their mechanism of action by allowing the investigation of activity over time domains precluded by traditional microbiology.

Assessment of hygienic quality of surfaces in retail food service establishments based on microbial counts and real-time detection of ATP

Clean food contact surfaces are important in reducing the likelihood of foodborne disease transmission. The goal of this study was to assess and compare baseline cleanliness of food contact and environmental surfaces in retail food establishments by using ATP bioluminescence (ATP-B), visual assessment, and surface contact plates. Four hundred eighty-nine surface samples were collected from three food service establishments at the University of Minnesota-Twin Cities (Minneapolis) and analyzed for either ATP (252) or total aerobic plate count bacteria (237). ATP levels ranged from a minimum of 4 relative light units (RLU; 0.60 log RLU) on a clean slicer to a maximum of 506,618 RLU (5.77 log RLU) on a dirty cutting board. The overall mean was 1,950 RLU (3.29 log RLU). Cutting boards had the highest ATP levels (mean, 5,495 RLU or 3.74 log RLU; median, 6,761 RLU or 3.83 log RLU). Of the 128 samples judged visually clean at the time of sampling, 70.3 % failed ATP-B testing. Sixty-one (26 % ) of the 237 total aerobic plate count samples yielded counts of over 125 CFU/50 cm(2) (failed), and of those that failed, 40 % were assessed as visually clean before sampling. The highest average counts in CFU/50 cm(2) were found on slicers (104) and cutting boards (87). The results of this study suggest that the current practice of evaluating food contact surface cleanliness by sight and touch to meet regulatory requirements might be inadequate. ATP-B testing may be an efficient tool to facilitate creation, implementation, and validation of more effective food contact surface cleaning in food establishments.