A comparison of commercial ATP hygiene monitoring systems

What was investigated? The application of ATP bioluminescence for hygiene monitoring provides a simple, rapid, direct, objective test for cleaning verification. It is a sophisticated sensitive indicator test of hygienic status and potential risk. The method and application are not intended to be a precise quantitative determination for ATP, and the test is not intended to be a direct replacement for the traditional culture microbiological test.

“The application of ATP hygiene monitoring is intended as a post-cleaning verification test for the removal of product residues. The results from ATP surface hygiene monitoring are different to those of microbial enumeration methods and give additional information that the microbial test cannot provide”
-Hygenia

An extensive laboratory study of commercially available ATP hygiene monitoring systems was conducted by a leading independent food safety and quality testing organisation in USA.

This comprehensive study generated over 5000 data points and the investigation determined linearity, repeatability, and sensitivity of systems by comparing:

• Five ATP instrument systems from  leading suppliers including UniLite NG (3M), MVP Lightning (BioControl), Novalum (Charm Sciences), SystemSURE Plus (Hygiena International) and AccuPoint (Neogen)
• The manufacturers recommended swabs were tested as well as  the universal ATP swab Snapshot (Hygiena International)
• Six ATP concentrations including 0.1, 1.0, 5.0, 10.0 , 100.0 and 1000.0 fmols ATP and ATP-free water as the negative control (or blank sample)
• Four common foods representing different categories of foodstuffs including ground beef, pasteurised milk, pasteurised fresh orange juice and prepared mixed salad greens
• Five microbial species representing Gram positive and Gram negative bacteria, and yeasts 
• Ten replicates samples at each test parameter were tested and the results examined by statistical analysis.

How do the systems compare for ATP detection

Table I: Comparative performance for ATP detection system

* does not detect below 10 fmols at which level the instrument shows 0 RLU.

Table 1 summarises the data obtained and shows that;

• The Linearity of all systems are very good (0.94 - 0.98) but the systems from Neogen and Charm ceased to become linear below a set RLU threshold where only zero RLU values were displayed by the instrument (see Figure 1, below)



• BioControl and Charm have high RLU outputs per unit of ATP but this high RLU does not impart greater sensitivity or better performance to the system
• The most consistent system was Hygiena SystemSURE Plus (also shown in Figure 2, below)



• The least repeatable system was Neogen AccuPoint and Charm Novalum with their respective swabs
• The manufacturers recommended Fail point of ATP systems is usually expressed in RLU values which typically equate to 30 - 100 fmols ATP. Figure 1 shows variation of all systems at 100fmol ATP
• The least sensitive systems were Neogen AccuPoint and Charm Novalum with their respective swabs. The limit of detection of these systems was 10 fmols ATP which is not sufficient to meet typical industry Pass levels of 5 - 10 fmols ATP
• The most sensitive system was Hygiena SystemSURE Plus

In order to reliably detect contamination left behind after cleaning it is important to be able to recover as much ATP from the swab as possible so that RLU output is a true representation of what is present on the surface. Charm Pocketswab and 3M BioTrace CleanTrace only recovered 50 - 60% of the ATP. The Hygiena SystemSURE Plus and Ultrasnap showed 92% sample recovery with the smallest standard error and is therefore the most accurate and precise system.

How do the systems compare for the detection of food stuffs?

Table II: Detection of foodstuffs by ATP systems

*All four foodstuffs showed similar results

Dilutions of four different foodstuffs were measured by each ATP system and the results are summarised in Table II. There was a large range of ATP and RLU response between foodstuffs reflecting differences in the ATP content of foodstuff and the reagent performance of different systems and extractability of ATP.

• Foodstuffs contain variable amounts of ATP. Orange Juice contained the highest and ground beef the lowest amount of ATP
• There was a good linear correlation (r) for all systems ranging from 0.855 to 0.999
• Variation and repeatability was similar to the detection of ATP above
• Not all systems detected dilutions of foodstuff in range 1:10 to 1:10,000, so there were differences in sensitivity. This was similar to the detection of ATP above
• Neogen and Charm systems were the least sensitive systems
• There as little difference between BioControl and 3M systems
• Hygiena SystemSURE Plus & Supersnap detected the lowest dilution of foodstuff

Can ATP systems detect of microbes?

Micro-organisms contain ATP, but this is dependent on the type of microbes, their size and state of health. ATP Hygiene monitoring systems can detect microbes but the sensitivity of the test was 10,000 - 100,000 bacteria /ml (or ~1000 yeast / ml). There was no significant difference between ATP detection systems tested.

The standard used by most foods microbiologist for post-cleaning surface contamination is typically 100 - 500 bacteria / 100cm², which is lower than the detection limit for the ATP test. However, the ATP content of foodstuffs is far greater than that of microbes, and the ATP detection method cannot differentiate between different sources of ATP.

The application of ATP hygiene monitoring is intended as a post-cleaning verification test for the removal of product residues. The results from ATP surface hygiene monitoring are different to those of microbial enumeration methods and give additional information that the microbial test cannot provide.

ATP tests are not intended to replace microbial tests, but there is concurrent direct correlation between the results of the two methods as cleaning simultaneously removes both organic residues and microbes.

Universal ATP swab

SnapShot is a universal ATP swab that is designed to be used with other luminometers such as 3M UniLite NG, BioControl MVP and Charm Novalum. Table II shows snapshot performance for ATP detection compared with the recommended swabs for these instruments.

Snapshot increases the performance of other luminometers by;

• Increasing the linearity of ATP response
• Reducing the background RLU and giving similar (or better) RLU output per unit of ATP
• Reducing the variation and thereby increasing repeatability and consistency of ATP detection
• Increasing the recovery of ATP and thereby increasing the accuracy of the measurement and
• Improving the sensitivity of the system

Similar results were obtained for SnapShot when testing foodstuffs, and Snapshot also improved sample recovery from dry surfaces (see Figure 3). This is attributed to Snapshot's unique swab that ensure better recovery of sample and increases RLU output compared to other swabs.

Figure 3: SnapShot enhances detection of product residues from dry surfaces

Summary

Five commercial ATP detection systems where compared for the detection and measurement of ATP, food residues and micro-organisms. All systems were shown to give a good linear response to contaminants. However there was a difference in the repeatability, accuracy and sensitivity between systems.

The least sensitive and most variable systems were the Neogen AccuPoint and Charm Novalum systems with their respective swabs. There was little difference between BioControl and 3M systems.

The Universal swab SnapShot improved the repeatability and sensitivity of 3M UniLite NG, BioControl MVP and Charm Novalum luminometers.

The most precise, accurate and repeatable systems was the Hygiena SystemSURE Plus with either Ultrasnap or Supersnap swabs.

Table III: SnapShot comparative performance in different luminometer