Hygiene Monitoring Strategies that Hit the Mark

There are three primary tools to sample a surface: the classic swab, the sponge, and the wipe. Many studies have been done through the years to ascertain which extracts the most soil or microbes for sampling. But the critical factor is that one must understand the limits of the sampling system.

For example, a swab is an excellent tool to assay a gasket or a tight area, but has a lower recovery of viable microbes than a sponge or wipe. Meanwhile a sponge swab or RODAC plate is effective for a flat surface, while a curved tank wall may prohibit the use of RODACs but is conducive to sampling by a sponge system.

A comprehensive national study published in Applied and Environmental Microbiology utilized both sponge sticks (3M), and wipes to recover Bacillus anthracis spores showed that the gauze wipes had 35 percent rate of spore recovery while the sponge sticks had a recovery range of 26 percent to 36 percent.

Using both methods, the sponge, as is typically done, is placed into a sterile sampling bag or stomacher bag and is transported with either a peptone water or other recovery broth. A recovery or resuscitation broth is critical for stressed/sublethally injured vegetative microbes, but is not essential for spores.

The utilization of the sponge stick or solar-cult devices enables one to use one sponge face for horizontal direction of a surface, the other for vertical, and the edges for the diagonal of the same sampling surface. This is done omitting the variable of handling the sponge directly with gloved hands.

Best recovery of low numbers for enumeration is achieved via membrane filtration and plating. For pathogen presence/absence sequential incubations in AOAC BAM approved broths is done coupled with confirmation by selective platings. Sponge systems are also utilized for carcass detection of EHEC microbes in numerous USDA plants.

Soil detection systems. There are many different ATP units with varying features. All have evolved into more compact units, with self-containing ATP swab pens coupled with excellent software to download and interpret data for your hygiene validation verification programs.

There are many units on the market, but there has been consolidation of some companies the past 10 years. Examples of hygiene monitoring with ATP units include: AccuClean (Neogen), Charm, CleanTrace (3M), Ensure (Hygiena), HyLite (EM Millipore), and SystemSure Plus (Hygiena). Most utilize a swab that is pre-moistened. The AccuClean has a small sponge-like sampling area instead of a swab. Some utilize a lyophilized pellet of the enzymes that gets reconstituted; others, like Hygiena’s Ensure and SystemSure Plus use a liquid system.

Once the surface is assayed, the ATP swab pens are activated by twisting, cracking the chamber containing the enzymes needed to activate the firefly reaction, then placed into the ATP luminometer chamber where the photodiode measures the Relative Light Units (RLUs) released. The higher the RLU reading, the greater the soil. Unfortunately, RLU scales vary widely between ATP luminometer. This historically was done by manufacturers to tie the user into one unit since all the surface ATP swab history is based upon a luminometer type’s specific scale.

Years ago, faulty attempts were made to correlate ATP with microbial levels. This is highly problematic because ATP assays measure organic soil load that is lowest in bacteria. Yeasts and molds have much higher levels of ATP per microbe than do bacteria, so if a soil matrix has active spoilage fungi, the RLU reading will be higher than with vegetative bacteria.