Future techniques for disinfectant efficacy testing

The current disinfectant testing position for the food industry is that disinfectant manufacturers rely on suspension tests to provide data for recommended in-use concentrations. In the food industry, however, disinfection typically follows a cleaning phase in which microorganisms surviving prior to disinfection will be predominantly surface attached. Simple surface tests are also available to assess the efficacy of disinfectants against surface adhered microorganisms in which test microorganisms are dried onto surfaces, disinfected and then removed for enumeration by traditional techniques. Both current suspension and surface tests are relatively simple and cheap and can thus be undertaken by a range of laboratories. They can also mimic a range of potential in-use conditions e.g. contact times and temperatures, interfering substances and surface properties. They bear little relationship to factory disinfection, however, as the condition of the test microorganisms does not reflect that of environmental growth (e.g. attached cells or biofilms), only a live/dead result can be obtained (not biostasis), the effects of the cleaning phase are not taken into account and, for the surface test, the microorganisms have to be removed from the surface to be enumerated, which is not 100% efficient and may add additional stresses. This paper reviews some of the available techniques that in the short term may be incorporated into existing methodology to enhance their applicability to the food industry and in the long term may enable laboratory based test methods to more closely mimic the realities of the complete food factory sanitation programme. In particular, techniques which will more closely model surface attachment and disinfectant application strategies will be described, which are at the stage of incorporation into existing surface test methodologies. Future techniques based around vital stains, impedance and bioluminescence methodologies are also indicated that allow surface adhered microorganisms to be enumerated in situ, an assessment of their ability to grow to be made immediately following disinfection and to encompass typical cleaning stressors prior to disinfection. The role of field trials in truly reflecting the efficacy of disinfectants in the food factory environment is also reviewed.