Evaluation Of The Effectiveness Of Disinfection

The effectiveness of a disinfectant can only be undertaken by assessing viable microbial levels before and after exposure. Ideally, this should be carried out in the field, but due to problems with reproducibility and scale (assessing only a small area of the total plant), this may take many weeks before satisfactory results are achieved. Disinfectant testing is, therefore, usually undertaken in the laboratory under strictly defined conditions to enable reproducible and rapid results.

At their simplest, disinfectant test methods consist of adding a known concentration of disinfectant to a known inoculum of bacteria for a defined time and temperature period and assessing surviving bacterial numbers. Microorganism survival may be assessed by inoculating a sample of the disinfectant/microorganism mixture into traditional culture medium and enumerating any microcolonies produced or by the use of a disinfectant concentration/ microorganism mixture dilution range and recording the disinfectant dilution that just prevents microbial growth. These disinfectant tests, referred to as suspension tests, are simple to undertake but can only be used to screen potential products for disinfectant action or to confirm the biocidal abilities of known disinfectants as a quality control procedure.

More extensive suspension test methodologies are available that simulate some of the conditions under which disinfectants may have to work. Such conditions may include the presence of soil, different contact times, alternative temperatures, a variety of bacterial types and the degree of water hardness (43). The results of suspension tests have been used to ascertain recommended in-use dis

Table 4. Accuracy in the Estimation of Surface Microbial Populations for Various Hygiene Assessment Methods as Compared to DEM

Prediction of a DEM count (cm2)

Table 4. Accuracy in the Estimation of Surface Microbial Populations for Various Hygiene Assessment Methods as Compared to DEM

Prediction of a DEM count (cm2)

Method used

Repeats

104

106

108

2SD2

Commercial contact A

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