Critical review on: feasibility of horizontal standard rapid method for detection of Clostridium perfringens and enterococci in sludges, soil, soil improvers, growing media and biowastes

The existing methods currently available for the detection and enumeration of clostridia and enterococci in sludges and treated biowastes have been evaluated with a view to possible standardisation. The main methods used for the detection and enumeration of Clostridium and Enterococcus spp. have been developed largely for analysis of food and water and can be broadly divided into three groups. Quantification of colonies on agar media; most probable number (MPN) quantification in indicator broth using conventional test tube technology; and proprietary Quantitray® technology equivalent to the 5-tube MPN technique employing disposable plastic trays for enumeration of enterococci. The merits of each are described. At least one report has suggested that the use of m-CP agar medium, which is used in the reference method in the European Union, is not suitable for recovering C. perfringens spores from groundwater. This questions its possible use as a method for detecting C. perfringens in sludge, soil, soil improvers, growing media, and biowaste. Indeed, all of the methods described for detection of C. perfringens and enterococci have strengths and weaknesses, dependent on not only the Regulators’ types of requirements for sludge, soil and biowaste analysis but also their sensitivity, specificity, speed and cost. Nevertheless, it is considered feasible to formulate horizontal standards to cover analysis of C. perfringens and enterococci in sludge, soil, soil improvers, growing media, and biowaste. However, none of the methods have been extensively evaluated for these waste types. As such, there is an urgent need for their modification and evaluation as part of the next phase of the Project Horizontal