Characterization of sludges - Detection and enumeration of Salmonella spp. in sludges, soils, soil improvers, growing media and biowastes - Part 1: Membrane filtration method for quantitative resuscitation of sub-lethally stressed bacteria (to confirm efficacy of log drop treatment procedures)
This part of the CEN Technical Report specifies a membrane filtration procedure for the quantitative
resuscitation and enumeration, by culture of individual colonies on chromogenic agar media, of Salmonella spp. including potentially sub-lethally damaged Salmonella spp. in sewage sludges. It may be suitable for other sludges, soils, soil improvers, growing media and biowastes but the user shall validate the method using these materials. The fully defined scope will be determined after the proposed validation trials have been agreed and carried out.
NOTE 1 The objective is to cover untreated and treated sludges, soils, soil improvers, growing media and biowastes.
The method is particularly suited to determining the efficiency of treatment procedures for the elimination of pathogens in sewage sludge as outlined in the Revision of Directive 86/278/EEC (3rd Draft, CEN/TC 308 –
doc 525). Treatment type A processes are initially to be validated through a to be defined Log10 reduction with a test organism such as Salmonella senftenberg W775.
The method has a limit of detection of approximately 1 cfu/g wet weight sludge, dependent on the solids content which at high concentrations (> 20 % (w/v)) can restrict filtration of the sample volume through the membrane if not first diluted.
NOTE 2 Salmonella spp. can be present in biosolids including untreated and treated sewage sludge as both vegetative and sub-lethally damaged cells; the latter require resuscitation to enable colony growth for accurate enumeration on agar media.
NOTE 3 This method is not suitable for treated sludges containing less than 1 viable Salmonella spp. per 1 g wet weight.
NOTE 4 This method is not suitable for untreated sludges containing low levels of Salmonella.