Spectrophotometric determination of biofilm formation by Mycobacterium avium ssp. paratuberculosis in aqueous extract of schmutzdecke for clarifying untreated water in water treatment operations

Mycobacteria possess a characteristic hydrophobic cell wall, and have the genetic competence to form biofilms.1‒4 They can attach and grow in biofilm on suitable substrata depending on growth requirements of the species involved, prevailing conditions in the environment during colonisation and properties of the substrata.5 For instance, some non-tuberculous opportunistic pathogens of mycobacterial species were recovered from biofilm associated with drinking water systems.6 Also, Schulze-Röbbecke & Fischeder7 and Schulze-Röbbecke et al.,8 recovered some species of both slow and rapidly growing mycobacteria in 45 of 50 biofilm samples taken from municipal or domestic water supplies in Germany and France. Pickup et al.,9 also found Map in biofilm on Nantgaredig Bridge spanning the River Tywi in Wales and on an abstraction site grating. These reports demonstrate the possibility that Map being a Mycobacterium, could also form biofilm since previous work has shown its occurrence and persistence in water treatment operations.10‒13 Furthermore, the presence of organic sediment, with which mycobacterial species are associated as part of biofilm microflora, is an important feature in their persistence in lakes and rivers.14,15 However, in the case of water treatment systems, the schmutzdecke which is a meshwork of biologically active matter atop a slow sand filter bed, may either promote or suppress the growth of mycobacteria. Even though to the authors knowledge, biofilm formation by Map in the water environment has not been reported, it does have a lipid cell wall16 which contains on the cell envelope glycopeptidolipids (GPLs) which convey hydrophobic properties.17 This makes Map potentially capable of attaching to a suitable surface as GPLs are directly or indirectly required for colonisation of some surfaces.18 In this study, biofilm formation by 2 environmental and 1 human isolates of Map was investigated under laboratory conditions, to establish their ability to form biofilm, in particular, in the water environment where schmutzdecke may provide proliferative support to environmentally persistent microorganisms for their consequential access to domestic water outlets.