Recovery of Spores from Thermophilic Dairy Bacilli and Effects of Their Surface Characteristics on Attachment to Different Surfaces

Abstract

Spores from four Geobacillus spp. were isolated from a milk powder manufacturing line in New Zealand. Liquid sporulation media produced spore yields of ϳ10 7 spores ml ؊1 ; spores were purified using a two-phase system created with polyethylene glycol 4000 and 3 M phosphate buffer. The zeta potentials of the spores from the four isolates ranged from ؊10 to ؊20 mV at neutral pH, with an isoelectric point between pH 3 and 4. Through contact angle measurements, spores were found to be hydrophilic and had relative hydrophobicity values of 10 to 40%, as measured by the microbial adhesion to hexadecane assay. The most hydrophilic spore isolate with the smallest negative charge attached in the highest numbers to Thermanox and stainless steel (1 ؋ 10 4 spores cm ؊2 ), with fewer spores attaching to glass (3 ؋ 10 3 spores cm ؊2 ). However, spores produced by the other three strains attached in similar numbers (P > 0.05) to all substrata (ϳ1 ؋ 10 3 spores cm ؊2), indicating that there was no simple relationship between individual physicochemical interactions and spore adherence. Therefore, surface modifications which limit the attachment of one strain may not be effective for all stains, and control regimens need to be devised with reference to the characteristics of the particular strains of concern.The presence of spores of thermophilic bacilli are a common problem during milk powder manufacture (32). Thermophilic spores from bacteria such as Geobacillus spp. are normally present in low numbers in the raw milk (31). However, high numbers are often found in the milk powder. The source of these spores is believed to be thermophilic bacteria growing on the surfaces within the heat exchangers and evaporators (43). Biofilms are formed when spores present in the raw milk survive pasteurization, adhere to stainless steel surfaces, and germinate when and where conditions are suitable. As the biofilm matures, cells and spores can slough off and contaminate the product flowing past (13). Spore concentrations as high as 10 5 spores g Ϫ1 can occur in milk powder, resulting in it being downgraded to a lower-value product. As established biofilms are difficult to eradicate (20), prevention of the initial attachment is an alternative approach to control biofilm formation. The initial attachment of microorganisms, including spores, to surfaces is due to physicochemical interactions between their surfaces and the substratum, which are described by the extended Derjaguin, Landau, Verwey, and Overbeek theory (53). Such forces include Lifshitz-van der Waal's, acid/base, and electrostatic interactions. An improved understanding of the interactions that impact spore attachment may help in the development of strategies to reduce spore adherence.Several studies have used electron microscopy and atomic force microscopy to examine the physical structure of the spore's surface (7,18,28). However there have been few studies of the surface chemistry of spores, and it is likely that what little information is known may not be broadly applicable acro...

Morphological, physiological and biochemical characterizations of some soil isolates of Bacillus cereus group from Algeria

“…On the other hand, the hydrophilic character of the soil isolates of B. cereus could also be related to an adaptation to alkaline pH conditions. This notice is an accordance with those mentioned by Seale et al (2008). They stated that hydrophobicity increased at acidic pH while it decreased at alkaline pH (Giotis et al, 2009).…”

Hydrophobicity and specific biofilm features of Bacillus cereus spores subjected to pH stresses

“…Spores of B. cereus are generally recognized to be hydrophobic or highly hydrophobic (Simmonds et al, 2003;Tauveron et al, 2006, Ankelokar andLabbé, 2010). Hydrophilic spores have already been reported among strains of B. cereus isolated in the dairy environment Salustiano et al, 2010), and strains of thermophilic bacilli isolated from milk powder (Seale et al, 2008). Accordingly, the dairy environment appeared to be a source of hydrophilic spores of both mesophilic and thermophilic bacilli.…”

Inactivation of Bacillus atrophaeus spores in healthcare waste by uv light coupled with H2O2

“…The recovery levels obtained in the present study are much higher than the typical values presented in the literature (Brown et al, 2007;Hodges et al, 2006;Nicholson and Law, 1999;Perez et al, 2005), and this improvement can be attributed to the differences in the extraction methodology and the microorganism species involved. In the present case, the dispersion of the inoculated waste in a large volume of saline solution and the surface properties of B. atrophaeus fostered improved spore extraction (Chen et al, 2010b;Parkar et al, 2001;Seale et al, 2008). Figure 1 indicates that the spore inactivation fraction was essentially constant as a function of the UV light power per unit of waste mass (P/M).…”