Impact of Growth Phase and Natural Organic Matter on the Attachment Kinetics of Salmonella typhimurium to Solid Surfaces

Abstract

The impact of biological interactions on the transport and attachment of Salmonella typhimurium was investigated using cells grown to the mid-and late-exponential phases under a range of ionic strength (IS) conditions, ion valence (KCl vs. CaCl 2 ), and the presence of natural organic matter (NOM). A parallel plate flow chamber was used for the observation of bacterial cell attachment kinetics onto a glass surface with an optical microscope. The physicochemical interactions occurring between the bacteria and surface, as well as the contribution of growth phase and NOM were evaluated. Results showed that none of the cells harvested at the mid-and lateexponential phases attached to glass surfaces at low IS condition (10 -3 M KCl), whereas maximum attachment was observed at high IS (10 -1 M KCl) for both growth phases. Meanwhile, the presence of NOM reduced the attachment of the Salmonella cells significantly under all conditions. Without NOM, attachment efficiencies (a) in KCl were similar at both growth phases; however, in the presence of the divalent ions, a decreased as the cells aged. In the presence of NOM, a was significantly lower at the late-exponential phase than the midexponential phase. Cellular characterization suggested that bacterial cell surface heterogeneity and functional groups due to growth phase is one of the primary contributors to the observed attachment trends, affected by both NOM and ion valence. These trends indicate the complex role of NOM in the fate and transport mechanisms of Salmonella, coupled with ion valence and growth phase.

Natural freeze-thaw cycles may increase the risk associated with Salmonella contamination in surface and groundwater environments

“…In representative aquifer environments, both temperature and dissolved organic matter affect the survival rate of microorganisms and are therefore important factors to incorporate in risk assessment studies of groundwater contamination (Avery et al., 2004; Chowdhury et al., 2015). Humic acids are the major organic constituents of surface soil and their concentrations can influence the transport and fate of microorganisms.…”

“…Humic acids are the major organic constituents of surface soil and their concentrations can influence the transport and fate of microorganisms. For instance, the presence of humic acids reduced the attachment efficiency of Salmonella cells onto a model aquifer grain (glass bead) surface (Chowdhury et al., 2015) and significantly reduced their inactivation in terms of loss in culturability (Ramamurthy et al., 2014). In this latter study, the change in pH upon addition of NOM was not accounted for and may have contributed to the observed effect.…”

“…A few studies have investigated the inactivation and transport behavior of microorganisms in the presence of dissolved organic matter (Johnson and Logan, 1996; Chowdhury et al., 2015) or in response to variable temperature (John and Rose, 2005), however, most studies have overlooked the combined effect of varying cold temperatures in the presence of dissolved organic matter (Chowdhury et al., 2015; Davies and Evison, 1991; Walker et al., 2006).…”