Survival of animal and human associated Listeria monocytogenes in drinking water and biofilms

Land slugs are occasionally observed as contaminants in groundwater wells and drinking water treatment plants including storage tanks. Slugs may feed on carrion and feces, and they are potential vectors of pathogens such as Listeria monocytogenes. We isolated L monocytogenes from the pest slug Arion vulgaris and examined the persistence and survival of human- and slug-derived L. monocytogenes in groundwater-based drinking water and biofilms. L monocytogenes survival was evaluated using cultivation and cultivation-independent techniques. L monocytogenes remained culturable for 35-47 days in drinking water with first-order decay rates between 0.314 and 0.457 hr¹ (T99 >10 days). Attachment of L monocytogenes to filter sand delayed washout from drinking water filters and increased persistence 2-3-fold. Indigenous biofilms stimulated initial surface attachment 10-100-fold butL. monocytogenes declined more rapidly in drinking water biofilms compared with virgin filters not colonized by microorganisms. Grazing by protozoa likely attenuated L monocytogenes survival in some drinking water biofilms. A comparable survival pattern was observed for L monocytogenes and the fecal indicator bacterium E. coli. The study suggests that live L monocytogenes can persist for weeks as sessile organisms in groundwater-based drinking water supplies and may subsequently be released to the drinking water.