The efficacy of biocides and other chemical additives in cooling water systems in the control of amoebae

Abstract

Aims: In vitro experiments were undertaken to evaluate biocide formulations commonly used in cooling water systems against protozoa previously isolated from cooling towers. The investigations evaluated the efficacy of these formulations against amoebic cysts and trophozoites. Methods and Results: Laboratory challenges against protozoa isolated from cooling towers using chlorine, bromine and isothiazolinone biocides showed that all were effective after 4 h. The presence of molybdate and organic phosphates resulted in longer kill times for bromine and isothiazolinones. All treatments resulted in no detectable viable protozoa after 4 h of exposure. Conclusions: The chemical disinfection of planktonic protozoa in cooling water systems is strongly influenced by the residence time of the formulation and less so by its active constituent. Bromine and isothiazolinone formulations may require higher dosage of concentrations than currently practiced if used in conjunction with molybdate‐ and phosphate‐based scale/corrosion inhibitors. Significance and Impact of the Study: Cooling water systems are complex microbial ecosystems in which predator–prey relationships play a key role in the dissemination of Legionella. This study demonstrated that at recommended dosing concentrations, biocides had species‐specific effects on environmental isolates of amoebae that may act as reservoirs for Legionella multiplication in cooling water systems.

Impact of Acanthamoeba Cysts on Stress Resistance of Salmonella enterica Serovar Typhimurium, Yersinia enterocolitica 4/O:3, Listeria monocytogenes 1/2a, and Escherichia coli O:26

“…Sodium hypochlorite, or household bleach, is known to have a broad spectrum of antimicrobial activity and is already widely used in the food industry, e.g., for sanitizing food contact surfaces. The effectiveness of hypochlorite in killing Acanthamoeba cysts (17,21,22) has been confirmed in the present study. The microbiocidal activity of chlorine is mainly attributed to undissociated hypochlorous acid, but the exact action mechanisms are still unknown.…”

Resistance of Acanthamoeba Cysts to Disinfection Treatments Used in Health Care Settings

“…Surprisingly, ortho-phthalaldehyde alone showed better efficacy than an OPA-based product after 10 min exposure for strains 1, 2, and 3 and the three collection strains. This might be due to additional compounds (phosphate buffering salts, corrosion inhibitors, chelating agents) in the formulation, changing the biocidal activity or availability of the active molecule against cysts (16). The OPA-based product showed good efficacy after 20 min exposure but required 30 min exposure to become fully efficient against resistant strains 3 and 4.…”

Vermamoeba vermiformis-Aspergillus fumigatus relationships and comparison with other phagocytic cells

“…It is also frequently recovered from hospital water networks as shown by several authors (Rohr et al 1998;Thomas et al 2006;Ovrutsky et al 2013;Pagnier et al 2015). Acanthamoeba, another genus of FLA commonly found in soil and water, has, as V. vermiformis, a two-staged life cycle: an actively feeding, dividing trophozoite form corresponding to the period of metabolic activity of the amoeba and a dormant cyst that can resist hostile environmental conditions such as nutrient depletion, osmotic stress, temperature changes, pH variations and water disinfection (Critchley and Bentham 2009;Fouque et al 2012). Besides digestion by trophozoites and use of the obtained nutrients, an adaptation to the protistan niche has been described for some bacteria, with survival and sometimes multiplication of ingested microorganisms with or without lysis of amoeba, leading to bacterial protection and colonization of other environments (Thomas and Ashbolt 2011;Cateau et al 2014a).…”