Persistence of Enterococcus faecalis in Aquatic Environments via Surface Interactions with Copepods

Abstract

Several human pathogens and fecal-pollution indicators may persist as viable organisms in natural environments, owing to their ability to activate different types of survival strategies. These strategies include adhesion on both abiotic and biotic surfaces and the entrance to the so-called viable but nonculturable (VBNC) state. In an 18-month survey for the detection of enterococci in both lake water and seawater, C. Several human pathogens and fecal-pollution indicators may persist as viable organisms in natural environments because of their ability to activate different types of survival strategies. These strategies include adhesion, possibly the formation of biofilm on both abiotic and biotic surfaces (5, 13-15, 23, 34), and the entry into the so-called viable but nonculturable (VBNC) state. Bacteria in the VBNC state are characterized by loss of culturability on conventional growth media, but cells maintain viability, pathogenicity factors, and the potential ability to reinfect humans on resuscitation to the culturable state (2, 8-10, 17, 20, 21, 26).Among human pathogens, the role of the adhesion of Vibrio cholerae, the etiological agent of a severe waterborne diarrheal disease (cholera), as well as of other vibrios, was extensively investigated, and it has been suggested that altered forms of V. cholerae in specific association with plankton organisms are the most plausible reservoirs of fully virulent strains during interepidemic periods (9). Bacterial binding to various surfaces involves several forces, ranging from hydrophobic and ionic bonds to the lectin-like interactions between the bacterial ligand(s) and complementary receptor(s) displayed by the substrate. A few examples of specific interactions between humanpathogenic bacteria and chitin-containing surfaces are known, but they are entirely restricted to the Vibrio genera. Lectins with specificity for N-acetylglucosamine (GlcNAc), the sugar component of chitin, have been demonstrated to occur in V. cholerae, Vibrio harveyi, Vibrio damsela, and Vibrio furnissii (24,29,36). In addition, specific chitin-binding proteins (CBPs) are displayed on the surfaces of V. cholerae (29,35), Vibrio alginolyticus (5, 27), and V. harveyi (24) and have been shown to be directly correlated to the binding ability of the microorganisms to various substrates.In an 18-month survey for the detection of enterococci in both lake water and seawater, Signoretto et al. (32) have shown that Enterococcus faecalis was bound mostly to plankton when present. In addition, E. faecalis, either in bound or in free form, was most frequently detected in the VBNC state. We believe that this unexpected result deserves particular attention because it constitutes new evidence which, together with the vibrio model, indicates that this may be the main mode of persistence of medically important bacteria in surface waters. The creation of an unexpected pathogen reservoir might possibly invalidate the culture methods currently used to assess the microbiological quality of surface waters in that...

Peptidoglycan O Acetylation and Autolysin Profile ofEnterococcus faecalisin the Viable but Nonculturable State

“…Moreover, although considered to be the major autolysin produced by E. faecalis, the muramidase is not essential for cell growth and plays no significant role in virulence (34). It has been proposed that this muramidase may aid in the persistence of VBNC E. faecalis in aquatic environments by participating at the cell surface in adhesion of the cells to surfaces, such as the chitin walls of copepods (38). No impairment of such adhesion was found with a Lyt mutant of E. faecalis, which produces the muramidase with apparently reduced hydrolytic activity (13); this finding resulted in dismissal of this proposal (38).…”

“…It has been proposed that this muramidase may aid in the persistence of VBNC E. faecalis in aquatic environments by participating at the cell surface in adhesion of the cells to surfaces, such as the chitin walls of copepods (38). No impairment of such adhesion was found with a Lyt mutant of E. faecalis, which produces the muramidase with apparently reduced hydrolytic activity (13); this finding resulted in dismissal of this proposal (38). However, the muramidase extracted from the Lyt mutant did not differ from the parent enzyme in terms of the ability to bind to cell wall substrates (13), leaving the possibility that the "dysfunctional" derivative of the muramidase may nonetheless be expressed and perform this binding function.…”

Changes in Enterococcal Populations and Related Antibiotic Resistance along a Medical Center-Wastewater Treatment Plant-River Continuum

“…Once they are released in environmental water, survival of enterococci depends on biotic and abiotic factors, mainly, their ability to overcome environmental stresses (oligotrophy, sunlight, salinity), the viral lysis, and protozoan predation. Moreover, persistence of enterococci in water is greatly influenced by their association with organic matter, such as biofilms on copepods or plankton (12,13). However, little is currently known about the evolution of the contamination by both antibiotic compounds and antibiotic-resistant bacteria in aquatic environments from the source of contamination to the river.…”

Retreat sites of rain forest stream frogs are not a reservoir for Batrachochytrium dendrobatidis in northern Queensland, Australia

“…A number of aquatic pathogens are able to persist as viable organisms in the environment by forming biofilms on both abiotic and biotic surfaces (Carli et al 1993, Hood & Winter 1997, Signoretto et al 2005. Zoospores of many chytrids can persist in films of water on plants and in soil, and in ponds and rivers (Carlile & Watkinson 1994), and have been detected on mossy rocks (Dewel et al 1985) and canopy leaves (Longcore 2005).…”

“…The broad host range of B. dendrobatidis also provides a reservoir of infection, enabling the species most susceptible to chytridiomycosis to be driven to extinction (Berger et al 2004). An alternative source of infection that could facilitate extinction is the persistence of free-living stages , Godfray et al 1999.A number of aquatic pathogens are able to persist as viable organisms in the environment by forming biofilms on both abiotic and biotic surfaces (Carli et al 1993, Hood & Winter 1997, Signoretto et al 2005. Zoospores of many chytrids can persist in films of water on plants and in soil, and in ponds and rivers (Carlile & Watkinson 1994), and have been detected on mossy rocks (Dewel et al 1985) and canopy leaves (Longcore 2005).…”