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Applied and Environmental Microbiology, May 2005, p. 2756-2761, Vol. 71, No. 5
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.5.2756-2761.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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Dipartimento di Patologia, Sezione di Microbiologia, Università di Verona, 37134 Verona,1 Dipartimento di Biologia Sperimentale, Ambientale ed Applicata, Università di Genova, 16132 Genova, Italy2
Received 27 September 2004/ Accepted 23 November 2004
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. Signoretto et al. (Appl. Environ. Microbiol. 70:6892-6896, 2004) have shown that Enterococcus faecalis was detected mostly bound to plankton and in the VBNC state. In the present study, we show that in vitro adhesion of E. faecalis to copepods accelerated the entry of cells into the VBNC state relative to that of planktonic bacteria. VBNC E. faecalis cells maintained their adhesive properties to copepods and chitin (the main component of the copepod carapace), though to a reduced extent in comparison with growing cells. Sugar competition experiments showed interference with adhesion to both copepods and chitin by GlcNAc and only to copepods by D-mannose. Four enterococcal cell wall proteins present in both growing and VBNC cells and lipoteichoic acid were shown to be capable of binding chitin. The results indicate that copepods may represent an additional environmental reservoir of enterococci, thus suggesting the advisability of redesigning the protocols currently used for microbial detection during the evaluation of the microbiological quality of environmental samples.
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