Downloaded from www.microbiologyresearch.org by IP: 54.198.203.27 On: Wed, 30 Nov 2016 15:09:54 Probiotic Escherichia coli strain Nissle 1917 outcompetes intestinal pathogens during biofilm formation Viktoria Hancock, Malin Dahl and Per Klemm Correspondence Per Klemm pkl@cbs.dtu.dk Microbial Genomics Group, Center for Biological Sequence Analysis, Technical University of Denmark, Lyngby, Denmark Received 11 December 2008 Accepted 25 January 2010 Many bacterial infections are associated with biofilm formation. Bacterial biofilms can develop on essentially all kinds of surfaces, producing chronic and often intractable infections. Escherichia coli is an important pathogen causing a wide range of gastrointestinal infections. E. coli strain Nissle 1917 has been used for many decades as a probiotic against a variety of intestinal disorders and is probably the best field-tested E. coli strain in the world. Here we have investigated the biofilm-forming capacity of Nissle 1917. We found that the strain was a good biofilm former. Not only was it significantly better at biofilm formation than enteropathogenic, enterotoxigenic and enterohaemorrhagic E. coli strains, it was also able to outcompete such strains during biofilm formation. The results support the notion of bacterial prophylaxis employing Nissle 1917 and may partially explain why the strain has a beneficial effect on many intestinal disorders. INTRODUCTION Many bacteria live as sessile communities adhered to surfaces, rather than as planktonic isolated cells. These compact microbial consortia, referred to as biofilms, are commonly associated with many economic and health problems (Costerton et al., 1999). In medicine, biofilm- associated infections have a major impact on permanent and temporary artificial implants placed in the human body, often with devastating consequences. Many per- sistent and chronic bacterial infections are now believed to be linked to the formation of biofilms (Costerton et al., 1995, 1999). Bacterial biofilms can develop on many living surfaces and virtually all artificial implants, producing chronic and often intractable infections. Notable biofilm-associated infections include chronic cystitis, endocarditis, otitis media, periodontitis, prosta- titis, wound infections and catheter- and stent-associated infections (Warren, 2001; Costerton et al., 2003; Parsek & Singh, 2003; Brady et al., 2008). Bacterial biofilms have been reported to affect 90 % of indwelling stents in patients (Reid et al., 1992). Biofilm-forming Escherichia coli strains are responsible for most infections in patients with indwelling bladder catheters (Warren, 2001). Biofilm-associated bacteria are often hard to eradicate by antibiotics and can tolerate hundred- or thousandfold higher doses than the corresponding planktonic bacteria (Costerton et al., 1999). E. coli has also been reported to be able to form intracellular biofilm-like aggregates inside bladder cells, making them hard to reach by both host defence mechanisms and antibiotics (Anderson et al., 2003). E. coli strain Nissle 1917, of serotype O6 : K5 : H1, is an excellent colonizer of the human gut and has been reported to be able to colonize and establish itself in the human intestine even in the presence of a natural resident bacte- rial flora (Lodinova-Zadnikova et al., 1992; Schulze & Sonnenborn, 1995; Lodinova-Zadnikova & Sonnenborn, 1997). The strain was originally isolated during World War I from a soldier who escaped a severe outbreak of diarrhoea affecting his regiment. Nissle 1917 seems to have a bene- ficial effect on several types of intestinal disorders and appears to be well tolerated by humans. Nissle 1917 has been marketed as a probiotic remedy against intestinal disorders in several European countries since the 1920s (Schulze & Sonnenborn, 1995). During this period of time, it has been ingested by an appreciable number of people and is probably the best ‘field-tested’ E. coli strain in humans in the world. The large intestine and colon are the sites most heavily colonized by micro-organisms in the gastrointestinal tract. There is mounting evidence that bacterial biofilm forma- tion plays an important role in intestinal colonization. Notably there is growing interest in biofilms in the colon with respect to their role in bowel disease (reviewed by Macfarlane & Dillon, 2007). In this background, we have studied the biofilm-forming capacity on abiotic surfaces of Nissle 1917 and compared it with a range of other intestinal strains. Notably, we have probed the ability of Abbreviations: EPEC, enteropathogenic E. coli; ETEC, enterotoxigenic E. coli. Journal of Medical Microbiology (2010), 59, 392–399 DOI 10.1099/jmm.0.008672-0 392 008672 G 2010 SGM Printed in Great Britain