Salmonella enterica serovar Typhimurium exploits inflammation to modify swine intestinal microbiota.

ORIGINAL RESEARCH published: 22 January 2016 doi: 10.3389/fcimb.2015.00106 Salmonella enterica Serovar Typhimurium Exploits Inflammation to Modify Swine Intestinal Microbiota Rosanna Drumo 1, 2 † , Michele Pesciaroli 1, 3 † , Jessica Ruggeri 4 , Michela Tarantino 1 , Barbara Chirullo 1 , Claudia Pistoia 1 , Paola Petrucci 1 , Nicola Martinelli 4 , Livia Moscati 5 , Elisabetta Manuali 5 , Silvia Pavone 5 , Matteo Picciolini 6 , Serena Ammendola 7 , Gianfranco Gabai 2 , Andrea Battistoni 7 , Giovanni Pezzotti 5 , Giovanni L. Alborali 4 , Valerio Napolioni 6 , Paolo Pasquali 1* and Chiara F. Magistrali 5* 1 Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy, 2 Department of Comparative Biomedicine and Food Science, University of Padua, Padua, Italy, 3 VISAVET Health Surveillance Centre, Universidad Complutense Madrid, Madrid, Spain, 4 Department of Veterinary Diagnostic, Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia Romagna, Brescia, Italy, 5 Research and Development Area, Istituto Zooprofilattico Sperimentale dell’Umbria e della Marche, Perugia, Italy, 6 Department of Experimental Medicine, University of Perugia, Perugia, Italy, 7 Department of Biology, University of Roma Tor Vergata, Rome, Italy Edited by: D. Scott Merrell, Uniformed Services University, USA Reviewed by: Richard E. Isaacson, University of Minnesota, USA Johanna R. Elfenbein, North Carolina State University, USA *Correspondence: Paolo Pasquali ; Chiara F. Magistrali † These authors have contributed equally to this work. Received: 12 September 2015 Accepted: 28 December 2015 Published: 22 January 2016 Citation: Drumo R, Pesciaroli M, Ruggeri J, Tarantino M, Chirullo B, Pistoia C, Petrucci P, Martinelli N, Moscati L, Manuali E, Pavone S, Picciolini M, Ammendola S, Gabai G, Battistoni A, Pezzotti G, Alborali GL, Napolioni V, Pasquali P and Magistrali CF (2016) Salmonella enterica Serovar Typhimurium Exploits Inflammation to Modify Swine Intestinal Microbiota. Front. Cell. Infect. Microbiol. 5:106. doi: 10.3389/fcimb.2015.00106 Salmonella enterica serovar Typhimurium is an important zoonotic gastrointestinal pathogen responsible for foodborne disease worldwide. It is a successful enteric pathogen because it has developed virulence strategies allowing it to survive in a highly inflamed intestinal environment exploiting inflammation to overcome colonization resistance provided by intestinal microbiota. In this study, we used piglets featuring an intact microbiota, which naturally develop gastroenteritis, as model for salmonellosis. We compared the effects on the intestinal microbiota induced by a wild type and an attenuated S. Typhimurium in order to evaluate whether the modifications are correlated with the virulence of the strain. This study showed that Salmonella alters microbiota in a virulence-dependent manner. We found that the wild type S. Typhimurium induced inflammation and a reduction of specific protecting microbiota species (SCFA-producing bacteria) normally involved in providing a barrier against pathogens. Both these effects could contribute to impair colonization resistance, increasing the host susceptibility to wild type S. Typhimurium colonization. In contrast, the attenuated S. Typhimurium, which is characterized by a reduced ability to colonize the intestine, and by a very mild inflammatory response, was unable to successfully sustain competition with the microbiota. Keywords: Salmonella Typhimurium, microbiota, inflammation, immune response, pig, salmonellosis INTRODUCTION Nontyphoidal salmonellae (NTS) as Salmonella enterica serovar Typhimurium are a leading cause of acute food-borne zoonoses worldwide being responsible for hundreds of millions of cases of gastroenteritis and bacteremia annually (Hohmann, 2001). Pigs are important reservoir of infection for humans as they are asymptomatic carriers of broad host-range serovars of Salmonella (Funk and Gebreyes, 2004; Pires et al., 2011). The intestine is considered to be the biological niche of Frontiers in Cellular and Infection Microbiology | www.frontiersin.org 1 January 2016 | Volume 5 | Article 106 Drumo et al. Salmonella Alters Gut Microbiota in Piglets through the reduction of microbiota members normally involved in the intestinal homeostasis and in the inhibition of pathogen growth. Salmonella with the intestinal mucosa having a central role in regulating the immune response to bacteria (Hallstrom and McCormick, 2011). However, Salmonella has developed strategies to overcome and cope with most of the immune defenses developed by the host (Behnsen et al., 2015). Examples of the strategies used by Salmonella to evade mucosal innate immunity include the ability to resist to the reactive oxygen species generated during inflammation (Bogomolnaya et al., 2013), in order to produce energy by an anaerobic respiration chain which uses an electron acceptor specifically generated in the gut under oxidative stress (Winter et al., 2010) and to resist to the sequestration of essential nutrients such as iron and zinc (Raffatellu et al., 2009; Liu et al., 2012). As a matter of fact, the ability to resist to the antimicrobial host responses characterizing gut inflammation promotes the growth of Salmonella in the intestinal lumen over the competing microbiota. During the past few years, there has been an expanding interest concerning the role played by intestinal microbiota in the susceptibility to enteric pathogens. Microbiota contributes to the digestion of dietary substances and to the synthesis of essential food supplements such as vitamins, and to the development or maintenance of the mucosal immune system (Littman and Pamer, 2011). Moreover, it acts as a barrier against invading bacteria both physically, blocking pathogen access to the epithelial layer, and also by outcompeting for nutrients reducing the survival and invasiveness of enteric pathogens (Hallstrom and McCormick, 2011; Sassone-Corsi and Raffatellu, 2015). However, it has been known that S. Typhimurium requires intestinal inflammation to circumvent “colonization resistance” provided by the intestinal microbiota (Santos et al., 2009). It has been shown that Salmonella can alter the normal composition of the gut microbiota, and this influence is associated with Salmonella virulence factors that induce inflammatory mucosal host responses (Barman et al., 2008). Furthermore, animals with disrupted microbiota have an increased susceptibility to infection (Barman et al., 2008; Juricova et al., 2013). Most of the studies examining salmonellosis have been carried out in murine models that naturally do not develop gastroenteritis. To resemble the disease in humans, mice can be subjected to antibiotic treatment in order to eliminate microbiota and to develop colitis (Ahmer and Gunn, 2011). Therefore, due to the lack of an intact microbiota, murine models are not suitable for the comprehension of the mechanisms (...truncated)