Short Communication Investigating the correlation of constitutive proteins with the growth limits of Salmonella enterica isolates from feeds in response to temperature, pH, formic and lactic acid Spiros Paramithiotis ⁎, Nikos Grivokostopoulos, Panagiotis N. Skandamis Laboratory of Food Quality Control and Hygiene, Department of Food Science and Technology, Agricultural University of Athens, Iera Odos 75, GR-11855 Athens, Greece abstract article info Article history: Received 7 February 2013 Accepted 5 May 2013 Available online 13 May 2013 Keywords: Salmonella enterica Feed Growth limits Proteomic map The aim of this study was to assess growth/no growth interface of several Salmonella enterica strains isolated from contaminated feeding stuffs at various pH values and temperatures, in the presence of lactic or formic acid and to analyze the proteomic map of the most interesting ones. Addition of lactic acid resulted in an in- crease of the minimum pH value required for growth with decreasing temperature; addition of formic acid resulted in no detectable growth at 10 and 15 °C, the latter with the exception of strains 23 and 15100, while only minor differences were exhibited at 20 and 25 °C. The complexity of the mechanisms by which organic acids affect microbial growth has been highlighted, and factors such as type and concentration of the acid, pH, temperature as well as specific attributes of the microbial strains, should be taken into consid- eration. A large number of protein spots, with no significant variation, have been observed, representing the housekeeping proteome of the species and on the other hand, a rather limited amount of uniquely expressed proteins has been identified, representing differences that require further study for their assignment to serovar/strain variability or possess a role in pathogenesis. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Salmonella is the causative agent of a considerable number of human infections worldwide. In the E.U. a statistically significant decrease trend over the last 5 years has been recognized, most probably due to the successful Salmonella control programs in fowl populations (EFSA, 2012). Animal feeding stuffs have been acknowledged as a possible route by which Salmonella can enter the food chain. Indeed, Salmonella has been detected in a variety of ingredients as well as mash and pelleted final products (Bucher et al., 2007; Hacking, Mitchell, & Carlson, 1978; Harris, Fedorka-Cray, Gray, Thomas, & Ferris, 1997). Moreover, it has been documented that, processed feed ingredients, such as various meals and proteins are characterized by higher prevalence than non-processed ones, such as cereals and grains (Jones & Richardson, 2004; Malmqvist et al., 1995; McChesney, Kaplan, & Gardner, 1995; Veldman, Vahl, Borggreve, & Fuller, 1995). The ability of salmonellae to adapt, survive or even grow in a wide range of stressful environments has been well documented (Spector & Kenyon, 2012). More accurately, the effect of the levels and sequence of acid and osmotic stress, interventions used for the preservation of feedingstuffs, has been evaluated (Tiganitas, Zeaki, Gounadaki, Drosinos, & Skandamis, 2009). However, literature is currently lacking sufficient data regarding the growth limits of Salmonella strains (or serovars) isolated from feeding stuffs and how they are affected by pH, type of acidulant and temperature. Moreover, little is known about the potential mechanisms underpinning the ability of certain Salmonella strains (or serovars) to persist in feeds, contrary to other mi- croorganisms, such as Listeria mononcytogenes and Bacillus cereus, for which, potential biomarkers associated with the resistance of the or- ganisms to food-related stresses (e.g., acidity, heating, sanitizers, etc.) have been recognized (Den Besten et al., 2007, 2010; Fox, Leonard, & Jordan, 2011). The aim of the present study was to assess the growth/no growth in- terface of Salmonella enterica strains isolated from feedingstuffs at vari- ous pH values and temperatures in the presence of lactic or formic acid and to analyze the proteomic map of the most interesting ones. 2. Materials and Methods 2.1. Bacterial strains S. enterica strains used throughout this study are given in Table 1. All the strains used in the present study, except for strain 15100, were obtained from the culture collection of the National Veterinary Institute, Sweden. They were stored at -20 °C in nutrient broth supplemented with 50% glycerol. Before experimental use, each strain was grown twice in Brain Heart Infusion broth (Biolife, Milan, Italy) at 37 °C for 24 h. Food Research International 53 (2013) 291–296 ⁎ Corresponding author. Tel.: +30 2105294705; fax: +30 2105294683. E-mail address: sdp@aua.gr (S. Paramithiotis). 0963-9969/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodres.2013.05.009 Contents lists available at SciVerse ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres