Biocide susceptibility in bifidobacteria of human origin Marina Elli a, *, Stefania Arioli b , Simone Guglielmetti b , Diego Mora b a AAT-Advanced Analytical Technologies Srl, Via Martiri della Resistenza, Galleria San Giuseppe 1, 29122 Piacenza, Italy b DeFENS Department of Food, Environmental and Nutritional Sciences, University of Milan, Via Mangiagalli 25, 20122 Milan, Italy 1. Introduction Disinfectants have been used for years to lower the microbio- logical load of carcasses [1], to remove microbiological contami- nation from fresh products [2] and to kill micro-organisms in a variety of environmental applications [3]. In an effort to improve hygiene measures and to ensure food safety, the food industry has increased the use of biocides and chemical-based disinfectants to control the microbial ecology at production sites [4]. Biocides can be bactericidal, sporicidal, fungicidal, virucidal, or a combination of these [2]. Biocides have no specific target, unlike antibiotics that are selected to combat a particular bacterial species or group of bacterial species. In contrast to chemical sterilisation, disinfection, as defined in the Codex Alimentarius [5], allows the survival of some cells after a normal disinfectant application; thus, disinfected items are not expected to be completely free from living micro-organisms. Controversy has arisen about the use of the term ‘resistance’ with reference to antibiotics and disinfectants [2]; many propose that ‘reduction in susceptibility’ is a more appropriate description than ‘increase in resistance’ [6]. Studies on the mechanisms of action of antibiotics have described resistance following different criteria: (a) phenotypic or genotypic trait of bacteria, based on the growth pattern and/or the presence of target genes; (b) origin (intrinsic versus acquired resistance); and (c) type of resistance (single, multiple or cross-resistance) [7]. Unlike antibiotics, disinfectants can ‘affect multiple cellular components’ [8] or have ‘multiple target sites within the microbial cell’ [9]. Also, disin- fectants ‘contain antibacterial chemicals that are at sufficient concentrations to affect multiple, rather than singular, cell targets’ [10]. A defined mechanism of action has been demonstrated for triclosan (TRI) [11] and chlorhexidine (CHX) [12]. These agents, respectively, block lipid synthesis in Escherichia coli and interact with bacterial plasma membranes. The minimum inhibitory concentration (MIC) of disinfectants can be determined with the same method used for antibiotics [13,14], as previously used for lactic acid bacteria (LAB) [15]; however, in-use concentrations of disinfectants should more appropriately refer to the minimum bactericidal concentration [16,17]. In 2010, the International Organization for Standardization (ISO) introduced the standard ISO 10932 for MIC determination [18]. This supplied microbiologists with the first official interna- tional tool for determining the MIC of antibiotics against LAB and bifidobacteria. This norm was recently mentioned by the European Food Safety Authority (EFSA 2012). They mentioned it, among Journal of Global Antimicrobial Resistance 1 (2013) 97–101 ARTICLE INFO Article history: Received 10 January 2013 Received in revised form 26 February 2013 Accepted 18 March 2013 Keywords: Biocide Bifidobacterium Susceptibility Sensitivity Disinfectant ABSTRACT Disinfectants have been used in a variety of environmental applications, in products for personal care and in the food industry. The food industry has increased the use of biocides and chemical-based disinfectants to control microbial ecology at production sites in an effort to improve hygiene measures and food safety. However, the susceptibility profile of micro-organisms to disinfectants has been largely neglected. This study therefore aimed to provide this type of information by focusing on the four most commonly used biocides in the food industry, determining their minimum inhibitory concentrations (MICs) and analysing the distribution of MICs across a variety of micro-organisms. In total, 99 different strains of Bifidobacterium spp. were studied. Results showed a unimodal distribution of MICs for chlorhexidine, triclosan (Irgasan) and sodium hypochlorite with no apparent species-specific correlation. Conversely, part of the tested bifidobacteria population (20%) showed reduced susceptibility to benzalkonium chloride compared with the susceptibility exhibited by the majority of the tested bacterial community. The highest MICs were distributed among almost all of the considered Bifidobacterium spp. In generally, the sensitivity of the studied strains to the four tested biocides appeared to be a genus-related trait. ß 2013 Published by Elsevier Ltd on behalf of International Society for Chemotherapy of Infection and Cancer. * Corresponding author. Tel.: +39 0523 461 483; fax: +39 0523 451 497. E-mail address: marina.elli@aat-taa.eu (M. Elli). Contents lists available at SciVerse ScienceDirect Journal of Global Antimicrobial Resistance journal homepage: www.elsevier.com/locate/jgar 2213-7165/$ – see front matter ß 2013 Published by Elsevier Ltd on behalf of International Society for Chemotherapy of Infection and Cancer. http://dx.doi.org/10.1016/j.jgar.2013.03.007