Prevalence, populations and pheno- and genotypic characteristics of Listeria monocytogenes isolated from ready-to-eat vegetables marketed in São Paulo, Brazil Anderson S. Sant'Ana ⁎, Maria Crystina Igarashi, Mariza Landgraf, Maria Teresa Destro, Bernadette D.G.M. Franco ⁎ Department of Food and Experimental Nutrition, Faculty of Pharmaceutical Sciences, University of São Paulo. São Paulo, SP, Brazil abstract article info Article history: Received 16 November 2011 Received in revised form 18 December 2011 Accepted 19 December 2011 Available online 11 January 2012 Keywords: Listeria monocytogenes Ready-to-eat vegetables Serotype Ribotype Biofilm Sanitizer Listeria monocytogenes is a foodborne pathogen of great concern due to the high fatality rates of listeriosis. The consumption of RTE vegetables has increased in Brazil over the last two decades, but little is known about the risks associated to the consumption of these products. This study evaluated the prevalence and counts of L. monocytogenes in 512 packages of ready-to-eat vegetables marketed in São Paulo. The isolates were characterized for their serotypes, ribotypes, positivity for virulence genes inlA, inlC and inlJ, resistance to chlorine, growth rate variability and capability to form biofilm on stainless steel (AISI 304, #4) coupons. L. monocytogenes was detected in 3.1% of the samples. Only five samples presented countable levels, with counts between 1.0 × 10 1 and 2.6 × 10 2 CFU/g. Isolates belonged to serotypes 1/2b or 4b and most were pos- itive for genes inlC and inlJ. Ribotypable isolates were grouped into four groups: 1038 (69.4%), 19175 (11.3%), 19191 (17.7%) and 18604 (one isolate). Most isolates survived to exposure to 125 ppm of a chlorine-based disinfectant for 3 min. All isolates were capable to attach to the coupons, reaching counts above 4 log 10 CFU/cm 2 and the growth rate (μ) at 25 °C of the majority of the isolates varied between 0.1 and 0.2 log OD/h, but for few strains the μ was as high as 0.26 log OD/h. Results of this survey indicate that RTE vegeta- bles may be vehicles of L. monocytogenes strains with limited variation in serotype, ribotype and virulence factors but varying significantly in resistance to chlorine disinfectants, capability of forming biofilm and growth rate. Data obtained is of foremost importance to serve as baseline for the development of scientific-based policies to control the incidence of L. monocytogenes in RTE vegetables in Brazil. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Listeria monocytogenes is a foodborne pathogen of great concern due to the high fatality rates of listeriosis (Vázquez-Boland et al., 2001b), and capability to survive stress conditions commonly en- countered in foods such as high salt concentration, low temperature and low pH (Warriner and Namvar, 2009). Although surveillance data indicate that foodborne listeriosis outbreaks are mainly linked to poultry, beef, dairy products and ready-to-eat (RTE) foods, vegeta- bles have also been identified as vehicles of transmission (Behravesh et al., 2011; CDC, 2011; Todd and Notermans, 2011). Besides, the oc- currence of sporadic cases of listeriosis linked to the consumption of foods neither usually nor previously associated with this disease such as melons, hummus and vegetables is an additional concern for fresh produce industries and consumers (Wagner and Allerberger, 2003; Varma et al., 2007; Martins et al., 2010). The consumption of RTE vegetables has increased in Brazil over the last two decades (Sato et al., 2007), but little is known about the risks associated with the consumption of these products. Al- though studies have reported that the occurrence of L. monocytogenes in RTE vegetables in several parts of the world may be as high as 25%, less studies either in Brazil or abroad have focused on the quantifica- tion of this microorganism in these products (Francis and O'Beirne, 2006; Crépet et al., 2007; Fröder et al., 2007; Lianou and Sofos, 2007; Little et al., 2007; Abadias et al., 2008; Cordano and Jacquet, 2009; Giusti et al., 2010; Oliveira et al., 2010). As L. monocytogenes is a challenge for the safety of RTE foods (Luber et al., 2011) and that RTE vegetables are consumed without a killing step before con- sumption, fresh produce plays an important role in listeriosis epide- miology. In the context of risk assessment, the availability of data on the prevalence, counts and growth of foodborne pathogens is of foremost importance for proper building and refining of mathemati- cal models for estimating risks (Crépet et al., 2007). As virulence in L. monocytogenes is highly variable among strains (Velge and Roche, 2010), the differentiation between virulent and non-virulent strains is of great importance in evaluating the potential International Journal of Food Microbiology 155 (2012) 1–9 ⁎ Corresponding authors. Tel./fax: + 55 11 3091 2191. E-mail addresses: assantana@usp.br (A.S. Sant'Ana), bfranco@usp.br (B.D.G.M. Franco). 0168-1605/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2011.12.036 Contents lists available at SciVerse ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro