Characterization of clinical and food Listeria monocytogenes isolates with different antibiotic resistance patterns through simulated gastrointestinal tract conditions and environmental stresses

Thirty-three Listeria monocytogenes isolates previously collected from two sources, food (n = 18) and human patients suffering from listeriosis (n = 15), with variable antibiotic susceptibility profiles (sensitive/resistant) to erythromycin, ciprofloxacin and nitrofurantoin, were studied for their ability to survive (i) the environmental stress provided by sequential conditions that simulate the digestive tract, and (ii) extreme pH values (1.5–12). The results showed a response that was only strain dependent. There were no variability in survival results based on type of stress (low or high pH), source (food or clinical), or sensitivity/resistance to antibiotics (p > 0.01). Some strains of L. monocytogenes are able to survive extreme acid and alkaline conditions, and conditions that mimic the sequential stressors found in the gastro-intestinal tract. The resistance to the antibiotics tested in this study by some L. monocytogenes strains did not confer any cross-protection to acid or alkaline stressors.his work was supported by funding from the National Funds from the Fundação para a Ciência e a Tecnologia (FCT) through project Pest-OE/EQB/LA0016/2013 and “KLEAR - Knowledge and tools for safety, quality and competitiveness in the food chain.” n º NORTE-07-0124-FEDER-000052, co-funded by Fundo Europeu de Desenvolvimento Regional (FEDER), under Programa ON2, Eixo Prior- itário 01-01 – Competitividade, Inovação e Conhecimento, Tipologia 01-01-01-24 – Apoio a Entidades do Sistema Científico e Tecnológico. Financial support for authors Rui Magalhães and Vânia Ferreira was provided by FCT through doctoral fellowship SFRH/BD/71704/2010 and postdoctoral fellowship SFRH/BPD/72617/2010, respectively. Editing of this paper by Dr. P. A. Gibbs is gratefully acknowledge