title: Impact of acid adaptation on attachment of Listeria monocytogenes to stainless steel during long-term incubation under low or moderate temperature conditions and on subsequent recalcitrance of attached cells to lethal acid treatments.
abstract: This study aimed to evaluate the possible impact of acid adaptation of Listeria monocytogenes cells on their attachment to stainless steel (SS) during long-term incubation under either low or moderate temperature conditions and on the subsequent recalcitrance of attached cells to lethal acid treatments. Initially, nonadapted or acid-adapted stationary phase L. monocytogenes cells were used to inoculate (ca. 10⁸ CFU/ml) brain-heart infusion (BHI) broth in test tubes containing vertically placed SS coupons. Incubation was carried out at either 5 or 30 °C for up to 15 days, under static conditions. On the 5th, 10th and 15th days of incubation, attached cells were subjected to lethal acid treatments by exposing them, for either 6 or 60 min, to pH 2, adjusted with either hydrochloric or lactic acid. Following the acid treatments, remaining viable cells were detached (through strong vortexing with glass beads) and enumerated by agar plating, and also indirectly quantified by conductance measurements via their metabolic activity. Results obtained from both quantification techniques, employed here in parallel, revealed that although the numbers of attached cells for nonadapted and acid-adapted ones were similar, the latter were found to present significantly (p<0.05) increased recalcitrance to all the acid treatments for both incubation temperatures and all sampling days. In addition and regardless of acid adaptation, when long (60 min) acid treatments were applied, conductance measurements revealed that the weak organic lactic acid exhibited significantly (p<0.05) stronger antilisterial activity compared to the strong inorganic hydrochloric acid (at the same pH value of 2). To conclude, present results show that acid adaptation of L. monocytogenes cells during their planktonic growth is conserved even after 15 days of incubation under both low and moderate temperature conditions, and results in the increased recalcitrance of their sessile population to otherwise lethal acid treatments. This "stress hardening" should be severely taken into account when acidic decontamination interventions are used to kill attached to equipment surfaces cells of this important pathogenic bacterium.
authors.affiliation: Department of Food Science and Nutrition, Faculty of the Environment, University of the Aegean, Mitropoliti Ioakeim 2, Myrina 81400, Lemnos Island, Greece. Electronic address: stagiaouris@aegean.gr.
authors.forename: Efstathios
authors.initials: E
authors.lastname: Giaouris
authors.affiliation: Veterinary Research Institute of Athens, Greek Agricultural Organization "Demeter", Neapoleos 25, Aghia Paraskeui 15310, Greece.
authors.forename: Nikos
authors.initials: N
authors.lastname: Chorianopoulos
authors.affiliation: Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Human Nutrition, Faculty of Foods, Biotechnology and Development, Agricultural University of Athens (AUA) Iera Odos 75, Athens 11855, Greece.
authors.forename: George-John
authors.initials: GJ
authors.lastname: Nychas
mesh_terms: D000143:Acids / Q000494:pharmacology*; D000222:Adaptation, Physiological / Q000187:drug effects; D015169:Colony Count, Microbial; D003470:Culture Media; D003666:Decontamination; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology*; D013193:Stainless Steel; D013696:Temperature; D013997:Time Factors
chemical_list: D000143:Acids; D003470:Culture Media; D013193:Stainless Steel
keywords: Acid adaptation; Attachment; Cold stress; Conductance; Listeria monocytogenes; Stainless steel