Effects of Short-Term Alkaline Adaptation on Surface Properties of Listeria monocytogenes 10403S

Efstathios S. Giotis*, Ian S. Blair, David A. McDowell
Food Microbiology Research Group, University of Ulster, Northern Ireland, UK.

© 2009 Giotis et al.;

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Centre for Endemic, Emerg-ing and Exotic Diseases (CEEED), Royal Veterinary College, London, Hawkshead Lane, AL9 7TA, UK; Tel: ++44(0)1707667038, 028 90 366697; Mobile: ++44(0)7896498097; Fax: +44(0)1707667051, 02890368811; E-mail:


The changes in cell surface properties associated with alkali stress can significantly disrupt cell metabolism and structures, preventing effective interactions between bacterial cells and their environment. Listeria monocytogenes is known to display an adaptive response to alkali stress that enhances its capacity to more effectively survive subsequent severe alkali challenge. In this study, we examined the effects of adaptation to alkali conditions (pH 9.5/ 1h) in reducing detrimental effects in hydrophobicity and cell morphology in Listeria monocytogenes 10403S during severe (subsequent) short-term alkali challenge (pH 12.0/ 1h). Severe alkali challenge induced larger reductions in hydrophobicity (i.e., lower MATH values) in non adapted control cells than in mild alkali adapted cells. SEM revealed greater morphological diversity in suspensions of non alkali adapted cells than in suspensions of mild alkali adapted cells, i.e., a larger proportion of alkali adapted cells retained the normal (bacillary) morphology. Non adapted cells displayed considerable morphological heterogeneity including elongation, rupture and cellular deformation. Short-term alkaline adaptation in L. monocytogenes involves direct changes in the cell surface properties and organisation which facilitate the well recognised phenotypic abilities of this pathogen to persist and/or grow in alkaline conditions. Alkali adaptation may be significant in the persistence of this pathogen in the presence of alkali detergents in food processing environments and alkali natural habitats, and has direct clinical implications in relation to virulence and response to mammalian defence mechanisms.

Keywords: Listeria, alkali, stress, hydrophobicity, surface, morphology.