Aims: The aim of this study was to examine the contribution of a five-gene islet (lmo0444 - lmo0448) to the growth of Listeria monocytogenes under suboptimal conditions. Methods and Results: Bioinformatics and PCR analyses revealed that a five-gene islet is present in c. half of all L. monocytogenes strains examined (66 in total). A deletion mutant that lacks the entire c. 8 center dot 7-kb islet was created in L. monocytogenes strain LO28. This mutant was impaired in growth at low pH and at high salt concentrations and demonstrated a decreased ability to survive and grow in a model food system (frankfurters). Transcriptional analysis revealed that the islet is self-regulated in that the product of lmo0445 regulates the expression of the other four genes. A role of the alternative stress sigma factor SigB in regulating the islet was also uncovered. Conclusions: The five-gene islet (herein designated as SSI-1; stress survival islet 1) contributes to the growth of L. monocytogenes under suboptimal conditions. Significance and Impact of the Study: SSI-1 may contribute to the survival of certain strains of L. monocytogenes in food environments.