GENERAL STRESS TRANSCRIPTION FACTOR-SIGMA(B) AND ITS ROLE IN ACID TOLERANCE AND VIRULENCE OF LISTERIA-MONOCYTOGENES

The gene encoding the general stress transcription factor sigma(B) in the gram positive bacterium Listeria monocytogenes was isolated with d egenerate PCR primers followed by inverse PCR amplification. Evidence for gene identification includes the following: (i) phylogenetic analy ses of reported amino acid sequences for sigma(B) and the closely rela ted sigma(F) proteins grouped L. monocytogenes sigma(B) in the same cl uster with the sigma(B) proteins from Bacillus subtilis and Staphyloco ccus aureus, (ii) the gene order in the 2,668-bp portion of the L. mon ocytogenes sigB operon is rsbU-rsbV-rsbW-sigB-rsbX and is therefore id entical to the order of the last five genes of the B. subtilis sigB op eron, and (iii) an L. monocytogenes sigma(B) mutant had reduced resist ance to acid stress in comparison with its isogenic parent strain. The sigB mutant was further characterized in mouse models of listeriosis by determining recovery rates of the wild-type and mutant strains from livers and spleens following intragastric or intraperitoneal infectio n. Our results suggest that sigma(B)-directed genes do not appear to b e essential for the spread of L. monocytogenes to mouse liver or splee n at 2 and 4 days following intragastric or intraperitoneal infection.