Adaptive response to cold temperatures and characterization of cspA in Salmonella typhimurium LT2

Salmonella typhimurium is a major foodborne microbial pathogen which primar ily contaminates poultry products causing salmonellosis in humans. S. typhi murium LT2 cultures, when transferred from 37 degrees C to 5 degrees C or 1 0 degrees C, showed an initial lag period in growth with an approximate gen eration time of 10-25 h. Western blot assay using E. coli CS7.4 antibody an d analysis of radiolabeled total cellular proteins from S. typhimurium cult ures after exposure to 10 degrees C or 5 degrees C showed elevated expressi on of a major cold shock protein, CS7.4. Identification of a decreased leve l of CS7.4 at 37 degrees C suggests that the expression of this protein may require a large temperature downshift. Putative regulatory protein binding segment on the 5'-untranslated region referred as 'Fragment 7' in S. typhi murium exhibited a 90.6% and a 56.25% nucleotide sequence identity when com pared with the Fragment 7 of E. coli and S. enteritidis, respectively. The differences in the nucleotide sequence within the Fragment 7 between S. typ himurium and S. enteritidis may explain the differential expression of CspA at 37 degrees C. The nucleotide sequence of the open reading frame of S. t yphimurium cspA gene showed a single base difference at 816 bp position fro m a G to a C which altered the amino acid residue from a glycine to an alan ine. In addition to CspA, an elevated expression of a 105 kDa, and decrease d expression of 6 proteins were evidenced when cultures of S. typhimurium w ere exposed to 10 degrees C or 5 degrees C. Differential expression of the CspA and other proteins in S. typhimurium following exposure to cold temper atures suggest that adaptation and continued growth and survival at cold te mperatures in this pathogen may be aided by these cold-responsive proteins.