Changes of physiological and biochemical properties of Salmonella enterica serovar Typhimurium by deletion of cpxR and lon genes using allelic exchange method

To construct a novel Salmonella attenuated live vaccine, the cpxR and lon genes were deleted from a wild-type Salmonella enterica serovar Typhimurium ( S. Typhimurium) using allelic exchange method, resulting in S. Typhimurium CK31 (Δ cpxR), CK38 (Δ lon), and CK111 (Δ cpxR/ lon). These mutated strains were grown normally, as was the wild-type strain. The biochemical properties of the mutants remained highly similar to those of the wild-type. In comparison with the wild-type, 1.5 to 3.3-fold increases of fimbrial products such as Agf, Fim, and Pef fimbria in the mutants CK31, CK38, and CK111 were observed by using a transmission electron microscope and dot blotting. Furthermore, CK38 and CK111 morphologically appeared elongated in shape and produced 2.0- and 3.2-fold increases, respectively, of capsular polysaccharide, which is a major antigenic component. Approximately 10 4-fold attenuation assessed by analysis of LD 50 of BALB/c mouse was observed by deleting the lon/cpxR (CK111) genes. This result indicated that deletion of lon and cpxR genes induced significant attenuation.