Invasiveness in chickens, stress resistance and RpoS status of wild-type Salmonella enterica subsp. enterica serovar Typhimurium definitive type 104 and serovar Enteritidis phage type 4 strains

Abstract

The heat and acid resistance and the ability to survive airdrying on commonly used kitchen surfaces were assessed for clinical and environmental strains of Salmonella enterica subsp. enterica serovar Typhimurium, definitive type (DT) 104. Three out of thirty-eight strains of DT 104 were found to be more sensitive in stationary phase to the stresses examined than the other strains. This compares to a previous study by the authors which showed that seven out of forty serovar Enteritidis phage type (PT) 4 strains were more sensitive. RpoS activity was examined indirectly in selected strains of DT 104 and PT 4. In those with normal stress resistance a 100-fold induction of an RpoS-dependent spvR/A' ::luxCDABE fusion was observed upon entry into stationary phase. The sensitive strains examined showed either no induction or a reduced level of spvR/A' ::luxCDABE expression. The rpoS gene was sequenced from these strains and three were found to harbour mutations including one deletion, one base-pair substitution resulting in a nonsense codon, and one insertion causing a frameshift resulting in an early stop codon. Strains with negligible or reduced spvR/A' ::luxCDABE expression had low stress resistance. All strains of DT 104 could be recovered from liver and spleen tissues of infected hens 14 d post-infection, but one with no induction of spvR/A' ::luxCDABE expression was significantly less likely to be recovered from chicken reproductive tissues, liver or spleen than the majority of other strains, including one with reduced spvR/A' ::luxCDABE expression. This work has demonstrated that clinical and environmental strains of DT 104 and PT 4 not infrequently harbour mutations in the rpoS allele. It is possible that the rpoS mutations may have occurred during the initial isolation of the strains. The ability of a strain to cause infection, however, also depends on factors such as host susceptibility and dose.

Characterization of the RpoS Status of Clinical Isolates of Salmonella enterica

“…Sequence variations were detected, but phenotypic differences were not sought. In another study (21), 1 of 38 strains of Salmonella serotype Typhimurium (DT104) and 2 of 40 S. enterica serotype Enteritidis phage type 4 strains were found to be rpoS mutants and were more sensitive to stresses than other strains. We found that rpoS mutants having a null or attenuated phenotype can frequently be found among Salmonella serotype Typhi clinical isolates (36%).…”

“…rpoS allelic variation has also been observed in highly passaged laboratory strains of Salmonella (36,41,42,46). However, little information is available concerning the presence of mutant rpoS alleles in clinical isolates of Salmonella (20,21). Our aim was to determine the prevalence of rpoS mutant alleles in recent human clinical isolates of Salmonella serotype Typhi and Salmonella serotype Typhimurium.…”

Comparative Genetics of the rdar Morphotype inSalmonella

“…The other isolates, Sarc4 and Sarc16, were identified as being RpoS deficient. Mutations in rpoS have been detected in other Salmonella isolates and are thought to reflect either natural variation or laboratory-induced changes (34,47,60).…”

Effect of Challenge Temperature and Solute Type on Heat Tolerance of Salmonella Serovars at Low Water Activity

“…Salmonella serovar Typhimurium DT104 strain 30 (62) was selected for this study on the basis of its relative tolerance of high temperature and low a w as separate stresses (32,44). Salmonella serovar Typhimurium DT104 strain 16 (41), serovar Enteritidis PT4 strain E (27), and S. enterica serovar Senftenberg 775W (63) were selected on the basis of their stress tolerance.…”