Rapid and economical method for biochemical screening of stool isolates for Salmonella and Shigella species

CadC has a global translational effect during acid adaptation in Salmonella enterica serovar Typhimurium

In Salmonella enterica serovar Typhimurium, the membrane-localized CadC is a transcriptional activator of the cadBA operon, which contributes to the acid tolerance response. Unlike in Escherichia coli, in which transcription of cadC is constitutive, in S. enterica serovar Typhimurium cadC expression is induced by low pH and lysine. Inactivation of cadC suppresses the acid-sensitive phenotype of a cadA mutation, suggesting the existence of other CadC-dependent genes in addition to the cadBA operon. Using a proteomic approach, we identified 8 of the putative CadC-induced proteins and 15 of the putative CadC-repressed proteins. The former include porin proteins OmpC and OmpF. The latter include proteins involved in glycolysis, energy production, and stress tolerance. To better understand the altered levels of OmpC and OmpF, we compared expression of ompR in S. enterica serovar Typhimurium wild-type and cadC mutant strains and determined that CadC exerted a negative influence on ompR transcription. Taken together, our findings strongly suggest that CadC may be a global regulator involved in the OmpR regulatory system during acid adaptation.

Estimated Numbers of Community Cases of Illness Due to Salmonella, Campylobacter and Verotoxigenic Escherichia Coli: Pathogen-specific Community Rates

OBJECTIVE

To estimate the annual number of cases of illness due to verotoxigenic Escherichia coli (VTEC), Salmonella and Campylobacter in the Canadian population, using data from the National Notifiable Disease registry (NND), estimates of under-reporting derived from several National Studies on Acute Gastrointestinal Illness, and the literature.

METHODS

For each of the three pathogens (VTEC, Salmonella and Campylobacter), data were used to estimate the percentage of cases reported at each step in the surveillance system. The number of reported cases in the NND for each pathogen was then divided by these percentages. In cases where the pathogen-specific estimates were unavailable, data on acute gastrointestinal illness were used, accounting for differences between those with bloody and nonbloody diarrhea.

RESULTS

For every case of VTEC, Salmonella and Campylobacter infection reported in the NND, there were an estimated 10 to 47, 13 to 37, and 23 to 49 cases annually in the Canadian population, respectively.

CONCLUSIONS

The authors estimate that a significant number of infections due to VTEC, Salmonella and Campylobacter occur each year in Canada, highlighting the fact that these enteric pathogens still pose a significant health burden. Recognizing the significant amount of under-reporting is essential to designing appropriate interventions and assessing the impact of these pathogens in the population.

Characterization of lysine decarboxylase-negative strains of Salmonella enterica serovar Enteritidis disseminated in Japan

Salmonella enterica serovar Enteritidis is one of the leading causes of food-borne diseases in Japan. Typically, Salmonella spp. test positive for lysine-decarboxylase. However, the number of isolates of serovar Enteritidis without lysine-decarboxylase activity increased in Japan in 2003. Among 109 strains from distinct outbreaks, 10 lacked lysine-decarboxylase activity. Nine of the ten lysine-decarboxylase-negative strains showed quite similar pulsed-field gel electrophoresis profiles. Their lysine-decarboxylase phenotype was recovered by introduction of the cadBA locus from an lysine-decarboxylase-positive strain. Although the cad loci of the lysine-decarboxylase-negative strains seemed to be intact without any insertion sequences, cadC, a positive regulator of cadBA, had a single-base deletion at the same position, the 973rd base (cytosine), in all the nine lysine-decarboxylase-negative strains, whereas the wild-type cadC gene has a 1542 bp coding region (514 amino acids). This deletion was expected to produce a truncated (338 amino acids) form of CadC due to a frameshift. Because CadC senses environmental cues such as external pH and lysine through its putative C-terminal periplasmic domain, it is likely that the truncated CadC is not sensitive enough to external signaling to activate the cadBA operon, resulting in loss of the lysine-decarboxylase activity. Our results suggest that dissemination of these genetically closely related strains of serovar Enteritidis accounts for the unusual increase in the isolation of lysine-decarboxylase-negative strains.