Comparative analysis of BI/NAP1/027 hypervirulent strains reveals novel toxin B-encoding gene (tcdB) sequences.

The reported incidence and mortality of Clostridium difficile-associated disease has increased significantly, which in part is likely to be due to the emergence of a new, highly virulent strain in North America and Europe. This epidemic strain, referred to as BI/NAP1/027, has increased virulence, attributed to overexpression of the two toxin-encoding genes, tcdA and tcdB, which may be due to truncation of the negative regulator (tcdC) by a 1 bp deletion. In a previous study of whole-genome comparisons using microarray analysis of 75 C. difficile isolates, it was noted that the 20,027 strains, which formed a hypervirulent clade, possessed a unique hybridization pattern for the 7 toxin B microarray reporters. This unique pattern was conserved in all of these 027 strains. The pattern was different for the 55 non-027 strains tested. These data, along with the knowledge that 027 strains are toxinotype III (i.e. possess a complete tcdB gene of comparable size to toxin reference strain VPI 10463), suggest that the sequence of the N-terminal binding domain of toxin B must be divergent from C. difficile strain 630 (and the other 55 strains tested). Additionally, these 027 strains had comparable hybridization patterns across the whole microarray, as well as for tcdB. Therefore, it was suggested that they share a similar, novel N-terminal binding domain. The aim of this study was to ascertain the sequence variation in tcdB from eight characterized BI/NAP1/027 strains. The study confirmed significant sequence variation of tcdB from the sequenced strain 630 and slight variation in tcdB among the eight 027 strains. These results suggest that toxin B from 027 strains may have a different binding capacity compared with its less-virulent counterparts and may, in addition to the mutated tcdC regulator, be responsible for the increased virulence of 027 strains.

Prevalence of Salmonella and Vibrio spp. in seafood products sold in Singapore.

Foodborne hazards in seafood have only recently received increased attention in Singapore since the illness outbreak in 2009 that was associated with consumption of Indian rojak (a traditional salad of fruits, vegetables, and seafood). The microbiological quality of seafood must be evaluated for assurance of food safety. The aim of this study was to evaluate the microbiological quality and to determine the prevalence of Salmonella and Vibrio spp. in seafood sold in Singapore. A total of 116 samples (41 prawn, 44 shellfish, and 31 fishball samples) were collected from major supermarkets and wet markets in Singapore. The mesophilic and psychrotrophic bacterial counts for prawn, shellfish, and fishballs were 2 to 7 log CFU/g. One Salmonella Lexington strain was isolated from a thawed-frozen shellfish product and two Vibrio parahaemolyticus strains were isolated from commercial fishball and shrimp meat products. Thus, seafood sold in Singapore has the potential to be contaminated with Vibrio spp. and Salmonella, and proper handling at food service establishments is required to ensure food safety. Effective control measures also are needed to prevent cross-contamination during postharvest seafood processing.

An outbreak of gastroenteritis caused by Salmonella enterica serotype Enteritidis traced to cream cakes.

INTRODUCTION: This paper describes the epidemiological, microbiological and environmental investigations conducted during an outbreak of Salmonella gastroenteritis in Singapore. METHODS: A case-control study was undertaken to identify the vehicle of transmission. Microbiological testing was performed on faecal, food and environmental samples. Isolates of Salmonella were further characterized by phage typing and ribotyping. RESULTS: There were 216 gastroenteritis cases reported from 20 November to 4 December 2007. The causative agent was identified as Salmonella enterica subspecies enterica serotype Enteritidis for 14 out of 20 cases tested. The vehicle of transmission was traced to cream cakes produced by a bakery and sold at its retail outlets (P < 0.001, OR = 143.00, 95% Cl = 27.23-759.10). More than two-thirds of the 40 Salmonella strains isolated from hospitalized cases, food samples and asymptomatic food handlers were of phage type 1; the others reacted but did not conform to any phage type. The phage types correlated well with their unique antibiograms. The ribotype patterns of 22 selected isolates tested were highly similar, indicating genetic relatedness. The dendrogram of the strains from the outbreak showed distinct clustering and correlation compared to the non-outbreak strains, confirming a common source of infection. DISCUSSION: The cream cakes were likely contaminated by one of the ingredients used in the icing. Cross-contamination down the production line and subsequent storage of cakes at ambient temperatures for a prolonged period before consumption could have contributed to the outbreak.

An outbreak of gastroenteritis caused by Salmonella enterica serotype Enteritidis traced to cream cakes

Introduction:This paper describes the epidemiological, microbiological and environmental investigations conducted during an outbreak of Salmonella gastroenteritis in Singapore. Methods:A case-control study was undertaken to identify the vehicle of transmission. Microbiological testing was performed on faecal, food and environmental samples. Isolates of Salmonella were further characterized by phage typing and ribotyping. Results:There were 216 gastroenteritis cases reported from 20 November to 4 December 2007. The causative agent was identified as Salmonella enterica subspecies enterica serotype Enteritidis for 14 out of 20 cases tested. The vehicle of transmission was traced to cream cakes produced by a bakery and sold at its retail outlets ( P Salmonella strains isolated from hospitalized cases, food samples and asymptomatic food handlers were of phage type 1; the others reacted but did not conform to any phage type. The phage types correlated well with their unique antibiograms. The ribotype patterns of 22 selected isolates tested were highly similar, indicating genetic relatedness. The dendrogram of the strains from the outbreak showed distinct clustering and correlation compared to the non-outbreak strains, confirming a common source of infection. Discussion:The cream cakes were likely contaminated by one of the ingredients used in the icing. Cross-contamination down the production line and subsequent storage of cakes at ambient temperatures for a prolonged period before consumption could have resulted in the outbreak.