Browsing by Subject "eläinlääketiede, elintarvikehygienia"

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  • Heikinheimo, Annamari (Helsingin yliopisto, 2008)
    The present thesis reveals new information, showing that healthy human is a rich reservoir for Clostridium perfringens enterotoxin (CPE)- producing Clostridium perfringens type A. The results show that healthy foodhandlers are commonly asymptomatic carriers of this pathogen. The findings indicate that persons handling foods should be considered a possible source of contamination for C. perfringens type A food poisoning. This work also found that the genotypes that previously were considered as atypical causative agents in food poisonings, in fact cause a notable proportion of C. perfringens type A food poisonings. CPE- producing C. perfringens type A is considered one of the most common causes of food poisonings in the industrialized world. This pathogen is also involved in antibiotic-associated diarrhea and sporadic diarrhea in humans as well as in animals. Recent findings of the variable loci (plasmid vs. chromosome) and different genetic arrangements adjacent to enterotoxin gene (cpe) have shown that CPE- producing C. perfringens type A isolates form in different subpopulations. These subpopulations are responsible for different CPE-associated diseases, i.e. chromosomal cpe-bearing strains are involved in food poisonings, whereas strains carrying cpe in the plasmid are typical in antibiotic-associated or sporadic diarrhea cases as well as in animal diarrheas. Not much is known about reservoirs or transmission routes of cpe-positive isolates. The present thesis aimed to improve diagnostics of cpe-positive C. perfringens by developing molecular methods for detection and isolation. Other objectives were to improve identification and typing of C. perfringens. With novel assays, molecular epidemiology of cpe-positive C. perfringens type A was further investigated. When investigating the presence of cpe-positive C. perfringens in the feces of healthy food- handlers, the organism was carried by 18% of the individuals. The presence of strains representing all previously identified genotypes (plasmid-borne IS1151-cpe, plasmid-borne IS1470-like-cpe, and chromosomal IS1470-cpe) as well as strains carrying previously unrecognized genetic arrangements attached to cpe shows that various different subpopulations of cpe-positive C. perfringens type A occur in the human gastrointestinal tract and that the healthy human is a rich reservoir for cpe-positive C. perfringens type A. The common carriage of cpe-positive C. perfringens type A of healthy food-handlers and the full capacity of these strains to produce CPE indicate that humans handling food should be considered a possible source of contamination of food. By showing that 25% of investigated C. perfringens type A food poisoning outbreaks were caused by strains carrying plasmid-borne cpe, we reveal that plasmid-borne cpe carrying C. perfringens type A is a common cause of food poisonings. The new data presented in this thesis improve the understanding of reservoirs and movements of enterotoxin producing C. perfringens type A. Therefore, CPE-associated diseases may be better controlled and prevented.