ENTEROTOXIN FORMATION IN FOODS BY CLOSTRIDIUM PERFRINGENS TYPE A

Detection of Clostridium perfringens in yearling lamb meat (barbacoa), head, and gut tacos from public markets in Mexico City

No reports on the incidence of Clostridium perfringens in popularly-consumed food from Mexico City have been published; neither are there any reports that have analyzed food consumed in popular markets and less established restaurants. Therefore, this study is aimed at providing data to evaluate the relevance of C. perfringens as an etiologic agent of food-borne diseases. Of the 650 analyzed samples, 106 (16.3%) were positive for C. perfringens; 6.4% (16/250) isolates were from barbacoa, 19% (38/200) from head, and 13% (52/200) from gut tacos. The presence of C. perfringens in these popular-consumed foods demonstrates its relevance as an etiologic agent of food-borne diseases, and confirms the great sanitary risk involved in their consumption. These results may serve as a basis for the Mexican sanitary authorities to control the microbiological quality of street-made foods.

Human disease associated with Clostridium perfringens enterotoxin

Clostridium perfringens continues to be a common cause of food-borne disease. Characteristics of this organism that contribute to its ability to cause food-borne illness include the formation of heat-resistant spores that survive normal cooking/heating temperatures, a rapid growth rate in warm food, and the production of enterotoxin (CPE) in the human gut. Time and temperature abuse associated with food preparation contributes to the majority of outbreaks of C. perfringens food-borne disease. CPE-induced diarrhea has been reported in the absence of a defined food vehicle. These cases have been typically associated with the elderly and following a course of antibiotic therapy. The incidence of CPE-induced diarrhea may be expected to increase with the growing population of immunocompromised (disease-, treatment-, or age-induced) individuals. Clostridium perfringens has been implicated as a possible contributor to the development of SIDS in susceptible individuals. Specifically, it has been hypothesized that CPE acts as a triggering agent, initiating the events associated with the development of SIDS. Continued refinement of both immunoassays and molecular methods for toxin and gene detection, respectively, will facilitate their eventual availability as commercial kits, providing rapid and simplified methods for the detection of C. perfringens isolates that produce or have the capacity to produce CPE as well as other toxins associated with this organism.

Immunological methods for detection of foodborne pathogens and their toxins

Improved methods to detect microorganisms and their toxins introduced during the last decade involve among others recombinant DNA techniques and various immuno-assays such as the enzyme-linked immunosorbent assay and the latex agglutination. Immuno-assays are based on a quantitative reaction of an antigen (bacterial metabolite, e.g., toxin) with its antibody. Therefore, they are suited for detection of microorganisms based on their production of specific antigens and for quantitative detection of bacterial toxins. Sensitivity and specificity of immuno-assays are mainly determined by the antiserum used. In this respect the use of well selected monoclonal antibodies can be of advantage. With the enzyme-linked immunosorbent assay and latex agglutination test quantities of 0.1-1 ng of antigen/ml can be detected. Of both techniques the latex agglutination method has several advantages; the method is simple, inexpensive and rapid. Since each immuno-assay is sensitive to non-specific reactions, recognition of false positive results is necessary. The most appropriate method for this is to add an inhibitor to the test sample which blocks specifically the paratope of the immunoglobulin. Another general disadvantage of immuno-assays is that only the antigenicity is determined and this may differ from the actual toxicity. Therefore, antibodies should be used that react with the toxic centre(s) of the molecule, which can be accomplished by using well selected monoclonal antibodies.

Partial purification and properties of phosphatidylserine synthase from Clostridium perfringens

The membrane-associated phospholipid biosynthetic enzyme cytidine 5'-diphospho-1,2-diacyl-sn-glycerol:L-serine O-phosphatidyltransferase (phosphatidylserine synthase; EC 2.7.8.8) was partially purified 337-fold from a cell-free extract of the gram-positive pathogenic anaerobe Clostridium perfringens (ATCC 3624). The purification procedure included extraction from the cell envelope with the nonionic detergent Triton X-100, followed by affinity chromatography on cytidine 5'-diphosphate-diacylglycerol-Sepharose. When the partially purified enzyme was subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, two major bands were evident with apparent minimum molecular weights of 39,000 and 31,000. Activity of phosphatidylserine synthase was dependent on the addition of manganese ions (3 mM) and Triton X-100 (2.7 mM) for maximum activity. The rate of catalysis was maximal at 40 degrees C (with rapid thermal inactivation above this temperature), and the pH optimum was 8.5. The apparent Km values for cytidine 5'-diphosphate-diacylglycerol and L-serine were 0.24 and 0.26 mM, respectively. The synthetic (forward) reaction was favored, as indicated by an equilibrium constant of 82, and the energy of activation was found to be 18 kcal/mol (75,362 J/mol).