Nonradioactive colony hybridization assay for detection and enumeration of enterotoxigenic Clostridium perfringens in raw beef

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.

Enumeration and isolation of cpe-positive Clostridium perfringens spores from feces

A hydrophobic grid membrane filter-colony hybridization (HGMF-CH) method for the enumeration and isolation of cpe gene-carrying (cpe-positive) Clostridium perfringens spores from feces was developed. A 425-bp DNA probe specific for the cpe gene was sensitive and specific when tested with bacterial DNA and pure cultures. The enumeration of cpe-positive C. perfringens by the HGMF-CH method proved to be as sensitive as nested PCR combined with the most-probable number technique when tested with fecal samples from healthy individuals. With the aid of the HGMF-CH method, positive hybridization signals were detected from two out of seven fecal samples obtained from healthy individuals. Furthermore, cpe-positive C. perfringens was successfully isolated from both of these samples. The detection of cpe-positive C. perfringens by the HGMF-CH method is dependent on the ratio of cpe-positive C. perfringens colonies to total C. perfringens colonies growing on the HGMF-tryptose-sulfite-cycloserine plate. cpe-positive C. perfringens could be isolated if the ratio of cpe-positive C. perfringens spores to total C. perfringens spores was 6 x 10(-5) or higher. The HGMF-CH method provides an aid in the investigation of fecal samples of patients suffering from food poisoning or other diseases caused by cpe-positive C. perfringens. The method also offers a new approach in the investigation of the epidemiology of cpe-positive C. perfringens strains.

Controlled multiplex PCR of enterotoxigenic Clostridium perfringens strains in food samples

A controlled multiplex polymerase chain reaction (PCR) for the detection of Clostridium(C.) perfringens enterotoxin gene (cpe) was established and compared with an in vitro antigenic detection method. Thecpe PCR and the classical method of electric immunodiffusion gave identical results. The predicted specific amplicon of the cpe gene was generated from all of the tested enterotoxigenic C. perfringens strains. In contrast, cultures of any other Clostridium species tested by PCR were negative (100% sensitivity, 100% specificity). Addition of an alphatoxin (plc) gene specific PCR as an in process control reaction was performed in order to prevent false negative PCR results. The PCR detection limit was 0.5 ng of genomic C. perfringens DNA per ml of bouillon culture. By contaminating minced meat with C. perfringens reference strains, the multiplex PCR was established as a tool for routine diagnostic laboratories. The detection limit was approximately 3.0x10(5)C. perfringens cells per gram meat. The results demonstrate the multiplex PCR as an easy, specific, sensitive and time saving diagnostic procedure. Application of this improved method should enhance the knowledge concerning epidemiological aspects of food borne diseases caused by enterotoxigenic C. perfringens.

Chemiluminescent enzyme immunoassay for detection of PCR-amplified enterotoxin A from Clostridium perfringens

A PCR protocol was developed for the rapid and specific detection of Clostridium perfringens strains harboring the enterotoxin A gene in artificially contaminated ground beef. A biotinylated primer pair was designed for amplification of a 750 bp fragment of the C. perfringens enterotoxin A gene. A combination of 4 h enrichment incubation and nucleic acid extraction, followed by 2 h of PCR amplification allowed detection at levels below 10 CFU of freshly grown cells in raw and cooked beef samples. PCR amplified products were confirmed by a Southern hybridization assay using a digoxigenin-labeled internal probe, and two hybridization ELISA protocols (PCR-ELISA) applying a streptavidin capture step for the hybridized PCR products. Both enzyme immunoassays utilized chemiluminescent detection with Lumiphos 530TM as substrate, after hybridization to an internal digoxigenin-labeled probe or a 5' conjugated alkaline phosphatase-labeled probe. The PCR-ELISA resulted in faster confirmation of the PCR products while providing a level of sensitivity comparable to Southern hybridization, and has potential for development into an automated method.