Detection of Clostridium perfringens type A enterotoxin in faecal and food samples using immunomagnetic separation (IMS)-ELISA

A sandwich duplex immuno PCR for rapid and sensitive identification of Clostridium perfringens alpha and enterotoxin

The prevalence and lethality associated with C. perfringens alpha (CPA) and enterotoxin (CPE) toxaemia necessitate the need for rapid and definitive detection systems to initiate management measures. In the present study, a sandwich duplex immuno-capture PCR (SD-IPCR) was developed by employing IgY antibodies against a bivalent protein r-Cpae derived from CPA and CPE for antigen capture and reporter antibodies against truncated CPA or CPE conjugated to oligomers of distinguishable size for antigen revealing and signal amplification. The avian immunoglobulin's (IgY) were devoid of reactivity with S. aureus protein A (SpA), a commensal that often co-exists with C. perfringens. The assay was specific, had a detection limit (LOD) of 1 pg/ml for both CPA and CPE in PBS and improved the LOD by 10⁴ folds compared to an analogous sandwich ELISA with same set of antibodies. In spiking studies, a ten-fold reduction in LOD was observed in case of intestinal tissue samples (10 pg/ml) however, no change in LOD was observed when SD-IPCR was applied on to faecal, serum or muscle tissue samples. Of the 136 natural samples examined, the SD-IPCR could detect CPA and CPE in 29.4% and 35.3% samples, while the sandwich ELISAs could detect the same in 25.7% and 25% samples respectively owing to the relatively lesser sensitivity. The LOD and specificity of the SD-IPCR demonstrates its applicability as an efficient and rapid platform for direct detection CPA and CPE from diverse samples matrices in clinical microbiological and meat testing laboratories.

Colorimetric detection of Shewanella oneidensis based on immunomagnetic capture and bacterial intrinsic peroxidase activity

Rapid detection and enumeration of target microorganisms is considered as a powerful tool for monitoring bioremediation process that typically involves cleaning up polluted environments with functional microbes. A novel colorimetric assay is presented based on immunomagnetic capture and bacterial intrinsic peroxidase activity for rapidly detecting Shewanella oneidensis, an important model organism for environmental bioremediation because of its remarkably diverse respiratory abilities. Analyte bacteria captured on the immunomagnetic beads provided a bacterial out-membrane peroxidase-amplified colorimetric readout of the immunorecognition event by oxidizing 3, 3′, 5, 5′-tetramethylbenzidine (TMB) in the present of hydrogen peroxide. The high-efficiency of immunomagnetic capture and signal amplification of peroxidase activity offers an excellent detection performance with a wide dynamic range between 5.0 × 10³ and 5.0 × 10⁶ CFU/mL toward target cells. Furthermore, this method was demonstrated to be feasible in detecting S. oneidensis cells spiked in environmental samples. The proposed colorimetric assay shows promising environmental applications for rapid detection of target microorganisms.

A novel enzyme-linked immunosorbent assay for detection of Escherichia coli O157:H7 using immunomagnetic and beacon gold nanoparticles

This paper presents a functional nanoparticle-enhanced enzyme-linked immunosorbent assay (FNP-ELISA) for detection of enterohemorrhagic Escherichia coli (EHEC) O157:H7. Immunomagnetic nanoparticles (IMMPs) conjugated with monoclonal anti-O157:H7 antibody were used to capture E. coli O157:H7. Beacon gold nanoparticles (B-GNPs) coated with polyclonal anti-O157:H7 and biotin single-stranded DNA (B-DNA) were then subjective to immunoreaction with E. coli O157:H7, which was followed by streptavidin-horseradish peroxidase (Strep-HRP) conjugated with B-GNPs based on a biotin-avidin system. The solutions containing E. coli O157:H7, IMMPs, B-GNPs, and Strep-HRP were collected for detecting color change. The signal was significantly amplified with detection limits of 68 CFU mL^-1 in PBS and 6.8 × 10² to 6.8 × 10³ CFU mL^-1 in the food samples. The FNP-ELISA method developed in this study was two orders of magnitude more sensitive than immunomagnetic separation ELISA (IMS-ELISA) and four orders of magnitude more sensitive than C-ELISA. The entire detection process of E. coli O157:H7 lasted only 3 h, and thus FNP-ELISA is considered as a time-saving method.

Rapid detection of enterotoxigenic Clostridium perfringens in meat samples using immunomagnetic separation polymerase chain reaction (IMS-PCR)

Rapid detection of enterotoxigenic Clostridium perfringens in meat samples was accomplished with an immunomagnetic separation polymerase chain reaction (IMS-PCR). First, a monoclonal antibody (mAb) specific to C. perfringens was generated. The antibody showed strong binding to C. perfringens and no binding to non- Clostridia bacteria, except a weak cross-reaction to Staphylococcus aureus based on the enzyme-linked immunosorbent assay (ELISA). Then, magnetic beads were coated with the mAb, and the IMS-PCR system was developed. With the optimized conditions, the IMS-PCR assay was capable of detecting as few as 10 colony forming units (CFU)/g of C. perfringens cells in the meat sample within 10 h. Of the 116 collected samples (26 chicken samples, 20 beef samples, 30 pork samples, 20 fish samples, and 20 processed meat samples) examined with IMS-PCR, 36 (31%) were C. perfringens -positive samples and 2 (1.7%) were enterotoxigenic C. perfringens -positive samples. The IMS-PCR results gave a good agreement with the results obtained by conventional culture methods. In comparison to conventional culture methods, the IMS-PCR is a rapid and specific method and has potential use as a screening tool for enterotoxigenic C. perfringens in food samples.

Bacterial Separation and Concentration from Complex Sample Matrices: A Review

The use of many rapid detection technologies could be expanded if the bacteria were separated, concentrated, and purified from the sample matrix before detection. Specific advantages of bacterial concentration might include facilitating the detection of multiple bacterial strains; removal of matrix-associated assay inhibitors; and provision of adequate sample size reduction to allow for the use of representative food sample sizes and/or small media volumes. Furthermore, bacterial concentration could aid in improving sampling techniques needed to detect low levels of pathogens or sporadic contamination, which may perhaps reduce or even eliminate the need for cultural enrichment prior to detection. Although bacterial concentration methods such as centrifugation, filtration, and immunomagnetic separation have been reported for food systems, none of these is ideal and in many cases a technique optimized for one food system or microorganism is not readily adaptable to others. Indeed, the separation and subsequent concentration of bacterial cells from a food sample during sample preparation continues to be a stumbling block in the advancement of molecular methods for the detection of foodborne pathogens. The purpose of this review is to provide a detailed understanding of the science, possibilities, and limitations of separating and concentrating bacterial cells from the food matrix in an effort to further improve our ability to harness molecular methods for the rapid detection of foodborne pathogens.

Methods for detection of Clostridium botulinum toxin in foods

Botulism is a deadly disease caused by ingestion of the preformed neurotoxin produced from the anaerobic spore-forming bacteria Clostridium botulinum. Botulinum neurotoxins are the most poisonous toxins known and have been a concern in the food industry for a long time. Therefore, rapid identification of botulinum neurotoxin using molecular and biochemical techniques is an essential component in the establishment of coordinated laboratory response systems and is the focus of current research and development. Because of the extreme toxicity of botulinum neurotoxin, some confirmatory testing with the mouse bioassay is still necessary, but rapid methods capable of screening large numbers of samples are also needed. This review is focused on the development of several detection methods for botulinum neurotoxins in foods.

Comparative studies of magnetic particle-based solid phase fluorogenic and electrochemiluminescent immunoassay

Two solid phase immunoassays, an electrochemiluminescent immunoassay (ECLIA) and a magnetic particle fluorogenic immunoassay (MPFIA) were evaluated and compared for bacterial detection. Briefly, the ECLIA is based on a redox reaction between ruthenium (II)-trisbipyridyl Ru[(bpy)3]2+ labeled antibody and the excess of tripropylamine, which generates photons. The entire reaction is carried on the near surface area between the spherical magnetic beads and an anode electrode. The detectable bacterial spores are at a linear range from 5 x 10(3) to 5 x 10(5) colony forming units (cfu) of Bacillus subtilis var. niger spores, 10(2) to 10(4) cfu of Bacillus anthrax spores and 10(2) to 10(6) cells of Escherichia coli O157:H7 in ECLIA. The unique MPFIA technique employs antibody-coated magnetic beads as solid phase in suspension for bacterial capture and concentration in a 96-well microplate format. Primary capturing antibodies, bacteria form a sandwich with alkaline phosphatase (AP)-labeled antibodies as reporter followed by a reaction with the AP substrate, AttoPhos to generate fluorescence for detection. Immunomagnetic separation permits direct isolating and concentrating bacterial cells from the crude samples, such as blood and environmental water. The results of MPFIA for detecting bacteria showed less sensitivity compared with that of ECLIA, however it provides a means for direct, high throughput screening bacteria from crude biological samples. Both ECLIA and MPFIA are rapid (less than one hour) and easy to use.

Development of a magnetic microplate chemifluorimmunoassay for rapid detection of bacteria and toxin in blood

A magnetic microplate chemifluorimmunoassay (MMCIA) is described using an immunomagnetic separation and a fluorescent microplate technique for rapid detection of low-level Escherichia coli O157:H7, Bacillus subtilis var. niger spores, and Staphylococcal enterotoxin type B from whole blood. In general, the MMCIA has at least several-fold more sensitivity than the conventional enzyme-linked immunosorbent assay. In addition, the assay sensitivities using direct fluorochrome label as the reporter, or alkaline phosphatase (AP) with various assay substrates, such as pNPP and AttoPhos, were assessed.

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.

Development of an immunomagnetic assay system for rapid detection of bacteria and leukocytes in body fluids

Immunomagnetic (IM) separation and concentration of specific target ligands or particles, such as bacteria or leukocytes, from complex mixtures, such as bone marrow, blood and other body fluids, is now a widely accepted technique. IM methodologies require high affinity antibodies or other receptors, but are potentially as effective as density gradient separations. Thus, a computer-controlled first-generation immunomagnetic assay system (IMAS) biodetector is being developed for clinical diagnostics. This system is fully automated and affords the advantage of rapid flow-through capture of all types of magnetic beads (MBs) and obviates operator contact with body fluid samples during the collection and analysis phases. In the present work, biotinylated capture antibodies were bound to streptavidin-coated MBs for capture of E. coli O157:H7, T cells and T cell subsets. Samples were automatically vortex mixed with antibody-coated MBs, stained with an acridine dye or fluorescent antibody and collected in a specially designed flow cell containing multiple steel pins, which concentrate external magnetic field lines. IM complexes were rapidly (within minutes), separated from their media in the magnetic field. Magnetically captured particles were automatically rinsed in the flow cell to remove unwanted materials and detection was achieved via a flow-through fluorimeter. Samples can be subsequently captured on a microbiological filter for microscopic visualization and image analysis. Preliminary results demonstrate that rapid detection of target bacteria and leukocytes at low concentrations in body fluids is possible with a total assay time under 1 h. This IM technology has many other potential clinical, industrial and environmental monitoring applications.

Immunomagnetic PCR and DNA probe for detection and identification of Porphyromonas gingivalis

The aim of the study that we describe was to combine an immunomagnetic separation and a PCR followed by dot blot hybridization with a DNA probe for the detection and identification of Porphyromonas gingivalis. Immunomagnetic particles were coated with monoclonal antibody specific for P. gingivalis and were incubated with a suspension containing seven oral bacterial species spiked with various dilutions of P. gingivalis. Beads with their load of bound bacterial were boiled in water, and the target DNA in the supernatant was amplified with a primer pair to generate a 593-bp PCR fragment specific for P. gingivalis. Finally, the product of amplification was detected by dot blot hybridization with a digoxigenin-labeled 593-bp probe. The detection limit was determined to be 100 bacterial cells per ml. The immunomagnetic-PCR/DNA probe procedure described here should be useful for the rapid, specific, and sensitive detection and identification of P. gingivalis in clinical samples.

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

A DNA probe endolabeled with digoxigenin by PCR was developed to detect and enumerate enterotoxigenic Clostridium perfringens in raw beef. After 2 h of hybridization, membranes were developed by using an anti-digoxigenin-alkaline phosphatase conjugated antibody. The resulting chromogenic reaction allowed us to detect and enumerate < or = 10 CFU of C. perfringens per g.

Verification of ELISA results by immunomagnetic isolation of antigens from extracts and analysis with SDS-PAGE and western blotting, demonstrated for Erwinia spp. in potatoes

Isolation of antigens on immunomagnetic beads and subsequent analysis with SDS-PAGE and Western blotting (immunomagnetic isolation-Western blotting (IMI-WB)) was used to verify positive ELISA results for Erwinia chrysanthemi and Erw. carotovora subsp. atroseptica in potato peel extracts. Direct analysis of highly contaminated extracts by Western blotting without previous immuno-isolation resulted in background reactions, whereas immunomagnetic isolation resulted in distinct bands of specific antigens. Target cells as well as antigenic cell products were captured in IMI-WB. Band patterns on IMI-WB of cell-free culture filtrates and cell suspensions were highly similar, but the removal of cells lowered the detection level by 10- to 100-fold. Threshold levels of IMI-WB were generally comparable with those of ELISA. No differences in threshold levels and band patterns were found between a direct format and an indirect format of immuno-isolation. In IMI-WB, blotting patterns differed between Erw. chrysanthemi and Erw. carotovora subsp. atroseptica. The patterns were identical for 15 Erw. chrysanthemi strains, isolated from potato peel extracts in The Netherlands. However, one of 15 strains of Erw, carotovora subsp. atroseptica from potato peel extracts in The Netherlands gave an aberrant pattern. Target bacteria could be easily distinguished from those of cross-reacting strains on the basis of band patterns. Potato peel extracts naturally contaminated with Erw. chrysanthemi gave IMI-WB patterns that were similar to pure cultures of the homologous strains.

Magnetic separation techniques in diagnostic microbiology

The principles of magnetic separation aided by antibodies or other specific binding molecules have been used for isolation of specific viable whole organisms, antigens, or nucleic acids. Whereas growth on selective media may be helpful in isolation of a certain bacterial species, immunomagnetic separation (IMS) technology can isolate strains possessing specific and characteristic surface antigens. Further separation, cultivation, and identification of the isolate can be performed by traditional biochemical, immunologic, or molecular methods. PCR can be used for amplification and identification of genes of diagnostic importance for a target organism. The combination of IMS and PCR reduces the assay time to several hours while increasing both specificity and sensitivity. Use of streptavidin-coated magnetic beads for separation of amplified DNA fragments, containing both biotin and a signal molecule, has allowed for the conversion of the traditional PCR into an easy-to-read microtiter plate format. The bead-bound PCR amplicons can also easily be sequenced in an automated DNA sequencer. The latter technique makes it possible to obtain sequence data of 300 to 600 bases from 20 to 30 strains, starting with clinical samples, within 12 to 24 h. Sequence data can be used for both diagnostic and epidemiologic purposes. IMS has been demonstrated to be a useful method in diagnostic microbiology. Most recent publications describe IMS as a method for enhancing the specificity and sensitivity of other detection systems, such as PCR, and providing considerable savings in time compared with traditional diagnostic systems. The relevance to clinical diagnosis has, however, not yet been fully established for all of these new test principles. In the case of PCR, for example, the presence of specific DNA in a food sample does not demonstrate the presence of a live organism capable of inducing a disease. However, all tests offering increased sensitivity and specificity of detection, combined with reduced time of analysis, have to be seriously evaluated.

Rapid detection of Shigella dysenteriae and Shigella flexneri in faeces by an immunomagnetic assay with monoclonal antibodies

A rapid and sensitive method for the detection of Shigella dysenteriae type 1 and Shigella flexneri serotypes in faeces based on capture of the bacteria with immunomagnetic particles is described. The particles were coated with either of two different monoclonal antibodies specific for the O-antigens of Shigella dysenteriae type 1 and Shigella flexneri serotypes. Captured bacteria were detected by an enzyme immunoassay with O-antigen specific rabbit antiserum. The whole assay required 2 to 3 hours to perform and the sensitivity limit was 10(3) cfu/ml as determined by viable cell counting. One hundred and fifty enterobacteria strains, including 100 Shigella strains from a strain collection, and 302 fresh faecal samples were used for the study. All Shigella dysenteriae type 1 and Shigella flexneri culture-positive faecal samples were positive in the immunomagnetic assay. In addition 18 of 252 culture-negative faecal samples were positive. The immunomagnetic assay was compared with latex agglutination and indirect immunofluorescence using culture as the reference method. The immunomagnetic assay had a sensitivity of 100%, latex agglutination a sensitivity of 72% with 28% false-negative results, and indirect immunofluorescence a sensitivity of 95%. The immunomagnetic assay was superior in sensitivity since it also detected Shigella in faecal samples up to two days after antibiotic therapy had been started, which both latex agglutination and indirect immunofluorescence failed to do. The high sensitivity in detecting live and dead bacteria, and the ease of performance of the immunomagnetic assay render it an attractive method for detection of Shigella.

Detection of Shigella dysenteriae type 1 and Shigella flexneri in feces by immunomagnetic isolation and polymerase chain reaction

A combination of immunomagnetic separation (IMS) and a polymerase chain reaction (PCR) procedure was used for direct isolation and identification of Shigella dysenteriae type 1 and Shigella flexneri from feces. Immunomagnetic particles were coated with monoclonal antibody MASFB, which is specific for a common epitope of the O polysaccharides of S. dysenteriae type 1 and S. flexneri. Bacteria bound to the beads were boiled in water, and target DNA was amplified with a primer pair specific for a gene coded on the invasion-associated locus (ial) of the large virulence plasmid of all four Shigella spp. and enteroinvasive strains of Escherichia coli. A 320-bp DNA fragment was generated and detected by an alkaline phosphatase-conjugated probe. Nonviable cells were also captured and detected by this technique. The method is simple and fast (7 h) and has a detection limit of ca. 10 Shigella organisms per g in fecal samples. The combined IMS-PCR assay correctly identified all 57 samples carrying S. dysenteriae type 1 and 68 samples carrying S. flexneri from 238 fecal specimens and also permitted detection of 17 samples carrying Shigella spp. from 113 specimens from diarrheal patients in whom shigellae were not detected by conventional culture.

Evaluation of the bacteriological quality of seafood

Bacteria largely determine the quality of fresh and lightly preserved fish products. This paper surveys traditional and rapid methods for estimation of bacterial levels in seafood. The use of traditional agar techniques is discussed with reference to development of substrates and procedures suited for fish and fish products. This includes estimation of the bacteria specifically involved in the spoilage process. During the last decade, several microbiological rapid methods or principles (DEFT, microcolonies, Limulus lysate, ATP, conductance, microcalorimetry, reduction of trimethylamine oxide (TMAO)) have been suggested for estimating the bacteriological quality of seafoods. A brief survey of these methods and the results obtained is given. Preliminary results on development of poly- and monoclonal antibodies against Shewanella putrefaciens are mentioned. Future research may involve the development of DNA-probes against genes coding for specific spoilage reactions.

Immunomagnetic separation of Salmonella from foods

Salmonella could be separated from different inoculated foods using antibody-coated immunomagnetic beads. When applied on suitable foods, the immunomagnetic separation technique showed a sensitivity of 10-20 Salmonella cells/g of the original sample. The technology appeared less useful for some food items.