Detection of Necrotic Enteritis B–like Toxin Secreted by Clostridium perfringens Using Capture Enzyme-Linked Immunosorbent Assay

Three-mode ratiometric biosensor based on integrated DNA-driven magnetic beads for Clostridium perfringens detection

A three-mode biosensor incorporated ratiometric (electrochemical/colorimetric, electrochemical/photothermal) into its design was constructed using DNA-driven magnetic beads (DMBs) as a bridge to detect C. perfringens. It further enhances the accuracy of detection results while maintaining compatibility with applications in multiple scenarios. Briefly, the G-quadruplex was combined with aptamer and immobilized onto magnetic beads through amide-bond, resulting in the integration of DMBs. The DMBs and supernatant were separated by magnetic separation when the target was present. Subsequently, the DMBs were utilized to construct the electrochemical biosensor, whereas the supernatant was used to construct colorimetric and photothermal biosensors. The limits of detection the ratiometric biosensor were ultimately reduced to 0.26 and 0.27 lg CFU g-1, respectively, in comparison to the single three-mode biosensor. Moreover, this biosensor had been applied in real-sample assays successfully. The establishment of this platform provides a new method for detecting pathogens in the fields of food safety and environmental monitoring.

Development of a new immunodiagnostic tool for poultry coccidiosis using an antigen-capture sandwich assay based on monoclonal antibodies detecting an immunodominant antigen of Eimeria

This study was conducted to develop an antigen-capture ELISA that detects an immunodominant antigen of Eimeria, 3-1E which is present in all Eimeria species, using a set of 3-1E-specific mouse monoclonal antibodies (mAbs). Highly sensitive 3-1E-specific antigen-capture ELISA was established using compatible mAb pairs (#318 and #320) selected from 6 mAbs (#312, #317, #318, #319, #320, and #323) with high binding activity against recombinant 3-1E protein. These anti-3-1E mAbs specifically recognized E. tenella sporozoites and a higher level of 3-1E was detected in the lysate of sporozoites than in sporocysts. Immunofluorescence assay (IFA) using 2 mAbs (#318 and #320) showed specific staining around the membrane of E. tenella sporozoites. In order to measure the changes in the 3-1E level during in coccidiosis, serum, feces, jejunal, and cecal contents were individually collected daily for 7-days postinfection (dpi) with E. maxima and E. tenella. The new ELISA was sensitive and specific for 3-1E detection in all samples collected daily from E. maxima- and E. tenella-infected chickens for a week, and the detection sensitivity ranges were 2 to 5 ng/mL and 1 to 5 ng/mL in serum, 4 to 25 ng/mL and 4 to 30 ng/mL in feces, 1 to 3 ng/mL and 1 to 10 ng/mL in cecal contents, and 3 to 65 ng/mL and 4 to 22 ng/mL in jejunal contents. Following coccidiosis, the overall 3-1E levels started to increase from 4 dpi, and the highest production was shown on 5 dpi. Among the samples collected from Eimeria-infected chickens, the highest detection level was found in the jejunal contents of E. maxima-infected chickens. Furthermore, the level of IFN-γ in serum was significantly (P < 0.05) increased from 3 dpi and peaked on 5 dpi post E. maxima infection. Post E. tenella infection, the level of IFN-γ in serum gradually (P < 0.05) increased from 2 to 5 dpi and plateaued at 7 dpi. The level of TNF-α in serum was rapidly (P < 0.05) increased from 4 dpi and those levels were kept until 7 dpi post both Eimeria infections (E. maxima and E. tenella). More importantly, the daily changes in the 3-1E levels in different samples from E. maxima- and E. tenella-infected chickens were effectively monitored with this new antigen-capture ELISA. Therefore, this new immunoassay is a sensitive diagnostic tool to monitor coccidiosis in a large field population in the commercial poultry farms before clinical symptoms develop using serum, feces, and gut samples during the entire period of infection cycle starting from 1 d after infection.

Collagen adhesin protein and necrotic enteritis B-like toxin as biomarkers for early diagnosis of necrotic enteritis in commercial broiler chickens

Mouse monoclonal antibodies (mAbs) reactive with Clostridium perfringens collagen adhesin protein (CNA) and necrotic enteritis B-like toxin (NetB) were developed. The best capture/detection mAb pairs for CNA and NetB were selected based on their affinity and specificity to develop sandwich enzyme-linked immunosorbent assays (ELISAs) to detect CNA and NetB proteins, respectively, in jejunal digesta samples from commercial broiler farms in the United States. Prior to the analysis of samples from commercial broiler flocks, the specificity and sensitivity of the CNA and NetB ELISAs were validated using sera, jejunal digesta, and fecal samples from chickens coinfected with Eimeria maxima and CNA+/NetB+C. perfringens in an animal model of necrotic enteritis (NE). Subsequently, a total of 251 field samples were collected from 74 commercial poultry farms. Among these, 18 samples were from 6 broiler farms that used certified organics (CO), and 155 samples were from 42 farms with nonantibiotics (NA). In jejunal digesta samples, CNA levels ranged from 0.02 to 0.59 ng/mL and NetB levels ranged from 0.09 to 1.91 ng/mL. CNA and NetB levels showed a positive correlation with each other (Pearson correlation coefficient r = 0.772, P < 0.001). CNA and NetB levels in jejunal digesta were significantly decreased in CO farms compared with those from NA farms (P < 0.001). In conclusion, these new C. perfringens antigen-specific sandwich ELISAs offer a sensitive and specific means to detect C. perfringens CNA and NetB proteins as biomarkers of early NE occurrence in field samples from commercial broiler chickens.

Role of Clostridium perfringens Necrotic Enteritis B-like Toxin in Disease Pathogenesis

Necrotic enteritis (NE) is a devastating enteric disease caused by Clostridium perfringens type A/G that impacts the global poultry industry by compromising the performance, health, and welfare of chickens. Coccidiosis is a major contributing factor to NE. Although NE pathogenesis was believed to be facilitated by α-toxin, a chromosome-encoded phospholipase C enzyme, recent studies have indicated that NE B-like (NetB) toxin, a plasmid-encoded pore-forming heptameric protein, is the primary virulence factor. Since the discovery of NetB toxin, the occurrence of NetB⁺ C. perfringens strains has been increasingly reported in NE-afflicted poultry flocks globally. It is generally accepted that NetB toxin is the primary virulent factor in NE pathogenesis although scientific evidence is emerging that suggests other toxins contribute to NE. Because of the complex nature of the host-pathogen interaction in NE pathogenesis, the interaction of NetB with other potential virulent factors of C. perfringens needs better characterization. This short review will summarize the primary virulence factors involved in NE pathogenesis with an emphasis on NetB toxin, and a new detection method for large-scale field screening of NetB toxin in biological samples from NE-afflicted commercial broiler flocks.

A Rapid and Simple Assay Correlates In Vitro NetB Activity with Clostridium perfringens Pathogenicity in Chickens

Necrotic enteritis is an important enteric disease in poultry, caused by NetB-producing Clostridium (C.) perfringens strains. As no straight-forward method to assess the NetB activity of C. perfringens was available, we aimed to develop an easy, high-throughput method to measure the NetB activity produced by C. perfringens. First, the appearance of C. perfringens on different avian blood agar plates was assessed. Based on the size of the haemolysis surrounding the C. perfringens colonies, NetB-positive strains could phenotypically be discriminated from NetB-negative strains on both chicken and duck blood agar. Additionally, strains producing the consensus NetB protein induced more pronounced haemolysis on chicken blood agar as compared to the weak outer haemolysis induced by A168T NetB-variant-producing C. perfringens strains. Next, a 96-well plate-based haemolysis assay to screen NetB activity in the C. perfringens culture supernatants was developed. Using this assay, a positive correlation between the in vitro NetB activity and virulence of the C. perfringens strains was shown. The developed activity assay allows us to screen novel C. perfringens isolates for their in vitro NetB activity, which could give valuable information on their disease-inducing potential, or identify molecules and (bacterial) metabolites that affect NetB expression and activity.

Research Note: First report on the detection of necrotic enteritis (NE) B-like toxin in biological samples from NE-afflicted chickens using capture enzyme-linked immunosorbent assay

Necrotic enteritis (NE) is a devastating enteric disease caused by Clostridium perfringens type G. One of the pore-forming toxins, NE B-like (NetB) toxin, secreted by pathogenic C. perfringens type G, has been proposed to be the main virulent factor in NE pathogenesis. The present study aimed to detect the presence of NetB toxin in biological samples of NE-afflicted chickens using NetB-specific monoclonal-based enzyme-linked immunosorbent assay (ELISA). Biological samples, including serum, digesta, and fecal droppings, were obtained from three previous NE studies (designated as Trials 1 to 3). In Trials 1 and 2, broiler chicks were infected with Eimeria maxima strain 41A on day 1 and followed by the netB-positive C. perfringens on day 18. Serum samples were obtained at 20 d post-hatch (i.e., 2 d post C. perfringens infection). In addition, various samples, including serum, gut digesta, and fecal droppings, that had been collected 0, 6, 24, and 30 h post C. perfringens infection were obtained. In Trial 3, broiler chicks were indirectly infected with litter-contaminated E. maxima on d 14 and followed by netB-positive C. perfringens via drinking water on days 18, 19, and 20. Serum samples and fecal droppings were obtained 21 d post-hatch (i.e., 1 d post last C. perfringens infection). The results showed that NetB toxin was not detected in serum samples in Trials 1 and 3. No NetB toxin was detected in all samples obtained before C. perfringens infection in Trial 2. Low but detectable amounts of NetB toxin were found in the serum samples obtained 6 h post C. perfringens infection in Trial 2. While NetB toxin in digesta and fecal droppings was detected 6 h post C. perfringens infection, its level plateaued 24 and 30 h post C. perfringens infection. In Trial 3, NetB toxin was detected in fecal droppings from the NE group, and its concentration ranged from 2.9 to 3.1 ng/g of wet feces. In Trial 2, NE-specific lesions were not seen 0 and 6 h post C. perfringens infection but exhibited lesions were moderate to severe 24 h post infection, leading to a moderate association (r = +0.527) between NE lesions and NetB toxin in the gut digesta. This is the first study to use NetB-specific monoclonal-based capture ELISA to determine and report the presence of native NetB toxin in biological samples from NE-induced chickens.