Immunocapture and real-time PCR to detect Campylobacter spp

Sensitive detection of Campylobacter jejuni using one-step strategy based on functional nanospheres of immunomagnetic capture and quantum dots

Campylobacter jejuni has emerged as the most common bacterial foodborne illness in the developed world. Here, we demonstrate a convenient one-step strategy for detecting C. jejuni. Immunomagnetic nanospheres (IMNS) and immunofluorescent nanospheres (IFNS, quantum dots) were used for the simultaneous, sensitive capture and recognition of C. jejuni. After magnetic separation with the IMNS, detection of C. jejuni was achieved with fluorescence measurement of the IFNS in the sandwich complexes (IMNS-bacteria-IFNS). The limit of detection of this assay was 10³ CFU/mL, and the linear range was from 10⁵ to 10⁷ CFU/mL (R² = 0.9994). When compared with a conventional two-step detection strategy, in which C. jejuni was first captured with the IMNS and then detected using the IFNS, this one-step detection strategy enhance sensitivity and save time. This suggested that the developed method has the potential for use as an alternative to the standard method for food quality assurance, as it provides rapid detection of C. jejuni in foodstuffs and the environment.

Detection of Campylobacter DNA using magnetic nanoparticles coupled with PCR and a colorimetric end-point system

Campylobacter is an important food-borne pathogen causing acute gastroenteritis worldwide. Magnetic nanoparticle-based PCR coupled with streptavidin-horseradish peroxidase and a substrate was used for colorimetric detection. Forward primers conjugated to magnetic nanoparticles facilitated separation and concentration of Campylobacter DNA in a sample matrix. After PCR, a green color developed and was observed using the unaided eye, or detected using a spectrophotometer. High specificity and sensitivity of the 100 fg DNA/PCR reaction were achieved in pure culture experiments. The technique was applied for detection of Campylobacter on naturally contaminated chicken skin. All positive results were in agreement with results achieved using a conventional culture method. The magnetic nanoparticle-PCR-enzyme linked gene assay was practical and useful for detection of Campylobacter in complex matrices with PCR-interfering substances.

Improvement of capture efficacy of immunomagnetic beads forCampylobacter jejuniusing reagents that alter its motility

Previous studies using the immunomagnetic beads separation (IMS) technique have shown high detection limits of live campylobacters but low detection limits of formalin-killed campylobacters. The present study investigated if the addition of various concentrations of reagents that alter the motility of live Campylobacter jejuni could enhance the recovery of the organisms by IMS. The addition of 5% glycerol, 0.001% formalin, 10% polyethylene glycol, or 0.001% agarose in a buffer slowed down the movement of C. jejuni and increased the recovery of live C. jejuni, using beads coated with specific monoclonal antibodies (mAbs). The highest recovery yielded was 5.2- ± 3.3-fold with 5% glycerol at 105colony-forming units (CFU)·mL−1. The addition of 5% glycerol also improved isolation at lower concentrations of C. jejuni (102to 104CFU·mL−1) in buffer. The recovery by IMS of C. jejuni killed by 1% formalin was increased up to as high as 17-fold compared with the recovery of live organisms, as detected using a real-time polymerase chain reaction assay. The reagents investigated did not enhance the immunological reactivity of the mAbs to this organism. These results indicate that the addition of several reagents enhanced the capture of C. jejuni by IMS, which could be partially due to the slowing down of the movement or the altering of the motility of C. jejuni and to the increasing of the contact time between C. jejuni and immunomagnetic beads.

Dual enlargement of gold nanoparticles: from mechanism to scanometric detection of pathogenic bacteria

A mechanism of dual enlargement of gold nanoparticles (AuNPs) comprising two steps is described. In the first step, the AuNPs are enlarged by depositing Au atoms on their crystalline faces. In this process, the particles are not only enlarged but they are also observed to multiply: new Au nuclei are formed by the budding and division of the enlarged particles. In the second step, a silver enhancement is subsequently performed by the deposition of silver atoms on the enlarged and newly formed AuNPs to generate bimetallic Au@Ag core-shell structures. The dual nanocatalysis greatly enhances the electron density of the nanostructures, leading to a stronger intensity for colorimetric discrimination as well as better sensitivity for quantitative measurement. Based on this, a simple scanometric assay for the on-slide detection of the food-born pathogen Campylobacter jejuni is developed. After capturing the target bacteria, gold-tagged immunoprobes are added to create a signal on a solid substrate. The signal is then amplified by the dual enlargement process, resulting in a strong color intensity that can easily be recognized by the unaided eye, or measured by an inexpensive flatbed scanner. In this paper, dual nanocatalysis is reported for the first time. It provides a valuable mechanistic insight into the development of a simple and cost-effective detection format.

Rapid quantification of viable Campylobacter bacteria on chicken carcasses, using real-time PCR and propidium monoazide treatment, as a tool for quantitative risk assessment

A number of intervention strategies against Campylobacter-contaminated poultry focus on postslaughter reduction of the number of cells, emphasizing the need for rapid and reliable quantitative detection of only viable Campylobacter bacteria. We present a new and rapid quantitative approach to the enumeration of food-borne Campylobacter bacteria that combines real-time quantitative PCR (Q-PCR) with simple propidium monoazide (PMA) sample treatment. In less than 3 h, this method generates a signal from only viable and viable but nonculturable (VBNC) Campylobacter bacteria with an intact membrane. The method's performance was evaluated by assessing the contributions to variability by individual chicken carcass rinse matrices, species of Campylobacter, and differences in efficiency of DNA extraction with differing cell inputs. The method was compared with culture-based enumeration on 50 naturally infected chickens. The cell contents correlated with cycle threshold (C(T)) values (R(2) = 0.993), with a quantification range of 1 x 10(2) to 1 x 10(7) CFU/ml. The correlation between the Campylobacter counts obtained by PMA-PCR and culture on naturally contaminated chickens was high (R(2) = 0.844). The amplification efficiency of the Q-PCR method was not affected by the chicken rinse matrix or by the species of Campylobacter. No Q-PCR signals were obtained from artificially inoculated chicken rinse when PMA sample treatment was applied. In conclusion, this study presents a rapid tool for producing reliable quantitative data on viable Campylobacter bacteria in chicken carcass rinse. The proposed method does not detect DNA from dead Campylobacter bacteria but recognizes the infectious potential of the VBNC state and is thereby able to assess the effect of control strategies and provide trustworthy data for risk assessment.