Comparison of an LPS-specific competitive ELISA with a motility enrichment culture method (MSRV) for detection of Salmonella typhimurium and S. enteritidis in chickens

A new colorimetric peptide nucleic acid-based assay for the specific detection of bacteria

AIM

Developments on synthetic molecules, such as peptide nucleic acid (PNA), make FISH procedures more robust for microbial identification. Fluorochromes use might hinder a broader implementation of PNA-FISH, but colorimetric applications are inexistent so far.

METHODS

A biotin-labeled eubacteria probe was used to develop a colorimetric PNA-in situ hybridization (ISH) assay. An enzymatic-conjugate, targeting biotin, was introduced. The procedure was optimized and evaluated regarding sensitivity, specificity and detection limit.

RESULTS

RESULTS have shown strong ISH signals. The method was specific, but permeabilization problems were observed for Gram-positive bacteria. Detection limit was 5 × 10(7) CFU/ml, limiting current applications to pre-enriched samples.

CONCLUSION

The PNA-ISH procedure described here is a simple alternative to other detection methods, and is also the base for the development of other PNA colorimetric systems.

Development of a highly sensitive bacteria detection assay using fluorescent pH-responsive polymeric micelles

The detection and control of bacteria is extremely important in the safety of food products and health systems. The conventional microbiological methods based on culture enrichment techniques and plating procedures are highly sensitive and selective for bacterial detection but are expensive, cumbersome and time-consuming. Here we report the development of a simple and sensitive bioassay to detect Escherichia coli (E. coli) bacteria by using self assembled pH-responsive polymeric micelles that have been bioconjugated to anti-E. coli (capturing agent). Poly(ethylene glycol-b-trimethylsilyl methacrylate), containing silicon moieties that can be cleaved under mildly acidic conditions, was synthesized and self-assembled into micelles, that were loaded with a fluorescent dye (1-methylpyrene). The polymer silicon protecting groups are used as a tool to remotely activate the dye release by means of pH. The high sensitivity of the newly developed bioassay, which is capable of detecting 15 bacteria per milliliter of solution, is due to an amplification effect generated by the optical signal of millions of fluorophores released from a single micelle upon attachment to a bacterium. Fluorescence probing involves the measurements of changes in the emission spectra, through the disappearance of the excimer band, which only occurs when the dye molecules are trapped within the polymeric micelles.

An Au/Si hetero-nanorod-based biosensor for Salmonella detection

We present a novel and effective food-borne bacteria detection method. A hetero-structured silicon/gold nanorod array fabricated by the glancing angle deposition method is functionalized with anti-Salmonella antibodies and organic dye molecules. Due to the high aspect ratio nature of the Si nanorods, dye molecules attached to the Si nanorods produce an enhanced fluorescence upon capture and detection of Salmonella. This bio-functional hetero-nanorod detection method has great potential in the food safety industry as well as in biomedical diagnostics.

Comparison of four different methods for Salmonella detection in fecal samples of porcine origin

Performances of four detection methods were evaluated for recovery of Salmonella spp. in naturally contaminated fecal specimens of porcine origin. The NMKL 71 method consisted of enrichment in Rappaport-Vassiliadis broth and plating on xylose-lysine-desoxycholate medium, whereas the SP-VG-M002 method relied on a Diasalm enrichment followed by streaking on xylose-lysine-tergitol 4 agar (XLT-4). The VIDAS SLM method was composed of double enrichment in Muller-Kauffmann tetrathionate broth and in M broths before processing in a VIDAS device. If the results were positive, the VIDAS ICS immunoenrichment was performed and the result transferred onto three different selective media. The VIDAS ICS protocol is an immunoconcentration step followed by plating on XLT-4. Seventy-eight samples were tested with all four methods simultaneously, leading to 34 positive samples with at least one method. For this assay, VIDAS SLM revealed 31 positive samples (91.2%), whereas the average positive percentage of the three other methods was 37.3% (P < 0.001). Two-paired comparisons with the VIDAS SLM method were also performed. McNemar values were systematically highly significant (P < 0.001). The proportion of agreement was significantly inferior (P < 0.05) for the comparison of VIDAS ICS and VIDAS SLM (68.7%) compared with the two other paired comparisons (average percentage, 81.5%). The conclusion reached by this trial is that VIDAS SLM significantly improves the recovery of Salmonella in naturally contaminated fecal specimens. For the paired-comparisons, NMKL 71 and SP-VG-M002 were comparable in terms of efficiency, whereas the VIDAS ICS protocol, as established by the manufacturer for food samples only, seemed less efficient than the other two.