Evaluation of the BAX Gel and Fluorometric Systems for the Detection of Foodborne Salmonella

Abstract

The present study compared the sensitivity of the BAX automated fluorometric and the recently discontinued BAX gel electrophoresis systems with a standard culture method to detect Salmonella in 333 high-moisture and 171 low-moisture foods. A total of 95 naturally contaminated foods, including 63 high-moisture and 32 low-moisture foods, were detected by the standard culture method. No contaminated samples were identified exclusively by the BAX systems. By means of the analytical protocol stipulated by the manufacturer, the BAX fluorometric system detected 36 (57.1%) and 29 (90.6%) of the contaminated high- and low-moisture foods, respectively. Similar results were obtained with the BAX gel electrophoresis system, which identified 40 (63.5%) and 26 (81.3%) of the contaminated high- and low-moisture foods. The rate of false-positive reactions with the BAX systems was low. Our results indicate that the low sensitivity of the BAX systems with high-moisture foods, notably raw meats and poultry products, was serovar-independent. The high levels of background microflora that commonly occur in raw meat and on fresh fruit and vegetable products, and the high successive dilutions of test materials for PCR analysis, suggestively undermined the sensitivity of the gel and the fluorometric BAX assays. The potential benefits of immunomagnetic separation of Salmonella in preenrichment cultures, of selective broth enrichment following preenrichment to markedly reduce levels of background microflora in PCR test materials, and the use of larger portions of test materials in PCR analyses should be investigated.

Rapid detection, characterization, and enumeration of foodborne pathogens

“…Although many commercial PCR kits include easy‐to‐use sample treatments protocols that (apparently) work, independent studies show a remarkably low diagnostic sensitivity when testing naturally contaminated samples (D’Aoust et al., 2007).…”

Factors affecting cell population density during enrichment and subsequent molecular detection of Salmonella enterica and Escherichia coli O157:H7 on lettuce contaminated during field production

“…Quantitative real time PCR (qRTPCR), provides great target specificity, particularly among those that utilize target-specific probes. However independent studies have demonstrated that the accuracy of PCR based methods, in general, might be challenged when testing naturally contaminated samples as their sensitivity can be compromised by intrinsic or extrinsic factors (D'Aoust et al, 2007;Hoorfar, 2011). These challenges involve the inability of differentiating viable from dead cells, without significant additional sample processing, or those cells that can be in a viable but not culturable physiological condition (VBNC) (Moyne, Harris, & Marco, 2013).…”

Salmonella in food surveillance: PCR, immunoassays, and other rapid detection and quantification methods

“…Reports on the comparison of performance between the BAX system and other analytical methods, for example, the immunoassay-based and the standard reference culture methods, for Salmonella detection are also available. The BAX system was found to have very low false-positive and false-negative rate and generated results comparable with those of the standard culture methods, ISO 6579, HPA F13, and MFHPB-20 (Cheung et al, 2007;D'Aoust & Purvis, 1998;D'Aoust et al, 2007;Tomazelli et al, 2008). Furthermore, for raw samples with higher background flora inoculated with Salmonella Typhi, positive results could be obtained with the BAX system, whereas false negatives were generated by the immunoassay-based Tecra Unique™ Salmonella test and the standard culture method (Cheung et al, 2007).…”