Protein particulate retention and microorganism recovery for rapid detection of Salmonella

The rapid detection of Salmonella in ground meat requires that living microorganisms be brought to levels detectable by PCR, immunoassays, or similar techniques within 8 h. Previously, we employed microfiltration using hollow fiber membranes to rapidly process and concentrate viable bacteria in food extracts through a combination of enzyme treatment and prefiltration in order to prevent blockage or fouling of the hollow fiber membranes. However, scanning electron microscopy and particle size analysis of enzyme hydrolysates showed that enzyme treatment followed by filtration caused submicron particles to form and be trapped within the prefiltration media, which in turn, retained about 80% of the bacteria. Filtering prior to enzyme treatment resulted in formation of a filter cake consisting of protein particles retained on the surface of the filter, while facilitating passage of the much smaller microorganisms through the filter, separating them from particulates. Subsequent enzyme treatment of the filtrate resulted in an extract that was microfiltered in less than an hour, while concentrating viable microorganisms in the extract by 500×. An inoculum of Salmonella enterica cells into turkey burger containing of 1-20 CFU/mL, consisting of spiked cells plus cells already present in the turkey burger sample, was rapidly brought to levels detectable by conventional PCR and BAX^® PCR assays. The entire procedure from sample processing to detection of Salmonella enterica was achieved in less than 8 h. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:687-695, 2017.