Search

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 [ABSTRACT FROM AUTHOR]

Microfiltration of chicken extracts has the potential to significantly decrease the time required to detect Salmonella, as long as the extract can be efficiently filtered and the pathogenic microorganisms kept in a viable state during this process. We present conditions that enable microfiltration by adding endopeptidase from Bacillus amyloliquefaciens to chicken extracts or chicken rinse, prior to microfiltration with fluid flow on both retentate and permeate sides of 0.2 μm cutoff polysulfone and polyethersulfone hollow fiber membranes. After treatment with this protease, the distribution of micron, submicron, and nanometer particles in chicken extracts changes so that the size of the remaining particles corresponds to 0.4-1 μm. Together with alteration of dissolved proteins, this change helps to explain how membrane fouling might be minimized because the potential foulants are significantly smaller or larger than the membrane pore size. At the same time, we found that the presence of protein protects Salmonella from protease action, thus maintaining cell viability. Concentration and recovery of 1-10 CFU Salmonella/mL from 400 mL chicken rinse is possible in less than 4 h, with the microfiltration step requiring less than 25 min at fluxes of 0.028-0.32 mL/cm2 min. The entire procedure--from sample processing to detection by polymerase chain reaction--is completed in 8 h. [ABSTRACT FROM AUTHOR]