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The detection of Salmonella in skimmed milk powder enrichments using conventional methods and immunomagnetic
D Dziadkowiec1, L P Mansfield, S J Forsythe
1Department of Life Sciences, Nottingham Trent University, UK.
Abstract:
Skimmed milk powders were spiked with one of three Salmonella serovars and incubated in buffered peptone water for 24 h. No false-negative results were obtained by immunomagnetic separation (IMS), compared to seven for selenite cysteine, one for Müller-Kauffmann tetrathionate and two for Rappaport-Vassiliadis enrichment broths. Salmonella virchow was detected and enumerated during the pre-enrichment incubation by IMS and indirect conductance techniques. The Salm. virchow cell number did not increase after 12 h incubation and remained at 3 x 10(6) cfu ml-1. IMS was able to capture Salm. virchow cells at cell numbers ca 50 ml-1 in the presence of a 1000 greater number of non-salmonella cells.
Insights
Immunomagnetic separation (IMS) offers a superior method for detecting Salmonella in skimmed milk, significantly reducing false-negative results compared to traditional enrichment broths. This technique enables accurate enumeration and detection even at low cell concentrations.
Area of Science:
- Food Microbiology
- Bacteriology
- Analytical Chemistry
Background:
- Accurate detection of Salmonella serovars in food products like skimmed milk is crucial for public health.
- Traditional enrichment broths can yield false-negative results, compromising food safety.
- Immunomagnetic separation (IMS) presents a promising alternative for sensitive pathogen detection.
Purpose of the Study:
- To evaluate the efficacy of immunomagnetic separation (IMS) for detecting Salmonella in spiked skimmed milk.
- To compare the performance of IMS against conventional enrichment broths (selenite cysteine, Müller-Kauffmann tetrathionate, Rappaport-Vassiliadis).
- To assess the ability of IMS to detect and enumerate Salmonella virchow during pre-enrichment.
Main Methods:
- Skimmed milk powder was artificially contaminated with three Salmonella serovars.
- Samples were incubated in buffered peptone water for 24 hours.
- Detection and enumeration were performed using IMS, indirect conductance, and conventional enrichment broths.
Main Results:
- Immunomagnetic separation (IMS) yielded no false-negative results, outperforming all tested enrichment broths.
- Seven false-negative results were observed with selenite cysteine broth.
- Salmonella virchow was successfully detected and enumerated using IMS and indirect conductance during pre-enrichment, even at low cell densities (approx. 50 cells/mL) amidst a high background of non-Salmonella cells.
Conclusions:
- IMS is a highly sensitive and specific method for the detection of Salmonella in skimmed milk.
- IMS significantly reduces the incidence of false-negative results compared to conventional enrichment methods.
- The study demonstrates the effectiveness of IMS for early detection and enumeration of Salmonella during food processing.