Optimization of Enrichment Broth for the Detection of Salmonella in Spices (Garlic, Onion, Cinnamon, Chili Pepper Powders) and Tea

Introduction: Recent studies have reported that as much as 7% of imported spices are contaminated with Salmonella. Detection of Salmonella in contaminated spice samples is often problematic due to the presence of inhibitory compounds in the spices which hinder enrichment of Salmonella to detectable levels. There is a great need for robust enrichment methods that allow for sensitive detection of Salmonella in spices.

Purpose: To validate enrichment protocols for the growth of Salmonella in spices, and its downstream detection using conventional PCR, within 24 h.

Methods: Twenty-five (25) g of the respective spice (garlic powder, onion powder, chili peppers, cinnamon, and green tea) was mixed with double strength Buffered Peptone Water supplemented with L-cysteine (30 mmol/L) and spiked with Salmonella enterica Typhimurium to a final concentration of 20 CFU/25 g. Sample to broth ratios varied from 1:9 (garlic powder, chili peppers and tea), 1:50 (onion powder) to 1:100 (cinnamon). After 24 h of growth at 37°C, 5 ml of the mixture was filtered through cheesecloth and 1 ml of the filtrate was used for DNA extraction. The Hil-A gene was amplified by conventional PCR as an indicator of pathogen presence.  Amplicons were visualized by gel electrophoresis.

Results: After 24 h of incubation, more than 1.0 x 10⁵ CFU/ml of Salmonella was recovered for each spice studied. The pH value of each enrichment varied but remained above 5.25. Addition of cysteine to the broth allowed the recovery and growth of Salmonella in garlic powder, and had no influence on Salmonella growth in other spices, as evidenced by a PCR amplicon in all reactions.

Significance: Detection of Salmonella was possible within 24 h following incubation in 2x BPW+cysteine. This work could allow a more rapid, robust, and sensitive detection method for Salmonella in spices, based on a single enrichment step followed by RT-PCR.