Comparison of Enrichment Broths for the Recovery of Healthy and Heat-injured Salmonella Typhimurium on Duck Wing

Introduction: Some salmonellosis have been reported by consumption of duck meat, a widely consumed poultry in Asian countries. In general, these pathogens in food matrix are present in low concentration and sub-lethally injured due to the harsh processing conditions, which may cause false negative results if no appropriate enrichment was applied.

Purpose: This study compared available enrichment broths to find out a better broth to recover the healthy and heat-injured Salmonella Typhimurium with low concentrations on duck wing.

Methods: Healthy or heat-injured S. Typhimurium was inoculated at the level of 10², 10¹ or 10⁰ CFU/25g on duck wing. Five non-selective enrichment broths, tryptone soy broth (TSB), lactose broth (LB), buffered peptone water (BPW), nutrient broth (NB) and universal pre-enrichment broth (UPB), and four selective enrichment broths, ONE broth-Salmonella (OB), selenite broth (SB), Salmonella AD media (AD), and MP media (MP) were evaluated in this study. Four growth parameters, LPD (lag phase duration), MGR (maximum growth rate), DT (doubling time), and MPD (maximum population density), from the growth model using DMfit were calculated. Mean values were compared using ANOVA. 

Results: Most of enrichment broths recovered S. Typhimurium by more than 6.0 log CFU/ml. Among broths, Salmonella in AD, MP and OB had significantly (P < 0.05) higher MGR (0.9-1.0/h) and lower DT (0.7-0.8 h). BPW, AD, MP and OB recovered healthy and 50%-injured cells at low inoculum levels by more than 6.0 log CFU/ml and OB had the highest level (7.62 and 7.92 log CFU/ml) of Salmonella cells after 24-h incubation. However, the 85%-injured cells were only recovered in OB by more than 7.0 log CFU/ml.

Significance: This study suggests that OB may be a suitable enrichment broth for the Salmonella detection to avoid false negative results, thereby ensuring the safety of duck meat.