In a recent study, research team Sarjit & Dykes (2015) evaluated the efficacy of two antimicrobials, trisodium phosphate (TSP) and sodium hypochlorite (SH), to reduce foodborne pathogens Campylobacter and Salmonella in duck meat.1 While antimicrobial activity in a chicken matrix is well-studied, duck meat has received little attention despite its growing popularity in some regions and its implication in outbreaks of foodborne illness.
To do this, the team composed two bacteria cocktails using six strains each of Campylobacter (C. jejuni and C. coli) and Salmonella (S. Enteritidis, S. Typhimurium, and S. enterica subsp. arizonae). They grew the first pathogen on Campylobacter blood-free selective agar or in Mueller-Hinton broth using the Campygen Campylobacter System in AnaeroJars and the second on xylose lysine deoxycholate agar or in tryptone soya broth (all Thermo Scientific). They used these to inoculate both duck and chicken meat at two dilution levels: ~104 and ~108 cfu/ml.
The team also exposed the meat samples to three concentrations each of TSP (8, 10 and 12% (w/v), pH 11.5) or SH (40, 50 and 60 ppm, pH 5.5) in two treatment formats. In separate substudies, they used a pre-inoculation treatment to model cross contamination by pathogens after antimicrobial application and a post-inoculation treatment to examine how the poultry surfaces impact antimicrobial activity against bacteria already adhered to the meat products.
The researchers used the thin agar layer method for enumeration, relying on Campylobacter blood-free selective agar and Mueller-Hinton agar for Campylobacter counts and xylose deoxycholate agar and tryptone soya agar for Salmonella counts. They note that this is the first known application of this technique for Campylobacter enumeration.
Sarjit & Dykes report that all tested concentrations of TSP reduced both Campylobacter (~1.2–6.4 log cfu/cm2) and Salmonella (~0.4–6.6 log cfu/cm2). Specific to duck meat, they found that Campylobacter numbers fell below the limit of detection (LOD) at higher concentrations (10 and 12% post-inoculation treatments at both inoculum levels, 12% pre-inoculation treatment at 104 cfu/ml inoculum). Salmonella numbers hit below the LOD at all but one concentration (8% pre-inoculation treatment at 108 cfu/ml inoculum). For chicken meat, the counts for both pathogens only fell below the LOD at a high concentration of TSP (12% at 104 cfu/ml inoculum). The team posits that differences in the composition of duck versus chicken meat (i.e. duck meat contains less protein and fewer crevices in the skin) may explain this differential efficacy.
On the other hand, only some tested concentrations of SH reduced Campylobacter and Salmonella (~0.2–1.5 log cfu/cm2) in chicken and duck meat. None of the treatments dropped the numbers below the LOD. While higher concentrations of SH could be more effective, they may affect the taste and appearance of the poultry product, rendering them unsuitable.
Overall, Sarjit & Dykes offer TSP as the more effective antimicrobial choice for applications involving Campylobacter and Salmonella in poultry matrices. They note its particular efficacy for addressing foodborne pathogens in duck meat products at 8 to 12% concentrations.
1 Sarjit, A. and Dykes, G.A. (2015) ‘Trisodium phosphate and sodium hypochlorite are more effective as antimicrobials against Campylobacter and Salmonella on duck as compared to chicken meat.’ International Journal of Food Microbiology, 203: 63–69.