Predictive Microbiology Approach for Enumeration of Salmonella on Chicken Parts during Pre-enrichment

Introduction:  A data gap identified in risk assessments for Salmonella and chicken is lack of quantitative data.  Enumeration of Salmonella on chicken parts is difficult because Salmonella are often present in low numbers.  However, during the pre-enrichment phase of Salmonella isolation from chicken parts there is a mathematical relationship between the initial number of Salmonella on the chicken part and the number of Salmonellain the pre-enrichment broth at early times of pre-enrichment.

Purpose:  Therefore, the current study was undertaken to develop a predictive microbiology approach for enumerating Salmonella on chicken parts during pre-enrichment.

Methods:  A sterile cutting board and knife were used to partition a whole chicken into two wings, two breasts, two drumsticks and two thighs.  A sterile, cooked chicken breast was then cut into two equal-sized portions using the cutting board and knife used to partition the whole raw chicken; this was done to study transfer of Salmonella from raw chicken to cooked chicken during meal preparation.  Chicken parts were pre-enriched in 400 ml of buffered peptone water (BPW) for 6 h at 42°C and 80 rpm.  For predictive model development, chicken parts were inoculated with 0.36 to 4.86 logs of Salmonella.  At 6 h of incubation, the concentration of Salmonella in the BPW pre-enrichment was determined by spiral plating onto XLT4 agar media.  A two-phase linear model was used to model the concentration of Salmonella in BPW as a function of the log number of Salmonellainoculated.

Results:  All standard curves had high goodness-of-fit (R² from 0.92 to 0.99) to the two-phase linear model regardless of the serotype (n = 4) of Salmonella used.  Prevalence of Salmonellaamong chicken parts was 2.84% (5/176).  The positive chicken parts were thigh from chicken #4, which was contaminated with 3 cells of serotype Kentucky, and both wings, one thigh and one cooked breast portion from chicken #15, which were all contaminated with 1 cell of serotype 8,20:-:z6.

Significance:  These results indicate that a predictive microbiology approach can be used to enumerate low numbers of Salmonella on chicken parts during pre-enrichment.  However, because of the low prevalence of Salmonella on the chicken parts examined it was not possible, at this time, to fill the data gap for enumeration data identified in recent risk assessments for Salmonella and chicken.