Behaviour of co-inoculated pathogenic and spoilage bacteria on poultry following several decontamination treatments

The potential of chemical decontaminants to cause harmful effects on human health is among the causes of the rejection of antimicrobial treatments for removing surface contamination from poultry carcasses in the European Union. This study was undertaken to determine whether decontaminants might give a competitive advantage to pathogenic bacteria on poultry and involve a potential risk to consumer. A total of 144 chicken legs were co-inoculated with similar concentrations of pathogenic bacteria (Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica serotype Enteritidis or Escherichia coli) and spoilage bacteria (Brochothrix thermosphacta or Pseudomonas fluorescens). Samples were dipped for 15 min in solutions (w/v) of trisodium phosphate (12%; TSP), acidified sodium chlorite (1200 ppm; ASC), citric acid (2%; CA), peroxyacids (220 ppm; PA) or chlorine dioxide (50 ppm; CD), or were left untreated (control). Microbiological analyses were carried out on day 0 and every 24 h until day 7 of storage (at 10 ± 1 °C). The modified Gompertz equation was used as the primary model to fit observed data. TSP, ASC and CA were effective in extending the lag phase (L, ranging from 1.47 ± 1.34 days to 4.06 ± 1.16 days) and in decreasing the concentration of bacteria during the stationary phase (D, ranging from 2.46 ± 0.51 log10 cfu/cm2 to 8.64 ± 0.53 log10 cfu/cm2), relative to the control samples (L values ranging from 0.59 ± 0.38 days and 2.52 ± 2.28 days, and D values ranging from 6.32 ± 0.89 log10 cfu/cm2 to 9.39 ± 0.39 log10 cfu/cm2, respectively). Both on untreated and on most decontaminated samples the overgrowth of spoilage bacteria among the species tested was observed throughout storage, suggesting that spoilage would occur prior to any noteworthy increase in the levels of pathogenic microorganisms. However, L. monocytogenes counts similar to, or higher than, those for spoilage bacteria were observed on samples treated with TSP, ASC or CA, suggesting that these treatments might pose a danger to consumers. However, these results derive from laboratory-based experiments testing artificially-inoculated bacteria. Further investigations of the natural micro-biota of poultry carcasses would be appropriate in order to substantiate these findings.