Influence of poultry carcass skin sample site on the effectiveness of trisodium phosphate against Listeria monocytogenes

Synergistic Antibacterial Mechanism of Mannosylerythritol Lipid-A and Lactic Acid on Listeria monocytogenes Based on Transcriptomic Analysis

Mannosylerythritol lipids-A (MEL-A) is a novel biosurfactant with multiple biological effects. The synergistic antibacterial activity and mechanism of MEL-A and lactic acid (LA) against Listeria monocytogenes were investigated. The synergistic effect resulted in a significant increase in the antibacterial rate compared to LA treatment alone. Genome-wide transcriptomic analysis was applied to deeply investigate the synergistic antibacterial mechanism. Gene Ontology (GO) enrichment analysis showed that the synergy between MEL-A and LA affected many potential cellular responses, including the sugar phosphotransferase system, carbohydrate transport, and ribosomes. KEGG enrichment analysis showed that the PTS system and ribosome-related pathways were significantly enriched. In addition, synergistic treatment affected locomotion and membrane-related cellular responses in GO enrichment analysis and carbohydrate metabolism and amino acid metabolism pathways in KEGG enrichment analysis compared to LA treatment alone. The accuracy of the transcriptome analysis results was verified by qPCR (R² = 0.9903). This study will provide new insights for the prevention and control of L. monocytogenes.

Effect of lactic acid spray on microbial and quality parameters of buffalo meat

We evaluated the effect of lactic acid spray on micro-flora, instrumental color, shelf-life and sensory attributes of buffalo meat displayed under Modified Atmosphere Packaging. Buffalo calf carcasses (n = 12) were sliced into equal sagittal halves, n = 6 halves were randomly assigned to each of four treatments i.e. 2% LA, 4% LA, 6% LA and control. Afterwards, sirloin and tenderloin were vacuum packed and aged for 7 days. Later, steaks were packed in high-oxygen MAP. Microbial load, instrumental color, shelf-life and sensory attributes were evaluated at different days. Aerobic plate count of sprayed carcass and steaks was significantly lower than un-sprayed control. Similarly, though non-significant, redness and chroma value of sprayed carcass meat was found better than un-sprayed control. Lactic acid sprayed meat did not differ in terms of sensory attributes. It is concluded that spraying buffalo carcasses with 2-4% lactic acid after slaughter not only enhances microbial quality but it may also improve its instrumental color.

Effect of the temperature of the dipping solution on the antimicrobial effectiveness of various chemical decontaminants against pathogenic and spoilage bacteria on poultry

The influence of the temperature of the dipping solution on the antimicrobial effectiveness of several chemical poultry decontaminants was assessed. A total of 765 poultry legs were inoculated with gram-positive bacteria (Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, or Brochothrix thermosphacta) or gram-negative bacteria (Salmonella enterica serotype Enteritidis, Escherichia coli, Yersinia enterocolitica, or Pseudomonas fluorescens). Samples were dipped for 15 min in solutions (wt/vol) of trisodium phosphate (12%), acidified sodium chlorite (1,200 ppm), citric acid (2%), peroxyacids (220 ppm), chlorine dioxide (50 ppm), or tap water or were left untreated (control). The temperatures of the dipping solutions were 4, 20, or 50°C. Microbiological analyses and pH determinations were carried out after 0, 1, 3, and 5 days of storage at 4°C. In comparison with the control samples, all chemical solutions were effective for reducing microbial loads. The temperature of treatment affected the microbial reductions caused by all chemicals (P < 0.001). The lowest average bacterial reductions caused by trisodium phosphate, acidified sodium chlorite, citric acid, and peroxyacids were observed at 4°C, all sampling days and microbial groups being considered simultaneously. The highest and the lowest effectiveness for chlorine dioxide were observed at 4 and 50°C, respectively. These results may be of use to meat processors for selecting the best conditions for decontamination treatments and may help the European Regulatory Authorities make their decisions for authorization of poultry decontamination treatments.

Decontamination treatments can increase the prevalence of resistance to antibiotics of Escherichia coli naturally present on poultry

The main objective of this study was to determine the ability of various decontaminants to increase the prevalence of resistance to antibiotics in Escherichia coli populations on poultry. Chicken legs were dipped for 15 min into aqueous solutions (wt/vol) of trisodium phosphate (TSP; 12%), acidified sodium chlorite (ASC; 1200 ppm), ascorbic acid (AA; 2%) or citric acid (CA; 2%), or tap water (control). Samples were analyzed immediately after treatment (day 0) and after five days of storage at 7 ± 1 °C. A total of 250 E. coli isolates (50 from each group of samples; 25 on day 0 and 25 on day 5) were tested against twelve antibiotics of clinical significance by means of a standard disc-diffusion technique. A high prevalence of resistance to antibiotics was observed for E. coli strains from control samples, with three (6.0%) isolates sensitive, three (6.0%) resistant to one antibiotic and 44 (88.0%) isolates resistant to two or more antibiotics. Isolates from control samples had a lower prevalence of resistance than those from treated samples to ampicillin-sulbactam (P < 0.01, samples treated with TSP), amoxicillin-clavulanic acid (P < 0.001, ASC, AA and CA), cephotaxime (P < 0.05, TSP), trimethoprim-sulphamethoxazole (P < 0.05, AA; P < 0.01, CA), tetracycline (P < 0.01, CA), ciprofloxacin (P < 0.001, ASC; P < 0.05, AA; P < 0.01, CA) and nitrofurantoin (P < 0.01, TSP). These results suggest that the chemical decontaminants tested could favor the emergence, selection and/or proliferation of antibiotic-resistant strains in microbial populations on poultry meat.

Decontamination of chicken skin surfaces inoculated with Listeria innocua, Salmonella enteritidis and Campylobacter jejuni by contact with a concentrated lactic acid solution

1. The aim was to establish how poultry skin could be efficiently decontaminated without changing its organoleptic properties. 2. Chicken skins were surface inoculated with Listeria innocua and treated with different acid solutions (2 and 10% lactic acid for 1 and 30 min). Surviving bacteria were enumerated immediately after treatment and after 7 d storage at 4 degrees C. 3. Reductions of up to 2.6 log were reached immediately after treatment. The treatment effect persisted for 7 d storage, when the reduction exceeded 4.59 log for the strongest treatment. 4. Residual levels of lactic acid were not significantly higher than in untreated controls, except for the strongest treatment. A tasting panel found no significant difference between controls and samples. 5. After the initial results, an apparently optimal treatment (5% lactic acid for 1 min) was applied on chicken skins' surface inoculated with a mix of Listeria innocua, Salmonella enteritidis and Campylobacter jejuni. Treatment efficacy was assessed immediately after treatment and after 1, 4 and 7 d storage. 6. This treatment seems to be very promising from a food processing standpoint, being fast and allowing decimal reductions of 2.00 log for Listeria innocua and 2.38 log for Salmonella enteritidis after 7 d storage, neither significantly increasing skin lactic acid nor causing any organoleptic modifications to the product. The effect of the treatment is significant after one day storage for Listeria innocua and after 4 d storage for Salmonella enteritidis.

Chemical decontamination of Campylobacter jejuni on chicken skin and meat

This study evaluated the effectiveness of 11 chemical compounds to reduce Campylobacter jejuni on chicken skin and meat samples dipped in chemical solutions. Treatment of skin samples for 1 min using tartaric acid (2%) and caprylic acid sodium salt (5%) caused reductions of C. jejuni NCTC11168, which were not significantly different from the reduction obtained by sterile water (0.95 log). Statistically larger reductions (1.57 to 3.81 log) were caused by formic acid (2%), lactic acid (2.5%), trisodium phosphate (10%), capric acid sodium salt (5%), grapefruit seed extract (1.6%), and chlorhexidine diacetate salt hydrate (1%). The most effective compounds were cetylpyridinium chloride (0.5%) and benzalkonium chloride (1%) (>4.2 log). However, when these treated samples were stored for 24 h at 5 degrees C, cetylpyridinium chloride, benzalkonium chloride, and grapefruit seed extract were less effective, indicating that some cells may recover after a 1-min treatment with these chemicals. An increase in treatment time to 15 min resulted in higher effectiveness of trisodium phosphate and formic acid. Interestingly, when reduction of the C. jejuni population was compared on chicken skin and meat, sterile water and lactic acid caused considerably larger reductions on skin than on meat, whereas the opposite was seen for caprylic acid sodium salt. In conclusion, this study has identified chemicals with substantial reduction effects on C. jejuni. The analysis has further emphasized that treatment time and food matrix affect the outcome in an unpredictable manner and, therefore, detailed studies are needed to evaluate the reduction effectiveness of chemicals.

Effect of various chemical decontamination treatments on natural microflora and sensory characteristics of poultry

Regulation (EC) No. 853/2004 of the European Parliament and of the Council provides a legal basis permitting the use of antimicrobial treatments to remove surface contamination from poultry. This paper reports the results of research into the effects on natural microflora, pH, and sensorial characteristics achieved by dipping chicken legs (15 min, 18+/-1 degrees C) into solutions (wt/vol) of 12% trisodium phosphate (TSP), 1200 ppm acidified sodium chlorite (ASC), 2% citric acid (CA), 220 ppm peroxyacids (Inspexx 100; PA), and water. Samples were collected immediately after evisceration, subjected to the treatments listed or left untreated (control) and tested after 0, 1, 3 and 5 days of storage (3 degrees C+/-1 degrees C). For most microbial groups similar counts were observed on water-dipped and on untreated legs. All the chemical compounds were effective in reducing microbial populations throughout storage, with TSP, ASC and CA showing the strongest antimicrobial activity. The average reductions (mean+/-standard deviation) relative to untreated samples caused by chemical treatments when considering simultaneously all storage days ranged (log(10) cfu/g skin) from 0.53+/-0.83 (PA) to 1.98+/-0.62 (TSP) for mesophilic aerobic counts, from 0.11+/-0.89 (PA) to 1.27+/-1.02 (CA) (psychrotrophs), from 1.34+/-1.40 (PA) to 2.15+/-1.20 (CA) (Enterobacteriaceae), from 1.18+/-1.24 (PA) to 1.98+/-1.16 (CA) (coliforms), from 0.66+/-0.99 (PA) to 1.86+/-1.80 (TSP) (Micrococcaceae), from 0.54+/-0.74 (TSP) to 2.17+/-1.37 (CA) (enterococci), from 0.72+/-0.66 (TSP) to 2.08+/-1.60 (CA) (Brochothrix thermosphacta), from 0.78+/-1.02 (PA) to 1.99+/-0.96 (TSP) (pseudomonads), from 0.21+/-0.61 (PA) to 1.23+/-0.60 (TSP) (lactic acid bacteria), and from 1.14+/-0.89 (PA) to 1.45+/-0.61 (ASC) (moulds and yeasts). The microbial reductions throughout storage increased, decreased, or did not vary, in accordance with microbial group and chemical involved. Similar pH values were observed for untreated samples and for those dipped in PA and water on all sampling days. ASC-treated samples showed a lower pH than controls to day 1. TSP-treated legs exhibited the highest pH values and CA-treated ones the lowest, throughout storage. Hedonic evaluation (nine-point structured scale, untrained panellists) showed similar colour, smell and overall acceptability scores for dipped and untreated samples on day 0 and day 1. From day 3 sensorial attributes scored lower for untreated, PA- and water-dipped legs, as compared to legs treated with TSP, ASC and CA. Only for these three groups of samples were average scores higher than 6 (shelf-life limit value) observed by the end of storage. Results from the present study suggest that the treatments tested improve the microbial quality of chicken without adverse sensorial effects.

Effectiveness of trisodium phosphate treatment against pathogenic and spoilage bacteria on poultry during refrigerated storage

To determine the efficacy of trisodium phosphate (TSP) against pathogenic and spoilage bacteria on poultry and to assess the influence of the bacterial combination of inoculum on TSP effect, chicken legs were coinoculated with similar concentrations of a pathogenic (Salmonella enterica ser. Enteritidis or Listeria monocytogenes) and a spoilage (Pseudomonas fluorescens or Brochothrix thermosphacta) bacteria. Samples were dipped in TSP (12%, 15 min) or were not treated (control). Microbiological analysis and pH determinations were carried out at 0, 1, 3, and 5 days of storage (3 degrees C). Significant bacterial reductions (marked in gram-negative species) were observed on TSP-treated samples throughout refrigerated storage. Inoculum composition scarcely influenced the TSP effect against gram-positive bacteria. However, greater reductions were observed on gram-negative bacteria (Salmonella Enteritidis and P. fluorescens) when samples were coinoculated with B. thermosphacta and L. monocytogenes, respectively. Values of pH were higher in TSP-treated than in control samples at all sampling times. The combination of bacteria in inocula did not have a significant influence on pH values.

Effectiveness of trisodium phosphate against Listeria monocytogenes on excised and nonexcised chicken skin

The influence of sample type (i.e., excised versus nonexcised chicken skin) on the efficiency of trisodium phosphate (TSP) solutions in reducing Listeria monocytogenes populations and inhibiting their growth during refrigerated storage was studied. Whole chicken legs and excised chicken leg skin fragments inoculated with 10(8) CFU of L. monocytogenes per ml were dipped for 15 min in sterile tap water (control) or in a solution containing 8, 10, or 12% TSP. L. monocytogenes counts were determined after 0, 1, 3, and 5 days of refrigerated storage (2 degrees C). The decontamination effect of TSP was greater for excised skin than for whole legs. Microbial differences between control and TSP-treated samples were significantly larger for excised skin than for whole legs for 9 (75%) of 12 tested combinations of TSP concentrations and storage times. These differences varied from 1.05 +/- 0.26 log10 cycles (day 1) to 3.30 +/- 0.14 log10 cycles (day 5) for nonexcised-skin samples (whole legs) and from 1.54 +/- 0.48 log10 cycles (day 1) to 4.28 +/- 0.86 log10 cycles (day 5) for excised-skin samples. Significantly larger reductions were observed from the third day of refrigerated storage onward. The TSP concentration was a significant factor in the reduction of L. monocytogenes populations. These results suggest that bacteria are more readily accessible to TSP in excised than in nonexcised chicken skin and that the type of sample used to ascertain the efficacy of antimicrobial surface treatments may influence the findings of this type of study.