Salmonella and Listeria from stainless steel, polyurethane and polyethylene surfaces in the cutting room of a poultry slaughterhouse

ABSTRACT

Background: The cleaning process in poultry slaughterhouses consists basically on the use of hot water, detergents and disinfectants. The disinfection, which is the last stage of the cleaning process, seeks to reduce the number of total microorganisms and eliminating pathogen, so that levels are kept safe for good quality products. Pathogenic microorganisms such as Salmonella and Listeria are of utmost importance since they may cause foodborne diseases and consequently result in public health and economic losses in the domestic and in exporting markets. Materials, Methods & Results: This study was conducted in the cutting room of a poultry slaughterhouse with capacity to process 20.000 animals per hour in the Southern state of Rio Grande do Sul, Brazil. Samples were collected during preoperational cleaning before the surfaces were washed (without the removal of residues); after washing with hot water at 45 to 50°C and 22.5 bar pressure; and after washing with 2% sodium hydroxide detergent. Three disinfectants were tested 0.5% peracetic acid, 2% quaternary ammonium and 1% biguanide, all of them for 15 min, followed by rinsing with hot water. Evaluations were made in three processing lines for cutting chicken legs at the same time and on fully randomized sites of three surfaces stainless steel tables, polyurethane conveyors, and polyethylene cutting boards. The pre-enrichment method used 100 mL of 1% peptone water added to a bag with the sponge. After 1 min in a stomacher blender, an aliquot of 50 mL was transferred to a sterilized container and incubated at 30 ± 1°C for 18-24 h to isolate Listeria while the remaining 100 mL was incubated at 36 ± 1°C for 16-20 h for the isolation of Salmonella. Selective enrichment for Salmonella was conducted in Rappaport-Vassiliadis medium and selenite cystine broth, for 24 to 30 h at 41 ± 0.5°C in a water bath. Isolation was conducted in chromogenic agar for Salmonella and brilliant-green phenol-red lactose sucrose agar, incubated at 36 ± 1°C for 18-24 h. Colonies compatible with Salmonella were confi rmed using biochemical and serological tests. For Listeria isolation, selective enrichment was performed in Fraser broth for 18-24 h at 30 ± 1°C, Listeria agar and Modifi ed Oxford - MOX agar, incubated at 35 ± 2°C for 24-48 h. Colonies compatible with Listeria spp. were confi rmed for L. monocytogenes and other species by using biochemical tests. Results were described as presence or absence of Salmonella or Listeria. Discussion: Salmonella was not found on the surfaces studied, which may be due to the fact that the batch of slaughtered broilers was free of this microorganism or that good production practices and hazard analysis and critical control points procedures in this industry were adequately applied. Listeria welshmeri was isolated from the polyurethane conveyor and Listeria monocytogenes from the stainless steel table, both when the surfaces had food residues, before washing. The isolation of different Listeria species on the same surface (polyurethane conveyor) may be explained by the fact that four different sites were examined for sample collection, and that there might have been different species simultaneously contaminating the surfaces on random sites. After washing with hot water, Listeria monocytogenes was still isolated from the polyurethane conveyor, but it was not isolated after disinfection with 2% quaternary ammonium. After this stage of disinfection, Listeria was no longer isolated, which indicates that the use of a detergent and posterior use of quaternary ammonium was effi cacious in removing the microorganisms from this surface.