SALMONELLA CONTAMINATION ON PORK CARCASSES: A STUDY OF CRITICAL POINTS

The aim of the present study was to determine the frequency and distribution of Salmonella contaminations throughout the slaughtering process of pigs. The investigation was car- ried out in two slaughterhouses that were visited four times each on different days. Samples were taken from lairage areas, fecal contents, carcasses at different stages of processing and from the environment. Bacteriological analysis of the samples was carried out by a standard pro- cedure consisting of a pre-enrichment and selective enrichment. Salmonella isolates were also serotyped. In total, 720 carcass swabs and 185 environmental samples were collected. Contamination was high in the lairage area (70.8% of the samples) and relatively low at the final step of carcass processing (3.7%). However, at intermediate phases, the frequency of contamina- tion was higher, particularly after evisceration (6.2%). Global prevalence of fecal carriers was 12.5%. Salmonella was also isolated from hands of personnel in both abattoirs. Also in both cases, some samples taken in the slaughterline before the start of the operation were positive. The most spread serotype was Typhimurium; although other serotypes predominated at particular points. These results suggest that contamination is widespread in the slaughterhouses and that the patterns of spreading of the contamination are complex. Introduction Contamination of pig carcasses at the slaughterhouses is a critical point to allow the presence of Salmonella in pig meat. If the slaughtering process developed with absolute efficien- cy, carriage of Salmonella in lymph nodes or fecal contents would not contaminate the carcass. However, all studies done show that the process is less than perfect and contamination of pig carcasses is common (Swanenburg et al., 2001). Therefore, knowledge of the hazard points for contamination and evaluation of the risk of each step in the slaughterline is important to design corrective measures aimed to decrease the frequency of contaminated carcasses at the end of the slaughtering process. Beforehand, lairage areas, equipment and personnel are the most prob- able sources of external contamination while laceration of intestines of infected pigs is the other potential source. The present study was aimed to determine the frequency of Salmonella contam- inations along the slaughtering process of pigs in two abattoirs of Catalonia, Spain. Materials and Methods Two commercial pig slaughterhouses of Catalonia were investigated. Slaughterhouse A slaughtered approximately 350 pigs per hour and slaughterhouse B processed approximately 650 pigs per hour. Slaughter operations and procedures were similar in both slaughterhouses except for the scalding. In slaughterhouse A, carcasses were scalded using water vapor while in slaughterhouse B there was a "scald tank" (60±1°C). Sampling was repeat- ed four times at each slaughterhouse on different days. Samples were collected from carcasses (after evisceration, after polishing and before chilling), fecal contents, environment (lairage areas, scalding tank, evisceration drainages), equipment (knives, polishing brushes, rectal pistols, trim- ming devices) and from hands of the personnel. For each round of sampling, the same 30 pigs were marked and were followed up throughout the slaughterline. Carcasses were sampled by vig- orous rubbing of ham, belly, jowl and back. Environmental sampling was carried out three times a day, at the beginning of the working day, one hour later and 3-4 hours after the beginning of the operation. Microbiological analysis were done using a pre-enrichment step in buffered peptone- water (37°C, 18h), selective enrichment in Rappaport-Vassiliadis broth (42°C, 48 h), and final plat- ing in XLT4 agar. Suspect colonies were identified by means of API20E (Bio-Merieux) and Salmonella isolates were further serotyped according to the Kauffman-White-LeMinor scheme. Results Contamination was more frequent in slaughterhouse B where 5.3% (19/360) of the car- casses swabs were positive compared to 1.4% (5/360) in slaughterhouse A (p<0.05). Regarding