Longitudinal Dissemination of Salmonella enterica Clonal Groups through the Slaughter Process of Salmonella-Positive Pig Batches

Abstract

This study was conducted to assess the dissemination of Salmonella clonal groups in slaughterhouses that received batches of Salmonella -positive pigs and used different routine processing procedures. Eight serial sampling sessions were conducted in three slaughterhouses (A, B, and C). Blood was collected randomly (n = 25) from each batch of pigs and processed for serology. Carcasses (n = 12) were identified and sampled after dehairing, after singeing, after evisceration, and before chilling. A section of cecum also was collected. Salmonella isolates were submitted to pulsed-field gel electrophoresis. The overall seroprevalence of Salmonella was 80.6% (316 of 392 samples), and cecal contents were positive for Salmonella in 23.8% (26 of 109) of the pigs sampled. Carcasses after dehairing had a significantly higher prevalence of Salmonella (P = 0.004) and the highest Salmonella levels (median = 0.26 log CFU/300 cm(2)). The singeing step significantly affected the Salmonella status of the carcasses (P = 0.001); however, the efficacy of singeing differed among slaughterhouses. In the prechilling step, 14.7% (16 of 109) of the carcasses were positive for Salmonella. Salmonella pulsotypes found on the prechill carcasses were also found in the lairage, in the cecal contents, and on carcasses after dehairing, suggesting that the main source of contamination was the slaughter process before singeing. Slaughterhouse C was the most likely (odds ration [OR] = 6.51) to have pigs carrying Salmonella in the gut, and slaughterhouse B was the most likely (OR = 14.66) to have contaminated carcasses at the prechilling step. These findings indicate that the procedures adopted in slaughterhouse B contributed to the spread of Salmonella strains. In contrast, in slaughterhouse C the Salmonella strains carried by the pigs or found in the lairage were not recovered from prechilled carcasses, validating the effectiveness of the slaughterhouse interventions. These results indicate that an effective slaughter process can help decrease the number of Salmonella-positive carcasses in slaughterhouses that receive Salmonella-positive pig batches.

Effect of slaughterhouse and day of sample on the probability of a pig carcass being Salmonella-positive according to the Enterobacteriaceae count in the largest Brazilian pork production region

“…The presence of Salmonella in the house flora associated with the splitting saw was also considered critical for carcass contamination during splitting . Similar findings were found in a survey that included some slaughterhouses enrolled in this study (Silva et al, 2012), in which no distinct increase in either Salmonella number or prevalence was found after evisceration. Bolton et al (2002) also observed no increase in total bacterial count after evisceration, suggesting good practices in the slaughterhouse concerning training of operators and hygiene.…”

“…Slaughterhouse and a day-to-day variation in prevalence are frequently reported in Salmonella epidemiological studies performed in pig slaughterhouses (Baptista et al, 2010;Botteldoorn et al, 2003;De Busser et al, 2011;Delhalle et al, 2008;Hald et al, 2003;Prendergast et al, 2008;Silva et al, 2012). Many of these studies reported a correlation between seroprevalence, and the number of pigs shedding Salmonella in their feces, with carcass contamination (Botteldoorn et al, 2003;Duggan et al, 2010;Silva et al, 2012).…”

“…In southern Brazil, previous studies reported 24% (Kich et al, 2011) and 14.7% (Silva et al, 2012) of Salmonella positive pre-chill carcasses. However, these studies included only three slaughterhouses and used a distinct sampling scheme, which may have led to frequencies that reflected the slaughter day rather than the overall prevalence.…”

“…Many of these studies reported a correlation between seroprevalence, and the number of pigs shedding Salmonella in their feces, with carcass contamination (Botteldoorn et al, 2003;Duggan et al, 2010;Silva et al, 2012). Based on a previous serological survey conducted in 188 finishing farms in Brazil (Schwarz et al, 2010), exposure to the pathogen on farm seems to be high, since 142 farms (75.5%) had a seroprevalence greater than 70% in their Table 4 Results of the mixed logistic regression models (MLRs 1, 2, and 3) with random intercepts and fixed slopes that included the presence of Salmonella in pork carcasses as response variable, and fitted log of the Enterobacteriaceae count (EC) or size of the slaughterhouses along with EC as fixed effects.…”

“…However, environmentally related sources of contamination such as contact surfaces of equipment and handling by workers have also been described (Berends et al, 1997;Botteldoorn et al, 2003;Duggan et al, 2010;Giovannacci et al, 2001;Hald et al, 2003), and direct transfer of house flora present in the slaughterhouse has been found to be an important source of contamination for carcasses Van Hoek et al, 2012). Moreover, the extent of contamination may vary significantly depending on the slaughterhouse and sampling day (Berends et al, 1997;Botteldoorn et al, 2003;Hald et al, 2003;Silva et al, 2012).…”