Phenotypic and Molecular Typing of Salmonella Strains Reveals Different Contamination Sources in Two Commercial Pig Slaughterhouses

Abstract

This study aimed to define the origin of Salmonella contamination on swine carcasses and the distribution of Salmonella serotypes in two commercial slaughterhouses during normal activity. Salmonellae were isolated from carcasses, from colons and mesenteric lymph nodes of individual pigs, and from the slaughterhouse environment. All strains were serotyped; Salmonella enterica serotype Typhimurium and Salmonella enterica serotype Derby isolates were additionally typed beyond the serotype level by pulsed-field gel electrophoresis (PFGE) and antibiotic resistance profiling (ARP); and a subset of 31 serotype Typhimurium strains were additionally phage typed. PFGE and ARP had the same discriminative possibility. Phage typing in combination with PFGE could give extra information for some strains. In one slaughterhouse, 21% of the carcasses were contaminated, reflecting a correlation with the delivery of infected pigs. Carcass contamination did not result only from infection of the corresponding pig; only 25% of the positive carcasses were contaminated with the same serotype or genotype found in the corresponding feces or mesenteric lymph nodes. In the other slaughterhouse, 70% of the carcasses were contaminated, and only in 4% was the same genotype or serotype detected as in the feces of the corresponding pigs. The other positive carcasses in both slaughterhouses were contaminated by genotypes present in the feces or lymph nodes of pigs slaughtered earlier that day or from dispersed sources in the environment. In slaughterhouses, complex contamination cycles may be present, resulting in the isolation of many different genotypes circulating in the environment due to the supply of positive animals and in the contamination of carcasses, probably through aerosols.

Comparison of Multilocus Sequence Typing, Pulsed-Field Gel Electrophoresis, and Antimicrobial Susceptibility Typing for Characterization of Salmonella enterica Serotype Newport Isolates

“…Numerous reports have documented the highly discriminatory nature of PFGE in successfully tracking infections of different Salmonella serotypes to certain geographic areas, including particular farms, and have subsequently linked human illness to exposure to animals or contaminated foods (4,16,17,28,36,42,48,49). However, a more discriminating method may be required to understand the evolutionary relatedness of epidemiologically unrelated populations (9,11,24,29,43,46).…”

“…Due to its limitations, many studies have compared PFGE to other genetic typing methods in attempts to identify more powerful tools for epidemiological investigations and evolutionary analyses. Comparisons have been made with various typing schemes, including serotyping and phage typing, repetitive-element PCR, multilocus variable-number tandem repeat analysis, amplified fragment length polymorphism, antibiotic susceptibility typing, and DNA sequence typing (4,14,19,21,22,29,32,44,45,59).…”

Comparison of Five Repetitive-Sequence-Based PCR Typing Methods for Molecular Discrimination of Salmonella enterica Isolates

“…The aim of this experiment was to investigate whether genetically different strains of the same serotype resulted in the same fingerprint. The genetic diversity of the strains had been tested by pulsed-field gel electrophoresis using XbaI as the restriction enzyme (2 PCR. PCR amplifications were performed in a Perkin-Elmer 9700.…”

Detection of <i>Salmonella enterica</i> Serovar Rissen in Slaughter Pigs in Northern Ireland

“…Of the S. Rissen isolated from pigs in Europe, tetracycline is the most common resistance phenotype [7] [19] [25]. Garcia-Feliz [26] investigating the antibiotic resistance of a panel of 114 S. Rissen isolates, all originating from pigs, recorded that over 50% of isolates were resistant to tetracycline alone.…”