| Salmonella is one of the significant pathogens causing foodborne illness in human with animals also being affected. Eggs, poultry and pork are always considered to be three major sources of human salmonellosis. During the last years, the prevalence of Salmonella in eggs and poultry has greatly declined with the implementation of Salmonella control programs in avian production. Therefore, many developed countries attached importance on producing safe pork and pork products. Slaughterhouse and retail markets are two vital points in pork production chain, and the slaughtering process along with sanitation conditions of retail have profound effects on the propagation of Salmonella. This study aims to investigate the prevalence, serovars and antimicrobial resistance of Salmonella spp. in slaughterhouse, retail markets and humans from Yangzhou city. We then used different molecular typing methods, such as multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and clustered regularly interspaced short palindromic repeat sequences (CRISPR) to determine the relationship between these strains and identify the potential transmission route of them, providing informative data for the control of Salmonella.From October 2013 to December 2014,392 slaughterhouse samples and 178 pork samples were collected and detected form a slaughterhouse and its downstream retail markets in Yangzhou, respectively. The positive rate of Salmonella spp. was 70.2% (275/392) and 73.0% (130/178), respectively. Forty-nine strains isolated from human were donated by CDCs in Yangzhou and Taizhou. Statistical analysis showed that there was no significant difference among five samplings at different time of one year from the same slaughterhouse (P> 0.05), indicating that the seasonal factor did little effect on the prevalence of Salmonella. Identification of Salmonella serovars showed that Salmeonella Derby was the most widespread serotype in both slaughterhouse and retail markets, but it was the second most prevalent serotype in human isolates. Other serovars such as S. Typhimurium,S. Anatum and S. London were also widely spread in the three sources. Antimicrobial sensitivity test indicated that the highest resistance rate was against tetracycline (30.9%), nalidixic acid (33.1%) and ampicillin (55.1%) in isolates from the slaughterhouse, retail markets and humans, respectively. Among the β-lactams drugs, a significant high level of resistance to penicillins was detected in isolates from three sources compared to the rate of resistance to cephalosporins (P< 0.05). The same case was observed for resistance to NAL and other antimicrobial agents belonging to the quinolone and fluoroquinolone families (P< 0.05). Resistance to other antimicrobial agents such as streptomycin and trimethoprim-sulfamethoxazole were also common. Multidrug resistance was frequently observed in S. Typhimurium, S. London and S. Derby, among which S. Typhimurium was most prominent. In particular, one S. Indiana strain from human showed resistance to all the sixteen antimicrobial agents used in this study. In addition, the most frequent antimicrobial resistance pattern was NAL in isolates from the three sources, suggesting the propagation of Salmonella may exist in slaughterhouse, retail markets and human.17,13 and 12 sequence types (STs) were identified among the Salmonella isolates from the slaughterhouse, retail markets and humans, respectively. ST40 was the most prevalent ST in all of the three sources. Many isolates showing the same STs were found in different points of the slaughterhouse, indicating that these Salmonella isolates could spread along the slaughter line in the slaughterhouse. PFGE analysis subdivided the 50 S. Derby and 27 S. Typhimurium isolates into 46 and 17 distinct pulsotypes, respectively. Among the isolates from the first slaughterhouse sampling, PFGE patterns of S. Typhimurium P2-D13, P2-E13 and P2-S1 from carcass dressing, evisceration and submitting, respectively, were found to have the identical pulsotype, demonstrating that these three strains may belong to the same clone and it maybe caused by horizontal transmission of the strain along the slaughter line. The similarity of pulsotype among S. Typhimurium P4-L1, N2-J3, and YZJK2-17 from the slaughterhouse, retail markets and humans, respectively, surpassed 90%, implying that these strains were probably propagated along the pork production and consumption chain.27 S. Typhimurium strains from the three sources could be subdivided into seven disparate CRISPR types using CRISPR subtyping method. The spacer numbers and sequences of Salmonella strains P2-D13, P2-E13 and P2-S1 from different points of the slaughterhouse were absolutely identical, which was also found in the strains P4-L1, N2-J3 and YZJK2-17 from slaughterhouse, retail markets and humans, respectively. The phenomenom proved that Salmonella could not only spread along the slaughter line, but also propagate in the whole pork production and consumption chain. |
PDF Full Text Request