Isolation Of Salmonella From Diseased Pigs And The Reversal Of Multidrug Resistance For Salmonella Typhimurium

Members of genus Salmonella are Gram-negative facultative intracellular bacteria belonging to Enterobacteriaceae. The organisms are often referred to as universal pathogens because they are extremely ubiquitous in nature and can be recovered from nearly all vertebrates as well as insects。Salmonella can cause most animals and people febrile, gastroenteritis, diarrhea and septicemia. For humans, non-typhoid salmonellosis is the most common foodborne illness throughout the world. The antimicrobial resistance of Salmonella spreads rapidly in all countries as a result of disease treatment and animal feed supplementation and is a global health concern. Pig salmonellosis is of our particular concern because China has the largest pig population in the world.The present study focused on the importance of pig salmonellosis by isolating salmonella from diseased pigs and the multidrug resistance Salmonella typhimurium. The multidrug resistance was further removed to determine resistance mechamism. The results were summarized as follows:1. 41 salmonellosis cases were identified in 903 diseased pig herds mainly from central China. Six different serotypes were identified. Salmonella choleraesuis constituted 21 of isolates. Whereas, S. typhimurium accounted for 8.2. The 21 antimicrobials were tested and 94.3% of the isolates were resistant to at least 10 antimicrobials. However, most serotypes except S. typhimurium were sensitive to amikacin, fluoroquinolones, furazolidone, polymyxin B, cephalosporins (cephradine and cefazolin). S. typhimurium isolates were susceptible only to amikacin and cephalosporins (cephradine and cefazolin).3. S. typhimurium 17y, isolated from diseased pigs, was a multiresistance strain with resistance to tested 14 antibiotics. In this study, the resistance to 11 antimicrobials was eliminated by high temperature and high concentration (0.5%) of SDS, resulting in the sensitive strain 17S1.4. By PCR, we demonstrated that BlaTEM, blaOXA-1, cat1, tet(B), aacC2 located on the plasmid. Furthermore, the class I integron, carring dhfr X Ⅱ for trimethoprim resistance, aadA18b for aminoglycoside resistance and sull for sulfamethoxazole resistance, was identified in the plasmid.5. Because the target genes gyrA and parC for quinolone category were detected by PCR from both resistant and sensitive strains, it was determined that the genes gyrA and parC were located in the bacterial genome. The gene sequencing of gyrA and parC revealed that an mutation of N87D (AAC→GAC) occurred in the sensitive strain...