Investigation Of Salmonella Carrying Rate On The Clinical Health Swine And Research Of Drug Resistance On Salmonella Isolates

Salmonella are an important class of foodborne pathogens causing serious harm worldwide. Past three decades, drug-resistance of Salmonella has been significantly enhanced accompanying with continuously widened spectrum of multiple drug resistance. This phenomenon has caused great difficulties on prevention and treatment of salmonellosis. As one of the main host of Salmonella, pig plays an important role on the spread of salmonella and contamination on foods.PCR technology combined with conventional separation methods were used for isolation and identification of Salmonella derived from three growth stages of clinical health swine in commercial swine farms among different parts of Anhui Province. Using these methods, a total of 540 rectal swab samples were collected from different growth stages of clinical health swine in six commercial swine farms among different areas in Anhui Province to conducting the investigation of Salmonella carrying case. A total of 22 strains of Salmonella were isolated with an isolation rate of 4.07% (22/540). The detection rate of reast-feeding, conservation and growth stage were 1.67% (3/180), 9.44% (17/180) and 1.11% (2/180) respectively. In the six surveyed farms, the farm in Anqing area got the highest detection rate of 18.89% (17/90). 22 Salmonella isolates belonged to three serogroups, of which 3 strains belonged to group B, 2 strains belonged to E1 group and 17 strains belonged to group F. In the antibiotics susceptibility test, 15 kinds of antibiotics were choosed. The amoxicillin and tetracycline got the highest resistance rate of 90.9%, while the most sensitive antibiotics were ceftriaxone and cefoperazone with sensitivity rate of up to 100% among the 22 strains of Salmonella. Multiple antibiotic-resistant strains which resistanted to more then 4 kinds of antibiotics accounted for 90.9% (20/22), the multiple drug resistance spectrum was AMX-TET-KAN-CHL- FFC. The results indicated that different growth stages of clinical health swine has different levels of Salmonella carrying rate in commercial swine farms among different parts in Anhui Province. The drug resistant phenomenon of all Salmonella isolates was serious and the multiple drug resistance rate was quite high. Most isolates were belonged to the rare group F.Common PCR technique was used in this trial to detect class I integron and 19 kinds of drug resistance genes. 19 strains of 22 Salmonella were class I integron positive with rate of 86.4%. A total of 11 kinds and eight kinds of drug resistance genes were detected on genomic and plasmid DNA respectively. The research has established two triple PCR methods to detect drug resistance genes belonged to chloromycetin class and aminoglycoside class respectively. The research has also established a double PCR to detect drug resistance genes belonged to tetracycline class. This approach not only improves the detection efficiency, while ensuring the sensitivity and specificity of detection. The aph(3)-IIa gene which got the highest detection rate was choosed as target gene to establish a Real-Time PCR method successfully with the detection degree of 8copies/μL. This Real-Time PCR method can quickly and effectively detected aph (3)-IIa gene from genomic and plasmid DNA on Salmonella. The results showed that the quantitative PCR method is rapid, sensitive and specific which can replace ordinary PCR method to detect drug resistance genes. The survey on 22 Salmonella strains indicated that a good correlation exists between multidrug-resistance and the carrier condition of class 1 integron. The phenotype of multidrug-resistance and the drug-resistant genes were consistent. The genome DNA carried more drug resistance genes than the plasmid.