| Salmonella is a widely spread zoonoses bacterial pathogen. The infection of Salmonella is a major threat to animal health, and subsequently to human through consumption of contaminated food of animal origin. It has been reported that Salmonella infection is the most common foodborne illness in China. Among which, around 90% are through poultry products including meat, eggs and milk. Chicken, as one of the main poultry in China, is highly vulnerable to contamination of Salmonella. In addition, the antibiotic resistance due to the abuse of antibiotics in poultry farms is increasing drastically, and spreading to others including human, through food chain. Therefore, in terms of food security, it is of great importance to study the distribution and spreading of Salmonella, particularly the resistant Salmonella, in retail chicken. This study aimed to analysis the antibacterial resistance, carrying integeon-1 and sulfonamides-resistant genes from 61 species of Salmonella isolated from the 400 pieces of retail chicken in partial areas of Sichuan province1. Isolation and Serotype of Salmonella.From 2012 to 2013,400 chicken samples were collected in partial areas of Sichuan province. Using standard protocol, we isolated 61 species of Salmonella from the 400 chicken samples, Further was performed using PCR targeting invA and hut genes within Salmonella, resulting in an exactlly contamination rate of 15.3%. The result of serotype showed that among the 61 Salmonella species,45.90%(28/61) and 37.70%(23.61) are Salmonella enteritidis and Salmonella typhoidal, respectively.2. Antibiotic susceptibility of Salmonella isolates from market.Using disk diffusion method, we tested the 61 Salmonella for 10 different antibiotics. The results shows Salmonella are highly resistant to Nalidixic acid (100%), Ampicillin (90.16%), Tetracycline (68.85%), Ciprofloxacin (60.66%), Spectinomycin (47.54%) and Sulfamethoxazole(39.34%). On the contrary, the Salmonella shows relatively less resistance rate to Amoxicillin (19.67%), Florfenicol (14.75%), Cefiriaxone (9.84%) and Gentamicin (8.20%). Notably, the intermediate resistance to AMC is as high as 54.10% and 22 resistant spectrums against the 10 antibiotics have been found in the 61 Salmonella species. multidrug-resistance was observed in 72.13%(44/61) of all Salmonella species.3. Antimicrobial resistance mechanism testing in multidrug-resistant Salmonella.(1) Prevalence of class I integrons and the gene cassettes for PCR:The PCR detection of integron-1 with intl gene was performed on the multidrug resistant species. Among 44 multi-drug resistant Salmonella,17 species were found intl gene, implying a positive rate of 38.64%. In addition,16 species showed resistance to more than 5 antimicrobials. Further sequencing found all 15 species carried bla(OXA-30)-aadAl gene cassette, which is related to the resistance to β-lactam, aminoglycoside and sulfanilamide antibiotics. Moreover,2 species carried dfrAl-orfC gene cassette. The 2 species have broader resistance spectrum and showed resistance to 9 drugs out of the 10 tested.(2) Multiple-resistant Salmonella of Sulfonamide-resistance for PCR. Among 24 SXT-resistant species,11,22, and 10 were detected sull, sul2 and sulS gene. The detection sul gene was as high as 91.67%, indicating a coincidence rate of 91.67% for resistance gene. Lastly, in 17 class I integron positive species, there are three pieces carry sul1+sul2 gene, one carriy sul1+sul2+sul3 gene. It account for close correlation exist between class I integron and sulfonamide resistance.In this study, we have performed detailed analysis to evaluate the contamination rate and resistance of Salmonella in retail chicken samples collected from Sichuan province. Our results from antibiotic susceptibility assay and resistance genotyping provide primary data for the monitoring of Salmonella contamination in retail chicken. In addition, the data also has great impact in the epidemiology and drug discovery against Salmonella infection. |
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