| Salmonella is a facultative anaerobic Gram-negative bacterium of the Enterobacter,which is an important zoonotic disease that can be directly or indirectly transmitted between animals and animals,and between humans and animals.There are many serotypes of Salmonella.S.typhimurium,S.paratyphoid-A and S.schottmuelleri mainly cause intestinal fever,and most other Salmonella are pathogenic to some animals,including poultry,livestock,rodents and pets,etc.Which cause a variety of clinical manifestations such as gastroenteritis and sepsis.According to data from the National Center for Disease Control and Prevention in 2013,up to 549 out of every 100,000 people carry Salmonella.People infected with Salmonell are mostly caused by eating food contaminated with Salmonella,such as meat,milk,eggs and seafood.The widespread presence of Salmonella poses a significant threat to human and animal health and food hygiene.In the breeding process of animal husbandry,antibacterial drugs are not only used to prevent,control,treat animal diseases,but also play an important role in animal growth.The results of domestic and foreign resistance to Salmonella is already very serious,and with the passage of time,the resistance rate is increasing and the multi-drug resistance phenomenon is also serious.As one of the most important drugs for the clinical treatment of Salmonella infection,the drug resistance situation of quinolones is also quite severe.This study collected 1,850 samples from chicken farms,cattle farms,sheep farms,pig farms,slaughterhouses and pet hospitals in some areas of Chongqing on 2016.08-2019.01 for the isolation and identification of Salmonella.Results a total of 91 Salmonella isolates were detected from 1,850 samples,with a total isolation rate of 4.9%.From the animal source,the isolation rate of pig-associated strains and dog-associated strains was the highest,6.1% and 6% respectively,followed by cattle-associated strains and goatassociated strains,and the isolation rate was 3%.91 strains of Salmonella include 67 strains of pig-associated strains,9 strains of goat-associated strains,6 strains of chickenassociated and pet-associated strains respectively and 3 strains of cattle-associated strains.From the regional perspective,the isolation rate of Salmonella in Nanchuan of Chongqing is the highest(11%),and the isolation rate of Salmonella in Dianjiang and Fuling of Chongqing is the lowest(both 2%).Among 91 strains of Salmonella from different animal sources,10 serotypes were identified by serotype identification,82 of which were covered with 10 serotypes.The most common serotype was Samonella Derby(44 strains,accounting for 48.4 % of the total),followed by Samonella Agona(10 strains,11.1% of the total),Samonella Rissen(7 strains,7.7% of the total)。A sensitivity test was conducted on 91 strains of Salmonella isolated.The results showed that the resistance rates to tetracycline and doxycycline exceeded 80%,for ampicillin,chloramphenicol and fluorobenzene.resistance rate is also over 60%,and resistance to cotrimoxazole and trimethoprim is also above 50%.At the same time,the cefazolin resistance rate is as high as 30%.Among the quinolones,the resistance rate of ciprofloxacin and enrofloxacin also reached 20%,and the multi-drug resistance rate was as high as 95.6%.Among them,chicken-associated strains is the most resistant,and 50% of the strains are resistant to more than 10 drugs.Followed by pig-associated strains,resistance to more than 10 drugs accounted for 22.4%.PCR and sequencing were used to detect the prevalence of PMQR gene and the mutation of target gene QRDR.The results showed that 76.9% of Salmonella carried at least one PMQR gene,the highest detection rate of oqxB(57.1%),followed by oqxA(51.6%),qnrS(30.8%)and aac(6′)-Ib-cr(30.8%),and oqxA+oqxB usually coexist in the same strain.The common gene phenotypes in all PMQR-positive strains were oqxA+oqxB+aac(6′)-Ib-cr and qnrB+oqxA+oqxB+aac(6′)-Ib-cr,accounting for 11.4% and 14.3% of the total,respectively.After sequencing,4 strains of qnrD-positive bacteria were identified as qnrD1;among 19 strains of qnrB-positive bacteria,16 strains were qnrB6.A total of three subtypes were detected in qnrS,which were qnrS1(5 strains),qnrS2(6 strains),and qnrS10(15 strains).At the same time,oqxA also detected two subtypes,oqxA1(29 strains)and oqxA2(1 strain);oqxB was mostly oqxB5.According to the analysis of DRDR mutation,90.1% of the strains had mutations in the target gene,and the single mutation of T57S(82 strains)of parC gene was the most common,and G72C(2 strains)and L131M(4 strains)were also detected.In addition,three types of mutations were detected in the gyrA gene,namely V143G(1 strain),S83L(1 strain),and D87Y(1 strain).parE detected a mutation type of M438I(1 strain)and no mutation in gyrB was detected.The strains in which the gyrA mutation occurred were all resistant to nalidixic acid or ciprofloxacin. |
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