Isolation, Identification, Drug Resistance Detection And Resistant Gene Location Of Salmonella From Chickens

Salmonellosis is one of the common infection disease of chickens,it can be divided into Pullorum,Typhusavium and Paratyphusavium,which is a major hazard to chickens.In the last two decades,the incidence of resistance to antimicrobial agents among salmonella has been steadily rising in food as well as in clinical isolates.This increase seems to be associated with the high use of antibiotics in livestock and in human health care.Particularly the emergence and dissemination of MDR Salmonella have become a major concern for both public health and production agriculture. This study aimed to evaluate the antimicrobial susceptibility profiles,prevalence of MDR,Serotype, plasmids presence and resistant gene location based on identification of pathogenic salmonella isolated from chickens.1.Ten pathogenic sahnonella strains were isolated from chickens which were ill or dead because of being contracted with salmonella in Chongqing from 2006 to 2008.The isolates were identified by biochemical;Serogroups were determined by 30 kinds of salmonella diagnostic serum using the slide agglutination method.Putative isolates were definitively identified as Salmonella spp.by PCR with the primers,which amplify a 373-bp Sahnonella-specific product from the invA gene.The results indicted that the ten studied Sahnonella isolates belonged 4 serogroup:A(n=1,S9),B(n=1, S6),C1(n=2,S1,S5) and D(n=6,S2,S3,S4,S7,S8,S10).The superiority group is D(60%).All of the isolates were positive when amplifying the InvA gene.2.Ten isolates were tested for their sensitivity to 21 antimicrobial agents by Kirby-Bauer method, The susceptibility and resistance of the Salmonella strains were defined according to the criteria suggested by the NCCLS;Plasmids were purified from isolates by alkaline-lysis method and electrophoresed in 0.7%(w/v) agarose.Analyzed the relationship between resistance pattern and plasmid profile.Our studies revealed that all of the isolates have strong resistance and the rate of the resist were 24%-71%to the 21 antimicrobial,all of the isolated strains identified were resistant to at least five antimicrobials:P-G,AMX,ERY,TET and PRF.Resistance to SXT(80%),AMP (60%),CMP(60%),CIP(50%)and NOR(50%) were most common.Plasmids were discovered in 6 strains(S1,S4,S6,S8,S9,S10) of salmonella isolates(60%).There are 3 size(36kb,15 kb,1.4 kb) of plasmids were detected in S1;4 size(36 kb,6.8 kb,4.9 kb,2.2 kb) of plasmids were detected in S4;3 size(36kb,2.8kb,2.2 kb) of plasmids were detected in S6;2 size(15 kb,1.8 kb) of plasmids were detected in S8;5 size(36kb,15 kb,6.8kb,3.6 kb,1.6 kb) of plasmids were detected in S9;1 size(36kb) of plasmid was detected in S10.There are no obvious relationships between resistance pattern and plasmid profile.3.The plasmids which presenced in the isolates were eliminated by high temperature and SDS. The plasmid-mediated resistance were located by the pair sensitivity tests before and after the plasmids eliminated.Our studies revealed that plasmids of 6 isolates were completely(100%) eliminated.The pair sensitivity tests before and after the plasmids eliminated suggested that the genetic determinants conferring resistance to AMX,GEN,ERY,TET,CIP,NOR and CMP were present in the plasmids of S1(47%),to AMX,ERY and TET were present in the plasmids of S4(60%),to AMX,GEN,ERY,TET,CIP,OFL,NOR,LVX and CMP were present in the plasmids of S6(60%),to AMX,ERY,TET,CIP,NOR and CMP were present in the plasmids of S8(60%),to AMX,ERY,TET,CIP,OFL,NOR,LVX,SXT and CMP were present in the plasmids of S9(75%),to AMX,GEN,ERY,TET,CIP,NOR and CMP were present in the plasmids of S10(64%).