The Epide Miological Study Of The Prevalence Of Antimicrobial Resistance And Plasmid-me Diated Quinolone Resistance Genes In Salmonella Isolated From Animal China

Salmonella is one of the major causes of food-borne gastroenteritis in humans worldwide.The most common syndrome associated with Salmonella is a self-limited gastroenteritis that does not require chemotherapy.Quinolone/fluoroquinolone resistance in Salmonella enterica is of clinical importance because ciprofloxacin is the drug of choice for treating invasive human Salmonella.Informations from the antimicronial sensitivity test and molecular epidemiological study of plasmid-mediated quinolone resistance genes in Salmonella can learn mergence and dissemination of resistant genes,and guide the rational use of antimicrobial agents.In this study,we obtained seventy-seven Salmonella isolates from diseased chickens,ducks and pigs in Guangdong Province.The isolation rates from chickens,ducks and pigs were 11.3%(11/97),15.4%(53/344)and 3.0%(13/434),respectively.The most predominant serovar was S.enterica serovar Typhimurium(81.8%,63/77),followed by serovars Meleagridis(2.6%,2/77)and Abaetetuba(1.3%,1/77).Antimicrobial susceptibility tests showed that all 77 Salmonella isolates were highly resistant to ampicillin(98.7%),nalidixic acid(66.2%),tetracycline(62.3%)and sulfamethoxazole/trimethoprim(55.8%).The antimicrobial resistance rates to other antibiotics were as follows: doxycycline(46.8%),olaquindox(32.5%),florfenicol(27.3%),colistin(26.0%),enrofloxacin(20.8%),ciprofloxacin(16.9%),gentamicin(15.6%),fosfomycin(13.0%)and ceftiofur(6.5%).We found that 88.3% of the Salmonella isolates were multidrug resistant.This high occurrence of ampicillin,nalidixic acid and tetracycline,resistance is similar to that found in previous studies and may be a consequence of overuse of antimicrobials in animals feeds in China.Our results indicate that the multi-resistant Salmonella isolates are of high prevalence among food-producing animals in China.We detected quinolone-resistant genes from 77 Salmonella strains,the most prevalent PMQR gene was aac(6')-Ib-cr(18%)followed by oqx AB(9.1%)and qnr S(7.8%),none of the isolations were positive for qnr A,qnr B,qnr C,qnr D or qep A.We identified QRDR mutations in the gyr A and par C genes in the 42 Salmonella isolates that had MICs for CIP ? 0.25 ?g/ml.No mutation was detected in 18 isolates and twenty-four(57.1%)mutations were detected in Gyr A.We found six mutations and S83 Y predominated and was the sole mutation in 15/24 of the isolates.We used cluster analysis of the 42 Salmonella isolates with reduced resistance to CIP(MICs ? 0.25 ?g/m L)to generate dendrograms from PFGE profiles.We found 22 different PFGE-types,two large clusters(C luster G and J)contained five and four isolates,respectively.C lusters A and N contained three isolates each,and the other clusters contained two each.The PFGE patterns for strains of the same serotype were similar as were their ciprofloxacin MICs.This suggests that resistance plasmids were horizontally transmitted and clonally spread.In this study,we investigated quinolone resistance mechanisms from Salmonella strains.Sixteen Salmonella strains possessed resistant phenotypes in the absence of PMQR and QRDR genes suggesting novel mechanisms for quinolone resistance.These findings indicate a need for enhanced efforts to control Salmonella quinolone resistance in food-producing animals.