Antimicrobial Resistance And Ceftriaxone Resistance Mechanism In Clinical Isolates Of Non-typhoidal Salmonella

Objective: To investigate commonly used antimicrobial susceptibilities of clinical isolates of non-typhoidal Salmonella(NTS) in Tianjin, and to determine the molecular typing and detecte ESBLs and Amp C genes of ceftriaxone resistant strains and ceftriaxone intermediate strains. The aim of this study is to improve prudent aitibiotics use and prevention and control for NTS infection.Methods: 1.Strains identification and antimicrobial susceptibility test: NTS isolates were collected from stool specimens of patients with acute diarrhea in the Second Hospital and the General Hospital of Tianjin Medical University from May to October of 2014. After the samples were cultured, we could identify the NTS strains by the biochemical identification, serological identification and PCR techniques for inv A gene. Detected the susceptibility of 11 kinds of antimicrobial agents about NTS and then detected the susceptibility of azithromycin about ceftriaxone resistant strains and ceftriaxone intermediate strains. 2.PFGE and MLST: determined the molecular typing about ceftriaxone resistant strains and ceftriaxone intermediate strains by PFGE and MLST methods. The strains were genotyped by PFGE of Xbal-digested chromosomal DNA and formation the clustering analysis graph. MLST amplified seven housekeeping genes(thr A, pur E, suc A, his D, aro C, hem D and dna N), respectively, the sequenced results would be submitted to the international MLST database website to obtain strain's allele maps and the corresponding ST types(STs). 3.ESBLs and Amp C genes detection: amplified and sequenced the ESBLs genes(TEM?SHV?CTX-M?OXA) and Amp C genes(ACC?CMY)about ceftriaxone resistant strains and ceftriaxone intermediate strains by PCR.Results: 1.Biochemical identification and serological identification results and identification results of PCR amplification of inv A gene were consistent. Non repetitive 108 strains of NTS were isolated, 88 strains from the Second Hospital ofTianjin Medical University, 20 strains from the General Hospital of Tianjin Medical University. 2. In total 108 NTS isolates, the multidrug resistant(MDR) rate was 17.6%, the susceptibility rate of nalidixic acid, ciprofloxacitn, levofloxacin, ceftriaxone, ertapenem were 61.10%,68.50%,66.70%,97.10% and 100.00%, respectively. 3. We found three ceftriaxone non-duplicate isolates. Strains Sa8709 and Sa8771 were ceftriaxone resistant strains, strain Sa8763 was ceftriaxone intermediate strain. They were all the MDR strains. Sa8709 was isolated from the Second Hospital of Tianjin Medical University, resistant to ampicillin, nalidixic acid, ceftriaxone and azithromycin, intermediate resistant to ciprofloxacin; Sa8771 was isolated from the General Hospital of Tianjin Medical University, resistant to ampicillin, streptomycin, nalidixic acid, ceftriaxone and ceftazidime, intermediate resistant to ciprofloxacin and levofloxacin; Sa8763 was also isolated from the General Hospital of Tianjin Medical University, resistant to ampicillin, nalidixic acid, levofloxacin, ciprofloxacin, chloramphenicol, tetracycline and azithromycin, intermediate resistant to ceftriaxone. 4.Sa8709 and Sa8771 were also Salmonella Enteritidis, Sa8763 was Salmonella Typhimurium. The three strains with different types of PFGE, and clustering analysis showed that Sa8709 and Sa8771 had high similarity was 91.70%, and the Sa8763 similarity was low, only 55.80%. The classification of MLST, Sa8709 and Sa8771 were ST11, Sa8763 was ST34. 5. Sa8709 was amplified with the expected fragment length of CTX-M gene, Sa8771 was amplified with the expected fragment length of CTX-M and TEM genes, Sa8763 was amplified with the expected fragment length of OXA gene. By sequencing and Gen Bank gene sequence comparison, the corresponding similarity were all above 98%.Conclusion: 1. The local clinical isolates of non-typhoidal Salmonella showed multiple drug resistance, but not found resistant to carbapenem. 2. Antimicrobial susceptibility of clinical isolates of non-typhoidal Salmonella in our region to fluoroquinolones including ciprofloxacin and levofloxacin were less than 70%, so we should consider reassessment of fluoroquinolones were still suitablefor non-typhoidal Salmonella infection empirical treatment and bacterial infection diarrhea empirical treatment. 3.We found producing ESBLs genes of Salmonella Enteritidis and Salmonella Typhimurium, resistant to fluoroquinolone, ceftriaxone and azithromycin, it was a major threat to public health in our region. 4.It should be continued to carrying out molecular typing and antimicrobial resistance monitoring research of clinical isolates of non-typhoidal Salmonella in our region.