| Objective:Aeromonas spp. isolated from the clinical patients and from the environment were investigated in Zhejiang region. We analyzed the current situation of antibiotic resistance and the presences of resistance genes, were explored the mechanism of resistance to quinolones. The objectives were to provide an important basis for clinical treatment and prevention of Aeromonas infections and lay the foundation for future research.Methods:Aeromonas strains were collected in outpatients with diarrhea (intestinal group) and inpatients of the First Affiliated Hospital of Zhejiang University with extraintestinal infections(extra-intestinal group) from June2010to December2014, as well as from the environment (June2013to December2014, named the environmental group). Aeromonas strains were analyzed for antibiotics sensitivity of20drugs. Polymerase chain reaction (PCR) was performed to amplify quinolone resistance genes gyrA, gyrB, parC, parE, qnrA, qnrB, qnrS, aac (6’)-Ib-cr and qepA, and sequencing was used to screen the mutation of gene gyrA, gyrB, parC and parE, analyzing the relationship between the resistance phenotype to quinolone and resistance-related genes of Aeromonas isolates.Results:1. A total of303Aeromonas strains were isolated from intestinal infections. A. caviae was the most common, accounting for37.3%of all isolates.118Aeromonas strains were isolated from extraintestinal infections, with A. hydrophila the most prevalent, accounting for55.9%.79Aeromonas strains were isolated from the environment, with A. veronii bv. sobria the most common and accounted for58.2%of the environmental strains. There were significant differences in species distribution among the three groups (p<0.01).2. The highest resistance rates of all tested antibiotics were ampicillin-sulbactam, amoxicillin-clavulanic acid and cefazolin. the resistance rates of intestinal Aeromonas strains to the above antibiotics were94.1%,92.1%and58.7%, respectively. In contrast, the resistance rates of extraintestinal Aeromonas strains to the above antibiotics were95.8%,95.8%, and83.1%, respectively. The resistance rates of environmental Aeromonas strains to the above antibiotics were68.4%,64.6%and38.0%, respectively. All groups were sensitive to the second-and third-generation cephalosporins and carbapenems. Excepting ampicillin-sulbactam and amoxicillin-clavulanic acid, the difference in the antibiotics resistance rate between intestinal and extraintestinal Aeromonas was significance. In addition, the resistance rate of nalidixic acid was up to66.1%.3.16.1%of the extraintestinal Aeromonas strains carried qnrS gene, while19.5%were positive for aac (6’)-Ib-cr gene. There were9strains (7.6%) positive for both qnrS and aac (6’)-Ib-cr gene, but none of the strains was detected qnrA, qnrB or qepA gene. GyrA gene was identified from39strains (33.1%), while82strains (69.5%) carried gyrB gene,52strains (44.1%) carried gyrC gene and none carried gyrE gene. There were three points of mutation possessing at QRDRs of gyrA gene, including82,83and86point, with the most common mutation Ser83â†'Ile. The mutation of QRDRs in gyrC gene included78and80amino acid point. By contrast, no mutation was detected in the QRDRs of qnrB gene.Conclusions:1. There were significant differences in species distribution among the intestinal, extraintestinal and environmental Aeromonas strains.2. Aeromonas stains showed varied resistance to β-lactam antibiotics, but maintained sensitivity to the second-and third-generation of cephalosporins and carbapenems. The resistance rate of extraintestinal-Aeromonas strains was significantly higher than the intestinal and environmental Aeromonas strains.3. The gyrA gene was the main target of quinolones, with the highest frequency as mutation of Ser83â†'Ile. The parC gene was the second target of quinolones, with mutation at position80the most common.4. Strains carrying two mutations have higher resistance rate to quinolones than that presented as single mutation. Although aac (6’)-Ib-cr and qnrS gene mediated resistance at low level, they may promote the degree of resistance.5. The MIC value of ciprofloxacin and mutation of resistance genes of Aeromonas strains suggested that the criteria of MIC judgement deserves further study. |
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