Surveillance Of Antimicrobial Resistance And Study Of Plasmid-Mediated Quinolone Resistance Among Aeromonas Isolates From Different Aquatic Animals

The aeromonas are conditional pathogenic bacteria, and they are ubiquitous found in aquacultural environment. Quinolones are widely used in aquaculture but lead to serious problem of bacterial resistance when they are not used properly. Plasmid-mediated quinolone resistance is an important part of the quinolone resistance mechanism, and it can cause low level drug resistance to fluroquinolone in aeromonas.Presumptive Aeromonas isolates were identified and the minimal inhibitory concentrations of these bacterial strains against 8 types of 22 kinds of common antimicrobial agents were examined by microbroth double dilution. PMQR genes were detected by PCR and plasmids of the PMQR positive isolates were also extracted. Target genes of the quinolone resistance determining region(QRDR) were also amplified by PCR to ananyize the relationship between PMQR and QRDR.116 strains were isolated from different aquatic animals collected during 1990-2014 and were identified as Aeromonas spp. These aeromonas include 68 strains of Aeromonas hydrophila, 30 strains of Aeromonas veronii, 7 strains of Aeromonas caviae, 5 strains of Aeromonas dhakensis, 4 strains of Aeromonas jandaei, 1 strain of Aeromonas media, and 1 strains of Aeromonas sobria. Evidently, A.hydrophila was the dominant species, followed by A.veronii. A. hydrophila is the major pathogen of fish, reptiles and amphibians. Highly resistance rates were found in Aeromonas from turtles and amphibians.The MICs of 116 Aeromonas isolates were determined by microbroth double dilution. Results showed that 98.27% of the strains were resistant to ampicilin due to their intrinsic resistance;92.24% of the strains were resistant to amoxicillin/clavulanat;83.62% of the strains were resistant to sulfamonomethoxine; the resistance rates of nalidixicacid, oxytetracycline, sulfamethoxazole/ trimethoprim and doxycycline ranged from 25%-50%;less than 15% of the strains were resistant to chloramphenicol, enrofloxacin, ciprofloxacin, florfenicol, gentamicin, neomycin, amikacin, cefotaxime and ceftriaxone. 28(24.13%) Aeromonas appear multidrug resistance, resistance turtles source Aeromonas relatively high.Eighteen strains were detected carrying PMQR gene, accounting for 15.52%; among these strains, 8 and 9 strains carried qnr S2 gene and aac(6′)-Ib-cr gene, respectively. One strain carried both of these two genes. qnr A, qnr B and qep A were not detected. The nucleotide sequences of gyr A and par C QRDR of 18 PMQR-positive strains were determined via PCR amplification and direct sequencing. Eleven strains with a Ser-83-Ile substitution, in the QRDR of Gyr A, and 9 strains had a Ser-80-Arg mutation in the QRDR of Par C simultaneously. Seven strains were found no mutation in QRDR.Among 18 PMQR positive strains, 11 were resistant to one or more drugs of quinolones detected. With the exception of single strains carrying qnr S alone were resistant to ciprofloxacin, 7 strains were susptible to 3 drugs of quinolones examined, which were also found no mutations in QRDR of Gyr A and Par C. Among 10 aac(6’)-Ib-cr positive strains, 8 strains were resistant to ciprofloxacin, they were found mutation in both gyr A and par C,whereas 2 strains only mutated in gyr A.In conclusion, A. hydrophilic was predominant pathogens responsible for aeromonasis of aquatic animals in Guangdong province. Resistance rates of different classes of antimicrobial agents varied in Aeromonas from clinical aquatic animals. Multiple resistance was more serious in Aeromonas from turtles and amphibian. qnr S2 and aac(6’)-Ib-cr genes were detected in Aeromonas from Different Aquatic Animals.