Characterization of plasmids isolated from Aeromonas spp. obtained from South African aquaculture systems

[摘要] ENGLISH ABSTRACT: The plasmid content of 37 Aeromonas spp. isolates, obtained from South African tilapia,trout and koi aquaculture systems, was evaluated and 17 Aeromonas spp. isolatesappeared to contain one or more plasmids ranging in size from 1 to 35 kb. Largeplasmids (75-200 kb) were detected using S 1 nuclease pulsed-field gel electrophoresis inseven isolates. Twenty-three Escherichia coli transforrnants containing single/multipleplasmids from the 17 plasmid-containing isolates were characterized with respect to thetransferred antimicrobial resistance phenotypes. Transforrnants displayed diversephenotypes with the co-transfer of unrelated antibiotics. ~-lactam resistance wasidentified as the dominant resistance phenotype displayed by 13 transforrnants. Cotransferof ampicillin, amoxycillin, augmentin, ceftriaxone, cefuroxime and the firstgeneration quinolone, nalidixic acid occurred in 4 7 .8% of trans formants. Southernhybridization experiments with tetA, bla-TEM and strA-strB gene probes indicated theprevalence of the respective genes in 47.l %, 35.3% and 17.6% of the 17 plasmidcontainingAeromonas spp., respectively. Low incidences of mobile genetic elements,i.e., Tnl 721 and inti were also detected. Analysis of the transformed plasmids' backboneDNA revealed the presence of possible broad-host-range plasmids based on their abilityto replicate in the absence of host-encoded factors. Plasmids p3 l Tl and p36T2, isolatedfrom A. sobria and A. hydrophila, respectively, were identified as potential lncQ-likeplasmids based on positive hybridization signals with the repC gene from pRAS3.l,mobilization by the IncPa. plasmid RP4, and the relatively small size (14 kb). A 26.6 kbColE-type plasmid isolated from A. sobria was characterized by the transferred resistancephenotype, endonuclease restriction mapping and partial sequencing. Failure to transfer the plasmid by conjugation indicated that this plasmid was not self-transmissible, whileantibiotic susceptibility testing revealed indicated the transfer of resistance to 14antibiotics to E. coli DH5a.. Overall, results indicated the high level of plasmid diversityand potential transfer of antibiotic resistance determinants between Aeromonas spp.,emphasizing the role of plasmids and other mobile genetic elements in the disseminationof antibiotic resistance genes, especially in the aquaculture environment.

[发布机构] Stellenbosch University