Distribution of Oxytetracycline Resistance Plasmids between Aeromonads in Hospital and Aquaculture Environments: Implication of Tn 1721 in Dissemination of the Tetracycline Resistance Determinant Tet A

Abstract

Oxytetracycline-resistant (OT r ) mesophilic aeromonads were recovered from untreated hospital effluent (72 isolates) and from fish farm hatchery tanks (91 isolates) at sites within the English Lake District, Cumbria, England. The transfer of OT r plasmids from these isolates was investigated. Using Escherichia coli J53-1 as a recipient, 11 isolates from the hospital site and 6 isolates from the fish farm site transferred OT r plasmids (designated pFBAOT1 to 17). Original isolates were identified using fatty acid methyl ester and fluorescent amplified fragment length polymorphism comparisons as either Aeromonas hydrophila HG3 (eight isolates), A. veronii b.v. sobria HG8 (six isolates), and A. caviae HGB5 (one isolate). One isolate remained unidentified, and one could not be assigned a taxonomic designation beyond the genus level. Plasmids pFBAOT1 to -17 were screened for the presence of the tetracycline resistance determinants Tet A to E and Tet G. Only determinant Tet A (10 plasmids) was detected in these plasmids, with 7 tet gene determinants remaining unclassified. In all cases, Tet A was located on a 5.5-kb EcoRI restriction fragment. Hybridization with inc-rep probes N, P, Q, W, and U showed pFBAOT3, -4, -5, -6, -7, -9, and -11, from the hospital environment, to be IncU plasmids. Further, restriction fragment length polymorphism (RFLP) analyses and DNA probing demonstrated that pFBAOT plasmids were closely related to IncU OT r plasmids pASOT, pASOT2, pASOT3, pRAS1 (originally isolated from A. salmonicida strains from fish farms in Scotland and Norway, respectively), and pIE420 (isolated from a German hospital E. coli strain). In addition, DNA analyses demonstrated that plasmids pRAS1 and pIE420 had identical RFLP profiles and that all fragments hybridized to each other. The presence of tetracycline resistance transposon Tn1721 in its entirety or in a truncated form in these plasmids was demonstrated. These results provided direct evidence that related tetracycline resistance-encoding plasmids have disseminated between different Aeromonas species and E. coli and between the human and aquaculture environments in distinct geographical locations. Collectively, these findings provide evidence to support the hypothesis that the aquaculture and human compartments of the environment behave as a single interactive compartment.

The involvement of tetA and tetE tetracycline resistance genes in plasmid and chromosomal resistance of Aeromonas in Brazilian strains

“…strains has already been reported (Rhodes et al 2000, Schmidt et al 2001a. It was observed that tetA is generally associated with conjugative plasmids (Chopra & Roberts 2001).…”

“…Many authors have described the presence of tetracycline resistance plasmids in Aeromonas species (Rhodes et al 2000;Schmidt et al 2001a;L'Abée-Lund & Sorum 2002). Genes of the tet family are often associated with conjugative and mobilizable elements, such as plasmids, transposons and integrons (Chopra & Roberts 2001, Schmidt et al 2001b).…”

Unexpected Occurrence of Plasmid-Mediated Quinolone Resistance Determinants in EnvironmentalAeromonasspp.

“…Identifi cation of QnrS determinants in Aeromonas spp. indicates that those bacterial species may play a role as a reservoir of the qnrS genes in an aquatic environment, as already evidenced for tet genes (34,35). However, whether Aeromonas species are a main or an accessory reservoir of plasmid-mediated quinolone resistance determinants in regard to Enterobacteriaceae remains to be determined.…”

Abundance and Diversity of Tetracycline Resistance Genes in Soils Adjacent to Representative Swine Feedlots in China

“…Growing evidence exists that antibiotics used in the animal industry may transfer antibiotic resistance genes into the environment through a variety of pathways connected with common waste disposal practices, such as land application of manures (1,6). However, it is difficult to demonstrate a direct link between agricultural usage of antibiotics and increased levels of resistance in pathogens (7), the potential consequences are serious, and the World Health Organization has recommended that antimicrobials be phased out as animal growth promoters (8). In China, more than 8000 tons of antibiotics are used as feed additives each year (9), but there is no regulation on antibiotics used as feed additives for growth promotion at present (9) or legislation in China for the limits of antibiotics in the environment.…”