Prevalence and characterization of integrons from bacteria isolated from a slaughterhouse wastewater treatment plant.
OBJECTIVE
To investigate the presence and distribution of integron-carrying bacteria from a slaughterhouse wastewater treatment plant (WWTP).


METHODS
Enterobacteriaceae and aeromonads were isolated at different stages of the wastewater treatment process and screened for the presence of integrase genes by dot-blot hybridization. Integrase-positive strains were characterized in terms of phylogenetic affiliation, genetic content of integrons and antimicrobial resistance profiles. Plasmid location of some integrons was established by Southern-blot hybridization. Strains containing integron-carrying plasmids were selected for mating experiments.


RESULTS
Integrase genes were present in all samples, including the final effluent. The global prevalence was determined to be 35%, higher than in other aquatic environments. Forty-two integrase-positive isolates were further characterized. Nine distinct cassette arrays were found, containing genes encoding resistance to beta-lactams (bla(OXA-30)), aminoglycosides (aadA1, aadA2, aadA13, aadB), streptothricin (sat1, sat2), trimethoprim (dfrA1, dfrA12), a putative esterase (estX) and a protein with unknown function (orfF). Gene cassette arrays aadA1, dfrAI-aadA1 and estX-sat2-aadA1 were common to aeromonads and Enterobacteriaceae. The class 2 integron containing an estX-sat2-aadA1 cassette array was detected for the first time in Aeromonas sp. Nearly 12% (5 out of 43) of intI genes were located in plasmids. intI genes from isolates MM.1.3 and MM.1.5 were successfully conjugated into Escherichia coli at frequencies of 3.79 x 10(-5) and 5.46 x 10(-5) per recipient cell, respectively.


CONCLUSIONS
Our data support the hypothesis that WWTPs constitute a potential hot spot for horizontal gene transfer and for selection of antimicrobial resistance genes among aquatic bacteria. Moreover, water discharges represent a possible risk for dissemination of undesirable genetic traits.
Moura
Alexandra
A
CESAM & Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal. amoura@ua.pt
Henriques
Isabel
I
Ribeiro
Rogério
R
Correia
António
A
D000003:Abattoirs; D000333:Aeromonas / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D003227:Conjugation, Genetic; D024881:Drug Resistance, Bacterial; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification*; D022761:Gene Transfer, Horizontal; D019426:Integrases / Q000235:genetics; D032023:Integrons / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010802:Phylogeny; D015995:Prevalence; D017422:Sequence Analysis, DNA; D014865:Waste Disposal, Fluid / Q000379:methods*; D014871:Water Microbiology
D000900:Anti-Bacterial Agents; D019426:Integrases