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JAC Advance Access originally published online on October 2, 2007
Journal of Antimicrobial Chemotherapy 2007 60(6):1243-1250; doi:10.1093/jac/dkm340
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© The Author 2007. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Prevalence and characterization of integrons from bacteria isolated from a slaughterhouse wastewater treatment plant

Alexandra Moura1,*, Isabel Henriques1, Rogério Ribeiro2 and António Correia1

1 CESAM & Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 2 IperÁgua, Lda—Tratamento de Águas e Águas Residuais, Apartado 52, S. Bernardo, 3811-601 Aveiro, Portugal

Received 9 March 2007; returned 6 April 2007; revised 10 August 2007; accepted 13 August 2007

* Corresponding author. Tel: +351-234370970; Fax: +351-234426408; E-mail: amoura{at}ua.pt

Objectives: 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 ß-lactams (blaOXA-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.

Keywords: horizontal gene transfer , integrons , Aeromonas , Enterobacteriaceae


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