Abstract
Samples of effluent and soil were collected from a reed bed system used to remediate liquid waste from a wool finishing mill with a high use of quaternary ammonium compounds (QACs) and were compared with samples of agricultural soils. Resistance quotients of aerobic gram-negative and gram-positive bacteria to ditallowdimethylammomium chloride (DTDMAC) and cetyltrimethylammonium bromide (CTAB) were established by plating onto nutrient agar containing 5 microg/ml or 50 microg/ml DTDMAC or CTAB. Approximately 500 isolates were obtained and screened for the presence of the intI1 (class 1 integrase), qacE (multidrug efflux), and qacE Delta1 (attenuated qacE) genes. QAC resistance was higher in isolates from reed bed samples, and class 1 integron incidence was significantly higher for populations that were preexposed to QACs. This is the first study to demonstrate that QAC selection in the natural environment has the potential to coselect for antibiotic resistance, as class 1 integrons are well-established vectors for cassette genes encoding antibiotic resistance.
Highlights
Integrons are recombination and expression systems that capture genes as part of a genetic element known as a gene cassette [33]
quaternary ammonium compounds (QACs) resistance was higher in isolates from reed bed samples, and class 1 integron incidence was significantly higher for populations that were preexposed to QACs
Other QAC resistance genes belong to the small multidrug resistance family and include qacC/D, known as smr, qacE, qacE⌬1, qacF, qacG, qacH, and qacJ [3, 7, 15,16,17, 21, 23, 31, 32]. qacE, qacE⌬1, qacF, and qacG have been identified on integrons, and the remaining genes have been identified on multiresistance plasmids in staphylococci
Summary
Integrons are recombination and expression systems that capture genes as part of a genetic element known as a gene cassette [33]. Other QAC resistance genes belong to the small multidrug resistance family and include qacC/D, known as smr, qacE, qacE⌬1, qacF, qacG, qacH, and qacJ [3, 7, 15,16,17, 21, 23, 31, 32]. Gene cassettes contain a protein coding region and a recombination site known as a 59-be site which is responsible for the orientation of integration [9]. The second, In5 type consists of qacE⌬1, sul, orf, orf, and a partial tni module, tni⌬, consisting of two transposition genes. A similar approach using degenerate primers targeting the conserved regions of 59-be sites identified 164 gene cassettes, with the majority showing no relationship to known sequences
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