Class 1 integron mediates antibiotic resistance in Aeromonas spp. from rainbow trout farms in Australia

Abstract number: 1733_14

Akinbowale O., Peng H., Barton M.

Objectives: As part of the work carried out in response to the Joint Expert Technical Advisory Committee on Antibiotic Resistance (JETACAR) recommendation on antibiotic resistance surveillance, the presence of integrons and other resistance determinants was investigated in 90 Aeromonas isolates derived from nine freshwater trout farms in Victoria (Australia).

Methods: Polymerase chain reaction (PCR) was carried out for the detection of integrase genes Int1, Int2, Int3, integron variable region, integron associated aadA gene with primers specific for the detection of the aadA1a gene cassette and other closely related aadA gene cassettes (with the exception of aadA4 and aadA5), streptomycin resistance genes strA-strB, sulphonamide resistance gene sul1, quaternary ammonium compound resistance gene qac1, beta lactamase resistance genes blaTEM, blaSHV, and tetracycline resistance gene tetA-E and tetM. Clonality analysis was performed by Pulse field gel electrophoresis (PFGE).

Results: Class 1 integrons were detected in 28 of the 90 (31%) strains investigated. Class 2 and 3 integrons were not detected. Using primers specific for the aadA gene, aadA gene was detected in 19 of the 27 (70%) streptomycin resistant strains. However, when the variable region of the integron was amplified, four strains with streptomycin MIC 128 mg/L and one with MIC >128 mg/L gave amplicon sizes of 1000 bp each. Other strains having MIC 16 mg/L did not give any amplicon possibly due to lack of the 3'conserved segment. Sequence analysis of the products reveals the presence of aadA2 gene. None of the strains harboured the strA-strB genes. PFGE analysis of the five strains reveals genetic relatedness with all five having the same banding pattern even though they came from different farms. Sul1 gene was detected in 13 of the 15 sulphonamide resistant strains and qac1 gene detected in 8 of the 28 integron bearing strains. TetC was detected in all and tetA in 9 of the 18 tetracycline resistant strains. No blaTEM and blaSHV was detected.

Conclusion: Although no antibiotics are licenced for use in Australian aquaculture and there has been no information on resistance determinants, our data suggests that Aeromonas carrying resistance genes as well as integrons are present in farm raised fish and sediments and different fish farms might share a common pool for the aadA2 gene.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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