Evaluation of identification techniques for the fish pathogen, Aeromonas hydrophila, from Indonesia

ABSTRACT

Aims: This study evaluated the accuracy of three methods used in the identification of Aeromonas hydrophila, a Gramnegative bacterium found in warm aquatic environments. A. hydrophila samples from Indonesia were tested using (a) SNI 7303, developed by the Indonesian government, (b) the method of Dorsch and (c) the method of Cascón. The results obtained were compared to that of the gold standard method, which used 16S rDNA sequences. Methodology and results: Based on the Indonesian government standard identification method SNI7303, we identified 56 out of 95 samples as A. hydrophila. The samples were then screened using the PCR amplification approach developed by Dorsch and Cascón. Of the 56 samples, only 20 samples were found to be positive by either the Dorsch or Cascón methods. DNA from these 20 samples was amplified using common 16S rDNA primers and the sequences compared with available 16S rDNA sequences from the GenBank. Phylogenetic analyses on the data were performed using Clustal X and MEGA 5 software. Conclusion, significance and impact of study Of the 56 samples positively identified as A. hydrophila using the BSN method, identity in only five samples were positively confirmed using the16S rDNA method, giving an accuracy of only 8.9%. In this connection, the Dorsch method was 31.3% accurate while the Cascón method provided 45.5% correct identification. When all three methods were used in combination, 71.4% of the samples were correctly identified. The results of the study show that methods used to identify A. hydrophila cannot be used with confidence to identify A. hydrophila from Indonesia and probably from other tropical regions as well. The genetic diversity of Aeromonas bacteria in Indonesia appears to be considerably higher than that encountered by Dorsch or Cascón. Therefore, there is a need to develop a new simple method to identify A. hydrophila from tropical regions.