In the present study, Aeromonas (A.) hydrophila was isolated from a captive-bred adult freshwater stingray (Potamotrygon motoro) reared at a commercial aquarium in Korea. The stingray had bites on its fins, hemorrhages on the ventral part, and congested internal organs. A bacterium was isolated from kidney and subsequently identified as A. hydrophila. Based on phylogenetic analysis results, the isolate in the present study (SNUAh-LA1) was most closely related to A. hydrophila AH10 (China) and A. hydrophila AKR1 (Korea). It is most likely that the pathogen infection resulted from Potamotrygon motoro cohabiting with ricefish (Oryzias latipes).

Identification of microorganisms, including bacteria, are widely used especially in environmental studies, biotechnology, clinical microbiology, microbial forensics, and in research study. The conventional method of bacteria identification is based on phenotypic observation techniques by profiling an organism’s metabolic attributes or some aspect of its chemical composition. Then, interpretation of test results involves substantial subjective judgement. Currently, general 16S rRNA sequencing and specific PCR play an important role in the accurate and faster identification of bacteria. The aim of this study is to compare the identification of the genus or species of bacteria from agricultural waste using conventional microbiology biochemical test and molecular techniques PCR 16S rRNA universal amplified ribosomal region (UARR) sequencing. A total of 72 agricultural waste samples and 2 ATCC culture as positive control were tested. Out of two ATCC bacteria and fifteen bacteria isolates identified by the biochemical test, twelve species (71%) of bacteria gave exactly the same bacteria genus as the 16S rRNA sequencing results. Aeromonas hydrophilia, Alcaligenes faecalis and Acinetobacter calcoaceticus was revealed as Pseudomonas sp. from the sequencing results. As for Alcaligenes sp., the results from the sequencing is Stenotrophomonas maltophilia. Previous reports also showed different results of the same isolate which were from similar classification, and closely related to each other. The limited number of biochemical tests available in a laboratory will contribute to misidentification of a proposed specie.

Moribund albino catfish, Clarias sp., displayed from an indoor private commercial aquarium were submitted in the laboratory for diagnostic examination. Dense culture of bacteria was recovered from the kidney and was characterized using Vitek System 2 and showed 98% probability to Aeromonas (A.) hydrophila. PCR result showed positive using A. hydrophila extracellular hemolysin gene ahh1 (130 bp) and aerolysin gene aerA (309 bp). The 16S rRNA gene was identical and exhibited 97% sequence similarity with the other known isolates of A. hydrophila available in the GenBank. In this paper, we reported the isolation and molecular detection of A. hydrophila from an albino catfish.

Objective: The aerolysin (aerA) is a virulence indicator used to identify the pathogenicity of the Aeromonas strain. Targeting a pathogen's crucial virulence gene for detection is essential, as it determines the potential threat to the host. This study aimed to develop a gold nanoparticle (AuNP) probe for detecting the gene aerA in Aeromonas hydrophila among field samples. Materials and Methods: Kidney samples among both healthy and sick Nile tilapias in five provinces of Luzon Island were collected for bacterial analysis. Screening using specific primers targeting aerA was conducted in parallel with testing the AuNPs probe on the same sample set. The positive control provided by BFAR-NFLD, confirmed by polymerase chain reaction (PCR) assay, was used as a positive sample containing the target gene. Results: The AuNP probe demonstrated a computed accuracy of 81.32%, sensitivity of 100%, and specificity of 81.26%. Among the 257 reactions, 59 were false positives, while no false negative results were observed. The AuNP probe could detect aerA at levels as low as 30 ng/μl. The low prevalence of the target gene may be attributed to the use of general media instead of specific media like Rimler-Shotts agar. Conclusion: The established colorimetric detection method for A. hydrophila with the aerA gene offers a swift alternative to PCR, negating the requirement for advanced equipment like a thermal cycler. [J Adv Vet Anim Res 2023; 10(4.000): 593-598]