Is it really Aeromonas hydrophila

We read with great interest the article by Coutinho et al. [1] who described a case of cutaneous abscess with sepsis caused by Aeromonas hydrophila. These authors reported the isolation of A. hydrophila from peripheral blood and abscess aspiration of a young man who developed an axillary abscess after bathing in a freshwater lake. In this case, A. hydrophila was identified by conventional laboratory (biochemical) methods that are standardly used in most hospital laboratories. However, such biochemical tests are unreliable to accurately identify Aeromonas to the species level. For example, Aravena-Roman et al. recently investigated 215 Aeromonas strains, including A. hydrophila, which represented more than 50 % of strains [2]. All of the isolates, which had been previously identified by a conventional biochemical scheme, were subjected to analysis of their nucleotide sequences derived from the gyrB and rpoD genes. The authors reported that correct identification had occurred in only about one-third of 104 strains that had been identified as A. hydrophila based on phenotypic characteristics. In contrast, two-thirds of the isolates were re-identified as non-hydrophila Aeromonas, with most being A. aquariorum strains (54 strains, 51.9 %) [2]. The same result was obtained in another case study by Wu et al. [3], who described a cirrhotic patient who developed septicemia caused by A. aquariorum, which was initially identified as A. hydrophila based on the results of biochemical tests. Therefore, we would like to suggest that genotypic methods should be applied for the accurate identification of Aeromonas species to avoid misidentification.