Identification of Aeromonas species in trout in Tunceli province by MALDI-TOF MS method

The genus Aeromonas has undergone a number of taxonomic and nomenclature revisions over the past 20 years, and new (sub)species and biogroups are continuously described. The genus Aeromonas comprises more than thirty Gram-negative bacterial species which mostly act as opportunistic microorganisms. These bacteria are distributed naturally in diverse aquatic ecosystems, where they are easily isolated from animals such as fish and crustaceans. Standard identification methods such as biochemical characterization have deficiencies and do not allow clarification of the taxonomic position. This study describes the development of a matrix-assisted laser desorption/ionisation–time of flight mass spectrometry (MALDI-TOF MS) identification database for a rapid identification of clinical and environmental Aeromonas isolates. In this study tissue, samples taken from the liver, intestine, spleen and kidneys of 200 rainbow trout obtained from 16 facilities rainbow trout in net cages and concrete ponds in Mazgirt, Ovacık, Çemişgezek and Pertek districts in Tunceli province in April, May, December, January and 64 water samples were analysed. The aim of this study was to determine the prevalence of Aeromonas species in freshwater fish farms and factors affecting their prevalence in Tunceli province. In addition, it was aimed to compare the ldifferent methods such as MALDI-TOF MS, 16S rDNA sequencing and housekeeping gene sequencing (gyrB), method for species class identification of Aeromonas. As a result of the analysis with MALDI-TOF MS of 526 suspected isolates isolated by the traditional method; 526 bacteria belonging to 13 families including Basillaceae, Comamonadaceae, Enterobacteriaceae, Enterococcaceae, Erwiniaceae, Moraxellaceae, Nocardiaceae, Pseudomonadaceae, Sthaphylococcaceae, Streptococcaceae, Xanthomonadaceaea, Yersiniaceae and Aeromonadaceae were identified. In a cross-sectional study from 16 farms in four districts of raised in net cages and concrete ponds in Mazgirt, Ovacık, Çemişgezek and Pertek districts in Tunceli province, 5 species of Aeromonas were identified by 16S rDNA and gyrB sequencing. Five species of Aeromonas were more prevalent (MP) in fish farms, A. sobria (%47,52) was the highest, followed by A. veronii (%26,95), A. media (%12,06) and A. hydrophila(%7,80). The less prevalent species were A. salmonicida (%5,67). Spatial variation in the prevalence of Aeromonas species was observed. In our study, the accuracy of MALDI-TOF MS results of 141 isolates identified as Aeromonas species was found to be %100 (141 isolates) at genus level and%92,2 (130 isolates) at species level. It is recommended to use the MALDI-TOF MS method because it gives accurate and fast results in molecular analysis. However, it has been concluded that 16S rDNA and gyrB gene sequencing methods are more reliable methods at the point where no distinction can be made in identification at the species level due to the higher capacity to distinguish between species in phylogenetic studies of the genus Aeromonas. This study, conducted in our country for the identification of Aeromonas species by MALDI-TOF MS method in rainbow trout in the Upper Euphrates basin and Tunceli province, is one of the pioneering studies in terms of its subject. Our study will be a guide for future research in this field. This is the first study that determined the prevalence and identified the factors that affect the prevalence of Aeromonas species in freshwater fish farms. This information will be useful in managing Aeromonas infection in fish and their risks to public health.