Characterization of the Biofilm-Forming Ability and Certain Virulence Characters of Aeromonas spp. Isolates From Rainbow Trout

Abstract

Aeromonas spp., commonly found in the aquatic environment, cause infections in both fish and humans. Their pathogenicity depends on various virulence factors and ability to form biofilm. The current study aimed to determine the biofilm-forming capabilities and certain virulence characteristics of 25 Aeromonas spp. isolates obtained from rainbow trout in T & uuml;rkiye. The biofilm-forming abilities of isolates were investigated comparatively using Congo red agar (CRA), the tube method (TM), and tissue culture plates (TCPs). Potential virulence factors, including hemolytic activity, gelatinase production, serine protease activity, DNase activity, and motility, were evaluated using phenotypic tests. Additionally, the distribution of four known virulence genes, namely aerA, exu, fla, and ser, were screened by polymerase chain reaction. It was determined by CRA, TM, and TCP that 68%, 48%, and 60% of the isolates formed biofilms, respectively, whereas combining the results obtained from the three methods, 92% of the isolates formed biofilms. Virulence factors were expressed at variable levels both phenotypically and genotypically among the isolates. Notably, A. bestiarum isolates exhibited positive results for swimming motility, serine protease activity, gelatinase production, DNase activity, and beta-hemolysis activity, and carried at least three virulence genes, indicating their potential pathogenicity. Although a negative association was detected between biofilm formation (using different methods) and certain phenotypic and genetic virulence markers, positive correlations were found between the phenotypic and genetic virulence markers themselves. This research highlights the significance of using multiple techniques to evaluate the biofilm formation capabilities of Aeromonas spp. from fish. The high incidence of biofilm formation among the isolates raises concerns, as it may increase the risk of reinfection in aquaculture facilities. Therefore, regular monitoring of biofilm formation and certain virulence factors in Aeromonas spp. from fish is imperative, alongside the establishment of new disease prevention and control strategies to combat Aeromonas infections, particularly to inhibit biofilm formation.