Prevalence, molecular characterization, virulotyping, and antibiotic resistance of motile aeromonads isolated from Nile tilapia farms at northern Egypt

Abstract

Objective: This study was aimed to survey Aeromonas spp associated with cultured Nile tilapia Oreochromis niloticus (O. niloticus) showing signs of motile Aeromonas septicemia (MAS) at different fish farms; molecular characterization and identification of test isolates; and to test the isolates for their antimicrobial and virulence activities that contribute to its pathogenesis. Design: Observational study Animals: 280 Nile tilapia Procedures: Clinically diseased 280 Nile tilapia, were collected from different localities at Kafr El-Sheik and Dakahlia governorates. The clinical picture and gross lesions were recorded. Aeromonas spp were isolated and presumptively identified using API20E. The identification was confirmed using PCR. Hemolysin (hylA), lipase, and aerolysin (aerA) virulence genes were detected among isolates obtained from different sampling sites. Besides, antimicrobial activity was reported for the identified A. hydrophila. Results: General septicemic signs were evident on Nile tilapia including, skin hemorrhages and ulcerations, bilateral exophthalmia, congested internal organs with significant mortalities. The prevalence of bacterial infection among naturally diseased Nile tilapia was 79.17, 70, and 58.33 in Kafr El-Sheikh, El- Manzala, and Gamsa fish farms, respectively. The most prevalent bacterial isolates were aeromonads (29.84 %), of all, 65.63 A. hydrophila, 18.75 A. caviae, and 15.63 A. sobria. All isolates were positively amplified using a species-specifying primer to determine A. hydrophila. Virulence genes detection revealed that five A. hydrophila isolates (83.3 %) harbored the aerA gene. Meanwhile, hylA and lipase genes positive isolates were lower reaching 16.7 % for both genes. A. hydrophila was highly sensitive to ciprofloxacin, amikacin, trimethoprim, and chloramphenicol, and MAR index of A. hydrophila isolates was ranged from 0.16-0.42 Conclusion and clinical relevance: Our findings demonstrate that Aeromonas spp are among the bacterial pathogens implicated in summer mortalities in tilapia fish farms in Egypt. Besides, determination of the prevalence, virulence genes, and antibiotic resistance pattern associated with the disease outbreaks is critical data that warrant the development of strategies to proper monitoring and farm management practices.

Investigation of the Prevalence, Virulence Genes, and Antibiogram of Motile Aeromonads Isolated from Nile Tilapia Fish Farms in Egypt and Assessment of their Water Quality

“…These findings are related to the poor water quality parameters evaluated in the examined farms, as the highest aeromonads prevalence was noticed in farm IV and farm III, particularly in August and June. These present findings are consistent with other studies reported elsewhere [ 50 , 53 ]. Taken into account, the highest prevalence of Aeromonas during summer could be attributed to improper water quality parameters as measured herein, where shifting from normal ranges poses stress on fish with subsequent lowering in their resistance to bacterial infections [ 50 , 54 ].…”

“…Our findings were consistent with previous studies that showed similar histopathological lesions due to MAS [81][82][83]. These observations were supportive to the motile aeromonads virulence genes herein, as well as the extracellular products, enzymes, and enterotoxins produced by motile aeromonads that together led to a systemic damage to the internal organs, mainly, liver, kidney and spleen with eventual death [9,50,67,81].…”

“…Among others, motile Aeromonas septicemia (MAS), caused by Aeromonas spp., is one of such important bacterial infections, leading to fish mass mortalities and substantial economic losses [ 17 , 45 , 46 ]. Our results of clinical signs and postmortem lesions on affected fish coincided with previous studies reported elsewhere [ 47 , 48 , 49 , 50 ].…”

“…A MAR index of our isolates showed high ranges between 0.27 and 0.82. In the same context, MAR index ranges of 0.25–0.68 [ 66 ] and 0.16–0.42 [ 50 ] were recorded in different Aeromonas spp. isolated from various aquatic sources.…”

Prevalence and Antibiogram of Vibrio parahaemolyticus and Aeromonas hydrophila in the Flesh of Nile Tilapia, with Special Reference to Their Virulence Genes Detected Using Multiplex PCR Technique

“…However, another study reported a lower rate of 66.7% [90]. For instance, in another study, the prevalence of the aerA gene was high (83.3%) and that of the ahh1 gene was low (16.7%) [91].…”