article · BMC Veterinary Research
A study investigating farmed fish in Egypt found a widespread presence of Aeromonas hydrophila alongside dangerous patterns of antimicrobial resistance. The bacteria were recovered from nearly a third of sampled fish across different seasons in Suez Canal regions. Laboratory screening confirmed multiple virulence genes, with the aerolysin gene occurring in more than half of the isolates. Resistance profiles revealed widespread resistance determinants, with every isolate carrying the bla_pse1 gene and substantial proportions carrying resistance markers for other classes of antibiotics. Over sixty percent of the bacterial strains were classified as multidrug-resistant, while nearly thirty percent exhibited extensive drug resistance. Several isolates combined multiple virulence traits with heavy resistance burdens. Pathogenicity trials further demonstrated their capacity to cause disease in fish. These characteristics demonstrate substantial disease risks for fish populations and highlight challenges for standard treatment regimens.
The widespread presence of multidrug-resistant and extensively drug-resistant bacteria in commercial fish stocks complicates disease treatment and threatens farm productivity. Because resistant strains and their resistance genes can spread through aquatic environments and the food supply, this poses serious risks to both aquaculture biosecurity and broader public health.
This research provides baseline surveillance data that could inform diagnostic test developers, fish health professionals, and aquaculture operators seeking to monitor pathogen resistance in hatcheries and grow-out facilities. However, the study focuses strictly on surveillance and characterisation, placing any direct commercial or therapeutic applications at an early stage. Real-world interventions will require separate applied development into targeted diagnostics, alternative treatments, or refined management protocols.
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In the present study, Aeromonas hydrophila was isolated from Tilapia zillii and Mugil cephalus samples collected during different seasons from various Suez Canal areas in Egypt. The prevalence of A. hydrophila, virulence genes, and antibiotic resistance profile of the isolates to the commonly used antibiotics in aquaculture were investigated to identify multiple drug resistance (MDR) and extensive drug-resistant (XDR) strains. In addition, a pathogenicity test was conducted using A. hydrophila, which was isolated and selected based on the prevalence of virulence and resistance genes, and morbidity of natural infected fish. The results revealed that A. hydrophila was isolated from 38 of the 120 collected fish samples (31.6%) and confirmed phenotypically and biochemically. Several virulence genes were detected in retrieved A. hydrophila isolates, including aerolysin aerA (57.9%), ser (28.9%), alt (26.3%), ast (13.1%), act (7.9%), hlyA (7.9%), and nuc (18.4%). Detection of antibiotic-resistant genes revealed that all isolates were positive for bla<sub>pse1</sub> (100%), bla<sub>SHV</sub> (42.1%), tetA (60.5%), and sul1 (42.1%). 63.1% of recovered isolates were considered MDR, while 28.9% of recovered isolates were considered XDR. Some isolates harbor both virulence and MDR genes; the highest percentage carried 11, followed by isolates harboring 9 virulence and resistance genes. It could be concluded that the high prevalence of A. hydrophila in aquaculture species and their diverse antibiotic resistance and virulence genes suggest the high risk of Aeromonas infection and could have important implications for aquaculture and public health.
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DOI: 10.1186/s12917-024-03942-y
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