Antibiotic Resistance in Bacteria from Farmed Tilapia and Mullet Fish

Jenn Hoskins
11th March, 2024

Antibiotic Resistance in Bacteria from Farmed Tilapia and Mullet Fish

Image Source: Natural Science News, 2024

Key Findings

  • In Egypt's Suez Canal, 31.6% of tested fish carry the disease-causing bacterium A. hydrophila
  • The bacterium in these fish has multiple genes enabling it to infect and resist common antibiotics
  • Fish with more of these genes are more likely to die, posing risks to aquaculture and public health
Aquaculture, the farming of fish and other aquatic organisms, is a rapidly growing industry, but it faces significant challenges from bacterial infections. One such bacterium causing concern is Aeromonas hydrophila, known to cause disease in fish and potentially impact human health as a zoonotic agent. A recent investigation by the Central Laboratory for Aquaculture Research (CLAR) in Egypt sheds light on the prevalence of this pathogen, its resistance to antibiotics, and the virulence factors that make it a formidable threat in aquaculture[1]. The study focused on A. hydrophila isolated from two species of fish, Tilapia zillii and Mugil cephalus, collected from the Suez Canal area. Out of 120 fish samples, A. hydrophila was detected in 38, indicating a 31.6% prevalence rate. This finding aligns with earlier research that highlighted the widespread nature of Aeromonas species in water and fish sources, emphasizing the potential public health risks[2]. Researchers at CLAR identified several virulence genes in the A. hydrophila isolates. These genes are responsible for the bacterium's ability to cause disease. The most common was the aerolysin gene (aerA), found in 57.9% of isolates. Other virulence genes detected included those responsible for serine protease (ser), another enterotoxin (alt), a heat-stable toxin (ast), cytotoxic enterotoxin (act), hemolysin A (hlyA), and a nuclease (nuc). The presence of these genes suggests that the isolates have a range of tools to infect and damage host tissues, which can lead to sepsis and ulcer syndromes in fish[3]. The study went further to examine the antibiotic resistance profiles of the A. hydrophila isolates. Alarmingly, all isolates carried the blapse1 gene, which confers resistance to penicillins, and many had additional resistance genes, including those providing resistance to tetracyclines (tetA) and sulfonamides (sul1). The researchers categorized 63.1% of the isolates as multidrug-resistant (MDR), meaning they were resistant to at least one agent in three or more antimicrobial categories. Even more concerning was that 28.9% were classified as extensively drug-resistant (XDR), resistant to at least one agent in all but two or fewer antimicrobial categories. This high level of antibiotic resistance is particularly troubling considering the reliance on antibiotics in aquaculture. Prior studies have shown a similar trend, with a high percentage of Aeromonas isolates being resistant to common antibiotics, which limits the options for treating infected fish[4]. The pathogenicity test conducted by CLAR revealed a direct relationship between the number of virulence genes an isolate carried and its ability to cause disease. Isolates with a greater number of virulence genes were associated with higher mortality rates in infected fish. This observation underscores the importance of monitoring and managing the presence of these virulence factors to prevent significant losses in aquaculture. The findings from CLAR's study are a cause for concern not only for the aquaculture industry but also for public health. The fact that A. hydrophila is present in a substantial percentage of fish and carries multiple virulence and resistance genes indicates a significant risk of infection. Moreover, the genetic relatedness of isolates from water and fish suggests that virulent clones could be circulating in the aquatic environment[2]. In summary, the study by CLAR provides crucial insights into the threat posed by A. hydrophila in aquaculture. The high prevalence of virulent and antibiotic-resistant strains of A. hydrophila in the Suez Canal area highlights the need for vigilant monitoring, responsible antibiotic use, and the development of effective control measures, such as vaccination strategies, to safeguard the health of farmed fish and protect public health[5].

BiotechGeneticsMarine Biology


Main Study

1) Phenotypic, molecular detection, and Antibiotic Resistance Profile (MDR and XDR) of Aeromonas hydrophila isolated from Farmed Tilapia zillii and Mugil cephalus.

Published 8th March, 2024

Related Studies

2) Enterotoxin gene profile and molecular epidemiology of Aeromonas species from fish and diverse water sources.

3) Aeromonasveronii Infection in Commercial Freshwater Fish: A Potential Threat to Public Health.

4) Virulence genes contributing to Aeromonas hydrophila pathogenicity in Oreochromis niloticus.

5) Efficacy of Injectable and Immersion Polyvalent Vaccine against Streptococcal Infections in Broodstock and Offspring of Nile tilapia (Oreochromis niloticus).

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