Aeromonas hydrophila ST251 and Aeromonas dhakensis are major emerging pathogens of striped catfish in Vietnam

Abstract

IntroductionAeromonads are ubiquitous in aquatic environments and several species are opportunistic pathogens of fish. Disease losses caused by motile Aeromonas species, particularly Aeromonas hydrophila, can be challenging in intensive aquaculture, such as at striped catfish (Pangasianodon hypophthalmus) farms in Vietnam. Outbreaks require antibiotic treatments, but their application is undesirable due to risks posed by resistance. Vaccines are an attractive prophylactic and they must protect against the prevalent strains responsible for ongoing outbreaks.MethodsThis present study aimed to characterize A. hydrophila strains associated with mortalities in striped catfish culture in the Mekong Delta by a polyphasic genotyping approach, with a view to developing more effective vaccines.ResultsDuring 2013–2019, 345 presumptive Aeromonas spp. isolates were collected at farms in eight provinces. Repetitive element sequence-based PCR, multi-locus sequence typing and whole-genome sequencing revealed most of the suspected 202 A. hydrophila isolates to belong to ST656 (n = 151), which corresponds to the closely-related species Aeromonas dhakensis, with a lesser proportion belonging to ST251 (n = 51), a hypervirulent lineage (vAh) of A. hydrophila already causing concern in global aquaculture. The A. dhakensis ST656 and vAh ST251 isolates from outbreaks possessed unique gene sets compared to published A. dhakensis and vAh ST251 genomes, including antibiotic-resistance genes. The sharing of resistance determinants to sulphonamides (sul1) and trimethoprim (dfrA1) suggests similar selection pressures acting on A. dhakensis ST656 and vAh ST251 lineages. The earliest isolate (a vAh ST251 from 2013) lacked most resistance genes, suggesting relatively recent acquisition and selection, and this underscores the need to reduce antibiotics use where possible to prolong their effectiveness. A novel PCR assay was designed and validated to distinguish A. dhakensis and vAh ST251 strains.DiscussionThis present study highlights for the first time A. dhakensis, a zoonotic species that can cause fatal human infection, to be an emerging pathogen in aquaculture in Vietnam, with widespread distribution in recent outbreaks of motile Aeromonas septicaemia in striped catfish. It also confirms vAh ST251 to have been present in the Mekong Delta since at least 2013. Appropriate isolates of A. dhakensis and vAh should be included in vaccines to prevent outbreaks and reduce the threat posed by antibiotic resistance.

Isolation, genetic characterization, and virulence profiling of different Aeromonas species recovered from moribund hybrid catfish (Clarias spp.)

“…Aeromonas dhakensis was the predominant Aeromonas species isolated from freshwater fish in nine fish farms in Malaysia [ 67 ]. Aeromonas dhakensis is a major emerging pathogen of striped catfish in Vietnam [ 68 ]. Aeromonas dhakensis is possibly an important pathogen in catfish and other freshwater fishes, either in Indonesia or around the world.…”

First report and genetic characterization of Aeromonas dhakensis in Aldabra giant tortoise

“…To date, there have been several reports of A. dhakensis as a causative pathogen in various animals worldwide. These include dolphins and eels in Spain [6, 13], pacu sh in Brazil [33], oil sardine in India [34], aquaculture sh in South Korea [19], Nile tilapia in Mexico [20], striped cat sh in Vietnam [14] and Malaysia [35], sea lions and farmed Siamese crocodiles in China [15,21]. However, there have been no previous reports of A. dhakensis infection in tortoises.…”

“…The genus Aeromonas is widely distributed in various ecological systems, including underground water, drinking water, river water, oceanic water, irrigating water, and regenerating wastewater [1][2][3][4][5][6]. Some species of Aeromonas are opportunistic pathogenic bacteria that infect humans [7][8][9] and a wide range of animals such as sh, amphibians, aquatic animals, and reptiles [10][11][12][13][14]. The most common Aeromonas infections include enter gastritis, skin and soft-tissue infections, bacteremia, septicemia, as well as other infections affecting the hepatobiliary system, respiratory system, bones, and joints [8, 9,14,15].…”

“…Some species of Aeromonas are opportunistic pathogenic bacteria that infect humans [7][8][9] and a wide range of animals such as sh, amphibians, aquatic animals, and reptiles [10][11][12][13][14]. The most common Aeromonas infections include enter gastritis, skin and soft-tissue infections, bacteremia, septicemia, as well as other infections affecting the hepatobiliary system, respiratory system, bones, and joints [8, 9,14,15]. These bacteria can be transmitted to humans and animals mainly through the ingestion of contaminated water or food, as well as exposure to fecal pollution, thereby presenting challenges in the context of One Health [16].…”

“…It has also been found in skin tissue of ornamental sh in Portugal [6,18], diseased eels [6] and diseased dolphin in Spain [13]. Furthermore, it has been detected in diseased sh in South Korea [19] and Mexico [20], striped cat sh in Vietnam [14], a diseased sea lion [15] and farmed Siamese crocodiles in China [21]. A. dhakensis has caused serious infections in humans [9,[22][23][24], demonstrating higher virulence compared to other Aeromonas species [21,25].…”