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Aeromonas hydrophila subsp. dhakensis isolated from feces, water and fish in Mediterranean Spain.

ABSTRACT: Eight Aeromonas hydrophila-like arabinose-negative isolates from diverse sources (i.e., river freshwater, cooling-system water pond, diseased wild European eels, and human stools) sampled in Valencia (Spain) during 2004-2005, were characterized by 16S rRNA gene sequencing and extensive biochemical testing along with reference strains of most Aeromonas species. These isolates and all reference strains of A. hydrophila subsp. dhakensis and A. aquariorum showed a 16S rRNA sequence similarity of 99.8-100%, and they all shared an identical phenotype. This matched exactly with that of A. hydrophila subsp. dhakensis since all strains displayed positive responses to the Voges-Prokauer test and to the use of dl-lactate. This is the first report of A. hydrophila subsp. dhakensis recovered from environmental samples, and further, from its original isolation in India during 1993-1994. This was accurately identified and segregated from other clinical aeromonads (A. hydrophila subsp. hydrophila, A. caviae, A. veronii biovars veronii and sobria, A. trota, A. schubertii and A. jandaei) by using biochemical key tests. The API 20 E profile for all strains included in A. hydrophila subsp. dhakensis was 7047125. The prevalence of this species in Spanish sources was higher for water (9.4%) than for feces (6%) or eels (1.3%). Isolates recovered as pure cultures from diseased eels were moderately virulent (LD(50) of 3.3×10(6) CFU fish(-1)) to challenged eels in experimental trials. They were all resistant to ticarcillin, amoxicillin-clavuranic acid, cefoxitin, and imipenem, regardless of its source. Our data point to A. hydrophila subsp. dhakensis as an emerging pathogen for humans and fish in temperate countries.

SUBMITTER: Esteve C

PROVIDER: S-EPMC4103543 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Aeromonas hydrophila subsp. dhakensis isolated from feces, water and fish in Mediterranean Spain.

Esteve Consuelo C Alcaide Elena E Blasco María Dolores MD

Microbes and environments 20120403 4

Eight Aeromonas hydrophila-like arabinose-negative isolates from diverse sources (i.e., river freshwater, cooling-system water pond, diseased wild European eels, and human stools) sampled in Valencia (Spain) during 2004-2005, were characterized by 16S rRNA gene sequencing and extensive biochemical testing along with reference strains of most Aeromonas species. These isolates and all reference strains of A. hydrophila subsp. dhakensis and A. aquariorum showed a 16S rRNA sequence similarity of 99. ...[more]

PMID: 22472298

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Project description: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.

Project description:IntroductionMotile Aeromonas septicemia (MAS) is a burden for striped catfish (Pangasius hypophthalmus) farmers in Vietnam. MAS can be caused by several species of Aeromonas but Aeromonas hydrophila is seen as the leading cause of MAS in aquaculture, but recent reports suggest that A. dhakensis is also causing MAS.MethodsHere we investigated the bacterial etiology of MAS and compared the genomic features of A. hydrophila and A. dhakensis. We collected 86 isolates from diseased striped catfish fingerlings over 5 years from eight provinces in Vietnam. Species identification was done using PCR, MALDI-TOF and whole genome sequence (WGS). The MICs of commonly used antimicrobials was established. Thirty presumed A. hydrophila isolates were sequenced for species confirmation and genomic comparison. A phylogenetic analysis was conducted using publicly available sequences and sequences from this study.ResultsA total of 25/30 isolates were A. dhakensis sequence type (ST) 656 and 5/30 isolates were A. hydrophila ST 251. Our isolates and all publicly available A. hydrophila isolates from Vietnam belonged to ST 251 and differed with <200 single nucleotide polymorphisms (SNP). Similarly, all A. dhakensis isolates from Vietnam belonged to ST 656 and differed with <100 SNPs. The tet(A) gene was found in 1/5 A. hydrophila and 19/25 A. dhakensis. All A. hydrophila had an MIC ≤2 mg/L while 19/25 A. dhakensis had MIC ≥8 mg/L for oxytetracycline. The floR gene was only found in A. dhakensis (14/25) which showed a MIC ≥8 mg/L for florfenicol. Key virulence genes, i.e., aerA/act, ahh1 and hlyA were present in all genomes, while ast was only present in A. dhakensis.DiscussionThis study confirms previous findings where A. dhakensis was the dominating pathogen causing MAS and that the importance of A. hydrophila has likely been overestimated. The differences in antimicrobial susceptibility between the two species could indicate a need for targeted antimicrobial treatment plans. The lipopolysaccharide regions and outer membrane proteins did not significantly differ in their immunogenic potentials, but it remains to be determined with in vivo experiments whether there is a difference in the efficacy of available vaccines against A. hydrophila and A. dhakensis.

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Aeromonas hydrophila subsp. dhakensis isolated from feces, water and fish in Mediterranean Spain.

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Aeromonas hydrophila subsp. dhakensis isolated from feces, water and fish in Mediterranean Spain.

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