Detection of hemolytic strains of Aeromonas hydrophila and A . sobria along with other Aeromonas spp. from fish and fishery products by multiplex PCR

Development of a surface plasmon resonance (SPR) assay for rapid detection of Aeromonas hydrophila

Aquaculture plays an increasingly important if not critical role in the current and future world food supply. Aeromonas hydrophila, a heterotrophic, Gram-negative, bacterium found in fresh or brackish water in warm climates poses a serious threat to the aquaculture industry in many areas, causing significant economic losses. Rapid, portable detection methods of A. hydrophila are needed for its effective control and mitigation. We have developed a surface plasmon resonance (SPR) technique to detect PCR (polymerase chain reaction) products that can replace agarose gel electrophoresis, or otherwise provide an alternative to costlier and more complicated real-time, fluorescence-based detection. The SPR method provides sensitivity comparable to gel electrophoresis, while reducing labor, cross-contamination, and test time, and employs simpler instrumentation with lower cost than real-time PCR.

A novel detection method for the pathogenic Aeromonas hydrophila expressing aerA gene and/or hlyA gene based on dualplex RAA and CRISPR/Cas12a

Aeromonas hydrophila is an emerging waterborne and foodborne pathogen with pathogenicity to humans and warm water fishes, which severely threatens human health, food safety and aquaculture. A novel method for the rapid, accurate, and sensitive detection of pathogenic A. hydrophila is still needed to reduce the impact on human health and aquaculture. In this work, we developed a rapid, accurate, sensitive, and visual detection method (dRAA-CRISPR/Cas12a), without elaborate instruments, integrating the dualplex recombinase-assisted amplification (dRAA) assay and CRISPR/Cas12a system to detect pathogenic A. hydrophila expressing aerA and/or hlyA virulence genes. The dRAA-CRISPR/Cas12a method has high sensitivity, which can rapidly detect (about 45 min) A. hydrophila with the limit of detection in 2 copies of genomic DNA per reaction, and has high specificity for three pathogenic A. hydrophila strains (aerA⁺hlyA⁻, aerA⁻hlyA⁺, and aerA⁺hlyA⁺). Moreover, dRAA-CRISPR/Cas12a method shows satisfactory practicability in the analysis of the spiked human blood and stool and fish samples. These results demonstrate that our developed pathogenic A. hydrophila detection method, dRAA-CRISPR/Cas12a, is a promising potential method for the early diagnosis of human A. hydrophila infection and on-site detection of A. hydrophila in food and aquaculture.

Antibiotic Resistance and Virulence Factor Gene Profile of Aeromonas hydrophila Isolated from Carp (Cyprinidae) Suspected with Hemorrhagic Septicemia in Gilan, Iran

The present study was conducted to determine the antibacterial resistance profile of Aeromonas hydrophila (n= 42) isolated from the 100 hemorrhagic septicemia-suspected carp in Gilan, Iran. The prevalence of class 1 and 2 integrons, antibiotic resistance genes (ARG), and virulence factor genes (VFG) among these isolates was investigated using PCR. Also, the possible association between the presence of VFGs and the antibiotic resistance profile of isolates was assessed. The majority of A. hydrophila isolates (83.33%) exhibited multi-drug resistance (MDR) profile, and all isolates were resistant to clindamycin, while all isolates were susceptible to amikacin. intI1 and intI2 gene was found in 26.2% and 4.8% isolates, respectively. This is the first report of the presence of the intI2 gene in A. hydrophila isolates in Iran. The bla_TEM (40.5%) and tetA (33.3%) genes were found as the predominant ARGs. The most frequently detected VFGs were lip and ahh1(90.5%), while the examined isolates carrying at least three VFGs and the most prevalent VFGs profile was ast+, act+, alt+, ahhl+, aerA+, ahyB+, and lip+. The results of this study indicate a positive association between the presence of VFGs and antibiotic resistance, and most MDR A. hydrophila isolates showed high frequencies of VFGs.

Effects of environmental salinity on the immune response of the coastal fish Scatophagus argus during bacterial infection

The coastal aquaculture is characterized with environmental salinity fluctuation, and the effects of salinity stress on the immunity of cultured fish are needed to be further explored. Scatophagus argus is an important species in the wild fisheries and aquaculture industry, it would be of great value to reveal the impact of salinity change on the immune response in this species. Understanding the effects of salinity stress on immune response can provide valuable insights into salinity management in the aquacultural process. The head kidney, which is an organ unique for teleost fish, functions not only as a central immune organ but also as a crucial role in the stress response during which the secretion of immunoregulatory molecules i.e. cytokines is facilitated. In the present study, Individuals of S. argus acclimated to 3 different salinities [0‰ (FW), 10‰ (BW), and 25‰ (SW)] were injected intraperitoneally with A. hydrophila, and then monitored throughout one week. The effects of environmental salinity on the immune response in S. argus stimulated by A. hydrophila infection were investigated. mRNA expression profiles of cytokine genes IL-1β, IL-6, IL-10 and TNF-α in different salinity groups was quite different. mRNA expression of cytokine genes in BW group and SW group rose more quickly and significantly higher than FW group (p < 0.05) at early stages (6-24 hpi) after bacterial injection, and before 96 hpi, the highest value of cytokine expression at each time point was recorded in SW group. Immune parameters such as lysozyme level, complement C3 activity and IgM content in BW and FW groups were lower than SW group at each time point from 24 to 144 hpi after bacterial injection. In addition, leukocyte profiles in the head kidney and blood were also investigated. Although hypoosmotic acclimation could temporarily stimulate monocyte and neutrophil proliferation, it was observed that the number of monocytes, neutrophils and lymphocytes of the head kidney and blood in SW group increased more quickly than BW and FW groups after bacterial infection. Our results indicate that hypoosmotic stress due to the decrease of environmental salinity has suppressive immunoregulatory effects on the immune response of S. argus.

Prevalence, antibiotic susceptibility, and presence of drug resistance genes in Aeromonas spp. isolated from freshwater fish in Kelantan and Terengganu states, Malaysia

Background and Aim:

The emergence of antibiotic-resistant bacterial pathogens has been increasingly reported, which has resulted in a decreasing ability to treat bacterial infections. Therefore, this study investigated the presence of Aeromonas spp., including its antibiotic resistance in various fish samples, Oreochromis spp., Clarias gariepinus, and Pangasius hypophthalmus, obtained from Kelantan and Terengganu, Malaysia.

Materials and Methods:

In this study, 221 fish samples, of which 108 (Oreochromis spp., n=38; C. gariepinus, n=35; and P. hypophthalmus, n=35) were from Kelantan and 113 (Oreochromis spp., n=38; C. gariepinus, n=35; and P. hypophthalmus, n=40) were from Terengganu, were caught using cast nets. Then, samples from their kidneys were cultured on a Rimler Shott agar to isolate Aeromonas spp. Polymerase chain reaction (PCR) was used to confirm this isolation using specific gene primers for species identification. Subsequently, the isolates were tested for their sensitivity to 14 antibiotics using the Kirby–Bauer method, after which the PCR was conducted again to detect resistance genes: sul1, strA-strB, aadA, bla_TEM, bla_SHV, tetA-tetE, and tetM.

Results:

From the results, 61 isolates were identified as being from the genus Aeromonas using PCR, of which 28 were Aeromonas jandaei, 19 were Aeromonas veronii, seven were Aeromonas hydrophila, and seven were Aeromonas sobria. Moreover, 8, 12, and 8 of A. jandaei; 4, 3, and 12 of A. veronii; 6, 0, and 1 of A. hydrophila; and 3, 3, and 1 of A. sobria were obtained from Oreochromis spp., C. gariepinus, and P. hypophthalmus, respectively. In addition, the isolates showed the highest level of resistance to ampicillin (100%), followed by streptomycin (59.0%), each kanamycin and nalidixic acid (41.0%), neomycin (36.1%), tetracycline (19.7%), sulfamethoxazole (14.8%), and oxytetracycline (13.1%). Resistance to gentamicin and ciprofloxacin both had the same percentage (9.8%), whereas isolates showed the lowest resistance to norfloxacin (8.2%) and doxycycline (1.6%). Notably, all Aeromonas isolates were susceptible to chloramphenicol and nitrofurantoin. Results also revealed that the multiple antibiotic resistances index of the isolates ranged from 0.07 to 0.64, suggesting that the farmed fish in these areas were introduced to the logged antibiotics indiscriminately and constantly during their cultivation stages. Results also revealed that the sul1 gene was detected in 19.7% of the Aeromonas isolates, whereas the tetracycline resistance genes, tetA and tetE, were detected in 27.9% and 4.9% of the isolates, respectively. However, β-lactam resistance genes, bla_TEM and bla_SHV, were found in 44.3% and 13.1% of Aeromonas isolates, respectively, whereas strA-strB and aadA genes were found in 3.3% and 13.1% of the isolates, respectively.

Conclusion:

This study, therefore, calls for continuous surveillance of antibiotic-resistant Aeromonas spp. in cultured freshwater fish to aid disease management and better understand their implications to public health.

Development of a real-time recombinase polymerase amplification assay for rapid detection of Aeromonas hydrophila

Aeromonas hydrophila is ubiquitous in the aquaculture industry and a constant cause of severe disease and economic losses. The early diagnosis of these infections is crucial for disease surveillance and prevention. We developed a real-time recombinase polymerase amplification (real-time RPA) assay for detection of A. hydrophila using the haemolysin gene. The assay was performed at 37°C for 20 min and was highly specific with no cross-reaction with other fish pathogens or with other Aeromonas species. The assay detection limit was 10² copies of the Aeromonas hydrophila per reaction. Compared with traditional culture-based method or real-time PCR, the diagnostic sensitivity and specificity of the real-time RPA were 73.7 and 100%, as well as 64.7 and 93%. Our newly developed real-time RPA was specific and sensitive and can be used in large-scale and point-of-care field investigations of A. hydrophila infections to enable earlier diagnoses.

Characterization and expression analysis of tandemly-replicated asc genes in the Japanese medaka, Oryzias latipes

ASC is a component of the inflammasome playing crucial roles in the inflammatory response. In mammals, ASC induces pyroptosis and inflammatory cytokine production. In this study, three asc genes (asc1, asc2, and asc3) from the Japanese medaka (Oryzias latipes) were identified and characterized. These asc genes were tandem replicates on chromosome 16, and their exon-intron structures differed between them. All three ASCs conserved the pyrin and caspase-recruitment domains, which are important for inflammasome formation. In phylogenetic analysis, all ASCs clustered with those of other teleosts. The asc1 expression levels were significantly higher in several organs than those of asc2 and asc3, suggesting that asc1 may act as a dominant asc in the Japanese medaka. Expression of the three asc genes showed different patterns during Aeromonas hydrophila and Edwardsiella piscicida infections. Furthermore, their expression was adequately down-regulated in the medaka fin-derived cells stimulated with ATP for 12 h, while asc2 expression was statistically up-regulated after nigericin stimulation for 24 h. Moreover, the expression of asc2 and asc3 was significantly higher in the skin of ASC-1-knockout medaka than in that of the wild type medaka during A. hydrophila infection.

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

AIMS

This investigation was undertaken to study the prevalence, enterotoxin gene profile and molecular epidemiology of Aeromonads from various sources of water (182) and fish (173).

METHODS AND RESULTS

A total of 116 Aeromonas sp. were isolated, of which 48 (26·37%) were from water and 68 (34·62%) were from fish samples collected from retail markets and fish farms. The Aeromonads were recovered from all types of water sources viz. drinking water (13%), surface waters (26%) and fish ponds (69%). The most prevalent species recovered from drinking water was A. hydrophila, from fish ponds it was A. caviae, from surface water sources A. hydrophila and A. caviae were recovered more frequently, and A. hydrophila and A. veronii bv. sobria were isolated predominantly from gills of fish samples. On multiplex PCR analysis for the detection of enterotoxin genes (act, alt, ast), the above mentioned Aeromonas species frequently contained enterotoxin genes, irrespective of their sources. From isolates across all the sources, act (63%) and alt (57%) genes were encountered more frequently than ast (6%). The enterobacterial repetitive intergenic consensus sequences polymerase chain reaction was used for typing of isolates and most of the isolates from water and fish were related, owing to similar ecosystem.

CONCLUSION

A wide distribution of enterotoxin genes in Aeromonads from water and fish is a potential public health threat and molecular genotyping can be helpful to study epidemiology of the pathogen.

SIGNIFICANCE AND IMPACT OF THE STUDY

A high proportion of isolates recovered from diverse water sources, particularly potable drinking water and fish samples carried one or more enterotoxin genes thereby indicating a potential pathogenic nature of isolates from these sources. The genetic relatedness was detected amongst many isolates recovered from water sources and fish samples indicating circulation of familiar virulent clones in the aquatic environments.

A novel multiplex PCR assay for rapid detection of virulent Aeromonas in cultured eels

AIMS

Under intensive and stressful aquaculture conditions, cultured eels are highly susceptible to virulent Aeromonas sp. infections. To rapidly and simultaneously confirm Aeromonas isolate and its virulence, a two-tube multiplex PCR (mPCR) assay incorporating gyrB gene for genus-specific recognition and seven major virulence genes for virulence assessment was developed.

METHODS AND RESULTS

Eight pairs of primers were designed and divided into two groups-gyrB, ahpA, epr and aerA in tube 1 and alt, act, ast and hlyA in tube 2. The optimized mPCR conditions were the same except for their final concentrations. The specificity of the mPCR was validated by the extracted DNA of 10 Aeromonas and 8 non-Aeromonas species, or mixed DNA templates. Detection limits were determined to be 200 copies per μl in tube 1 and 20 copies per μl in tube 2. The mPCR reproducibility was tested by both artificial challenge and clinical samples.

CONCLUSIONS

The results showed this two-tube mPCR assay was rapid, specific, sensitive and reliable.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first report to distinguish virulent Aeromonas isolates from nonvirulent ones by seven popular and major virulence genes at the genus-specific level. And it will be useful for large-scale screening of virulent Aeromonas sp. in cultured eels.

Detection and characterization of potentially pathogenic Aeromonas sobria isolated from fish Hypophthalmichthys molitrix (Cypriniformes: Cyprinidae)

The current study focuses on the detection and characterization of potentially pathogenic Aeromonas sobria from fish silver carp (Hypophthalmichthys molitrix). Assessment of clinical, microbiological, pathological and biochemical characteristics of A. sobria were taken into account in order to understand the epidemiology, frequency and occurrence of this infection. Clinically the infected fish (H. molitrix) was observed for various types of symptoms. A total of 33 colonies of A. sobria strain were isolated from 20 cultured H. molitrix, collected from controlled fish pond. Microscopic examination revealed that the strains were rod-shaped, Gram negative bacteria. The revealed percent probability identification of A. sobria from the biochemical characterization in VITEK system was 93% with gram negative (GN) card. The histopathology of Gills caused by this bacterium, A. sobria indicate haemorrhagic gill epithelia and epithelial hyperplasia. Lamelar epithelial hypertrophy and hyperplasia with degenerative changes of the epithelium and hypertrophic epitheliocystis infected cells on gills of H. molitrix were observed during the present study.

Development of cross-priming amplification assays for rapid and sensitive detection of Aeromonas hydrophila

Aeromonas hydrophila has been increasingly implicated as the aetiologic agent of various human diseases. Therefore, reliable laboratory detection and identification of this bacterium has become clinically and epidemiologically desirable. We developed a nearly instrument-free, simple molecular method for rapid detection of Aer. hydrophila using a cross-priming amplification (CPA) assay with the desA gene as the target. The desA gene is crucial for the survival and growth of Aer. hydrophila under iron starvation. The results can be visualized as colour changes without opening the reaction tubes. No false-positive results were observed for the 33 non-Aer. hydrophila strains tested to evaluate assay specificity. The limit of detection for Aer. hydrophila was approximately 200 copies of desA per reaction (on reference plasmids) and 5 × 10(3)  CFU g(-1) Aer. hydrophila in simulated human stool, which is the same sensitivity as a qPCR assay. The performance of the CPA assay was also evaluated with 100 stool specimens from diarrhoea patients and 40 environmental water samples. In conclusion, the simplicity, cost-effectiveness and nearly instrument-free platform of the CPA assay make it practical for use in primary care facilities and smaller clinical laboratories.

SIGNIFICANCE AND IMPACT OF THE STUDY

Aeromonas hydrophila is a human pathogen that infects via exposed wounds or ingestion of contaminated water and food. In this study, a CPA-based PCR method was developed for specific, rapid, cost-effective detection of Aer. hydrophila, and the test results could be visualized without opening the reaction tubes. This is the first report on the application of the CPA method for the detection of Aer. hydrophila. This novel method could be practical for use in primary care facilities and smaller clinical laboratories.