Prevalence of Aeromonas hydrophila in fish and prawns from the seafood market of Coimbatore, South India

Microbiota diversity of three Brazilian native fishes during ice and frozen storage

This study aimed to assess the bacterial microbiota involved in the spoilage of pacu (Piaractus mesopotamics), patinga (female Piaractus mesopotamics x male Piaractus brachypomus), and tambacu (female Colossoma macropomum × male Piaractus mesopotamics) during ice and frozen storage. Changes in the microbiota of three fish species (N = 22) during storage were studied through 16S rRNA amplicon-based sequencing and correlated with volatile organic compounds (VOCs) and metabolites assessed by nuclear magnetic resonance (NMR). Storage conditions (time and temperature) affected the microbiota diversity in all fish samples. Fish microbiota comprised mainly of Pseudomonas sp., Brochothrix sp., Acinetobacter sp., Bacillus sp., Lactiplantibacillus sp., Kocuria sp., and Enterococcus sp. The relative abundance of Kocuria, P. fragi, L. plantarum, Enterococcus, and Acinetobacter was positively correlated with the metabolic pathways of ether lipid metabolism while B. thermosphacta and P. fragi were correlated with metabolic pathways involved in amino acid metabolism. P. fragi was the most prevalent spoilage bacteria in both storage conditions (ice and frozen), followed by B. thermosphacta. Moreover, the relative abundance of identified Bacillus strains in fish samples stored in ice was positively correlated with the production of VOCs (1-hexanol, nonanal, octenol, and 2-ethyl-1-hexanol) associated with off-flavors. 1H NMR analysis confirmed that amino acids, acetic acid, and ATP degradation products increase over (ice) storage, and therefore considered chemical spoilage index of fish fillets.

Ventilator-associated pneumonia due to Aeromonas hydrophila: A rare case report

Introduction

Aeromonas hydrophila is an opportunistic pathogen that can cause various infections, including pneumonia, in immunocompromised individuals. This case report presents a rare occurrence of ventilator-associated pneumonia (VAP) caused by Aeromonas hydrophila in an apparently non-immunocompromised patient.

Case presentation

The patient exhibited signs and symptoms of VAP and was successfully treated with intravenous ciprofloxacin. The discussion highlights the characteristics of Aeromonas species, its virulence factors, risk factors for infection, and antibiotic profile.

Conclusion

It emphasizes the need for awareness and suspicion of Aeromonas as a potential cause of VAP in ICU settings, as well as the importance of early detection and appropriate treatment for improved outcomes.

Phenotypic, molecular detection and antibiogram analysis of Aeromonas Hydrophila from Oreochromis Niloticus (Nile Tilapia) and Ready-To- eat fish products in selected Rift Valley lakes of Ethiopia

BACKGROUND

Aeromonas hydrophila is a zoonotic bacterial pathogen that frequently causes disease and mass mortalities among cultured and feral fishes worldwide. In Ethiopia, A. hydrophila outbreak was reported in Sebeta fish ponds and in Lake Tana fishery. However, there is no to little information on the molecular, and phenotypical characteristics of A. hydrophila in Ethiopian fisheries. Therefore, a cross-sectional study was conducted from November 2020 to May 2021 in selected Ethiopian Rift valley lakes.

RESULTS

A total of 140 samples were collected aseptically from fish (Muscle, Gill, Intestine, Spleen and Kidney) from fish landing sites, market and restaurants with purposive sampling methods. Aeromonas selective media (AMB), morphological and biochemical tests were used to isolate and identify A. hydrophila. Accordingly, the pathogen was isolated from 81 (60.45%) of samples. Among the isolates 92.59% expressed virulence trait through β hemolysis on blood agar media with 5% sheep blood. Moreover, 54 strains (66.67%) were further confirmed with Real-Time PCR (qPCR) using ahaI gene specific primers and optimized protocol. The highest (68.51%) were detected from live fish, (24.07%) were from market fish and the lowest (7.4%%) were from ready-to-eat products. Antibiogram analysis was conducted on ten representative isolates. Accordingly, A. hydrophila isolates were susceptible to ciprofloxacin (100%), chloramphenicol (100%) and ceftriaxone (100%). However, all ten isolates were resistant to Amoxicillin and Penicillin.

CONCLUSIONS

The study indicates A. hydrophila strains carrying virulence ahaI gene that were ß-hemolytic and resistant to antibiotics commonly used in human and veterinary medicine are circulating in the fishery. The detection of the pathogen in 140 of the sampled fish population is alarming for potential outbreaks and zoonosis. Therefore, further molecular epidemiology of the disease should be studied to establish potential inter host transmission and antibiotic resistance traits. Therefore, raising the public awareness on risk associated with consuming undercooked or raw fish meat is pertinent.

Occurrence of Aeromonas Species in the Cutaneous Mucus of Barbour’s Seahorses (Hippocampus barbouri) as Revealed by High-Throughput Sequencing

Although several studies have described the bacterial community composition associated with marine fish, there is limited information related to seahorses. Moreover, previous studies have demonstrated that the skin microbiota is useful for determining health status and common disorders in the host. This study, therefore, aimed to explore the skin bacterial community composition in Barbour’s seahorse (Hippocampus barbouri) using high-throughput sequencing of 16S ribosomal RNA genes. Water and sediment samples from the surrounding environment were also analyzed for comparative purposes. The results revealed that sequences affiliated with the Shewanellaceae family were dominant in the skin of female Barbour’s seahorses and sediment samples, whereas sequences affiliated with the Bacillaceae family were dominant in the skin of male Barbour’s seahorses. Interestingly, sequences affiliated with the Aeromonas genus were found in the skin of Barbour’s seahorses, whose abundance was slightly similar between the female and male specimens. Further comparative analysis showed that the presence of Aeromonas species in the skin of Barbour’s seahorses was strongly influenced by the surrounding sediment. Given that some Aeromonas species are known to be important pathogens in humans and fish, these results may be used for further research on the dependency of the skin microbial composition on the environment as well as determine whether the presence of Aeromonas and other detected species has implications on seahorse health.

Aeromonas species isolated from aquatic organisms, insects, chicken, and humans in India show similar antimicrobial resistance profiles

Aeromonas species are Gram-negative bacteria that infect various living organisms and are ubiquitously found in different aquatic environments. In this study, we used whole genome sequencing (WGS) to identify and compare the antimicrobial resistance (AMR) genes, integrons, transposases and plasmids found in Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii isolated from Indian major carp (Catla catla), Indian carp (Labeo rohita), catfish (Clarias batrachus) and Nile tilapia (Oreochromis niloticus) sampled in India. To gain a wider comparison, we included 11 whole genome sequences of Aeromonas spp. from different host species in India deposited in the National Center for Biotechnology Information (NCBI). Our findings show that all 15 Aeromonas sequences examined had multiple AMR genes of which the Ambler classes B, C and D β-lactamase genes were the most dominant. The high similarity of AMR genes in the Aeromonas sequences obtained from different host species point to interspecies transmission of AMR genes. Our findings also show that all Aeromonas sequences examined encoded several multidrug efflux-pump proteins. As for genes linked to mobile genetic elements (MBE), only the class I integrase was detected from two fish isolates, while all transposases detected belonged to the insertion sequence (IS) family. Only seven of the 15 Aeromonas sequences examined had plasmids and none of the plasmids encoded AMR genes. In summary, our findings show that Aeromonas spp. isolated from different host species in India carry multiple AMR genes. Thus, we advocate that the control of AMR caused by Aeromonas spp. in India should be based on a One Health approach.

Mutation of TL1, encoding a novel C2H2 zinc finger protein, improves grains eating and cooking quality in rice

The cloning and characterization of a novel C₂H₂ zinc finger protein that affects rice eating and cooking quality by regulating amylose content and amylopectin chain-length distribution in rice. One of the major objectives in rice breeding aims to increase simultaneously yield and grain quality especially eating and cooking quality (ECQ). Controlling amylose content (AC) and amylopectin chain-length distribution (ACLD) in rice is a major strategy for improving rice ECQ. Previous studies show that some starch synthesis-related genes (SSRGs) are required for normal AC and ACLD, but its underlying regulating network is still unclear. Here, we report the cloning and characterization of a novel C₂H₂ zinc finger protein TL1 (Translucent endosperm 1) that positively regulates amylose synthesis in rice grains. Loss of TL1 function reduced apparent amylose content (AAC), total starch, gel consistency, and gelatinisation temperature, whereas increased viscosity, total lipid, and ratio of amylopectin A chains with degree of polymerization (DP) 6-12 to B₁ chains with DP 13-24, resulting in an enhanced grain ECQ. The improved ECQ was accompanied by altered expression patterns of several tested SSRGs in tl1 mutant grains. Furthermore, knockout of TL1 in the high-yielding rice variety JiaHua NO.1 reduced AAC without obvious side effects on major agronomic traits. These findings expand our understanding of the regulating networks of grain starch metabolism and provide new insights into how rice ECQ quality can be improved via genetic approach.

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.

Essential Oils From Citrus unshiu Marc. Effectively Kill Aeromonas hydrophila by Destroying Cell Membrane Integrity, Influencing Cell Potential, and Leaking Intracellular Substances

Aeromonas hydrophila is one of the important pathogenic bacteria in aquaculture causing serious losses every year. Essential oils are usually used as natural antimicrobial agents to reduce or replace the use of antibiotics. The aim of this study was to evaluate the antibacterial activity and explore the mechanisms of essential oil from satsuma mandarin (Citrus unshiu Marc.) (SMEO) against A. hydrophila. The results of the gas chromatography-mass spectrometer demonstrated that SMEO contains 79 chemical components with the highest proportion of limonene (70.22%). SMEO exhibited strong antibacterial activity against A. hydrophila in vitro, the diameter of the inhibition zone was 31.22 ± 0.46 mm, and the MIC and MBC values were all 1% (v/v). Intracellular material release, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and flow cytometry analysis revealed the dynamic antibacterial process of SMEO, the morphological changes of bacterial cells, and the leakage process of intracellular components. These results demonstrated that SMEO disrupted the extracellular membrane permeability. Our study demonstrated that SEMO has the potential to be used to control and prevent A. hydrophila infections in aquaculture.

Pathogenicity and seasonal variation of Aeromonas hydrophila isolated from seafood and ready-to-eat sushi in South Korea

Aeromonas hydrophila is an emerging foodborne pathogen capable of causing human gastroenteritis, and the main reservoir is the aquatic environment. In this study, the prevalence and virulence of A. hydrophila in seafoods and ready-to-eat (RTE) sushi distributed in various conditions (refrigerated, dried, or frozen) or seasons was investigated. Strains were isolated from seafood (refrigerated or frozen oysters, sashimi, and processed fish; n = 333) and RTE sushi (n = 88) samples collected in South Korea and then genetically analyzed for gastroenteritis-related virulence genes (aer, ast, and alt). Raw oysters showed the highest prevalence of A. hydrophila (57.1%; 47/91) among all seafoods. Among the sashimi samples, flatfish sashimi (54.8%; 34/62) and salmon sushi (51.4%; 18/35) were the most prevalent. A. hydrophila was not detected in the oysters or anchovies distributed as either frozen or dried products. Seasonal investigations of sashimi and sushi showed that the summer prevalence of A. hydrophila with putative virulence genes was significantly lower in sashimi but highest in sushi. These results indicated that sushi could have been contaminated from several sources during the manufacturing or distribution processes. Significant correlations among the prevalence of putative virulence genes were confirmed, although no combination of genes presented a Phi correlation coefficient above 0.5 (0.26-0.43). To our knowledge, this is the first study to investigate the prevalence of A. hydrophila in various types of retail seafoods and RTE sushi in the East Asia region and then relate the prevalence to the distribution conditions of the samples. This study provides background information on the level of potential risk posed by A. hydrophila in retail seafoods and RTE sushi.

Advances in the Identification of Quantitative Trait Loci and Genes Involved in Seed Vigor in Rice

Seed vigor is a complex trait, including the seed germination, seedling emergence, and growth, as well as seed storability and stress tolerance, which is important for direct seeding in rice. Seed vigor is established during seed development, and its level is decreased during seed storage. Seed vigor is influenced by genetic and environmental factors during seed development, storage, and germination stages. A lot of factors, such as nutrient reserves, seed dying, seed dormancy, seed deterioration, stress conditions, and seed treatments, will influence seed vigor during seed development to germination stages. This review highlights the current advances on the identification of quantitative trait loci (QTLs) and regulatory genes involved in seed vigor at seed development, storage, and germination stages in rice. These identified QTLs and regulatory genes will contribute to the improvement of seed vigor by breeding, biotechnological, and treatment approaches.

The microbial safety of fish and fish products: Recent advances in understanding its significance, contamination sources, and control strategies

Microorganisms play a crucial and unique role in fish and fish product safety. The presence of human pathogens and the formation of histamine caused by spoilage bacteria make the control of both pathogenic and spoilage microorganisms critical for fish product safety. To provide a comprehensive and updated overview of the involvement of microorganisms in fish and fish product safety, this paper reviewed outbreak and recall surveillance data obtained from government agencies from 1998 to 2018 and identified major safety concerns associated with both domestic and imported fish products. The review also summarized all available literature about the prevalence of major and emerging microbial safety concerns, including Salmonella spp., Listeria monocytogenes, and Aeromonas hydrophila, in different fish and fish products and the survival of these pathogens under different storage conditions. The prevalence of antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs), two emerging food safety concerns, is also reviewed. Pathogenic and spoilage microorganisms as well as ARB and ARGs can be introduced into fish and fish products in both preharvest and postharvest stages. Many novel intervention strategies have been proposed and tested for the control of different microorganisms on fish and fish products. One key question that needs to be considered when developing and implementing novel control measures is how to ensure that the measures are cost and environment friendly as well as sustainable. Over the years, regulations have been established to provide guidance documents for good farming and processing practices. To be more prepared for the globalization of the food chain, harmonization of regulations is still needed.

Inactivation of Aeromonas hydrophila and Vibrio parahaemolyticus by Curcumin-Mediated Photosensitization and Nanobubble-Ultrasonication Approaches

The antimicrobial efficacy of novel photodynamic inactivation and nanobubble technologies was evaluated against Vibrio parahaemolyticus and Aeromonas hydrophila as two important aquatic microbial pathogens. Photodynamic inactivation results showed that LED (470 nm) and UV-A (400 nm)-activated curcumin caused a complete reduction in V. parahaemolyticus at 4 and 22 °C, and a greater than 2 log cfu/mL reduction in A. hydrophila, which was curcumin concentration-dependent (p < 0.05). Furthermore, the photodynamic approach caused a greater than 6 log cfu/mL V. parahaemolyticus reduction and more than 4 log cfu/mL of A. hydrophila reduction in aquaponic water samples (p < 0.05). Our results with the nanobubble technology showed that the nanobubbles alone did not significantly reduce bacteria (p > 0.05). However, a greater than 6 log cfu/mL A. hydrophila reduction and a greater than 3 log cfu/mL of V. parahaemolyticus reduction were achieved when nanobubble technology was combined with ultrasound (p < 0.05). The findings described in this study illustrate the potential of applying photodynamic inactivation and nanobubble-ultrasound antimicrobial approaches as alternative novel methods for inactivating fish and shellfish pathogens.

Vibriosis and Aeromonas infection in shrimp: Isolation, sequencing, and control

Background and Aim: Shrimp is one of the most commonly consumed types of seafood. It is a very nutritious healthy food. Shrimp is low in calories and rich in protein and healthy fats. It also contains a treasure trove of vitamins and minerals. On the negative side, it may be affected by many bacterial diseases which affect its health. Furthermore, it may be incriminated as a vector of foodborne illnesses that range from mild gastrointestinal upset to life-threatening diseases. This study was designed to assess the clinical picture and zoonotic importance of vibriosis and Aeromonas infection in live shrimp and to study the antibacterial effect of citric acid (lemon juice) and acetic acid (vinegar) on these pathogens. Materials and Methods: A total of 170 live shrimp (Metapenaeus monoceros) samples were collected from Suez City, Egypt. The samples were examined clinically, and then, they were enriched into alkaline peptone water and cultivated on thiosulfate-citrate-bile salts-sucrose agar and ampicillin MacConkey agar for the isolation of Vibrio and Aeromonas species, respectively. The recovered isolates were confirmed biochemically and genotypically using duplex polymerase chain reaction (PCR) and sequencing. The germicidal effects of vinegar and lemon on artificially contaminated shrimp samples with Aeromonas hydrophila and Vibrio parahaemolyticus at different times (0.25, 1, 1.5, and 24 h) and temperatures (5° and 30°C) were studied. Results: The results revealed that some of the infected shrimp were hypoxic, lethargic with abnormal swimming behavior. In most cases, body appendages, telsons, uropods, and gills took black coloration. In addition, the hepatopancreas appeared soft, swollen, and congested. The prevalence rates of vibriosis in each of the musculature and hepatopancreas were 4.7%, while the prevalence rates of Aeromonas infection in the musculature and hepatopancreas were 11.8% and 11.2%, respectively. Duplex PCR showed that Aeromonas isolates gave double bands: 237 bp specific for gcat and 500 bp specific for 16S rRNA, while Vibrio spp. and Plesiomonas shigelloides isolates gave single band at 500 bp. The effect of organic acid treatment showed that acetic acid (vinegar 5%) had increasing reduction rates that reached its maximum level after 24 h; where it caused (100% inhibition) for A. hydrophila at both temperatures and (33.63% and 60% inhibition) for V. parahaemolyticus at refrigerator and room temperatures, respectively. Moreover, acetic acid was more effective at room temperature than at refrigerator temperature. Concerning the effect of lemon juice (citric acid), it was more effective than acetic acid at short marination (0.25 and 1 h) at both temperatures for the two pathogens. Moreover, lemon was more effective at refrigerator temperature than at room temperature at the same aforementioned time. The difference between the reduction effects of the two acids on both pathogens was statistically significant (p<0.0001). Conclusion: Overall, the examined shrimp samples were found to be vectors for Vibrio and Aeromonas spp. Application of hygienic measures during handling and cooking of shrimp should be esteemed. The organic acid treatment trial showed that vinegar and lemon juice can be used as a safe and economic method to limit the microbial contamination in seafood.

Molecular Cloning, Characterization, and mRNA Expression of Hemocyanin Subunit in Oriental River Prawn Macrobrachium nipponense

Hemocyanin is a copper-containing protein with immune function against disease. In this study, a hemocyanin subunit named MnHc-1 was cloned from Macrobrachium nipponense. The full-length cDNA of MnHc-1 was 2,163 bp with a 2,028-bp open reading frame (ORF) encoding a polypeptide of 675 amino acids. The MnHc-1 mRNA was expressed in the hepatopancreas, gill, hemocytes, intestine, ovary, and stomach, with the highest level in the hepatopancreas. In the infection trial, the MnHc-1 mRNA transcripts in the hemocytes were significantly downregulated at 3 h after injection of Aeromonas hydrophila and then upregulated at 6 h and 12 h, followed by a gradual recovery from 24 to 48 h. The MnHc-1 transcriptional expression in the hepatopancreas was measured after M. nipponense were fed seven diets with 2.8, 12.2, 20.9, 29.8, 43.1, 78.9, and 157.1 mg Cu kg⁻¹ for 8 weeks, respectively. The level of MnHc-1 mRNA was significantly higher in the prawns fed 43.1–157.1 mg Cu kg⁻¹ diet than in that fed 2.8–29.8 mg Cu kg⁻¹ diet. This study indicated that the MnHc-1 expression can be affected by dietary copper and the hemocyanin may potentially participate in the antibacterial defense of M. nipponense.

Draft Genome Sequence of Aeromonas dhakensis Strain F2S2-1, Isolated from the Skin Surface of an Indian Oil Sardine ( Sardinella longiceps )

Draft genome sequencing of Aeromonas dhakensis strain F2S2-1, isolated from the skin surface of an Indian oil sardine (Sardinella longiceps), has been carried out. The draft genome was roughly 4.7 Mb in size with 61.7% G+C content. Annotation of the genome yielded 4,337 genes coding for proteins, tRNAs, and rRNAs. Annotation also revealed the presence of 52 genes linked to resistance to antibiotics/toxic compounds. Pathway analysis revealed the presence of novobiocin biosynthetic genes and genes for biosynthesis of a siderophore group on nonsynthetic peptides.

Isolation and Seroprevalence of Aeromonas spp. Among Common Food Animals Slaughtered in Nagpur, Central India

Aeromonads are ubiquitous foodborne pathogens with a global distribution. Animal-origin foods and contaminated animals are the main sources of Aeromonas infection to humans. So far little is known about the occurrence of Aeromonas spp. in food-producing animals in India. The present study was conducted to determine the prevalence and seroprevalence of Aeromonas species from 50 each of meat, blood, and sera samples collected from cattle, buffaloes, goats, and pigs slaughtered in and around Nagpur, Central India. Alkaline peptone water and ampicillin dextrin agar were used to isolate Aeromonas spp. An indirect enzyme-linked immunosorbent assay (ELISA) was standardized by use of whole-cell antigen (WC) and outer membrane protein (OMP) of Aeromonas hydrophila (MTCC 646). Aeromonads were isolated from 44 (22%) of the meat samples, and 1 (0.5%) from the blood samples. Seroprevalence by indirect ELISA-based WC antigen was estimated as 68% in cattle, 44% in buffaloes, 60% in goats, and 30% in pigs. OMP-based ELISA yielded a seroprevalence of 56%, 48%, 52%, and 22% in cattle, buffaloes, goats, and pigs, respectively. The results revealed that OMP-based ELISA and WC-based ELISA were in agreement with one another. Isolation along with high seropositivity demonstrates the presence of foodborne Aeromonas spp. in the Nagpur city of Central India.

Food Safety: Emerging Pathogens

This article presents information related to emerging pathogens that are foodborne or have the potential to be foodborne including bacteria, viruses, and parasites. The phenotypic characteristics of these pathogens, their epidemiology, prevalence in foods, and transmission routes to humans as well as means for their control are also discussed.

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

Hemolytic strains of Aeromonas spp. from fish and fishery products were detected by multiplex PCR. The selected primers for the amplification of segments of ahh1, asa1 and 16S rRNA gene yielded products with the size of 130 bp, 249 bp and 356 bp, respectively. This assay was found to be highly sensitive, as it could detect 7 and 9 cells of Aeromonas hydrophila and A. sobria with a detection limit of 1 pg of pure genomic DNA. The assay, when screened for 73 commercial fish and fishery product samples consisting of freshwater, marine fish and shellfish, showed 56 % positive for Aeromonas spp., 16 % for Aeromonas hydrophila and 13 % for A. sobria. This assay provides specific and reliable results and can be a powerful tool for the simultaneous detection of hemolytic strains of A. hydrophila A. sobria and other Aeromonas spp. from fish and fishery products.

A novel effect of imidazole derivative KK-42 on increasing survival of Aeromonas hydrophila challenged prawn Macrobrachium nipponense

Imidazole derivative KK-42 is well known as the insect growth regulator. Here we find that KK-42 pretreatment could promote the survival of Macrobrachium nipponense infected with Aeromonas hydrophila, which is considered to be possibly related to the prophenoloxidase (proPO), a conserved copper-containing enzyme that plays an important role in defense against pathogens. In this study, a full-length of proPO gene from M. nipponense haemocytes, designated as MnproPO, was firstly cloned and characterized. The full-length cDNA contained 2428 bp with a 2013 bp open reading frame encoding a putative proPO protein of 671 amino acids with a predicted molecular mass of 76.5 kDa and pI of 7.31. It was predicted to possess all the expected features of proPO members, including two putative copper-binding sites with six histidine residues and a thiol ester-like motif. Sequence analysis showed that MnproPO exhibited the highest amino acid sequence similarity (93%) to a proPO of Macrobrachium rosenbergii. The gene was expressed highly in haemocytes and weakly in hepatopancreas. Real-time PCR analysis revealed that the MnproPO expression increased significantly at 3, 12 and 24 h after KK-42 treatment, the PO activity also importantly rose from 6 to 48 h in KK-42-treated prawns and reached the maximum at 24 h with a 2.3-fold higher than that in control group. Injection of A. hydrophila could stimulate the MnproPO transcription and PO activity whether or not the prawns were pretreated by KK-42, the mRNA level increased obviously only at 3 h and 6 h after the bacterium injection (challenged control), but increased constantly during the phase of experiment except at 6 h under the condition of KK-42 pretreatment (challenged treatment group). The change trend of PO activity was basically similar to that of MnproPO expression. Our present results demonstrate that the MnproPO expression as well as PO activity may be induced by KK-42, which is likely one of the molecular mechanisms of KK-42 acts for increasing survival of the prawn infected with A. hydrophila.

Bdellovibrios, potential biocontrol bacteria against pathogenic Aeromonas hydrophila

Recent studies have revealed that the use of bdellovibrios is an alternative to control bacteriosis. However, no bdellovibrios are available against Aeromonas hydrophila infections in sturgeons. In the present study, a potential Bdellovibrio strain F16 was isolated from sturgeon gut samples, using a sturgeon-pathogenic A. hydrophila as the prey bacterium. It was initially identified as a Bdellovibrio strain using morphological characteristics and specific PCR amplification, and confirmed to be Bdellovibrio sp. strain ETB (GenBank Accession No. DQ302728) and Bdellovibrio bacteriovorus strain SRA9 (GenBank Accession No. AF263833) by phylogenetic analysis. In addition, it was shown to be safe for mammalians and sturgeons, had a wide prey range, and exhibited significant bacteriolytic effects on the pathogenic A. hydrophila. To the best of our knowledge, this is the first report on a promising gut Bdellovibrio strain against pathogenic A. hydrophila.

Occurrence and characterization of Aeromonas spp. in mussels from the Adriatic Sea

Samples of mussels (Mytilus galloprovincialis) were collected from natural beds on the Adriatic Sea in front of Ancona Province (Marches, Central Italy) officially recognized for human consumption. The mussels were analyzed to evaluate the prevalence of Aeromonas spp. pathogenic strains. Out of 144 samples, 32 Aeromonas strains were isolated and 12 showed virulence and enterophatogenicity on mice. Isolates were also examined to check their sensitivity to different antimicrobial agents. All isolates were sensitive to imepenem, neomycin, ciprofloxacin, tetracycline, oxytetracycline, doxycicline, chloramphenicol, polymyxin B, and colistin sulfate, but resistant to penicillin, carbenicillin, cephalotin, sulfamethoxazole, lincomycin, novobiocin, and rifampicin. Multiple resistance to antimicrobial agents with different mechanism of action was observed. Owing to the high occurrence of pathogenic Aeromonas strains, the risk of developing human infections by eating raw or undercooked mussels is envisaged.