Aeromonas hydrophilafrom marketed mullet (Mugil cephalus) in Egypt: PCR characterization ofβ-lactam resistance and virulence genes

Antimicrobial use, residues and resistance in fish production in Africa: systematic review and meta-analysis

In low- and middle-income countries, data on antimicrobial use (AMU) and antimicrobial resistance (AMR) in aquaculture are scarce. Therefore, summarizing documented data on AMU, antimicrobial residue (AR), and AMR in aquaculture in Africa is key to understanding the risk to public health. Google Scholar, PubMed, African Journals online, and Medline were searched for articles published in English and French following the PRISMA guidelines. A structured search string was used with strict inclusion and exclusion criteria to retrieve and screen the articles. The pooled prevalence and 95% confidence intervals were calculated for each pathogen-antimicrobial pair using random effects models. Among the 113 full-text articles reviewed, 41 met the eligibility criteria. The majority of the articles reported AMR (35; 85.4%), while a few were on AMU (3; 7.3%) and AR (3; 7.3%) in fish. The articles originated from West Africa (23; 56.1%), North Africa (8; 19.7%), and East Africa (7; 17.1%). Concerning the antimicrobial agents used in fish farming, tetracycline was the most common antimicrobial class used, which justified the high prevalence of residues (up to 56.7%) observed in fish. For AMR, a total of 69 antimicrobial agents were tested against 24 types of bacteria isolated. Bacteria were resistant to all classes of antimicrobial agents and exhibited high levels of multidrug resistance. Escherichia coli, Salmonella spp., and Staphylococcus spp. were reported in 16, 10, and 8 studies, respectively, with multidrug resistance rates of 43.1% [95% CI (32.0-55.0)], 40.3% [95% CI (24.1-58.1)] and 31.3% [95% CI (17.5-49.4)], respectively. This review highlights the high multidrug resistance rate of bacteria from aquaculture to commonly used antimicrobial agents, such as tetracycline, ampicillin, cotrimoxazole, gentamicin, and amoxicillin, in Africa. These findings also highlighted the lack of data on AMU and residue in the aquaculture sector, and additional efforts should be made to fill these gaps and mitigate the burden of AMR on public health in Africa.

Biocontrol of multidrug resistant pathogens isolated from fish farms using silver nanoparticles combined with hydrogen peroxide insight to its modulatory effect

This study was divided into two parts. The first part involved the isolation, and detection of the prevalence and antimicrobial resistance profile of Aeromonas hydrophila, Pseudomonas aeruginosa, and Vibrio species from Nile tilapia fish and marine aquatic water. One hundred freshly dead Nile tilapia fish were collected from freshwater aquaculture fish farms located in Al-Abbassah district, Sharkia Governorate, and 100 samples of marine aquatic water were collected from fish farms in Port Said. The second part of the study focused on determining the in vitro inhibitory effect of dual-combination of AgNPs-H2O2 on bacterial growth and its down regulatory effect on crucial virulence factors using RT-PCR. The highest levels of A. hydrophila and P. aeruginosa were detected in 43%, and 34% of Nile tilapia fish samples, respectively. Meanwhile, the highest level of Vibrio species was found in 37% of marine water samples. Additionally, most of the isolated A. hydrophila, P. aeruginosa and Vibrio species exhibited a multi-drug resistance profile. The MIC and MBC results indicated a bactericidal effect of AgNPs-H2O2. Furthermore, a transcriptional modulation effect of AgNPs-H2O2 on the virulence-associated genes resulted in a significant down-regulation of aerA, exoU, and trh genes in A. hydrophila, P. aeruginosa, and Vibrio spp., respectively. The findings of this study suggest the effectiveness of AgNPs-H2O2 against drug resistant pathogens related to aquaculture.

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

In the present study, Aeromonas hydrophila was isolated from Tilapia zillii and Mugil cephalus samples collected during different seasons from various Suez Canal areas in Egypt. The prevalence of A. hydrophila, virulence genes, and antibiotic resistance profile of the isolates to the commonly used antibiotics in aquaculture were investigated to identify multiple drug resistance (MDR) and extensive drug-resistant (XDR) strains. In addition, a pathogenicity test was conducted using A. hydrophila, which was isolated and selected based on the prevalence of virulence and resistance genes, and morbidity of natural infected fish. The results revealed that A. hydrophila was isolated from 38 of the 120 collected fish samples (31.6%) and confirmed phenotypically and biochemically. Several virulence genes were detected in retrieved A. hydrophila isolates, including aerolysin aerA (57.9%), ser (28.9%), alt (26.3%), ast (13.1%), act (7.9%), hlyA (7.9%), and nuc (18.4%). Detection of antibiotic-resistant genes revealed that all isolates were positive for blapse1 (100%), blaSHV (42.1%), tetA (60.5%), and sul1 (42.1%). 63.1% of recovered isolates were considered MDR, while 28.9% of recovered isolates were considered XDR. Some isolates harbor both virulence and MDR genes; the highest percentage carried 11, followed by isolates harboring 9 virulence and resistance genes. It could be concluded that the high prevalence of A. hydrophila in aquaculture species and their diverse antibiotic resistance and virulence genes suggest the high risk of Aeromonas infection and could have important implications for aquaculture and public health.

Genotype diversity and antibiotic resistance risk in Aeromonas hydrophila in Sichuan, China

Sichuan is a significant aquaculture province in China, with a total aquaculture output of 1.72 × 106 tons in 2022. One of the most significant microorganisms hurting the Sichuan aquaculture is Aeromonas hydrophila, whose genotype and antibiotic resistance are yet unknown. This study isolated a total of 64 strains of A. hydrophila from various regions during September 2019 to June 2021 within Sichuan province, China. The technique of Multi-Locus Sequence Typing (MLST) was used for the purpose of molecular typing. Meanwhile, identification of antibiotic resistance phenotype and antibiotic resistance gene was performed. The findings of the study revealed that 64 isolates exhibited 29 sequence types (ST) throughout different regions in Sichuan, with 25 of these ST types being newly identified. Notably, the ST251 emerged as the predominant sequence type responsible for the pandemic. The resistance rate of isolated strains to roxithromycin was as high as 98.3%, followed by co-trimoxazole (87.5%), sulfafurazole (87.5%), imipenem (80%), amoxicillin (60%), and clindamycin (57.8%). Fifteen strains of A. hydrophila exhibited resistance to medicines across a minimum of three categories, suggesting the development of multidrug resistance in these isolates. A total of 63 ARGs were detected from the isolates, which mediated a range of antibiotic resistance mechanisms, with deactivation and efflux potentially serving as the primary mechanisms of antibiotic resistance. This study revealed the diversity of A. hydrophila genotypes and the risk of antibiotic resistance in Sichuan, providing reference for scientific and effective control of A. hydrophila infection.

Cross-sectional analysis of risk factors associated with Mugil cephalus in retail fish markets concerning methicillin-resistant Staphylococcus aureus and Aeromonas hydrophila

Introduction

Aeromonas hydrophila and methicillin-resistant Staphylococcus aureus (MRSA) are potent bacterial pathogens posing major hazards to human health via consuming fish harboring these pathogens or by cross-contamination beyond the contaminated environment. The aim of this study was to determine risk variables associated with the presence of certain pathogenic bacteria from Mugil cephalus fish in retail markets in Egypt. The virulence genes of A. hydrophila and S. aureus were also studied. Furthermore, the antibiotic sensitivity and multidrug resistance of the microorganisms were evaluated.

Methods

In a cross-sectional investigation, 370 samples were collected from mullet skin and muscle samples, washing water, fish handlers, knives, and chopping boards. Furthermore, fish handlers' public health implications were assessed via their response to a descriptive questionnaire.

Results

S. aureus and Aeromonas species dominated the investigated samples with percentages of 26.76% and 30.81%, respectively. Furthermore, A. hydrophila and MRSA were the predominant recovered bacterial pathogens among washing water and knives (53.85% and 46.66%, respectively). The virulence markers aerA and hlyA were found in 90.7% and 46.5% of A. hydrophila isolates, respectively. Moreover, the virulence genes nuc and mec were prevalent in 80% and 60% of S. aureus isolates, respectively. Antimicrobial susceptibility results revealed that all A. hydrophila isolates were resistant to amoxicillin and all MRSA isolates were resistant to amoxicillin and ampicillin. Remarkably, multiple drug resistance (MDR) patterns were detected in high proportions in A. hydrophila (88.37%) and MRSA (100%) isolates. The prevalence of Aeromonas spp. and S. aureus had a positive significant correlation with the frequency of handwashing and use of sanitizer in cleaning of instruments. MRSA showed the highest significant prevalence rate in the oldest age category.

Conclusion

The pathogenic bacteria recovered in this study were virulent and had a significant correlation with risk factors associated with improper fish handling. Furthermore, a high frequency of MDR was detected in these pathogenic bacteria, posing a significant risk to food safety and public health.

Aeromonas spp. in drinking water and food: Occurrence, virulence potential and antimicrobial resistance

Aeromonas sp. is a Gram-negative, non-spore-forming, rod-shaped, oxidase-positive, facultative anaerobic bacterium and a natural contaminant found in aquatic environments. Some species can invade, colonize, and damage host cells due to the presence of virulence factors, such as flagella, elastase, hemolysins, aerolysins, adhesins, enterotoxins, phospholipases and lipases, that lead to pathogenic activities. Consequently, can cause many health disorders that range from gastrointestinal problems, enteric infections, and ulcers to hemorrhagic septicemia. Aeromonas has been isolated and identified from a variety of sources, including drinking water and ready-to-eat foods (fish, meat, fresh vegetables, dairy products, and others). Some species of this opportunistic pathogen are resistant to several commercial antibiotics, including some used as a last resort for treatment, which represents a major challenge in the clinical segment. Antimicrobial resistance can be attributed to the indiscriminate use of antibiotics by society in aquaculture and horticulture. In addition, antibiotic resistance is attributed to plasmid transfer between microorganisms and horizontal gene transfer. This review aimed to (i) verify the occurrence of Aeromonas species in water and food intended for human consumption; (ii) identify the methods used to detect Aeromonas species; (iii) report on the virulence genes carried by different species; and (iv) report on the antimicrobial resistance of this genus in the last 5 years of research. Additionally, we present the existence of Aeromonas spp. resistant to antimicrobials in food and drinking water represents a potential threat to public health.

Detection of chromosome-mediated blaNDM-1-carrying Aeromonas spp. in the intestinal contents of fresh water river fish in Ho Chi Minh City, Vietnam

The spread of antibiotic-resistant bacteria is a global problem that should be addressed through the perspective of the "one health" concept. The purpose of this study was to determine the contamination rate of antibiotic-resistant Aeromonas spp. in fresh water river fish purchased from a fish market in Vietnam. We then defined the pattern of antibiotic resistance to assess antibiotic-resistant contamination. Antibiotic-resistant Aeromonas spp. were detected in the intestinal contents of 32 of 80 fish. blaNDM-1 was detected in seven strains. Extended-spectrum β-lactamase and AmpC β-lactamase-related genes were detected in 28 strains, including blaCTX-M-55, blaCTX-M-15, blaCTX-M-1, and blaDHA,blaFOX, and blaMOX. The blaNDM-1 detected in the seven Aeromonas spp. strains were found chromosomally. This finding suggests that the blaNDM gene is stable in the natural environment and may spread widely into animals and humans via Aeromonas spp. with a transposon. Our results suggest the importance of continuing to monitor carbapenemase genes in Aeromonas spp. to evaluate the possibility that they may spread in other Enterobacterales, and to elucidate the mechanism of spread.

Pathogens and antibiotic resistance genes during the landfill leachate treatment process: Occurrence, fate, and impact on groundwater

Landfill leachate is an essential source of pathogens and antibiotic resistance genes (ARGs) in the environment. However, information on the removal behavior of pathogens and ARGs during the leachate treatment and the impact on surrounding groundwater is limited. In this study, we investigated the effects of leachate treatment on the removal of pathogens and ARGs with metagenomic sequencing, as well as the impact of landfill effluent on groundwater. It is shown that the leachate treatment could not completely remove pathogens and ARGs. Twenty-nine additional pathogens and twenty-nine ARGs were newly identified in the landfill effluent. The relative abundance of pathogens and multiple antibiotic resistance genes decreased after ultrafiltration but relative abundance increased after reverse osmosis. In addition, the relative abundances of Acinetobacter baumannii, Erwinia amylovora, Escherichia coli, Fusarium graminearum, Klebsiella pneumoniae, and Magnaporthe oryzae, as well as mdtH, VanZ, and blaOXA-53 increased significantly in the landfill effluent compared to the untreated leachate. The relative abundance of some mobile genetic elements (tniA, tniB, tnpA, istA, IS91) in leachate also increased after ultrafiltration and reverse osmosis. The size of pathogens, the size and properties of ARGs and mobile genetic elements, and the materials of ultrafiltration and reverse osmosis membranes may affect the removal effect of pathogens, ARGs and mobile genetic elements in leachate treatment process. Interestingly, the pathogens and ARGs in landfill effluent were transferred to groundwater according to SourceTracker. The ARGs, mobile genetic elements, and pathogens that are difficult to remove in the leachate treatment process, provide a reference for optimizing the leachate treatment process and improving the control of pathogens and ARGs. Furthermore, this study clarifies the effect of landfill leachate sources of pathogens and ARGs in groundwater.

Comparative meta-analysis of antimicrobial resistance from different food sources along with one health approach in the Egypt and UK

BACKGROUND

Antimicrobial resistance (AMR) is a critical global issue that poses significant threats to human health, animal welfare, and the environment. With the increasing emergence of resistant microorganisms, the effectiveness of current antimicrobial medicines against common infections is diminishing. This study aims to conduct a competitive meta-analysis of surveillance data on resistant microorganisms and their antimicrobial resistance patterns in two countries, Egypt and the United Kingdom (UK).

METHODS

Data for this study were obtained from published reports spanning the period from 2013 to 2022. In Egypt and the UK, a total of 9,751 and 10,602 food samples were analyzed, respectively. Among these samples, 3,205 (32.87%) in Egypt and 4,447 (41.94%) in the UK were found to contain AMR bacteria.

RESULTS

In Egypt, the predominant resistance was observed against β-lactam and aminoglycosides, while in the United Kingdom, most isolates exhibited resistance to tetracycline and β-lactam. The findings from the analysis underscore the increasing prevalence of AMR in certain microorganisms, raising concerns about the development of multidrug resistance.

CONCLUSION

This meta-analysis sheds light on the escalating AMR problem associated with certain microorganisms that pose a higher risk of multidrug resistance development. The significance of implementing One Health AMR surveillance is emphasized to bridge knowledge gaps and facilitate accurate AMR risk assessments, ensuring consumer safety. Urgent actions are needed on a global scale to combat AMR and preserve the effectiveness of antimicrobial treatments for the well-being of all living beings.

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.

Chitosan nanoparticles and green synthesized silver nanoparticles as novel alternatives to antibiotics for preventing A.hydrophila subsp. hydrophila infection in Nile tilapia, Oreochromis niloticus

Recently, nanoparticles have attracted attention as a preventive tool for certain infectious diseases affecting fish in aquaculture. Furthermore, freshwater fishes are frequently vulnerable to summer mass morality caused by Aeromonas bacteria. In this regard, we focused on the evaluation of the in vitro and in vivo antimicrobial activity of chitosan (CNPs) and silver (AgNPs) nanoparticles against Aeromonas hydrophila subsp. hydrophila. CNPs and AgNPs were prepared at a mean particle size of 9.03 and 12.8 nm and a charge equalled+36.4 and -19.3 mV for CNPs and AgNPs, respectively. A. hydrophila subsp. hydrophila, Aeromonas caviae, and Aeromonas punctata were retrieved and identified by traditional and molecular techniques. The sensitivity of the obtained bacteria to eight different antibiotic discs was also tested. The antibiotic sensitivity studies revealed the presence of multidrug-resistant (MDR) Aeromonas species (spp.). The bacterium that showed the highest multidrug resistance against the tested antibiotic discs was Aeromonas hydrophila subsp. hydrophila. Therefore, CNPs and AgNPs were in vitro tested against the isolated bacterium and exhibited inhibition zones of 15 and 25 mm, respectively. TEM images also showed that CNPs and AgNPs had an antagonistic action against the same bacterium causing loss of architecture and bacterial death.

Multidrug-resistant Aeromonas bacteria prevalence in Nile tilapia broodstock

BACKGROUND

Aeromonas hydrophila is an opportunistic pathogen. Thus, it has received significant attention mainly in the fish sectors with high production scales. Nile tilapia broodstock confined in the environment of fish hatcheries can be stressed. Hence, they are vulnerable to A. hydrophila.

RESULTS

Sequencing of the gyr B gene revealed the presence of 18 different A. hydrophila strains (kdy 10,620-10,637), which were deposited in the NCBI under accession numbers ON745861-ON745878. The median lethal doses of the isolates ranged from 2.62 × 10⁴ to 3.02 × 10⁶ CFU/mL. Antibiotic resistant genes, sulfonamide (sul1) and tetracycline (tetA) were found in the eighteen isolates. Approximately 83.3% of A. hydrophila strains were sensitive to ciprofloxacin and florfenicol. Further, eight A. hydrophila strains had high MDR indices at 0.27-0.45. All isolates presented with hemolysin activity. However, only 72.22% of them had proteolytic activity, and only 61.11% could form biofilms. Bacterial isolates harbored different pattern virulence genes, the heat-stable cytotonic enterotoxin (ast), cytotoxic enterotoxin (act), and hemolysin (hly) genes were the most prevalent. Also, a trial to inhibit bacterial growth was conducted using titanium dioxide nanoparticles (TiO₂ NPs) with three sizes (13, 32, and 123 nm). If A. hydrophila strains with a high MDR index were tested against TiO₂ NPs (20 µg/mL) for 1, 12, and 24 h, those with a small size had a greater bactericidal action than large ones. Bacterial strains were inhibited at different percentages in response to TiO₂ NP treatment.

CONCLUSIONS

Nile tilapia broodstock, mortality is associated with different A. hydrophila strains, which harbored virulent and MDR genes. Furthermore, TiO₂ NPs had bactericidal activity, thereby resulting in a considerable reduction in bacterial load.

Antibiotic Resistance, Virulence Gene Detection, and Biofilm Formation in Aeromonas spp. Isolated from Fish and Humans in Egypt

The genus Aeromonas is widely distributed in aquatic environments and is recognized as a potential human pathogen. Some Aeromonas species are able to cause a wide spectrum of diseases, mainly gastroenteritis, skin and soft-tissue infections, bacteremia, and sepsis. The aim of the current study was to determine the prevalence of Aeromonas spp. in raw fish markets and humans in Zagazig, Egypt; identify the factors that contribute to virulence; determine the isolates’ profile of antibiotic resistance; and to elucidate the ability of Aeromonas spp. to form biofilms. The examined samples included fish tissues and organs from tilapia (Oreochromis niloticus, n = 160) and mugil (Mugil cephalus, n = 105), and human skin swabs (n = 51) and fecal samples (n = 27). Based on biochemical and PCR assays, 11 isolates (3.2%) were confirmed as Aeromonas spp. and four isolates (1.2%) were confirmed as A. hydrophila. The virulence genes including haemolysin (hyl A) and aerolysin (aer) were detected using PCR in A. hydrophila in percentages of 25% and 50%, respectively. The antimicrobial resistance of Aeromonas spp. was assessed against 14 antibiotics comprising six classes. The resistance to cefixime (81.8%) and tobramycin (45.4%) was observed. The multiple antibiotic resistance (MAR) index ranged between 0.142–0.642 with 64.2% of the isolates having MAR values equal to 0.642. Biofilm formation capacity was assessed using a microtiter plate assay, and two isolates (18.1%) were classified as biofilm producers. This study establishes a baseline for monitoring and controlling the multidrug-resistant Aeromonas spp. and especially A. hydrophila in marine foods consumed in our country to protect humans and animals.

Protective effects of the fructooligosaccharide on the growth performance, biochemical indexes, and intestinal morphology of blunt snout bream (Megalobrama amblycephala) infected by Aeromonas hydrophila

The purpose of the study was to investigate the effects of dietary fructooligosaccharide (FOS) on growth performance, biochemical indexes, intestinal morphology, and growth-related gene expression of blunt snout bream (Megalobrama amblycephala) infected by Aeromonas hydrophila (AH). Two hundred twenty-five healthy blunt snout bream with an initial body weight of 38.41 ± 0.88 g were randomly divided into five groups with three replicates: control (basal diet), model (AH + basal diet), SFOS (AH + 2 g/kg FOS), MFOS (AH + 4 g/kg FOS), LFOS (AH + 6 g/kg FOS). After 9 weeks of feeding, the results showed that the FOS-added diet abrogated AH-induced retardation, hemorrhage, and inflammatory infiltration. FOS supplementation enhanced the growth performance degradation caused by AH, and the highest growth performance was observed at MFOS. Meanwhile, the addition of FOS to feed improved the blood immunity reduced by AH. In expansion, the mucosal epithelium of intestinal villi exfoliated, exposing the lamina propria, and a few villi were genuinely harmed in the model group. Fish fed with MFOS ameliorated the damaged intestine, evidenced by well-preserved intestine architecture. Furthermore, the model group downregulated the expression of growth-related genes (growth hormone receptor (GHR), insulin-like growth factor 1 (IGF-1)). Fish fed with 2 g/kg or 4 g/kg FOS upregulated the genes specified above expressions in the liver compared with the model group. In conclusion, the results mentioned above suggested that the dietary FOS could relieve the pressure to elevate the immune damage and intestine injury induced by AH and enhance the hepatic expression of IGF-1 and GHR.

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.

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.

Emergence of extensively drug-resistant Aeromonas hydrophila complex isolated from wild Mugil cephalus (striped mullet) and Mediterranean seawater

Background and Aim:

Antibiotic resistance has been a progressively documented problem, resulting in treatment failure in humans and animals. This study aimed to investigate the antimicrobial susceptibility and virulence of extensively drug-resistant (XDR) Aeromonas spp. in wild Mugil cephalus and its surrounding seawater along the coastal road of Port Said, Egypt.

Materials and Methods:

Specimens were examined bacteriologically, confirmed biochemically, and tested for their sensitivity against 11 antimicrobial agents. Molecular confirmation of the obtained isolates by 16S rRNA was performed, followed by the detection of antimicrobial resistance and virulence genes.

Results:

Aeromonas spp. was recovered from fish (44%) and water samples (36%). A. hydrophila was the most prevalent identified strain, followed by Aeromonas sobria, Aeromonas caviae, and Aeromonas schubertii. Moreover, 90% of the tested isolates were multidrug-resistant (MDR), while 26.67% were XDR. Tested isolates were resistant to b-lactams and sulfonamides (100%), oxytetracycline (90%), and streptomycin (62.22%) but completely susceptible to cefotaxime. XDR isolates successfully amplified resistance genes (bla_TEM , sul1, and tetA(A)) but not the (aadA1) gene, although there was phenotypic resistance to streptomycin on plates. All XDR isolates carry the cytotoxic enterotoxin gene (act), but alt gene was detected in only one isolate (12.5%).

Conclusion:

Data in this study provide a recent update and highlight the role of wild mullet and seawater as reservoirs for MDR and XDR Aeromonas spp. that may pose a risk to humans as food-borne infection or following direct contact.

Distinction between Antimicrobial Resistance and Putative Virulence Genes Characterization in Plesiomonas shigelloides Isolated from Different Sources

Plesiomonas shigelloides are gram-negative, thermotolerant, motile, and pleomorphic microorganisms that are only distantly related to those of the Enterobacteriaceae and Vibrionaceae families. One of the most common sources of P. shigelloides contamination is human stool, but it may also be found in a wide range of other animals, plants, and aquatic habitats. Antimicrobial resistance in P. shigelloides from seawater and shellfish was investigated, and pathogenicity involved genes were characterized as part of this study. Out of 384 samples of shellfish, 5.7% included P. shigelloides. The presence of P. shigelloides was also discovered in 5% of the seawater sampled. The antimicrobial resistance of 23 P. shigelloides isolates derived from those samples was investigated. All isolates were sensitive to nalidixic acid, carbenicillin, cephalothin, erythromycin, kanamycin, tetracycline, and ciprofloxacin in the study. Several strains isolated from diseased shellfish were tested for virulence in shellfish by intraperitoneal injections. The LD₅₀ values ranged from 12 × 10⁸ to 3 × 10¹² cfu/shellfish. When looking for possible virulence factors that may play a significant role in bacterial infection in the current study, we found that all of these genes were present in these strains. These include genes such as elastase, lipase, flagellin, enterotoxin, and DNases. According to these findings, shellfish may serve as a reservoir for multi-resistant P. shigelloides and help spread virulence genes across the environment.

Metagenomic and Recombination Analyses of Antimicrobial Resistance Genes from Recreational Waters of Black Sea Coastal Areas and Other Marine Environments Unveil Extensive Evidence for Their both Intrageneric and Intergeneric Transmission across Genetically Very Diverse Microbial Communities

Microbial communities of marine coastal recreation waters have become large reservoirs of AMR genes (ARGs), contributing to the emergence and transmission of various zoonotic, foodborne and other infections that exhibit resistance to various antibiotics. Thus, it is highly imperative to determine ARGs assemblages as well as mechanisms and trajectories of their transmission across these microbial communities for our better understanding of the evolutionary trends of AMR (AMR). In this study, using metagenomics approaches, we screened for ARGs in recreation waters of the Black Sea coastal areas of the Batumi City (Georgia). Also, a large array of the recombination detection algorithms of the SplitsTree, RDP4, and GARD was applied to elucidate genetic recombination of ARGs and trajectories of their transmission across various marine microbial communities. The metagenomics analyses of sea water samples, obtained from across the above marine sites, could identify putative ARGs encoding for multidrug resistance efflux transporters mainly from the Major Facilitator and Resistance Nodulation Division superfamilies. The data, generated by SplitsTree (fit ≥95.619; bootstrap values ≥ 95; Phi p ≤ 0.0494), RDP4 (p ≤ 0.0490), and GARD, provided strong statistical evidence not only for intrageneric recombination of these ARGs, but also for their intergeneric recombination across fairly large and diverse microbial communities of marine environment. These bacteria included both human pathogenic and nonpathogenic species, exhibiting collectively the genera of Vibrio, Aeromonas, Synechococcus, Citromicrobium, Rhodobacteraceae, Pseudoalteromonas, Altererythrobacter, Erythrobacter, Altererythrobacter, Marivivens, Xuhuaishuia, and Loktanella. The above nonpathogenic bacteria are strongly suggested to contribute to ARGs transmission in marine ecosystems.

Virulent and Multiple Antimicrobial Resistance Aeromonas hydrophila Isolated from Diseased Nile Tilapia Fish (Oreochromis niloticus) in Egypt with Sequencing of Some Virulence-Associated Genes

Aeromonas hydrophila is a major waterborne pathogen, which induces various diseases in freshwater fish with the capability for zoonotic potential. This study was applied to investigate the prevalence of A. hydrophila in diseased Nile tilapia fish, genetic characterization of the virulence encoding genes (act, aerA, alt, and ast genes), and antibiotic susceptibility. Out of the 500 diseased Nile tilapia fish samples, 70% (350/500) Aeromonas species were isolated. From which 53.4% (187/350) of Aeromonas hydrophila strains were identified. A. hydrophila was detected in kidneys, followed by liver, spleen, intestine, and gills. The results of virulotyping displayed the presence of act, and aerA genes in a high percentage of 40%, followed by alt gene (30%), but ast gene was not detected (0%) in A. hydrophila strains. Based on DNA sequence analysis of three virulence associated-genes (act, aerA, and alt genes), the phylogenetic tree showed the genetic relationship with related species. Finally, the antibiotic susceptibility tests revealed high resistance toward chloramphenicol (67.4%), followed by amikacin (51.9%) and gentamicin (47.1%), whereas a high sensitivity was exhibited toward meropenem (90.9%), followed by ciprofloxacin (84.2%), amoxicillin-clavulanic acid (73.3%) and trimethoprim-sulfamethoxazole (64.2%). The multidrug-resistant A. hydrophila strains were observed in 69.0% of strains with six resistance patterns.

Detection of Antimicrobial and Heavy-Metal Resistance Genes in Aeromonas spp. Isolated from Hard-Shelled Mussel (Mytilus Coruscus)

Hard-shelled mussel (Mytilus coruscus) is a popular seafood in South Korea because of its delicacy and high nutritional value. Our study aimed to identify antimicrobial and heavy-metal resistance determinants in Aeromonas isolates from marketed hard-shelled mussel in South Korea. A total of 33 Aeromonas species were isolated, and antimicrobial disk diffusion test was done to observe antimicrobial resistance patterns. In addition, broth microdilution test was performed to determine resistance to heavy-metals. PCR amplification was done to detect resistance genes. High resistance to amoxicillin (100.0%), ampicillin (93.9%), rifampicin (78.8%), and cephalothin (48.5%) was observed where least resistance to other antimicrobials was also detected. In addition, the isolates showed high resistance to cadmium (Cd) (57.6%), and 42.4% and 27.3% were resistant to chromium (Cr) and copper (Cu). The occurrence of antimicrobial resistance genes, such as blaTEM, blaSHV, blaCTX-M, tetB, tetE, and intI1 genes, was observed in 9 (27.3%), 8 (24.2%), 8 (24.2%), 6 (18.2%), 5 (15.2%), and 9 (27.3%) isolates, respectively. Also, heavy-metal resistance genes, czcA, copA, and merA were detected in 17 (51.5%), 11 (33.3%), and 7 (21.2%) of the isolates, respectively. The results suggest that mussels are a reservoir of multidrug and heavy-metal-resistant Aeromonas spp.

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.

Prevalence, antibiogram and virulence characterization of Vibrio isolates from fish and shellfish in Egypt: a possible zoonotic hazard to humans

AIMS

Infection of seafood with pathogenic species of the genus Vibrio causes human food-borne illnesses. This study was executed to examine the antimicrobial resistance phenotypes, biofilm-forming capability and virulence-associated genes of Vibrio from fish and shellfishes.

METHODS AND RESULTS

Three hundred fresh water and marine fish and shellfish samples were collected from wet markets and supermarkets in Mansoura, Egypt. Bacteriological examination and PCR amplification identified 92 Vibrio spp., including 42 Vibrio parahaemolyticus and 50 Vibrio alginolyticus isolates from the examined fish and shellfish (infection rate: 30·67%). However, V. vulnificus was not found in this study. Vibrio spp. exhibited variable frequencies of antimicrobial resistance with higher percentages to ampicillin and penicillin. Multidrug resistance (MDR) was detected in 69·04 and 38% of V. parahaemolyticus and V. alginolyticus respectively. PCR testing of virulence genes, tdh, trh and tlh revealed the presence of tlh and trh in 100 and 11·9% of V. parahaemolyticus isolates respectively and none of V. alginolyticus carried any of these genes. Biofilm-forming capability was displayed by 76% of V. parahaemolyticus and 73·8% of V. alginolyticus isolates. Both V. parahaemolyticus and V. alginolyticus showed nonsignificant weak positive correlations (r < 0·4) between antimicrobial pairs belonging to different classes; however, a significant positive correlation (P <0·05) between trh and resistance to erythromycin (r = 0·45) and imipenem (r = 0·38) was only identified in V. parahaemolyticus.

CONCLUSIONS

This study reports the existence of MDR strains of V. parahaemolyticus and V. alginolyticus from the common types of fishes and shellfishes in Egypt. Furthermore, the presence of virulence genes in these isolates and the ability to produce a biofilm in vitro pose potential health hazards to consumers.

SIGNIFICANCE AND IMPACT OF THE STUDY

Frequent monitoring of seafood for the presence of Vibrio spp. and their antimicrobial susceptibility, virulence determinants and biofilm-forming capability is important for assessing the risk posed by these organisms to the public and for improving food safety.

Abdelhamid F, El-Mleeh A, Elmahallawy EK, Elsayed MM. Investigation of the Prevalence, Virulence Genes, and Antibiogram of Motile Aeromonads Isolated from Nile Tilapia Fish Farms in Egypt and Assessment of their Water Quality

The aquaculture industry is a fast-growing sector in Egypt; however, the progress of this industry is impeded by many challenges such as poor water quality and associated bacterial infections. Among others, Motile Aeromonas Septicemia (MAS), caused by aeromonads, is among the most important bacterial diseases affecting aquaculture due to its zoonotic potential. In the present work, motile aeromonads were isolated from water samples (n= 8) and Nile tilapia (n= 240) in four fish farms (farms I, II, III, and IV) in Kafr El-Sheikh province during the period March to August 2017. This step was followed by investigation of the prevalence and phenotypic, molecular, and histopathological characterization of aeromonads. In addition, antimicrobial susceptibility and virulence gene detection were analyzed. Interestingly, physicochemical water analysis revealed different ranges in relation to the fish farms and seasons. More importantly, Aeromonas isolates were phenotypically identified in 33.3% and 12.5% from fish and water samples, respectively. The highest prevalence of motile aeromonads (46.7%) was recorded from farm IV, and only 12.5% of water samples were positive for them. Out of 80 isolates, 65 (81.25%) were molecularly identified at the genus level using gyrase B (gyrB). The prevalence of the virulence genes detected in the isolated motile aeromonads was aerolysin (aer), 52.2%; elastase (ahp), 26.25%; hemolysin (hyl), 35%; and lipase (lip), 3.75%. The antibiogram profile revealed that the highest resistance of aeromonads isolates (80%) was recorded to chloramphenicol, kanamycin, and azithromycin. Meanwhile, lower resistance levels of 40%, 30%, and 20% were found for streptomycin, cefotaxime, and amoxicillin, respectively. The multiple antibiotic resistance (MAR) index values ranged between 0.27 and 0.82 of motile aeromonads isolates. Furthermore, the histopathological examinations of naturally diseased tilapia revealed widespread hepatocellular necrosis with diffuse, numerous rod-shaped bacteria in liver with melanomacrophages and lymphocytic depletion with edema and hemosiderosis in the spleen. Our findings provide an updated epidemiological baseline for future reference and highlight the likely role of the adverse impact of water quality in the outbreaks of motile aeromonads with special reference to virulence genes and antibiotic resistant traits.

Insights into the Inhibition of Aeromonas hydrophila d-Alanine-d-Alanine Ligase by Integration of Kinetics and Structural Analysis

Aeromonas hydrophila, a pathogenic bacterium, is harmful to humans, domestic animals, and fishes and, moreover, of public health concern due to the emergence of multiple drug-resistant strains. The cell wall has been discovered as a novel and efficient drug target against bacteria, and d-alanine-d-alanine ligase (Ddl) is considered as an essential enzyme in bacterial cell wall biosynthesis. Herein, we studied the A. hydrophila HBNUAh01 Ddl (AhDdl) enzyme activity and kinetics and determined the crystal structure of AhDdl/d-Ala complex at 2.7 Å resolution. An enzymatic assay showed that AhDdl exhibited higher affinity to ATP (K_m: 54.1 ± 9.1 μM) compared to d-alanine (K_m: 1.01 ± 0.19 mM). The kinetic studies indicated a competitive inhibition of AhDdl by d-cycloserine (DCS), with an inhibition constant (K_i) of 120 μM and the 50% inhibitory concentrations (IC₅₀) value of 0.5 mM. Meanwhile, structural analysis indicated that the AhDdl/d-Ala complex structure adopted a semi-closed conformation form, and the active site was extremely conserved. Noteworthy is that the substrate d-Ala occupied the second d-Ala position, not the first d-Ala position. These results provided more insights for understanding the details of the catalytic mechanism and resources for the development of novel drugs against the diseases caused by A. hydrophila.

Multi-drug resistant mesophilic aeromonads isolated from marketed scallops (Patinopecten yessoensis) harboring resistance genes

Antimicrobial resistance properties of 32 Aeromonas strains isolated from fresh scallops (Patinopecten yessoensis (Jay)) marketed in Korea were assessed. All the Aeromonas spp., including A. salmonicida, were mesophilic and grew very well at 37°C. The isolates were tested for susceptibility to 19 antimicrobials belonging to eight antimicrobial classes. All isolates were multi-drug resistant, which means they were resistant to five or more antimicrobials. Higher resistance rates (≥ 50%) were observed for ampicillin, piperacillin, cephalothin, imipenem, meropenem, trimethoprim-sulfamethoxazole, tetracycline, oxytetracycline, and nalidixic acid while intermediate resistance was also determined. PCR assays revealed the presence of many antimicrobial resistance genes among the isolates in varying combinations. Among them, some isolates harbored higher numbers of resistant genes, e.g., A. veronii-V1 (aac(6’)-Ib, tetE, qnrS, IntI1), A. salmonicida–SL10 (IntI1, blaCTX, aac(3’)-Ib, aac(6’)-Ib, qnrS), A. hydrophila–H13 (IntI1, blaTEM, qnrS, aac(6’)-Ib, strA-strB). However, neither the blaSHV, blaIMP, tetB, qnrA, qnrB, and aphAI-IAB genes nor class1 integrons were detected in any of the isolates. Discrepancies between phenotypic and genetic resistance traits were observed in some isolates. With respect to outcomes, scallops are proposed as a source of multi-drug resistant Aeromonas spp. that harbor antimicrobial resistant genes.

An in silico analysis of acquired antimicrobial resistance genes in Aeromonas plasmids

Sequences of 105 Aeromonas species plasmids were probed for acquired anti-microbial resistance (AMR) genes using a bioinformatics approach. The plasmids showed no positive linear correlation between size and GC content and up to 55 acquired AMR genes were found in 39 (37%) plasmids after in silico screening for resistance against 15 antibiotic drug classes. Overall, potential multiple antibiotic resistance (p-MAR) index ranged from 0.07 to 0.53. Up to 18 plasmids were predicted to mediate multiple drug resistance (MDR). Plasmids pS121-1a (A. salmonicida), pWCX23_1 (A. hydrophila) and pASP-a58 (A. veronii) harboured 18, 15 and 14 AMR genes respectively. The five most occurring drug classes for which AMR genes were detected were aminoglycosides (27%), followed by beta-lactams (17%), sulphonamides (13%), fluoroquinolones (13%), and phenicols (10%). The most prevalent genes were a sulphonamide resistant gene Sul1, the gene aac (6')-Ib-cr (aminoglycoside 6'-N-acetyl transferase type Ib-cr) resistant to aminoglycosides and the blaKPC-2 gene, which encodes carbapenemase-production. Plasmid acquisition of AMR genes was mainly inter-genus rather than intra-genus. Eighteen plasmids showed template or host genes acquired from Pseudomonas monteilii, Salmonella enterica or Escherichia coli. The most occurring antimicrobial resistance determinants (ARDs) were beta-lactamase, followed by aminoglycosides acetyl-transferases, and then efflux pumps. Screening of new isolates in vitro and in vivo is required to ascertain the level of phenotypic expression of colistin and other acquired AMR genes detected.

Species identification, virulence markers and antimicrobial resistance profiles of Aeromonas sp. isolated from marketed hard-shelled mussel (Mytilus coruscus) in Korea

Hard-shelled mussel (Mytilus coruscus) is a popular seafood in Korea. This study aimed to determine the virulence markers and antimicrobial resistance patterns of 33 Aeromonas strains isolated from mussels. The isolates were identified as A. salmonicida (n = 14), A. veronii (n = 9), A. enteropelogenes (n = 4), A. caviae (n = 3), A. allosaccharophila (n = 2) and A. bivalvium (n = 1) by gyrB gene sequencing. The sequence divergence between and within the species ranged from 3·70 to 10·40% and 0-1·50% respectively. Every species formed a distinct group in a neighbour-joining phylogenetic tree. The DNase, gelatinase, caseinase, β-haemolysis, biofilm and lipase activities were observed in 33 (100·00%), 31 (93·93%), 30 (90·90%), 27 (81·81%), 21 (63·63%) and 17 (51·51%) isolates respectively. The virulence genes were detected by PCR in the following frequencies: fla (90·09%), aer (87·88%), hlyA (87·88%), ahyB (81·19%), gcaT (75·76%), ser (69·70%), lip (66·67%), alt (57·58%), ast (51·51%) and act (21·21%). Every isolate was resistant to at least three of 18 antimicrobials in the disk diffusion test. The multiple antimicrobial resistance index values ranged from 0·11 to 0·44 among the isolates. Our study suggests that mussels can be a potential reservoir of virulent and multidrug-resistant Aeromonas sp. SIGNIFICANCE AND IMPACT OF THE STUDY: Aeromonas sp. are known as common pathogenic bacteria isolated from seafood. The virulence factors and antimicrobial resistance profiles of mussel-borne Aeromonas sp. are poorly understood. This study demonstrated for the first time the existence of virulence markers and antimicrobial resistance of Aeromonas sp. from mussels in Korea. Majority of the isolates were positive for phenotypic virulence characteristics and harboured several virulence genes which reveal the potential virulence of mussel-borne Aeromonas sp. Multiple antimicrobial resistance was also observed among the isolates. Our study highlights the importance of food safety standards in mussel consumption.

An Update on the Genus Aeromonas: Taxonomy, Epidemiology, and Pathogenicity

The genus Aeromonas belongs to the Aeromonadaceae family and comprises a group of Gram-negative bacteria widely distributed in aquatic environments, with some species able to cause disease in humans, fish, and other aquatic animals. However, bacteria of this genus are isolated from many other habitats, environments, and food products. The taxonomy of this genus is complex when phenotypic identification methods are used because such methods might not correctly identify all the species. On the other hand, molecular methods have proven very reliable, such as using the sequences of concatenated housekeeping genes like gyrB and rpoD or comparing the genomes with the type strains using a genomic index, such as the average nucleotide identity (ANI) or in silico DNA–DNA hybridization (isDDH). So far, 36 species have been described in the genus Aeromonas of which at least 19 are considered emerging pathogens to humans, causing a broad spectrum of infections. Having said that, when classifying 1852 strains that have been reported in various recent clinical cases, 95.4% were identified as only four species: Aeromonas caviae (37.26%), Aeromonas dhakensis (23.49%), Aeromonas veronii (21.54%), and Aeromonas hydrophila (13.07%). Since aeromonads were first associated with human disease, gastroenteritis, bacteremia, and wound infections have dominated. The literature shows that the pathogenic potential of Aeromonas is considered multifactorial and the presence of several virulence factors allows these bacteria to adhere, invade, and destroy the host cells, overcoming the immune host response. Based on current information about the ecology, epidemiology, and pathogenicity of the genus Aeromonas, we should assume that the infections these bacteria produce will remain a great health problem in the future. The ubiquitous distribution of these bacteria and the increasing elderly population, to whom these bacteria are an opportunistic pathogen, will facilitate this problem. In addition, using data from outbreak studies, it has been recognized that in cases of diarrhea, the infective dose of Aeromonas is relatively low. These poorly known bacteria should therefore be considered similarly as enteropathogens like Salmonella and Campylobacter.

Prevalence of virulence and antimicrobial resistance genes in Aeromonas species isolated from marketed cockles (Tegillarca granosa) in Korea

This study aimed to examine incidence, virulence and antimicrobial properties in Aeromonas spp. isolated from cockles (Tegillarca granosa) in Korea. Firstly, genomic DNA was extracted from 32 Aeromonas spp. isolates, and PCR screening for virulence, antimicrobial resistance genes was carried out. The disk diffusion assay was used to examine antimicrobial susceptibility. Aeromonas spp. isolates comprised, A. hydrophila (n = 8), A. veronii (n = 15), A. media (n = 2), A. salmonicida (n = 2), A. allosaccharophila (n = 1), A. bestiarum (n = 1), A. culicicola (n = 1), A. enteropelogenes (n = 1) and A. rivipollensis (n = 1). High prevalence of virulence-related genes reported as; act (69%), alt (47%), ast (41%), aerA (56%), lip (50%), ahyB (47%), ser (28%), fla (66%), gcat (44%), ascV (50%) and hlyA (72%). All isolates were multidrug resistant, while highest resistance level observed for ampicillin (100%), followed by imipenem (81%), rifampicin (78%), cephalothin (72%), piperacillin (47%) and Colistin sulfate (31%). The presence of bla_SHV , bla_CTX , tetE, aac(6')-Ib, strA-strB, qnrS, qnrB and IntI1 genes were reported in varying combinations. Nevertheless, bla_TEM , bla_IMP , tetA, tetB, qnrA, qnrB and aphAI-IAB genes and the class1 integron were not detected. The high occurrence of virulence and antimicrobial resistance genes in cockles reveals that it can be a potential health risk source for consumers.

Aeromonas Isolates from Fish and Patients in Tainan City, Taiwan: Genotypic and Phenotypic Characteristics

The present study aimed to isolate Aeromonas from fish sold in the markets as well as in sushi and seafood shops and compare their virulence factors and antimicrobial characteristics with those of clinical isolates. Among the 128 fish isolates and 47 clinical isolates, Aeromonas caviae, A. dhakensis, and A. veronii were the principal species. A. dhakensis isolates carried at least 5 virulence genes, more than other Aeromonas species. The predominant genotype of virulence genes was hlyA lip alt col ela in both A. dhakensis and A. hydrophila isolates, alt col ela in A. caviae isolates, and act in A. veronii isolates. A. dhakensis, A. hydrophila, and A. veronii isolates more often exhibited hemolytic and proteolytic activity and showed greater virulence than A. caviae isolates in Caenorhabditis elegans and the C2C12 cell line. However, the link between the genotypes and phenotypes of the studied virulence genes in Aeromonas species was not evident. Among the four major clinical Aeromonas species, nearly all (99.0%) A. dhakensis, A. hydrophila, and A. veronii isolates harbored bla _CphA, which encodes a carbapenemase, but only a minority (6.7%, 7/104) were nonsusceptible to carbapenem. Regarding AmpC β-lactamase genes, bla _AQU-1 was exclusively found in A. dhakensis isolates, and bla _MOX3 was found only in A. caviae isolates, but only 7.6% (n = 6) of the 79 Aeromonas isolates carrying bla _AQU-1 or bla _MOX3 exhibited a cefotaxime resistance phenotype. In conclusion, fish Aeromonas isolates carry a variety of combinations of virulence and β-lactamase resistance genes and exhibit virulence phenotypes and antimicrobial resistance profiles similar to those of clinical isolates.IMPORTANCE Aeromonas species can cause severe infections in immunocompromised individuals upon exposure to virulent pathogens in the environment, but the characteristics of environmental Aeromonas species remain unclear. Our study showed that several pathogenic Aeromonas species possessing virulence traits and antimicrobial resistance similar to those of Aeromonas isolates causing clinical diseases were present in fish intended for human consumption in Tainan City, Taiwan.

Identity and virulence properties of Aeromonas isolates from healthy Northern snakehead (Channa argus) in China

Members of the genus Aeromonas are opportunistic pathogen of a variety of aquatic animals that exhibits multidrug resistance, phenotypes, virulence genes and virulence. The present study described the species distribution and the potential pathogenicity of Aeromonas isolated from healthy Northern snakehead (Channa argus) in China. Molecular identification revealed that A. veronii biovar veronii (69/167; 41·3%) and A. hydrophila (41/167; 24·6%) were the most common species found in Northern snakehead intestine based on sequencing of the 16S rRNA gene and DNA gyrase subunit B protein. The distribution of seven virulence factors including aer (84·4%), act (80·8%), ser (40·1%), Aha (27·5%), lip (23·4%), exu (15·0%) and LuxS (12·6%) were determined exclusively in Aeromonas isolates. All the seven virulence genes were present in 9·6% (16/167), among which 11 strains were identified as A. veronii biovar veronii. For the strains harbouring seven virulence genes, the 50% lethal doses (LD₅₀ ) of isolates were lower compared to the isolates carrying two virulence genes. The challenge tests revealed that isolate W31 had the lowest lethal dose, causing 50% mortality at 4·5 × 10³ colony-forming units (CFU) per ml. Furthermore, histopathology of Northern snakehead infected with Aeromonas strains showed necrosis and congestion in liver, spleen and kidney and also damage to the intestine. This study confirms that the Aeromonas strains isolated from healthy Northern snakehead may be a cause of concern for public health. SIGNIFICANCE AND IMPACT OF THE STUDY: Aeromonas species are widely distributed in aquatic environments and have considerable virulence potential. The aim of this study was to identify Aeromonas strains isolated from healthy Northern snakehead, and to investigate if Aeromonas species isolated from healthy fish potential pathogenicity with special reference to virulence and epidemiology studies.

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.