Recent advances in the study of the taxonomy, pathogenicity, and infectious syndromes associated with the genus Aeromonas

Characterization of Aeromonas Strains Isolated from Adult Patients with Diarrhea and Aquatic Environments - Beijing Municipality, China, 2016-2022

Introduction

Aeromonas is widely distributed in aquatic environments. This study describes the pathogenic characteristics of Aeromonas isolated from adult diarrhea patients and aquatic environments in Beijing, China.

Methods

Aeromonas isolates from patients with diarrhea and river water samples were assessed using whole-genome sequencing (WGS) and antibiotic resistance profiling.

Results

In total, 38 Aeromonas isolates were collected. Among these, 13 isolates were from patients with common clinical symptoms, including diarrhea, abdominal pain, and nausea. Four of 13 Aeromonas-positive patients were co-infected with other intestinal pathogens. Patient-derived Aeromonas isolates showed high resistance to ampicillin, ampicillin-sulbactam, nalidixic acid, and tetracycline, whereas water-derived isolates showed high resistance to ampicillin, ampicillin-sulbactam, and nalidixic acid. Phylogenetic analysis revealed seven independent branches, without significant clustering among patient- and water-derived isolates.

Conclusions

This study provides valuable insights into the prevalence and characteristics of Aeromonas. The intertwined distribution of patient- and water-derived isolates in the phylogenetic tree deserves attention.

A 26-year-old man with multiple organ failure caused by Aeromonas dhakensis infection: a case report and literature review

Background

Infections in humans are mainly caused by Aeromonas hydrophila, Aeromonas caviae, and Aeromonas veronii. In recent years, Aeromonas dhakensis has been recognized as widely distributed in the environment, with strong virulence. However, this bacterial infection usually does not appear in patients with pneumonia as the first symptom.

Case report

We report a 26-year-old man who was admitted to the hospital with community-acquired pneumonia as the first symptom and developed serious conditions such as hemolytic uremic syndrome, multiple organ dysfunction, and hemorrhagic shock within a short period. He died after 13 h of admission, and the subsequent metagenomic-next generation sequencing test confirmed the finally identified pathogen of infection as A. dhakensis.

Conclusion

Aeromonas is a rare pathogen identified in the diagnosis of community-acquired pneumonia. Hence, doctors need to develop their experience in identifying the difference between infections caused by pathogenic microorganisms. Medical attention is essential during the occurrence of respiratory symptoms that could be controlled by empirical drugs, such as cephalosporins or quinolones. When patients with community-acquired pneumonia present hemoptysis and multiple organ dysfunction in clinical treatment, an unusual pathogen infection should be considered, and the underlying etiology should be clarified at the earliest for timely treatment.

Good Performance of Revised Scoring Systems in Predicting Clinical Outcomes of Aeromonas Bacteremia in the Emergency Department: A Retrospective Observational Study

BACKGROUND

Aeromonas species, Gram-negative, non-sporulating, facultative, and anaerobic bacilli, widely distributed in aquatic environments, derive various infections, including bacteremia. Most of these infections were opportunistic and found in patients with predisposing conditions. Among the infections, bacteremia remains with notable mortality, reported from 15% to 45%. However, predicting systems for assessing the mortality risk of this disease have yet to be investigated. We aimed to validate the performance of specific predictive scoring systems to assess the clinical outcomes of Aeromonas bacteremia and applied the revised systems to predict mortality risk.

METHODS

A retrospective observational study reviewed patients with bacteremia caused by Aeromonas spp. based on at least one positive blood culture sample collected in the emergency department from January 2012 to December 2020. The outcome was in-hospital mortality. We used seven predictive scoring systems to predict the clinical outcome. According to the effectiveness in predicting mortality, we revised three of the seven predictive scoring systems by specific characteristics to refine their risk-predicting performances.

RESULTS

We enrolled 165 patients with bacteremia caused by Aeromonas spp., including 121 males (73.3%) and 44 females (26.7%), with a mean age of 66.1 ± 14.9 years and an average length of hospital stay of 12.4 ± 10.9 days. The overall mortality rate was 32.7% (54/165). The non-survivors had significantly higher scores in MEDS (6.7 ± 4.2 vs. 12.2 ± 3.3, p < 0.001), NEWS (4.0 ± 2.8 vs. 5.3 ± 3.0, p = 0.008), and qSOFA (0.3 ± 0.6 vs. 0.6 ± 0.7, p = 0.007). Regarding mortality risk prediction, the MEDS demonstrated the best predictive power with AUC of ROC measured up to 0.834, followed by NEWS (0.626) and qSOFA (0.608). We revised the MEDS, NEWS, and qSOFA by hemoglobin and lactate. We found that the revised scores had better powerful performance, including 0.859, 0.767, and 0.691 of the AUC of ROC, if the revised MEDS ≥10, revised NEWS ≥8, and revised qSOFA ≥2, respectively.

CONCLUSIONS

MEDS, NEWS, and qSOFA were good tools for predicting outcomes in patients with Aeromonas spp. bacteremia. The revised MEDS, NEWS, and qSOFA demonstrated more powerful predicting performance than the original scoring systems. We suggested that patients with higher scores in revised MEDS (≥10), revised NEWS (≥8), and revised qSOFA (≥2) received early goal-directed therapy and appropriate broad-spectrum antibiotic treatment as early as possible to reduce mortality.

Evaluation of the Antimicrobial Activity of Phytochemicals from Tea and Agarwood Leaf Extracts against Isolated Bacteria from Poultry and Curd

Antibiotic-resistant bacteria are becoming increasingly common, leading to a global health crisis. The effects of abusing antibiotics not only increase pathogenic resistance but also cause various diseases and syndromes. Gut microbiota contains many beneficial roles for health, while antibiotics kill both pathogens and gut microbiota which is considered one of the major side effects of antibiotics. In fact, new antibiotic compounds are needed in this urgent scenario; phytoremediation is the oldest but most effective method, and research on the antibacterial properties of several types of medicinal plants has already been conducted. Tea and agarwood plants are well known for their economic contribution in both beverage and cosmetic production, as well as for their medicinal value. In this study, tea and agarwood leaf extracts were analyzed for their antimicrobial activity against both pathogenic and beneficial bacteria. Fresh tea (Camellia sinensis) leaves were collected in three varieties, namely, BT-6 from Sylhet, BT-7 from Moulvibazar, and BT-8 from Habiganj; also, green tea (nonfermented tea), black tea (fully fermented tea), and agarwood (Aquilaria malaccensis) were collected from Sylhet region of Bangladesh. Unlike commercial antibiotics, which have side effects on probiotics (beneficiary bacteria), leaf extract activities were analyzed to check if they had positive effects on probiotics that can be found in the gastrointestinal tract as well as dairy products. Potential beneficiary bacteria, Lysinibacillus macroides strain SRU-001 (NCBI accession no. MW665108), and pathogenic bacteria, Aeromonas caviae strain YPLS-62 (NCBI accession no. MW666783), were isolated from the small intestine of poultry and curd, respectively. Tea and agarwood leaves (5 g powder/80 mL methanol) with solvents were kept for seven days at room temperature, and extracts were applied for antimicrobial assays by the disc diffusion assay against the isolated bacteria. 50 µL of each leaf extract was examined against 50 µL of each bacterial culture, where gentamicin was a control. After 24 hours of incubation, tea and agarwood leaf extracts showed an 11-15 mm zone of inhibition against pathogenic A. caviae, while only BT-8 showed 7 mm (disc diameter 6 mm) against probiotic L. macroides. However, compared to leaf extracts, gentamicin showed a 27 mm zone of inhibition against both L. macroides strain SRU-001 and A. caviae strain YPLS-62 bacteria. This research clearly indicates that gentamicin kills both pathogenic and beneficiary bacteria, while leaf extracts from tea and agarwood plants contain antimicrobial activity against only pathogenic A. caviae but no effects on probiotic L. macroides. This outcome indicates not only the potential therapeutic values of tea and agarwood leaves as antibiotics over commercial antibiotics but also the chance of having pathogens in curd and potential beneficial bacteria from the poultry small intestine.

De novo whole transcriptome analysis of Aeromonas hydrophila isolated from the gut of an infected Labeo rohita

Aeromonas hydrophila is a major generalist bacterial pathogen causing severe infections and mortalities in aquatic animals. Its genome, which was the first to be sequenced from the Aeromonas genus, may serve as a model for studying pathogenic mechanisms. To explore the pathogen-host fitness mechanism of bacterium, a comprehensive comparative transcriptome ecotype analysis of A. hydrophila isolated from the gut of Labeo rohita during infection was performed. Special characteristics in gene expression, gene ontology terms and expression of pathogenesis-associated genes, including genes encoding secreted proteins, candidate effectors, hydrolases, and proteins involved in secondary metabolite production were revealed. Among the database, 6,533 were gene ontology (GO) annotated, while 1,480 were not allocated in any GO terms. Investigation on GO illustrated that the articulated genes were improved with molecular function, cellular components, and biological processes. Further bioinformatics analysis identified the outer membrane protein genes (ompA, ompts, ompw, omp38, and omp48), cytotoxin, amylase, and lipase genes. Overall, this work allowed to designate, for the first time, a global view on the pathogenicity of Aeromonas hydrophila during infection. Furthermore, the study provides information on the fitness of A. hydrophila, a severe pathogen with a wide host range.

In Vitro Antibiofilm Activity of Resveratrol against Aeromonas hydrophila

Aeromonas hydrophila is a Gram-negative bacterium that widely exists in various aquatic environments and causes septicemia in fish and humans. Resveratrol, a natural polyterpenoid product, has potential chemo-preventive and antibacterial properties. In this study, we investigated the effect of resveratrol on A. hydrophila biofilm formation and motility. The results demonstrated that resveratrol, at sub-MIC levels, can significantly inhibit the biofilm formation of A. hydrophila, and the biofilm was decreased with increasing concentrations. The motility assay showed that resveratrol could diminish the swimming and swarming motility of A. hydrophila. Transcriptome analyses (RNA-seq) showed that A. hydrophila treated with 50 and 100 μg/mL resveratrol, respectively, presented 230 and 308 differentially expressed genes (DEGs), including 90 or 130 upregulated genes and 130 or 178 downregulated genes. Among them, genes related to flagellar, type IV pilus and chemotaxis were significantly repressed. In addition, mRNA of virulence factors OmpA, extracellular proteases, lipases and T6SS were dramatically suppressed. Further analysis revealed that the major DEGs involved in flagellar assembly and bacterial chemotaxis pathways could be regulated by cyclic-di-guanosine monophosphate (c-di-GMP)- and LysR-Type transcriptional regulator (LTTR)-dependent quorum sensing (QS) systems. Overall, our results indicate that resveratrol can inhibit A. hydrophila biofilm formation by disturbing motility and QS systems, and can be used as a promising candidate drug against motile Aeromonad septicemia.

Complete Genomic Sequences of Two Aeromonas hydrophila Isolates Derived from Diseased Fish in South Korea

Aeromonas hydrophila is a Gram-negative pathogen that is associated with motile aeromonad septicemia in various fish species. Here, we report the complete genomic sequences of two A. hydrophila isolates derived from diseased fish in South Korea.

Clinical characteristics and risk factors of Aeromonas bloodstream infections in patients with hematological diseases

BACKGROUND

To analyze the clinical features, risk factors and outcomes of Aeromonas bloodstream infections (BSIs) in patients with hematological diseases to establish an effective optimal therapy against it.

METHODS

A retrospective study was performed by reviewing medical records of patients admitted to a tertiary blood disease hospital in China. Patients with hematological diseases who suffered from Aeromonas bacteremia during January 2002 to December 2020 were enrolled in this study.

RESULTS

A total of 63 patients who developed Aeromonas bacteremia were enrolled in the study, and 91.9% of patients were neutropenic at the onset of BSIs. The major complications were skin and soft tissue infection (SSTI) (22.2%), followed by gastroenteritis (19.0%) and pneumonia (14.3%). High carbapenem resistance rates (70.8% for imipenem, 71.4% for meropenem) were note among the cases. Furthermore, Aeromonas strains isolated from five individuals developed resistance to quinolone, β-lactams and tigecycline during the therapy. The 30-day mortality rate was 15.9%, while bacteremia with SSTI showed a much worse prognosis, with 50.0% (7/14) of the patients dying within 30 days of initiating the therapy. In the multivariate analysis, SSTI (OR = 28.72; 95% CI, 1.50-551.30; P = 0.026) and shock (OR = 47.58; 95% CI,1.06-2126.80; P = 0.046) were independent risk factors for mortality.

CONCLUSIONS

Aeromonas bacteremia usually occurred in patients with neutropenic status, and patients with SSTIs were more likely to show a worse prognosis. Carbapenems should be avoided in patients with Aeromonas BSIs and SSTIs given high resistance rate.

Genistein Inhibits the Pathogenesis of Aeromonas hydrophila by Disrupting Quorum Sensing Mediated Biofilm Formation and Aerolysin Production

Aeromonas hydrophila is an opportunistic pathogen that is responsible for a variety of infectious diseases both in human and animals, particularly aquatic animals. Moreover, the pathogen has become a foodborne pathogen by transmitting from seafood to human. The abuse of antibiotics in aquaculture results in the emergence of antibiotic resistance and treatment failure. Therefore, novel approaches are urgently needed for managing resistant A. hydrophila associated infections. Aerolysin, an essential virulence factor of pathogenic A. hydrophila strain, has been identified as target developing novel drugs against pathogenesis of A. hydrophila. In the present study, genistein, without anti-A. hydrophila activity, was identified that could decrease the production of aerolysin and biofilm formation at a dose-dependent manner. Transcription of aerolysin encoding gene aerA and quorum sensing related genes ahyI and ahyR was significantly down-regulated when co-cultured with genistein. Cell viability studies demonstrated that genistein could significantly improve aerolysin mediated A549 cell injury. Furthermore, genistein could provide a remarkable protection to channel catfish infected with A. hydrophila. These findings indicate that targeting quorum sensing and virulence can be a useful approach developing drugs against A. hydrophila infections in aquaculture. Moreover, genistein can be chosen as a promising candidate in developing drugs against A. hydrophila.

Clinical and microbiological characteristics of Aeromonas bacteremia in Turkey

We investigated the cases with Aeromonas bacteremia in terms of clinical and microbiological characteristics, underlying disease and mortality rates. Patients with positive blood cultures were included in this research. Aeromonas bacteremia was diagnosed as at least one positive blood culture for Aeromonas species. The bacteremia was defined as community origin if the onset was in the community or within 72 hours of hospital admission. The others were considered as nosocomial. All bacteria were defined as Aeromonas with conventional method. Species identification was verified by VITEK system. Antibiotic susceptibility tests were analyzed with the disc diffusion, E-test method or VITEK system. Thirty-three patients were diagnosed with bacteremia due to Aeromonas spp. Hematologic and solid tumors were the leading underlying conditions, followed by cirrhosis. Two patients (6%) had community-acquired infections. Aeromonas hydrophila was the most common isolated bacterium. The crude mortality rate was 36%. 12 patients died and 6 deaths and 4 deaths were detected in patients with bacteremia caused by A. hydrophila and Aeromonas sobria respectively. All strains were resistant to ampicillin and more than 90% of the strains were susceptible to trimethoprim-sulfamethoxazole, fluoroquinolone, third generation cephalosporins, and carbapenems. Aeromonas sp. is not a frequent cause of bacteremia however, it may lead to high mortality rates, especially in the immunocompromised hosts and patients with liver cirrhosis. Nosocomial Aeromonas bacteremia is not uncommon in these populations. Broad-spectrum cephalosporins, piperacillin-tazobactam, fluoroquinolones, and carbapenems remain as effective antimicrobial agents for therapy of Aeromonas bacteremia.

Virulence and antimicrobial resistance potential of Aeromonas spp. associated with shellfish

Aeromonas spp. are associated with seafood-related outbreaks worldwide. In seafood industry, shellfish play a major role in global seafood production. With this emerging trend of shellfish consumption, shellfish-related bacterial infections are being reported frequently. Aeromonas spp. are natural contaminants found in shellfish. Although 36 species have been identified, some species including Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii biotype sobria have dragged major attention as foodborne pathogenic bacteria. The ability to elaborate a variety of virulence factors of Aeromonas spp. contributes to the pathogenic activities. Also, emerging antimicrobial resistance in Aeromonas spp. has become a huge challenge in seafood industry. Furthermore, multidrug resistance increases the risk of consumer health. Studies have supplied pieces of evidence about the emerging health risk of Aeromonas spp. isolated from seafood. Therefore, the present review was intended to highlight the prevalence, virulence and antimicrobial resistance of Aeromonas spp. isolated from various types of shellfish.

Enteropathogenic Bacterial and Intestinal Parasitic Infections among Asymptomatic Food Handlers in Rangsit University Canteens, Central Thailand

Food handlers play an important role in the transmission of foodborne diseases. 108 asymptomatic food handlers work in RSU canteens and have never been checked for intestinal bacteria and parasites, which might be a potential source of infection for customers. This study is aimed at estimating the prevalence of enteropathogenic bacterial and intestinal parasitic infections among food handlers in Rangsit University canteens, central Thailand. A total of 79 food handlers were enrolled, and each provided one stool sample (response rate of 73.2%). Females comprised 93.7% of study participants, and the largest age group was 41-50 years (34.2%). The prevalence of enteropathogenic bacteria in stool cultures was 2.5%, and only Aeromonas spp. were detected. The pathogenic protozoa Giardia duodenalis was detected in 1.3% of samples, and nonpathogenic protozoa was found in 11.4%. No helminths were found in any samples. Approximately 80% of food handlers demonstrated good hygiene practices, including regular hand washing after visiting the toilet, regular hand washing when preparing food, using soap when washing hands, wearing uniforms/gowns, practicing correct hand washing techniques, and having short fingernails. However, the results showed a lack of personal hygiene training and routine medical care (>50% of samples). Stronger intervention would help to eliminate future infections.

Motile aeromonad septicemia (MAS) at Cyprinus carpio L., 1758 (Actinopterygii:Cyprinidae) in Lake Tödürge (Sivas/Turkey)

ABSTRACT In this study, fish’s morphologic and anatomic lesions caused by motile aeromonad septicemia (MAS) depending on environmental stress in carp, Cyprinus carpio population living in Lake Tödürge were identified. Various morphological and anatomical deformations and lesions were observed in the body of approximately 17% (252 fish specimens) of a total of 1488 carp samples. Bacteria are grown from all wipe samples. Bacterial colonies have a gray-white appearance with round, convex and smooth edges. 15-20 cfu colonies were observed in each aerop culture. As a result of analysis of wet wipe samples from infected fish’s skin, gill, kidney and liver, it is determined that the bacteria which causes septicemia is Aeromonas sobria from the Aeromonadaceae family (with 99.2% confidence value). No bacteria were grown in cultures except A. sobria. Some symptoms of the infection are inflammation on different parts of the fish bodies, eruption on skin and scales, dermal necrosis, degeneration at soft rays of the fins, exophthalmos, and purulent liquid accumulation in the abdominal cavity, etc. Infected fish were most commonly encountered in July and August (water temperature above 20ºC), the lowest in October and November (water temperature below 10ºC).

Enhanced Virulence of Aeromonas hydrophila Is Induced by Stress and Serial Passaging in Mice

Simple Summary

Aeromonas hydrophila, which is an opportunistic zoonotic bacterium, has the ability to infect animals with injuries involving the condition of the aquatic environments. Factors including poor sanitation and water quality, stress, overcrowding, and rough handling can make animals more sensitive to infections and trigger outbreaks of A. hydrophila. A. hydrophila was previously isolated from an African black-footed penguin that died while in captivity at a zoo, following clinical signs of depression and anorexia, and in this study, we investigated the effect of stress and serial passaging in mice on A. hydrophila virulence. Serial passaging in mice enhanced the virulence of A. hydrophila, and A. hydrophila infection combined with administration of stress hormones or fasting increased mortality.

Abstract

Aeromonas hydrophila was isolated from an African black-footed penguin (Spheniscus demersus) that died while in zoo captivity. At necropsy, the virulence of A. hydrophila appeared to be enhanced by stress, so was assessed in the presence of in vitro and in vivo stressors and serial passaging in mice. Virulence genes from the isolate were amplified by PCR. In vitro assays were conducted to test the hemolytic activity, cytotoxicity, and effect of stress hormones on A. hydrophila virulence. In vivo assays were conducted to test the stress effect on mortality of A. hydrophila-infected mice and virulence in mice. Two virulence genes coding for hemolysin (ahh1) and aerolysin (aerA) were detected, and the cytotoxic potential of the isolate was demonstrated in baby hamster kidney and Vero cells. Some or all mice inoculated with A. hydrophila and exposed to stress hormones (epinephrine and norepinephrine) or low temperature died, while mice inoculated with A. hydrophila and exposed to fasting or agitation stressors or no stressors survived. We concluded that stress can be fatal in mice experimentally infected with A. hydrophila and that serial passaging in mice dramatically enhances the virulence of A. hydrophila.

Recent Insights into Aeromonas salmonicida and Its Bacteriophages in Aquaculture: A Comprehensive Review

The emergence and spread of antimicrobial resistance in pathogenic bacteria of fish and shellfish have caused serious concerns in the aquaculture industry, owing to the potential health risks to humans and animals. Among these bacteria, Aeromonas salmonicida, which is one of the most important primary pathogens in salmonids, is responsible for significant economic losses in the global aquaculture industry, especially in salmonid farming because of its severe infectivity and acquisition of antimicrobial resistance. Therefore, interest in the use of alternative approaches to prevent and control A. salmonicida infections has increased in recent years, and several applications of bacteriophages (phages) have provided promising results. For several decades, A. salmonicida and phages infecting this fish pathogen have been thoroughly investigated in various research areas including aquaculture. The general overview of phage usage to control bacterial diseases in aquaculture, including the general advantages of this strategy, has been clearly described in previous reviews. Therefore, this review specifically focuses on providing insights into the phages infecting A. salmonicida, from basic research to biotechnological application in aquaculture, as well as recent advances in the study of A. salmonicida.

Wild Nutria (Myocastor coypus) Is a Potential Reservoir of Carbapenem-Resistant and Zoonotic Aeromonas spp. in Korea

The emergence and spread of antibiotic-resistant Aeromonas spp. is a serious public and animal health concern. Wild animals serve as reservoirs, vectors, and sentinels of these bacteria and can facilitate their transmission to humans and livestock. The nutria (Myocastor coypus), a semi-aquatic rodent, currently is globally considered an invasive alien species that has harmful impacts on natural ecosystems and carries various zoonotic aquatic pathogens. This study aimed to determine the prevalence of antibiotic-resistant zoonotic Aeromonas spp. in wild invasive nutrias captured in Korea during governmental eradication program. Three potential zoonotic Aeromonas spp. (A. hydrophila, A. caviae, and A. dhakensis) were identified among isolates from nutria. Some strains showed unexpected resistance to fluoroquinolones, third-generation cephalosporins, and carbapenems. In carbapenem-resistant isolates, the cphA gene, which is related to intrinsic resistance of Aeromonas to carbapenems, was identified, and phylogenetic analysis based on this gene revealed the presence of two major groups represented by A. hydrophila (including A. dhakensis) and other Aeromonas spp. These results indicate that wild nutrias in Korea are a potential reservoir of zoonotic and antibiotic-resistant Aeromonas spp. that can cause infection and treatment failure in humans. Thus, measures to prevent contact of wild nutrias with livestock and humans are needed.

Structural and Serological Studies of the O6-Related Antigen of Aeromonas veronii bv. sobria Strain K557 Isolated from Cyprinus carpio on a Polish Fish Farm, which Contains L-perosamine (4-amino-4,6-dideoxy-L-mannose), a Unique Sugar Characteristic for Aeromonas Serogroup O6

Amongst Aeromonas spp. strains that are pathogenic to fish in Polish aquacultures, serogroup O6 was one of the five most commonly identified immunotypes especially among carp isolates. Here, we report immunochemical studies of the lipopolysaccharide (LPS) including the O-specific polysaccharide (O-antigen) of A. veronii bv. sobria strain K557, serogroup O6, isolated from a common carp during an outbreak of motile aeromonad septicemia (MAS) on a Polish fish farm. The O-polysaccharide was obtained by mild acid degradation of the LPS and studied by chemical analyses, mass spectrometry, and ¹H and ¹³C NMR spectroscopy. It was revealed that the O-antigen was composed of two O-polysaccharides, both containing a unique sugar 4-amino-4,6-dideoxy-l-mannose (N-acetyl-l-perosamine, l-Rhap4NAc). The following structures of the O-polysaccharides (O-PS 1 and O-PS 2) were established: O-PS 1: →2)-α-l-Rhap4NAc-(1→; O-PS 2: →2)-α-l-Rhap4NAc-(1→3)-α-l-Rhap4NAc-(1→3)-α-l-Rhap4NAc-(1→. Western blotting and an enzyme-linked immunosorbent assay (ELISA) showed that the cross-reactivity between the LPS of A. veronii bv. sobria K557 and the A. hydrophila JCM 3968 O6 antiserum, and vice versa, is caused by the occurrence of common α-l-Rhap4NAc-(1→2)-α-l-Rhap4NAc and α-l-Rhap4NAc-(1→3)-α-l-Rhap4NAc disaccharides, whereas an additional →4)-α-d-GalpNAc-associated epitope defines the specificity of the O6 reference antiserum. Investigations of the serological and structural similarities and differences in the O-antigens provide knowledge of the immunospecificity of Aeromonas bacteria and are relevant in epidemiological studies and for the elucidation of the routes of transmission and relationships with pathogenicity.

A Unique Sugar l-Perosamine (4-Amino-4,6-dideoxy-l-mannose) Is a Compound Building Two O-Chain Polysaccharides in the Lipopolysaccharide of Aeromonas hydrophila Strain JCM 3968, Serogroup O6

Lipopolysaccharide (LPS) is the major glycolipid and virulence factor of Gram-negative bacteria, including Aeromonas spp. The O-specific polysaccharide (O-PS, O-chain, O-antigen), i.e., the surface-exposed part of LPS, which is a hetero- or homopolysaccharide, determines the serospecificity of bacterial strains. Here, chemical analyses, mass spectrometry, and ¹H and ¹³C NMR spectroscopy techniques were employed to study the O-PS of Aeromonas hydrophila strain JCM 3968, serogroup O6. MALDI-TOF mass spectrometry revealed that the LPS of A. hydrophila JCM 3968 has a hexaacylated lipid A with conserved architecture of the backbone and a core oligosaccharide composed of Hep₆Hex₁HexN₁HexNAc₁Kdo₁P₁. To liberate the O-antigen, LPS was subjected to mild acid hydrolysis followed by gel-permeation-chromatography and revealed two O-polysaccharides that were found to contain a unique sugar 4-amino-4,6-dideoxy-l-mannose (N-acetyl-l-perosamine, l-Rhap4NAc), which may further determine the specificity of the serogroup. The first O-polysaccharide (O-PS1) was built up of trisaccharide repeating units composed of one α-d-GalpNAc and two α-l-Rhap4NAc residues, whereas the other one, O-PS2, is an α1→2 linked homopolymer of l-Rhap4NAc. The following structures of the O-polysaccharides were established: O-PS1

→3)-α-l-Rhap4NAc-(1→4)-α-d-GalpNAc-(1→3)-α-l-Rhap4NAc-(1→

O-PS2

→2)-α-l-Rhap4NAc-(1→

The present paper is the first work that reveals the occurrence of perosamine in the l-configuration as a component of bacterial O-chain polysaccharides.

The genus Aeromonas: A general approach

The genus Aeromonas comprises more than thirty Gram-negative bacterial species which mostly act as opportunistic microorganisms. These bacteria are distributed naturally in diverse aquatic ecosystems, where they are easily isolated from animals such as fish and crustaceans. A capacity for adaptation also makes Aeromonas able to colonize terrestrial environments and their inhabitants, so these microorganisms can be identified from different sources, such as soils, plants, fruits, vegetables, birds, reptiles, amphibians, among others. Infectious processes usually develop in immunocompromised humans; in fish and other marine animals this process occurs under conditions of stress. Such events are most often associated with incorrect practices in aquaculture. Aeromonas has element diverse ranges, denominated virulence factors, which promote adhesion, colonization and invasion into host cells. These virulence factors, such as membrane components, enzymes and toxins, for example, are differentially expressed among species, making some strains more virulent than others. Due to their diversity, no single virulence factor was considered determinant in the infectious process generated by these microorganisms. Unlike other genera, Aeromonas species are erroneously differentiated by conventional biochemical tests. Therefore, molecular assays are necessary for this purpose. Nevertheless, new means of identification have been considered in order to generate methods that, like molecular tests, can correctly identify these microorganisms. The main objectives of this review are to explain environmental and structural characteristics of the Aeromonas genus and to discuss virulence mechanisms that these bacteria use to infect aquatic organisms and humans, which are important aspects for aquaculture and public health, respectively. In addition, this review aims to clarify new tests for the precise identification of the species of Aeromonas, contributing to the exact and specific diagnosis of infections by these microorganisms and consequently the treatment.

Biofilm and Sediment are Major Reservoirs of Virulent Aeromonas hydrophila (vAh) in Catfish Production Ponds

The genus Aeromonas comprises more than 60 recognized species that include many important fish pathogens such as the causative agents of furunculosis and motile Aeromonas septicemia (MAS). Although MAS is typically considered a secondary infection, a new virulent A. hydrophila (vAh) strain has been causing devastating losses to the catfish industry in Alabama since 2009. The objective of this study was to characterize the spatiotemporal distribution of Aeromonas sp. and, specifically, vAh in a commercial catfish farm in western Alabama. We sampled biofilm, sediment, and water from three ponds during four consecutive months during the growing season. Total aerobic counts were between 8.8 × 10⁵ and 1.5 × 10⁶  CFU/mL but were significantly higher in biofilm and sediment than in water throughout the sampling period. Total Aeromonas counts in water samples significantly increased in all three ponds after the month of August and ranged from 7.8 × 10³ to 4.9 × 10⁴  CFU/mL. A similar trend was observed in biofilm and sediment samples for which total Aeromonas counts increased in samples taken in late summer to early fall. Over time, the concentration of Aeromonas in water samples decreased by one order of magnitude, while there was a significant increase in sediments as temperature dropped. The virulent vAh was detected in 35.4% of biofilm samples and 22.9% of sediment samples, suggesting that both environments serve as the major reservoir for this pathogen. Future monitoring efforts should focus on targeting sediment and biofilms since samples of these appear to naturally enrich for the presence of vAh and other Aeromonas species.

Multidrug-resistant Aeromonas hydrophila causing fatal bilateral necrotizing fasciitis in an immunocompromised patient: a case report

BACKGROUND

Aeromonas hydrophila is a water-dwelling, gram-negative rod-shaped bacterium, associated with diarrheal illness and, less commonly, necrotizing skin and soft tissue infections, especially among immunocompromised patients. Necrotizing fasciitis is associated with a high mortality rate, especially when caused by Aeromonas spp. Our patient was infected with an extremely aggressive form of multidrug-resistant Aeromonas spp. that produced both an extended-spectrum β-lactamase and an AmpC enzyme. Aeromonads are being recognized as important emerging pathogens because of their inherent antibiotic resistance profiles compounded by other virulence factors. These difficult-to-treat organisms can have significant implications in both clinical and public health settings.

CASE PRESENTATION

A 37-year-old Caucasian male with immunosuppression due to aplastic anemia being treated with cyclosporine, presented to hospital with relapsed disease. While in hospital, he subsequently developed overwhelming sepsis secondary to bilateral lower extremity necrotizing fasciitis. The necrotizing fasciitis was caused by a multidrug-resistant strain of A. hydrophila. Despite broad-spectrum antibiotics and aggressive surgical debridement, he succumbed to this severe invasive infection.

CONCLUSIONS

Necrotizing fasciitis caused by Aeromonas spp. is a rare infection that may have a poor clinical outcome, particularly if the diagnosis is delayed and/or the organism is highly virulent and multidrug resistant. Enhanced education of clinicians and microbiologists is required to prevent unnecessary complications and improve survival.

Aeromonas sobria serine protease (ASP): a subtilisin family endopeptidase with multiple virulence activities

Aeromonas sobria serine protease (ASP) is secreted from Aeromonas sobria, a pathogen causing gastroenteritis and sepsis. ASP resembles Saccharomyces cerevisiae Kex2, a member of the subtilisin family, and preferentially cleaves peptide bonds at the C-terminal side of paired basic amino acid residues; also accepting unpaired arginine at the P1 site. Unlike Kex2, however, ASP lacks an intramolecular chaperone N-terminal propeptide, instead utilizes the external chaperone ORF2 for proper folding, therefore, ASP and its homologues constitute a new subfamily in the subtilisin family. Through activation of the kallikrein/kinin system, ASP induces vascular leakage, and presumably causes edema and septic shock. ASP accelerates plasma clotting by α-thrombin generation from prothrombin, whereas it impairs plasma clottability by fibrinogen degradation, together bringing about blood coagulation disorder that occurs in disseminated intravascular coagulation, a major complication of sepsis. From complement C5 ASP liberates C5a that induces neutrophil recruitment and superoxide release, and mast cell degranulation, which are associated with pus formation, tissue injury and diarrhea, respectively. Nicked two-chain ASP also secreted from A. sobria is more resistant to inactivation by α2-macroglobulin than single-chain ASP, thereby raising virulence activities. Thus, ASP is a potent virulence factor and may participate in the pathogenesis of A. sobria infection.

Draft Genome Sequence of Aeromonas hydrophila Strain BSK-10 (Serotype O97), Isolated from Carassius carassius with Motile Aeromonad Septicemia in China

We report here a draft genome sequence of Aeromonas hydrophila strain BSK-10, belonging to serotype O97, isolated from crucian carp (Carassius carassius) with motile aeromonad septicemia in Zhejiang, China. The assembly resulted in 34 scaffolds totaling approximately 4.97 Mb, with an average G+C content of 60.97% and 4,594 predicted coding genes.

Genome Sequence of Hypervirulent Aeromonas hydrophila Strain HZAUAH

Aeromonas hydrophila, a zoonotic bacterium found in an expansive range of aquatic ecosystems, has been reported to cause severe diseases in fish, amphibians, reptiles, and mammals, including humans. Herein, we report the draft genome of the hypervirulent A. hydrophila strain HZAUAH isolated from a crucian in China.

Use of Metagenomic Shotgun Sequencing Technology To Detect Foodborne Pathogens within the Microbiome of the Beef Production Chain

Foodborne illnesses associated with pathogenic bacteria are a global public health and economic challenge. The diversity of microorganisms (pathogenic and nonpathogenic) that exists within the food and meat industries complicates efforts to understand pathogen ecology. Further, little is known about the interaction of pathogens within the microbiome throughout the meat production chain. Here, a metagenomic approach and shotgun sequencing technology were used as tools to detect pathogenic bacteria in environmental samples collected from the same groups of cattle at different longitudinal processing steps of the beef production chain: cattle entry to feedlot, exit from feedlot, cattle transport trucks, abattoir holding pens, and the end of the fabrication system. The log read counts classified as pathogens per million reads for Salmonella enterica,Listeria monocytogenes,Escherichia coli,Staphylococcus aureus, Clostridium spp. (C. botulinum and C. perfringens), and Campylobacter spp. (C. jejuni,C. coli, and C. fetus) decreased over subsequential processing steps. Furthermore, the normalized read counts for S. enterica,E. coli, and C. botulinumwere greater in the final product than at the feedlots, indicating that the proportion of these bacteria increased (the effect on absolute numbers was unknown) within the remaining microbiome. From an ecological perspective, data indicated that shotgun metagenomics can be used to evaluate not only the microbiome but also shifts in pathogen populations during beef production. Nonetheless, there were several challenges in this analysis approach, one of the main ones being the identification of the specific pathogen from which the sequence reads originated, which makes this approach impractical for use in pathogen identification for regulatory and confirmation purposes.

Contribution of nuclease to the pathogenesis of Aeromonas hydrophila

Aeromonas hydrophila is a gram-negative bacterium that is widely distributed in aquatic environments and can cause septicemia in both fish and humans. However, the underlying mechanisms leading to severe infection are not well understood. In this study, an A. hydrophila nuclease (ahn) deletion mutant was constructed to investigate its contribution to pathogenesis. This mutant did not differ from the wild-type strain in terms of its growth or hemolytic phenotype. However, the ahn-deficient mutant was more susceptible to being killed by fish macrophages and mouse blood in vitro. Furthermore, evidence obtained using both fish and murine infection models strongly indicated that the inactivation of Ahn impaired the ability of A. hydrophila to evade innate immune clearance in vivo. More importantly, the virulence of the mutant was attenuated in both fish and mice, with reductions in dissemination capacities and mortality rates. These findings implicate Ahn in A. hydrophila virulence, with important functions in evading innate immune defenses.

Multiple approaches to microbial source tracking in tropical northern Australia

Microbial source tracking is an area of research in which multiple approaches are used to identify the sources of elevated bacterial concentrations in recreational lakes and beaches. At our study location in Darwin, northern Australia, water quality in the harbor is generally good, however dry-season beach closures due to elevated Escherichia coli and enterococci counts are a cause for concern. The sources of these high bacteria counts are currently unknown. To address this, we sampled sewage outfalls, other potential inputs, such as urban rivers and drains, and surrounding beaches, and used genetic fingerprints from E. coli and enterococci communities, fecal markers and 454 pyrosequencing to track contamination sources. A sewage effluent outfall (Larrakeyah discharge) was a source of bacteria, including fecal bacteria that impacted nearby beaches. Two other treated effluent discharges did not appear to influence sites other than those directly adjacent. Several beaches contained fecal indicator bacteria that likely originated from urban rivers and creeks within the catchment. Generally, connectivity between the sites was observed within distinct geographical locations and it appeared that most of the bacterial contamination on Darwin beaches was confined to local sources.

Aeromonas sobria necrotizing fasciitis and sepsis in an immunocompromised patient: a case report and review of the literature

Introduction

Aeromonas veronii biovar sobria is a rare cause of bacteremia, with several studies indicating that this isolate may be of particular clinical significance since it is enterotoxin producing. A wide spectrum of infections has been associated with Aeromonas species in developing countries that include gastroenteritis, wound infections, septicemia and lung infections. This infection, caused by Aeromonas species, is usually more severe in immunocompromised than immunocompetent individuals. We here describe a case of soft tissue infection and severe sepsis due to Aeromonas sobria in an immunocompromised patient.

Case presentation

A 74-year-old Caucasian man with a clinical history of chronic lymphocytic leukemia and immune thrombocytopenia, periodically treated with steroids, was admitted to our Intensive Care Unit because of necrotizing fasciitis and multiorgan failure due to Aeromonas sobria, which resulted in his death. The unfortunate coexistence of a Candida albicans infection played a key role in the clinical course.

Conclusion

Our experience suggests that early recognition and aggressive medical and surgical therapy are determinants in the treatment of severe septicemia caused by an Aeromonas sobria in an immunocompromised patient.

Structure of the O-specific polysaccharide from the lipopolysaccharide of Aeromonas sobria strain Pt312

The O-specific polysaccharide (OPS) obtained by mild-acid degradation of the lipopolysaccharide from Aeromonas sobria strain Pt312 was studied by sugar and methylation analyses along with 1H and 13C NMR spectroscopy, including 2D 1H,1H COSY, TOCSY, NOESY, 1H-detected 1H,13C HSQC, and HMBC experiments. The sequence of the sugar residues was determined using 1H,1H NOESY and 1H,13C HMBC experiments. It was found that the OPS was built up of disaccharide repeating units composed of GlcpNAc and non-stoichiometrically O-acetylated Rhap residues, and had the structure.

Gram-negative marine bacteria: structural features of lipopolysaccharides and their relevance for economically important diseases

Gram-negative marine bacteria can thrive in harsh oceanic conditions, partly because of the structural diversity of the cell wall and its components, particularly lipopolysaccharide (LPS). LPS is composed of three main parts, an O-antigen, lipid A, and a core region, all of which display immense structural variations among different bacterial species. These components not only provide cell integrity but also elicit an immune response in the host, which ranges from other marine organisms to humans. Toll-like receptor 4 and its homologs are the dedicated receptors that detect LPS and trigger the immune system to respond, often causing a wide variety of inflammatory diseases and even death. This review describes the structural organization of selected LPSes and their association with economically important diseases in marine organisms. In addition, the potential therapeutic use of LPS as an immune adjuvant in different diseases is highlighted.

Structural studies of the lipopolysaccharide from the fish pathogen Aeromonas veronii strain Bs19, serotype O16

Chemical analyses, mass spectrometry, and NMR spectroscopy were applied to study the structure of the lipopolysaccharide (LPS) isolated from Aeromonas veronii strain Bs19, serotype O16. ESI-MS revealed that the most abundant LPS glycoforms have tetra-acylated or hexa-acylated lipid A species, consisting of a bisphosphorylated GlcN disaccharide with an AraN residue as a non-stoichiometric substituent, and a core oligosaccharide composed of Hep₅Hex₃HexN₁Kdo₁P₁. Sugar and methylation analysis together with 1D and 2D ¹H and ¹³C NMR spectroscopy were the main methods used, and revealed that the O-specific polysaccharide (OPS) of A. veronii Bs19 was built up of tetrasaccharide repeating units with the structure: →4)-α-d-Quip3NAc-(1→3)-α-l-Rhap-(1→4)-β-d-Galp-(1→3)-α-d-GalpNAc-(1→. This composition was confirmed by mass spectrometry. The charge-deconvoluted ESI FT-ICR MS recorded for the LPS preparations identified mass peaks of SR- and R-form LPS species, that differed by Δm = 698.27 u, a value corresponding to the calculated molecular mass of one OPS repeating unit (6dHexNAc6dHexHexHexNAc-H₂O). Moreover, unspecific fragmentation spectra confirmed the sequence of the sugar residues in the OPS and allowed to assume that the elucidated structure also represented the biological repeating unit.

Plant growth promoting capability and genetic diversity of bacteria isolated from mud volcano and lime cave of Andaman and Nicobar Islands

Twenty four bacterial strains from four different regions of mud volcano and lime cave were isolated to estimate their diversity, plant growth promoting and biocontrol activities to use them as inoculant strains in the fields. An excellent antagonistic effect against four plant pathogens and plant growth promoting properties such as IAA production, HCN production, phosphate solubilization, siderophore production, starch hydrolysis and hydrolytic enzymes syntheses were identified in OM5 (Pantoea agglomerans) and EM9 (Exiguobacterium sp.) of 24 studied isolates. Seeds (Chili and tomato) inoculation with plant growth promoting strains resulted in increased percentage of seedling emergence, root length and plant weight. Results indicated that co-inoculation gave a more pronounced effects on seedling emergence, secondary root numbers, primary root length and stem length, while inoculation by alone isolate showed a lower effect. Our results suggest that the mixed inocula of OM5 and EM9 strains as biofertilizers could significantly increase the production of food crops in Andaman archipelago by means of sustainable and organic agricultural system.

The occurrence of Aeromonas in drinking water, tap water and the porsuk river

The occurrence of Aeromonas spp. in the Porsuk River, public drinking water and tap water in the City of Eskisehir (Turkey) was monitored. Fresh water samples were collected from several sampling sites during a period of one year. Total 102 typical colonies of Aeromonas spp. were submitted to biochemical tests for species differentiation and of 60 isolates were confirmed by biochemical tests. Further identifications of isolates were carried out first with the VITEK system (BioMe˜rieux) and then selected isolates from different phenotypes (VITEK types) were identified using the DuPont Qualicon RiboPrinter® system. Aeromonas spp. was detected only in the samples from the Porsuk River. According to the results obtained with the VITEK system, our isolates were 13% Aeromonas hydrophila, 37% Aeromonas caviae, 35% Pseudomonas putida, and 15% Pseudomonas acidovorans. In addition Pseudomonas sp., Pseudomonas maltophila, Aeromonas salmonicida, Aeromonas hydrophila, and Aeromonas media species were determined using the RiboPrinter® system. The samples taken from the Porsuk River were found to contain very diverse Aeromonas populations that can pose a risk for the residents of the city. On the other hand, drinking water and tap water of the City are free from Aeromonas pathogens and seem to be reliable water sources for the community.

Gene network analysis of Aeromonas hydrophila for novel drug target discovery

Increasing the multi-drug resistance Aeromonas hydrophila creates a health problem regularly thus, an urgent needs to develop and screen potent antibiotics for controlling of the infections. There are many studies have focused on interactions between specific drugs, little is known about the system properties of a full drug interaction in gene network. Thus, an attractive approach for developing novel antibiotics against DNA gyrase, an enzyme essential for DNA replication, transcription, repair and recombination mechanisms which is important for bacterial growth and cell division. Homology modeling method was used to generate the 3-D structure of B subunit of DNA gyrase (gyrB) using known crystal structure. The active amino acids in 3-D structure of gyrB were targeted for structure based virtual screening of potent drugs by molecular docking. Number of drugs and analogs were selected and used for docking against gryB. The drugs Cinodine I, Cyclothialidine and Novobiocin were found to be more binding affinity with gyrB-drug interaction. The homology of gyrB protein sequence of A. hydrophila resembles with other species of Aeromonas closely showed relationship in phylogenetic tree. We have also demonstrated the gene network interactions of gyrB with other cellular proteins which are playing the key role in gene regulation. These findings provide new insight to understand the 3-D structure of gyrB which can be used in structure-based drug discovery; and development of novel, potent and specific drug against B subunit of DNA gyrase.

Structural and immunochemical studies of the lipopolysaccharide from the fish pathogen, Aeromonas bestiarum strain K296, serotype O18

Chemical analyses and mass spectrometry were used to study the structure of the lipopolysaccharide (LPS) isolated from Aeromonas bestiarum strain K296, serotype O18. ESI-MS revealed that the most abundant A. bestiarum LPS glycoforms have a hexa-acylated or tetra-acylated lipid A with conserved architecture of the backbone, consisting of a 1,4′-bisphosphorylated β-(1→6)-linked d-GlcN disaccharide with an AraN residue as a non-stoichiometric substituent and a core oligosaccharide composed of Kdo₁Hep₆Hex₁HexN₁P₁. 1D and 2D NMR spectroscopy revealed that the O-specific polysaccharide (OPS) of A. bestiarum K296 consists of a branched tetrasaccharide repeating unit containing two 6-deoxy-l-talose (6dTalp), one Manp and one GalpNAc residues; thus, it is similar to that of the OPS of A. hydrophila AH-3 (serotype O34) in both the sugar composition and the glycosylation pattern. Moreover, 3-substituted 6dTalp was 2-O-acetylated and additional O-acetyl groups were identified at O-2 and O-4 (or O-3) positions of the terminal 6dTalp. Western blots with polyclonal rabbit sera showed that serotypes O18 and O34 share some epitopes in the LPS. The very weak reaction of the anti-O34 serum with the O-deacylated LPS of A. bestiarum K296 might have been due to the different O-acetylation pattern of the terminal 6dTalp. The latter suggestion was further confirmed by NMR.

A Case of Extrusion of a Solid Silicone Tire Migrating through the Superior Rectus Muscle with Aeromonas hydrophila Infection following a Scleral Buckling Procedure

To our knowledge, there are no reports of Aeromonas hydrophila infection after a scleral buckling procedure. Also, migration of a silicone explant element through the rectus muscles is extremely rare. Herein, we describe a case experiencing extrusion of a solid silicone tire migrating through the superior rectus muscle with Aeromonas hydrophila infection following a scleral buckling procedure. A 42-year-old man was referred to our hospital complaining of ocular pain and purulent discharge in his left eye which has persisted for several months. He had a history of bilateral rhegmatogenous retinal detachment which had been treated with scleral buckling. The left eye showed extrusion of the solid silicone buckle which had migrated through the superior rectus muscle and an infection in the upper quadrant of the sclera. The buckle was removed, and the patient was treated with antibiotics. After the removal of the buckle, the symptoms showed rapid amelioration and there was no recurrence of retinal detachment. Aeromonas hydrophila was isolated from the discharge and the removed explant. He used well water in daily life. In this case, the Aeromonas hydrophila infection of the extruded buckle might have originated from contaminated well water.

The tail nick augments Aeromonas sobria serine protease (ASP) activity in plasma through retarding inhibition by α2-macroglobulin

ASP is a serine protease secreted by Aeromonas sobria, a sepsis-causing bacterium, and induces sepsis-mimicking disorders through plasma protein cleavage. The pathogen also secretes nASP that has a nick in the carboxy-terminal region. Compared with single-chain ASP (sASP), nASP had near-equivalent activity for small peptide substrates but was less proteolytic. Surprisingly, nASP cleaved proteins more in plasma and was inhibited by human α(2)-macroglobulin more slowly than sASP. Retarded inhibition by α(2)-macroglobulin allows nASP to keep proteolytic activity for longer in the host and exacerbate disorders at Aeromonas sobria infection sites. nASP may be an evolutional form to augment ASP virulence.

Culturable gut microbiota diversity in zebrafish

The zebrafish (Danio rerio) is an increasingly used laboratory animal model in basic biology and biomedicine, novel drug development, and toxicology. The wide use has increased the demand for optimized husbandry protocols to ensure animal health care and welfare. The knowledge about the correlation between culturable zebrafish intestinal microbiota and health in relation to environmental factors and management procedures is very limited. A semi-quantitative level of growth of individual types of bacteria was determined and associated with sampling points. A total of 72 TAB line zebrafish from four laboratories (Labs A-D) in the Zebrafish Network Norway were used. Diagnostic was based on traditional bacterial culture methods and biochemical characterization using commercial kits, followed by 16S rDNA gene sequencing from pure subcultures. Also selected Gram-negative isolates were analyzed for antibiotic susceptibility to 8 different antibiotics. A total of 13 morphologically different bacterial species were the most prevalent: Aeromonas hydrophila, Aeromonas sobria, Vibrio parahaemolyticus, Photobacterium damselae, Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas luteola, Comamonas testosteroni, Ochrobactrum anthropi, Staphylococcus cohnii, Staphylococcus epidermidis, Staphylococcus capitis, and Staphylococcus warneri. Only Lab B had significantly higher levels of total bacterial growth (OR=2.03), whereas numbers from Lab C (OR=1.01) and Lab D (OR=1.12) were found to be similar to the baseline Lab A. Sexually immature individuals had a significantly higher level of harvested total bacterial growth than mature fish (OR=0.82), no statistically significant differences were found between male and female fish (OR=1.01), and the posterior intestinal segment demonstrated a higher degree of culturable bacteria than the anterior segment (OR=4.1). Multiple antibiotic (>3) resistance was observed in 17% of the strains. We propose that a rapid conventional diagnostic bacteriological assay on the culturable microbiota profiles can be designed and used as quality measure of the husbandry routines of a zebrafish facility to ensure a bacterial standard safeguarding the zebrafish health and welfare.

The main Aeromonas pathogenic factors

The members of the Aeromonas genus are ubiquitous, water-borne bacteria. They have been isolated from marine waters, rivers, lakes, swamps, sediments, chlorine water, water distribution systems, drinking water and residual waters; different types of food, such as meat, fish, seafood, vegetables, and processed foods. Aeromonas strains are predominantly pathogenic to poikilothermic animals, and the mesophilic strains are emerging as important pathogens in humans, causing a variety of extraintestinal and systemic infections as well as gastrointestinal infections. The most commonly described disease caused by Aeromonas is the gastroenteritis; however, no adequate animal model is available to reproduce this illness caused by Aeromonas. The main pathogenic factors associated with Aeromonas are: surface polysaccharides (capsule, lipopolysaccharide, and glucan), S-layers, iron-binding systems, exotoxins and extracellular enzymes, secretion systems, fimbriae and other nonfilamentous adhesins, motility and flagella.

Soft tissue infections caused by marine bacterial pathogens: epidemiology, diagnosis, and management

Skin and soft tissue infections (SSTIs) are one of the most common infection syndromes and may be caused by a large number of microorganisms. Some principles of aquatic injuries are different than those of land-based trauma. Wounds sustained in marine environment are exposed to a milieu of bacteria rarely encountered in different settings. These include Vibrio spp., Aeromonas spp., Shewanella spp., Erysipelothrix rhusiopathiae, Mycobacterium marinum, Streptococcus iniae, and other microbes. Failure to recognize and treat these uncommon pathogens in a timely manner may result in significant morbidity or death. These infections are frequently contracted as a result of recreational swimming, fishing injuries, or seafood handling. The spectrum of manifestations is wide, varying from cases of mild cellulitis, to severe life-threatening necrotizing fasciitis requiring radical surgery, to sepsis and death. This review will focus on the epidemiology, clinical manifestations, and treatment of SSTIs caused by the most important marine pathogens.

The two-component QseBC signalling system regulates in vitro and in vivo virulence of Aeromonas hydrophila

We recently demonstrated that the N-acyl-homoserine lactone [autoinducer (AI)-1] and LuxS (AI-2)-based quorum-sensing (QS) systems exerted positive and negative regulation, respectively, on the virulence of a diarrhoeal isolate SSU of Aeromonas hydrophila. However, the role of a newly identified, two-component-based QseBC QS system in the regulation of bacterial virulence in general is not well understood, with only a limited number of studies showing its function in bacterial pathogenesis. In this report, we identified and characterized the QseBC QS system in A. hydrophila SSU and found that, as was the case with enterohaemorrhagic Escherichia coli, the open reading frames for the qseB (the response regulator) and qseC (the sensor histidine kinase) genes overlapped by 4 bp at the ATGA motif. Our data provide evidence that deletion of the qseB gene from A. hydrophila resulted in attenuation of bacterial virulence in a septicaemic mouse model of infection and diminished swimming and swarming motility, and the mutant bacteria formed denser biofilms compared with those from the parental strain of A. hydrophila. The decrease in the virulence of the A. hydrophila ΔqseB mutant correlated with reduced production of protease and the cytotoxic enterotoxin, which has associated haemolytic activity. The swimming and swarming motility, haemolytic activity, protease production and biofilm formation were restored in the qseBC-complemented strain to a level similar to that of the wild-type A. hydrophila SSU. Our study is the first, to our knowledge, to report a functional QseBC QS system in A. hydrophila which may be linked to AI-1 and AI-2 QS systems in modulating bacterial virulence, possibly through the cyclic diguanosine monophosphate.

Bacteriocin activity and probiotic activity of Aeromonas media

Three strains of Aeromonas media (161, A164 and A199) were shown to be active in-vitro producers of bacteriocin-like inhibitory substances (BLIS). For example, the producer strain, Aer. media A199, displayed antagonistic activity against all strains tested of Aer. caviae, Aer. hydrophila, Aer. salmonicida, Aer. veronii var. sobria, Listonella anguillarum, Photobacterium damsella, eight species of Vibrio and Yersinia ruckeri. Because of this wide-ranging activity against fish/shellfish pathogens, A199 was chosen for the probiotic work. By contrast, however, the BLIS produced by A199 did not inhibit the growth of Enterococcus seriolicida. The aim of the project was to ascertain whether or not the activity observed in vitro could be repeated in vivo. The ability of BLIS-producing strain A199 to act as a probiotic was assessed on the host animal, Crassostrea gigas, by testing whether or not strain A199 could prevent death of the oyster larvae when challenged with V. tubiashit. Whereas larvae, challenged with the Vibrio, died within 5 days, the presence of both the pathogen and the probiotic strain, together, did not affect the viability of the larvae over the same time period; the viability of larvae challenged with A199 alone was also unaffected when compared with the viability of unchallenged larvae (controls). These findings have important, economic implications for those engaged in the oyster producing industry where heavy losses can be experienced as a result of an infectious outbreak. At this stage, the association between BLIS activity and probiotic activity is circumstantial and, hence, future work will involve the use of non-BLIS-producing strains of Aer. media and BLIS-negative variants of the producer. Moreover, extension of the project will involve the use of other BLIS-producing strains (A161, and A164), hosts (salmon, crayfish, scallops and abalone) and pathogens.