Lateral flagella of Aeromonas species are essential for epithelial cell adherence and biofilm formation

Genomic analysis of clinical Aeromonas isolates reveals genetic diversity but little evidence of genetic determinants for diarrhoeal disease

Aeromonas spp. are associated with a number of infectious syndromes in humans including gastroenteritis and dysentery. Our understanding of the genetic diversity, population structure, virulence determinants and antimicrobial resistance of the genus has been limited by a lack of sequenced genomes linked to metadata. We performed a comprehensive analysis of the whole genome sequences of 447 Aeromonas isolates from children in Karachi, Pakistan, with moderate-to-severe diarrhoea (MSD) and from matched controls without diarrhoea that were collected as part of the Global Enteric Multicenter Study (GEMS). Human-associated Aeromonas isolates exhibited high species diversity and extensive antimicrobial and virulence gene content. Aeromonas caviae, A. dhankensis, A. veronii and A. enteropelogenes were all significantly associated with MSD in at least one cohort group. The maf2 and lafT genes that encode components of polar and lateral flagella, respectively, exhibited a weak association with isolates originating from cases of gastroenteritis.

Vibrio metschnikovii as an emergent pathogen: analyses of phylogeny and O-antigen and identification of possible virulence characteristics

Vibrio metschnikovii is an emergent pathogen that causes human infections which may be fatal. However, the phylogenetic characteristics and pathogenicity determinants of V. metschnikovii are poorly understood. Here, the whole-genome features of 103 V. metschnikovii strains isolated from different sources are described. On phylogenetic analysis V. metschnikovii populations could be divided into two major lineages, defined as lineage 1 (L1) and 2 (L2), of which L1 was more likely to be associated with human activity. Meanwhile, we defined 29 V. metschnikovii O-genotypes (VMOg, named VMOg1-VMOg29) by analysis of the O-antigen biosynthesis gene clusters (O-AGCs). Most VMOgs (VMOg1 to VMOg28) were assembled by the Wzx/Wzy pathway, while only VMOg29 used the ABC transporter pathway. Based on the sequence variation of the wzx and wzt genes, an in silico O-genotyping system for V. metschnikovii was developed. Furthermore, nineteen virulence-associated factors involving 161 genes were identified within the V. metschnikovii genomes, including genes encoding motility, adherence, toxins, and secretion systems. In particular, V. metschnikovii was found to promote a high level of cytotoxicity through the synergistic action of the lateral flagella and T6SS. The lateral flagellar-associated flhA gene played an important role in the adhesion and colonization of V. metschnikovii during the early stages of infection. Overall, this study provides an enhanced understanding of the genomic evolution, O-AGCs diversity, and potential pathogenic features of V. metschnikovii.

Chromosomal gene of hybrid multisensor histidine kinase is involved in motility regulation in the rhizobacterium Azospirillum baldaniorum Sp245 under mechanical and water stress

Azospirillum alphaproteobacteria, which live in the rhizosphere of many crops, are used widely as biofertilizers. Two-component signal transduction systems (TCSs) mediate the bacterial perception of signals and the corresponding adjustment of behavior facilitating the adaptation of bacteria to their habitats. In this study, we obtained the A. baldaniorum Sp245 mutant for the AZOBR_150176 gene, which encodes the TCS of the hybrid histidine kinase/response sensory regulator (HSHK-RR). Inactivation of this gene affected bacterial morphology and motility. In mutant Sp245-HSHKΔRR-Km, the cells were still able to synthesize a functioning polar flagellum (Fla), were shorter than those of strain Sp245, and were impaired in aerotaxis, elaboration of inducible lateral flagella (Laf), and motility in semiliquid media. The mutant showed decreased transcription of the genes encoding the proteins of the secretion apparatus, which ensures the assembly of Laf, Laf flagellin, and the repressor protein of translation of the Laf flagellin's mRNA. The study examined the effects of polyethylene glycol 6000 (PEG 6000), an agent used to simulate osmotic stress and drought conditions. Under osmotic stress, the mutant was no longer able to use collective motility in semiliquid media but formed more biofilm biomass than did strain Sp245. Introduction into mutant cells of the AZOBR_150176 gene as part of an expression vector led to recovery of the lost traits, including those mediating bacterial motility under mechanical stress induced by increased medium density. The results suggest that the HSHK-RR under study modulates the response of A. baldaniorum Sp245 to mechanical and osmotic/water stress.

Complete Genome Sequencing of Three Clade-1 Xanthomonads Reveals Genetic Determinants for a Lateral Flagellin and the Biosynthesis of Coronatine-Like Molecules in Xanthomonas

Evolutionarily, early-branching xanthomonads, also referred to as clade-1 xanthomonads, include major plant pathogens, most of which colonize monocotyledonous plants. Seven species have been validly described, among them the two sugarcane pathogens Xanthomonas albilineans and Xanthomonas sacchari, as well as Xanthomonas translucens, which infects small-grain cereals and diverse grasses but also asparagus and pistachio trees. Single-gene sequencing and genomic approaches have indicated that this clade likely contains more, yet-undescribed species. In this study, we sequenced representative strains of three novel species using long-read sequencing technology. Xanthomonas campestris pv. phormiicola strain CFBP 8444 causes bacterial streak on New Zealand flax, another monocotyledonous plant. Xanthomonas sp. strain CFBP 8443 has been isolated from common bean, and Xanthomonas sp. strain CFBP 8445 originated from banana. Complete assemblies of the chromosomes confirmed their unique phylogenetic position within clade 1 of Xanthomonas. Genome mining revealed novel genetic features, hitherto undescribed in other members of the Xanthomonas genus. In strain CFBP 8444, we identified genes related to the synthesis of coronatine-like compounds, a phytotoxin produced by several pseudomonads, which raises interesting questions about the evolution and pathogenicity of this pathogen. Furthermore, strain CFBP 8444 was found to contain a second, atypical flagellar gene cluster in addition to the canonical flagellar gene cluster. Overall, this research represents an important step toward better understanding the evolutionary history and biology of early-branching xanthomonads.

The role of flagellin F in Vibrio Parahaemolyticus-induced intestinal immunity and functional domain identification

The marine pathogen Vibrio parahaemolyticus has caused huge economic losses to aquaculture. Flagellin is a key bacterial virulence factor that induces an inflammatory response via activation of Toll-like receptor 5 (TLR5) signaling. Herein, to explore the inflammatory activity of V. parahaemolyticus flagellins (flaA, flaB, flaC, flaD, flaE, and flaF), we investigated their ability to induce apoptosis in a fish cell line. All six flagellins induced severe apoptosis. Moreover, treatment with V. parahaemolyticus flagellins increased TLR5 and myeloid differentiation factor 88 (MyD88) expression and the production of TNF-α and IL-8 significantly. This indicated that flagellins might induce a TLR5-meditated immune response via an MyD88-dependent pathway. FlaF exhibited the strongest immunostimulatory effect; therefore, the interaction between TLR5 and flaF was screened using the yeast two-hybrid system. A significant interaction between the two proteins was observed, indicating that flaF binds directly to TLR5. Finally, the amino acids that participate in the TLR5-flaF interaction were identified using molecular simulation, which indicated three binding sites. These results deepen our understanding of the immunogenic properties of flagellins from V. parahaemolyticus, which could be used for vaccine development in the future.

Flagellar motility mediates biofilm formation in Aeromonas dhakensis

Aeromonas dhakensis possesses dual flagellar systems for motility under different environments. Flagella-mediated motility is necessary for biofilm formation through an initial attachment of bacteria to the surface, but this has not been elucidated in A. dhakensis. This study investigates the role of polar (flaH, maf1) and lateral (lafB, lafK and lafS) flagellar genes in the biofilm formation of a clinical A. dhakensis strain WT187 isolated from burn wound infection. Five deletion mutants and corresponding complemented strains were constructed using pDM4 and pBAD33 vectors, respectively, and analyzed for motility and biofilm formation using crystal violet staining and real-time impedance-based assays. All mutants were significantly reduced in swimming (p < 0.0001), swarming (p < 0.0001) and biofilm formation using crystal violet assay (p < 0.05). Real-time impedance-based analysis revealed WT187 biofilm was formed between 6 to 21 h, consisting of early (6-10 h), middle (11-18 h), and late (19-21 h) stages. The highest cell index of 0.0746 was recorded at 22-23 h and biofilms began to disperse starting from 24 h. Mutants Δmaf1, ΔlafB, ΔlafK and ΔlafS exhibited reduced cell index values at 6-48 h when compared to WT187 which indicates less biofilm formation. Two complemented strains cmaf1 and clafB exhibited full restoration to wild-type level in swimming, swarming, and biofilm formation using crystal violet assay, hence suggesting that both maf1 and lafB genes are involved in biofilm formation through flagella-mediated motility and surface attachment. Our study shows the role of flagella in A. dhakensis biofilm formation warrants further investigations.

Genetic characterization and virulence determinants of multidrug-resistant NDM-1-producing Aeromonas caviae

The emergence of carbapenemase significantly threatens public health. It is prevalent worldwide but rare in Aeromonas caviae. Unlike most bacterial species, A. caviae has two distinct flagella systems, which are closely related to biofilm formation. The ability to form biofilms on host tissues or inert surfaces constitutes an important cause of many persistent infections, which causes difficulties in clinical treatment. Here, we report on a multidrug-resistant (MDR) A. caviae carrying bla _NDM-1 with a novel sequence type 1,416. The strong ability of biofilm formation of FAHZZU2447 was verified by a crystal violet assay. The resistome profile and location of the bla _NDM-1 gene were determined by antimicrobial susceptibility testing, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE), and Southern blot analysis. Moreover, the strain underwent whole-genome sequencing to identify its genomic characteristics. In addition, the bla _NDM-1 gene was located on a ∼243 kb plasmid with genetic context IS1R-bla _NDM-1-ble-trpF-dsbD-hp-sul1-qacE. Phylogenetic analysis indicated the transmission of A. caviae in China, Japan, and Thailand. Our study aimed to elucidate the genomic features of bla _NDM-1-producing A. caviae, thereby clarifying the distribution of A. caviae worldwide and emphasizing the harmfulness of biofilm formation to the clinic. Further comprehensive surveillance of this species is needed to control further dissemination.

Potential Pathogenicity of Aeromonas spp. Recovered in River Water, Soil, and Vegetation from a Natural Recreational Area

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. Currently, untreated river water is used for irrigation and recreational purposes. In this study, the Aeromonas spp. present in a river recreational environment was investigated by quantifying its presence in water, soil, and vegetation using three techniques: qPCR, plate counting in selective ADA medium, and Most Probable Number, in parallel. The presence of clones in the three types of samples was elucidated through genotyping with the ERIC-PCR technique, whereas the identification of the isolated Aeromonas was carried out by sequencing the rpoD gene. Finally, the pathogenic potential of some of the strains was explored by studying the presence and expression of virulence genes characteristic of the genus, their antimicrobial susceptibility profile, as well as the quantification of their cell damage and intracellular survival in an in vitro macrophages infection model. The results showed the presence of Aeromonas in all samples with the three quantification methods, with Aeromonas popoffii being the most prevalent species. The presence of strains with the same genotype (ERIC-PCR) was also confirmed in different samples. Some of the strains showed a high level of cell damage and intracellular bacterial survival, as well as the presence of various virulence factors. Furthermore, these strains showed resistance to some of the antibiotics tested and used therapeutically in both humans and animals. These results indicate that the presence of Aeromonas in this environment may represent a biosanitary risk that could be a public health problem.

Utilizing Immunoinformatics to Target Brain Tumors; An Aid to Current Neurosurgical Practice

Context: Despite major advancements in the field, the current neurosurgical practice requires an interdisciplinary approach. It is known that surgical practice and other cancer-eliminating treatments can be combined for optimal results. However, recent attempts have failed to address many debilitating conditions, indicating an emergent need for novel interdisciplinary therapeutic approaches. Evidence Acquisition: We searched PubMed and Google Scholar for the keywords “immunoinformatics,” “in silico,” “neurology,” and “neurosurgery.” Without time restriction. Results: The immune system is versatile because it is involved in physiological brain function and affects the course of central nervous system (CNS) disease and infection. A novel approach combines neurosurgery and immunoinformatics for optimal results. For instance, brain tumors, such as glioblastoma multiforme (GBM), are still associated with a severely reduced survival of patients, and resection of tumors may provide little help. In silico approaches could help to identify molecular pathways and design immunotherapies for such conditions at a significantly increased speed compared to traditional vaccinology approaches. Conclusions: The neurosurgical practice could be affected by different infectious organisms. These organisms can be targeted by in silico vaccinology techniques. Here, we provide a brief overview of bioinformatics/immunoinformatics and discuss the possible role of immunoinformatics in neurosurgery. In light of the current Coronavirus disease-2019 (COVID-19) epidemic, projections for future studies are also included.

Colonization of biofilm in wastewater treatment: A review

The attachment and colonization process of microorganisms on a carrier is an interdisciplinary research field. Through a series of physical, chemical, and biological actions, the microorganisms can eventually reproduce on the carrier. This article introduces biofilm start-up and its applications, and explores the current issues to look forward to future development directions. Firstly, the mechanism of microbial film formation is analyzed from the microbial community colonization and reproduction process. Secondly, when analyzing the factors influencing microbial membrane formation, the effect of microbial properties (e.g., genes, proteins, lipids) and external conditions (i.e., carrier, operating environment, and regulation mechanism among microbial communities) were discussed in depth. Aimed at exploring the mechanisms and influencing factors of biofilm start-up, this article proposes the application measures to strengthen this process. Finally, the problems encountered and the future development direction of the technology are analyzed and prospected.

Surface Glucan Structures in Aeromonas spp

Aeromonas spp. are generally found in aquatic environments, although they have also been isolated from both fresh and processed food. These Gram-negative, rod-shaped bacteria are mostly infective to poikilothermic animals, although they are also considered opportunistic pathogens of both aquatic and terrestrial homeotherms, and some species have been associated with gastrointestinal and extraintestinal septicemic infections in humans. Among the different pathogenic factors associated with virulence, several cell-surface glucans have been shown to contribute to colonization and survival of Aeromonas pathogenic strains, in different hosts. Lipopolysaccharide (LPS), capsule and α-glucan structures, for instance, have been shown to play important roles in bacterial–host interactions related to pathogenesis, such as adherence, biofilm formation, or immune evasion. In addition, glycosylation of both polar and lateral flagella has been shown to be mandatory for flagella production and motility in different Aeromonas strains, and has also been associated with increased bacterial adhesion, biofilm formation, and induction of the host proinflammatory response. The main aspects of these structures are covered in this review.

Comparative and Evolutionary Genomics of Isolates Provide Insight into the Pathoadaptation of Aeromonas

Aeromonads are ubiquitous aquatic bacteria that cause opportunistic infections in humans, but their pathogenesis remains poorly understood. A pathogenomic approach was undertaken to provide insights into the emergence and evolution of pathogenic traits in aeromonads. The genomes of 64 Aeromonas strains representative of the whole genus were analyzed to study the distribution, phylogeny, and synteny of the flanking sequences of 13 virulence-associated genes. The reconstructed evolutionary histories varied markedly depending on the gene analyzed and ranged from vertical evolution, which followed the core genome evolution (alt and colAh), to complex evolution, involving gene loss by insertion sequence-driven gene disruption, horizontal gene transfer, and paraphyly with some virulence genes associated with a phylogroup (aer, ser, and type 3 secretion system components) or no phylogroup (type 3 secretion system effectors, Ast, ExoA, and RtxA toxins). The general pathogenomic overview of aeromonads showed great complexity with diverse evolution modes and gene organization and uneven distribution of virulence genes in the genus; the results provided insights into aeromonad pathoadaptation or the ability of members of this group to emerge as pathogens. Finally, these findings suggest that aeromonad virulence-associated genes should be examined at the population level and that studies performed on type or model strains at the species level cannot be generalized to the whole species.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Identification, antibiotic resistance, and virulence profiling of Aeromonas and Pseudomonas species from wastewater and surface water

Aquatic environments are hotspots for the spread of antibiotic-resistant bacteria and genes due to pollution caused mainly by anthropogenic activities. The aim of this study was to evaluate the impact of wastewater effluents, informal settlements, hospital, and veterinary clinic discharges on the occurrence, antibiotic resistance profile and virulence signatures of Aeromonas spp. and Pseudomonas spp. isolated from surface water and wastewater. High counts of Aeromonas spp. (2.5 (± 0.8) - 3.3 (± 0.4) log₁₀ CFU mL^-1) and Pseudomonas spp. (0.6 (± 1.0) - 1.8 (± 1.0) log₁₀ CFU mL^-1) were obtained. Polymerase chain reaction (PCR) and MALDI-TOF characterization identified four species of Aeromonas and five of Pseudomonas. The isolates displayed resistance to 3 or more antibiotics (71% of Aeromonas and 94% of Pseudomonas). Aeromonas spp. showed significant association with the antibiotic meropenem (χ² = 3.993, P < 0.05). The virulence gene aer in Aeromonas was found to be positively associated with the antibiotic resistance gene blaOXA (χ² = 6.657, P < 0.05) and the antibiotic ceftazidime (χ² = 7.537, P < 0.05). Aeromonas recovered from both wastewater and surface water displayed high resistance to ampicillin and had higher multiple antibiotic resistance (MAR) indices close to the hospital. Pseudomonas isolates on the other hand exhibited low resistance to carbapenems but very high resistance to the third-generation cephalosporins and cefixime. The results showed that some of the Pseudomonas spp. and Aeromonas spp. isolates were extended-spectrum β-lactamase producing bacteria. In conclusion, the strong association between virulence genes and antibiotic resistance in the isolates shows the potential health risk to communities through direct and indirect exposure to the water.

Polar Flagella Glycosylation in Aeromonas: Genomic Characterization and Involvement of a Specific Glycosyltransferase (Fgi-1) in Heterogeneous Flagella Glycosylation

Polar flagella from mesophilic Aeromonas strains have previously been shown to be modified with a range of glycans. Mass spectrometry studies of purified polar flagellins suggested the glycan typically includes a putative pseudaminic acid like derivative; while some strains are modified with this single monosaccharide, others modified with a heterologous glycan. In the current study, we demonstrate that genes involved in polar flagella glycosylation are clustered in highly polymorphic genomic islands flanked by pseudaminic acid biosynthetic genes (pse). Bioinformatic analysis of mesophilic Aeromonas genomes identified three types of polar flagella glycosylation islands (FGIs), denoted Group I, II and III. FGI Groups I and III are small genomic islands present in Aeromonas strains with flagellins modified with a single monosaccharide pseudaminic acid derivative. Group II were large genomic islands, present in strains found to modify polar flagellins with heterogeneous glycan moieties. Group II, in addition to pse genes, contained numerous glycosyltransferases and other biosynthetic enzymes. All Group II strains shared a common glycosyltransferase downstream of luxC that we named flagella glycosylation island 1, fgi-1, in A. piscicola AH-3. We demonstrate that Fgi-1 transfers the first sugar of the heterogeneous glycan to the pseudaminic acid derivative linked to polar flagellins and could be used as marker for polysaccharidic glycosylation of Aeromonas polar flagella.

Differential production and secretion of potentially toxigenic extracellular proteins from hypervirulent Aeromonas hydrophila under biofilm and planktonic culture

Background

Hypervirulent Aeromonas hydrophila (vAh) is an emerging pathogen in freshwater aquaculture that results in the loss of over 3 million pounds of marketable channel catfish, Ictalurus punctatus, and channel catfish hybrids (I. punctatus, ♀ x blue catfish, I. furcatus, ♂) each year from freshwater catfish production systems in Alabama, U.S.A. vAh isolates are clonal in nature and are genetically unique from, and significantly more virulent than, traditional A. hydrophila isolates from fish. Even with the increased virulence, natural infections cannot be reproduced in aquaria challenges making it difficult to determine modes of infection and the pathophysiology behind the devastating mortalities that are commonly observed. Despite the intimate connection between environmental adaptation and plastic response, the role of environmental adaption on vAh pathogenicity and virulence has not been previously explored. In this study, secreted proteins of vAh cultured as free-living planktonic cells and within a biofilm were compared to elucidate the role of biofilm growth on virulence.

Results

Functional proteolytic assays found significantly increased degradative activity in biofilm secretomes; in contrast, planktonic secretomes had significantly increased hemolytic activity, suggesting higher toxigenic potential. Intramuscular injection challenges in a channel catfish model showed that in vitro degradative activity translated into in vivo tissue destruction. Identification of secreted proteins by HPLC-MS/MS revealed the presence of many putative virulence proteins under both growth conditions. Biofilm grown vAh produced higher levels of proteolytic enzymes and adhesins, whereas planktonically grown cells secreted higher levels of toxins, porins, and fimbrial proteins.

Conclusions

This study is the first comparison of the secreted proteomes of vAh when grown in two distinct ecological niches. These data on the adaptive physiological response of vAh based on growth condition increase our understanding of how environmental niche partitioning could affect vAh pathogenicity and virulence. Increased secretion of colonization factors and degradative enzymes during biofilm growth and residency may increase bacterial attachment and host invasiveness, while increased secretion of hemolysins, porins, and other potential toxins under planktonic growth (or after host invasion) could result in increased host mortality. The results of this research underscore the need to use culture methods that more closely mimic natural ecological habitat growth to improve our understanding of vAh pathogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-020-02065-2.

Antibiotics modulate biofilm formation in fish pathogenic isolates of atypical Aeromonas salmonicida

Atypical Aeromonas salmonicida causes furunculosis infections of non-salmonid fish, which requires antibiotic therapy. However, antibiotics may induce biofilm in some bacteria, which protects them against hostile conditions while allowing them to persist on surfaces, thus forming a reservoir for infection. The aim of this study was to determine whether atypical isolates of A. salmonicida increased biofilm in the presence of two antibiotics, florfenicol and oxytetracycline. A microtitre plate assay was used to quantify biofilm in the presence and absence of each antibiotic. Fifteen of 28 isolates formed biofilms under control conditions, while 23 of 28 isolates increased biofilm formation in the presence of at least one concentration of at least one antibiotic. For oxytetracycline, the most effective concentration causing biofilm to increase was one-quarter of that preventing visible bacterial growth, whereas for florfenicol it was one-half of this value. This is the first study to demonstrate that a bacterial pathogen of fish increases biofilm in response to antibiotics. Biofilm formation may increase the risk of re-infection in culture systems and this lifestyle favours the transmission of genetic material, which has implications for the dissemination of antibiotic-resistance genes and demonstrates the need for enhanced disease prevention measures against atypical A. salmonicida.

Methylation of Salmonella Typhimurium flagella promotes bacterial adhesion and host cell invasion

The long external filament of bacterial flagella is composed of several thousand copies of a single protein, flagellin. Here, we explore the role played by lysine methylation of flagellin in Salmonella, which requires the methylase FliB. We show that both flagellins of Salmonella enterica serovar Typhimurium, FliC and FljB, are methylated at surface-exposed lysine residues by FliB. A Salmonella Typhimurium mutant deficient in flagellin methylation is outcompeted for gut colonization in a gastroenteritis mouse model, and methylation of flagellin promotes bacterial invasion of epithelial cells in vitro. Lysine methylation increases the surface hydrophobicity of flagellin, and enhances flagella-dependent adhesion of Salmonella to phosphatidylcholine vesicles and epithelial cells. Therefore, posttranslational methylation of flagellin facilitates adhesion of Salmonella Typhimurium to hydrophobic host cell surfaces, and contributes to efficient gut colonization and host infection.

Flagellin proteins of Salmonella flagella are methylated. Here, the authors show that flagellin methylation facilitates adhesion of Salmonella to hydrophobic host-cell surfaces, and contributes to efficient gut colonization and host infection.

Pinpointing the role of Aeromonas salmonicida in the development of skin ulcerations in common dab (Limanda limanda)

Aeromonas salmonicida was isolated from ulcerations in common dab (Limanda limanda). An experiment was performed to pinpoint its role in ulceration development, considering the importance of the skin barrier and the pigmented and non-pigmented sides. The skin of dab was treated in three zones, one where scales and epidermis were removed, one where mucus was discarded and one non-treated zone. Fish were tagged to allow individual identification and challenged with A. salmonicida. Mortality and severity of the developing lesions were recorded for 21 days post-inoculation. Starting 12 days post-inoculation, mortality occurred gradually in challenged fish; however, no direct cause could be established. Both control fish and challenged fish developed ulcerations containing A. salmonicida. Sequencing of vapA gene revealed that isolates retrieved from both groups were distinct, suggesting the presence of A. salmonicida prior to the trial. Most ulcerations developed in zones where skin was removed, suggesting that abrasion might be a predisposing factor in ulceration development. Ulcerations were also observed at the insertion site of the tag, where exposed muscle tissue might have favoured the development of ulcerations. In conclusion, A. salmonicida seems to be involved in the development of skin ulcerations in dab, although the exact pathogenesis needs to be elucidated.

Lypd8 inhibits attachment of pathogenic bacteria to colonic epithelia

Mucosal barriers segregate commensal microbes from the intestinal epithelia to maintain gut homeostasis. Ly6/Plaur domain-containing 8 (Lypd8), a highly glycosylated glycosylphosphatidylinositol-anchored protein selectively expressed on colonic enterocytes, promotes this segregation by inhibiting bacterial invasion of the inner mucus layer and colonic epithelia. However, it remains unclear whether Lypd8 prevents infection with enteric bacterial pathogens. Here, we demonstrate that Lypd8 strongly contributes to early-phase defense against Citrobacter rodentium, which causes colitis by inducing attachment and effacement (A/E) lesions on colonic epithelia. Lypd8 inhibits C. rodentium attachment to intestinal epithelial cells by binding to intimin, thereby suppressing the interaction between intimin and translocated intimin receptor. Lypd8 deficiency leads to rapid C. rodentium colonization in the colon, resulting in severe colitis with Th17-cell and neutrophil expansion in the lamina propria. This study identifies a novel function for Lypd8 against A/E bacteria and highlights the role of enterocytes as crucial players in innate immunity for protection against enteric bacterial pathogens.

Draft Whole-Genome Sequences of 10 Aeromonas Strains from Clinical and Environmental Sources

Aeromonas bacteria are able to cause disease in a wide range of animals from humans to fish. In this article, we report the draft whole-genome sequences of 10 Aeromonas strains from clinical and environmental sources. These genome sequences will provide a repository of information for further investigations into the pathogenicity of this enigmatic pathogen.

Aeromonas bacteria are able to cause disease in a wide range of animals from humans to fish. In this article, we report the draft whole-genome sequences of 10 Aeromonas strains from clinical and environmental sources. These genome sequences will provide a repository of information for further investigations into the pathogenicity of this enigmatic pathogen.

Diagnostic methods for identifying different Aeromonas species and examining their pathogenicity factors, their correlation to cytotoxicity and adherence to fish mucus

Aeromonas spp. are ubiquitous in the aquatic environment, acting as facultative or obligate pathogens for fish. Identifying Aeromonas spp. is important for pathogenesis and prognosis in diagnostic cases but can be difficult because of their close relationship. Forty-four already characterized isolates of Aeromonas spp. were analysed by 16S rRNA gene sequencing, by gyrase B sequencing, by analysing their fatty acid profiles, by biochemical reactions and by MALDI-TOF MS. To determine their pathogenicity, cytotoxicity, adhesion to mucus and the expression of 12 virulence factors were tested. The susceptibility of the isolates towards 13 different antibiotics was determined. MALDI-TOF MS was found to be an acceptable identification method for Aeromonas spp. Although the method does not detect all species correctly, it is time-effective and entails relatively low costs and no other methods achieved better results. A high prevalence of virulence-related gene fragments was detected in almost all examined Aeromonas spp., especially in A. hydrophila and A. salmonicida, and most isolates exhibited a cytotoxic effect. Single isolates of A. hydrophila and A. salmonicida showed multiple resistance to antibiotics. These results might indicate the potentially pathogenic capacity of Aeromonas spp., suggesting a risk for aquatic animals and even humans, given their ubiquitous nature.

Polar flagellum of the alphaproteobacterium Azospirillum brasilense Sp245 plays a role in biofilm biomass accumulation and in biofilm maintenance under stationary and dynamic conditions

Bacteria Azospirillum brasilense may swim and swarm owing to the rotation of a constitutive polar flagellum (Fla) and inducible lateral flagella (Laf). They also construct sessile biofilms on various interfaces. As compared to the wild-type strain Sp245, the previously characterized Fla^- Laf^- flhB1 mutant Sp245.1063 accumulated less biomass in mature biofilms, which also were susceptible to the forces of hydrodynamic shear. In this study, we compared biofilms formed by strain Sp245 and its previously constructed derivatives on the interfaces between a minimal (malate-salt medium, or MSM) or rich (LB) liquid growth medium and a hydrophilic (glass) or hydrophobic (polystyrene) solid surface under static or dynamic conditions. In all experimental settings, the alterations in Sp245.1063's mature biofilm traits were partially (in MSM) or completely (in LB) rescued in the complemented mutant Sp245.1063 (pRK415-150177), which received the pRK415-borne coding sequence for the putative FlhB1 protein of the flagellar type III secretion system. Although Laf were not found in the biofilms of azospirilla, Fla was present on the biofilm cells of the complemented mutant Sp245.1063 (pRK415-150177) and other studied strains, which had normal flagellation on liquid and solid nutritional media. Accordingly, mature biofilms of these strains contained more biomass and were significantly more resistant to shaking at 140 rpm, as compared to the biofilms of the flagella-free mutant bacteria. These data proved that the polar flagellum of A. brasilense Sp245 plays a significant positive role in biofilm biomass increase and in biofilm stabilization.

Detecção de Aeromonas spp. e do gene de virulência aerolisina em tilápias do Nilo (Oreochromis niloticus) com a técnica de mPCR

RESUMO: As infecções causadas por bactérias do gênero Aeromonas estão entre as doenças mais comuns em peixes cultivados em todo o mundo, com ocorrência de aeromoniose em todos os países que possuem cultivo de tilápia do Nilo (Oreochromis niloticus). O presente trabalho descreve o desenvolvimento de uma nova multiplex PCR (mPCR) para diagnóstico de Aeromonas spp. e identificação do gene aerolisina (aerA). Para padronização da mPCR foram utilizadas cepas de referência de várias espécies do gênero Aeromonas e de outros gêneros. Também foram usadas cepas de campo de A. hydrophila oriundas de cultivos de peixes pacamãs (Lophiosilurus alexandri) e Aeromonas spp. de tilápias do Nilo. Os primers foram desenhados com base na região 16S rRNA e aerA. Para verificar a melhor temperatura de anelamento foram utilizados gradientes entre 59°C a 61°C com 40ng de DNA molde. Os produtos da amplificação da região 16S rRNA e do gene aerA apresentaram 786 e 550pb, respectivamente. A mPCR apresentou melhor temperatura de anelamento a 57,6°C com limite de detecção das concentrações de DNA em ambos genes (16S rRNA and aerA) de 10-10g/μL. A mPCR padronizada é rápida, sensível e específica no diagnóstico de Aeromonas spp. e identificação do gene aerolisina. Esta metodologia apresenta vantagens quando comparada aos métodos de diagnóstico convencionais, podendo ser utilizada em cultivos comerciais de tilápias do Nilo ou outros peixes. A identificação do gene aerolisina é uma importante ferramenta na determinação do potencial patogênico dos isolados de Aeromonas spp. estudados.

A putative lateral flagella of the cystic fibrosis pathogen Burkholderia dolosa regulates swimming motility and host cytokine production

Burkholderia dolosa caused an outbreak in the cystic fibrosis clinic at Boston Children's Hospital and was associated with high mortality in these patients. This species is part of a larger complex of opportunistic pathogens known as the Burkholderia cepacia complex (Bcc). Compared to other species in the Bcc, B. dolosa is highly transmissible; thus understanding its virulence mechanisms is important for preventing future outbreaks. The genome of one of the outbreak strains, AU0158, revealed a homolog of the lafA gene encoding a putative lateral flagellin, which, in other non-Bcc species, is used for movement on solid surfaces, attachment to host cells, or movement inside host cells. Here, we analyzed the conservation of the lafA gene and protein sequences, which are distinct from those of the polar flagella, and found lafA homologs to be present in numerous β-proteobacteria but notably absent from most other Bcc species. A lafA deletion mutant in B. dolosa showed a greater swimming motility than wild-type due to an increase in the number of polar flagella, but did not appear to contribute to biofilm formation, host cell invasion, or murine lung colonization or persistence over time. However, the lafA gene was important for cytokine production in human peripheral blood mononuclear cells, suggesting it may have a role in recognition by the human immune response.

The Social Life of Aeromonas through Biofilm and Quorum Sensing Systems

Bacteria of the genus Aeromonas display multicellular behaviors herein referred to as “social life”. Since the 1990s, interest has grown in cell-to-cell communication through quorum sensing signals and biofilm formation. As they are interconnected, these two self-organizing systems deserve to be considered together for a fresh perspective on the natural history and lifestyles of aeromonads. In this review, we focus on the multicellular behaviors of Aeromonas, i.e., its social life. First, we review and discuss the available knowledge at the molecular and cellular levels for biofilm and quorum sensing. We then discuss the complex, subtle, and nested interconnections between the two systems. Finally, we focus on the aeromonad multicellular coordinated behaviors involved in heterotrophy and virulence that represent technological opportunities and applied research challenges.

Cross-Talk between the Aeromonas hydrophila Type III Secretion System and Lateral Flagella System

Aeromonas hydrophila is responsible for aeromonad septicaemia in fish, and gastroenteritis and wound infections in humans. The type III secretion system (T3SS) is utilized by aeromonads to inject protein effectors directly into host cells. One of the major genetic regulators of the T3SS in several bacterial species is the AraC-like protein ExsA. Previous studies have suggested a link between T3SS regulation and lateral flagella expression. The aim of this study was to determine the genetic regulation of the T3SS and its potential interaction with the lateral flagella system in A. hydrophila. To investigate the genes encoding the T3SS regulatory components exsA, exsD, exsC, and exsE were mutated and the activities of the T3SS promoters were measured in wild type and mutant backgrounds demonstrating a regulatory network. The Exs proteins were shown to interact with each other by BACTH assay and Far-Western Blot. The findings suggested a regulatory cascade in which ExsE was bound to the chaperone protein ExsC. When ExsC was free it sequestered the anti-activator ExsD thus stopping the inhibition of the T3SS master regulator ExsA allowing T3SS expression. The T3SS regulatory components were also shown to affect the expression of the lateral flagella system. The activities of the lateral flagella promoters were shown to be repressed by the absence of ExsD and ExsE, suggesting that the T3SS master regulator ExsA was a negative regulator of the lateral flagella system.

The FlgT Protein Is Involved in Aeromonas hydrophila Polar Flagella Stability and Not Affects Anchorage of Lateral Flagella

Aeromonas hydrophila sodium-driven polar flagellum has a complex stator-motor. Consist of two sets of redundant and non-exchangeable proteins (PomA/PomB and PomA₂/PomB₂), which are homologs to other sodium-conducting polar flagellum stator motors; and also two essential proteins (MotX and MotY), that they interact with one of those two redundant pairs of proteins and form the T-ring. In this work, we described an essential protein for polar flagellum stability and rotation which is orthologs to Vibrio spp. FlgT and it is encoded outside of the A. hydrophila polar flagellum regions. The flgT was present in all mesophilic Aeromonas strains tested and also in the non-motile Aeromonas salmonicida. The A. hydrophila ΔflgT mutant is able to assemble the polar flagellum but is more unstable and released into the culture supernatant from the cell upon completion assembly. Presence of FlgT in purified polar hook-basal bodies (HBB) of wild-type strain was confirmed by Western blotting and electron microscopy observations showed an outer ring of the T-ring (H-ring) which is not present in the ΔflgT mutant. Anchoring and motility of proton-driven lateral flagella was not affected in the ΔflgT mutant and specific antibodies did not detect FlgT in purified lateral HBB of wild type strain.

Biofilm Formation by Cryptococcus neoformans

The fungus Cryptococcus neoformans possesses a polysaccharide capsule and can form biofilms on medical devices. The increasing use of ventriculoperitoneal shunts to manage intracranial hypertension associated with cryptococcal meningoencephalitis highlights the importance of investigating the biofilm-forming properties of this organism. Like other microbe-forming biofilms, C. neoformans biofilms are resistant to antimicrobial agents and host defense mechanisms, causing significant morbidity and mortality. This chapter discusses the recent advances in the understanding of cryptococcal biofilms, including the role of its polysaccharide capsule in adherence, gene expression, and quorum sensing in biofilm formation. We describe novel strategies for the prevention or eradication of cryptococcal colonization of medical prosthetic devices. Finally, we provide fresh thoughts on the diverse but interesting directions of research in this field that may result in new insights into C. neoformans biology.

Characterization of Virulence Properties of Aeromonas veronii Isolated from Diseased Gibel Carp (Carassius gibelio)

Aeromonas veronii is a kind of opportunistic pathogen to fish and humans, significantly impending aquaculture production. Recently, we isolated two A. veronii strains, named GYC1 and GYC2, from diseased Gibel carp (Carassiusgibelio) in China. Based on gyrB (DNA gyrase B subunit) genes of GYC1 and GYC2, the constructed phylogenetic tree showed that the two strains were clustered with A. veronii. Sixteen virulence genes related to the pathogenicity of Aeromonas spp. were subjected to PCR assay. The genes of ompAI, ompAII, lafA, act, aer, fla, gcaT and acg were detected in the two strains, while genes of hly, ahp, lip, ast and alt were not detected. Additionally, genes eprCAI, ela and exu were only detected in the strain GYC1. Furthermore, the results of extracellular enzyme analysis revealed that the two isolates can produce hemolysin, caseinase, esterase, amylase and lecithinase, which were closely related to the pathogenicity of the two strains. However, the results showed that there was no gelatinase activity in either strain. According to the antibiotic resistant assay, the two strains were sensitive to cephalosporins and aminoglycosides, while they were resistant to penicillins and quinolones. Through this study, the virulence characteristics, including virulence genes and extracellular enzymes, the pathogenicity of A. veronii was clarified, enhancing the understanding about this pathogenic bacterium and providing the theoretical basis in disease control.

Detection of antibiotic resistance, virulence gene determinants and biofilm formation in Aeromonas species isolated from cattle

This study aimed to assess the antibiogram of Aeromonas strains recovered from cattle faeces and the potential pathogenic status of the isolates. The antibiogram of the Aeromonas isolates demonstrated total resistance to clindamycin oxacillin, trimethoprim, novobiocin and ticarcillin. However, Aeromonas strains were sensitive to cefotaxime, oxytetracycline and tobramycin. The Aeromonas strains from Lovedale and Fort Cox farms were found to possess some virulence genes. The percentage distribution was aer 71.4%, ast 35.7%, fla 60.7%, lip 35.7% and hlyA 25% for Lovedale farm and aer 63.1%, alt 10.5%, ast 55.2%, fla 78.9%, lip 21% and hlyA 35.9% for Fort Cox farm. Class 1 integron was present in 27% of Aeromonas isolates; the bla TEM gene was present in 34.8%, while the blaP1 class A β-lactamase gene was detected in 12.1% of the isolates. Approximately 86% of the isolates formed a biofilm on microtitre plates. The presence of multiple antibiotic resistance and virulence genes in Aeromonas isolates from cattle faeces reveals the pathogenic and infectious importance of these isolates and is of great significance to public health. The possession of a biofilm-forming capability by such isolates may lead to difficulty during the management of infection related to Aeromonas species.

Biofilm formation on the surface of polylactide during its biodegradation in different environments

The research was aimed at determining the abundance and viability of biofilm formed on the surface of polylactide (PLA) during its biodegradation in different environments. It was also aimed at isolating biofilm forming bacteria, determining their hydrolytic activity and taxonomic status. The first step was to evaluate PLA biodegradability in lake water, compost and soil, using OxiTop Control. The next step was to assess the ability of isolated bacteria to form biofilm in the investigated environments and to evaluate the biofilm structure. The results indicate that PLA is sensitive to biodegradation in any environment, particularly in compost. During this process biofilm of high viability was observed on the surface of PLA. Based on the 16S rRNA gene sequence, the biofilm-forming bacteria were classified as the following species: Acidovorax sp. LW9, Chryseobacterium sp. LW2, Aeromonas veronii LW8, Arthrobacter aurescens LG2, Arthrobacter sp. LG12, A. aurescens LG9, Elizabethkingia meningoseptica LK3, A. aurescens LK9, A. aurescens and LK7. The results show that different bacterial species formed biofilm of different abundance and hydrolytic activitiy levels.

The polar and lateral flagella from Plesiomonas shigelloides are glycosylated with legionaminic acid

Plesiomonas shigelloides is the unique member of the Enterobacteriaceae family able to produce polar flagella when grow in liquid medium and lateral flagella when grown in solid or semisolid media. In this study on P. shigelloides 302-73 strain, we found two different gene clusters, one exclusively for the lateral flagella biosynthesis and the other one containing the biosynthetic polar flagella genes with additional putative glycosylation genes. P. shigelloides is the first Enterobacteriaceae were a complete lateral flagella cluster leading to a lateral flagella production is described. We also show that both flagella in P. shigelloides 302-73 strain are glycosylated by a derivative of legionaminic acid (Leg), which explains the presence of Leg pathway genes between the two polar flagella regions in their biosynthetic gene cluster. It is the first bacterium reported with O-glycosylated Leg in both polar and lateral flagella. The flagella O-glycosylation is essential for bacterial flagella formation, either polar or lateral, because gene mutants on the biosynthesis of Leg are non-flagellated. Furthermore, the presence of the lateral flagella cluster and Leg O-flagella glycosylation genes are widely spread features among the P. shigelloides strains tested.

Flagellar motility contributes to the invasion and survival of Aeromonas hydrophila in Anguilla japonica macrophages

The interaction between pathogenic bacteria and the host phagocytes is complicated. It is generally believed that only obligate intracellular pathogens can invade and survive in host phagocytes. In this study, we revealed that the pathogenic Aeromonas hydrophila B11 can also invade and survive in the macrophages of its host Anguilla japonica in vitro. To further investigate the mechanisms of A. hydrophila invasion and survival in host macrophages, a mini-Tn10 transposon mutagenesis system was used to generate an insertion mutant library by cell conjugation between the donor Escherichia coli Sm10 (pLOFKm) and the recipient A. hydrophila B11. Out of 465 individual colonies, 13 mutants impaired in survival within macrophages were selected, and the mutant BM116 was the most seriously impaired strain. Molecular analysis showed that an ORF of approximately 1335 bp (GenBank accession numbers JQ974982) of the mutant BM116 was inserted by mini-Tn10. This ORF putatively encodes a deduced 445 amino acids protein that displays the highest identity (99.6%) with the flagellar hook protein FlgE of A. hydrophila subsp. hydrophila ATCC 7966. The biological characteristics of the wild-type B11, the mutant B116 and the complemented strain were investigated. The results reveal that the flagella of the mutant BM116 was absent and that these mutant bacteria exhibited defective motility, adhesion, and invasion and survival in host macrophages when compared with the wild type and the complemented strain. These findings indicate that flgE is required for flagellum biogenesis in A. hydrophila and that flagellar motility is required for A. hydrophila invasion and survival in the macrophages of its host. Our findings provide an important new understanding of the nonintracellular pathogenic bacteria invasion and survival in host phagocytes and the interactions between the pathogens and their host.

Gram-negative flagella glycosylation

Protein glycosylation had been considered as an eccentricity of a few bacteria. However, through advances in analytical methods and genome sequencing, it is now established that bacteria possess both N-linked and O-linked glycosylation pathways. Both glycosylation pathways can modify multiple proteins, flagellins from Archaea and Eubacteria being one of these. Flagella O-glycosylation has been demonstrated in many polar flagellins from Gram-negative bacteria and in only the Gram-positive genera Clostridium and Listeria. Furthermore, O-glycosylation has also been demonstrated in a limited number of lateral flagellins. In this work, we revised the current advances in flagellar glycosylation from Gram-negative bacteria, focusing on the structural diversity of glycans, the O-linked pathway and the biological function of flagella glycosylation.

Aeromonas flagella and colonisation mechanisms

Aeromonas species are inhabitants of aquatic environments and are able to cause disease in humans and fish among other animals. In aquaculture, they are responsible for the economically important diseases of furunculosis and motile Aeromonas septicaemia (MAS). Whereas gastroenteritis and wound infections are the major human diseases associated with the genus. As they inhabit and survive in diverse environments, aeromonads possess a wide range of colonisation factors. The motile species are able to swim in liquid environments through the action of a single polar flagellum, the flagellin subunits of which are glycosylated; although essential for function the biological role of glycan addition is yet to be determined. Approximately 60% of aeromonads possess a second lateral flagella system that is expressed in viscous environments for swarming over surfaces; both flagellar systems have been shown to be important in the initial colonisation of surfaces. Subsequently, other non-flagellar colonisation factors are employed; these can be both filamentous and non-filamentous. The aeromonads possess a number of fimbrial systems with the bundle-forming MSHA type IV pilus system, having a major role in human cell adherence. Furthermore, a series of outer-membrane proteins have also been implicated in the aeromonad adhesion process. A number of strains are also capable of cell invasion and that maybe linked with the more invasive diseases of bacteraemia or wound infections. These strains employ cell surface factors that allow the colonisation of these niches that protect them from the host's immune system such as S-layers, capsules or particular lipopolysaccharides.

Genomic study of polyhydroxyalkanoates producing Aeromonas hydrophila 4AK4

The complete genome of Gram-negative Aeromonas hydrophila 4AK4 that has been used for industrial production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) was sequenced and annotated. Its chromosome is 4,527,993 bp in size encoding 4,272 genes, including 28 rRNA genes and 104 tRNA genes. Comparative analysis indicated that genome of A. hydrophila 4AK4 was similar to that of the A. hydrophila ATCC 7966(T), an intensively studied aeromonad for its pathogenicity related to its genomic information. Genes possibly coming from other species or even other genus were identified in A. hydrophila 4AK4. A large number of putative virulent genes were predicted. However, a cytotonic enterotoxin (Ast) is absent in A. hydrophila 4AK4, allowing the industrial strain to be different from other A. hydrophila strains, indicating possible reduced virulence of strain 4AK4, which is very important for industrial fermentation. Genes involved in polyhydroxyalkanoate (PHA) metabolism were predicted and analyzed. The resulting genomic information is useful for improved production of PHA via metabolic engineering of A. hydrophila 4AK4.

FliS modulates FlgM activity by acting as a non-canonical chaperone to control late flagellar gene expression, motility and biofilm formation in Yersinia pseudotuberculosis

The FlgM-FliA regulatory circuit plays a central role in coordinating bacterial flagellar assembly. In this study, we identified multiple novel binding partners of FlgM using bacterial two-hybrid screening. Among these binding partners, FliS, the secretion chaperone of the filament protein FliC, was identified to compete with FliA for the binding of FlgM. We further showed that by binding to FlgM, FliS protects it from secretion and degradation, thus maintaining an intracellular pool of FlgM reserved as the FliS-FlgM complex. Consequently, we found that the flagellar late-class promoter activities are significantly increased in the fliS deletion mutant. The fliS mutant is weakly motile and shows significantly increased biofilm formation on biotic surface. Based on the results obtained, we established for the first time the regulatory role of the flagellin chaperone FliS to fine-tune late flagellar assembly by modulating FlgM activity.

Characterization of Aeromonas hydrophila wound pathotypes by comparative genomic and functional analyses of virulence genes

Aeromonas hydrophila has increasingly been implicated as a virulent and antibiotic-resistant etiologic agent in various human diseases. In a previously published case report, we described a subject with a polymicrobial wound infection that included a persistent and aggressive strain of A. hydrophila (E1), as well as a more antibiotic-resistant strain of A. hydrophila (E2). To better understand the differences between pathogenic and environmental strains of A. hydrophila, we conducted comparative genomic and functional analyses of virulence-associated genes of these two wound isolates (E1 and E2), the environmental type strain A. hydrophila ATCC 7966^T, and four other isolates belonging to A. aquariorum, A. veronii, A. salmonicida, and A. caviae. Full-genome sequencing of strains E1 and E2 revealed extensive differences between the two and strain ATCC 7966^T. The more persistent wound infection strain, E1, harbored coding sequences for a cytotoxic enterotoxin (Act), a type 3 secretion system (T3SS), flagella, hemolysins, and a homolog of exotoxin A found in Pseudomonas aeruginosa. Corresponding phenotypic analyses with A. hydrophila ATCC 7966^T and SSU as reference strains demonstrated the functionality of these virulence genes, with strain E1 displaying enhanced swimming and swarming motility, lateral flagella on electron microscopy, the presence of T3SS effector AexU, and enhanced lethality in a mouse model of Aeromonas infection. By combining sequence-based analysis and functional assays, we characterized an A. hydrophila pathotype, exemplified by strain E1, that exhibited increased virulence in a mouse model of infection, likely because of encapsulation, enhanced motility, toxin secretion, and cellular toxicity.

Aeromonas hydrophila is a common aquatic bacterium that has increasingly been implicated in serious human infections. While many determinants of virulence have been identified in Aeromonas, rapid identification of pathogenic versus nonpathogenic strains remains a challenge for this genus, as it is for other opportunistic pathogens. This paper demonstrates, by using whole-genome sequencing of clinical Aeromonas strains, followed by corresponding virulence assays, that comparative genomics can be used to identify a virulent subtype of A. hydrophila that is aggressive during human infection and more lethal in a mouse model of infection. This aggressive pathotype contained genes for toxin production, toxin secretion, and bacterial motility that likely enabled its pathogenicity. Our results highlight the potential of whole-genome sequencing to transform microbial diagnostics; with further advances in rapid sequencing and annotation, genomic analysis will be able to provide timely information on the identities and virulence potential of clinically isolated microorganisms.

Reduction of Aeromonas hidrophyla biofilm on stainless stell surface by essential oils

This study demonstrates the possibility of using sanitizing detergents based on natural products for the elimination and/or reduction of Aeromonas hydrophila biofilm formed on stainless steel surfaces. The goal of this work was to determine the reduction effect of sanitizing detergents containing essential oils of Thymus vulgaris (thyme) and Cymbopogon citratus (lemongrass) on biofilm formed by A. hydrophila on AISI 304 stainless steel coupons, using UHT skimmed milk as substratum. There was adhesion and biofilm formation by A. hydrophila at 28 °C, presenting 7.60 log cfu.cm⁻² after the fourth day of cultivation. There was no significant difference between the lemongrass treatment and that of the thyme oil (p < 0.05). However, both treatments significantly reduced the biofilm, differing significantly from the NaOH control (p > 0.05). The treatment with lemongrass solution reduced the biofilm by 4.51 log cfu cm⁻² at 25 °C. The thyme detergent also reduced the number of cfu cm⁻² by 3.84 log cycles at 25 °C. The use of the lemongrass and thyme solutions efficiently reduced the A. hydrophila biofilm.

Aeromonas hydrophila lateral flagellar gene transcriptional hierarchy

Aeromonas hydrophila AH-3 lateral flagella are not assembled when bacteria grow in liquid media; however, lateral flagellar genes are transcribed. Our results indicate that A. hydrophila lateral flagellar genes are transcribed at three levels (class I to III genes) and share some similarities with, but have many important differences from, genes of Vibrio parahaemolyticus. A. hydrophila lateral flagellum class I gene transcription is σ(70) dependent, which is consistent with the fact that lateral flagellum is constitutively transcribed, in contrast to the characteristics of V. parahaemolyticus. The fact that multiple genes are included in class I highlights that lateral flagellar genes are less hierarchically transcribed than polar flagellum genes. The A. hydrophila lafK-fliEJL gene cluster (where the subscript L distinguishes genes for lateral flagella from those for polar flagella) is exclusively from class I and is in V. parahaemolyticus class I and II. Furthermore, the A. hydrophila flgAMNL cluster is not transcribed from the σ(54)/LafK-dependent promoter and does not contain class II genes. Here, we propose a gene transcriptional hierarchy for the A. hydrophila lateral flagella.