UvrY is required for the full virulence of Aeromonas dhakensis

PRMT-7/PRMT7 activates HLH-30/TFEB to guard plasma membrane integrity compromised by bacterial pore-forming toxins

Bacterial pore-forming toxins (PFTs) that disrupt host plasma membrane integrity (PMI) significantly contribute to the virulence of various pathogens. However, how host cells protect PMI in response to PFT perforation in vivo remains obscure. Previously, we demonstrated that the HLH-30/TFEB-dependent intrinsic cellular defense (INCED) is elicited by PFT to maintain PMI in Caenorhabditis elegans intestinal epithelium. Yet, the molecular mechanism for the full activation of HLH-30/TFEB by PFT remains elusive. Here, we reveal that PRMT-7 (protein arginine methyltransferase-7) is indispensable to the nuclear transactivation of HLH-30 elicited by PFTs. We demonstrate that PRMT-7 participates in the methylation of HLH-30 on its RAG complex binding domain to facilitate its nuclear localization and activation. Moreover, we showed that PRMT7 is evolutionarily conserved to regulate TFEB cellular localization and repair plasma damage caused by PFTs in human intestinal cells. Together, our observations not only unveil a novel PRMT-7/PRMT7-dependent post-translational regulation of HLH-30/TFEB but also shed insight on the evolutionarily conserved mechanism of the INCED against PFT in metazoans.

Aeromonas dhakensis: A Zoonotic Bacterium of Increasing Importance in Aquaculture

Aeromonas dhakensis is increasingly recognised to be an important pathogen responsible for disease losses in warm-water aquaculture and, similar to several other Aeromonas species, it can infect humans. Knowledge of A. dhakensis is accumulating, but this species remains relatively under-investigated compared to its close relative, Aeromonas hydrophila. The significance of A. dhakensis may have been overlooked in disease events of aquatic animals due to issues with reliable identification. Critical to appreciating the importance of this pathogen is the application of dependable molecular tools that enable accurate identification and discrimination from A. hydrophila and other motile aeromonads. This review aims to synthesise the key literature on A. dhakensis, particularly with relevance to aquaculture, including knowledge of the bacterium derived from disease case studies in aquatic hosts. Identification methods and strain phylogeny are discussed, with accurate detection important for prompt diagnosis and for distinguishing strains with heightened virulence. Increasing evidence suggests that A. dhakensis may be more virulent than A. hydrophila and correct identification is required to determine the zoonotic risks posed, which includes concerns for antibiotic-resistant strains. This review provides an impetus to improve species identification in the future and screen strain collections of presumptive Aeromonas spp. retrospectively to reveal the true prevalence and impact of A. dhakensis in aquaculture, the environment, and healthcare settings.

Haemolysin Ahh1 secreted from Aeromonas dhakensis activates the NLRP3 inflammasome in macrophages and mediates severe soft tissue infection

Severe soft tissue infections caused by Aeromonas dhakensis, such as necrotizing fasciitis or cellulitis, are prevalent in southern Taiwan and around the world. However, the mechanism by which A. dhakensis causes tissue damage remains unclear. Here, we found that the haemolysin Ahh1, which is the major virulence factor of A. dhakensis, causes cellular damage and activates the NLR family pyrin domain containing 3 (NLRP3) inflammasome signalling pathway. Deletion of ahh1 significantly downregulated caspase-1, the proinflammatory cytokine interleukin 1β (IL-1β) and gasdermin D (GSDMD) and further decreased the damage caused by A. dhakensis in THP-1 cells. In addition, we found that knockdown of the NLRP3 inflammasome confers resistance to A. dhakensis infection in both THP-1 NLRP3-/- cells and C57BL/6 NLRP3-/- mice. In addition, we demonstrated that severe soft-tissue infections treated with antibiotics combined with a neutralizing antibody targeting IL-1β significantly increased the survival rate and alleviated the degree of tissue damage in model mice compared control mice. These findings show that antibiotics combined with therapies targeting IL-1β are potential strategies to treat severe tissue infections caused by toxin-producing bacteria.

Quantitative Proteomics Analysis Reveals the Effect of a MarR Family Transcriptional Regulator AHA_2124 on Aeromonas hydrophila

The transcriptional regulators of the MarR family play an important role in diverse bacterial physiologic functions, whereas their effect and intrinsic regulatory mechanism on the aquatic pathogenic bacterium Aeromonas hydrophila are, clearly, still unknown. In this study, we firstly constructed a deletion strain of AHA_2124 (ΔAHA_2124) of a MarR family transcriptional regulator in Aeromonas hydrophila ATCC 7966 (wild type), and found that the deletion of AHA_2124 caused significantly enhanced hemolytic activity, extracellular protease activity, and motility when compared with the wild type. The differentially abundant proteins (DAPs) were compared by using data-independent acquisition (DIA), based on a quantitative proteomics technology, between the ΔAHA_2124 strain and wild type, and there were 178 DAPs including 80 proteins up-regulated and 98 proteins down-regulated. The bioinformatics analysis showed that the deletion of gene AHA_2124 led to some changes in the abundance of proteins related to multiple biological processes, such as translation, peptide transport, and oxidation and reduction. These results provided a theoretical basis for better exploring the regulatory mechanism of the MarR family transcriptional regulators of Aeromonas hydrophila on bacterial physiological functions.

Cytotoxicity and Antimicrobial Resistance of Aeromonas Strains Isolated from Fresh Produce and Irrigation Water

The genus Aeromonas has received constant attention in different areas, from aquaculture and veterinary medicine to food safety, where more and more frequent isolates are occurring with increased resistance to antibiotics. The present paper studied the interaction of Aeromonas strains isolated from fresh produce and water with different eukaryotic cell types with the aim of better understanding the cytotoxic capacity of these strains. To study host-cell pathogen interactions in Aeromonas, we used HT-29, Vero, J774A.1, and primary mouse embryonic fibroblasts. These interactions were analyzed by confocal microscopy to determine the cytotoxicity of the strains. We also used Galleria mellonella larvae to test their pathogenicity in this experimental model. Our results demonstrated that two strains showed high cytotoxicity in epithelial cells, fibroblasts, and macrophages. Furthermore, these strains showed high virulence using the G. mellonella model. All strains used in this paper generally showed low levels of resistance to the different families of the antibiotics being tested. These results indicated that some strains of Aeromonas present in vegetables and water pose a potential health hazard, displaying very high in vitro and in vivo virulence. This pathogenic potential, and some recent concerning findings on antimicrobial resistance in Aeromonas, encourage further efforts in examining the precise significance of Aeromonas strains isolated from foods for human consumption.

A Novel Role of the Two-Component System Response Regulator UvrY in Enterohemorrhagic Escherichia coli O157:H7 Pathogenicity Regulation

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is an important human pathogen causing severe diseases, such as hemorrhagic colitis and lethal hemolytic uremic syndrome. The signal-sensing capability of EHEC O157:H7 at specific host colonization sites via different two-component systems (TCSs) is closely related to its pathogenicity during infection. However, the types of systems involved and the regulatory mechanisms are not fully understood. Here, we investigated the function of the TCS BarA/UvrY regulator UvrY in the pathogenicity regulation of EHEC O157:H7. Our results showed that UvrY acts as a positive regulator of EHEC O157:H7 for cellular adherence and mouse colonization through the transcriptional activation of the locus for enterocyte effacement (LEE) pathogenic genes. Furthermore, this regulation is mediated by the LEE island master regulator, Ler. Our results highlight the significance of UvrY in EHEC O157:H7 pathogenicity and underline the unknown importance of BarA/UvrY in colonization establishment and intestinal adaptability during infection.

Effect of spatio-temporal variables, host fish species and on-farm biosecurity measures on the prevalence of potentially pathogenic Aeromonas species in freshwater fish farms

AIMS

To determine the prevalence of Aeromonas species in freshwater fish farms, factors affecting their prevalence and virulence factors associated with each species.

METHODS AND RESULTS

In a cross-sectional study from 128 farms in four districts of Uttar Pradesh, India, 11 species of Aeromonas were identified by gyrB sequencing including the first report of Aeromonas crassostreae from fish. Four species of Aeromonas were more prevalent (MP) in fish farms, A. veronii bv. sobria (50.0%) was the highest, followed by A. caviae (18.8%), A. veronii bv. veronii (11.7%) and A. dhakensis (7.0%). The less prevalent (LP) species were A. hydrophila, A. media, A. jandaei, A. allosaccharophila, A. salmonicida, A. crassostreae and A. taiwanensis. Spatial variation in the prevalence of Aeromonas species was observed. Dominance of biovar sobria ranged from 33.3 to 68.6%, notably lesser in farms with on-farm biosecurity measures. The prevalence of biovar veronii was significantly associated with pangas fish, rainy season and farms with on-farm biosecurity measures. The prevalence of LP species was significantly higher in mrigal fish and winter season. Multiple virulence factors (>6) were detected in 70.2% of the Aeromonas species. Significant association of β-hemolysin, DNase, slime production, act, ahh1, aexT and lip was observed with different species of Aeromonas. Moreover, 75.8% of Aeromonas species possessed one or more enterotoxins genes (act/alt/ast).

CONCLUSION

Significant association of spatio-temporal variables, host fish species and on-farm biosecurity measures were observed on the prevalence of some of the Aeromonas species in freshwater fish farms. Most of the Aeromonas species harboured virulence factors indicating their potential for pathogenicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study that determined the prevalence and identified the factors that affect the prevalence of Aeromonas species in freshwater fish farms. This information will be useful in managing Aeromonas infection in fish and their risks to public health.

Corynebacterium diphtheriae Virulence Analyses Using a Caenorhabditis elegans Model

Corynebacterium diphtheriae is the leading cause of pharyngeal diphtheria, a respiratory disease characterized by formation of a pseudomembrane at the site of infection. Although outbreaks of C. diphtheriae infections are rare nowadays, the emergence of multidrug-resistant C. diphtheriae strains is one of the most significant public health concerns worldwide. Although C. diphtheriae has been studied for more than a century and diphtheria toxin and pili have been identified as major virulence factors, little is known about factors involved in bacterial colonization and development of disease. Here, we describe the utilization of Caenorhabditis elegans as a cost-effective, versatile model of infection to evaluate C. diphtheriae virulence. We provide detailed protocols for nematode synchronization and for evaluation of nematode survival and formation of a deformed anal region induced by C. diphtheriae infection. These protocols will permit future high-throughput screenings of virulence factors in C. diphtheriae and advance our knowledge of C. diphtheriae pathogenesis. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Synchronization of nematodes Basic Protocol 2: Assay for nematode survival following C. diphtheriae infection Basic Protocol 3: Assays for bacterial colonization and formation of deformed anal region.

Taxonomy, virulence determinants and antimicrobial susceptibility of Aeromonas spp. isolated from bacteremia in southeastern China

Background

The study aimed to elucidate the species taxonomy, clinical manifestations, virulence gene profiles and antimicrobial susceptibilities of Aeromonas strains isolated from life-threatening bacteremia in southeastern China.

Methods

Clinical samples of Aeromonas causing bacteremia were isolated from a teaching hospital in Wenzhou from 2013 to 2018 and a retrospective cohort study was performed. Aeromonas strains were identified at species level by housekeeping gene gyrB. Virulence and drug resistance-associated genes were screened by polymerase chain reaction (PCR) and antimicrobial susceptibility testing (AST) was performed by the VITEK 2 Compact system.

Results

A total of 58 Aeromonas isolated from patients with bacteremia were collected during 6 years (2013–2018). 58 isolates were identified to five different species, where Aeromonas dhakensis appeared to be the predominant species (26/58), followed by Aeromonas veronii (13/58), Aeromonas caviae (10/58), Aeromonas hydrophila (7/58) and Aeromonas jandaei (2/58). 16 of 58 patients had poor prognosis. Poor prognosis was significantly associated with liver cirrhosis and inappropriate empirical antimicrobials therapy. The progression of bacteremia caused by Aeromonas was extremely fast, especially in A. dhakensis infections. Virulence genes aer, lip, hlyA, alt, ast, and act, were detected at ratios of 24.1% (14/58), 62.1% (36/58), 65.5% (38/58), 58.6% (34/58), 15.5% (9/58) and 65.5% (38/58), respectively. Antimicrobial susceptibility testing exhibited that 9 out of 58 isolates were identified as multi-drug resistant (MDR) organism. The bla_TEM gene was identified in all 9 MDR isolates. bla_SHV, bla_AQU-1, bla_MOX, bla_CepH, bla_CphA and aac(6′)-Ib-cr were detected in 4 isolates, 2 isolates, 1 isolate, 3 isolates, 8 isolates, and 3 isolates, respectively. The majority of Aeromonas strains maintained susceptible to 3rd generation cephalosporins, aminoglycosides, fluoroquinolones and furantoin.

Conclusions

The prevalence and dangerousness of Aeromonas infections, especially A. dhakensis, are underestimated in clinic. Continuous monitoring is essential to keep track of MDR Aeromonas due to the increasing prevalence recently and a more effective measure is required to control the spread of resistance determinants.