Assessment of the correlation among antibiotic resistance, adherence to abiotic and biotic surfaces, invasion and cytotoxicity of Pseudomonas aeruginosa isolated from diseased gilthead sea bream

Emergence of colistin-resistant Stenotrophomonas maltophilia with high virulence in natural aquatic environments

The presence of Stenotrophomonas maltophilia in aquatic environments poses great health risks to immunocompromised individuals because of its multidrug resistance and resultant high mortality. However, a significant gap exists in the isolation and understanding of colistin-resistant S. maltophilia in aquatic environments. In this study, nine colistin-resistant S. maltophilia strains isolated from natural lakes were explored, and their phylogenetic relationship, biofilm formation, virulence, and antibiotic resistance profiles and underlying genetic determinants were assessed. After genome analysis, besides known multi-locus sequence typing (MLST) of ST532, new assigned ST965 and ST966 which phylogenetically clustered into soil isolates were found firstly. All the isolates exhibited resistance to multiple antibiotics, including aminoglycosides, beta-lactams, tetracyclines, and even colistin, with the highest minimum inhibitory concentration (MIC) against colistin reaching 640 mg/L. Comparative genomic analysis revealed aph(3')-Iic, blaL1, tetT, phoP, mcr-3, arnA, pmrE, and efflux pump genes as the genetic determinants underlying this multidrug resistance. Notably, the biofilm-forming capacities of the newly discovered ST965 and ST966 isolates were significant stronger than those of the known ST532 isolates (p < 0.01), resulting in the death of over 50 % of the Galleria mellonella population within 1 day of injection. The ST965 isolates demonstrated the highest virulence against G. mellonella, followed by the ST966 isolates and ST532 isolates which was phylogenetically clustered with clinical isolates, indicating that the novel S. maltophilia strains of ST965 and ST966 may pose considerable health risks to humans. Our findings provide insights into colistin-resistant S. maltophilia in aquatic environments and raise concerns about the health risks posed by the newly assigned sequence types of colistin-resistant S. maltophilia with potential high virulence in natural aquatic environments.

Chemical control over Asialo-GM1: A dual ligand for pili and Lectin A that activates swarming motility and facilitates adherence of Pseudomonas aeruginosa

Glycolipid, ganglio-N-tetraosylceramide (asialo-GM1), on the mammalian cells are known to be recognized by type IV pili of Pseudomonas aeruginosa. In this work, we show that asialo-GM1 can also be recognized by Lectin A (LecA), another adhesin protein of the P. aeruginosa, by a fluorescent polarization assay, a label-free bacterial motility enabled binding assay, and bacterial mutant studies. On hydrated semi-solid gel surfaces, asialo-GM1 enables swarming and twitching motilities, while on solid surfaces facilitates the bacterial adherence of P. aeruginosa. These results indicate that asialo-GM1 can modulate bioactivities, adherence, and motilities, that are controlled by opposite signaling pathways. We demonstrate that when a solution of pilin monomers or LecA proteins are spread on hydrated gel surfaces, the asialo-GM1 mediated swarming motility is inhibited. Treatment of artificial liposomes containing asialo-GM1 as a component of lipid bilayer with pilin monomers or LecA proteins caused transient leakage of encapsulated dye from liposomes. These results suggest that pili and LecA proteins not only bind to asialo-GM1 but can also cause asialo-GM1 mediated leakage. We also show that both pili and LecA mutants of P. aeruginosa adhere to asialo-GM1 coated solid surfaces, and that a class of synthetic ligands for pili and LecA inhibits both pili and LecA-mediated adherence of P. aeruginosa on asialo-GM1-coated surfaces.

In Vivo Bacteriophages’ Application for the Prevention and Therapy of Aquaculture Animals–Chosen Aspects

To meet the nutritional requirements of our growing population, animal production must double by 2050, and due to the exhaustion of environmental capacity, any growth will have to come from aquaculture. Aquaculture is currently undergoing a dynamic development, but the intensification of production increases the risk of bacterial diseases. In recent years, there has been a drastic development in the resistance of pathogenic bacteria to antibiotics and chemotherapeutic agents approved for use, which has also taken place in aquaculture. Consequently, animal mortality and economic losses in livestock have increased. The use of drugs in closed systems is an additional challenge as it can damage biological filters. For this reason, there has been a growing interest in natural methods of combating pathogens. One of the methods is the use of bacteriophages both for prophylactic purposes and therapy. This work summarizes the diverse results of the in vivo application of bacteriophages for the prevention and control of bacterial pathogens in aquatic animals to provide a reference for further research on bacteriophages in aquaculture and to compare major achievements in the field.

Antibiotics, antibiotic-resistant bacteria, and resistance genes in aquaculture: risks, current concern, and future thinking

Aquaculture is remarkably one of the most promising industries among the food-producing industries in the world. Aquaculture production as well as fish consumption per capita have been dramatically increasing over the past two decades. Shifting of culture method from semi-intensive to intensive technique and applying of antibiotics to control the disease outbreak are the major factors for the increasing trend of aquaculture production. Antibiotics are usually present at subtherapeutic levels in the aquaculture environment, which increases the selective pressure to the resistant bacteria and stimulates resistant gene transfer in the aquatic environment. It is now widely documented that antibiotic resistance genes and resistant bacteria are transported from the aquatic environment to the terrestrial environment and may pose adverse effects on human and animal health. However, data related to antibiotic usage and bacterial resistance in aquaculture is very limited or even absent in major aquaculture-producing countries. In particular, residual levels of antibiotics in fish and shellfish are not well documented. Recently, some of the countries have already decided the maximum residue levels (MRLs) of antibiotics in fish muscle or skin; however, many antibiotics are yet not to be decided. Therefore, an urgent universal effort needs to be taken to monitor antibiotic concentration and resistant bacteria particularly multiple antibiotic-resistant bacteria and to assess the associated risks in aquaculture. Finally, we suggest to take an initiative to make a uniform antibiotic registration process, to establish the MRLs for fish/shrimp and to ensure the use of only aquaculture antibiotics in fish and shellfish farming globally.

Architectured Cu–TNTZ Bilayered Coatings Showing Bacterial Inactivation under Indoor Light and Controllable Copper Release: Effect of the Microstructure on Copper Diffusion

A Ti–23Nb–0.7Ta–2Zr–1.2O alloy (at %), called “gum metal”, was deposited by direct-current magnetron sputtering (DCMS) on an under layer of copper. By varying the working pressure during the deposition, columnar TNTZ (Ti–Nb–Ta–Zr) nanoarchitectures were obtained. At low working pressures, the upper layer was dense with a coarse surface (Ra = 12 nm) with a maximum height of 163 nm; however, the other samples prepared at high working pressures showed columnar architectures with voids and an average roughness of 4 nm. The prepared coatings were characterized using atomic force microscopy (AFM) for surface topography, energy dispersive X-ray spectroscopy (EDX) for atomic mapping, scanning electron microscopy (SEM) for cross-section imaging, contact angle measurements for hydrophilic/hydrophobic balance of the prepared surfaces, and X-ray diffraction (XRD) for the crystallographic structures of the prepared coatings. The morphology and the density of the prepared coatings were seen to influence the hydrophilic properties of the surface. The antibacterial activity of the prepared coatings was tested in the dark and under low-intensity indoor light. Bacterial inactivation was seen to happen in the dark from samples presenting columnar nanoarchitectures. This was attributed to the diffusion of copper ions from the under layer. To verify the copper release from the prepared samples, an inductively coupled plasma mass spectrometer (ICP-MS) was used. Additionally, the atomic depth profiling of the elements was carried out by X-ray photoelectron spectroscopy (XPS) for the as-prepared samples and for the samples used for bacterial inactivation. The low amount of copper in the bulk of the TNTZ upper layer justifies its diffusion to the surface. Recycling of the antibacterial activity was also investigated and revealed a stable activity over cycles.

Comparative analysis of cutaneous bacterial communities of farmed Rana dybowskii after gentamycin bath

Introduction

Pathogenic bacteria limit the success of Rana dybowskii breeding. Gentamicin is used to treat R. dybowskii disease. To understand the effects of gentamicin on the composition and structure of the cutaneous bacterial community of R. dybowskii, three groups (control, gentamicin and recovery) were established in this study.

Materials & Methods

The V3-V4 hypervariable region of the 16S rRNA gene was analyzed in samples by high-throughput sequencing. Alpha diversity and beta diversity were evaluated to compare the cutaneous bacterial community diversity.

Results

A total of 1,159,668 valid sequences and 3,132 operational taxonomic units (OTUs) were obtained from these three experimental groups. The number of OTUs obtained in the control group, gentamicin group and recovery group were 2,194, 2,288, and 2,047, respectively, and the number of shared OTUs was 1,313. The alpha diversity of the cutaneous bacterial community was not significantly affected by gentamicin, while beta diversity was significantly affected.

Discussion & Conclusions

The effect of a gentamicin bath on relative species abundance was greater than the effect on the species composition. The changes in Proteobacteria, Acinetobacter, and Chryseobacterium were significant, and reductions were observed after the recovery period. Six potentially pathogenic genera were detected, including Aeromonas, Citrobacter, Chryseobacterium, Pseudomonas, Staphylococcus, and Streptococcus. Among them, Aeromonas and Chryseobacterium were significantly inhibited by the gentamicin bath. The results of this study provide a theoretical basis for the application of gentamicin in R. dybowskii breeding.

Interaction of Vibrio to Biotic and Abiotic Surfaces: Relationship between Hydrophobicity, Cell Adherence, Biofilm Production, and Cytotoxic Activity

Vibrio parahaemolyticus and Vibrio alginolyticus are important pathogenic agents for both humans and aquatic animals. Twenty-five bacterial strains were isolated from infected sea bass (Dicentrarchus labrax) on thiosulfate citrate bile salts sucrose (TCBS) agar plates. For the species-specific detection of V. alginolyticus and V. parahaemolyticus, a multiplex PCR assay using two collagenase-targeted primer pairs allows the detection of four strains of V. parahaemolyticus and three strains of V. alginolyticus. The seven identified isolates were partitioned for capsule production, hydrophobicity, adherence, biofilm formation, invasion, and cytotoxicity against Hep-2 cells. Two V. parahaemolyticus (Spa2 and Spa3) and one V. alginolyticus (Va01) were capsule producers developing almost black colonies on CRA, they showed a strong hydrophobicity using bacterial adhesion to hydrocarbons test (BATH), and were able to produce high biofilm. Isolates were able to adhere and invade Hep-2 cells and exhibited dissimilar levels of cytotoxicity in epithelial cells. This study shows the strong relationship between adhesion, biofilm formation, invasion and the cytotoxicity of Vibrio strains. Thus, we found a strong and significant positive correlation between different virulence properties of these isolates. The present study shows that bacterial contact with the cells as well as adhesion and invasion are essential steps to induce cytotoxicity. However, the invasion is seen to be a post adherence event.

Involvement of xanthine oxidase inhibition with the antioxidant property of nanoencapsulated Melaleuca alternifolia essential oil in fish experimentally infected with Pseudomonas aeruginosa

Nanoencapsulated Melaleuca alternifolia essential oil (tea tree oil, TTO) is a natural alternative treatment, with 100% therapeutic efficacy in fish experimentally infected with Pseudomonas aeruginosa, and has also potent protective effects linked with antioxidant properties. However, the pathways responsible for the antioxidant capacity remain unknown. Thus, this study evaluated whether the inhibition of seric xanthine oxidase (XO) activity can be considered a pathway involved in the antioxidant capacity of nanoencapsulated TTO in fish experimentally infected with P. aeruginosa. Seric samples from fish infected with P. aeruginosa showed increased XO activity, as well as increased uric acid and reactive oxygen species (ROS) levels. In contrast, the prophylactic treatment with nanoencapsulated TTO prevented these infection-induced alterations. Based on the evidence obtained, the upregulation of seric XO activity induced pro-oxidative effects in the serum of fish experimentally infected with P. aeruginosa, due to excessive formation of uric acid, which stimulates the release of ROS. This treatment was able to prevent the upregulated seric XO activity and, consequently, the excessive formation of uric acid and ROS. In summary, inhibition of seric XO activity can be considered a pathway involved in the antioxidant capacity of nanoencapsulated TTO in fish experimentally infected with P. aeruginosa.