Sessile Cells Research Articles

Characterization of dual-species biofilms formed by bacteria isolated from milk

This study evaluated biofilm formation of bacteria isolated from raw milk and investigated the composition of extracellular polymeric substances (EPS) using Raman spectroscopy. Biofilms were formed from six isolates on a 96-well microplate at 7 and 25 °C in 1 and 10% reconstituted whole milk. Biofilms were then formed on stainless steel coupons at 7 °C from two isolates identified as strong biofilm producers. Pseudomonas fluorescens, a frequent contaminant of raw milk, forms single or dual-species biofilms with Staphylococcus aureus; however, the sessile cell number of S. aureus remained constant over ten days. Raman spectroscopy identified that EPS composition varied with carbohydrate and protein substrates, the predominant components in P. fluorescens single or dual-species biofilms. Understanding the formation and composition of biofilms at different temperatures and in milk concentrations that simulate the equipment used in the dairy industry is a significant subsidy for establishing adequate sanitary protocols for their mitigation.

Effects of alternating current on microbiologically synergistic corrosion of pipeline steel X80 applied by elastic stress

Microorganisms play an important role in multi-factor synergistic corrosion. The synergistic effects of which are greatly stronger than elastic stress and alternative current. Changes of alternative current directly dominate the effect of microbial synergy. With increasing AC current density, corrosion rate of pipeline steel X80 increased first and then decreased, reaching a peak at 100 A m−2. Number of SRB cells vaired as a function of AC current density. Lower current density promoted SRB growth while high current density inhibited SRB growth. When sessile cells are more than 105 cell cm−2, the dominant role of microorganisms is strong, and corrosion rate increases with current density. The maximum value is reached at 100 A m−2. However, when the cells are less than 103 cell cm−2, the dominant effect is greatly reduced, leading to a reduction in the synergistic effect of the multi-factor, and finally reduced corrosion rate to 200 A m−2.

Corrosion of Pseudomonas aeruginosa toward a Cu-Zn-Ni alloy inhibited by the simulative tidal region.

The corrosion of marine engineering equipment not only threatens human security and ecological environment but also increases energy consumption, restricting the sustainable development of marine economies and industries. The tidal region is a complex and challenging environment that can cause severe corrosion of facilities and affect microbial activities. However, the current understanding of the mechanisms underlying microbiologically influenced corrosion (MIC) of tidal region is insufficient. To address this issue, the effect of Pseudomonas aeruginosa on a Cu-Zn-Ni alloy in the simulative tidal region was investigated by chemical and molecular biological analysis in this study. The results demonstrated that P. aeruginosa formed thicker biofilms on the Cu-Zn-Ni alloy samples under the full exposure, accelerating corrosion compared to sterile controls. Interestingly, the corrosion of P. aeruginosa toward the Cu-Zn-Ni alloy was inhibited in the simulative tidal region. This inhibition behavior was relevant to the reduction in the quantity of sessile cells and cell activities. The expression down-regulation of genes encoding phenazines induced the decrease in electron transfer mediators and weakened the MIC of P. aeruginosa on alloy samples in the simulative tidal region. The research sheds light on the characteristics of P. aeruginosa and corrosion products on the Cu-Zn-Ni alloy, as well as their interaction mechanisms underlying corrosion in the simulative tidal region. The study will facilitate the evaluation and control of MIC in the tidal region, contributing to the development of sustainable strategies for preserving the integrity and safety of marine facilities.

Antimicrobial Activity of Bovine Bone Scaffolds Impregnated with Silver Nanoparticles on New Delhi Metallo-β-Lactamase-Producing Gram-Negative Bacilli Biofilms

Introduction: The antibiofilm activity of silver nanoparticles has been extensively investigated in common bacteria. Metallo-β-lactamase-producing Gram-negative bacteria are hard-to-treat microorganisms with few therapeutic options, and silver nanoparticles were not evaluated on the biofilm of these bacteria. Objectives: The aim of this study was to evaluate the antibiofilm activity of a bone scaffold impregnated with silver nanoparticles in NDM-producing Gram-negative bacilli. Methods: Bone scaffolds from bovine femur were used for the tests and impregnated with silver nanoparticles (50 nm) by physical adsorption. Silver nitrate minimal inhibitory and bactericidal concentrations (MIC and MBC) were performed on NDM-producing Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Disc diffusion tests for silver nanoparticles’ susceptibility and the quantification of biofilm production on plate and bone with sessile cell count were performed. Results: The MIC results demonstrated that silver nitrate had an antimicrobial effect on all microorganisms, inactivating the growth of isolates from a concentration of 8 µg/mL. MBC results showed that E. coli 16.211 was the only isolate to present MIC that were different from MBC, with a value of 16 µg/mL. Conclusion: Bone scaffolds impregnated with silver nanoparticles can significantly reduce the biofilm of multidrug-resistant bacteria. This is a strategical material that can be used as bone implant in different clinical conditions.

PYED-1 Overcomes Colistin Resistance in Acinetobacter baumannii.

Antibiotic resistance has become more and more widespread over the recent decades, becoming a major global health problem and causing colistin to be increasingly used as an antibiotic of last resort. Acinetobacter baumannii, an opportunistic pathogen that has rapidly evolved into a superbug exhibiting multidrug-resistant phenotypes, is responsible for a large number of hospital infection outbreaks. With the intensive use of colistin, A. baumannii resistance to colistin has been found to increase significantly. In previous work, we identified a deflazacort derivative, PYED-1 (pregnadiene-11-hydroxy-16,17-epoxy-3,20-dione-1), which exhibits either direct-acting or synergistic activity against Gram-positive and Gram-negative species and Candida spp., including A. baumannii. The aim of this study was to evaluate the antibacterial activity of PYED-1 in combination with colistin against both A. baumannii planktonic and sessile cells. Furthermore, the cytotoxicity of PYED-1 with and without colistin was assessed. Our results show that PYED-1 and colistin can act synergistically to produce a strong antimicrobial effect against multidrug-resistant populations of A. baumannii. Interestingly, our data reveal that PYED-1 is able to restore the efficacy of colistin against all colistin-resistant A. baumannii isolates. This drug combination could achieve a much stronger antimicrobial effect than colistin while using a much smaller dosage of the drugs, additionally eliminating the toxicity and resistance issues associated with the use of colistin.

Impact of Desulfovibrio ferrophilus IS5 biocorrosion time on X80 carbon steel mechanical property degradation

Three different incubation times (7, 14 and 21 d) were used to immerse X80 carbon steel dogbone coupons in deoxygenated enriched artificial seawater at 28 °C inoculated with Desulfovibrio ferrophilus (strain IS5), a very corrosive sulfate reducing bacterium to cause microbiologically influenced corrosion (MIC). It was found that 21 d immersion had the largest weight loss (24.8 mg cm−2 equivalent to 0.55 mm/year corrosion rate), smallest sessile cell count (6.8 × 108 cell/cm2), deepest pit depth (30.6 μm), and most severe mechanical degradation (9 % loss in ultimate strength and 18 % loss in ultimate strain). Due to nutrient depletion in the static incubation system, corrosion rate and sessile cell count were the highest at 0.82 mm/year and 1.1 × 109 cell cm−2, respectively at 7 d. The results from scanning electron microscopy, X-ray photoelectron spectroscopy and confocal laser scanning microscopy analyses and electrochemical corrosion measurements supported the sessile cell counts and biocorrosion weight loss data.

Attenuation of biofilm and quorum sensing regulated virulence factors of an opportunistic pathogen Pseudomonas aeruginosa by phytofabricated silver nanoparticles

Green-synthesized nanoparticles provide an effective strategy for inhibiting microbial pathogenesis by affecting biofilm formation, quorum sensing (QS), and other surface properties of microorganisms. QS is a density-dependent communication signaling cascade that regulates biofilm formation and other pathogenic factors of Pseudomonas aeruginosa. In this context, the effect of phytofabricated silver nanoparticles (CC-AgNPs) synthesized using Cuphea carthagenensis extract on biofilm, QS, and QS-dependent virulence factors of P. aeruginosa were evaluated in this study. CC-AgNPs demonstrated significant attenuation of biofilm, QS, and QS-dependent virulence factors at sub-MICs. A significant inhibition of 88.39 ± 4.32 %, 79.64 ± 3.31 %, 73.07 ± 3.0 %, and 61.67 ± 1.5 % of biofilm formation, quorum sensing, pyocyanin, and LasB elastase, respectively was reported in the study at 20 μg/mL. The study also demonstrated a significant reduction of LasA Staphylolytic activity and 91.37 ± 1.05 % exoprotease production in comparison to untreated control. The lower concentrations of CC-AgNPs also demonstrated significant attenuation of biofilm and other virulence factors suggesting the strong potency of NPs against P. aeruginosa. XTT analysis reported the effect of CC-AgNPs on sessile cells of P. aeruginosa without impacting growth of planktonic cells at sub-MICs. Cell-proliferation study in human cell lines (HEK 293 and Caco-2 cells) demonstrated the safe nature of CC-AgNPs at tested concentrations. This study is novel in a way that environmentally friendly CC-AgNPs were used to inhibit QS at sub-MICs without killing the tested strains, therefore, could be developed as an anti-virulent drug to overcome biofilm and antimicrobial resistance problems.

Microbiologically influenced corrosion inhibition of two marine structural steels caused by Halomonas titanicae in aerobic environments

Corrosion is a global problem, especially in marine environments. The currently popular corrosion mitigation methods have the drawbacks of being costly, susceptible to environmental limitations, or causing environmental contamination. Microbiologically influenced corrosion inhibition (MICI), as a widespread phenomenon, can provide a new strategy utilizing bacteria to control corrosion. This study investigated the MICI mechanism of Halomonas titanicae on two marine structural steels (EH36-low alloy steel (E-LAS) (with copper) and Q235-carbon steel (Q-CS) (without copper)) in aerobic environments. Results show that the corrosion of E-LAS and Q-CS was both inhibited by H. titanicae in an aerobic enriched seawater. It was found that the aerobic respiration mode of H. titanicae was very different from its anaerobic respiration. The former respiration mode significantly reduced the dissolved oxygen (DO) concentrations in the medium. In addition, the DO levels in the biotic medium immersed with the two steels were similar, but the corrosion inhibition degree of E-LAS (22% drop) caused by H. titanicae was weaker than that of Q-CS (55% drop), indicating that the MICI mechanism of H. titanicae goes beyond simply reducing the DO concentration. The number of sessile cells on E-LAS was only 20% of that on Q-CS due to Cu in E-LAS, which led to a thinner extracellular polymeric substance (EPS) film and a corrosion product film with less Fe(II) content. This reduced the Rf values significantly. Therefore, the EPS and corrosion product films caused by H. titanicae aerobic respiration are also important in the corrosion inhibition process.

Understanding the transcriptomic response of Lactiplantibacillus pentosus LPG1 during Spanish-style green table olive fermentations.

Lactiplantibacillus pentosus (Lbp. pentosus) is a species of lactic acid bacteria with a great relevance during the table olive fermentation process, with ability to form non-pathogenic biofilms on olive epidermis. The objective of this work is to deepen into the genetic mechanisms of adaptation of Lpb. pentosus LPG1 during Spanish-style green table olive fermentations, as well as to obtain a better understanding of the mechanisms of adherence of this species to the fruit surface. For this purpose, we have carried out a transcriptomic analysis of the differential gene expression of this bacterium during 60 days of fermentation in both brine and biofilms ecosystems. In brines, it was noticed that a total of 235 genes from Lpb. pentosus LPG1 were differentially expressed during course of fermentation and grouped into 9 clusters according to time-course analysis. Transport and metabolism of carbohydrates and amino acids, energy production, lactic acid and exopolysaccharide synthesis genes increased their expression in the planktonic cells during course of fermentation. On the other hand, expression of genes associated to stress response, bacteriocin synthesis and membrane protein decreased. A total of 127 genes showed significant differential expression between Lpb. pentosus LPG1 planktonic (brine) and sessile (biofilms) cells at the end of fermentation process (60 days). Among the 64 upregulated genes in biofilms, we found genes involved in adhesion (strA), exopolysaccharide production (ywqD, ywqE, and wbnH), cell shape and elongation (MreB), and well as prophage excision. Deeping into the genetic bases of beneficial biofilm formation by Lpb. pentosus strains with probiotic potential will help to turn this fermented vegetable into a carrier of beneficial microorganisms to the final consumers.

The Facile Synthesis of Eco-Friendly Zinc Magnesium Bimetal Nanoparticles and its Application in the Eradication of Xanthomonas oryzae pv. oryzae that Causes Leaf Blight Disease of Rice.

In this research work, we formulated and successfully assessed the antibacterial capability of zinc magnesium bimetal nanoparticles (ZnMgNPs) against Xanthomonas oryzae pv. oryzae (Xoo), the pathogenic microorganism responsible for causing the destructive leaf blight disease in rice. Successful preparation of ZnMgNPs were determined by UV-vis spectroscopy, EDX (Energy dispersive X-ray), FTIR (Fourier transform infrared) and SEM (Scanning Electron Microscopy). ZnMgNPs had antibacterial efficacy towards Xoo at MIC (minimum inhibitory concentration) 50µg/ml. ZnMgNPs impeded the formation of biofilm of Xoo by drastically reducing the amount of EPS (extracellular polymeric substances) production and number of sessile cells. The ZnMgNPs also reduced several pathogenic traits of Xoo like motility, xanthomonadin and exoenzymes production. ZnMgNPs target cell membrane of Xoo and also induced oxidative damage as mechanisms of its antibacterial activity. As revealed by an ex-vivo study, ZnMgNPs diminished BLB (bacterial leaf blight) disease symptoms in rice leaves, ZnMgNPs had no effect on rice seed germination, and that following foliar application, the length and biomass of roots and shoots of rice seedling were unaffected, low cytotoxic to A549 cell line showing that ZnMgNPs are non-toxic. However, with ZnMgNPs treatment, the chlorophyll content index (CCI) increased significantly, indicating a good impact on rice physiology. All of these findings suggest that ZnMgNPs could be applied in agriculture to combat the Xoo-caused BLB disease.

Pectic homogalacturonan sensed by Bacillus acts as host associated cue to promote establishment and persistence in the rhizosphere

Bacillus velezensis isolates are among the most promising plant-associated beneficial bacteria used as biocontrol agents. However, various aspects of the chemical communication between the plant and these beneficials, determining root colonization ability, remain poorly described. Here we investigated the molecular basis of such interkingdom interaction occurring upon contact between Bacillus velezensis and its host via the sensing of pectin backbone homogalacturonan (HG). We showed that B. velezensis stimulates key developmental traits via a dynamic process involving two conserved pectinolytic enzymes. This response integrates transcriptional changes leading to the switch from planktonic to sessile cells, a strong increase in biofilm formation, and an accelerated sporulation dynamics while conserving the potential to efficiently produce specialized secondary metabolites. As a whole, we anticipate that this response of Bacillus to cell wall-derived host cues contributes to its establishment and persistence in the competitive rhizosphere niche and ipso facto to its activity as biocontrol agent.

The Deciphering of Growth-Dependent Strategies for Quorum-Sensing Networks in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is recognized as a significant cause of morbidity and mortality among nosocomial pathogens. In respiratory infections, P. aeruginosa acts not only as a single player but also collaborates with the opportunistic fungal pathogen Aspergillus fumigatus. This study introduced a QS molecule portfolio as a potential new biomarker that affects the secretion of virulence factors and biofilm formation. The quantitative levels of QS molecules, including 3-o-C12-HSL, 3-o-C8-HSL, C4-HSL, C6-HSL, HHQ, PQS, and PYO, measured using mass spectrometry in a monoculture, indicated metabolic changes during the transition from planktonic to sessile cells. In the co-cultures with A. fumigatus, the profile of abundant QS molecules was reduced to 3-o-C12-HSL, C4-HSL, PQS, and PYO. A decrease in C4-HSL by 50% to 170.6 ± 11.8 ng/mL and an increase 3-o-C12-HSL by 30% up to 784.4 ± 0.6 ng/mL were detected at the stage of the coverage of the hyphae with bacteria. Using scanning electron microscopy, we showed the morphological stages of the P. aeruginosa biofilm, such as cell aggregates, maturated biofilm, and cell dispersion. qPCR quantification of the genome equivalents of both microorganisms suggested that they exhibited an interplay strategy rather than antagonism. This is the first study demonstrating the quantitative growth-dependent appearance of QS molecule secretion in a monoculture of P. aeruginosa and a co-culture with A. fumigatus.

Rhamnolipid 89 Biosurfactant Is Effective against Streptococcus oralis Biofilm and Preserves Osteoblast Behavior: Perspectives in Dental Implantology.

Biofilm-related peri-implant diseases represent the major complication for osteointegrated dental implants, requiring complex treatments or implant removal. Microbial biosurfactants emerged as new antibiofilm coating agents for implantable devices thanks to their high biocompatibility. This study aimed to assess the efficacy of the rhamnolipid 89 biosurfactant (R89BS) in limiting Streptococcus oralis biofilm formation and dislodging sessile cells from medical grade titanium, but preserving adhesion and proliferation of human osteoblasts. The inhibitory activity of a R89BS coating on S. oralis biofilm formation was assayed by quantifying biofilm biomass and microbial cells on titanium discs incubated up to 72 h. R89BS dispersal activity was addressed by measuring residual biomass of pre-formed biofilms after rhamnolipid treatment up to 24 h. Adhesion and proliferation of human primary osteoblasts on R89BS-coated titanium were evaluated by cell count and adenosine-triphosphate quantification, while cell differentiation was studied by measuring alkaline phosphatase activity and observing mineral deposition. Results showed that R89BS coating inhibited S. oralis biofilm formation by 80% at 72 h and dislodged 63-86% of pre-formed biofilms in 24 h according to concentration. No change in the adhesion of human osteoblasts was observed, whereas proliferation was reduced accompanied by an increase in cell differentiation. R89BS effectively counteracts S. oralis biofilm formation on titanium and preserves overall osteoblasts behavior representing a promising preventive strategy against biofilm-related peri-implant diseases.

Effect of ginger essential oil and 6-gingerol on a multispecies biofilm of Listeria monocytogenes, Salmonella Typhimurium, and Pseudomonas aeruginosa.

The objective of this study was to evaluate the potential antimicrobial and antibiofilm effect of ginger essential oil (GEO) and 6-gingerol on a multispecies biofilm formed by Listeria monocytogenes, Salmonella Typhimurium, and Pseudomonas aeruginosa on a polypropylene surface. The minimum inhibitory concentration concentrations obtained for GEO were 100 and 50mg/mL and for 6-gingerol 1.25mg/mL. Sessile cell counts ranged within 5.35-7.35 log CFU/cm2 in the control biofilm, with the highest sessile growth at 72h. GEO treatments acted on the total population regardless of concentration at 1 and 48h. L. monocytogenes behaved similarly to the total population, showing GEO action at 1h and keeping the same pattern at 48, 72, and 96h. Better action on S. Typhimurium was obtained at times of 1, 72, and 96h. P. aeruginosa showed logarithmic reduction only when treated with GEO 50mg at 24h. As for 6-gingerol, in general, there was no significant action (p > 0.05) on the evaluated sessile cells. GEO showed antimicrobial activity againstL. monocytogenes, S. Typhimurium, and P. aeruginosa, acting as an inhibitor of biofilm formation. As for 6-gingerol, it was considered a possible antimicrobial agent but without efficacy during biofilm formation.

Antimicrobial Synergistic Effects of Linezolid and Vancomycin with a Small Synthesized 2-Mercaptobenzothiazole Derivative: A Challenge for MRSA Solving.

Methicillin-resistant Staphylococcus aureus (MRSA) emerged as one of the leading causes of persistent human infections and makes it difficult to treat bacteremia, especially with biofilm formation. In this work, we investigated the in vitro synergism between Linezolid (LNZ) and Vancomycin (VAN) with a 2-mercaptobenzothiazole derivative, resulting in a new small-molecule antibacterial compound that we named BTZ2e, on several clinical MRSA, MRSE (methicillin-resistant Staphylococcus epidermidis) and control (ATCC Collection) strains in their planktonic and biofilms cultures. The broth microdilution method evaluated the susceptibility of planktonic cells to each investigated antibiotic combined with BTZ2e. The biofilm's metabolic activity was studied with the XTT reduction assay. As a result, in this study, biofilm formation was significantly suppressed by the BTZ2e treatment. In terms of minimal biofilm inhibitory concentration (MBIC), BTZ2e revealed an MBIC50 value of 32 μg/mL against methicillin-susceptible S. aureus (MSSA) and 16 μg/mL against methicillin-resistant S. aureus ATCC 43300 biofilms. An inhibition range of 32 μg/mL and 256 μg/mL was registered for the clinical isolates. Interestingly, a synergistic effect (FICI ≤ 0.5) was encountered for the combination of BTZ2e with LNZ and VAN on several planktonic and sessile strains. In particular, the best result against planktonic cells emerged as a result of the synergistic association between LNZ and BTZ2e, while against sessile cells, the best synergistic association resulted from VAN and BTZ2e. The consistent results indicate BTZ2e as a promising adjuvant against multi-resistant strains such as MRSA and MRSE.

Stress corrosion cracking failure of X80 carbon steel U-bend caused by Desulfovibrio vulgaris biocorrosion

Sulfate reducing bacteria (SRB) are widely present in oil and gas industry, causing pitting corrosion on pipeline steel. Stress corrosion cracking (SCC) often occurs in the presence of mechanical stress before pitting perforation failure, leading to economic losses and even catastrophic accidents. In this study, stress distribution simulation using the finite element method (FEM), corrosion analysis techniques and electrochemical corrosion measurements were employed to investigate the SCC mechanism of X80 pipeline steel caused by Desulfovibrio vulgaris, which is a common SRB strain used in microbiologically influenced corrosion (MIC) studies. It was found that D. vulgaris MIC caused sharp microcracks on an X80 U-bend coupon after only 2 weeks of immersion at 37 °C in the deoxygenated ATCC 1249 culture medium inoculated with D. vulgaris. The X80 U-bend coupon's weight loss-based uniform corrosion rate for the 12 cm2 surface was 60% of that for the unstressed flat square coupon (2.3 mg cm−2 vs. 3.8 mg cm−2). This was likely because the square coupon had wide MIC pits, providing a larger effective surface area for more sessile cells (4.2×108 cells cm−2 on square coupon vs. 2.4×108 cells cm−2 on U-bend coupon) to attach and harvest more electrons. An SCC failure occurred on an X80 U-bend pre-cracked at the outer bottom after a 6-week immersion in the D. vulgaris broth. Apart from MIC damage, this could also be because D. vulgaris metabolism increased the availability hydrogen atoms on the steel surface, and promoted the diffusion of hydrogen atoms into the metal lattice, thus increasing the brittleness of the steel.

In Vitro Evaluation of Candida albicans Adhesion on Heat-Cured Resin-Based Dental Composites.

Microbial adhesion on dental restorative materials may jeopardize the restorative treatment long-term outcome. The goal of this in vitro study was to assess Candida albicans capability to adhere and form a biofilm on the surface of heat-cured dental composites having different formulations but subjected to identical surface treatments and polymerization protocols. Three commercially available composites were evaluated: GrandioSO (GR), Venus Diamond (VD) and Enamel Plus HRi Biofunction (BF). Cylindrical specimens were prepared for quantitative determination of C. albicans S5 planktonic CFU count, sessile cells CFU count and biomass optical density (OD570 nm). Qualitative Concanavalin-A assays (for extracellular polymeric substances of a biofilm matrix) and Scanning Electron Microscope (SEM) analyses (for the morphology of sessile colonies) were also performed. Focusing on planktonic CFU count, a slight but not significant reduction was observed with VD as compared to GR. Regarding sessile cells CFU count and biomass OD570 nm, a significant increase was observed for VD compared to GR and BF. Concanavalin-A assays and SEM analyses confirmed the quantitative results. Different formulations of commercially available resin composites may differently interact with C. albicans. The present results showed a relatively more pronounced antiadhesive effect for BF and GR, with a reduction in sessile cells CFU count and biomass quantification.

X80 U-bend stress corrosion cracking (SCC) crack tip dissolution by fast corroding Desulfovibrio ferrophilus IS5 biofilm

Stress corrosion cracking (SCC) is a serious problem threatening structural integrity and safety. Metal corrosion pits can develop into more harmful cracks under mechanical stress. It is known in abiotic corrosion that fast corrosion does not necessarily cause more severe SCC. This is because fast corrosion can prevent or dissolve crack tips and convert them into less harmful pits if the uniform corrosion rate is fast enough. This work experimentally proved the hypothesis that the same phenomenon occurs in biotic corrosion. It was found that a highly corrosive SRB (sulfate reducing bacterium) strain, namely Desulfovibrio ferrophilus (strain IS5), caused fast uniform corrosion and dull pits, but no SCC cracks against X80 carbon steel U-bend coupons (stressed). In comparison, Desulfovibrio vulgaris, a far less corrosive SRB strain caused less corrosion, but generated sharp pits and SCC cracks in a 3-month lab test. This work also revealed that the X80 U-bend had a 44% higher sessile cell count and 34% higher weight loss after a 14-d D. ferrophilus incubation in deoxygenated enriched artificial seawater culture medium at 28 °C when compared with the (flat) square coupons (no stress). This weight loss trend was corroborated by transient electrochemical measurements.

Ascending renal infection following experimental candiduria by Candida tropicalis in immunocompromised mice

The present study evaluated renal infection resulting from the implantation of C. tropicalis in the bladder of immunosuppressed mice. Yeasts were implanted in two manners: planktonic and via preformed biofilm on a small catheter fragment (SCF). Renal histopathology and cultures was performed 72 and 144 h after cystotomy was carried out in mice from three groups: group I contained non-contaminated mice implanted with a sterile SCF; group II mice received a sterile SCF plus a yeast suspension containing 1 × 107 yeasts/mL in a planktonic form; group III mice were implanted with a SCF containing preformed C. tropicalis biofilm. Viable yeasts were found in the kidneys of mice from both groups II and III. However, after 72 h the planktonic cells (group II) invaded more quickly than the sessile cells (group III). Over a longer period (144 h), group III exhibited a more invasive infection (50% of the animals presented renal infection and the renal fungal load was 3.2 log10 CFU/g tissue) than in group II, where yeasts were not found. C. tropicalis introduced into the bladder in two ways (in planktonic or biofilm form) were able to reach the kidney and establish a renal fungal infection, causing interstitial disorders. The data of the present study therefore support the hypothesis of an ascending pathway for renal infections by C. tropicalis. Furthermore, the biofilm resulted in a greater and progressive risk of renal infection, attributed to the slow detachment of the yeasts.

Mitigation of EH36 ship steel biocorrosion using an antimicrobial peptide as a green biocide enhancer

In this study, a 13-mer antimicrobial peptide (RRWRIVVIRVRRC) named by E6 was used as an enhancer of a green biocide to mitigate the biocorrosion of EH36 ship steel. Results show that a low concentration of E6 (100 nM) alone was no-biocidal and could not resist the Desulfovibrio vulgaris adhesion on the EH36 steel surface. However, E6 enhanced the bactericidal effect of tetrakis hydroxymethyl phosphonium sulfate (THPS). When E6 and THPS were both added to the bacteria and steel system, both the sessile D. vulgaris cells and biocorrosion rate of EH36 steel decreased significantly. Compared with the 80 ppm THPS alone treatment, the combination of 100 nM E6 + 80 ppm THPS led to an extra 1.6-log reduction in the sessile cell count. Fewer sessile D. vulgaris cells led to a lower extracellular electron transfer (EET) rate, directly resulting in 78% and 83% decreases in weight loss and pit depth of EH36 steel, respectively. E6 saved more than 50% of THPS dosage in this work to achieve a similar biocorrosion mitigation effect on EH36 steel.