Evaluation of Mangifera indica, Anacardium occidentale leaf extracts and 0.2% Chlorhexidine gluconate on disinfection of maxillofacial silicone material surface contaminated with microorganisms - An invitro study

Maintenance of the quality and hygiene of maxillofacial prosthesis allows to maintain the health of the residual tissues. Sampling of the maxillofacial prostheses has relieved presence of microbial colonization on silicone surfaces. Cleaning procedures of maxillofacial silicones are done using mechanical means or using adjunctive with chemical means. Cleaning with a 2-4% chlorhexidine gluconate spray or dipping in solution for a minute and then washing under running water can sufficiently condition to reduce the amount of bacterial contamination. Due to rising microorganism resistance and fewer adverse effects, phytoextracts appear to be a viable option. Additionally, the use of excipients derived from plants is provides new opportunities for the pharmaceutical industry into the creation of innovative pharmaceutical products that are sustainable.

Aim

To evaluate and compare the leaf extracts of Mangifera indica (M.indica), Anacardium occidentale(A.occidentale) and 0.2% chlorhexidine gluconate (CHX) on disinfection of maxillofacial silicone material surface contaminated with Staphylococcus aureus (S.aureus) and Candida albicans (C.albicans).

Methods

Of the 150 maxillofacial silicone elastomer silicone samples, 75 samples were contaminated with S. aureus and 75 with C.albicans. The contaminated disc was rolled on blood agar and pre-disinfection Colony Forming Units (CFU) were evaluated followed by subjecting the discs to disinfection protocols. The contaminated discs with S. aureus and C.albicans were disinfected using M.indica leaf extracts, A.occidentale leaf extracts and 0.2% CHX for 10 min. Post-disinfection CFUs were evaluated by rolling the disc on blood agar. The results were tabulated and analysed using dependent t-test, one-way ANOVA and Tukeys multiple posthoc procedure.

Results

Pair-wise comparison of pre-and post-disinfection log CFU counts of S.aureus gave a statistical significance between 0.2% CHX and and M.indica leaf extract. No statistically significant results were found between 0.2% CHX and A.occidentale. Pair wise comparison of the log CFU from pre-disinfection to post-disinfection of C.albicans gave a statistical significance between all the three groups.

Conclusions

In the present study A.occidentale leaf extract and M.indica leaf extract have shown significant reduction in CFU of both the organisms. 0.2% CHX showed the most CFU reduction post disinfection of maxillofacial silicone material surface contaminated S.aureus and C.albicans followed by A.occidentale leaf extracts and M.indica leaf extracts. Given the limitations of the current research, A.occidentale leaf extract and M.indica leaf extract can be used as an alternative for disinfection of maxillofacial silicone prosthesis.

Structurally stable but functionally disrupted marine microbial communities under a future climate change scenario: Potential importance for nitrous oxide emissions

The blue mussel Mytilus edulis is a widespread and abundant bivalve species along the North Sea with high economic and ecological importance as an engineer species. The shell of mussels is intensively colonized by microbial organisms that can produce significant quantities of nitrous oxide (N2O), a potent greenhouse gas. To characterize the impacts of climate change on the composition, structure and functioning of microbial biofilms on the shell surface of M. edulis, we experimentally exposed them to orthogonal combinations of increased seawater temperature (20 vs. 23 °C) and decreased pH (8.0 vs. 7.7) for six weeks. We used amplicon sequencing of the 16S rRNA gene to characterize the alpha and beta diversity of microbial communities on the mussel shell. The functioning of microbial biofilms was assessed by measuring aerobic respiration and nitrogen emission rates. We did not report any significant impacts of climate change treatments on the diversity of mussel microbiomes nor on the structure of these communities. Lowered pH and increased temperature had antagonistic effects on the functioning of microbial communities with decreased aerobic respiration and N2O emission rates of microbial biofilms in acidified seawater compared to increased rates in warmer conditions. An overriding impact of acidification over warming was finally observed on N2O emissions when the two factors were combined. Although acidification and warming in combination significantly reduced N2O biofilm emissions, the promotion of aquaculture activities in coastal waters where shellfish do not normally occur at high biomass and density could nonetheless result in unwanted emissions of this greenhouse gas in a near future.

Advancing understanding of microbial biofilms through machine learning-powered studies

Microbial biofilms are prevalent in various environments and pose significant challenges to food safety and public health. The biofilms formed by pathogens can cause food spoilage, foodborne illness, and infectious diseases, which are difficult to treat due to their enhanced antimicrobial resistance. While the composition and development of biofilms have been widely studied, their profound impact on food, the food industry, and public health has not been sufficiently recapitulated. This review aims to provide a comprehensive overview of microbial biofilms in the food industry and their implication on public health. It highlights the existence of biofilms along the food-producing chains and the underlying mechanisms of biofilm-associated diseases. Furthermore, this review thoroughly summarizes the enhanced understanding of microbial biofilms achieved through machine learning approaches in biofilm research. By consolidating existing knowledge, this review intends to facilitate developing effective strategies to combat biofilm-associated infections in both the food industry and public health.

Staphylococcus aureus microbial biofilms degradation using cellobiose dehydrogenase from Thermothelomyces thermophilus M77

This work reports biochemical characterization of Thermothelomyces thermophilus cellobiose dehydrogenase (TthCDHIIa) and its application as an antimicrobial and antibiofilm agent. We demonstrate that TthCDHIIa is thermostable in different ionic solutions and is capable of oxidizing multiple mono and oligosaccharide substrates and to continuously produce H2O2. Kinetics measurements depict the enzyme catalytic characteristics consistent with an Ascomycota class II CDH. Our structural analyses show that TthCDHIIa substrate binding pocket is spacious enough to accommodate larger cello and xylooligosaccharides. We also reveal that TthCDHIIa supplemented with cellobiose reduces the viability of S. aureus ATCC 25923 up to 32 % in a planktonic growth model and also inhibits its biofilm growth on 62.5 %. Furthermore, TthCDHIIa eradicates preformed S. aureus biofilms via H2O2 oxidative degradation of the biofilm matrix, making these bacteria considerably more susceptible to gentamicin and tetracycline.

WssI from the Gram-Negative Bacterial Cellulose Synthase is an O-acetyltransferase that Acts on Cello-oligomers with Several Acetyl Donor Substrates

In microbial biofilms, bacterial cells are encased in a self-produced matrix of polymers (e.g., exopolysaccharides) that enable surface adherence and protect against environmental stressors. For example, the wrinkly spreader phenotype of Pseudomonas fluorescens colonizes food/water sources and human tissue to form robust biofilms that can spread across surfaces. This biofilm largely consists of bacterial cellulose produced by the cellulose synthase proteins encoded by the wss operon, which also occurs in other species, including pathogenic Achromobacter species. Although phenotypic mutant analysis of the wssFGHI genes has previously shown that they are responsible for acetylation of bacterial cellulose, their specific roles remain unknown and distinct from the recently identified cellulose phosphoethanolamine modification found in other species. Here we have purified the C-terminal soluble form of WssI from P. fluorescens and A. insuavis and demonstrated acetyl-esterase activity with chromogenic substrates. The kinetic parameters (k_cat/K_M values of 13 and 8.0 M^-1∙ s^-1, respectively) indicate that these enzymes are up to four times more catalytically efficient than the closest characterized homolog, AlgJ from the alginate synthase. Unlike AlgJ and its cognate alginate polymer, WssI also demonstrated acetyltransferase activity onto cellulose oligomers (e.g., cellotetraose to cellohexaose) with multiple acetyl-donor substrates (pNP-Ac, MU-Ac and acetyl-CoA). Finally, a high-throughput screen identified three low micromolar WssI inhibitors that may be useful for chemically interrogating cellulose acetylation and biofilm formation.

Smart delivery systems for microbial biofilm therapy: Dissecting design, drug release and toxicological features

Bacterial biofilms are highly protected surface attached communities of bacteria that typically cause chronic infections. To address their recalcitrance to antibiotics and minimise side effects of current therapies, smart drug carriers are being explored as promising platforms for antimicrobials. Herein, we briefly summarize recent efforts and considerations that have been applied in the design of these smart carriers. We guide readers on a journey on how they can leverage the inherent biofilm microenvironment, external stimuli, or combine both types of stimuli in a predictable manner. The specific carrier features that are responsible for their 'on-demand' properties are detailed and their impact on antibiofilm property are further discussed. Moreover, an analysis on the impact of such features on drug release profiles is provided. Since nanotechnology represents a significant slice of the drug delivery pie, some insights on the potential toxicity are also depicted. We hope that this review inspires researchers to use their knowledge and creativity to design responsive systems that can eradicate biofilm infections.

Responses of submerged macrophyte Ceratophyllum demersum to the gradient concentrations of microcystin-LR (MC-LR)

The responses of Ceratophyllum demersum to gradient concentrations (0, 0.8, 3.2, and 10 µg/L) of microcystin-LR (MC-LR) were comprehensively investigated by laboratory simulation experiments. The high reduction and accumulation efficiency of MC-LR by C. demersum were verified in this study. Results showed that the reduction ratio of MC-LR in the cultivation medium was up to 99% after 14 days of exposure, and the accumulation of MC-LR in C. demersum was highest at an exposure concentration of 10 μg/L, the value of which was 0.9 ng/g fresh weight (FW). Meanwhile, a series of negative effects on C. demersum was detectable, accompanied by a significant biomass reduction of the plant and changes in microbial community composition. In particular, this study indicated that the amount of Flavobacteria was elevated under the stress of MC-LR, provoking great threats to aquatic ecosystems. Moreover, oxidative damage was evidenced by the changes in total antioxidant capacity, superoxide dismutase, and glutathione. The results also demonstrated significant increases in sugar (0.025 mg/g FW), protein (0.3 mg/g FW), and carotenoids (0.6 mg/g FW) in C. demersum stressed by 10 μg/L of MC-LR, compared with the control without microcystins, which were among the defense strategies for dealing with adverse conditions. These results verified the good potential of submerged macrophytes as an eco-friendly strategy for controlling cyanobacterial blooms. However, the negative effects of MC-LR on the macrophytes themselves were also demonstrated, which would be considered in future practice and management.

Microplastic pollution in fragile coastal ecosystems with special reference to the X-Press Pearl maritime disaster, southeast coast of India

Microplastics (MPs) are a global environmental concern and pose a serious threat to marine ecosystems. This study aimed to determine the abundance and distribution of MPs in beach sediments (12 beaches), marine biota (6 beaches) and the influence of microbes on MPs degradation in eco-sensitive Palk Bay and Gulf of Mannar coast. The mean MP abundance 65.4 ± 39.8 particles/m² in beach sediments; 0.19 ± 1.3 particles/individual fish and 0.22 ± 0.11 particles g^-1 wet weight in barnacles. Polyethylene fragments (33.4%) and fibres (48%) were the most abundant MPs identified in sediments and finfish, respectively. Histopathological examination of fish has revealed health consequences such as respiratory system damage, epithelial degradation and enterocyte vacuolization. In addition, eight bacterial and seventeen fungal strains were isolated from the beached MPs. The results also indicated weathering of MPs due to microbial interactions. Model simulations helped in tracking the fate and transboundary landfall of spilled MPs across the Indian Ocean coastline after the X-Press Pearl disaster. Due to regional circulations induced by the monsoonal wind fields, a potential dispersal of pellets has occurred along the coast of Sri Lanka, but no landfall and ecological damage are predicted along the coast of India.

Inhibition and disintegration of Bacillus subtilis biofilm with small molecule inhibitors identified through virtual screening for targeting TasA(28-261), the major protein component of ECM

Microbial biofilms have been recognized for a vital role in antibiotic resistance and chronic microbial infections for 2-3 decades; still, there are no 'anti-biofilm drugs' available for human applications. There is an urgent need to develop novel 'anti-biofilms' therapeutics to manage biofilm-associated infectious diseases. Several reports have suggested that targeting molecules involved in quorum sensing or biofilm-specific transcription may inhibit biofilm formation. However, the possibility of targeting other vital components of microbial biofilms, especially the extracellular matrix (ECM) components, has remained largely unexplored. Here we report targeting TasA_(28-261), the major proteinaceous component of Bacillus subtilis ECM with two small molecule inhibitors (lovastatin and simvastatin) identified through virtual screening and drug repurposing, resulted in complete inhibition of biofilm. In molecular docking and dynamics simulation studies, lovastatin was observed to make stable interactions with TasA_(28-261), whereas the simvastatin - TasA_(28-261) interactions were relatively less stable. However, in subsequent in vitro studies, both lovastatin and simvastatin successfully inhibited B. subtilis biofilm formation at MIC values of < 10 µg/ml. Besides, these potential inhibitors also caused the disintegration of pre-formed biofilms. Results presented here provide 'proof of concept' for the hypothesis that targeting the extracellular matrix's vital component(s) could be one of the most efficient approaches for inhibiting microbial biofilms and disintegrating the pre-formed biofilms. We propose that a similar approach targeting ECM-associated proteins with FDA-approved drugs could be implemented to develop novel anti-biofilm therapeutic strategies against biofilm-forming chronic microbial pathogens.Communicated by Ramaswamy H. Sarma.

Regulatory network controls microbial biofilm development, with Candida albicans as a representative: from adhesion to dispersal

Microorganisms mainly exist in the form of biofilm in nature. Biofilm can contaminate food and drinking water system, as well as cause chronic wound infections, thereby posing a potential threat to public health safety. In the last two decades, researchers have made efforts to investigate the genetic contributors control different stages of biofilm development (adherence, initiation, maturation, and dispersal). As an opportunistic pathogen, C. albicans causes severe superficial or systemic infections with high morbidity and mortality under conditions of immune dysfunction. It has been reported that 80% of C. albicans infections are directly or indirectly associated with biofilm formation on host or abiotic surfaces including indwelling medical devices, resulting in high morbidity and mortality. Significantly, the outcome of C. albicans biofilm development includes enhanced invasion, exacerbated inflammatory responses and intrinsic resistance to antimicrobial chemotherapy. Thus, this review aimed at providing a comprehensive overview of the regulatory network controls microbial biofilm development, with C. albicans as a representative, served as reference for therapeutic targets.

Microbial biofilms in biorefinery - Towards a sustainable production of low-value bulk chemicals and fuels

Harnessing the potential of biocatalytic conversion of renewable biomass into value-added products is still hampered by unfavorable process economics. This has promoted the use of biofilms as an alternative to overcome the limitations of traditional planktonic systems. In this paper, the benefits and challenges of biofilm fermentations are reviewed with a focus on the production of low-value bulk chemicals and fuels from waste biomass. Our study demonstrates that biofilm fermentations can potentially improve productivities and product yields by increasing biomass retention and allowing for continuous operation at high dilution rates. Furthermore, we show that biofilms can tolerate hazardous environments, which improve the conversion of crude biomass under substrate and product inhibitory conditions. Additionally, we present examples for the improved conversion of pure and crude substrates into bulk chemicals by mixed microbial biofilms, which can benefit from microenvironments in biofilms for synergistic multi-species reactions, and improved resistance to contaminants. Finally, we suggest the use of mathematical models as useful tools to supplement experimental insights related to the effects of physico-chemical and biological phenomena on the process. Major challenges for biofilm fermentations arise from inconsistent fermentation performance, slow reactor start-up, biofilm carrier costs and carrier clogging, insufficient biofilm monitoring and process control, challenges in reactor sterilization and scale-up, and issues in recovering dilute products. The key to a successful commercialization of the technology is likely going to be an interdisciplinary approach. Crucial research areas might include genetic engineering combined with the development of specialized biofilm reactors, biofilm carrier development, in-situ biofilm monitoring, model-based process control, mixed microbial biofilm technology, development of suitable biofilm reactor scale-up criteria, and in-situ product recovery.

Investigation of materials for reactive permeable barrier in removing cadmium and chromium(VI) from aquifer near a solid domestic waste landfill

The sorption characteristics of raw and biofilm-coated materials: vermiculite, lightweight expanded clay aggregate (LECA), perlite, zeolite, and shungite toward Cd and Cr(VI) ions were investigated to evaluate the possibility of their use as filtration barrier in the aquifer near a solid domestic waste landfill. The effectiveness of Cr(VI) removal by the raw materials changed in the following order: shungite > zeolite > perlite > vermiculite > LECA and for Cd: zeolite > shungite > vermiculite > perlite > LECA. After biofilm formation on the surface of the materials, the sorption capacity increased in some (perlite, LECA), while in others (zeolite) it was reduced. Four kinetic models were used to describe the experimental data. Mechanisms of metal removal were proposed: for Cr(VI), a characteristic combination of sorption processes was suggested, while the removal of Cd ions could occur by ion exchange and by complexation on the surface of the sorbent. Cr(VI) reduction by living bacterial cells forming a biofilm on the sorbent surface was assessed.

Increased antibiotic efficacy and noninvasive monitoring of Staphylococcus epidermidis biofilms using per-cysteamine-substituted γ-cyclodextrin - A delivery effect validated by fluorescence microscopy

Limited and poor delivery of antibiotics is cited as one reason for the difficulty in treating antibiotic-resistant biofilms associated with chronic infections. We investigate the effectiveness of a positively charged, single isomer cyclodextrin derivative, octakis[6-(2-aminoethylthio)-6-deoxy]-γ-CD (γCys) to improve the delivery of antibiotics to biofilms. Using multiphoton laser scanning microscopy complemented with super-resolution fluorescence microscopy, we showed that γCys tagged with fluorescein (FITC) is uniformly distributed throughout live S. epidermidis biofilm cultures in vitro and results suggest it is localized extracellularly in the biofilm matrix. NMR spectroscopic data in aqueous solution confirm that γCys forms inclusion complexes with both the antibiotics oxacillin and rifampicin. Efficacy of γCys/antibiotic (oxacillin and rifampicin) was measured in the biofilms. While treatment with γCys/oxacillin had little improvement over oxacillin alone, γCys/rifampicin reduced the biofilm viability to background levels demonstrating a remarkable improvement over rifampicin alone. The strong synergistic effect for γCys/rifampicin is at this stage not clearly understood, but plausible explanations are related to increased solubility of rifampicin upon complexation and/or synergistic interference with components of the biofilm. The results demonstrate that designed cyclodextrin nanocarriers, like γCys, efficiently deliver suitable antibiotics to biofilms and that fluorescence microscopy offers a novel approach for mechanistic investigations.

Computational investigation for modeling the protein-protein interaction of TasA(28-261)-TapA(33-253): a decisive process in biofilm formation by Bacillus subtilis

Biofilms have a significant role in microbial persistence, antibiotic resistance, and chronic infections; consequently, there is a pressing need for development of novel "anti-biofilm strategies." One of the fundamental mechanisms involved in biofilm formation is protein-protein interactions of "amyloid-like proteins" (ALPs) in the extracellular matrix. Such interactions could be potential targets for development of novel anti-biofilm strategies; therefore, assessing the structural features of these interactions could be of great scientific value. Characterization of structural features the of protein-protein interaction with conventional structure biology tools including X-ray diffraction and nuclear magnetic resonance is technically challenging, expensive, and time-consuming. In contrast, modeling such interactions is time-efficient and economical, and might provide deeper understanding of structural basis of interactions. Although it is often acknowledged that molecular modeling methods have varying accuracy, their careful implementation with supplementary verification methods can provide valuable insight and directions for future studies. With this reasoning, during the present study, the protein-protein interaction of TasA_(28-261)-TapA_(33-253) (which is a decisive process for biofilm formation by Bacillus subtilis) was modeled using in silico approaches, viz., molecular modeling, protein-protein docking, and molecular dynamics simulations. Results obtained here identified amino acid residues present within intrinsically disordered regions of both proteins to be critical for interaction. These results were further supported with principal component analyses (PCA) and free energy landscape (FEL) analyses. Results presented here represent novel finding, and we hypothesize that amino acid residues identified during the present study could be targeted for inhibition of biofilm formation by B. subtilis.

Photo-sonodynamic antimicrobial chemotherapy via chitosan nanoparticles-indocyanine green against polymicrobial periopathogenic biofilms: Ex vivo study on dental implants

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) is a treatment to deal with microorganisms, which is limited to treating microbial biofilms due to poor light penetration. Sonodynamic antimicrobial chemotherapy (SACT) can be used for circumventing the limitations of aPDT to inhibit the polymicrobial biofilms. The objective of this study has been focused on the simultaneous use of aPDT and SACT, which is called photo-sonodynamic antimicrobial chemotherapy (P-SACT) to inhibit the biofilms of periopathogens bacteria on surfaces of the titanium dental implants.

MATERIALS AND METHODS

Following synthesis and confirmation of Chitosan Nanoparticles-Indocyanine green (CNPs-ICG) as photo-sonosensitizer, the mature biofilm model of the polymicrobial synergism of periopathogens was formed on the surface of the titanium dental implants. The quantitative and qualitative evaluations of periopathogens biofilms were performed using microbial viability and scanning electron microscopy analysis of the following groups of treatment modalities (n = 5): 1- Control (periopathogens biofilm without treatment), 2- ICG, 3- CNPs-ICG, 4- diode laser, 5- aPDT/ICG, 6- aPDT/CNPs-ICG, 7- ultrasound, 8- SACT/ICG, 9- SACT/CNPs-ICG, 10- PSACT/ICG, 11- PSACT/CNPs-ICG, and 12-0.2% chlorhexidine (CHX).

RESULTS

A significant reduction in the log₁₀ CFU/mL of periopathogens was observed in the groups treated with aPDT/ICG, aPDT/CNPs-ICG, SACT/ICG, SACT/CNPs-ICG, PSACT/ICG, PSACT/CNPs-ICG, and 0.2% CHX up to 5.3, 6.5, 5.6, 6.6, and 8.8 log, respectively, when compared with control group (P < 0.05). PSACT/CNPs-ICG group demonstrated significantly higher capacity in eliminating the periopathogens biofilm compared with other groups (P < 0.05). However, there was no significant difference between PSACT/CNPs-ICG and 0.2% CHX (P > 0.05). Microscopic images revealed that biofilms treated with PSACT were comprised mainly of deformed and dead cells.

CONCLUSIONS

These results highlight the potential of PSACT/CNPs-ICG for the decontamination of the dental implant surfaces from the polymicrobial synergism of periopathogens biofilm.

High-resolution imaging reveals microbial biofilms on patient urinary catheters despite antibiotic administration

PURPOSE

Catheter-associated urinary tract infections (CAUTIs) are a significant cause of morbidity worldwide, as they account for 40% of all hospital-associated infections. Microbial biofilm formation on urinary catheters (UCs) limits antibiotic efficacy, making CAUTI extremely difficult to treat. To gain insight into the spatiotemporal microbe interactions on the catheter surface we sought to determine how the presence or absence of bacteriuria prior to catheterization affects the organism that ultimately forms a biofilm on the UC and how long after catheterization they emerge.

METHODS

Thirty UCs were collected from patients who received a urine culture prior to catheterization, a UC, and antibiotics as part of standard of care. Immunofluorescence imaging and scanning electron microscopy were used to visualize patient UCs.

RESULTS

Most patients did not have bacteria in their urine (based on standard urinalysis) prior to catheterization, yet microbes were detected on the majority of UCs, even with dwell times of < 3 days. The most frequently identified microbes were Staphylococcus epidermidis, Enterococcus faecalis, and Escherichia coli.

CONCLUSIONS

This study indicates that despite patients having negative urine cultures and receiving antibiotics prior to catheter placement, microbes, including uropathogens associated with causing CAUTI, could be readily detected on UCs with short dwell times. This suggests that a potential microbial catheter reservoir can form soon after placement, even in the presence of antibiotics, which may serve to facilitate the development of CAUTI. Thus, removing and/or replacing UCs as soon as possible is of critical importance to reduce the risk of developing CAUTI.

Portraying manganese biofilms via a merger of EPR spectroscopy and cathodic polarization

Microbial biofilms on stainless steel surfaces exposed to water from a freshwater pond were dominated by manganese-oxidizing bacteria, as initially diagnosed by microscopy and elemental analysis. The application of electron paramagnetic resonance (EPR) spectroscopy revealed conspicuous sextet (six-line) patterns that intensified with immersion time, implying the gradual accumulation of Mn(II) in the biofilms. Correspondingly, cathodic polarization designated the manganese oxide (MnO_x) reduction peak in the form of a distinctive 'nose', which grew increasingly more negative with biofilm growth. The progressive expansion of cathodic current densities and the concurrent area-under-the-curve also allowed the quantification of microbially mediated MnO_x deposition_. Furthermore, the merger of EPR and cathodic polarization techniques yielded key insights, in tandem with Mn speciation data, into the pathways of microbial manganese transformations in biofilms, besides providing meaningful interpretations of prevailing literature. Accordingly, the natural freshwater biofilm was inferred as one supporting a complete manganese cycle encompassing multiple redox states.

Variations in the abundance and structural diversity of microbes forming biofilms in a thermally stressed coral reef system

Little information is known about biofilm formation in the thermally stressed coral reef systems north of the Arabian Gulf. The current study investigates the abundance and diversity of marine microbes involved in biofilm formation and their succession over a period of 14 weeks (May-August 2007) at temperatures exceeding 32 °C. The results showed variations in microbial numbers and the development of more stable biofilm communities as the biofilms aged. The culture-dependent technique and microscopic examination of the developed biofilms showed the dominance of key species known for their role in precipitating CaCO3 such as Vibrio and in facilitating coral larvae settlement and metamorphosis such as Pseudoalteromonas, Bacillariophyceae and Rhodophyceae. The results revealed biofilm formations with microbial diversities that have the potential to support the larval settlement and metamorphism of marine organisms and to consolidate and stabilize biofilms via the process of calcification in the thermally stressed coral reef system considered herein.

Toxicity of ciprofloxacin and sulfamethoxazole to marine periphytic algae and bacteria

Ciprofloxacin and sulfamethoxazole are two antibiotics commonly detected in the aquatic environment, but information on their toxicity towards natural microbial communities is largely absent. In particular no data are available for marine microorganisms. The aim of the current study was therefore to evaluate the chronic toxicity of ciprofloxacin and sulfamethoxazole to natural marine biofilms (periphyton), a complex ecological community comprising a variety of bacterial and algal species. The biofilms were sampled along the Swedish west coast and subsequently exposed over 4 days in a semi-static system to a concentration series of each antibiotic. Effects on the bacterial part of the periphyton community were assessed using Biolog Ecoplates, reflecting total respiration and functional diversity of the bacterial community. Exposure to either antibiotic resulted in a clear concentration-response relationship with EC10 and EC50 values for the inhibition of total carbon source utilization of 46.1nmol/L and 490.7nmol/L for ciprofloxacin, and 56nmol/L and 1073nmol/L for sulfamethoxazole. The NOEC for ciprofloxacin was 26nmol/L, with a minimum significant difference of 19.24%, for sulfamethoxazole it was 140nmol/L with a minimum significant difference of 14%. Multivariate data exploration of the whole carbon source utilization pattern confirmed these results. The data indicate that sulfamethoxazole leads to a general decrease in carbon source utilization, while ciprofloxacin exposure leads to a re-arrangement of the carbon-utilization pattern in the region of 20- 50% effect. This corresponds with the higher specificity of ciprofloxacin for certain bacterial species. Effects on the algal part of the communities were evaluated by analyzing the amount and composition of photosynthetic pigments, and neither ciprofloxacin nor sulfamethoxazole caused any inhibitory effects up to the maximum tested concentration of 9000nmol/L. However, sulfamethoxazole exposure did lead to a significant stimulation (75% above control level) of the total pigment content of the biofilm already at the lowest tested concentration of 5nmol/L. The stimulation then decreased with increasing concentrations to finally return to control level at 3000nmol/L. No shifts in the relative pigment composition were observed, indicating a generally increased algal biomass without major shifts in community composition.

Triclosan causes toxic effects to algae in marine biofilms, but does not inhibit the metabolic activity of marine biofilm bacteria

Effects of the antimicrobial agent triclosan to natural periphyton communities (biofilms, comprising primarily microalgae and bacteria) were assessed in two independent experiments during spring and summer. For that purpose a semi-static test system was used in which periphyton was exposed to a concentration range of 5-9054 nmol/L triclosan. Effects on algae were analyzed as content and composition of photosynthetic pigments. The corresponding EC50 values were 39.25 and 302.45 nmol/L for the spring and summer experiment, respectively. Effects on periphytic bacteria were assessed as effects on carbon utilization patterns, using Biolog Ecoplates. No inhibition of either total carbon utilization or functional diversity was observed, indicating a pronounced triclosan tolerance of the marine bacteria. In contrast, a small stimulation of the total carbon utilization was observed at triclosan concentrations exceeding 100 nmol/L.