Overview of multi-species biofilms in different ecosystems: wastewater treatment, soil and oral cavity

The role of human extracellular matrix proteins in defining Staphylococcus aureus biofilm infections

Twenty to forty one percent of the world's population is either transiently or permanently colonized by the Gram-positive bacterium, Staphylococcus aureus. In 2017, the CDC designated methicillin-resistant S. aureus (MRSA) as a serious threat, reporting ∼300 000 cases of MRSA-associated hospitalizations annually, resulting in over 19 000 deaths, surpassing that of HIV in the USA. S. aureus is a proficient biofilm-forming organism that rapidly acquires resistance to antibiotics, most commonly methicillin (MRSA). This review focuses on a large group of (>30) S. aureus adhesins, either surface-associated or secreted that are designed to specifically bind to 15 or more of the proteins that form key components of the human extracellular matrix (hECM). Importantly, this includes hECM proteins that are pivotal to the homeostasis of almost every tissue environment [collagen (skin), proteoglycans (lung), hemoglobin (blood), elastin, laminin, fibrinogen, fibronectin, and fibrin (multiple organs)]. These adhesins offer S. aureus the potential to establish an infection in every sterile tissue niche. These infections often endure repeated immune onslaught, developing into chronic, biofilm-associated conditions that are tolerant to ∼1000 times the clinically prescribed dose of antibiotics. Depending on the infection and the immune response, this allows S. aureus to seamlessly transition from colonizer to pathogen by subtly manipulating the host against itself while providing the time and stealth that it requires to establish and persist as a biofilm. This is a comprehensive discussion of the interaction between S. aureus biofilms and the hECM. We provide particular focus on the role of these interactions in pathogenesis and, consequently, the clinical implications for the prevention and treatment of S. aureus biofilm infections.

Correlation between use of different type protective facemasks and the oral ecosystem

BACKGROUND

Spread worldwide through droplets, the Virus Sars-Cov-19 has caused a global health emergency alarm. In order to limit its spread, the use of masks has become part of the daily life of the entire population, however, little is known about its constant use and the changes generated in the oral cavity. This work aims to investigate correlations between the continuous use of masks covering the nose and mouth for 3 h and changes in the ecological factors of the oral cavity.

METHODS

34 volunteers were divided into 2 groups: wear only the filtering facepiece code 2 (FFP2) mask (Group A) and wear the FFP2 mask covered by a surgical mask (Group B). Measurement of Volatile Organic Compounds (VOCs), saliva rehydration and consistency test, collection of basal saliva and saliva stimulated with paraffin gum and mucosal swab were collected and analyzed at two times: before using the mask(s) (T0) and 3 h after continuous use of the mask(s) (T1).

RESULTS

The results indicated a significant difference between the groups, in which the basal saliva volume and pH and the peaks of VOCs increased for group B between T0 and T1. The rehydration time decreased and the volume and pH of the stimulated saliva increased, but with no significant difference between the groups. Furthermore, group B showed a significant decrease in Candida albicans Colony Forming Units (CFUs) and Total Bacterial Count (TBC) between T0 and T1.

CONCLUSION

It is concluded that the prolonged use of the FFP2 mask covered by a surgical mask can generate oral alterations in the user.

Antimicrobial activity of phytofabricated silver nanoparticles using Carica papaya L. against Gram-negative bacteria

Background and Aim

Antibiotic resistance, especially in Gram-negative bacteria, is a major public health risk affecting all industries requiring the use of antibiotics, including agriculture and animal breeding. This study aimed to use papaya extracts to synthesize silver nanoparticles (AgNPs) and evaluate their antimicrobial activity against various Gram-negative bacteria.

Materials and Methods

Silver nanoparticles were synthesized from the aqueous extracts of papaya seed, root, and bark, with AgNO3 used as a reducing agent. The phytofabricated AgNPs were analyzed by ultraviolet-visible absorbance, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, and photon cross-correlation spectroscopy (PCCS). The disc-diffusion method was used to perform antibacterial analysis, and the minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations were determined. We also investigated the antibiofilm activity of AgNPs and attempted to elucidate the potential mechanism of action on Escherichia coli ATCC 25922.

Results

Phytofabrication of AgNPs was successful with papaya root (PR-AgNPs) and papaya seed (PS-AgNPs), but not with papaya bark. Silver nanoparticles using papaya root and PS-AgNPs were both cubic and showed maximum absorbances of 2.6 and 0.3 AUs at 411.6 and 416.8 nm wavelengths and average hydrodynamic diameters X50 of 59.46 ± 7.03 and 66.57 ± 8.89 nm, respectively. The Ag in both AgNPs was confirmed by X-ray fluorescence by a distinctive peak in the spectrum at the silver Kα line of 22.105 keV. Both AgNPs exhibited broad-spectrum antimicrobial and antibiofilm activity against all Gram-negative bacteria, and PR-AgNPs were slightly better than AgNPs-PS. The MIC ranged from 16 μg/mL-128 μg/mL and 16 μg/mL-64 μg/mL, respectively, for PS-AgNPs and PR-AgNPs. The elucidation of the mechanism of action revealed interference with E. coli ATCC 25922 growth kinetics and inhibition of H+-ATPase proton pumps.

Conclusion

Papaya seed and root extracts were efficient reducing agents for the biogenic synthesis of AgNPs, with noteworthy antibacterial and antibiofilm activities. Future studies should be conducted to identify the phytochemicals and the mechanism involved in AgNPs synthesis.

Biofilm-based technology for industrial wastewater treatment: current technology, applications and future perspectives

The microbial community in biofilm is safeguarded from the action of toxic chemicals, antimicrobial compounds, and harsh/stressful environmental circumstances. Therefore, biofilm-based technology has nowadays become a successful alternative for treating industrial wastewater as compared to suspended growth-based technologies. In biofilm reactors, microbial cells are attached to static or free-moving materials to form a biofilm which facilitates the process of liquid and solid separation in biofilm-mediated operations. This paper aims to review the state-of-the-art of recent research on bacterial biofilm in industrial wastewater treatment including biofilm fundamentals, possible applications and problems, and factors to regulate biofilm formation. We discussed in detail the treatment efficiencies of fluidized bed biofilm reactor (FBBR), trickling filter reactor (TFR), rotating biological contactor (RBC), membrane biofilm reactor (MBfR), and moving bed biofilm reactor (MBBR) for different types of industrial wastewater treatment. Besides, biofilms have many applications in food and agriculture, biofuel and bioenergy production, power generation, and plastic degradation. Furthermore, key factors for regulating biofilm formation were also emphasized. In conclusion, industrial applications make evident that biofilm-based treatment technology is impactful for pollutant removal. Future research to address and improve the limitations of biofilm-based technology in wastewater treatment is also discussed.

The potency of herbal extracts and its green synthesized nanoparticle formulation as antibacterial agents against Streptococcus mutans associated biofilms

This study aims to determine the effects of the extracts of Streblus asper, Cymbopogon citratus, Syzygium aromaticum and its formulation of green synthesized silver nanoparticle (AgNPs) on Streptococcus mutans growth and biofilm formation. The ethanolic extracts of S. asper, C. citratus, S. aromaticum, and a mix of the three herbs demonstrated antibacterial activity against S. mutans isolates by reducing bacterial biofilm formation and decreasing bacterial cell surface hydrophobicity. The formulated AgNPs from the ethanolic extracts could enhance the antibacterial activities of the plant extracts. Molecular docking found the best interaction between luteolin isolated from C. citratus and glucosyltransferase protein (GtfB), assuming the promising anti-biofilm activity. The scanning electron microscopy revealed morphological changes in the biofilm structure and a significant decrease in the biofilm area of the AgNPs treated. The study suggested that the extracts and its application could be used as natural alternative agents with multi-action against S. mutans infections.

Phytochemical Analysis, Antibacterial and Antibiofilm Activities of Aloe vera Aqueous Extract against Selected Resistant Gram-Negative Bacteria Involved in Urinary Tract Infections

In bacterial infections, including urinary tract infections (UTIs), the gap between the development of new antimicrobials and antimicrobial resistance is dramatically increasing, especially in Gram-negative (Gram–) bacteria. All healthy products that can be used per se or that may be sources of antibacterial compounds should be considered in the fight against this major public health threat. In the present study, the phytochemical composition of Aloe vera extract was investigated by HPLC–MS/MS, and we further evaluated its antibacterial and antibiofilm formation activity against selected resistant Gram– bacteria involved in UTIs, namely, Achromobacter xylosoxidans 4892, Citrobacter freundii 426, Escherichia coli 1449, Klebsiella oxytoca 3003, Moraxella catarrhalis 4222, Morganella morganii 1543, Pseudomonas aeruginosa 3057, and a reference strain E. coli ATCC 25922. Inhibition zones (IZs) of the extract were determined using the well diffusion method, minimum inhibitory (MIC), and bactericidal (MBC) concentration by the two-fold serial microdilution assay, and antibiofilm formation activity by the crystal violet attachment assay. Aloe-emodin and its derivatives were the major constituent (75.74%) of A. vera extract, the most important of them being aloesin (30.22%), aloe-emodin-diglucoside (12.58%), and 2′-p-methoxycoumaroylaloeresin B (9.64%). The minerals found in the extract were sulfur (S), silicon (Si), chlorine (Cl), potassium (K), and bromine (Br). Except for the clinical strain E. coli 1449, which was totally non-susceptible, A. vera demonstrated noteworthy antibacterial activity with MIC and MBC values ranging from 0.625 to 5 mg/mL and 5 to 10 mg/mL, respectively. A. vera also demonstrated dose-dependent antibacterial effects, and the reference strain E. coli ATCC 25922 was the most susceptible with MIC = 0.625 and IZ = 19 mm at 20 mg/mL. The antibiofilm formation potential of A. vera extract was strong at 2MIC and MIC (93–100% of biofilm formation inhibition), moderate at MIC/2 (32–41%), weak at MIC/4 (14–21%), and nil at MIC/8.

Homogeneously and heterogeneously structured biofilm models for wastewater treatment

Biofilm, a layer comprising extracellular polymeric substances, is the platform where the embedded living cells degrade the substances in the wastewaters. Biofilm models have been developed as part of the comprehensive models for the wastewater treatment process. This review summarizes the biofilm models applied in contemporary literature based on the spatial dimensions adopted for model build-up. The most commonly applied biofilm models are null-dimensional, considering the biofilm active biomass for the substrate sink's biological reaction. The one-dimensional, multi-species models are the second standard models for contemporary studies, providing transport and reaction resistances of substrates in the biofilm matrix and the interactions of competing or collaborating strains in the biofilm. The structural homogeneity of the biofilm challenges the validity of the uniformly structured models, highlighting the need to re-examine the validity of the uniformly structured models. The challenges and prospects of biofilm model developments and applications are outlined.

Targeting Persistent Biofilm Infections: Reconsidering the Topography of the Infection Site during Model Selection

The physiology of an organism in the environment reflects its interactions with the diverse physical, chemical, and biological properties of the surface. These principles come into consideration during model selection to study biofilm–host interactions. Biofilms are communities formed by beneficial and pathogenic bacteria, where cells are held together by a structured extracellular matrix. When biofilms are associated with a host, chemical gradients and their origins become highly relevant. Conventional biofilm laboratory models such as multiwall biofilm models and agar plate models poorly mimic these gradients. In contrast, ex vivo models possess the partial capacity to mimic the conditions of tissue-associated biofilm and a biofilm associated with a mineralized surface enriched in inorganic components, such as the human dentin. This review will highlight the progress achieved using these settings for two models of persistent infections: the infection of the lung tissue by Pseudomonas aeruginosa and the infection of the root canal by Enterococcus faecalis. For both models, we conclude that the limitations of the conventional in vitro systems necessitate a complimentary experimentation with clinically relevant ex vivo models during therapeutics development.