Microbial anti-biofilms: types and mechanism of action

Biofilms have been recognized as a serious threat to public health as it protects microbes from antimicrobials, immune defence mechanisms, chemical treatments and nutritional stress. Biofilms are also a source of concern in industries and water treatment because their presence compromises the integrity of equipment. To overcome these problems, it is necessary to identify novel anti-biofilm compounds. Products of microorganisms have been identified as promising broad-spectrum anti-biofilm agents. These natural products include biosurfactants, antimicrobial peptides, enzymes and bioactive compounds. Anti-biofilm products of microbial origin are chemically diverse and possess a broad spectrum of activities against biofilms. The objective of this review is to give an overview of the different types of microbial anti-biofilm products and their mechanisms of action.

Strategies and materials for the prevention and treatment of biofilms

Biofilms are aggregates of organized microbial growth that function as barriers and create a stable internal environment for cell survival. The bacteria in the biofilms exhibit characteristics that are quite different from the planktonic bacteria, such as strong resistance to antibiotics and other bactericides, getting out of host immunity, and developing in harsh environments, which all contribute to the persistent and intractable treatment. Hence, there is an urgent need to develop novel materials and strategies to combat biofilms. However, most of the reviews on anti-biofilms published in recent years are based on specific fields or materials. Microorganisms are ubiquitous, except in the context of medical and health issues; however, biofilms exert detrimental effects on the advancement and progress of various fields. Therefore, this review aims to provide a comprehensive summary of effective strategies and methodologies applicable across all industries. Firstly, the process of biofilms formation was introduced to enhance our comprehension of the "enemy". Secondly, strategies to intervene in the important links of biofilms formation were discussed, taking timely action during the early weak stages of the "enemy". Thirdly, treatment strategies for mature biofilms were summarized to deal with biofilms that break through the defense line. Finally, several substances with antibacterial properties were presented. The review concludes with the standpoint of the author about potential developments of anti-biofilms strategies. This review may help researchers quickly understand the research progress and challenges in the field of anti-biofilms to design more efficient methods and strategies to combat biofilms.

Hypoxia-sensitive adjuvant loaded liposomes enhance the antimicrobial activity of azithromycin via phospholipase-triggered releasing for Pseudomonas aeruginosa biofilms eradication

Robust biofilms and the complex airway environment with thick sputum, local hypoxia and persistent inflammation induce the intractability of chronic pulmonary infections caused by Pseudomonas aeruginosa (P. aeruginosa). Herein, we proposed a type of antibiotic-adjuvant liposomes (NANO@PS-LPs), co-incorporating azithromycin (AZI), adjuvant (2-nitroimidazole derivative, 6-NIH) and biofilm dispersant (nitric oxide donor, DETA NONOate). NANO@PS-LPs possessing negatively-charged surface and good hydrophilicity could easily penetrate through the sputum layer, then disassembled triggered by overexpressed phospholipase A₂ (PLA₂) in the microenvironment around biofilms. Nitric oxide produced by DETA NONOate promoted P. aeruginosa biofilms dispersal. 6-NIH was reduced to 2-aminomidazole derivative (6-AIH) under a hypoxic condition, and hence acted as an AZI adjuvant to enhance the antibacterial activity of AZI. It was found that NANO@PS-LPs could significantly eliminate mature P. aeruginosa biofilms, effectively kill dispersed bacteria, inhibit the metabolism of survivors and prevent P. aeruginosa adherence to airway epithelial cells, accordingly restrain recurrent infections. Additionally, NANO@PS-LPs performed a remarkable advantage in killing AZI-resistant P. aeruginosa and removing their biofilms. In summary, NANO@PS-LPs present a potential nano-strategy to treat stubborn pseudomonal pulmonary infections and overcome correlative drug resistance.

Inhibition of bacterial adhesion and biofilm formation by a textured fluorinated alkoxyphosphazene surface

The utilization of biomaterials in implanted blood-contacting medical devices often induces a persistent problem of microbial infection, which results from bacterial adhesion and biofilm formation on the surface of biomaterials. In this research, we developed new fluorinated alkoxyphosphazene materials, specifically poly[bis(octafluoropentoxy) phosphazene] (OFP) and crosslinkable OFP (X-OFP), with improved mechanical properties, and further modified the surface topography with ordered pillars to improve the antibacterial properties. Three X-OFP materials, X-OFP3.3, X-OFP8.1, X-OFP13.6, with different crosslinking densities were synthesized, and textured films with patterns of 500/500/600 nm (diameter/spacing/height) were fabricated via a two stage soft lithography molding process. Experiments with 3 bacterial strains: Staphylococcal epidermidis, Staphylococcal aureus, and Pseudomonas aeruginosa showed that bacterial adhesion coefficients were significantly lower on OFP and X-OFP smooth surfaces than on the polyurethane biomaterial, and surface texturing further reduced bacterial adhesion due to the reduction in accessible surface contact area. Furthermore the anti-bacterial adhesion effect shows a positive relationship with the crosslinking degree. Biofilm formation on the substrates was examined using a CDC biofilm reactor for 7 days and no biofilm formation was observed on textured X-OFP biomaterials. The results suggested that the combination of fluorocarbon chemistry and submicron topography modification in textured X-OFP materials may provide a practical approach to improve the biocompatibility of current biomaterials with significant reduction in risk of pathogenic infection.

Antibacterial, anti-biofilm activity and mechanism of action of pancreatin doped zinc oxide nanoparticles against methicillin resistant Staphylococcus aureus

Staphylococcus aureus are known to cause diseases from normal skin wound to life intimidating infections. Among the drug resistant strain, management of methicillin resistant Staphylococcus aureus (MRSA) is very difficult by using conventional antibiotic treatment. Both Zinc oxide nanoparticles (ZnONPs) and pancreatin (PK) are known to have antibacterial activity. Our main objective is to dope PK on ZnONPs to reduced zinc-oxide toxicity but increased anti-bacterial and anti-biofilms activity. In present study, we showed that, functions of zinc oxide nanoparticles with pancreatin enzyme (ZnONPs-PK) have anti-bacterial, anti-biofilms, anti-motility and anti-virulence properties against MRSA. Moreover, ZnONPs-PK were more potent to eradicate MRSA than only ZnONPs and PK. Application of the produced nano-composites as treatment on infected swine dermis predominantly reflects the potential treatment property of it. The vancomycin sensitivity of MRSA was significantly increased on application with ZnONPs-PK. Further study revealed cell membrane was the target of the ZnONPs-PK and that leads to oxidative damage of the cells. The produced nanoparticles were found completely non-toxic to human's keratinocytes and lung epithelial cell lines at its bactericidal concentration. Overall, this study emphasizes the potential mechanisms underlying the selective bactericidal properties of ZnONPs-PK against MRSA. This novel nanoparticle strategy may provide the ideal solution for comprehensive management of MRSA and its associated diseases with minimising the use of antibiotics.

Iranian propolis efficiently inhibits growth of oral streptococci and cancer cell lines

Background

Propolis is a natural bee product with a wide range of biological activities that are related to its chemical composition. The present study investigated the quantification of quercetin (Q) in Ardabil ethanol extract of propolis (AEEP), and then compared its anti-bacterial, anti- biofilm and cytotoxic effects on cancer and normal cell lines.

Method

In the present study, the chemical composition of AEEP was determined through the high-performance liquid chromatography (HPLC). The AEEP and its main component, quercetin (Q), were evaluated in vitro against 57 oral streptococci by a broth micro-dilution method. The biofilm formation was assessed through the crystal violet staining and MTT assays. The impact of AEEP and Q anti-proliferative effect were evaluated on the fibroblast as normal and cancer cell lines (KB and A431).

Results

The Q concentration in the composition of AEEP was 6.9% of all its components. The findings indicated that the AEEP and Q were efficient against the cariogenic bacteria and were able to inhibit the S.mutans biofilm adherence at a sub-MIC concentration. Moreover, electron micrographs indicated the inhibition of biofilms compared to control biofilms. In addition, the AEEP and Q indicated a dose-dependent cytotoxic effect on A431 and KB cell lines. On the contrary, they had no cytotoxic effect on fibroblast cells.

Conclusion

The results indicated that the synergistic impact of main components of AEEP was related to the inhibition of the cancer cell proliferation, cariogenic bacteria and oral biofilm formation. It may play a promising role in the complementary medicine and, it is suggested to be used as food additives.