Biofilms are a complex group of microbial cells that adhere to the exopolysaccharide matrix present on the surface of medical devices. Biofilm-associated infections in the medical devices pose a serious problem to the public health and adversely affect the function of the device. Medical implants used in oral and orthopedic surgery are fabricated using alloys such as stainless steel and titanium. The biological behavior, such as osseointegration and its antibacterial activity, essentially depends on both the chemical composition and the morphology of the surface of the device. Surface treatment of medical implants by various physical and chemical techniques are attempted in order to improve their surface properties so as to facilitate bio-integration and prevent bacterial adhesion. The potential source of infection of the surrounding tissue and antimicrobial strategies are from bacteria adherent to or in a biofilm on the implant which should prevent both biofilm formation and tissue colonization. This article provides an overview of bacterial biofilm formation and methods adopted for the inhibition of bacterial adhesion on medical implants.
Staphylococcus aureus is a Gram-positive pathogen that causes potentially life-threatening nosocomial- and community-acquired infections, such as osteomyelitis and endocarditis. Staphylococcus aureus has the ability to form multicellular, surface-adherent communities called biofilms, which enables it to survive in various sources of stress, including antibiotics, nutrient limitations, heat shock, and immune responses. Biofilm-forming capacity is now recognized as an important virulence determinant in the development of staphylococcal device-related infections. In light of the projected increase in the numbers of elderly patients who will require semi-permanent indwelling medical devices such as artificial knees and hips, we can anticipate an expanded need for new agents and treatment options to manage biofilm-associated infections in an expanding at-risk population. With better understanding of staphylococcal biofilm formation and growth, novel strategies that target biofilm-associated infections caused by S. aureus have recently been described and seem promising as future anti-biofilm therapies.
The increasing resistance of Candida yeasts towards antifungal compounds and the limited choice of therapeutic drugs have spurred great interest amongst the scientific community to search for alternative anti-Candida compounds. Mycocins and fungal metabolites have been reported to have the potential for treatment of fungal infections. In this study, the growth inhibition of Candida species by a mycocin produced by Wickerhamomyces anomalus and a lactone compound from Aureobasidium pullulans were investigated.
N-acylhomoserine lactone (AHL)-based quorum sensing (QS) is important for the regulation of proteobacterial virulence determinants. Thus, the inhibition of AHL synthases offers non-antibiotics-based therapeutic potentials against QS-mediated bacterial infections. In this work, functional AHL synthases of Pseudomonas aeruginosa LasI and RhlI were heterologously expressed in an AHL-negative Escherichia coli followed by assessments on their AHLs production using AHL biosensors and high resolution liquid chromatography-mass spectrometry (LCMS). These AHL-producing E. coli served as tools for screening AHL synthase inhibitors. Based on a campaign of screening synthetic molecules and natural products using our approach, three strongest inhibitors namely are salicylic acid, tannic acid and trans-cinnamaldehyde have been identified. LCMS analysis further confirmed tannic acid and trans-cinnemaldehyde efficiently inhibited AHL production by RhlI. We further demonstrated the application of trans-cinnemaldehyde inhibiting Rhl QS system regulated pyocyanin production in P. aeruginosa up to 42.06%. Molecular docking analysis suggested that trans-cinnemaldehyde binds to the LasI and EsaI with known structures mainly interacting with their substrate binding sites. Our data suggested a new class of QS-inhibiting agents from natural products targeting AHL synthase and provided a potential approach for facilitating the discovery of anti-QS signal synthesis as basis of novel anti-infective approach.
Nanomedicine is now being introduced as a recent trend in the field of medicine. It has been documented that metal nanoparticles have antimicrobial effects for bacteria, fungi and viruses. Recent advances in technology has revived the use of silver nanoparticles in the medical field; treatment, diagnosis, monitoring and control of disease. It has been used since ancient times for treating wide range of illnesses. Bacterial cells adheres to surfaces and develop structures known as biofilms. These structures are natural survival strategy of the bacteria to invade the host. They are more tolerant to commonly used antimicrobial agents, thus being more difficult to be controlled. This leads to increase in severity of infection. In this study, we have investigated the effect of silver nanoparticles in the formation of biofilm in multidrug resistant strains of Pseudomonas aeruginosa. Observation showed that biofilm formation occurred at bacterial concentration of 10(6) cfu/ml for the sensitive strain of P. aeruginosa while in the resistant strain, the biofilm was evident at bacterial concentration of about 10(3) cfu/ml. The biofilm were then tested against various concentrations of silver nanoparticles to determine the inhibitory effect of the silver nanoparticles. In the sensitive strain, 20 μg/ml of silver nanoparticles inhibited the growth optimally at bacterial concentration of 10(4) cfu/ml with an inhibition rate of 67%. Similarly, silver nanoparticles inhibited the formation of biofilm in the resistant strain at an optimal bacterial concentration of 10(5) cfu/ml with an inhibition rate of 56%. Thus, silver nanoparticles could be used as a potential alternative therapy to reduce severity of disease due to P. aeruginosa infections.
The purpose of this study was to investigate the activity of xanthorrhizol isolated from Curcuma xanthorrhiza Roxb. on Candida albicans biofilms at adherent, intermediate, and mature phase of growth. C. albicans biofilms were formed in flat-bottom 96-well microtiter plates. The biofilms of C. albicans at different phases of development were exposed to xanthorrhizol at different concentrations (0.5 µg/mL-256 µg/mL) for 24 h. The metabolic activity of cells within the biofilms was quantified using the XTT reduction assay. Sessile minimum inhibitory concentrations (SMICs) were determined at 50% and 80% reduction in the biofilm OD₄₉₀ compared to the control wells. The SMIC₅₀ and SMIC₈₀ of xanthorrhizol against 18 C. albicans biofilms were 4--16 µg/mL and 8--32 µg/mL, respectively. The results demonstrated that the activity of xanthorrhizol in reducing C. albicans biofilms OD₄₉₀ was dependent on the concentration and the phase of growth of biofilm. Xanthorrhizol at concentration of 8 µg/mL completely reduced in biofilm referring to XTT-colorimetric readings at adherent phase, whereas 32 µg/mL of xanthorrhizol reduced 87.95% and 67.48 % of biofilm referring to XTT-colorimetric readings at intermediate and mature phases, respectively. Xanthorrhizol displayed potent activity against C. albicans biofilms in vitro and therefore might have potential therapeutic implication for biofilm-associated candidal infections.
Aureobasidin A (AbA) is a cyclic depsipeptide antifungal compound that inhibits a wide range of pathogenic fungi. In this study, the in vitro susceptibility of 92 clinical isolates of various Candida species against AbA was assessed by determining the planktonic and biofilm MICs of the isolates. The MIC(50) and MIC(90) of the planktonic Candida yeast were 1 and 1 μg ml(-1), respectively, whereas the biofilm MIC(50) and MIC(90) of the isolates were 8 and ≥64 μg ml(-1) respectively. This study demonstrates AbA inhibition on filamentation and biofilm development of C. albicans. The production of short hyphae and a lack of filamentation might have impaired biofilm development of AbA-treated cells. The AbA resistance of mature Candidia biofilms (24 h adherent population) was demonstrated in this study.
The frequent occurrences of antibiotic-resistant biofilm forming pathogens have become global issue since various measures that had been taken to curb the situation led to failure. Euphorbia hirta, is a well-known ethnomedicinal plant of Malaysia with diverse biological activities. This plant has been used widely in traditional medicine for the treatment of gastrointestinal, bronchial and respiratory ailments caused by infectious agents.
Tea can inhibit the attachment of Streptococcus mutans to surfaces and subsequent biofilm formation. Five commercial tea extracts were screened for their ability to inhibit attachment and biofilm formation by two strains of S. mutans on glass and hydroxyapatite surfaces. The mechanisms of these effects were investigated using scanning electron microscopy (SEM) and phytochemical screening. The results indicated that extracts of oolong tea most effectively inhibited attachment and extracts of pu-erh tea most effectively inhibited biofilm formation. SEM images showed that the S. mutans cells treated with extracts of oolong tea, or grown in medium containing extracts of pu-erh tea, were coated with tea components and were larger with more rounded shapes. The coatings on the cells consisted of flavonoids, tannins and indolic compounds. The ratio of tannins to simple phenolics in each of the coating samples was ∼3:1. This study suggests potential mechanisms by which tea components may inhibit the attachment and subsequent biofilm formation of S. mutans on tooth surfaces, such as modification of cell surface properties and blocking of the activity of proteins and the structures used by the bacteria to interact with surfaces.
The in vitro antibacterial and antibiofilm activity of chlorogenic acid against clinical isolates of Stenotrophomonas maltophilia was investigated through disk diffusion, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-kill and biofilm assays. A total of 9 clinical S. maltophilia isolates including one isolate resistant to trimethoprim/sulfamethoxazole (TMP/SMX) were tested. The inhibition zone sizes for the isolates ranged from 17 to 29 mm, while the MIC and MBC values ranged from 8 to 16 μg mL(-1) and 16 to 32 μg mL(-1). Chlorogenic acid appeared to be strongly bactericidal at 4x MIC, with a 2-log reduction in viable bacteria at 10 h. In vitro antibiofilm testing showed a 4-fold reduction in biofilm viability at 4x MIC compared to 1x MIC values (0.085 < 0.397 A 490 nm) of chlorogenic acid. The data from this study support the notion that the chlorogenic acid has promising in vitro antibacterial and antibiofilm activities against S. maltophilia.
Candida (C.) albicans infection in its biofilm mode of growth has taken centre point with the increasing recognition of its role in human infections due to the development of resistance to the commonly used antibiotic or phenotypic adaptation within the biofilm. Hence, in this study the inhibitory effect of methanol extract of Cassia (C.) spectabilis leaves was evaluated against biofilm forming C. albicans.
This study describes the killer phenotypes of tropical environmental yeasts and the inhibition effects of the culture filtrates on the biofilm of Candida albicans. A total of 26 (10.5%) of 258 yeast isolates obtained from an environmental sampling study demonstrated killer activity to Candida species. The killer yeasts were identified as species belonging to the genus Aureobasidium, Pseudozyma, Ustilago and Candida based on sequence analysis of the ITS1-5.8S-ITS2 region of the yeasts. Pseudozyma showed the broadest killing effects against sensitive strains of Candida. New species of Ustilago and Pseudozyma demonstrating killer phenotypes were identified in this study. Interestingly, more than 50% reduction in the metabolic activity of Candida albicans biofilm was noted after exposure to the culture filtrates of the nine killer yeasts. Purification and characterization of toxin and metabolites are essential for understanding the yeast killing effects.
Upon implantation or insertion into patient's body for exerting the intended purpose like salvage of normal functions of vital organs, the medical devices are unfortunately becoming the sites of competition between host cell integration and microbial adhesion. Moreover, since there is an increased use of implanted medical devices, the incidence of biofilm-and medical devices-related nosocomial infections is also increasing progressively. To control microbial colonization and subsequent biofilm formation of the medical devices, different approaches either to enhance the efficiency of certain antimicrobial agents or to disrupt the basic physiology of the pathogenic microorganisms including novel small molecules and antipathogenic drugs are being explored. In addition, the various lipid-and polymer-based drug delivery carriers are also investigated for applying antibiofilm coating of the medical devices especially over catheters. The main intention of this review is therefore to summarize the major and/breakthrough inventions disclosed in patent literature as well as in research papers related to microbial colonization of medical devices and novel preventive strategies. This review starts with an overview of the preventive strategies followed by a short description about the potential of different lipidic-and polymeric-drug delivery carriers in eradicating the biofilm-associated infections from the medical devices.
The inhibitory effect of Cassia spectabilis methanol leaf extract was evaluated against biofilm forming Candida albicans, which was sensitive to 6.25 mg/ml concentration of the extract. Transmission (TEM) and scanning electron microscope (SEM) observations were used to study the anticandidal activity and prevention of biofilm formation by the C. spectabilis extract. SEM analysis further revealed reduction in C. albicans biofilm in response to the extract. The main abnormalities noted via TEM study was the alterations in morphology and complete collapse of the yeast cells after 36 h of exposure to the extract. The significant antifungal activity shown by this methanol extract of C. spectabilis suggests its potential against infections caused by C. albicans.
The purpose of this study was to investigate the antimicrobial efficacy of six groups of antibiotics and calcium hydroxide against Enterococcus faecalis biofilm in a membrane filter model. Two-day-old E. faecalis (ATCC 29212) biofilm was exposed to ampicillin, co-trimoxazole, erythr omycin, oxytetracycline, vancomycin, vancomycin followed by gentamicin, Ca(OH)(2), and phosphate-buffered saline (control). After 1 h of exposure, the antimicrobial activity was neutralized by washing each disc five times in PBS, and then the colony-forming units of the remaining viable bacteria on each disc were counted. The results revealed that only erythromycin, oxytetracycline and Ca(OH)2 showed 100% biofilm kill. An ANOVA with a Bonferroni post hoc test (P < 0.05) detected significant differences among the test agents, except in the ampicillin group versus the co-trimoxazole group. It is concluded that erythromycin, oxytetracycline and Ca(OH)2 are 100% effective in eliminating E. faecalis biofilm, whereas ampicillin, co-trimoxazole, vancomycin, and vancomycin followed by gentamicin are ineffective.