Antibacterial activity of a novel antimicrobial peptide [W7]KR12-KAEK derived from KR-12 against Streptococcus mutans planktonic cells and biofilms

The aims of this study were to describe the synthesis of a novel synthetic peptide based on the primary structure of the KR-12 peptide and to evaluate its antimicrobial and anti-biofilm activities against Streptococcus mutans. The antimicrobial effect of KR-12 and [W⁷]KR12-KAEK was assessed by determining the minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations. The evaluation of anti-biofilm activity was assessed through total biomass quantification, colony forming unit counting and scanning electron microscopy. [W⁷]KR12-KAEK showed MIC and MBC values ranging from 31.25 to 7.8 and 62.5 to 15.6 μg ml^?1, respectively. Furthermore, [W7]KR12-KAEK significantly reduced biofilm biomass (50–100%). Regarding cell viability, [W⁷]KR12-KAEK showed reductions in the number of CFUs at concentrations ranging from 62.5 to 7.8 μg ml^?1 and 500 to 62.5 μg ml^?1 with respect to biofilm formation and preformed biofilms, respectively. SEM micrographs of S. mutans treated with [W⁷]KR12-KAEK suggested damage to the bacterial surface. [W⁷]KR12-KAEK is demonstrated to be an antimicrobial agent to control microbial biofilms.     

The synthetic human beta-defensin-3 C15 peptide exhibits antimicrobial activity against <Emphasis Type="Italic">Streptococcus mutans</Emphasis>, both alone and in combination with dental disinfectants

Streptococcus mutans is a major etiologic agent of human dental caries that forms biofilms on hard tissues in the human oral cavity, such as tooth and dentinal surfaces. Human β-defensin-3 (HBD3) is a 45-amino-acid natural antimicrobial peptide that has broad spectrum antimicrobial activity against bacteria and fungi. A synthetic peptide consisting of the C-terminal 15 amino acids of HBD3 (HBD3-C15) was recently shown to be sufficient for its antimicrobial activity. Thus, clinical applications of this peptide have garnered attention. In this study, we investigated whether HBD3-C15 inhibits the growth of the representative cariogenic pathogen Streptococcus mutans and its biofilm formation. HBD3-C15 inhibited bacterial growth, exhibited bactericidal activity, and attenuated bacterial biofilm formation in a dose-dependent manner. HBD3-C15 potentiated the bactericidal and anti-biofilm activity of calcium hydroxide (CH) and chlorhexidine digluconate (CHX), which are representative disinfectants used in dental clinics, against S. mutans. Moreover, HBD3-C15 showed antimicrobial activity by inhibiting biofilm formation by S. mutans and other dentinophilic bacteria such as Enterococcus faecalis and Streptococcus gordonii, which are associated with dental caries and endodontic infection, on human dentin slices. These effects were observed for HBD3-C15 alone and for HBD3-C15 in combination with CH or CHX. Therefore, we suggest that HBD3-C15 is a potential alternative or additive disinfectant that can be used for the treatment of oral infectious diseases, including dental caries and endodontic infections.     

Antimicrobial and antibiofilm activity of pleurocidin against cariogenic microorganisms

Dental caries is a common oral bacterial infectious disease of global concern. Prevention and treatment of caries requires control of the dental plaque formed by pathogens such as Streptococcus mutans and Streptococcus sobrinus. Pleurocidin, produced by Pleuronectes americanus, is an antimicrobial peptide that exerts broad-spectrum activity against pathogenic bacteria and fungi. Moreover, pleurocidin shows less hemolysis and is less toxic than other natural peptides. In the present study, we investigated whether pleurocidin is an effective antibiotic peptide against common cariogenic microorganisms and performed a preliminary study of the antimicrobial mechanism. We assayed minimal inhibitory concentration (MIC), minimal bactericide concentration (MBC) and bactericidal kinetics and performed a spot-on-lawn assay. The BioFlux system was used to generate bacterial biofilms under controllable flow. Fluorescence microscopy and confocal laser scanning microscopy (CLSM) were used to analyze and observe biofilms. Scanning electron microscopy was used to observe the bacterial membrane. MIC and MBC results showed that pleurocidin had different antimicrobial activities against the tested oral strains. Although components of saliva could affect antimicrobial activity, pleurocidin dissolved in saliva still showed antimicrobial effects against oral microorganisms. Furthermore, pleurocidin showed a favorable killing effect against BioFlux flow biofilms in vitro. Our findings suggest that pleurocidin has the potential to kill dental biofilms and prevent dental caries.     

Nanographene oxides carrying antisense walR RNA regulates the Enterococcus faecalis biofilm formation and its susceptibility to chlorhexidine

Enterococcus faecalis is the dominant pathogen for persistent periapical periodontitis. The chlorhexidine (CHX) is used as conversional irrigation agents during endodontic root canal therapy. It was reported that the antisense walR RNA (ASwalR) suppressed the biofilm organization. The aim of this study was to investigate the antimicrobial effects of novel graphene oxide (GO)-polyethylenimine (PEI)-based antisense walR (ASwalR) on the inhibition of E. faecalis biofilm and its susceptibility to chlorhexidine. The recombinant ASwalR plasmids were modified with a gene encoding enhanced green fluorescent protein (ASwalR-eGFP) as a reporter gene so that the transformation efficiency could be evaluated by the fluorescence intensity. The GO-PEI-based ASwalR vector transformation strategy was developed to be transformed into E. faecalis and to over-produce ASwalR in biofilms. Colony forming units (CFU) and confocal laser scanning microscopy were used to investigate whether the antibacterial properties of antisense walR interference strategy sensitize E. faecalis biofilm to the CHX. The results indicated that overexpression of ASwalR by GO-PEI-based transformation strategy could inhibit biofilm formation, decrease the EPS synthesis and increase the susceptibility of E. faecalis biofilms to CHX. Our reports demonstrated that antisense walR RNA will be a supplementary strategy in treating E. faecalis with irrigation agents.     

Nanoparticle-Encapsulated Chlorhexidine against Oral Bacterial Biofilms

Background

Chlorhexidine (CHX) is a widely used antimicrobial agent in dentistry. Herein, we report the synthesis of a novel mesoporous silica nanoparticle-encapsulated pure CHX (Nano-CHX), and its mechanical profile and antimicrobial properties against oral biofilms.

Methodology/Principal Findings

The release of CHX from the Nano-CHX was characterized by UV/visible absorption spectroscopy. The antimicrobial properties of Nano-CHX were evaluated in both planktonic and biofilm modes of representative oral pathogenic bacteria. The Nano-CHX demonstrated potent antibacterial effects on planktonic bacteria and mono-species biofilms at the concentrations of 50–200 µg/mL against Streptococcus mutans, Streptococcus sobrinus, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans and Enterococccus faecalis. Moreover, Nano-CHX effectively suppressed multi-species biofilms such as S. mutans, F. nucleatum, A. actinomycetemcomitans and Porphyromonas gingivalis up to 72 h.

Conclusions/Significance

This pioneering study demonstrates the potent antibacterial effects of the Nano-CHX on oral biofilms, and it may be developed as a novel and promising anti-biofilm agent for clinical use.     

Antimicrobial activity of crude extracts from mangrove fungal endophytes

The aim of this work was to select endophytic fungi from mangrove plants that produced antimicrobial substances. Minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) or minimal fungicidal concentrations (MFC) of crude extracts from 150 isolates were determined against potential human pathogens by a colorimetric microdilution method. Ninety-two isolates (61.3%) produced inhibitory compounds. Most of the extracts (28–32%) inhibited Staphylococcus aureus (MIC/MBC 4–200/64–200 μg ml⁻¹). Only two extracts inhibited Pseudomonas aeruginosa (MIC/MBC 200/>200 μg ml⁻¹). 25.5 and 11.7% inhibited Microsporum gypseum and Cryptococcus neoformans (MIC/MFC 4–200/8–200 μg ml⁻¹ and 8–200/8–200 μg ml⁻¹, respectively), while 7.5% were active against Candida albicans (MIC/MFC 32–200/32–200 μg ml⁻¹). None of the extracts inhibited Escherichia coli. The most active fungal extracts were from six genera, Acremonium, Diaporthe, Hypoxylon, Pestalotiopsis, Phomopsis, and Xylaria as identified using morphological and molecular methods. Phomopsis sp. MA194 (GU592007, GU592018) isolated from Rhizophora apiculata showed the broadest antimicrobial spectrum with low MIC values of 8–32 μg ml⁻¹against Gram-positive bacteria, yeasts and M. gypseum. It was concluded that endophytic fungi from mangrove plants are diverse, many produce compounds with antimicrobial activity and could be suitable sources of new antimicrobial natural products.     

The human antimicrobial peptide LL-37 and its fragments possess both antimicrobial and antibiofilm activities against multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii infections are difficult to treat due to multidrug resistance. Biofilm formation by A. baumannii is an additional factor in its ability to resist antimicrobial therapy. The antibacterial and antibiofilm activities of the human antimicrobial peptide LL-37 and its fragments KS-30, KR-20 and KR-12 against clinical isolates of multidrug-resistant (MDR) A. baumannii were evaluated. The minimal inhibitory concentration (MIC) of LL-37 against MDR A. baumannii isolates ranged from 16 to 32 μg/mL. The MIC of KS-30 fragment varied from 8.0 to16 μg/mL and the KR-20 fragment MIC ranged from 16 to 64 μg/mL. LL-37 and KS-30 fragment exhibited 100% bactericidal activity against five A. baumannii strains, including four MDR clinical isolates, within 30 min at concentrations of 0.25–1 μg/mL. By 0.5 h, the fragments KR-20 and KR-12 eliminated all tested strains at 8 and 64 μg/mL respectively. LL-37 and its fragments displayed anti-adherence activities between 32-128 μg/mL. A minimum biofilm eradication concentration (MBEC) biofilm assay demonstrated that LL-37 inhibited and dispersed A. baumannii biofilms at 32 μg/mL respectively. Truncated fragments of LL-37 inhibited biofilms at concentrations of 64–128 μg/mL. KS-30, the truncated variant of LL-37, effectively dispersed biofilms at 64 μg/mL. At 24 h, no detectable toxicity was observed at the efficacious doses when cytotoxicity assays were performed. Thus, LL-37, KS-30 and KR-20 exhibit significant antimicrobial activity against MDR A. baumannii. The prevention of biofilm formation in vitro by LL-37, KS-30 and KR-20 adds significance to their efficacy. These peptides can be potential therapeutics against MDR A. baumannii infections.     

Promethazine improves antibiotic efficacy and disrupts biofilms of Burkholderia pseudomallei

Efflux pumps are important defense mechanisms against antimicrobial drugs and maintenance of Burkholderia pseudomallei biofilms. This study evaluated the effect of the efflux pump inhibitor promethazine on the structure and antimicrobial susceptibility of B. pseudomallei biofilms. Susceptibility of planktonic cells and biofilms to promethazine alone and combined with antimicrobials was assessed by the broth microdilution test and biofilm metabolic activity was determined with resazurin. The effect of promethazine on 48 h-grown biofilms was also evaluated through confocal and electronic microscopy. The minimum inhibitory concentration (MIC) of promethazine was 780 mg l^?1, while the minimum biofilm elimination concentration (MBEC) was 780–3,120 mg l^?1. Promethazine reduced the MIC values for erythromycin, trimethoprim/sulfamethoxazole, gentamicin and ciprofloxacin and reduced the MBEC values for all tested drugs (p<0.05). Microscopic analyses demonstrated that promethazine altered the biofilm structure of B. pseudomallei, even at subinhibitory concentrations, possibly facilitating antibiotic penetration. Promethazine improves antibiotics efficacy against B. pseudomallei biofilms, by disrupting biofilm structure.     

Comparative Effect of Chlorhexidine and Some Mouthrinses on Bacterial Biofilm Formation on Titanium Surface

The aim of the present study was to evaluate the effectiveness of chlorhexidine digluconate (CHX) and commonly used mouthrinses to single- and poly-species biofilms by S. mutans, S. aureus and P. aeruginosa, on titanium discs of grade IV. The formation of single- and poly-species biofilms at 16.5, 40.5 and 64.5-h incubation on titanium surface was evaluated by plate count (CFU ml⁻¹) before and after exposure to CHX and four mouthrinses (Curasept, Listerine, Meridol and Buccagel) and expressed as percentage of Inhibitory Activity (IA%). The application of the different anti-plaque formulations on biofilm can reduce the adhesion of bacteria to titanium surface with different degrees. The higher efficacy was observed for Listerine that shows IA% = 100 on the biofilm formed by S. mutans at 16.5 h. Log count of CFU was dependent to culture time and four mouthrinses for S. mutans and S. aureus, whilst was not dependent to culture time but to mouthrinses for P. aeruginosa. In general, the efficacy was particularly lesser to poly-species biofilms; no statistical differences were evidenced between all the mouthrinses and CHX as control group. The tested mouthrinses, compared to reference CHX 0.2%, have demonstrated a significant lower antibacterial activity than Listerine towards the experimental biofilms. This “in vitro” biofilm model should prove extremely useful for pre-clinical testing of anti-plaque agents, which inhibit biofilm formation, can prevent subsequent implant failure.     

Experimental and statistical methods to evaluate antibacterial activity of a quaternary pyridinium salt on planktonic,biofilm-forming,and biofilm states

Robust evaluation and comparison of antimicrobial technologies are critical to improving biofilm prevention and treatment. Herein, a multi-pronged experimental framework and statistical models were applied to determine the effects of quaternary pyridinium salt, 4-acetyl-1-hexadecylpyridin-1-ium iodide (QPS-1), on Streptococcus mutans in the planktonic, biofilm-forming and biofilm cell states. Minimum inhibitory and bactericidal concentrations (MIC and MBC, respectively) were determined via common methods with novel application of statistical approaches combining random effects models and interval censored data to estimate uncertainties. The MICs and MBCs for planktonic and biofilm-forming states ranged from 3.12 to 12.5 μg ml^?1, with biofilm values only ≈ 8 times higher. Potent anti-biofilm activity and reactive structural features make QPS-1 a promising antibacterial additive for dental and potentially other biomedical devices. Together, the experimental framework and statistical models provide estimates and uncertainties for effective antimicrobial concentrations in multiple cell states, enabling statistical comparisons and improved characterization of antibacterial agents.     

Antimicrobial activity and antibiotic synergy of a biphosphinic ruthenium complex against clinically relevant bacteria

Abstract

The aim of this study was to investigate the antibacterial activity, antibiotic-associated synergy, and anti-biofilm activity of the ruthenium complex, cis-[RuCl₂ (dppb) (bqdi)]²⁺ (RuNN). RuNN exhibited antimicrobial activity against Gram-positive bacteria with minimum inhibitory concentration (MIC) values ranging from 15.6 to 62.5?µg ml^?1 and minimum bactericidal concentration (MBC) values ranging from 62.5 to 125?µg ml^?1. A synergistic effect against Staphylococcus spp. was observed when RuNN was combined with ampicillin, and the range of associated fractional inhibitory concentration index (FICI) values was 0.187 to 0.312. A time-kill curve indicated the bactericidal activity of RuNN in the first 1–5?h. In general, RuNN inhibited biofilm formation and disrupted mature biofilms. Furthermore, RuNN altered the cellular morphology of S. aureus biofilms. Further, RuNN did not cause hemolysis of erythrocytes. The results of this study provide evidence that RuNN is a novel therapeutic candidate to treat bacterial infections caused by Staphylococcus biofilms.     

Effects of antimicrobial peptide L-K6, a temporin-1CEb analog on oral pathogen growth,Streptococcus mutans biofilm formation,and anti-inflammatory activity

Dental caries and periodontitis are common bacterial mouth infections. As a potentially attractive substitute for conventional antibiotics, antimicrobial peptides have been widely tested and used for controlling bacterial infections. In this study, we tested the efficacy of the peptides from the skin secretions of Rana chensinensis for killing several major cariogenic and periodontic pathogens as well as Candida albicans. L-K6, a temporin-1CEb analog, exhibited high antimicrobial activity against the tested oral pathogens and was able to inhibit Streptococcus mutans biofilm formation and reduce 1-day-old S. mutans biofilms with a minimum biofilm inhibitory concentration and reducing concentration of 3.13 and 6.25 μM, respectively. The results of confocal laser scanning microscopy demonstrated that the peptide significantly reduced cell viability within oral biofilms. Furthermore, as little as 5 μM L-K6 significantly inhibited lipopolysaccharide (LPS)- and interleukin-1β-induced productions of interleukin-8 and tumor necrosis factor-α from THP-1 monocytic cells. This anti-inflammatory activity is associated with the binding of L-K6 to LPS and neutralizing LPS-induced proinflammatory responses in THP-1 cells, as well as dissociating LPS aggregates. Our results suggest that L-K6 may have potential clinical applications in treating dental caries by killing S. mutans within dental plaque and acting as anti-inflammatory agents in infected tissues.     

In vitro antibacterial and cytotoxic activities of carvacrol and terpinen-4-ol against biofilm formation on titanium implant surfaces

Abstract

This study evaluated the antibacterial properties of carvacrol and terpinen-4-ol against Porphyromonas gingivalis and Fusobacterium nucleatum and its cytotoxic effects on fibroblast cells. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were examined. The minimum biofilm inhibition concentration (MBIC) was evaluated by XTT assay. Biofilm decontamination on titanium surfaces was quantified (CFU ml^?1), evaluated by confocal laser scanning microscopy (CLSM) and cytotoxic activity by MTT. The MIC and MBC for carvacrol were 0.007% and 0.002% for P. gingivalis and F. nucleatum, and 0.06% for terpinen-4-ol for both microorganisms. The MBIC for carvacrol was 0.03% and 0.06% for P. gingivalis and F. nucleatum, and for terpinen-4-ol was 0.06% and 0.24%. The results indicated anti-biofilm activity using carvacrol (0.26%, 0.06%) and terpinen-4-ol (0.95%, 0.24%) and showed cytotoxic activity similar to chlorohexidine (CHX). However, terpinen-4-ol (0.24%) showed higher cell viability than other treatments. Carvacrol and terpinen-4-ol showed antibacterial activity in respect of reducing biofilms. Moreover, CHX-like cytotoxicity was observed.     

Antifungal and antibacterial potential of methanol and chloroform extracts of Marchantia polymorpha L.

The methanol and chloroform extracts of Marchantia polymorpha were tested against three Gram-negative bacterial strains, viz. Xanthomonas oryzae pv. oryzae, Salmonella enterica and Pasturella multocida and four fungal strains, viz. Tilletia indica Mitra, Fusarium oxysporum f. sp. lini, Sclerotium rolfsii Sacc. and Rhizoctonia solani Kuhn. by using disc diffusion and micro broth dilution techniques. Both the extracts showed unique activity against X. oryzae and P.multocida [per cent inhibition (PI) 11.58 and 12.55, minimum inhibitory concentration (MIC) 2.50 and 1.25 μg/mL, minimum bactericidal concentration (MBC) 2.75 and 1.25 μg/mL, respectively] but for fungi, it was shown against S.rolfsii and F. oxysporum [PI 32.65 and 33.44, MIC 2.50 and 0.65 μg/mL, minimum fungicidal concentration (MFC) 4.50 and 0.65 μg/mL, respectively].The extracts possessed antimicrobial activity with different potency against variety of micro-organisms pathogenic to plants as well as animals. Some extracts were fungistatic and bacteriostatic (methanol extract against R. solani and chloroform extract against F. oxysporum and methanol extract for bacteria, respectively), while rest showed fungicidal/bactericidal potential. The results suggest the potential of M. polymorpha for developing a broad spectrum antimicrobial formulation in future.     

Inhibitory effect of methyl gallate and gallic acid on oral bacteria

This study examined the ability of methyl gallate (MG) and gallic acid (GA), the main compounds of gallo-tannins in Galla Rhois, to inhibit the proliferation of oral bacterial and the in vitro formation of Streptococcus mutans biofilms. The antimicrobial activities of these compounds were evaluated in vitro using the broth microdilution method and a beaker-wire test. Both MG and GA had inhibitory effects on the growth of cariogenic (MIC<8 mg/ml) and periodontopathic bacteria (MIC=1 mg/ml). Moreover, these compounds significantly inhibited the in vitro formation of S. mutans biofilms (MG, 1 mg/ml; GA, 4 mg/ml; P<0.05). MG was more effective in inhibiting bacterial growth and the formation of S. mutans biofilm than GA. In conclusion, MG and GA can inhibit the growth of oral pathogens and S. mutans biofilm formation, and may be used to prevent the formation of oral biofilms.     

Growth inhibitory properties of lactose fatty acid esters

Sugar esters are biodegradable, nonionic surfactants which have microbial inhibitory properties. The influence of the fatty acid chain length on the microbial inhibitory properties of lactose esters was investigated in this study. Specifically, lactose monooctanoate (LMO), lactose monodecanoate (LMD), lactose monolaurate (LML) and lactose monomyristate (LMM) were synthesized and dissolved in both dimethyl sulfoxide (DMSO) and ethanol. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined in growth media. LML was the most effective ester, exhibiting MIC values of <0.05 to <5 mg/ml for each Gram-positive bacteria tested (Bacillus cereus, Mycobacterium KMS, Streptococcus suis, Listeria monocytogenes, Enterococcus faecalis, and Streptococcus mutans) and MBC values of <3 to <5 mg/ml for B. cereus, M. KMS, S. suis, and L. monocytogenes. LMD showed MIC and MBC values of <1 to <5 mg/ml for B. cereus, M. KMS, S. suis, L. monocytogenes, and E. faecalis, with greater inhibition when dissolved in ethanol. LMM showed MIC and MBC values of <1 to <5 mg/ml for B. cereus, M. KMS, and S. suis. LMO was the least effective showing a MBC value of <5 mg/ml for only B. cereus, though MIC values for S. suis and L. monocytogenes were observed when dissolved in DMSO. B. cereus and S. suis were the most susceptible to the lactose esters tested, while S. mutans and E. faecalis were the most resilient and no esters were effective on Escherichia coli O157:H7. This research showed that lactose esters esterified with decanoic and lauric acids exhibited greater microbial inhibitory properties than lactose esters of octanoate and myristate against Gram-positive bacteria.     

Cytotoxicity and the effect of cationic peptide fragments against cariogenic bacteria under planktonic and biofilm conditions

This study evaluated the cytotoxicity and effect of fragments derived from three oral cationic peptides (CP): LL-37, D6-17 and D1-23 against cariogenic bacteria under planktonic and biofilm conditions. For cytotoxicity analysis, two epithelial cell lines were used. The minimum inhibitory concentration and the minimal bactericidal concentration were determined for the CP fragments and the control (chlorhexidine-CHX) against cariogenic bacteria. The fractional inhibitory concentration was obtained for the combinations of CP fragments on Streptococcus mutans. Biofilm assays were conducted with the best antimicrobial CP fragment against S. mutans. The results indicated that D6-17 was not cytotoxic. D1-23, LL-37 and CHX were not cytotoxic in low concentrations. D1-23 presented the best bactericidal activity against S. mutans, S. mitis and S. salivarius. Combinations of CP fragments did not show a synergic effect. D1-23 presented a higher activity against S. mutans biofilm than CHX. It was concluded that D1-23 showed a substantial effect against cariogenic bacteria and low cytotoxicity.     

Recombinant Production and Antimicrobial Assessment of <Emphasis Type="Italic">Beta</Emphasis> Casein- IbAMP<Subscript>4</Subscript> as a Novel Antimicrobial Polymeric Protein and its Synergistic Effects with Thymol

There is a growing research interest on products with antimicrobial activity. Antimicrobial polymers are one of the most surefire procedures to combat microbes. In the present study, the ability of Βeta-casein- one of the milk major self assembly proteins with high polymeric film production capability—as a fusion partner of Ib-AMP₄ antimicrobial peptide was investigated. Also, the antimicrobial activities of Βeta-casein- IbAMP₄ fusion protein antimicrobial against common food pathogens were assessed. The pET21a-BCN-Ib-AMP ₄ construct was transformed to Escherichia coli BL21 (DE3), and protein expression was induced under optimized conditions. Purified protein obtained from nickel affinity chromatography was refolded under optimized dialysis circumstances and concentrated to 1600 µg mL^?1 fusion protein by ultrafiltration. 5 μg mL^?1 H₂O₂ was applied for accelerating the formation of two necessary disulfide bonds. Antimicrobial assays were performed against E. coli, Salmonella typhimurium, Listeria monocytogenes, Staphylococcus aureus, Aspergillus flavus and Candida albicans. Results of antimicrobial tests confirmed the efficiency of BCN-IbAMP₄ against all tested microorganisms. Overall, the combination of thymol plus BCN-IbAMP₄ increased their antimicrobial activities. MIC, MBC, MFC, FICI and FBCI values showed strong synergistic activity between the two examined compounds. Time kill and growth kinetic studies indicated significant reduction of cell viability during first period of exposure to BCN-IbAMP₄ and thymol combination.     

Sodium trimetaphosphate and hexametaphosphate impregnated with silver nanoparticles: characteristics and antimicrobial efficacy

This study aimed to synthesize and characterize materials containing silver nanoparticles (AgNP) with polyphosphates (sodium trimetaphosphate (TMP) or sodium hexametaphosphate (HMP), and evaluate their effect against Candida albicans and Streptococcus mutans. The minimum inhibitory concentration (MIC) was determined, which was followed by the quantification of the biofilm by counting colony-forming units (CFUs), the amount of metabolic activity, and the total biomass. The MICs revealed greater effectiveness of composites containing 10% Ag (TMP + Ag10% (T10) and HMP + Ag10% (H10)) against both microorganisms. It was observed that T10 and H10 reduced the formation of biofilms by 56–76% for C. albicans and by 52–94% for S. mutans for total biomass and metabolic activity. These composites promoted significant log reductions in the number of CFUs, between 0.45–1.43 log₁₀ for C. albicans and 2.88–3.71 log₁₀ for S. mutans (p < .001). These composites demonstrated significant antimicrobial activity, especially against S. mutans, and may be considered a potential alternative for new dental materials.     

Thymbra capitata essential oil has a significant antimicrobial activity against methicillin-resistant Staphylococcus aureus pre-formed biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) is a multidrug-resistant opportunistic pathogen with a great ability to form biofilms. Herein, the antimicrobial potential of Thymbra capitata essential oil (EO) against MRSA biofilms was investigated. The determination of the minimum inhibitory concentration (MIC) and the minimum lethal concentration (MLC) of the T. capitata EO was first investigated on a group of clinical isolates from septicaemias, diabetic foot ulcers and osteomyelitis. Biofilms were incubated with the EO at the MLC and its anti-biofilm potential was investigated. A strong antimicrobial activity was observed, with MIC and MLC values between 0·32 and 0·64 mg l⁻¹. However, the concentration of EO necessary for the eradication of planktonic cells was insufficient to significantly reduce the biofilm biomass of some isolates. Nevertheless, cell culturability and overall cellular metabolism was strongly reduced in all biofilms tested, only when the EO was tested. Contrary to the tested antibiotics, T. capitata EO showed a significant antimicrobial activity against MRSA biofilms, by reducing cellular metabolism and cellular culturability.