Antibacterial and antibiofilm analyses of Melastoma malabathricum leaves extract against Streptococcus mutans on tooth surfaces

Aims@#Dental caries is a chronic infectious disease caused by Streptococcus mutans due to its ability to form biofilm. This study aims to assess the antimicrobial efficacy of Melastoma malabathricum leaf extract against S. mutans on the surface of tooth samples as a potential therapy for dental caries.@*Methodology and results@#Extraction of M. malabathricum leaves was done using acetone as the solvent and antibacterial activity of the extracts was determined by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Antibiofilm activity of M. malabathricum extract against S. mutans was determined by comparing the colony count, biofilm formation assay and morphology observation by scanning electron microscope (SEM). The MIC value of extracts was 6.25 mg/mL and MBC value was >25 mg/mL. A decrease in colony count was noted when tooth samples were incubated with M. malabathricum extract for 8 h compared to 4 h incubation. At pH 5, the formation of the colony was the least, medium at pH 8 and maximum at pH 7. A decrease in biofilm formation was observed when tooth samples were incubated with the extract for 8 h. SEM observations showed treatment with the extract caused S. mutans cell membrane to leak leading to cell morphology changes.@*Conclusion, significance and impact of study@#Acetone extract of M. malabathricum leaves showed excellent antibacterial activity against S. mutans. It has bactericidal activity with the ability to inhibit biofilm in dose-dependent manner against S. mutans. The morphological analyses suggested that the extract disrupted the cell membrane of the bacteria.

Orthosiphon stamineus water extracts inhibit human herpes virus 1 KOS-1 and acyclovir-resistant strains by virucidal activity and suppressing virus early infection

Aim@#To determine the efficacy and mode of action of hot and cold water extracts of Orthosiphon stamineus leaves against two strains of human herpes virus 1 (HHV-1) i.e. KOS-1 and acyclovir (ACV)-resistant UKM-1 (UKM-1) strains. @*Methodology and results@#Hot and cold water extracts of O. stamineus were not cytotoxic to vero cells as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) (MTT) assay with 50% cytotoxicity concentration (CC50) values of 3.4 and 3.3 mg/mL respectively. Antiviral activity was determined by plaque reduction assay in post-treatment, pre-treatment and virucidal assays followed by time-addition and time removal assay to relate with the stages during the viral infection cycle. Both extracts displayed antiviral activity against HHV-1 KOS-1 and HHV-1 UKM-1 strains with 50% effective concentration (EC50) values between 0.12-0.15 mg/mL in reducing plaque formation. The calculated selectivity indices (SI) were 23 and 28 for hot and cold water extract respectively, indicating that they have good potential as antiviral agent. The extracts were virucidal towards both HHV-1 KOS-1 and HHV-1 UKM-1 strains which may directly affects the virus structure. This is supported with the fact that exposure of the extracts inhibit viral attachment and penetration to the vero cells. In time-of addition assay, both extracts were effective during the early stage of virus infection cycle for HHV-1 KOS-1 strain which is in parallel with the results from the attachment and penetration studies. For HHV-1 UKM-1 strain, contact to the extracts at any time during post-infection inhibits virus replication and also progeny release. @*Conclusion, significance and impact of study@#Cold and hot water extracts of O. stamineus have good potential as antiviral agent against HHV-1 strain KOS-1 and more importantly against UKM-1 strain which is ACV-resistant. The extracts displayed virucidal effect and inhibition of early virus replication cycle involving viral attachment and penetration to cells.

The effect of FRAW towards the growth of chilli seedlings and its associated microorganisms

Abstract@#This study aims to evaluate the effect of Fermented Rice After-wash Water (FRAW) on chilli growth and to isolate microorganism present in three brands of white rice FRAW. The study showed that FRAW treatment was comparable with NPK fertiliser. In addition, a number of plant growth-promoting microbes associated with FRAW were also isolated. Isolated bacteria and fungi were then characterised according to their morphology and biochemical analysis. Thus the positive effect of FRAW on the chilli was likely due to the plant growth promoting microorganism present in FRAW.

The importance of GDN motif in domain III and GXGXG motif in domain VI of L protein in replication of Nipah virus

Abstracts@#This study aims to determine the importance of conserved GDN motif in domain III and GXGXG motif in domain VI in Nipah virus (NiV) L protein. Four mutated L genes produced in an earlier study were inserted individually into plasmid pCITE. Optimised transfection protocol was successful in transfecting these plasmids, two helper plasmids (coding for N and P protein), NiV minigenome containing chloramphenicol acetyltransferase (CAT) reporter gene and T7 promoter. Successful in vitro transcription/translation in the NiV minireplicon system was monitored by CAT expression. In conclusion, GXGXG motif was important in the NiV minireplicon system but change of GDN motif does not affect L protein.

Anti-herpes simplex virus type-1 activity of Eleusine indica methanol extract

Aims: The present study is aimed at determining the antiviral activity of Eleusine indica whole plant methanol extract. Methodology and results: Whole dried plants were extracted with methanol and the solvent was evaporated using a rotary evaporator. The crude methanol extract was previously shown to have antiviral activity towards herpes simplex virus type 1 (HSV-1) with selective index (SI = CC50 / EC50) of 12.2. The extract was further studied for the possible mode of action including pretreatment, attachment, penetration or virucidal activity. The observations suggested that E. indica crude methanol extract protects cells from HSV-1 infection, inhibits virus from docking to the surface of the cells and penetrating into the cells, as well as modifying virus through the virucidal effect. Conclusion, significance and impact of study: Methanol extract of E. indica is safe with antiviral potential as a prophylactic agent, inhibits viral attachment, penetration and virucidal effect.

In vitro antiviral activity of styrylpyrone derivative-incorporated formulations against Herpes simplex virus type-1

Aims: This study was aimed to evaluate in vitro antiviral activity of topical formulations incorporated with a styrylpyrone derivative (SPD) against Herpes Simplex Virus type 1 (HSV-1). Methodology and results: Two types of SPD-incorporated formulations (ointment and gel) were tested for their antiviral activity against HSV-1 clinical strain using plaque reduction assay on Vero cells. The antiviral activity was determined based on the percentage of plaque reduction occurred between treatment and control (non-treated infected cells). In this study, 10% SPD-gel (SPD = 0.004 mg) and 20% SPD-ointment (SPD = 0.003 mg) showed plaque reduction percentage of 87% and 79% respectively. Further evaluation on the ointment base, gel base (formulation without SPD) demonstrated less than 10% of antiviral activity while pure SPD at 0.0025 mg showed 81% of plaque reduction. These results indicated that the antiviral activity observed in both SPD-incorporated ointment and gel was mainly due to SPD regardless of formulation components. Furthermore, the antiviral activities observed in both SPD-incorporated products were also in agreement with the antiviral activity observed in pure SPD. Conclusion, significance and impact study: SPD-incorporated products retained the antiviral activity and can further be tested in animal model.

Antibacterial and biofilm inhibition activities of Melastoma malabathricum stem bark extract against Streptococcus mutants

Aim: This study was to determine the antibacterial activity of Melastoma malabathricum stem bark acetone extract (MMSBAE) against Streptococcus mutans. Methodology and results: Antibacterial activity of the extract was determined by minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC), biofilm formation, adherence inhibition, time kill studies and effect on S. mutans membrane integrity. MIC and MBC values of MMSBAE were 1.25 and 5 mg/mL, respectively. Time kill studies showed that reduction of colony forming unit in treated cells is 3 log10 after 10 h of treatment (p ˂ 0.05). The extracts reduced 50% biofilm and adherence activity of S. mutans at 1.88 mg/mL. The effect on S. mutans membrane integrity after exposure to MMSBAE for 90 and 120 min was determined by measuring leakage of cell content at 2 different wavelengths of 260 nm and 280 nm. In leakage assay, the percentage of absorbance (260 nm) in treated cell material showed 57% at 90 min and 60% at 120 min which is higher than negative control (<20%) but less than positive control (100%). The percentage absorbance of treated cell material (280 nm) was 61% at 90 min and 63% at 120 min. Identification of compound in MMSBAE was done by gas chromatography mass spectrometry (GCMS). Ten compounds were identified in the MMSBAE with some of them important in antimicrobial activity such as ethyl ester, undecene, and gamma sitosterol. Conclusion, significance and impact of study: MMSBAE showed excellent bactericidal and antibacterial activities against S. mutans. The antibacterial mode of action of MMSBAE is suggested to be the disruption of the S. mutans membrane structure. The MMSBAE significantly inhibited biofilm and adherence activities of S. mutans in dose dependent manner (p ˂ 0.05). MMSBAE has potential in the development of antibacterial agent with anti-biofilm and anti-adherence activities.