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.

Aims: The aim of the study was to isolate and characterise bacteriophages specific to Pseudomonas aeruginosa carrying virulence genes. Methodology and results: Four clinical strains of P. aeruginosa CL1, CL2, CL3 and CL4 were obtained from Queen Elizabeth Hospital, Kota Kinabalu, Sabah. The bacterial strains were screened for virulence genes exoS, toxA and oprI and biofilm production. Six P. aeruginosa specific bacteriophages, namely PAtk1, PAtk2, PAtk3, PAtk4, PAtk5 and PAtk6, were isolated from Tasik Kejuruteraan, Universiti Kebangsaan Malaysia. These bacteriophages were screened for lytic spectrum against P. aeruginosa and two species of Enterobacteriaceae (Escherechia coli and Salmonella Typhi). PCR results showed that all strains possessed exoS, toxA and oprI genes except CL2 that lacked exoS. Nevertheless, it was CL2 that produced the highest biofilm density. Further, based on Transmission Electron Microscopy, PAtk15 and PAtk6 were classified into the family Myoviridae and Siphoviridae, respectively. Among all six isolated phages, only PAtk4 and PAtk6 showed the broadest lytic spectrum in which lytic activity was observed against all clinical P. aeruginosa strains. Conclusion, significance and impact of study: In this study we reported the isolation of six bacteriophages from Myoviridae and Siphoviridae that are specific to P. aeruginosa possessing exoS, toxA and oprI genes. Bacteriophages Patk4 and PAtk6 were able to infect all four strains of P. aeruginosa, making these phages potential agents in combating infections by the bacterium.