Judul: Antibacterial Activity of Endophytic Actinobacteria Isolated from Ziziphus sp. against Multidrug-Resistant Strains and Their Identification
Abstrak: Eksplorasi aktivitas antibakteri dari aktinobakteri endofit asal bidara (Ziziphus sp.) perlu dilakukan untuk mendapatkan sumber alternatif baru penghasil antibiotik. Penelitian ini bertujuan mengevaluasi aktivitas antibakteri pada aktinobakteri endofit bidara terhadap lima bakteri multidrug- resistant dan mengidentifikasi isolat potensial melalui pendekatan molekuler berdasarkan gen 16S rRNA. Pada penelitian sebelumnya, 30 isolat aktinobakteri telah berhasil diisolasi dari dari akar, batang, dan daun bidara. Penapisan melalui metode double layer agar diffusion menunjukkan bahwa lima dari 30 isolat aktinobakteri (16%) memiliki aktivitas antibakteri spesifik terhadap methicillin-resistant Staphylococcus aureus (MRSA) dan Bacillus subtilis strain M18. Ekstrak kasar metabolit sekunder dari empat isolat terpilih (BBK 1, DBK 2, DBK 3, dan DBSB 1) juga secara konsisten menujukkan aktivitas penghambatannya terhadap MRSA dengan diamter zona hambat berkisar antara 8±0,8–11±2,9 mm. Minimum inhibitory concentration (MIC) yang ditentukan berdasarkan teknik microbroth-dilution menunjukkan bahwa keempat ekstrak tersebut memiliki MIC yang berkisar 2.500–5.000 μg/mL. Karakterisasi morfologi koloni dan sel pada keempat isolat tersebut menujukkan bahwa isolat-isolat tersebut tergolong aktinobakteri. Berdasarkan identifikasi sekuens gen 16S rRNA, keempat isolat termasuk pada kelompok Streptomyces spp. dengan nilai kemiripan > 99%. Keempat isolat terpilih dapat diteliti dan dikembangkan lebih lanjut sebagai penghasil senyawa anti-MRSA di masa depan.
Keyword: Aktinobakteri endofit, antibakteri, methicillin⎯resistant Staphylococcus aureus (MRSA), Streptomyces spp., Ziziphus sp.

Judul: Antibacterial Activity and Identification of Endophytic Bacteria Isolated from Ziziphus sp.
Abstrak: Penyakit infeksi yang disebabkan oleh bakteri patogen resistan antibiotik menjadi permasalahan utama kesehatan global. Bakteri endofit bidara (Ziziphus sp.) dapat menjadi sumber alternatif penghasil antibiotik baru. Penelitian ini bertujuan menganalisis aktivitas antibakteri isolat bakteri endofit bidara, mengidentifikasi isolat potensial melalui pendekatan molekuler, dan mengidentifikasi profil kimia dari isolat-isolat potensial. Sebanyak 21 isolat bakteri endofit telah berhasil diisolasi dari akar, batang, dan daun bidara. Dual-Culture Agar Diffusion Assay menunjukkan dua dari 21 isolat bakteri memiliki aktivitas antibakteri terhadap empat bakteri target. Estrak kasar metabolit sekunder kedua isolat potensial (80 mg/ml) mampu menghambat semua bakteri target dengan diameter zona hambat berkisar 8,3–15,0 mm. Nilai minimum inhibitory concentration (MIC) dan minimum bactericidal concentration (MBC) yang ditentukan dengan teknik microdilution menunjukkan bahwa kedua ekstrak tersebut memiliki nilai MIC berkisar antara 468,75–>30.000 µg/ml, dan MBC berkisar antara 468,75–>30.000 µg/ml. Berdasarkan analisis gen 16S rRNA, dua isolat potensial yaitu BBSB3 dan BDSB4 masing-masing memiliki kemiripan sekuens tertinggi dengan Pseudomonas aeruginosa strain DSM 50071 dan Pseudomonas aeruginosa strain N. Kedua isolat tersebut terdeteksi memiliki gen polyketide synthase I (PKS I) yang umumnya terlibat dalam biosintesis senyawa poliketida. Analisis liquid chromatograohy tandem mass spectrometry (LC-MS/MS) kedua ekstrak kasar menunjukkan keduanya memiliki berbagai senyawa aktif antibakteri., Infectious diseases caused by antibiotic-resistant pathogenic bacteria are one of the significant health problems worldwide. Exploring the antibacterial activity of endophytic bacteria associated with Ziziphus sp. may provide an alternative source of new antibiotics. This study aims to evaluate the antibacterial activity of endophytic bacteria isolated from Ziziphus sp., identify potential isolates through molecular approaches, and identify the chemical profiles of potential isolates. In previous research, 21 endophytic bacterial isolates were successfully isolated from Ziziphus sp. Antagonism assay showed that two of the 21 bacterial isolates had antibacterial activity against four target bacteria. At a concentration of 80 mg/ml, the crude extract of secondary metabolites of the two potential isolates could inhibit all target bacteria with inhibition zone diameters ranging from 8.3-15.0 mm. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of both extracts ranged from 468.75–>30,000 µg/ml. Based on their 16S rRNA sequences, the selected isolates were closely similar to Pseudomonas aeruginosa strain DSM 50071, and Pseudomonas aeruginosa strain N. Both isolates were also detected to have the PKS I gene, which is generally involved in the biosynthesis of polyketide compounds. LC-MS/MS analysis of the two crude extracts showed both to have various antibacterial active compounds.
Keyword: 16S rRNA, LC-MS/MS, MIC, Pseudomonas aeruginosa, Gen PKS I

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
Keyword: