Judul: Karakterisasi Senyawa Antibakteri dari Streptomyces spp.  Asosiasi Spons Laut terhadap Beberapa Bakteri Patogen Gram Negatif
Abstrak: The emerging threat of pathogenic bacteria that cause various infectious diseases is a great concern worldwide. This case poses a serious threat as pathogenic bacteria can develop resistance to commonly prescribed antibiotics, rendering many treatments ineffective against infectious diseases. Antibiotic-resistant pathogenic bacteria not only cause soaring economic burdens on health care and length of hospital stay but also increase morbidity and mortality. The antibiotic resistance crisis that occurs in pathogenic bacteria raises an urgent need for antibacterial agents, so some approaches to control the pathogenesis of these pathogens are required. One potential approach is to take advantage of the antibacterial potential of the microorganism, namely Streptomyces spp. Streptomyces is a Gram-positive bacterium from the phylum Actinobacteria, well-known for producing a variety of bioactive compounds, mainly antibiotics. Almost 80% of all commercial antibiotics used today are isolated from Streptomyces. Streptomyces is continuously being explored for the discovery of new antibacterial compounds with better efficacy and lower production costs. Therefore, this study aimed to characterize antibacterial compounds of marine sponge-associated Streptomyces spp. from the Seribu Islands of Indonesia against some Gram-negative pathogenic bacteria. The research started with antibiotic susceptibility testing using 12 commercially available antibiotic discs, to determine the antibiotic resistance profile of the Gram-negative pathogenic bacteria including Extended Spectrum ß-Lactamase (ESBL)-producing Escherichia coli, Providencia rettgeri, Proteus mirabilis, and Pseudomonas putida, so that it can guide in optimizing the production of antibacterial compounds by marine sponge-associated Streptomyces spp. inhibits pathogenic bacteria. Furthermore, the rejuvenation of 3 isolates of marine sponge-associated Streptomyces spp., namely Car21t, Crc27t, and Dbi28t on 3 growth media, International Streptomyces Project 2 (ISP2), ISP4, and modified molasses media, then continued with the process of optimizing growth conditions which include the selection of suitable media to support the availability of nutrients and organic matter that can affect the character and ability of Streptomyces spp. in producing more optimal antibacterial compounds. Optimization of the incubation time of marine sponge-associated Streptomyces spp. was also carried out to determine the optimal growth time of Streptomyces spp. in inhibiting pathogenic bacteria. The literature review shows that no data is available regarding the use of a modified molasses medium for the production of antibacterial compounds by marine sponge-associated Streptomyces spp. Furthermore, the incubation time optimization was also carried out by incubating 3 isolates of Streptomyces spp. at 4 different times, 5, 10, 15, and 20 days and each incubation period was completed, each culture of Streptomyces spp. was harvested, and an antibacterial test was carried out to determine the optimal growth time of Streptomyces spp. in inhibiting pathogenic bacteria. The production of antibacterial compounds by Streptomyces spp. is carried out by growing each Streptomyces spp. isolate at the best growth medium and incubation time, then extraction is carried out using ethyl acetate solvent. The ethyl acetate extract obtained was then subjected to antibacterial tests against test pathogenic bacteria. The ethyl acetate extract of Streptomyces spp. with the strongest antibacterial activity was selected to characterize the content of antibacterial compounds using Liquid Chromatography-tandem Mass spectrometry (LC-MS/MS). The result of the study showed that the Gram-negative pathogenic bacteria including
Keyword: antibacterial, antibiotic resistance, LC-MS/MS, molasses, Streptomyces

Judul: Sponge-associated Bacteria Producing Antimicrobial Compounds and their Genetic Diversity Analysis
Abstrak: Bacteria associated with the marine sponge Haliclona sp. from the coastal region of Waigeo Island were screened for antimicrobial activities using the agar-overlay method. There were 125 bacterial isolates recovered and were subjected to antimicrobial screening for antibiotic production against five test bacterial strains, viz., Bacillus subtilis, Escherichia coli, Staphylococcus aureus, Enteropathogenic Escherichia coli (EPEC), Pseudomonas aeruginosa and two fungal pathogen, viz., Candida albicans and Candida tropicalis. A total of 39 (31%) bacterial strains were found to be antimicrobial producers; however, 15 (38%) of these active strains were eliminated based on the results of Hemolytic Test. The remaining 24 isolates were further analyzed by amplified ribosomal DNA restriction analysis (ARDRA) to assess their genetic diversity and results obtained revealed eight phylotypes. There were nine isolates that were exhibiting wide spectrum of activities against the test strain. The Minimum Inhibitory Concentration of the nine strains was determined and three strains (HAL13, HAL74, and HAA01) showed bactericidal effects. Bacterial extracts were obtained using n-butanol and were subjected to bioactivity assay and TLC autobiography overlay assay. Phylogenetic analysis using 16S rRNA gene sequences revealed that the nine strains belong to the genus Bacillus. The isolation of sponge associated bacteria possessing inhibitory activity against clinical pathogenic strains suggests that they could be potential sources of novel marine natural products.
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Judul: Cycle Hamilton pada Graf Lengkap, Graf Regular, dan Graf 2-Connected 4-Regular Berorder Kurang dari Sepuluh
Abstrak: Suatu graf disebut graf Hamilton apabila graf tersebut memuat cycle Hamilton, yaitu cycle yang melewati setiap vertex tepat satu kali. Menentukan keberadaan cycle Hamilton pada suatu graf dapat menggunakan syarat cukup yang berupa teorema-teorema yang telah diperkenalkan sejak tahun 1950-an. Beberapa syarat cukup yang dibahas dalam karya ilmiah ini adalah syarat cukup yang berhubungan dengan graf lengkap dan graf regular. Suatu graf lengkap berorder 𝑛������ ≥ 3 dan graf r-regular berorder 𝑛������ ≤ 2𝑟������ + 1 merupakan graf Hamilton, Karena kedua graf tersebut memuat cycle Hamilton. Selanjutnya, syarat cukup tersebut digunakan untuk menentukan keberadaan cycle Hamilton pada graf 2-connected 4- regular berorder kurang dari 10.
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular