Judul: The Effect of Growth Medium and Glucose on Biofilm Formation by Local Isolates of Bacillus cereus on  Stainless steel Surfaces
Abstrak: Bacillus cereus merupakan bakteri yang sering dilaporkan menjadi penyebab terjadinya kejadian luar biasa penyakit bawaan pangan. Bakteri ini mampu membentuk spora yang menyebabkannya tahan terhadap kondisi panas, bahan kimia dan kondisi ekstrem lainnya. Selain itu bakteri telah dilaporkan membentuk biofilm yang juga dapat membuatnya lebih resisten. Biofilm yang terbentuk pada sarana pengolahan berpotensi menyebabkan kontaminasi bakteri pada produk pangan. Pembentukan biofilm ini dipengaruhi oleh berbagai kondisi salah satunya keberadaan nutrisi. Tujuan dari penelitian ini adalah untuk mempelajari pengaruh konsentrasi media pertumbuhan dan keberadaan matriks glukosa terhadap pembentukan biofilm oleh Bacillus cereus pada permukaan stainless steel. Pembentukan biofilm dilakukan dengan menginokulasikan kultur B. cereus WM-1SJ, NH1-BO1, dan LH10-KP1 pada permukaan stainless steel dalam media TSB dengan konsentrasi berbeda serta pada media dengan suplementasi glukosa. Biofilm dengan densitas tertinggi terbentuk pada media 1/5 TSB. Biofilm dengan densitas tertinggi dibentuk oleh isolat NH1-BO1 sebesar 4,81 log CFU/cm2 pada waktu inkubasi 24 jam. Media yang ditambahkan 0,5% glukosa menghasilkan biofilm dengan densitas yang lebih tinggi dibandingkan pada media dengan konsentrasi glukosa lainnya. Dalam media yang mengandung matriks glukosa, biofilm dengan densitas tertinggi dibentuk oleh isolat WM-1SJ pada waktu inkubasi 120 jam sebesar 5,14 log CFU/cm2. Penambahan glukosa konsentrasi rendah membentuk densitas biofilm lebih tinggi., Bacillus cereus is a bacterium that is often reported to cause foodborne disease outbreaks. The bacteria are capable of forming spores which make them resistant to heat, chemicals and other extreme conditions. In addition, B. cereus have been reported to form biofilms which also make them more resistant to extreme conditions. Biofilms formed in processing facilities have the potential to cause bacterial contamination of food products. The formation of biofilm is influenced by various conditions, one of which is the presence of nutrients. The purpose of this study was to study the effect of growth media concentration and the presence of a glucose matrix on the formation of biofilm by Bacillus cereus on the surface of stainless steel. Biofilm formation was carried out by inoculating B. cereus WM-1SJ, NH1-BO1, and LH10-KP1 cultures on stainless steel surfaces in TSB media with different concentrations and on media with glucose supplementation. Biofilms with the high densities (4,33 – 4,74 log CFU/cm2) were formed in 1/5 TSB media. B. cereus NH1-BO1 isolate grown for 24 hours produces, biofilms with the highest density (4.81 log CFU/cm2). When the 1/5 TSB medium was added with 0.5% glucose, B. cereus produced biofilms with a higher density than that supplemented with 1% and 2% glucose. In glucose supplemented media, biofilm with the highest density was formed by B. cereus WM-1SJ at 120 hours incubation time, i.e 5.14 log CFU/cm2. The addition of low concentrations of glucose to the growth medium formed a higher density of biofilm.
Keyword: Bacillus cereus, Biofilm, Glucose-supplemented medium, Growth medium

Judul: Bacterial Growth and Sporulation during Biofilm Formation by Vegetative Cells and Spores of Bacillus cereus
Abstrak: Bacillus cereus merupakan bakteri patogen pembentuk spora yang dapat menyebabkan keracunan pangan. Baik sel vegetatif maupun spora B. cereus telah dilaporkan dapat membentuk biofilm pada permukaan stainless steel (SS). Penelitian ini bertujuan untuk membandingkan pembentukan biofilm oleh sel vegetatif dan spora dan mengetahui terjadinya sporulasi selama pembentukan biofilm oleh tiga isolat lokal B. cereus. Sel vegetatif atau spora isolat lokal B. cereus diinokulasikan ke dalam Erlenmeyer berisi Tryptic Soy Broth (TSB) serta pelat SS ukuran 1 x 1 cm2 dan diinkubasi pada suhu 30-33oC. Setelah inkubasi selama 24, 72, 120, dan 168 jam, pelat SS diswab dan densitas biofilm dienumerasi pada Tryptic Soy Agar (TSA) dengan teknik cawan tuang. Densitas biofilm yang terbentuk baik oleh sel vegetatif dan spora B. cereus pada setiap waktu inkubasi adalah serupa. Densitas biofilm meningkat seiring berjalannya waktu inkubasi hingga mencapai 4,8 log CFU/cm2. Selama pembentukan biofilm terjadi sporulasi yang ditandai dengan dengan meningkatnya jumlah spora. Persentase spora pada biofilm meningkat seiring berjalannya waktu inkubasi hingga mencapai 89,13% dari total sel biofilm pada waktu inkubasi 168 jam. Kemampuan sel vegetatif dan spora B. cereus membentuk biofilm serta terjadinya sporulasi selama pembentukan biofilm berpotensi menjadi sumber cemaran yang sulit diinaktivasi di industri pangan., Bacillus cereus is a spore-forming pathogenic bacterium that can cause food poisoning. Both vegetative cells and B. cereus spores have been reported to form biofilms on stainless steel (SS) surfaces. This study aimed to compare biofilm formation by vegetative cells and spores and to determine the occurrence of sporulation during biofilm formation by three local isolates of B. cereus. Vegetative cells or spores of local isolates of B. cereus were inoculated into Erlenmeyer containing Tryptic Soy Broth (TSB) and 1 x 1 cm2 SS plate and incubated at 30-33oC. After incubation for 24, 72, 120, and 168 hours, the SS plates were swabbed and the biofilm density was enumerated on Tryptic Soy Agar (TSA) using the pour-plate technique. The density of the biofilm formed by both vegetative cells and B. cereus spores at each incubation time was similar. Biofilm density increased with incubation time until it reached 4,8 log CFU/cm2. During the formation of biofilms, sporulation occurs which is characterized by an increase in the number of spores. The percentage of spores in the biofilm increased with the incubation time until it reached 89.13% of the total biofilm cells at an incubation time of 168 hours. The ability of vegetative cells and B. cereus spores to form biofilms and the occurrence of sporulation during biofilm formation has the potential to be a source of contamination that is difficult to inactivate in the food industry.
Keyword: Bacillus cereus, biofilm, spores, sporulation, vegetative cells

Judul: Truncated Stop Loss as a Optimal Solution of Reinsurance Agreement in One-Period Model
Abstrak: Reinsurance is one of risk management efforts of an insurance company, which is called the cedent. Similar with insurance, reinsurance constitutes the cedent to pay the premium. We consider one-period reinsurance model and derive a rule which minimizes the ruin probability of the cedent for a fixed reinsurance premium. Therefore, it is needed to construct an optimal reinsurance agreement for the cedent. The premium is calculated according to four different principles, i.e. economic, generalized zero-utility, Esscher, and mean-variance principles. Stop loss is a reinsurance contract which protect the insurance company for losses that exceed a certain amount. The result of this research shows that a truncated stop loss is an optimal agreement in the class of all reinsurance contracts with various premiums calculated using above mentioned principles.
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