Judul: Prevalence of Toxigenic Bacillus cereus in Chili and White Pepper from Bogor Area, Indonesia
Abstrak: Chili and white pepper are widely used as spices and/or condiments in many Indonesian cuisines, especially Ready-to-eat (RTE) foods. These spices are often associated with pathogenic microorganisms such as Bacillus (B.) cereus, and have the potential to contaminate foods to which they are added. Bacillus cereus is a spore-forming bacterium widely found in the environment and is responsible for causing diarrheal and emetic syndromes. The organism has been implicated in various food borne outbreaks in different parts of the world. This study aimed to determine the prevalence and concentration of B. cereus in chili and white pepper from markets around Bogor, and to determine the potential toxicity of these isolates based on ces and nheA genes. The study consisted of several stages including sample collection and preparation, isolation and enumeration of Bacillus cereus on Mannitol-egg yolk- polymyxin agar (MYP), presumptive confirmation of the isolates based microscopic observations and biochemical tests, molecular confirmation by detection of 16S rRNA gene, 16S rRNA gene sequencing, phylogenetic analysis and analysis for the possession of nheA and ces toxigenic genes. Out of the forty (20 chili and 20 white pepper) samples analyzed, 33 (82.5%) contained presumptive Bacillus cereus. Ninety percent of white pepper samples (18/20) and 75% of chili samples (15/20) contained presumptive B. cereus. The highest B. cereus concentration in white pepper was 5.77 log10 CFU/g and the lowest was 1.70 log10 CFU/g while the highest in chili was 3.93 log 10 CFU/g and the lowest was 0.70 log10 CFU/g. Ninety five percent (19/20) of samples from the traditional markets and 70% (14/20) from supermarkets contained presumptive B. cereus. Samples from the traditional market had a higher mean log10 CFU/g of 3.25 compared to 2.55 log10 CFU/g from the supermarkets. However, the difference was not statistically significant (P > 0.05). Samples containing B. cereus of >5 log10 CFU/g were found in both market types. Twelve of 13 isolates tested were confirmed as B. cereus based on 16S rRNA gene and BLAST identification. The isolates shared similarity (>98%) with B. cereus strains from GenBank and were phylogenetically related to B cereus. All twelve isolates (100%) possessed the nheA gene but none of them owned the ces gene. Absence of ces gene suggests a reduced risk for emesis from chili and white pepper but the 100% prevalence of nheA gene presents a potential food safety concern and risk for B. cereus diarrheal food borne disease.
Keyword: chili, Indonesia, spices, toxigenic Bacillus cereus, white pepper

Judul: Isolation and Characterization of Bacillus cereus from Fresh Vegetables
Abstrak: Sayuran merupakan komoditas yang memiliki kandungan gizi dan kadar air tinggi sehingga rentan ditumbuhi oleh mikroorganisme, salah satunya Bacillus cereus. B. cereus dapat menyebabkan pembusukan dan penyakit bawaan pangan dan merupakan patogen penyebab penyakit bawaan pangan kedua terbesar di Indonesia. Oleh karena itu, penelitian mengenai keberadaannya dalam berbagai produk perlu dilakukan. Penelitian ini bertujuan mengetahui keberadaan, konsentrasi, dan karakteristik B. cereus dalam sayuran segar, serta mengonfirmasi isolat yang diperoleh menggunakan API 50 CHB. Penelitian dibagi menjadi isolasi, karakterisasi, serta konfirmasi isolat B. cereus yang diperoleh. Sebanyak 20 sampel sayuran diambil dan diisolasi menggunakan mannitol-egg yolk-polymyxin (MYP) agar. Koloni terduga selanjutnya dikarakterisasi dengan pewarnaan Gram, spora, uji katalase, dan dikonfirmasi dengan perangkat API 50 CHB. Isolasi menghasilkan 45 isolat terduga B. cereus dari 20 sampel, dengan konsentrasi 1,55 – 3,61 log CFU/g. Urutan sampel dari yang mengandung B. cereus paling banyak adalah kangkung, kentang, wortel dan bawang, lalu buncis. Karakterisasi dengan pewarnaan dan katalase menunjukkan 35 dari 45 isolat memiliki karakteristik morfologi serupa dengan B. cereus. Dari 20 sampel sayuran, 19 sampel mengandung isolat dengan katakteristik morfologi B. cereus sehingga prevalensinya adalah 95%. Sebanyak 4 isolat dengan karakteristik B. cereus dikonfirmasi dengan API 50 CHB dan terkonfirmasi sebagai B. cereus dengan persentase 99,70 – 99,90%, sementara itu 3 isolat yang tidak memiliki karakteristik B. cereus juga terkonfirmasi sebagai spesies selain B. cereus. Hal ini menunjukkan pewarnaan Gram, spora, dan uji katalase dapat digunakan sebagai pra-konfirmasi B. cereus dari pangan., Vegetables are commodities containing high nutrient and moisture content, so they are prone to microbial growth, such as Bacillus cereus. B. cereus in foods can cause spoilage and foodborne illnesses and was the second most pathogens to cause foodborne illnesses in Indonesia, hence research on its occurrence in various products needs to be done. This study aimed to determine the occurrence, concentration, and characteristics of B. cereus in fresh vegetables, and to confirm the isolates using API 50 CHB. The research consisted of isolation, characterization, and confirmation using a rapid test kit. Twenty samples of vegetables was collected and presumptive B. cereus was isolated using mannitol-egg yolk-polymyxin (MYP) agar. The suspected colonies were characterized by Gram, spores staining, catalase test, and confirmed using API 50 CHB.We obtained 45 suspected B. cereus isolates from all 20 samples, with concentration of 1,55 – 3,61 log CFU/g. The order of samples containing the most B. cereus was water spinach, potatoes, carrots and onions, then snap beans. Characterization concluded that 35 out of 45 suspects were having morphology resembling B. cereus. Of the 20 vegetables, 19 were confirmed to contain isolates with B. cereus morphology hence the prevalence of 95%. A total of 4 isolates with B. cereus morphology were confirmed as B. cereus 99,70 – 99,90% using API 50 CHB and 3 isolates without B. cereus morphology were confirmed as non B. cereus. The result indicates that Gram, spore staining and catalase test can be use for pre confirmation of B. cereus in foods.
Keyword: Bacillus cereus, biochemical confirmation, characterization, isolasi, isolation, karakterisasi, konfirmasi biokimiawi, sayuran, vegetables

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: