Judul: Isolation and identification of Enterobacter sakazakii from fresh vegetables and fruits samples from Bogor Indonesia
Abstrak: E.sakazakii is classified as a pathogenic bacterium that causes illness mostly to infants and immunocompromised individuals. This bacterium belongs to the group of Gram negative Enterobacteriaceae species, which was re-classified as Cronobacter spp. based on DNA hybridization and phenotyping. E. sakazakii has been widely implicated in a number of foodborne diseases, which are characterized by illnesses like meningitis and enteritis especially in pre-termed neonates and or with low birth weight infants. The bacterium has been isolated from various foods including fresh vegetables and fruits and also survives refrigeration temperatures. This research aim was to isolate E.sakazakii from a number of fresh vegetables and fruits samples available in local market surrounding Darmaga area, Bogor, Indonesia. The isolation followed FDA (2002) method modified by Iversen and Forsythe (2004). Rapid biochemical kit, API 20E, was used for biochemical characterization and identification. Molecular confirmation consisted of isolation of DNA and PCR to amplify the gene encoding for 16S rRNA using two different pair of primers, ESA-1/16SUNI-(R) and 16SUNI-L/Saka 2b. A total number of 19 samples tested positive to pre-enrichment and enrichment broth, in BPW (buffered peptone water) and EE (Enterobacteriaceae enrichment) broth, respectively. Isolation in VRBG (Violet Red Bile Glucose) agar yielded all positive results for all samples. However test on DFI (Druggan–Forsythe–Iversen) agar showed only four isolates producing typical blue/green colony, i.e. those isolated from cabbage, chaisin, apple “fuji” and apple “manalagi”. The biochemical test kit API 20E (Analytical Profile Index; bioMe´rieux) showed that none of the samples were positive for E.sakazakii. The PCR results showed that only one isolate i.e. from cabbage, successfully produced an amplicon of the 16S rRNA. This study suggests that isolation rate of E.sakazakii in vegetable is low at 5.2 %.
Keyword: Cronobacter spp., PCR, Enterobacter sakazakii, fresh produce, DNA fragments

Judul: Biotyping Isolat Lokal Enterobacter sakazakii (Cronobacter spp.) dan Keragamana Genetik Beberapa Isolat Berdasarkan Gen infB
Abstrak: E. sakazakii was initially described as E. cloacae with yellow pigment, and later were classified based on their biochemical reactions, antibiotics susceprability and DNA-DNA hybridization. In 2007, E. sakazakii was reclassified into Cronobacter spp. consisting of C. sakazakii, C. malonaticus, C. muytjensii, C. dublinensis and C. turicensis based on f-AFLP and production of acid from dulcitol, production of indole, malonate utilization and production of acid from methyl-α-D-glucoside. All local isolates obtained from powder infant formula, weaning foods, starch, flours and spices in Indonesia have been identified as Cronobacter spp. and were reported to have close genetic relatedness based on its partial gene sequence encoding for 16S rRNA. However, they have been reported to have different thermal resistance (Seftiono 2012). This study aims to identify and classify local isolates of C. sakazakii based on their biochemical properties and genetic relatedness based on infB genes which known thermal kinetics. Identification of the 19 local isolates using RapID onE suggested that 9 isolates were identified as E. sakazakii, 9 others were E. cloacae and 1 was E. cancerogenus. When the results were compared to the identification using API 20E (Gitapratiwi 2011; Hamdani 2012), 8 of the 19 isolates were identified as E. sakazakii by both kits. Based on classification using 4 biochemical reaction, 15 isolates can be identified as Cronobacter spp. whereas 4 isolates can not be identified. By evaluating biochemical reaction in the RapID onE test kit, it can be conclude that reaction of pyrohydonyl-β-naphthylamide can be used as the additional testing to classify the previously unclassified local isolates into C. sakazakii. Ten of the 19 biochemical tests in RapID onE were selected for the biotyping of Cronobacter spp local isolates since they give different result for all isolates studied. Based on the ten biochemical profiles, the 19 local isolates of Cronobacter spp. can be classified into 16 biotypes. When the results of biotyping with rapid kit RapID onE was compared to result with the four biochemical reaction by Iversen, biotype I-VIII is C. sakazakii; while biotype IX, X, XV and XVI is C. malonaticus; biotype XIII and XIV is C. muytjensii; and biotype XI, XII and XVI is C. turicensis. v Genotypic characterization of infB gene among local isolates showed that all tested isolates where closely related. Based on the BLAST program, it was revealed that the contig sequence of the infB genes was as a translation initiation factor IF2. Based on the infB gene the local isolates can be classified into 2 groups. Isolat DES b7a, DES b10, DES c13, YR t3a and E6 belong to C. sakazakii, while isolate YR c3a is C. malonaticus and C. dublinensis.
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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.
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