Judul: Cytotoxicity and Green Fluorescent Protein labeling of Cronobacter spp. to study its behaviour during corn drying
Abstrak: Cronobacter spp. (previously known as Enterobacter sakazakii) is a group of Gram-negative bacteria consisted of six species, including Cronobacter sakazakii and Cronobacter muytjensii (Iversen et al. 2008). Cronobacter spp. is regarded as an emerging foodborne pathogen that causes meningitis, bacteremia and necrotizing enterocolitis in certain groups of infants as a consequence of contaminated infant formulae consumption. Pathogenesis of Cronobacter is caused by several virulence factors, including its toxins. Medium free cells of Cronobacter spp. have been reported to cause alteration of Vero cells morphology due to its cytotoxic activity. In Indonesia, Cronobacter spp. have been isolated (Estuningsih et al. 2006, Meutia et al. 2008, Gitapratiwi et al. 2012 and Hamdani 2012). All of the isolates were obtained from dried food products; i.e powdered infant formula, weaning food, rice flour, tapioca, cornstarch, sugar, cocoa powder and dried spices, suggesting that they were able to survive drying. The data reported by FAO-WHO (2004) showed that the ingredient added through dry mixing process was one of the sources of Cronobacter spp. contaminant in powder infant formulae. Current researches supported this issue, Dewanti-Hariyadi et al. (2010) have isolated Cronobacter spp. from cornstarch and Fiegen (2010) have isolated the pathogen form cornstarch and other ingredients (lecithin, potato starch, rice starch and wheat starch). It is important to understand Cronobacter spp. survival during drying due to its presence in dried food products. Maize was chosen as a food model in this study due to its widespread use as raw materials for dried food products. For specific detection and enumeration, a Green Fluorescent Protein (GFP) was introduced into Cronobacter cells as a marker. GFP is a protein from jellyfish (Aequorea Victoria) which can fluoresce and its gene has been inserted into a plasmid (pGFP) as a vector. The pGFPuv is a GFP variant plasmid having fluorescence signal 45-fold greater than a standard pGFP and this was achieved by DNA shuffling. The mutant can grow in ampicillin containing medium and was seen as a green fluorescents colony. The objectives of this study were to evaluate cytotoxic activity of food originated isolates of C. sakazakii and C. muytjensii and to evaluate their survival, colonization and penetration during maize drying. This research was conducted in three steps: 1. In Vitro analysis of cytotoxic activity of C. sakazakii and C. muytjensii using Vero cell and haemolytic activity on blood agar medium; 2. Construction of GFP-labeled C. sakazakii and C. muytjensii, study of their stability and growth characteristics; 3. Use of the mutant to study the survival, colonization and penetration of C. sakazakii during maize drying. As much as nineteen C. sakazakii isolates dan one C. muytjensii isolate obtained from previous research were used for this study originated from cornstarch, tapioca, flour, infant milk formulae, weaning food and powder dried spices. Twenty isolates of C. sakazakii and C. muytjensii originated from food have different cytotoxic activity of their toxins. Thirteen out of 20 isolates (65% samples) were confirmed as cytotoxic positive including one isolate C. muytjensii while 7 isolates were grouped as nontoxic. Five isolates with the highest cytotoxic activity were C. sakazakii FWHb6,
Keyword: C. sakazakii, C. muytjensii, Green Fluorescent Protein, cytotoxicity, maize

Judul: Penggunaan pGFPuv Mutan Untuk Mempelajari Pengaruh Pengeringan Pada ketahanan hidup Cronobacter sakazakii Dalam Jagung.
Abstrak: Cronobacter sakazakii is an emerging Gram-negative foodborne bacterial pathogen regarded as the causative agent of meningitis and necrotizing enterocolitis in certain groups of infants. Several isolates of C C. sakazakii have been obtained from food samples in Indonesia and transformation with a Green Fluorescent Protein (GFP) plasmid has produced C. sakazakii pGFPuv mutants with growth pattern similar to that of the wild-type strains. Therefore, they are potential to be used for studying C. sakazakii behaviour without the need to suppress other microorganisms and the use of diagnostic media. The research activities focused on the following objectives : to study the effect of drying on water content and water activity of maize and to evaluate the survival of C. sakazakii pGFPuv as well as other naturally occurring microorganisms in maize during drying. Maize kernels with moisture content of 40% (d.b) were inoculated with C. sakazakii pGFPuv mutant such that the initial concentration in the maize was CFU/g and drying was performed at temperatures of 42 ºC, 46 ºC and 50 ºC for ten days in a drying chamber. Every day the maize samples were taken and the water content were analyzed using oven method while water activity by Aw meter. Total Plate Count and C. sakazakii surviving in the maize were enumerated by standard plate count. The survival rate of C. sakazakii during drying was determined by the slope of linear regression from C. sakazakii survival curve. The results showed that the fate of decrease of C. sakazakii during the rapid decline of water content and Aw can be divided into three phases, i.e. logarithmic decrement, static growth and the final decline. The critical water activity for these pathogenic bacteria was in the range of 0.85-0.86. Observation by SEM showed that C. sakazakii GFPuv form colonies on the surface of corn and the tip cap. This study showed that of C. sakazakii pGFPuv can be used to study the survival of C. sakazakii during corn drying.
Keyword: Cronobacter sakazaki, pGFPuv, maize, survival, drying, water activity

Judul: Formulasi Hamiltonian untuk Menggambarkan Gerak Gelombang Soliter Dimensi Tiga di Permukaan Laut
Abstrak: Gelombang permukaan adalah gelombang yang terjadi perbedaan rapat massa antara air dan udara. Salah satu gelombang permukaan yang ditinjau adalah gelombang soliter. Formulasi gelombang soliter dilakukan dengan menggunakan formulasi Hamiltonian.
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