Siti Nurjanah

Stability and growth characteristics of GFPuv-labeled Cronobacter sakazakii isolated from foods

Stability of ultraviolet green fluorescent protein (GFPuv)-labeled Cronobacter sakazakii and C. muytjensii isolated from foods and the effects of the plasmid GFPuv (pGFPuv) on growth were analyzed. PCR analysis and microscopic observation showed that C. sakazakii and C. muytjensii isolates took up the plasmid into cells and expressed the GFPuv gene. All Cronobacter transformants maintained this plasmid after frozen storage and 2 consecutive subcultures. The C. sakazakii FWHd16 transformant was the most stable, while the C. muytjensii FWHd11 transformant was the least stable. All transformants showed nearly identical growth curves during lag, log and stationary phases, compared to wild type parental isolates. The maximum bacterial growth rates (μmax) of the transformants and parents were similar, indicating that the presence of pGFPuv in transformants did not affect cell growth. Stable GFPuv-labeled Cronobacter has potential for use in tracking bacterial behavior during food handling and drying.

Identification of Listeria monocytogenes on Green Mussels and Cockle Shell

Abstract Green mussel (Perna viridis) and cockle shell (Anadara granosa) are one of many sources of animal protein which is many cultivated in Indonesia because their price is relatively affordable. This study was conducted to identify the presence of Listeria monocytogenes in 27 samples of green mussels and 3 samples of cockle shells using real-time Polymerase Chain Reaction (real-time PCR) and biochemical methods. The target gene for amplification in real-time PCR was an hlyA gene because this gene was a determinant of virulence genes that produce listeriolysin O. Primers used in this study were forward primer DG69 (GTG CCG GGT AAA AGA CCA TA) and reverse primer DG74 (CGC CAC TGA GAT ACT AT) and fluorescence signals indicator using SYBR Green I. The results of analysis using real-time PCR were negative Listeria monocytogenes in all samples, while using biochemical methods there was one of 30 samples contaminated by Listeria welshimeri.