A Growth Prediction Of Salmonella In Fresh Cut Lettuce And The Effect Of Anti-Osmotic Stress Response Gene RpoS On Salmonella

Salmonella is a widely spread foodbome pathogen in foods, which jeopardized not only the human health, but also the development of national economics. In order to prevent and control it, this study choosed Salmonella enterica serovar Typhimurium SL1344,SL1344/ArpoS, the former genomes had been sequenced, the latter is the rpoS gene deleted by the former, and a wild type Samonella LQG-1 for a study of microbial growth in stressful environment.First of all, we acclimatized the SL1344, and then periodically hypertonic stimulated it to explore the changes of the growth. Afterwards, SL1344, as original strain, was knocked out rpoS gene by the lambda red homologous recombination technology to build SL1344/?rpoS. Meanwhile, isolation and identification the Salmonella called LQG-1 from fresh pork. Finally, we compared the growth of SL1344, SL1344/ArpoS and LQG-1, to find the regulations and changes of rpoS gene at the transcription level in osmotic response. In order to study the influence of rpoS gene after infection of Salmonella between fresh meat and cut lettuce.In order to illustrate the impact of the periodically change environment on microbial adaptation we studied SL1344. After 3 or 4 subculture, SL1344 were acclimatized, which had the same maximum concentration if they inoculated with the same level, indicate that SL1344 can grow stably in BMM broth with only one carbon source of glucose. The SL1344 was inoculated in BMM broth with the different concentration of salt (3%?3.5%?4% and 5%), the appropriate concentration of NaCl (3.5%) was determined by the growth cycle and lag phase. The SL1344 was cultivated in BMM broth with or without NaCl(3.5%). The results showed that the strain, which without osmotic stress training process, the amount of bacteria reduction rate was declined significantly in the lag phase, and will spend longer time to reach the stationary phase. Furthermore, the reduction rate was decent. In the end, there will be no decrease when the SL1344 was transferred 4 times.Before we studied the influence of the stress response gene rpoS on the growth of Salmonella in food, we made a lot preparation. On the one hand, we built SL1344/?rpoS strain by the lambda red homologous recombination technology. On the other hand, isolation and identification a Salmonella called LQG-1 from fresh pork. By using the same primer for PCR amplification to identify rpoS gene(1344bp), resistance gene(1432bp) replaced of rpoS gene and the sequence (about 500bp) after resistance gene removed. It proves that rpoS gene was deleted. Meanwhile we confirmed that LQG-1 is a Salmonella after isolation and identification.In order to elucidate the effect of the stress response gene rpoS on the growth of Salmonella in food. SL1344, SL1344/ArpoS and LQG-1 were compared in LB broth, BMM with NaCl (3.5%) and on fresh cut lettuce, to determine whether the rpoS gene was important regulator in the stressful condition. The results showed that rpoS gene is important in the stress response.