Related Experiment Videos
Association with MDCK epithelial cells by Salmonella typhimurium is reduced during utilization of carbohydrates
1Department of Microbiology, Montana State University, Bozeman 59717.
Abstract:
Association of Salmonella typhimurium with MDCK epithelial cells in monolayers, represented primarily by intracellular bacteria after 30 min of contact, with centrifugation followed by vigorous washing, was measured during aerobic and anaerobic growth of the bacteria in brain heart infusion broth. Cell association was greatest during a short period in the late log phase of growth under aerobic conditions. At this time, the pH of the growth medium was changing from acid to alkaline and glucose (0.2% initially) was exhausted. Addition of excess glucose (0.5%) to brain heart infusion broth, which was not exhausted before the bacteria entered the stationary phase of growth, in which cell association dropped sharply, resulted in repression of cell association by the bacteria. The repressive effect of glucose on cell association could not be reversed by exogenous cyclic AMP in the bacterial growth medium. Under anaerobic conditions, the effect of glucose on cell association by the bacteria was not as great and the glucose was not exhausted before the bacteria entered the stationary phase. When S. typhimurium was grown in a rich but carbohydrate-free medium, cell association by the bacteria increased earlier in the growth cycle under both aerobic and anaerobic conditions. The addition of glucose and certain other utilizable carbohydrates to this medium caused a repression of cell association by S. typhimurium that was greater under aerobic growth conditions. These results show that cell association by S. typhimurium, which is accompanied by rapid internalization (cell invasion), is the same under aerobic and anaerobic conditions if the bacteria are grown to the log phase in a carbohydrate-free medium. This suggests that prior reports of greater cell invasion by S. typhimurium during anaerobic growth may have arisen from the use of media containing carbohydrates which were found to be more repressive during aerobic growth of the bacteria.
Insights
Glucose presence significantly impacts Salmonella typhimurium
Area of Science:
- Microbiology
- Cell Biology
- Bacterial Pathogenesis
Background:
- Salmonella typhimurium invasion of epithelial cells is crucial for pathogenesis.
- Factors influencing bacterial-host cell interactions require detailed investigation.
- Previous studies suggested differential invasion under aerobic vs. anaerobic conditions.
Purpose of the Study:
- To investigate the role of bacterial growth conditions, specifically glucose availability and oxygen levels, on Salmonella typhimurium association with epithelial cells.
- To elucidate the mechanisms underlying Salmonella typhimurium cell invasion.
- To re-evaluate the influence of aerobic versus anaerobic growth on bacterial cell association.
Main Methods:
- Quantification of Salmonella typhimurium association with MDCK epithelial cell monolayers.
- Cultivation of bacteria under aerobic and anaerobic conditions in media with varying glucose concentrations.
- Analysis of bacterial growth phases and medium composition (pH, glucose levels) during association assays.
Main Results:
- Cell association peaked in late log phase under aerobic conditions when glucose was depleted and pH shifted.
- Excess glucose repressed Salmonella typhimurium cell association, particularly under aerobic conditions.
- Carbohydrate-free media promoted earlier and similar cell association under both aerobic and anaerobic growth.
Conclusions:
- Glucose availability is a critical regulator of Salmonella typhimurium cell association and invasion.
- The repressive effect of glucose on bacterial invasion is more pronounced under aerobic conditions.
- Observed differences in invasion rates in prior studies may be attributed to carbohydrate content in growth media.