Listeria monocytogenes Oxygen Consumption

Listeria monocytogenes is a human pathogen responsible for foodborne illnesses with a high mortality rate. Similarly to many other enteric pathogens, it is a facultative anaerobe capable of growing under anoxic conditions such as some food packaging and our intestinal lumen. Therefore, to better understand how Listeria responds to fluctuating oxygen levels during transmission and infection, we measured oxygen consumption rate of Listeria grown under different conditions. Bacteria were grown overnight to stationary phase in BHI media aerobically or anaerobically and back diluted into fresh BHI for 2 hours to reach mid-log phase. The optical density of all cultures was measured and used to normalize oxygen consumption rate. The bacteria was centrifuged, washed, and resuspended into a concentrated suspension. The oxygen level was measured with the use of an oxygen probe inside an anaerobic chamber. The oxygen level of blank BHI media was measured and subtracted from the final oxygen rate. The results showed that anaerobically-grown mid-log phase bacteria has the fastest rate of oxygen consumption, followed by the aerobically-grown mid-log phase, then the anaerobically-grown and the aerobically-grown stationary phase bacteria. To test the role of electron transport chain in oxygen consumption rate, we treated the sample with the uncoupler CCCP during oxygen concentration measurement. Interestingly, the presence of CCCP did not significantly alter oxygen consumption rate, a result suggesting the presence of another oxygen consumption pathway other than the electron transport chain. The acutely toxic salt anion sodium azide will be tested next to determine if the cytochrome oxidase is involved in oxygen consumption. In summary, our results indicate a significantly different oxygen consumption potential between aerobically and anaerobically grown Listeria that may contribute to its transmission through environments with fluctuating oxygen levels