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The oxidative stress mechanisms of Streptococcus pneumoniae

Bakker, B. (2011) The oxidative stress mechanisms of Streptococcus pneumoniae. Bachelor's Thesis, Biology.

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Streptococcus pneumoniae is a catalase-negative facultative anaerobic organism which can survive the oxidative stress conditions found in the human naso-oropharynx. These conditions are the result of an aerobic environment as well as immune cells. Reactive Oxygen Species (ROS) in particular pose a threat to the pneumococcus. Although it is known that the pneumococcus can offer resistance to oxidative stress, it is not known precisely how this resistance is mediated. In this thesis an overview is given of the various mechanisms involved in this resistance. The pneumococcus relies upon an NADH oxidase and manganese dependent superoxide dismutase to offer resistance against molecular oxygen and superoxide. When components of this system are lost, the pneumococcus displays an increase in the sensitivity to these ROS, as well as a decrease in virulence in vivo. A delicate balance in intracellular manganese concentrations has also been established as a vital contributor to virulence and resistance to superoxide. Oxidative stress by hydrogen peroxide does not involve the Fenton reaction, as is the case is most other bacteria, but is likely due to Mode II killing. S. pneumoniae also produces endogenous hydrogen peroxide via SpxB. The endogenously produced hydrogen peroxide can be used to neutralise competing bacteria in the naso-oropharynx. Endogenous hydrogen peroxide is also involved in stationary growth killing, and low concentrations of this ROS are likely scavenged by the putative alkylhydroperoxidase spr0370. The regulation of the pneumococcal oxidative stress response is likely provided by a combination of various proteins, including htrA and rgg. Defects in these proteins show a pleiotropic effect on both resistance to oxidative stress as well as a loss in virulence. However, the precise mechanism by which regulation can occur via these proteins and genes remains unclear. It has been shown that the pneumococcus utilises a plethora of mechanisms to cope with oxidative stress, although the specific details of several of these mechanisms remain unclear. It’s argued that further investigation of these uncertainties may provide more insight into the unknowns concerning the oxidative stress response of S. pneumoniae.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Biology
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 07:45
Last Modified: 15 Feb 2018 07:45

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