Clostridium botulinum: An overview and the dangers of neurotoxicity and Botulism
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Overview
By Emily Buckwalter
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What is Clostridium botulinum?
Life Cycle
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Clostridium botulinum grows and reproduces via the process of endospore formation and germination [1]. Most bacteria experience vegetative growth, whereby the cell divides in a 1, 2, 4… fashion and continues to multiply and divide [2]. However in the case of spore-forming bacteria, given specific stimuli typically from the environment, the bacteria can pause vegetation growth and start germination [2]. Since C. botulinum is able to form spores, this not only provides the cell with a means of protection but it also promotes the production of BoTN during the process of germination [11].
It is also known that spores can be activated based on environmental signals such as specific pH concentrations or temperatures, which is important especially in the food industry for means of food preservation [8]. Clostridium botulinum grows best under acidic conditions, specifically around a pH of 5 [10]. Each of the two major groups (Group I and Group II) that target humans as hosts have their own optimal temperature for growth at 35℃ and 28℃ respectively [8]. However, it is interesting to note that the Group II phenotype of C. botulinum, with BoTN types B, E and F, is able to generate neurotoxin at 3-4℃, which is standard refrigeration temperature [8]. This is dangerous especially for food production and safety. Therefore, it is important that any materials associated with food processing are properly sterilized, using extreme heat and pressure [2].
By selecting a temperature that is well out of the growth temperature for C. botulinum, along with pressure, this will effectively ensure that almost every microbe has been killed so that they cannot grow once packaged and stored with food. This is one of the reasons why home-canned food is related to many recent outbreaks of botulism [8]. Home canned foods typically can not ensure the same level of safety as commercial canner’s who are using equipment that produces extreme heat and pressure to kill any spores of C. botulinum that may be contaminating the packaging of the product [8]. Some spores are able to resist the cooking and boiling process of at home canning processes [8].
The danger surrounding C. botulinum presents itself under temperatures ranging from 40℉ to 120℉, anaerobic and low pH environments such as in a can, where these heat resistant spores can then convert and mature into growing cells [12]. Previous research has found that each C. botulinum group demonstrates different levels of heat resistance, with Group I spores being the most heat resistant, Group II being the least heat resistant [13]. The spores of Clostridium botulinum have been able to achieve heat resistance through the structure of the spore formed [13].
Clostridium botulinum is an obligate anaerobe, meaning that it does not function under the presence of oxygen, and therefore must reside in low oxygen environments to prevent the toxicity of oxygen to the cells [1]. In order to metabolize sugars to produce energy for the bacterial cell, Clostridium botulinum primarily will use the anaerobic process of fermentation to produce energy. However it has been identified that some species of C. botulinum are able to use both fermentation pathways, while still being equipped with a glycolysis pathway [13]. The fermentation pathway consists largely of a series of oxidation-reduction reactions that are coupled and require electron transport via specific carriers such as NADH [2]. C. botulinum has been found to ferment specific amino acids including: glycine, proline, phenylalanine and leucine, all of which are nonpolar amino acids [13]. However one of the largest means of energy production for the bacterial species comes from the breakdown of chitin, a polysaccharide. The bacteria accomplish this via five different encoded enzymes, but also with the help of proteases which are able to cleave some of the large polysaccharide into more manageable, smaller molecules for metabolic pathways [14]. Chitin is most commonly used by this bacterial species due to its relative presence in the environment. Chitin is most commonly found in the exoskeletons of arthropods and insects as well as in the cell walls of fungi, both of which are prevalent in marine and soil environments where C. botulinum live. Additionally, chitin can be a source of supplementary carbon and nitrogen for the bacteria [14]. Every point of information REQUIRES CITATION using the citation tool shown above.
Lyme Disease- Overview
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Metabolism and Energetics
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Dangers of Neurotoxicity
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Historical Outbreaks
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Current Research
Conclusion
References
Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2022, Kenyon College
