Microbes And Their Interaction With Humans

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Microorganisms are very tiny organisms that has a great impact in life activities. These microorganisms have been a subject of research and more of microbial functions are yet to be discovered. The aim of this essay is to explore the classification, structure and functions of microorganisms, Microbial growth with growth curves and factors that affects microbial survival and lastly, the positive and negative interactions with humans and foods.

Microorganisms are classified into eukaryotic and prokaryotic cells based on their structures. The prokaryotic cells are cells that do not have envelope covered nucleus like bacteria. They are the simplest cells in terms of structure. Alberts, et al. (2015) referred to them as organisms which shows life stripped down to its essentials. The bacteria consist of components which serves different purposes in the cellular activities such as DNA which contains the cells genetic information, capsule which prevents cell dehydration, mesosome which carries out respiration by increasing the cell surface area, pili these are thin rigid fibers that attaches of the bacterial cell to surfaces and the flagellum which is primarily used in cell movement but can also be used as sensory organ. In contrast, eukaryotic cells consist of an enclosed nucleus and other membrane bound organelles that performs different functions and are present in both animals and plants cells.

The enclosed nucleus contains the cells genetic material, Endoplasmic reticulum, and it consist of both the smooth Endoplasmic reticulum that is responsible for lipid synthesis and rough endoplasmic reticulum that houses ribosomes responsible protein synthesis, Golgi body which packages cell-made materials, vesicles transports the packaged material from the Golgi body to regions of requirement either within or outside the cell, mitochondria is responsible for energy production in the cell, lysosomes contains enzymes responsible for the degradation of worn out intracellular substances. Despite the differences between the two cell types, they have similar structures like cell membrane which regulates the amount of substances that enters both eukaryotic and bacteria cells. Cell wall, which provides shape and protection to both eukaryotic plant cells and bacterial cells. Microbial knowledge has been impacted by the roles of microscopy. Forbes, et al. (2007) explained microscopy as using the microscope to visually increase objects that cannot be viewed with naked eyes. microscopes are of two types, the light microscope which has a magnification of 2000x and resolves structural details as small as 200nm and enables the viewing of cellular activities.

The electron microscope has a magnification of 1,000,000x, resolves structural details as small as 0.5nm, forms 3-D images, produces images in black and white and cell activities cannot be viewed as chemical treatments kills the cells. Microbial study involves processes that identifies specific organisms. The sample of microbial habitation like blood and soil are subjected to processes beginning with inoculation, which is placing the collected sample in a medium that provides nutrients. This medium can be liquid (broths) or solid (agar). Incubation which provides the inoculated media with controlled environment to enhance growth of mixed cultures in optimal conditions, isolation which involves separation of different microbes from the media by macroscopic features, inspection, which involves viewing of pure cultures under microscope for additional details by adding stains to enhance visibility, information gathering, involving the specialization of culture media for conducting additional tests for the functions of the microbes in the pure cultures, and identification which involves analysis of the collected data to identify the organism in the sample.

Microbes gradually adjust to new habitats through changes in anatomy and physiology adaptation. Several factors affect the survival of organisms which includes nutrient and energy sources, temperature, and relationship with other microorganisms. Organisms require nutrients for growth and these nutrients are classified into two which are the macro-elements and the microelements. Macro-elements are those elements that are required in large quantity by organisms because of the important role they play in cell structure. They are mainly obtained from macromolecules as they contain carbon, hydrogen and oxygen and are required for metabolic processes in the cell. Microelements are those nutrients that are required in small quantities as much of it poses danger to the organism. They include zinc, manganese, nickel among others. These nutrients are classified into two main sources which are the energy and carbon sources. The energy sources include phototrophs which derives energy from sunlight and chemotrophs which derives energy from chemicals. While the carbon sources are autotrophs which make their own food and heterotrophs which cannot produce their own food but depends on other organisms for food.

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Photoautotrophs are organisms that produce their biological materials using energy from sunlight and carbon from inorganic materials. They include green plants and photosynthetic bacteria. Chemoautotrophs are organisms that produce their biological materials using energy from chemicals and carbon from inorganic materials. They include nitrogen fixing bacteria and Sulphur oxidizing bacteria. Photo-heterotrophs are organisms that produce their own biological material using energy from sunlight and carbon from organic materials example Heliorestis spp.

Chemo-heterotrophs are organisms that produces their own biological materials using energy from chemicals and carbon from organic materials. Growth is the increase in size of organisms and synthesis of new components. Monod (1949) explained the growing bacteria in cultures as not a specific subject but a basic microbiological method. Bacteria grows through binary fission. The bacterial cell increases in size due to the duplication of DNA and internal components. The cell membrane starts to elongates and the components starts to separate within the cell and septum forms through the center of the cell membrane creating two separates cell chambers. Cytokinesis occurs and the parent cell is separated into two daughter cells. Each bacteria cells increases the population by a factor of two. The population growth continues to increase in favorable environmental conditions. Studies have shown that population growth shows a predictable pattern overtime and can be represented with curves. Bacteria cells are grown and studied in cultures. As the bacterial cells grows in the culture and monitored at intervals, it forms data for illustration through growth curves. The growth curve however, consist of four different stages which includes the lag stage, the log stage, the stationary stages and the decline/death stage.

  • Lag stage: the lag or initial stage is a phase where bacteria cells checks out the environment to ensure that nutrients and temperature necessary for growth is available and if not, tries to adapt to the insufficient environment.
  • Log/Exponential stage; represents rapid increase in population of cells. The population growth at this stage continues at a constant rate provided that the environment is conducive enough.
  • The stationary stage: at this stage, the cells have reach a maximum level of division. They stop dividing because nutrients and space have been used up and waste materials are accumulated. It is represented with a straight line on the curve.
  • Death stage: At this stage, cells dies off and as they die they release space and nutrients for more cell division that is why the death slope on the curve is gentle. some cells just remain dormant.

Bacteria are causes of food spoilage through anaerobic respiration through fermentation. Anaerobic respiration is simply respiration without oxygen. Fermentation can be defined as a process where pyruvate is metabolized and NADH is converted to NAD+ and small amount of energy is released and it is of two types which includes the fermentation of glucose to lactic acid which is carried out by animals and some bacteria like lactobacillus and the conversion of glucose to alcohol and carbon dioxide which is carried out plants and some microbes like yeast. Rawat, (2015) explained that food spoilage can be as result of different factors which includes enzymes reaction, physical damages and most of all microorganism invasion. Diverse microbes can be identified in a spoiling food but the microbes that are responsible for the food spoilage are known as Specific Spoilage Organism (SSO) examples are yeast, molds and bacteria.

Yeast like Zygosachanomyce causes the honey and fruits spoilage. Bacteria are organisms that mostly affect foods examples are Lactobacillus and Pedococcus are useful for fermenting foods like yoghurt and also cause spoilage such as meat greening, formation of gas in cheese and bad flavors in wine which occurs under low temperature, low oxygen and acidic environment. Pseudomonas sp. are organisms that are responsible for the spoilage of animal derived foods like meat and fish by lipase and protease secretion which forms bad odors and slimes on the surfaces of the food. As microorganisms affect foods, they also affect humans. Studies have proven that the human body is surrounded by microbes which are ten times the number of cells in the human body. Microbes are present in the mouth, nose, skin, gut and genital tract and the microbe and human relationship promotes healthy leaving as some microbes are commensal while some are mutualistic. The commensal microbes obtain nutrients from the host while both the host and microbes benefits from the mutualistic microbe relationship. For instance, the mutualistic microbes occupy a large area of the skin to prevent bad microbes from invasion. example of which is Bacillus Subtilis. According to Kumar and Chordia, (2017) they explained that Bacillus Subtilis is a gram positive bacteria that resides on the skin of the human host produces Bacitracin. Bacitracin is a chemical that combats bad microbes that are trying to invade the skin. This toxin has proven to be very effective as scientist have harnessed it and used it in the advancement of antibiotics. Some of the microorganisms in human hosts especially those present in the gut of the host help in digestion and strengthens the immune system.

However, despite that microbes promotes healthy living, they cause infections example is the Streptococcus mutans which is responsible for dental problems such as tooth decay. Some microbes which are not damaging tends to cause harm in host whose immune system are compromised. These group of microbes are known as opportunistic pathogens. Examples are Streptococcus pneumonia from the nasopharynx which causes pneumonia in AIDS patients and Clostridium sp. which enters the stomach from the intestine and causes food poisoning.

This essay has reviewed the classification of microorganisms, their structures, functions and study, growth and factors that affects the survival of microorganisms and the effects of microbial interaction with humans and foods. The essay explained from the researches and studies conducted by Alberts, et al. (2015) and Forbes, et al. (2007) that microorganisms are classified into two types they are the prokaryotic cells which are mostly bacteria and Archaea and the eukaryotic cells which are the plant and animal cells. It also explained the importance of the role of microscopy in the study of microorganisms and the types of microscope. From studies made from Monod, (1949) it was explained in the essay that the growth of bacterial cultures does not require any specific subject or branch study but is a basic method in microbiology. It also explained the factors that affects the survival of microorganisms which includes temperature, nutrition and relationship with other organisms more so, the stages of growth and its representation with the growth curve. Lastly, the essay explained from the studies made by Rawat, (2015) and Kumar and Chordia (2017) the positive and negative effects of the interactions of microbes with foods and humans.


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  2. Forbes, B. A. et al. (2007) Bailey & Scott’s Diagnostic Microbiology 12th edition[online]. St louis United States: Elsevier-Health Science division. Available from: https://www.elsevier.com/books/study-guide-for-bailey-and-scotts-diagnostic-microbiology/forbes/978-0-323-04780-7 [Accessed 10th October 2020].
  3. Monod, J. et al. (1949) Bacterial competition surviving and thriving in the bacterial jungle. The Growth of Bacterial Cultures [online]. pp.371-394 Available from: https://mcb.berkeley.edu/labs/garcia/sites/mcb.berkeley.edu.labs.garcia/files/Teaching/2017-MCB137/Monod1949.pdf [Accessed 20th October 2020].
  4. Rawat, S. (2015) Food spoilage: Microorganisms and their prevention[online]. India: department of Botany and microbiology, H.N.B. Garhwali (central) University, Srinagar, Uttarakhand. Available from: https://www.imedpub.com/articles/food-spoilage-microorganisms-and-their-prevention.pdf [Accessed 10th October 2020].
  5. Kumar, A. and Chordia, N. (2017) Applied Microbiology: Open Access. journal of roles microbes in human health[online]. Vol.3 (2) pp.1-3. Available from: https://www.longdom.org/open-access/role-of-microbes-in-human-health-2471-9315-1000131.pdf [Accessed 12th October].
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