1) Explain the theory of Louis Pasteur and what he proved.

2-Mention the 4 postulates of Koch's.

3-Mention the three domains of life. If they find a new organism, what do they use to find out which domain it belongs to?

4-Draw 5 morphologies of bacteria and give their name.

5-Draw and explain the Gram stain.

6-What is the difference between the cell wall of gram + and gram -?

7-Mention and explain 3 surface structures of bacteria.

8-Explain the sporulation process and its function in the body.

9-Draw a bacillus with some kind of flagellum. (all types of scourge)

10- Describe the complete life cycle (growth curve) of a bacterium. 4 STAGES

11-Mention 4 environmental factors that influence the growth of a bacterium.

Answer:
1. Explain the theory of Louis Pasteur and what he proved. 

Louis Pasteur's Germ Theory proved that the invasion of microorganisms or as we commonly know as "germs" can lead to disease, through their growth and replication inside the host's body. These microorganisms not only pertain to bacteria, but to any type of microorganism, which includes parasites, fungi, viruses, prions, etc. Diseases caused by these are usually infectious and together with other external factors (e.g. environment, genetics, etc.), they will often determine the severity of the infection.

 

2. Mention the 4 postulates of Koch's.

• (1) The suspected pathogen must be found in every case of disease and not be found in healthy individuals.
• (2) The suspected pathogen can be isolated and grown in pure culture.
• (3) A healthy test subject infected with the suspected pathogen must develop the same signs and symptoms of disease as seen in postulate 1.
• (4) The pathogen must be re-isolated from the new host and must be identical to the pathogen from postulate 2.

Information lifted from: https://ecampusontario.pressbooks.pub/microbio/chapter/how-pathogens-cause-disease/

 

3. Mention the three domains of life. If they find a new organism, what do they use to find out which domain it belongs to?

• There are 3 domains of life, mainly the Archaea, Bacteria, and Eukarya. 
• When a new organism is found, they classify this organism under the domains based on the differences in the ribosomal RNA (rRNA) structure of the organism. 
• The Archaea domain contains single-celled organisms and they have genes that are similar to both bacteria and eukaryotes. archaea are prokaryotic organisms and do not have a membrane-bound nucleus. They also lack internal cell organelles and many are about the same size as and similar in shape to bacteria. They reproduce by binary fission, have one circular chromosome, and use flagella to move around in their environment. Archaea are extreme organisms that live under some of the most extreme environmental conditions. 
• The Bacteria Domain are also prokaryotic organisms that do not have a membrane-bound nucleus. They have a unique cell wall composition and rRNA type. They may be pathogenic, which is capable of causing disease. However, they are also essential to life as some are part of the human microbiota since bacteria can perform vital functions, such as digestion and absorption. Bacteria can also be protective. For example, bacteria that live on the skin prevent pathogenic microbes from colonizing the area and also aid in the activation of the immune system. They are also important for the recycling of nutrients in the global ecosystem as they are primary decomposers.

Reference and please read additional information here from: https://www.thoughtco.com/three-domain-system-373413

 

4. Draw 5 morphologies of bacteria and give their name. 

Bacterial morphology deals with size, shape, and arrangement of bacterial cells.

Size of Bacteria

Bacteria are microscopic organisms that are less than 3 micrometeres (μm) in size. Size of cocci range from 0.5 to 3 μm, and the size of a rod shaped bacteria range from 0.15 to 2 μm (width) to 0.5 to 20 μm (length). Bacteria are measured using a calibrated slide under a compound microscope or using an electron microscope.

Shape of Bacteria

Coccus or Cocci are bacterial cells that are spherical, and resemble tiny balls. Strep throats which is caused by Streptococcus are tiny, spherical cells.

Bacillus or Bacilli are bacterial cells that are rod shaped, and resemble a pill. Some bacilli have rounded ends while others have squared ends. Anthrax is caused by Bacillus anthracis which are rod shaped.

Spiral bacteria have twisted or helical morphology that resembles little cork screws. They may appear as curved rods, called vibrios, as spirilla or spirochetes having pliant bodies. Gastritis, which is caused by Helicobacter pylori, is a spiral shaped bacteria.

Arrangement of cells

Bacteria are also characterized based on how cocci and bacilli aggregate themselves. The aggregation of cells is specific to each bacteria.

Arrangement of cocci cells

Singly: Bacteria that appear as single cell, is just called as cocci

Diplococci: These cells are found in pairs and they are found attached to each other

Streptococcus: These bacteria form long chains and remain attached to each other

Staphylococcus: These bacteria are arranged irregularly in clusters like grapes

Arrangement of Bacilli

Singly: Bacteria that exists as single cell, called bacilli

Diplobacilli: These bacteria has two rod shaped cells which are attached to each other

Streptobacilli: Cells are arranged as long chains in these bacteria

5. Draw and explain the Gram stain. 

Gram staining is the most important and widely used microbiological differential staining technique. It was developed by Dr. Christian Gram in 1884. The Principle of Gram staining will determine whether the organism is gram positive or negative. The procedure of Gram staining is as follows: 

Smear preparation

• Take a grease free dry slide
• Sterilize the inoculating loop on a flame of a Bunsen burner
• Transfer a loopful of culture (or the specimen) by sterile loop and make a smear at the center. Smear should not be very thin or very thick
• Allow the smear to dry in the air
• Fix the dry smear by passing the slide 3-4 times through the flame quickly with the smear side facing up.

Gram Staining (please refer to the image in Explanation for your drawing)

• Place the slides on the staining rods.
• Cover the smear with crystal violet stain and leave for 1 minute.
• Wash carefully under running tap water.
• Flood the smear with Gram's iodine solution and leave for 1 minute.
• Drain off the iodine Wash the slide for the again in a gentle stream of tap water.
• Flood the slide with the decolorizing agent then wait for 20-30 seconds. This can also be done by adding a drop by drop to the slide until the decolorizing agent running from the slides runs clear.
• Gently wash the slide under running tap water and drain completely.
• Counterstain with safranin for and and wait for about 30 seconds to 1 minute.
• Wash slide in a gentile and indirect stream of tap water until no color appears in the effluent and then blot dry with absorbent paper.
• Observe under microscope

Reference and please read additional information here from: https://laboratoryinfo.com/gram-staining-principle-procedure-interpretation-and-animation/

 

6. What is the difference between the cell wall of gram + and gram -? 

• The cell wall of Gram-positive bacteria is composed of a thick layer of peptidoglycan or murein. This enables it to retain the crystal violet dye color, therefore a gram-positive will stain purple after gram staining.  Also, the thick layers of peptidoglycan help to support the cell membrane and provide a place of attachment for other molecules. Gram positive cell walls also contain chains of teichoic acid that extend from the plasma membrane through the peptidoglycan cell wall. These sugar-containing polymers assist in maintaining cell shape and play a role in proper cell division. Teichoic acid helps some gram-positive bacteria to infect cells and cause disease.
• On the other hand, the cell wall of Gram-negative bacteria also has a peptidoglycan or murein layer but is thin, and they also have an outer lipopolysaccharide membrane (which is not found in gram-positive bacterial cell wall). They do not retain the initial crystal violet dye but picks up the pink color of the counterstain during gram staining. The cell wall structure of Gram negative bacteria is more complex than that of Gram positive bacteria. Located between the plasma membrane and the thin peptidoglycan layer is a gel-like matrix called periplasmic space. Unlike in gram-positive bacteria, gram-negative bacteria have an outer membrane layer that is external to the peptidoglycan cell wall. Membrane proteins, murein lipoproteins, attach the outer membrane to the cell wall. This lipopolysaccharide (LPS) is a large glycolipid complex that protects bacteria from harmful substances in their environment. It is also a bacterial toxin (endotoxin) that can cause inflammation and septic shock in humans if it enters the blood. There are three components of the LPS: Lipid A, a core polysaccharide, and an O antigen.

Reference and please read additional information here from: https://www.thoughtco.com/gram-positive-gram-negative-bacteria-4174239#:~:text=Gram%20positive%20bacteria%20have%20cell,known%20as%20peptidoglycan%2C%20or%20murein.&text=Gram%20negative%20bacteria%20have%20cell,found%20in%20Gram%20positive%20bacteria.

 

7. Mention and explain 3 surface structures of bacteria. 

The 3 surface structures of bacteria include the appendages, the cell envelope and  the cytoplasmic region. Appendages are the attachments on the cell surface of the bacteria in the form of flagella and pili/fimbriae. The cell envelope consists of a capsule, cell wall and plasma membrane. Lastly, the cytoplasmic region contains the cell chromosome (DNA) and ribosomes and various sorts of inclusions

 

8. Explain the sporulation process and its function in the body. 

Sporulation refers to the formation of spores from vegetative cells during unfavorable environmental conditions. As such, it may be described as an adaptive response that allows the organism to survive given adverse conditions (radiation, extreme heat or cold, lack of nutrition etc).

 

Please refer to the image in Explanation for the sporulation process. 

• Stage 0: Normal conditions of a vegetative cell
• Stage I: Axial filament formation stage
  • In this stage bacterial chromosome become thread like known as axial filament
  • Axial filaments attached to cytoplasmic membrane by mesosome
  • Elongation of cell take places
  • PHBA is the reserved food material in Bacillus spp is utilized in sporulation.
• Stage II: Forespore formation
  • Asymmetric cell division occurs
  • Cell membrane forms septum near one end which encloses a small portion of DNA forming forespore
• Stage III: engulfment of forespore
  • Mother cell membrane grow around the forespore engulfing it.
  • Fore spore now has two membrane layer
• Stage IV: synthesis of exosporium
  • Chromosome of mother cell disintegrates
  • Exosporium synthesis occurs
  • Forespore starts Forming primodial cortex between two membrane.
  • Dehydration of cell
• Stage V: synthesis of dipicolonic cacid
  • Production of SASPs and dipicolinic acid occurs
  • Incorporation of calcium ions with dipicolonic acid occur forming calcium dipicolonate
  • Further dehydration of cytoplasm
  • Formation of coat layer
• Stage VI: maturation: Maturation of endospore
• Stage VII: release of endospore: Cell lysis and release of endospore

Reference and please read additional information here from: https://www.onlinebiologynotes.com/bacterial-spore-structure-types-sporulation-germination/

 

9. Draw a bacillus with some kind of flagellum. (all types of scourge) 

Please refer to the image in Explanation for your drawing

Monotrichous

• Single polar flagellum
• Example: Vibrio cholerae

Amphitrichous

• Single flagellum on both sides
• Example: Alkaligens faecalis

Lophotrichous

• Tufts of flagella at one or both sides
• Example: Spirillum

Peritrichous

• Numerous falgella all over the bacterial body
• Example: Salmonella Typhi 

Reference and please read additional information here from: https://microbiologyinfo.com/flagella-introduction-types-examples-parts-functions-and-flagella-staining-principal-procedure-and-interpretation/

 

10. Describe the complete life cycle (growth curve) of a bacterium. 4 STAGES 

The bacterial growth curve represents the number of live cells in a bacterial population over a period of time.

• Lag Phase: This initial phase is characterized by cellular activity but not growth. A small group of cells are placed in a nutrient rich medium that allows them to synthesize proteins and other molecules necessary for replication. These cells increase in size, but no cell division occurs in the phase.
• Exponential (Log) Phase: After the lag phase, bacterial cells enter the exponential or log phase. This is the time when the cells are dividing by binary fission and doubling in numbers after each generation time. Metabolic activity is high as DNA, RNA, cell wall components, and other substances necessary for growth are generated for division. It is in this growth phase that antibiotics and disinfectants are most effective as these substances typically target bacteria cell walls or the protein synthesis processes of DNA transcription and RNA translation.
• Stationary Phase: Eventually, the population growth experienced in the log phase begins to decline as the available nutrients become depleted and waste products start to accumulate. Bacterial cell growth reaches a plateau, or stationary phase, where the number of dividing cells equal the number of dying cells. This results in no overall population growth. Under the less favorable conditions, competition for nutrients increases and the cells become less metabolically active. Spore forming bacteria produce endospores in this phase and pathogenic bacteria begin to generate substances (virulence factors) that help them survive harsh conditions and consequently cause disease.
• Death Phase: As nutrients become less available and waste products increase, the number of dying cells continues to rise. In the death phase, the number of living cells decreases exponentially and population growth experiences a sharp decline. As dying cells lyse or break open, they spill their contents into the environment making these nutrients available to other bacteria. This helps spore producing bacteria to survive long enough for spore production. Spores are able to survive the harsh conditions of the death phase and become growing bacteria when placed in an environment that supports life.

Reference and please read additional information here from: https://www.thoughtco.com/bacterial-growth-curve-phases-4172692#:~:text=Key%20Takeaways%3A%20Bacterial%20Growth%20Curve&text=There%20are%20four%20distinct%20phases,metabolically%20active%20but%20not%20dividing.&text=The%20death%20phase%20is%20characterized,the%20number%20of%20living%20cells.

 

11. Mention 4 environmental factors that influence the growth of a bacterium.

• Nutrition concentration
• Temperature
• Gaseous concentration
• pH
• Ions and salt concentration
• Available water

In depth discussion of these factors are discussed in this site: https://www.onlinebiologynotes.com/factor-affecting-bacterial-growth/

Step-by-step explanation

Drawings

4. Draw 5 morphologies of bacteria and give their name. 

5. Draw and explain the Gram stain. 

8. Explain the sporulation process and its function in the body. 

9. Draw a bacillus with some kind of flagellum. (all types of scourge) 

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