Introduction To Microbiology Flashcards
Who founded microscopes and is called the founder of microbiology
Antonie Van Leeuwenhoek
Who coined the germ theory and is the father of modern microbiology and found the vaccine against anthrax in animals
Louis Pasteur
Who is the father of immunology
Edward Jenner
Who is the founder of modern bacteriology , discovered Bacillus anthracis (Anthrax bacillus), Mycobacterium tuberculosis, and Vibrio cholerae. And modified Ziehl-Neelsen Acid Fast staining procedure which was introduced by Ehrlich. And is considered the father of medical microbiology
He also realized that microorganisms cause diseases
Robert Koch
Who founded penicillin(Penicillium notatum )which acts on Gram positive bacteria
Alexander Fleming
Who discovered hand hygiene( hand washing)
Ignaz Semmelweis
What are Koch’s postulates
- If a person A has a disease, the pathogen that caused the disease should be the same pathogen that caused the same disease in person B and that pathogen wil not be found in healthy people or the pathogen must be present in every case of the disease
ExMple if person A has fever and chills and it’s cAused by twisty germ, person B also having fever and chills , the disease should also be twisty germ - The pathogen should be isolated from the diseased host Nd grown in a pure culture to make sure that apart from the pathogen, no other microorganism grows or will be present
in the culture - When the pathogen (grown from the pure culture )that caused person B’s sickness is put
In a healthy susceptible person, the healthy person should show the same symptoms Person B is showing or the same disease must be reproduced - The pathogen inoculated ( introduced ) into the experimentally infected host( who was once healthy) should be recoverable
These postulates show whether a particular disease is caused by a particular pathogen
Limitations of Koch’s postulates
- not all pathogens inoculated into an experimentally infected person cause the person to produce symptoms.
- Pathogens can also be found in healthy individuals. Eg. H pylori is part of the bacteria normally found in the stomach and it also causes chronic gastritis. People can be healthy and still have the H pylori in their stomach. They also will not have chronic gastritis
- Not all bacteria can be cultured in a pure culture. Example, the bacteria that causes leprosy( Mycobacterium leprae )
- Not all human pathogens can be replicated in an animal host. ExMple viruses
- Not all people are susceptible to certain diseases thus they will not show any symptoms when the pathogen is introduced into their body.
- Not all people will show the exact same symptoms - limitations for postulate 3
- Those who show the same symptoms doesn’t necessarily mean that their diseases are caused by the same pathogen
Importance of capsules , cell wall,ribosomes , pili(fimbriae) flagella in bacteria
capsules play a number of roles, but the most important are to keep the bacterium from drying out and to protect it from phagocytosis (engulfing) by larger microorganisms. The capsule is a major virulence factor( Virulence factors are molecules produced by bacteria, viruses, fungi, and protozoa that add to their effectiveness and enable them to achieve their goal) In the major disease-causing bacteria
Cell wall- protects the cell from the environment and prevents the cell from bursting
Cytoplasmic membranes - a barrier that allows them to selectively interact with their environment. Membranes are also dynamic, constantly adapting to different conditions.
Flagella- The flagella beat in a propeller-like motion to help the bacterium move toward nutrients; away from toxic chemicals;
Pili (singular -pilus) Many species of bacteria have pili (singular, pilus), small hairlike projections emerging from the outside cell surface. These outgrowths assist the bacteria in attaching to other cells and surfaces, such as teeth, intestines, and rocks. Without pili, many disease-causing bacteria lose their ability to infect because they’re unable to attach to host tissue
Ribosomes-There are sufficient differences between bacterial ribosomes and eukaryotic ribosomes that some antibiotics will inhibit the functioning of bacterial ribosomes, but not a eukaryote’s, thus killing bacteria but not the eukaryotic organisms they are infecting.
Most antibiotics target which part of the bacteria cell
The cell wall
WhT are the Bacteria classification with respect to cell wall and who brought about the staining technique?
Gram positive - have thick peptidoglycan layer. ( this is the virulent factor for the gram positive)After staining it appears purple or violet
Gram negative- bunch lipopolysaccharides(endotoxins) but small peptidoglycan layer( this is the virulent factor for gram negative)
Gram negative is more toxic and easily leads to sepsis . After the stain, it appears pink
Hans Christian Joachim GRAM, Gram stain, still a standard technique to classify bacteria and make them more visible under a microscope.
Stains for Gram staining and why gram positive stains but gram negative doesn’t
Crystal violet
Methylene blue
Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with. Alternatively, Gram negative bacteria stain pink cuz it does not retain the crystal violet during the decoloring process.
Process of Gram Staining
Cells are stained with crystal violet dye. Next, a Gram’s iodine solution (iodine and potassium iodide) is added to form a complex between the crystal violet and iodine. This complex is a larger molecule than the original crystal violet stain and iodine and is insoluble in water.
decolorizer such as ethyl alcohol or acetone is added to the sample, which dehydrates the peptidoglycan layer, shrinking and tightening it. The large crystal violet-iodine complex is not able to penetrate this tightened peptidoglycan layer, and is thus trapped in the cell in Gram positive bacteria. Conversely, the the outer membrane of Gram negative bacteria is degraded and the thinner peptidoglycan layer of Gram negative cells is unable to retain the crystal violet-iodine complex and the color is lost.
A counterstain, such as the weakly water soluble safranin, is added to the sample, staining it red. Since the safranin is lighter than crystal violet, it does not disrupt the purple coloration in Gram positive cells. However, the decolorized Gram negative cells are stained red.
Reagents for Gram staining
Primary stain (crystal violet), Mordant (iodine), Decolorizer (ethanol or acid-alcohol) and Counter stain (safranin or dilute carbol-fuchsin).
Why doesn’t the Gram stain apply to some bacteria
Some bacteria produce the waxy substance mycolic acid when they construct their cell walls. Mycolic acid acts as a barrier, protecting the cells from dehydrating, as well as from phagocytosis by immune system cells in a host. This waxy barrier also prevents stains from penetrating the cell, which is why the Gram stain does not work with mycobacteria such as Mycobacterium, which are pathogens of humans and animals.
Principles of acid fast staining
When the smear is stained with carbol fuchsin, it solubilizes the lipoidal material present in the Mycobacterial cell wall but by the application of heat, carbol fuchsin further penetrates through lipoidal wall and enters into cytoplasm. Then after all cell appears red. Then the smear is decolorized with decolorizing agent (3% HCL in 95% alcohol) but the acid fast cells are resistant due to the presence of large amount of lipoidal material in their cell wall which prevents the penetration of decolorizing solution. The non-acid fast organism lack the lipoidal material in their cell wall due to which they are easily decolorized, leaving the cells colorless. Then the smear is stained with counterstain, methylene blue. Only decolorized cells absorb the counter stain and take its color and appears blue while acid-fast cells retain the red color.
