l1 micro medicine 2015 (1)
TRANSCRIPT
Introduction to Microbiology
Prokaryotic and Eukaryotic cells
Structure Of Bacterial Cell
LECTURE: 1
COURSE: PRINCIPLES OF DISEASE I
LEVEL 4 MEDICINE
Course Instructors: Course Coordinator:
Dr. RIM MOHAMED Dr. RIM MOHAMED
Dr. EIMAN ELNAKEEB
Dr. HESHAM AZIZ
Dr. MOURAD
Dr. RIHAM ELFAWAL
Dr. MOHAMED RAOUF 1
AIM: To describe the microbial world, especially prokaryotes and eukaryotes and to differentiate between them.
OBJECTIVE: To understand the general characteristics of prokaryotes and eukaryotes, the classification and taxonomy.
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Microbiology is the study of microorganisms.
Microorganisms are living organisms that
are usually too small to be seen clearly with the naked eye but can be seen by a microscope.
Microorganisms include Bacteria Fungi Viruses Protozoa Helminths Algae
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Microorganisms are present everywhere on earth -- humans, animals, plants, soil ,water and atmosphere.
Terminology:
Microbes that cause disease are called pathogens.
Parasite is an organism that lives on or in an organism of another species known as the host, from the body of which it obtained nutriment.
Most infectious disease is initiated by colonization
Disease occurs when the organism causes tissue damage and impairment of body function
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INFECTION: Infection is the invasion of a host organism's bodily tissues by disease-causing organisms, their multiplication, and the reaction of host tissues to these organisms and the toxins they produce
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Cellular Microorganisms
Prokaryotes Eukaryotes
Bacteria Fungi Protozoa Helminths
Atypical bacteria Typical bacteria Ex: Mycoplasma The cell wall determines shapes Chlamydia rod, sphere, spiral
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FUNGI PROTOZOA
1. Non-photosynthetic, saprophytic
filamentous (molds)
2. 2 forms
unicellular( yeast)
superficial mycoses
3. Diseases
deep mycoses
1. Single celled, non- photosynthetic
free living
2. 2 types
parasites of humans
3. Intra and extra-cellular parasites
Blood intestine
EUKARYOTES
Comparison of Prokaryotic and
Eukaryotic Cells
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prokaryotic cell
(do not have true nucleus)
eukaryotic cell
(have true nucleus)
VIRUSES
obligate intracellular parasites
do not have cellular structure
DNA virus or RNA virus , not both
either DNA or RNA surrounded by protein coat
require host’s cellular structure to complete the replication.
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The first letter of the genus name is always capitalized, and the species name begins with a lower case letter Exp: Staphylococcus aureus
Both names are printed in ilatics
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1- CELL ENVELOPE
CELL ENVELOPE = Cell wall + Cell membrane
= all materials external to cytoplasm
CELL WALL
outermost component of all bacteria (except Mycoplasma species)
The cell wall determines the shape of the cell
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CELL MEMBRANE
Cell membrane is semi- permeable barrier, that surrounds the cytoplasm of a cell.
Cell membrane is composed of phospholipid molecules.
Its function is to protect the integrity of the interior of the cell, while keeping other substances out.
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DIFFERENCES BETWEEN GRAM-
POSITIVE AND GRAM-NEGATIVE
SPECIES
1. Gram- positive organisms : Have thick, multilayered peptidoglycan cell walls
that are exterior to the membrane Positive result in the Gram Stain test ( Purple coloration )
Techoic acids are major cell surface antigens
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2. Gram- negative organisms:
Negative result in the Gram Stain test ( Pink coloration )
Have 2 membranes: outer membrane and inner membrane
Peptidoglycan layer is thin and located between the two membranes
Outer membrane is made up of lipopolysaccharide
Polysaccharide portion is antigenic and used to identify different strains and species
Lipid portion is toxic to humans and animals ( and is called as endotoxin)
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Despite their thicker peptidoglycan layer, gram positive bacteria are more receptive to antibiotics than gram negative, due to the absence of the outer membrane.
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EXTERNAL CAPSULE AND GLYCOCALYX
Many bacteria secrete a sticky , viscous material and forms an extra-cellular coating around the cell.
Protect bacteria from antibodies and phagocytosis
The material is usually polysaccharide (except pathogenic Bacillus anthracis, it is poly-D-glutamic acid)
tightly bound (capsule)
Material
loosely bound (slime layer
or glycocalyx)
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APPENDAGES = accessory structure
flagella pili
1. long, semi-rigid, helical , hollow 1. short and thin
2. USE: Propel (mobility) bacteria 2.USE: attachment,
for cell-to- cell contact
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SPORES
Some Gram-positive rods undergo some structural and metabolic changes and form dormant cell called endospore inside the original cell
Spores are the most resistant life-forms known
Resistant to heat( survive boiling), ultraviolet light and bactericidal chemical agents
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SPORULATION
Spore formation begins with the invagination of the parent cell membrane, producing a double membrane that encapsulates and isolates a copy of the bacterial DNA.
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SPORE GERMINATION
To return to the vegetative state, spores must first be subjected to heat or extreme pH
MEDICAL SIGNIFICANCE OF SPORULATION
Spore-forming pathogens – Bacillus anthracis (anthrax), Clostridium tetani (tetanus), Clostridium perfringens (food poisoning)
Spores are viable for many years and are generally not killed by boiling, but can be killed by sterilization (autoclaving).
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