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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Some possible outcomes following exposure to microorganisms 7

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

HELMINTHS

1. Multicellular

2. Helminths

Tapeworm Flukes Roundworms

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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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TAXONOMY

Kingdom

Phyla

Classes

Order

Families

Genera

Species 14

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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STRUCTURE OF BACTERIAL

CELL

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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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DIFFERENCES BETWEEN GRAM-POSITIVE AND

GRAM-NEGATIVE SPECIES

GRAM- POSITIVE GRAM- NEGATIVE

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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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Summary

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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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Normal Flora = usually beneficial The purpose of Lecture 2

Virulent bacteria = pathogenic bacteria

actively cause diseases

Opportunistic bacteria= when host with underline problem

immunocompromised humans

Human – Microbes

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