Microbiology Summary
Microbiology Summary
Microbiology Summary
Chapter 1
Microorganisms are very small creatures that are not directly visible with unaided
eye, with dramatical biologic diversity. E.g everything except plants and animals
Distribution of Microorganism
o Air
o Soil
o Water
o Animals
o Human Body
Beneficial Activity:
Environment—nitrogen, carbon cycles, etc
Medicine
Food
Industry
Biotechnology
Research
Harmful Activity:
Food and material spoilage
Some microbes cause disease
Medical microbiology is one of the essential basic science of medicine. It is the study
of biological characteristic of microorganism and their relationship with human host.
History of Medical Microbiology:
o Experience phase
o Experimental phase
Leuwenhoek
built microscopes that magnified over 200 times
in 1675 first saw microorganisms
Edward Jenner
In 1796 develop vaccines for small pox
Pasteur
In 1859 prove the absence of spontaneous generation of
microorganism
Technique of “Pasteurization, research on fermentation
Developed vaccines for preventing chicken cholera, anthrax, and
rabies.
Joseph Lister
In 1865 introduces antiseptic technique
Robert Koch
In 1876 prove that specific microorganism can cause specific
disease
Method for isolating pure culture of bacteria
New methods of staining bacteria
Koch's postulates, means:
o The microbe must be found in the body in all cases of the
disease
o It must be isolated from a case and grown in a series of
pure culture in vitro
o It reproduce the disease on the inoculation of a late pure
culture into a susceptible animal
o The microbe must be isolated again into pure culture
from such experimentally caused infection
Dimitry Iwanowski
In 1892 Discover virus
Paul Ehrlich
In 1894 discover the principle of chemotheraphy
Alexander Fleming
In 1929 discover penicillin
Lister
o Modern phase
Chapter 2—Bacterial Shape and Structure
Bacteria is a part of prokaryotes.
Size of Bacteria:
o Prokaryotic with single cell
o Small size
o the unit of measurement—micrometer (abbreviation μm)
μm=10-3 mm =10-6 m
o Can be seen under microscope
Basic shapes of bacteria:
o Spherical — cocci
Diplococcus
Streptococcus
Tetrad
Sarcina
Staphylococcus
o Straight — bacilli
Coccobacilli
Streptobacilli
Fusiform
o Curved or Spiral — spiral bacteria
Vibrio
Spirilla
Spirochetes
Structure of bacteria:
o Basic Structure
Cell wall—Gram positive and Gram negative
Cytoplasm membrane
Cytoplasm
Nucleoid
o Special Structure
Capsule
Flagellum
Pilus
Spore
o Basic Structure
Cell wall—Gram positive and Gram negative
outmost portion. 15-30 nm in thickness, 10%-25% of dry weight.
Function:
o Gives the bacterial shape and prevents osmotic lysis
o Transports materials inside and outside of bacterium
o Possesses antigenic specificity
o Provides many pathogenic properties
Cell Membrane Function:
o Site of biosynthesis of DNA, cell wall polymers and
membrane lipids.
o Selective permeability and transport of solutes into cells
o Electron transport and oxidative phosphorylation
o Excretion of hydrolytic exoenzymes
In Gr+ bacteria:
o Peptidoglycan
Carbohydrate Backbone
Tetrapeptide side chains
pentapeptide cross-bridges
For protection: Drug sensitivity—
penicillin; lysozyme
o Teichoic acid
Only found in G+ bacteria
Two types: Wall teichoic acid & Lipoteichoic acid
For antigen specificity and pathogenicity
In Gr- bacteria:
o Peptidoglycan
Thinner (1-2 layers)
No cross bridges
o Outer membrane
Only found in G- bacteria
Compositions: Lipoprotein, Lipid bilayer, and LPS
LPS (lipopolysaccharide)—endotoxin consist of:
Lipid A—for endotoxic properties
Core polysaccharide—as genus specificity
O polysaccharide (O Ag) — as species
specificity
Cytoplasm membrane
Mesosome
o Is the specialized structures formed by convoluted
invaginations of cytoplasmic membrane
o Divided into 2 types:
1) septal mesosoma—for formation of cross-wall during
cell division
2) lateral mesosoma—as extension of cell membrane
Cytoplasm
Ribosome—for protein synthesize
o 70S in size (50S+30S)
Streptomycin acts on 30S
Erythromycin acts on 50S
Plasmid— is an extrachromosomal genetic element that is
usually circular, covalently closed, double-stranded DNA not
essential for bacterial growth
Inclusion granule—is the storage area for nutrients
Nucleoid
Is the prokaryotic nuclear body, usually composed of a single
molecule of circular, chromosomal DNA
Nucleus: The eukaryotic nuclear body containing the
chromosomes of the cell. Enclosed by a nuclear membrane.
Note: L forms
L form is the bacteria that their peptidoglycan is destroyed or lost by various factors
but they can survive under highly osmotic environment.
Two types of L forms:
1) Protoplasts: L forms derived from G+ bacteria. Enclosed by cytoplasmic
membrane.
2) Spheroplasts: L forms derived from G- bacteria. Enclosed by partial cell
wall.
o Special Structure
Capsule
Capsule: is a well-organized layer of material firmly attached
to the outer surface of the bacterial cell wall.
Microcapsule: capsule less than 0.2μm thick.
Slime layer: an unorganized, loosely attached layer of material
surrounding a bacterial cell.
Function:
1) Antigenicity
o polysaccharide or polypeptide
o e.g., Streptococcus pneumoniae
2) Pathogenicity
o Anti-phagocytosis
o Protection
o Adherence
Flagellum
A long, thin protein appendage external to a cell and
responsible for motility.
Function
1) Motility: the bacteria move when flagella rotate
2) Pathogenicity
- e.g., Vibrio cholerae—aid in the penetration of
bacteria through the mucous layer covering the
intestinal epithelial surface.
3) Antigenicity
- protein
- Also called as H Ag
Villus
thin, hairlike appendages on the surface of many bacteria
Properties: Shorter and thinner and consist of protein
Types and functions
o ordinary pili—as Pathogenicity: adherence
o sex pili—as Variation: conjugation
Spore
Endospore(Spore)—is a resistant, thick-walled, dormant
survival cell produced by certain Gram-positive bacteria.
1. E.g Clostridium and Bacillus
2. Function:
a. Enhances the ability of
bacteria to resist to the
unfavorable environment.
b. Medical significance—the
criterion of sterilization
effect
3. Properties
1) Contains the whole life necessary materials
2) Possesses high resistance—because of:
a. Impermeability of the spore coat
b. Calcium-dipicolinate
c. Scarcity of water
3) Germinates under favorable conditions
a. Endospores Vegetative bacteria
b. involved in the transmission of some diseases to
humans