BMSC207 Lecture Notes - Lecture 3: Enterobacteriaceae, Globus Pallidus, Silage
Bacterial diversity:
Classification of bacteria•
Bacterial families
•
Where they are found•
Reservoirs of infection
•
Introduction (summary of last week):
Although free-living bacteria exist in huge numbers, relatively •
few species cause disease
Bacteria are si ngle cells prokaryotes, their DNA forming a long circular
•
molecule, nut not contained within a defined nucleus
Many are motile, using a unique pattern of flagella
•
The bacterial cell is surrounded by a complex cell wall and often a •
thick capsule
Reproduce by binary fissi on, often at very high rates and show a wide range of metabolic patterns including
aerobi c and anaerobic
•
Classification of bacteria uses both phenotypic and genotypic data•
Firmicutes:
The phylum firmicutes contain bacteria with a G+C content (the percentage of all base pairs that are guanine
-
cytosine base pairs) of less than 50%
•
Firmicutes include clostridia, mycosplasmas and other low G+C cocci and bacill i
•
Actinomycetes:
Actinomycetes
resemble fungi in that they produce spores and form filaments
•
Normally found in human mouths
Actinomyces
○
Useful in degradation of pollutants
Nocardia
○
Produces important antibiotics
Streptomyces○
This group includes
•
Protoeabacteria:
Phylum proteobacteria is a very large group of gram-negative bacteria•
The alpha○
Beta
○
Gamma
○
Delta○
And epsilon proteobacteria
○
It is divided into five classes:
•
Bacteriodetes:
The phylum Bacteriodetes is composed of three large classes of gram negative, non-sporeforming,•
anaerobi c or aerobic, and rod
-
shaped bacteria.
They are widely distributed in the environment, including in soil, sediments and sea water, as well as•
in the gut and on the skin of animals
Classification of bacteria:
Are they cocci/bacil i○
Gram positive/negative etc.
○
For clini cal purposes, the phenotypic data are of most practical value, and rest on an understandi ng of
structure and biology
•
Flagella are long helical filaments extending from the cell surface, which enable bacteria to move in their
environment
○
Flagella are built of protein components (flagellins), which are strongly antigenic○
These antigens, the H antigens, are important targets of protective antibody responses
○
Can be used to classify
○
Flagella:
•
Pili (fimbriae) are more rigid than flagella and function in attachment, either to other bacteria (the ‘sex’
or to host cells (the ‘common’ pili)
○
The presence of many pili may help to prevent phagocytosis, reducing host resi stance to bacterial
○
Although immunogenic, their antigens can be changed, al lowing the bacteria to avoid immune ○
Pilli:•
Gram staining is a basi c microbiologic procedure for detection and identification of bacteria
○
In gram positive bacteria, the peptidoglycan forms a thick layer external to the cell membrane, and may
contain other macromolecules (stain purple
-
retain)
○
In gram negative bacteria, the peptidoglycan layer is thin and is overlaid by and outer membrane,
to lipoprotein molecules in the peptidoglycan layer. The principal molecules of the outer membrane are
lipopolysaccharides and lipoprotein
○
Gram stain:
•
The cell wall is a major contributor to the ultimate shape of the organism,
○
an important characteristic for bacterial identification
In general, bacterial shapes are classified as cocci (sphere), bacilli (rod)
○
and helical (spirilla)
Cell wall:•
Gram positive cocci:
This genus contai ns over 30 species
○
Some strains produce capsules○
Humans (and animals associated with them)
Skin, especially nose and perineum
Normal habi tat:
○
Spread by contact and airborne routes
○
Staphylococcus:•
Lecture 2
-
8/8/16
Sunday, 7 August 2016
10:40 PM
Lectures Page 1
Document Summary
Although free-living bacteria exist in huge numbers, relatively few species cause disease. Bacteria are si ngle cells prokaryotes, their dna forming a long circular molecule, nut not contai ned within a defined nucleus. Many are motile, using a unique pattern of flagella. The bacterial cell is surrounded by a complex cell wall and often a thick capsule. Reproduce by binary fissi on, often at very high rates and show a wide range of metaboli c patterns includi ng aerobic and anaerobic. Classification of bacteria uses both phenotypic and genotypic data. The phylum firmicutes contain bacteria with a g+c content (the percentage of all base pairs that are guanine- cytosine base pairs) of less than 50% Firmicutes include clostridia, mycosplasmas and other low g+c cocci and bacill i. Actinomycetes resemble fungi in that they produce spores and form filaments. Phylum proteobacteria is a very large group of gram-negative bacteria.
