Transcript Microbiology Notes.ppt

Microbiology: Bacteria and
Viruses
Chapter 19
I. Classification of Bacteria
A. All bacteria are
prokaryotic cells
1. Prokaryotes are
the smallest living
organisms and
they lack a nucleus
and organelles
B. Bacteria are separated into 2 kingdoms:
Eubacteria and Archeabacteria
1. Eubacteria are the largest group of
bacteria and live almost everywhere
a. Generally surrounded by a cell wall
made of peptidoglycan, and have a cell
membrane
2. Archeabacteria are structurally different
from eubacteria because they lack
peptidoglycan in their cell walls and their DNA
is more closely related to eukaryotes
a. Live in extremely harsh environments
such as: hot springs, salty environments,
digestive tracts of animals
C. Bacteria are identified 4 ways: By their
shape, Cell walls, Movement, and ways they
obtain energy
1. Shape: There are 3 different shapes bacilli
(rod), cocci (sphere), and spirilla (spiral)
a. These bacteria can then arrange
themselves in different ways: long chains
or clusters
2. Cell Walls- Eubacteria have 2 different
types of cell wall and these can be
distinguished by a test called Gram Staining
1. Gram-positive bacteria turn violet due to
their cell wall containing mainly
peptidoglycan
2. Gram-negative bacteria have an extra
outer layer that absorbs red stain, so they
appear pink
Gram Staining
–
Gram Staining is the process used to differentiate
between types of cell walls
There are 2 dyes used in Gram Staining:
 Crystal
Violet (dye)- all cells turn violet.
This is absorbed by peptidoglycan in the
cell wall
 Methyl Red (dye)- dyes cells red.
This is absorbed by the outer cell wall
that is rich in carbohydrates and lipids
S. aureus: Gram + or -?
3. Movement: Bacteria move in different
ways or they may not move at all
a. Flagella are whip-like structures that
propel a bacteria forward
b. Cilia are small hair-like structures that
create a current
c. Bacteria can also lash, snake, or spiral
forward
4. Obtaining Energy: Prokaryotes can be classified
as either autotrophs or heterotrophs
a. Autotrophs make their own food using
either the energy from light
(photoautotrophs) or the energy from
chemicals (chemoautotrophs)
b. Heterotrophs obtain energy from
absorbing food
c. Photoheterotrophs are unique organisms that
make their own food by photosynthesis, but also
need to take in organic compounds for nutrition
D. Bacteria also release energy by either cellular
respiration or fermentation
1. Aerobes require oxygen to live and
anaerobes do not require oxygen
a. Obligate anaerobes cannot live
in the presence of oxygen.
Botulism is produced by this type of
organism
b. Facultative anaerobes can switch
between cellular respiration and
fermentation
E. Prokaryotes can multiply in as quickly as 20
minutes- in 48 hours they would be 4000x the mass
of the Earth!
1. They reproduce by binary fission- does
not exchange DNA with other bacteria so
this is asexual reproduction
2. Conjugation is how bacteria genetically
recombine their DNA and increase diversity
a. a hollow bridge connects 2 bacteria
3. Bacteria can produce spores when conditions
are not favorable. It is a thick internal wall that
encloses DNA and cytoplasm and allows the cell to
remain dormant
II. Bacteria in Nature
A. Bacteria are decomposers and are
responsible for recycling essential nutrients
through the ecosystem
1. Bacteria break down and digest dead
tissues into simpler substances, which are
then released into soil
2. Decomposition is essential for breaking
down human sewage
B. Nitrogen is essential to making amino acids
and proteins, but cannot be directly taken
from the atmospheric form
1. Bacteria are responsible for nitrogen
fixation- they convert atmospheric nitrogen
into ammonia and other forms that plants can
absorb through their roots
2. In some cases bacteria live in the roots of
plants and do nitrogen fixation and the plant
absorbs the ammonia
C. Some bacteria are pathogens, meaning they
cause disease
1. Disease is caused by 2 means: damaging
the tissue they are eating or releasing toxins
a.
Tetanus is a bacterial disease that causes
muscles to tighten and severe muscle spasms.
This can lead to breathing problems and be lifethreatening and occurs when bacteria enters an
open wound
b. Necrotizing fasciitis is also known as the flesh
eating disease. Cause by a bacteria that infects
the tissue around muscles and destroys the
tissues. This can be fatal
c. Tooth decay: Bacteria can make acid in the
presence of sugars and carbohydrates and the
acid will eat through the enamel of a tooth
d. Chlamydia is a sexually transmitted bacterial
infection that can cause damage to the
reproductive organs, sterilization, discharge, and
a burning sensation
e. Gonorrhea is a sexually transmitted
disease cause by bacteria. Symptoms
include discharge, burning sensations, and
swelling
2. Antibiotics prevent the growth and
reproduction of bacteria and can cure many
bacterial diseases
a. Bacteria can be resistant to antibiotics
b. Methacillin Resistant Staphylococcus
Aureus MRSA is a staph infection that
occurs in healthy people and appears as
a skin infection. S. aureus is resistant to
many common antibiotics
D. Humans are now able to use bacteria to
their advantage
1. Bacteria are used in the production of
many foods: sourdough, cheese, yogurt,
pickles
2. Bacteria can be used in industry to remove
waste, break down toxins, cleaning up oil
spills, and synthesizing drugs
E. Sterilization kills bacteria with heat or
chemical products
1. Most cannot withstand high temperatures
2. Refrigeration slows the growth of bacteria
Controlling Bacteria


Most bacteria are harmless, and many are
beneficial. However, the risks of bacterial
infections are great enough to warrant efforts
to control bacterial growth.
SO WHAT IS THE BEST WAY TO
PREVENT A BACTERAL INFECTION IN
YOU
WASH YOUR HANDS WELL FOR AT
LEAST 20 SECONDS WITH SOAP
III. Viruses
A. Viruses are not living things, but are defined
as a piece of nucleic acid encased in
protein
1. Viruses must infect a cell to reproduce
2. Viruses can be many different shapes
and sizes
 They are particles of nucleic acid, proteins,
and lipids that reproduces only by infecting
other organisms
B. The structure of a viruses is either DNA or
RNA, which contain between 1 and 100+
genes, and a protein coat called a capsid
that surrounds the DNA center
1. The capsid allows viruses to attach to
other cells and inject them with the DNA or
RNA
C. Viruses are very specific to the type of cell
they infect
1. Viruses bind to specific proteins in cells
2. Plant viruses usually cannot infect animal
cells
3. Viruses that infect bacteria are call
bacteriophages
D. Viral Infections occur when a virus breaks
into a cell and takes over the cell, which
destroys the cell in the process
1. In the lytic cycle a virus enters a cell,
makes copies of itself, and causes the cell to
burst
a. At the end of the lytic cycle the infected
cell is destroyed immediately
2. In the lysogenic cycle, the viral DNA is
inserted into the cell’s DNA and when the
cell’s DNA is copied, so is the viral DNA
a. Lysogenic cycle does not destroy the
cell immediately
3. How are the Lytic and Lysogenic
Cycles similar and different?
Lytic Cycle
Similarities
Lysogenic
Cycles
E. Viral Diseases- When viruses attack cells,
the cells are destroyed, which causes
symptoms
1. Polio is a viral infection that can cause flulike symptoms or can cause muscle paralysis
and death. It was eradicated in the western
hemisphere
2. Influenza Virus causes fever, headache,
muscle and body aches, sore throat, dry
cough, stuffy nose, and extreme tiredness
a. This is contagious and can lead to
death
3. Herpes Simplex 1 is a virus that causes
cold sores, painful blisters found on or
around the mouth
4. Herpes Simplex 2 is a sexually transmitted
disease and is expressed as blisters around
the genitals that can rupture and lead to
painful sores- there is NO cure
5. Human Immunodeficiency Virus (HIV) kills
and damages cell’s of the body’s immune
system and leaves people unable to fight off
illness and cancers
a. HIV/AIDS is a retrovirus- a retrovirus
contains RNA as the genetic information
and inserts a copy of itself into the DNA
of a host cell
b. Retroviruses are incurable
HIV
Why are some flu strains just a
nuisance, while others are dangerous?
Because of the way our immune system
identifies and attacks pathogens.
6. Oncogenic viruses carry genes that
interrupt the cell growth and division, which
can lead to cancer and HPV in eukaryotes.
F. The best way to treat viral infections is
prevention!
1. Vaccines are weakened or killed viral
proteins that stimulate an immune response
and produce protection against the disease