MIB151S: Microbial diversity – Bacteria and Viruses (Microbiology 1)
Cape Peninsula University of Technology
Lecture 7 Notes
Microbiology 1
7.1 Structural differences between bacteria and viruses
7.2 Classification of bacteria and viruses
7.3 Bacteriophages
7.4 Common bacterial diseases and pathogenesis
7.4.1 Escherichia coli (E. coli O157:H7)
7.4.2 Clostridium spp.
7.4.3 Campylobacter jejuni
7.4.4 Bacillus cereus
7.4.5 Salmonella spp.
7.4.6 Vibrio spp.
7.4.7 Staphylococcus aureus
7.4.8 Shigella
7.4.9 Listeria monocytogenes
7.4.10 Yersinia spp.
7.4.11 Mycobacterium tuberculosis
7.4.12 Mycobacterium bovis
7.4.13 Brucella spp.
7.5 Common viral species and pathogenicity
7.5.1 Hepatitis A
7.5.2 Noroviruses
7.6 Environmental conditions promoting and inhibiting bacterial and viral infections
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Microbial diversity – Bacteria and Viruses
7.1 Structural differences between bacteria and viruses
Compared to bacteria, viruses are much smaller and simpler – approximately 10 to 100
times smaller than bacteria;
The biggest difference between bacteria and viruses is that bacteria can grow on non-
living surfaces while viruses must have a living host, like a plant or animal to multiply;
Bacteria are intercellular organisms (i.e. they live in-between cells); whereas viruses are
intracellular organisms (they infiltrate the host cell and live inside the cell); They change
the host cell's genetic material from its normal function to producing the virus itself;
Apart from many harmful bacteria some may be useful, while all viruses are harmful;
Antibiotics cannot kill viruses, but can kill most bacteria, with the exception of most
Gram-negative bacteria;
An example of a disease caused by bacteria is strep throat (Group A Streptococcus (GAS)
bacteria, specifically Streptococcus pyogenes ) and an example of an affliction caused by a
virus is the flu (Influenza virus).
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,MIB151S: Microbial diversity – Bacteria and Viruses (Microbiology 1)
Cape Peninsula University of Technology
Lecture 7 Notes
Differences between bacteria and viruses
Bacteria Virus
Ribosomes Present Absent
Peptidoglycan / Lipopolysaccharide No cell wall. Protein coat present
Cell wall
instead.
Opinions differ on whether viruses
Living are a form of life or organic
attributes Living organism structures that interact with living
organisms.
Bacteria constitute a large domain of A virus is a small infectious agent
prokaryotic microorganisms. Typically a that replicates only inside the
few micrometers in length, bacteria have living cells of other organisms;
Size
a number of shapes, ranging from Smaller (20 - 400nm).
spheres to rods and spirals; Larger
(1000nm).
Nucleus Depends on prokaryotic or eukaryotic No
Number of cells Unicellular; one cell No cells; not living
DNA and RNA floating freely in DNA or RNA enclosed inside a
Structures cytoplasm. Has cell wall and cell coat of protein.
membrane.
Vaccines prevent the spread and
Antibiotics antiviral medications help to slow
Treatment
reproduction but cannot stop it
completely.
Enzymes Yes Yes, in some
Virulence Yes Yes
Infection Localized Systemic
Viruses are not beneficial.
However, a particular virus may be
Benefits Some bacteria are beneficial (e.g. able to destroy brain tumors.
certain bacteria are required in the gut) Viruses can be useful in genetic
engineering.
Invades a host cell and takes over
Fission - a form of asexual reproduction the cell causing it to make copies
Reproduction of the viral DNA/RNA. Destroys
the host cell releasing new
viruses.
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, MIB151S: Microbial diversity – Bacteria and Viruses (Microbiology 1)
Cape Peninsula University of Technology
Lecture 7 Notes
7.2 Classification of bacteria and viruses
Gram Positive Bacteria
Name Morphology O2 Commen Reservoirs Types of
Require= sal / Sites of Infections
ments colonizatio
n,
Transmissi
on
Staphylococci Cocci in facultative Yes Skin, nares / Soft
grapelike anaerobe endogenous tissue,
clusters , direct bone,
contact, joint,
aerosol endocardit
is, food
poisoning
Streptococci Cocci in pairs, facultative Some Oropharynx, Skin,
chains anaerobe species skin / pharyngitis
endogenous ,
, direct endocardit
contact, is, toxic
aerosol shock
Pneumococci Diplococci, facultative ± Oropharynx, Pneumoni
lancet shaped anaerobe sinus / a, otitis,
aerosol sinusitis,
meningitis
Enterococci Cocci in pairs, facultative Yes GI tract / UTI, GI,
chains anaerobe endogenous catheter-
, direct related
contact infections
Bacilli Rods, aerobic ± Soil, air, Anthrax,
sporeforming water, food
animals / poisoning,
aerosol, catheter-
contact related
infections
Clostridia Rods, spore anaerobic Some GI tract, Tetanus,
formers species soil / Breach diarrhea,
of skin, gas
endogenous gangrene,
, ingestion botulism
Corynebacterium Rods, facultative Some Skin Catheter-
nonspore- anaerobe species related
forming infections,
diphtheria
Listeria Rods, facultative No Animals, Meningitis
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