Microorganisms Flashcards
What are viruses?
- These are subcellular, nonliving particles that multiply
only when they are inside living cells. - They appear in different shapes, but have many features
in common - Louis Pasteur in 1884 suggested that something smaller
than bacteria was the cause of rabies. - In 1892, Dimitri Ivanowsky observed that the cause of
tobacco mosaic disease could be filtered through a finepore filter, enhancing Pasteur’s suggestion - Following the development of the electron microscope in
the 20th century, viruses were seen for the first time.
What is the virus structure?
- The size of a virus is comparable to that of a large
protein - Viruses can be purified and stored in crystalline form
- If given a chance to invade a living cell, they become
infectious. - A virus structure is usually made of an outer coat,
called the capsid surrounding either DNA or RNA - The coat may or may not be surrounded by an
envelope
How are viruses classified?
- Viruses may be classified according to various
criteria, but the most important one is the type of
nucleic acid - Accordingly, we recognize DNA viruses and RNA viruses
- RNA viruses (also called retroviruses) have a reverse
transcriptase enzyme capable of synthesizing DNA
from their genomic RNA - (HIV), which causes
AIDS, is a retrovirus
What is the lysogenic life cycle of a virus?
- Viral infection may cause cell lysis when the virus
goes through a cycle of replications, producing many
new virus particles, (i.e. lytic life cycle). - With other infections, the genetic material of the
virus becomes integrated with the host cell DNA. - The host cell remains alive and continues to release
virus particles at a slow rate. - This is known as the lysogenic life cycle
What is a virus that infects a bacterium called?
A virus that infects a bacterium is called a bacteriophage
or simply a phage
What is bacteria?
- Bacteria are prokaryotic single celled organisms that
lack nuclei (and other internal organelles) but are
capable of independent existence. - Some of these bacteria are parasitic on humans and
cause many diseases - The major characteristic of bacterial cells is the cell
wall that is made of peptidoglycan - Depending on the thickness of the peptidoglycan in
the cell wall bacteria are either Gram+ or Gram-
What is the gram stain?
- The Gram stain was named after the Danish
bacteriologist Hans Christian Gram who discovered
the procedure in the late 1880s - Bacteria with a thick peptidoglycan layer will retain
the dye and appear purple under the light microscope - While Gram negative bacteria, with a thin layer of
peptidoglycan, do not retain the dye and appear pink
How are some bacteria pathogenic?
- Most bacteria are free-living, but a few cause human
diseases that can often be cured by antibiotic therapy - To be a pathogen, a bacterium must:
- have an ability to pass from one host to the next
- penetrate into the host’s tissues
- withstand the host’s defense mechanisms
- induce illness in the host
What are examples of diseases by bacteria?
- Mycobacterium tuberculosis causes TB
- Mycobacterium leprae causes leprosy
- Helicobacter pylori causes peptic ulcer
- Cholera is caused by the bacterium Vibrio cholerae
- Salmonella enterica causes typhoid fever
- Dental caries (tooth decay) results from bacteria
metabolizing sugars on teeth surfaces. - Streptoccoccus mutans is one of the main cause of
dental caries.
What are antibiotics?
An antibiotic is a drug that kills or stops the
growth of bacteria, without harming the cells of
the infected organism.
* Antibiotics are derived from living organisms,
although they are often made more effective by
various chemical processes.
* There are a wide range of antibiotics to treat
bacterial infections.
* Other antimicrobial drugs such as isoniazid (used
for the treatment of TB) are synthetic
How do antibiotics work?
- Antibiotics interfere with some aspect of growth or
metabolism of the target bacterium. - These include:
- Synthesis of bacterial cell walls
- Activity of proteins in the cell membrane
- Enzyme action (by enzyme or coenzyme inhibition)
- DNA synthesis (replication)
- RNA synthesis (transcription)
- Protein synthesis (translation)
What is culture media?
Culture Media
– A medium is a solid or liquid preparation
containing nutrients for the culture
(growth) of micro-organisms, animal or
plant cells. e.g. nutrient agar
– A culture is a collection of “microbial” cells
growing on or in a medium.
What are some types of media?
- Enrichment media:
– These are media in which substances are added to
meet the requirements of certain micro-organisms
in preference to others. - Selective media:
– A selective medium is one in which substances are
added which inhibit the growth of all but one or a
few micro-organisms
What are some techinques used during bacterial growth?
- Aseptic Technique
– This refers to using sterilized equipment and
solutions and preventing their contamination
while in use; as by flame heating or the use of
filtered sterile air. - Inoculation
– The introduction of a small number of microorganisms into a nutrient medium is known as
inoculation
What is the rate of bacteria division and production?
- In a nutrient medium at optimal growth
conditions, bacteria divide (by binary fission)
every 30 minutes. - A single cell would produce some ten million
cells in 8 hours – exponential growth!
