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  • Explain the differences between Koch’s original postulates and the molecular Koch’s postulates.

Pathogenicity and virulence

The ability of a microbial agent to cause disease is called pathogenicity , and the degree to which an organism is pathogenic is called virulence . Virulence is a continuum. On one end of the spectrum are organisms that are avirulent (not harmful) and on the other are organisms that are highly virulent. Highly virulent pathogens will almost always lead to a disease state when introduced to the body, and some may even cause multi-organ and body system failure in healthy individuals. Less virulent pathogens may cause an initial infection, but may not always cause severe illness. Pathogens with low virulence would more likely result in mild signs and symptoms of disease, such as low-grade fever, headache, or muscle aches. Some individuals might even be asymptomatic.

An example of a highly virulent microorganism is Bacillus anthracis , the pathogen responsible for anthrax . B. anthracis can produce different forms of disease, depending on the route of transmission (e.g., cutaneous injection, inhalation, ingestion). The most serious form of anthrax is inhalation anthrax. After B. anthracis spores are inhaled, they germinate. An active infection develops and the bacteria release potent toxins that cause edema (fluid buildup in tissues), hypoxia (a condition preventing oxygen from reaching tissues), and necrosis (cell death and inflammation). Signs and symptoms of inhalation anthrax include high fever, difficulty breathing, vomiting and coughing up blood, and severe chest pains suggestive of a heart attack. With inhalation anthrax, the toxins and bacteria enter the bloodstream, which can lead to multi-organ failure and death of the patient. If a gene (or genes) involved in pathogenesis is inactivated, the bacteria become less virulent or nonpathogenic.

Virulence of a pathogen can be quantified using controlled experiments with laboratory animals. Two important indicators of virulence are the median infectious dose (ID 50 ) and the median lethal dose (LD 50 ) , both of which are typically determined experimentally using animal models. The ID 50 is the number of pathogen cells or virions required to cause active infection in 50% of inoculated animals. The LD 50 is the number of pathogenic cells, virions, or amount of toxin required to kill 50% of infected animals. To calculate these values, each group of animals is inoculated with one of a range of known numbers of pathogen cells or virions. In graphs like the one shown in [link] , the percentage of animals that have been infected (for ID 50 ) or killed (for LD 50 ) is plotted against the concentration of pathogen inoculated. [link] represents data graphed from a hypothetical experiment measuring the LD 50 of a pathogen. Interpretation of the data from this graph indicates that the LD 50 of the pathogen for the test animals is 10 4 pathogen cells or virions (depending upon the pathogen studied).

A graph with “number of pathogenic agents (cells or virions)” on the X axis and Percent mortality in experimental group on the Y axis. The graph begins at 0,0 and increases until there is nearly 100% death at 10 to the 5. The line then plateaus at 100%.  A 50% death rate occurs at 10 to the 4. This is the LD 50.
A graph like this is used to determine LD 50 by plotting pathogen concentration against the percent of infected test animals that have died. In this example, the LD 50 = 10 4 pathogenic particles.

Questions & Answers

what are the two acids the skin produce
Caro Reply
alpha hydroxy and beta hydroxy there are water soluble compounds and often use as exfoliant
Enow
what must a positive strand of an RNA virus do first
Kelsi-Ann Reply
A positive-sense single-stranded RNA virus (or (+)ssRNA virus) is a virus that uses positive sense single stranded RNA as its genetic material. Single stranded RNA viruses are classified as positive or negative depending on the sense or polarity of the RNA.
Dejene
 The positive-sense viral RNA genome can serve as messenger RNA and can be translated into protein in the host cell. Positive-sense ssRNA viruses belong to Group IV in the Baltimore classification. Positive-sense RNA viruses account for a large fraction of known viruses, including many pathogens
Dejene
such as the hepaci virus C, West nail virus, dengue virus, SARS and MERS coronaviruses, and SARS-CoV-2 as well as less clinically serious pathogens such as the rhinoviruses that cause the common cold.
Dejene
Why strong acid and alkline are not harmful to mycobacterium bacili?
Brian
What are the types of bacteria
John Reply
Do you mean the shapes or the the two different types of bacteria? Bacteria are often described in terms of their general shape. Common shapes include spherical (coccus), rod-shaped (bacillus), or curved (spirillum, spirochete, or vibrio) The two different types are gram negative or gram positive.
Melanie
what other characteristics of prokaryotes a bacteria don't have?
Brian
Prokaryotes are single-celled organisms belonging to the domains Bacteria and Archaea. Prokaryotic cells are much smaller than eukaryotic cells, have no nucelus, and lack organelles. All prokaryotic cells are encased by a cell wall. Many also have a capsule or slime layer made of polysaccharide.
Dejene
gram positive bacteria and gram negative bacteria
mubeen
Most bacteria can be broadly classified as Gram positive or Gram negative. Gram positive bacteria have cell walls composed of thick layers of peptidoglycan.cells stain purple when subjected to a Gram stain procedure. Gram negative bacteria have cell walls with a thin layer of peptidoglycan.
Dejene
all of you are amazing microbiologists
demisew
thanks demisew....
Dejene
guys what are the two acids the skin produce
Caro
what are the bacteria's involved in the decaying of food
Enow Reply
Some pathogenic bacteria, such as Clostridium perfringens and Bacillus cereus, are capable of causing spoilage.
Dejene
Corona has a gray and black cell structure ....if yes explain..if no explain
Joshua Reply
multiple questions and answers in microbiology and bio chemistry
Lakshmi Reply
is the study of a bacteria and other organisms
isir
yes..this book is about bacteria & others organisms
Hasan
biochemistry is the branch of science that dealing of chemical compounds reactions and other processes
isir
have you any question?
Hasan
yess, Why scientists not search coronavirus vaccines in short time.
demisew
they are on
Monyditchol
what are the symptoms for tuberculosis
Chiamaka
Most people infected with the bacteria that cause tuberculosis don't have symptoms. When symptoms do occur, they usually include a cough (sometimes blood-tinged), weight loss, night sweats and fever.
Dejene
symptoms tuberculosis. Fever Chills Night sweats Cough Loss of appetite Weight loss Blood in the sputum (phlegm) Loss of energy
lourdes
can corona virus transmitted from mother to her child through placenta ?
Abdul
probably
Mad
no
Oke
no,but it can through trait
Falere
mutation occur in the genome of corona virus. thats why the corona vaccines forming just difficult
Muzamil
intersted
Do
no
Esther
No
John
Yes
Suhaib
yes
Benjamin
yes coz it's spread through the soft body parts more so the openings in our bodies
Rebecca
Yes
Ayan
what is relation between fear (from covid 19 ) and immune sys ?
Abdul
because it damages the immune system by reduction the action of WBC
mike
reducing pls
mike
how is it possible for a woman to be pregnant and still See's her period
Prince Reply
we term it as discharge
Monyditchol
what is immunity
evans Reply
What is a varuis
evans
A submicroscopic infectious organism, now understood to be a non-cellular structure consisting of a core of DNA or RNA surrounded by a protein coat. It requires a living cell to replicate, and often causes disease
Ebo
A virus is a biological agent that reproduces inside the cells of living hosts. When infected by a virus, a host cell is forced to produce thousands of identical copies of the original virus at an extraordinary rate
Dejene
A virus is a microorganism which invade our bodies causing diseases due to eliciting immune responses by the body against it, can replicate using our genome inducing production of proteins helping them to establish new life inside our bodies.
What are the important of capsules
Marriam Reply
what are the roles of male sex hormones
Marriam
Testosterone is the principal sex hormone inmales and is produced in the testes (testicles). Dihydrotestosterone is a hormonein which the double bond of testosterone has been reduced by enzyrne reactions in the body. ... The testes perform two functions: They produce sperm, and they producetestoster
Dejene
Capsules in bacteria protect them from phagocytosis of eukaryotic organisms. This is what makes them virulent and harmful without antibodies.
Lewis
any one told me definition of amoebic dysentery & amoebic liver dysentery?
Mira
Amoebiasis, also known amoebic dysentery, is an infection caused by any of the amobae of the Entamoeba group. Symptoms are most common during infection by Entamoeba histolytica. Amoebiasis can be present with no, mild, or severe symptoms. Symptoms may include abdominal pain, diarrhea....
Dejene
tnx
Mira
u welcome mira
Dejene
people explain for me this words in public health.tb prevention 1:promotive 2:preventive 3:curative 4:rehabilitative
Obrian
Capsules function similarly to endospores they provide an extra layer of protection especially in acidic or basic environments. It is also a thicker membrane which can change the osmosis process and can provides resistance to antibotics depending if it is gram negative or positive.
Melanie
...As some antibotics focus on breaking down the cell wall and is not able to.
Melanie
what are the clinical classification of amoxicillin?
Rebecca
how does a autoimmune diso ders develop
Oliver Reply
simply autoimmune disease is not completely understood. There are many variations from genetically inherited to acquired by viruses like HIV. Genetically they may not be prominent until an unknown point in one's life. I am far from an expert, I am just reciting what I have learned. Take rheumatoid
Lewis
what is anatomy
Mohamed Reply
Anatomy is the study of parts of the human body
Matilda
the branch of science concerned with the bodily structure of humans, animals, and other living organisms, especially as revealed by dissection and the separation of parts.
Dejene
Describe the halden effect
Suleiman
The Haldane effect is a property of haemoglobin first described by John ScottHaldane. Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of carbon dioxide. This property is the Haldane effect.
Dejene
Difference between chief cells and parietal cells in the stomach
Suleiman
 Parietal cells are the epithelialcells that secrete HCl and intrinsic factor. They are located in the gastric glands found in lining of fundus and stomach. The gastric chief cells , are cells in the stomach that release pepsinogen and chymosin.
Dejene
is the study of structure and organs located in human life
isir
listen to Matilda
Lewis
essay on microbiology and how it contribute to the pharmacy assistant programme
Tagedevi Reply
I want to know how it contribute to the pharmacy assistant programme
chidiebube
Contribute how? If you want to contribute to pharmaceutical stuff you should look for websites with blogs that relate to your interests.
Lewis
hello i want to know how it contribute to microbiology programs
Dejene
Microbiology is the study of bacteria and and organisms such as viruses, fungi, and mold. How does this apply to medicine? It applies to medicine or pharmacology because when you get sick you are infected by a pathogen and understanding how these organisms interact with each other helps you to....
Melanie
develop medicine. A lot of bacteria infections can be cured with various medicines but not all medicines work equally. It depends if your sickness is based on gram positve or negative bacteria, if its s mold or fungus or a virius. Each medicine targets a certain one.
Melanie
If you need any ideas I recommend looking up Louis Pastar who used microbiology to invent a lot of medicines and contributed greatly to microbiology and pharmaceutical.
Melanie
what is a bacterial
Eric Reply
Bacteria is a microscopic organism belonging to the kingdom prokaryotic
John
what is prokaryotic
Oliver
if you are here, read this free book, it is mostly correct, there are a few pictures that should be corrected
Lewis
thanks
Eric
A prokaryotes does not have lipid- bilayer bound organelles, they can reproduce by binary fission, they have a DNA region, most have a cell well, contains a plasmid, 70s ribosomes, high mutation rate due lack of certain DNA replication enzymes.
Eric
HIV And Coronavírus, what is the difference ? Both are Retrovirus, please , I want to know. Thank you.
Cl Reply
does it mean Corona is incurable just like the HIV for the it to be retroviral too?
Joy
The reason researchers are looking to these medicines is that the new coronavirus—like HIV, Ebola, and hepatitis C—are all RNA viruses.but covid-19 is to detect human and animal virus. hiv is only human virus do not detecte animals
Dejene
***niaid.nih.gov/diseases-conditions/coronaviruses start here, since this is what is new, then recap yourself on autoimmune diseases that are not recoverable
Lewis
what happen when virus escape the host
Hailemichael
A virus must attach to a living cell, be taken inside, manufacture its proteins and copy its genome, and find a way to escape the cell so that the virus can infect other cells. Viruses can infect only certain species of hosts and only certain cells within that host.
Dejene
what is the difference between capsule and glycocylx in relation to prokaryotes
Felix Reply
However glycocalyx exists in bacteria as either a capsule or a slime layer. Thedifference between a capsule and a slime layer is that in a capsule polysaccharides are firmly attached to the cell wall, while in aslime layer, the glycoproteins are loosely attached to the cell wall.
Dejene
Glycocalyx is composed of glycosaminoglycans, proteoglycans and other glycoproteins bearing acidic oligosaccharides and terminal sialic acids. Capsule is Composed of polysaccharide (i.e. poly: many, saccharide: sugar). Exception: The capsule of Bacillus anthracis is composed of polymerized D-glutami
assarra
Capsule is located immediately exterior to the murein (peptidoglycan) layer  of gram-positive bacteria and the outer membrane (Lipopolysaccharide layer) of gram-negative bacteria The glycocalyx, which is located on the apical surface of endothelial cells, is composed of a negatively charged network
assarra
Meu I watch at microscopic HIV
Cl
assarra is paying attention. look into taking a course is you want to truly understand what is known now
Lewis

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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