Introduction Flashcards
What are characteristics of pathogenic bacteria?
The presence of pathogenicity genes which produce pathogenicity factors. These bacteria need to express these pathogenicity factors at the right time. Pathogenic bacteria also present genomic flexibility which contribute to fitness and establish antibiotic resistance
Describe the typical process of an infection?
For an infecious agent to cause disease it much have inoculated by a favourable infectious dose. First of all, the bacteria adhere to the host cell and its surface by fimbria and cell-wall associated proteins, adhesins. After that they destroy the tissue by the production of toxins and eventually invade and multiply by producing Invasins, which are a class of proteins associated with the penetration of pathogens into host cells. They play a role in promoting entry during the initial stage of infection. This leads to immune response, inflammation and further tissue damage.
for the infection to be sustained, infection processes inflicted ty the organism must be stronger then host defense mechanisms.
What are mobile genetic elements and in which processes are these involved?
Mobile genetic elements (MGEs) sometimes called selfish genetic elements are a type of genetic material that can move around within a genome, or that can be transferred from one species or replicon to another.
• Conjugative transposons. Integrated DNA elements that excise themselves to form a covalently closed circular intermediate. This circular intermediate can either reintegrate in the same cell (intracellular transposition) or transfer by conjugation to a recipient and integrate into the recipient’s genome (intercellular transposition).
• Pathogenicity islands. DNA sequences found in virulent bacteria that are mostly absent in avirulent bacteria which codes for toxins antibiotic resistance markers secretion system genes etc.
• Plasmids. small circular DNA molecule found in bacteria and some other microscopic organisms. They have a small number of genes usually associated with antibiotic resistance.
• Phages. A virus that is parasitic in bacteria.
• IS-elements. (Insertion sequence element) is a short DNA sequence that acts as a simple transposable element. Insertion sequences have two major characteristics: they are small relative to other transposable elements (generally around 700 to 2500 bp in length) and only code for proteins implicated in the transposition activity (they are thus different from other transposons, which also carry accessory genes such as antibiotic resistance genes).
• Integrons. Genetic mechanisms that allow bacteria to adapt and evolve rapidly through the stockpiling and expression of new genes. These genes are embedded in a specific genetic structure called gene cassette (a term that is lately changing to integron cassette) that generally carries one promoterless open reading frame (ORF) together with a recombination site (attC). Integron cassettes are incorporated to the attI site of the integron platform by site-specific recombination reactions mediated by the integrase.
• Transposons. DNA sequence that is able to move or insert itself at a new location in the genome
These elements confer the bacteria with high genome flexibility, which increases its fitness and help them be resistant to antibiotics to survive in the host, also transfer new pathogenicity factors from one species to other.
How develop novel pathogens and why can such pathogens affect humans
Host and pathogens are constantly adapting to each other’s genetic changes in a molecular arms race of compensatory genetic changes, which confer them new traits for pathogenicity. The presence of more virulence factors, the increase of the bacteria’s fitness, its increase of its antibiotic resistance and its genetic flexibility can be some reasons why new pathogens can emerge.
Why is it important to know the causative agent of an infection?
It is important in order to prevent misdiagnosis, unnecessary treatment, inconvenience and higher healthcare costs.
What was the hypothesis of Louis Pasteur`s experiment with the swan necked flaks and what was the outcome of this experiment?
That there was not such thing as spontaneous generation, which was a wide spread belief until the late 19th century. It was considered a strong proof for God’s existence in the world.
Thanks to his experiments we nowadays can preserve food by heat with the so called pasteurisation as well as sterilisation, the discovery of Lactobacilli and lactic fermentation and the vaccine development against fowl cholera, anthrax and canine madness (rabies).
Which are the Koch`s postulates in the germ theory of diseases?
- The suspected pathogen must be present in all sickened individuals and absent from healthy ones.
- The suspected pathogen should be grown in pure culture
- Microorganisms from the pure culture should cause disease in a healthy animal
- The microorganism should be reisolated and shown to be the same as the original.
What are limitations of these postulates?
- Healthy ones can be also infected but not developing the disease.
- In the case the particular bacteria (for example the one that causes leprosy) cannot be “grown in pure culture” in the laboratory. Sometimes you cannot isolate the bacteria from sickened organisms (H. pylori).
- In addition, not all organisms exposed to an infectious agent will acquire the infection as in the cases of tuberculosis and cholera (3rd Postulate). Non-infection may be due to such factors as general health and proper immune functioning.
And if there is no animal model of infection with that particular bacteria.
Why is the determination of the complete genome sequence of a pathogen important? What can be learned from the genome sequence?
- Its population structure and evolutionary history
- More knowledge about their specific sequences for strain detection and outbreak investigation
- Insight into growth requirements
- Useful for diagnosis
- Knowledge about its protein expression for drug design
- Insight into virulence factors and resistance.
- Deep insight into human microbiota
- Studying microbes even though they are not culturable
Which factors favour the appearance and spread of infectious diseases?
- Urbanisation of natural habitats, closer contact with remote environments
- Global warming and climate change
- Animal infections become transmissible to humans
- Importation and globalization
- Global travellers and tourism
- Mass migration
- Growth of urban slums
- Human sexual behaviour and drug abuse
- Institutional settings day care, hospitals
- Natural disasters and war
- Cutbacks in public health spendings and prevention programs
- Misuse and overuse of antibiotics
