L1. Introduction Flashcards
How many pathogenic bacterial species are described?
Less than 100 pathogenic bacterial species are described.
What percentage of bacterial diseases are caused by a small number of species?
1% of bacterial diseases are caused by several thousands of species, even though most infections are made up by the 100 described pathogenic species.
Does bacterial interaction occur in isolation?
No, bacterial interaction does not occur in a vacuum but only when interacting with a host (Nothing in this module happens in a vacuum, only when interacting with a host).
What happens during a real-life infection in terms of microbial presence?
During a real-life infection, there are lots of bacteria, fungi, archaea, etc., present in the environment, but the focus is on the one causing the disease; however, the others impact the infection massively.
How are non-pathogenic members of the normal flora described?
Non-pathogenic members of the normal flora are described as “commensals.”
Define commensalism.
Commensalism is an association between two organisms in which one benefits and the other derives neither benefit nor harm.
What is mutualism in the context of microbiota and an example?
Mutualism is a symbiotic relationship where both organisms benefit, such as the gut microbiome providing vitamin B12 and contributing to the calorie content of food.
How do gut microbiota benefit the host’s epithelial cells?
All energy supplied to epithelial cells comes from short-chained fatty acids produced by gut microbiota.
Describe a parasitic relationship in the context of microbiota.
A parasitic relationship causes slight harm to the host by using resources, but it is not too detrimental.
What can commensal organisms do under the right circumstances?
Commensal organisms can sometimes cause disease under the right circumstances, becoming opportunistic pathogens.
What is the focus of the module in terms of bacteria?
The focus is on bacteria that can become opportunistic pathogens.
What are the two possible outcomes of a pathogen infecting a host?
Asymptomatic carriage or disease development.
What is asymptomatic carriage?
When no symptoms of disease are shown, but the individual can still pass on the pathogen or even develop the disease later.
Give an example of an asymptomatic carrier.
Typhoid Mary.
Why don’t pathogens evolve to become less pathogenic?
It’s not in the pathogen’s interest to kill the host, but it makes no difference as once it can transmit and spread quickly, there is no selective pressure against death.
What happens if a pathogen isn’t good at transmitting?
Pathogenicity may decrease over time.
Why do some pathogens benefit from the host’s death?
Some anaerobes, like Clostridium tetanus, can’t live in the presence of oxygen and have evolved to kill the host, making the host an anaerobic fermenter (food source).
What are the two classes of virulence factors?
Factors for colonizing the host and factors that damage the host.
Name some virulence factors used for colonizing the host.
Adhesions, invasions, nutrient acquisition (e.g., Fe scavenging), motility, and chemotaxis.
Name some virulence factors that damage the host.
Exotoxins, endotoxins, proteases, DNase, lipase, and hemolysins.
How do host defenses push pathogens to become more asymptomatic or lead to recovery from disease?
Through physical barriers, innate immunity, and adaptive immunity.
What are the components of innate immunity that help fight pathogens?
Complement secretion, macrophages, and antimicrobial peptides.
What role do physical barriers play in host defense?
Skin and gut epithelium prevent bacteria from accessing more nutrients and usually need to be damaged for pathogens to enter.
What is the role of adaptive immunity in host defense?
B cells and T cells respond to pathogens, especially if the pathogen survives the initial innate immune response.
What is the importance of complement in innate immunity?
It involves the secretion of complement proteins that form a cascade to attack and lyse pathogens.
How do antimicrobial peptides contribute to host defense?
They lyse bacterial membranes, as are cationic peptides that insert and disrupt membranes, helping to kill pathogens.
What are Koch’s Postulates?
> In 1876 Robert Koch put forward 4 criteria that must be met in order to identify the etiological agent of a disease
- The microorganism must be found in abundance in all organisms suffering from the disease but not in healthy organisms.
- The microorganism must be isolated from a diseased organism and grown in pure culture.
- The cultured microorganism should cause disease when introduced into a healthy organism.
- The microorganism must be re-isolated from the diseased experimental host and identified as being identical to the original causative agent.
What are the molecular Kock’s postulates and what are they for?
> These are how to distinguish what a virulence factor is and what it does:
- The phenotype or property under investigation should be associated with pathogenic members of a genus or pathogenic strains of a species.
>Some commensals have strains which are pathogenic, so the genes studied are specific to the pathogen not the whole genus. - Specific inactivation of the gene(s) associated with the suspected virulence trait should lead to a measurable loss in pathogenicity or virulence.
>If you knockout a gene with a virulence trait, the bacteria pathogen becomes less pathogenic. - Reversion or allelic replacement of the mutated gene should lead to restoration of pathogenicity.
>Now referred to as complementation, if you want to know what a gene does- disrupt or remove gene, study change in phenotype, then restore genotype back, gives confidence that gene is for a phenotype.
What is one method used to study pathogenesis?
Genetic manipulation, which involves some readout of virulence using animal or surrogate models to assess virulence.
What does reductionist microbiology focus on in the study of pathogenesis?
Identifying virulence factors such as toxins, degradative enzymes, adhesins, invasins, chemotaxis and motility systems, nutrient acquisition, etc.
Why is reductionist microbiology often used in studying pathogenesis?
Because it is easier to work with pure cultures or single genes, whereas studying a pathogen in a mixed population is not easy.
What challenge arises from the fact that many virulence factors are also produced by non-pathogenic organisms?
It makes it difficult to identify a true virulence factor.
How does the presence of virulence factors in both pathogens and commensals complicate the identification of true virulence factors?
It raises the question of whether a factor is required for disease if both pathogens and commensals produce it.
Are all virulence factors clearly identifiable as essential for disease?
No, some virulence factors are clearly required for disease, while others are not as clear.
What organism releases the tetanus toxin?
The gram-positive spore-forming anaerobe Clostridium tetani, related to Clostridiodes difficile.
How does the tetanus toxin cause death?
The clostridial neurotoxin induces rigid paralysis by acting at the neuromuscular junction, preventing muscles from relaxing. This can lead to suffocation and broken bones due to muscle spasms.
