Microbiota + Pathogens Flashcards
What is symbiosis?
close interaction
between two organisms of different
species
What are the three different types of symbiotic relationships?
- Mutualism
- Commensalism
- Parasitism
What is mutualism?
*both species benefit from the interactions
What is an example of mutualism and how it benefits the bacteria and human/host?
- Bacterial species living in the gut (gut microbiota/flora)
The human gut harbours trillions of microbes
Benefit to the bacteria → Nutrients availability, physical requirements for their growth
(anaerobic conditions, pH suitability)
Benefits to the human → Bacteria aid digestion, breaking down food that the host cannot normally digest and producing vitamins (such as B and K)
What is commensalism?
*one partner in the relationship benefits
*the other neither benefits nor is harmed
What is an example of commensalism and how it benefits bacteria?
Commensal bacteria colonise epithelial surfaces of skin
E.g. Streptococcus epidermis
Benefit to the bacteria → Acquire nutrients, ability to grow, colonising niches, without causing neither harm nor help
Commensal bacteria may become opportunistic pathogenic (e.g. via broken skin) and cause disease
What is parasitism?
- One partner, the pathogen, harms the host, causing infectious disease
What is an example of parasitism + how this benefits/harms?
- SARS-CoV-2 or Influenza viruses infects human cells
of the respiratory system, causing COVID-19.
Benefit to the virus → Virus takes advantage of the translational machinery of the cell to replicate (multiply) virus particles. Viruses are defined as obligate intracellular parasites
Harm for the human cells → Viral infections lead to the death of the cells, tissue damage and inflammation.
What is microbiota?
all the microorganisms that
live in and on an organism
When does microbiota develop + where? + differences in birth
*microbiota begins developing at birth
*vaginal birth provides different microbiota than caesarean delivery
*breastfeeding affects microbiota
*bifidobacteria are important coloniser of the gut
- can ferment sugars found in human breast milk provides the infant with calories and lowers gut pH, limiting growth of pathogens.
What is the composition of microbiota?
*microbiota, bacteria, archaea, fungi and viruses reach adult like composition by age 3
*relatively stable in adults, changes with physiological states or lifestyle (diet, stress antibiotic therapy)
*variable from person - person, reduced variability in the elderly
What factors affect what/how microbiota are determined?
*nutrients
*physical and chemical factors
*host defences
*mechanical factors
-internal organs and tissues (brain, blood,cerebrospinal fluid, muscles) are normally free of microorganisms
What are the two types of microbiota species?
*resident flora
*transient flora
What is resident flora?
*permanently colonising host
What is transient flora?
*temporarily present with limited presence
What are the functions of human microbiota?
*protection against pathogens/infections
*regulate inflammation
*stimulate tissue development (intestines, lymphatic, capillary density)
*dietary fibre fermentation into short chain fatty acids
*synthesise vitamins (vit K and B12)
*modulate and affect the CNS (gut-brain axis)
How do human microbiota protect against pathogens/ infections?
- Competing for nutrients
- Exclusion of binding sites, preventing pathogens attachment/colonisation
- Production or stimulation of antimicrobial molecules
- Immune system stimulation/maturation
What is dysbiosis?
*imbalance of microbial composition
→ reduction in microbial diversity
can be caused by: diet, stress (psycho or physio) including oral Broad spectrum antibiotic use
↓
can cause diseases that involve inflammation.
What is an opportunistic infection?
Infections caused by commensals (normal microbiota) that do not usually harm the
host in a healthy individuals but in some cases can become opportunistic pathogen
What is an immunocompromised patient + when?
= permanent or temporary weakened immunity
*after treatments (anticancer chemo)
*after surgery
*disease (HIV)
*malnutrition - alcoholism - drug abuse - genetic defects
What is a probiotic?
live microorganisms to restore the normal balance of microbiota (gut and genital tract) and related functions, conferring a health benefit.
What is a prebiotic?
Non-digestable fibre compounds to stimulate the growth and colonisation of probiotic microbes within a microbiota → probiotic food
What is a synbiotic?
supplements that combine both prebiotics and probiotics
What is the definition of a pathogen?
any microorganism that causes disease in a defined host.
What is the definition of a opportunistic pathogen?
component of normal microbiota that can cause disease when host is immunocompromised or when they have chance to outgrowth.
What is the definition of pathogenicity?
ability of a pathogen to cause disease.
What is virulence?
degree of harm (pathogenicity) inflicted on its host.
What are the steps in pathogenesis of bacterial infections?
- Entry of pathogens into the body
Any organism that causes disease according to the transmission routes (e,g. penetration, inhalation, ingestion and introduction into the blood) - Attachment of the pathogen to some tissues
- Multiplication
- Invasion/spread of the pathogen
- Evasion if the host defences/immunity
- Damage to the host tissue(s)
What is entailed in the attachment of microbe to specific target cells?
*pili
*fimbriae
*glycocalyx (capsule)
all adherence structures
What is invasiveness?
ability to spread to adjacent/deeper tissues.
What are virulence factors?
adaptations used by microbes to invade and cause the host tissue damage
What is entailed in invasion? (active and passive) step 4
Active - (high virulent pathogens breaching tissue barriers
and disrupt the tissue integrity through secretion of:
* Toxins - poisonous for host tissues
* proteolytic enzymes – to dissolve tissue components
*E.g. C. difficile toxins disrupting the intestinal lining
Passive - exploiting pre-existing tissue alterations
>skin lesions, insect bites and wounds
What is entailed in overcoming host defences? (step 5)
- Find shelter to avoid recognition by immune cells (surviving and
replicating inside or between host cells, within biofilms) - Avoid phagocytosis (capsule).
- Produce enzymes that inactivate innate immunity.
- Mutate and/or reduce cell surface proteins detected by immune cells
What is entailed in damage to host tissues? (step 6)
- secreting proteolytic enzymes that degrade host cell for nutrients
- replicating inside the host cells and inducing apoptosis
- Toxins – disrupting the normal structure and function of host cells/tissues
- Exotoxins
- Endotoxins
- Inducing hypersensitivity reactions - excessive release of cytokines by
immune cells and exacerbating inflammatory responses, even life threating shock syndrome
What is the overview of exotoxins?
*produced inside mostly +ve gram bacteria
*released into surrounding medium
What is the overview of endotoxins?
*part of outer section of cell wall of -ve gram bacteria
*liberated when bacteria die and cell wall breaks apart
