Microbe-host interactions: Microbiota and pathogens Flashcards
Chemical agents
- Disinfection on inanimate objects and antiseptic for human tissue
- Only few chemicalsagen achieve sterility
Factors that influence efficacy
- Kind of organism
- Degree of contamination
- Time of exposure
- Nature of the material treated
- Concentration of disinfectant
Antimicrobial chemotherapy
- Administration of specific drugs to treat disease selective toxicity againt pathogen
Antibiotics
Bacterial infection
Selectivity
- Take advantage of difference between the structure of bacterial cell
- Concider gram positive and negativ e
- Diffrent spectrum activity
Symbiosis
Close interaction between two organisms of different species
Three symbiotic relationships:
- Mutualism
- Commensalism
- Parasitism
Mutualism
- Benefit to the bacteria - place to eat, survive and multiply
- Benefits to the human - Bacteria aid digestion, breaking down food that the host cannot normally digest and producing vitamins
Commensalism
- Benefit to the bacteria - Acquire nutrients consuming dead skin and a place to live and grow
- Commensal bacteria may become pathogenic and cause disease
Parasitism
- One partner, the pathogen, harms the host, causing infectious disease
- Benefit to the virus Virus takes advantage of the translational machinery of the cell to replicate
- Harm for the human cells - Viral infections lead to the death of the cells and tissue damage
Microbiota
- All the microorganisms that live in and on an organism
- 1-3% total body mass
- Generally non-pathogenic
- Symbiotic with host
Early Colonization
- Developing at birth
- Exposure to microbes from the mother’s birth canal
- Fementate the sugars in breast milk provide calories for baby
- Caesarean delivery provides microbe exposure from
initial caretakers
Bifidobacteria
Can ferment sugars found in human breast milk provides the infant with calories and lowers the gut pH, limiting growth of pathogens
Composition of microbiota
- Not static
- It reach a adult-like composition by age
3 - Stable in adult ages without any major physical or lifestyle changes
- Variable from person to person and at different sites within a person
Microbiota body sites
- Nutrients
- Physical and chemical factors
- Host defenses
- Mechanical factors
Microbiota functions
- Microbiota functions - short fatty acid chains
- Synthesise and excrete vitamins
- Prevent colonisation by pathogens - competitive exclusion and production and stimulationof antimicrobial molecules
- Stimulate the development of certain tissues
- Immune system stimulation/maturation
- Regulate inflammation
- Modulate and affect the central nervous system
Dysbiosis
Refers to an imbalance of microbial species and a reduction in microbial diversity within certain bodily
microbiomes
Causes of Dysbiosis
- Dietary changes
- Antibiotic use
- Psychological
- Physical stress
What can Dysbiosis lead to
- Can lead to infammation
Opportunistic infections
- Infection caused by commensals do not cause generally disease in a healthy host but in some circumstances can become opportunistic pathogen
How is Dysbiosis opportunistic
Altered microbiota can outgrow
Probiotics
- Live microoganisms that restore the normal balance of microbiota
- Beneficial functions, conferring a health benefit
to the host
Prebiotics
- Compound(s) added to enhance the colonization and positive health benefits of probiotic microbes
Synbiotics
- Foods or supplements that include both a prebiotic and a probiotic
Pathogen
Any organism that causes disease
Opportunistic pathogen
- May be part of normal microbiota and causes disease when the host is immunocompromised or when they have chance to outgrowth
Pathogenicity
Ability of a pathogen to cause disease
Virulence
- Degree of harm (pathogenicity) inflicted on its host
Steps in pathogenesis of bacterial infections
- Entry of pathogens into the body via transmission routes
- Attachment of the pathogen to some tissues
- Multiplication
- Invasion/spread of the pathogen
- Evasion if the host defences/immunity
- Damage to the host tissue
Portal of entry
- Skin, respiratory, gastrointestinal, urogenital
systems, or conjunctiva of eye
Attachment of microbe to specific target cells
Adhereance structure
- Pili
- Fimbriae
- Glycocalyx
Colonisation
Establish a site of microbial replication
on or within host
Invasiveness
Ability to spread to adjacent tissues
Active invasion
- Ability to spread to adjacent tissues - distruption of intestinal lining
Passive Invasion
- Host tissue alteration was already present and it was not caused by the pathogen
- Skin lesions, insect bites, wounds
Bacteremia
Presence of viable bacteria in the blood
Septicemia
Bacterial or fungal toxins in the blood.
Clostridium tetani
- noninvasive because it does not spread from one tissue to another, but toxins become blood borne
Bacillus anthracis
- Yersinia pestis (plague) also
produce toxins and are highly invasive
Streptococcus
span invasiveness
Overcoming Host Defences
- Pathogens overcome competition adaptive
immune system - Shelter to avoid recognition by defence cells.
- Survive and replicate inside host cells
- Squeeze between host cells.
- Avoid phagocytosis (capsule)
- Burrow under mucus.
- Find shelters within biofilms.
- Produce enzymes that inactivate innate resistance mechanisms.
- Excrete specialized proteins to selectively kill host cells
- Mutate and/or reduce cell surface proteins detected by immune cells
Meningitis and influenza
- Production of slippery mucoid capsule that prevents phagocytosis by host immune cells
Lipopolysaccharide overcoming host defence
- Eliminate O-antigen diminish immune recognition and clearance
Biofilm bacteria overcoming host defence
Protected from antimicrobial agents,
antibody and host immune cell
Damage to the host tissue
- Secreting enzymes that degrade host cell for nutrients
- Replicating inside the cells and inducing apoptosis
- Toxins disrupt the normal metabolism Exotoxins & Endotoxins
Hypersensitivity reactions
Inducing an excessive release of cytokines by immune cells and exacerbating inflammatory responses,
destroying tissues
Exotoxins
- In mostly gram positive bacteria part of growth and metabolism
- Released to surrounding medium
Endotoxins
- Part of outer portion of cell wall on gram negative bacteria
- Liberated when bacteria dies the cell wall then braks appart
