Microbiologie: Flore normale, pathogenèse et virulence Flashcards
What is colonization?
Presence of a microorganism in a host without necessarily causing an illness… the microorganism will still be able to replicate and be transmitted
Can be preemptive step to an infection
What is an infection?
Invasion of a host organism by a biologically active pathogen that can multiply and cause an illness (symptômes, signes cliniques, dysfonctions physiologiques, réponse immunitaire, inflammation) but may also be in sub-clinical latency or in the pre-symptomatic phase.
What is contamination?
Presence of a microorganism on nonliving things and contact with these items can lead to propagation of these infectious agents (fomites)
- fomites: objects or materials which are likely to carry infection, such as clothes, utensils, and furniture.
Contamination in the lab: evidence of microbes that aren’t from the area that was tested
What does a microorganism need to do to cause an illness? (6 steps)
- penetrate organism
- adhere to host cells (not always)
- compete with normal bacteria
- resist immune defenses, etc…
- invade target tissues
- cause physiological dysfunction
What are the different kinds of reservoirs for pathogens? (STEP 1)
Human:
- porteurs sains (healthy, not effected by illness)
- porteurs latents (has been controlled by their body)
- porteurs malades (can’t control it anyone… proliferates and can exit host and be spread)
Animals: zoonoses (ex: toxoplasma, anthrax, giardia)
Inanimés:
- earth (tetanus)
- water (cholera)
- food (gastroenteritis)
How are microbes transmitted? (STEP 1)
direct contact: intimate relations, droplets/aerosol
living vectors: malaria, Zika, Nile, tularemia, Lyme, the plague, encephalitis, etc…
inanimate carrier: knives, nails, needles, thorns, STETHOSCOPE, etc…
What is pathogénicité? (STEP 1)
The ability for a microorganism to cause an infection QUALITATIVE
What is a primary infection?
illness caused in healthy individuals
What is an opportunistic infection?
causes infections in people that are immunocompromised/immunodeficient or in barriers that are already broken which make the patient more susceptible to infection
What is virulence? (STEP 1)
The degree of pathogénicité QUANTITATIVE
How is virulence measured?
taux de morbidité
taux de mortalité/LD50
(can be made worse/better by mutations… these variants can change the virulence of a microorganism over time)
- ex: new strains of COVID
What are some risk factors? (STEP 1)
Genetics: M vs. W, deficiencies
Age: old, < 2 years old
Malnutrition, lifestyle, chronic illnesses (AIDS, CF), taking other medications (chemo), environment (weather, mosquitos?, animals?)
What are the two main ways microbes can enter the body? (STEP 1)
Muqueuses (ex: respiratory, digestive, genitals)
Skin (ex: follicles, cuts, etc.)
- voie parentérale (lesions, pokes, cuts, bites)
How do microbes adhere to host cells? (STEP 2)
adhésine: glycoprotein or lipoprotein on the surface of the bacteria (velcro)
recepteur: sugar on host cell
LOOK AT NOTION FOR SPECIFICS
How do microbes compete with “flore normale”? (STEP 3)
Many ways specific to location in the body
Human body: 10^13 eucaryotic cells (with RBCs… 10^14) and 10^14 microbes
What is the microflore?
Ecological communities of commensal, symbiotic and pathogenic microorganisms
What is the microbiome?
Microbiota + environment: genetic material of all the microbes (bacteria, fungi, protozoa and viruses) that live on and inside the human body
What is metagenomics?
study of genetic material recovered directly from environmental samples
What is the role of the “flore normale”?
protection, metabolism, stimulate immune response, can sometimes cause infections
Where can the “flore normale” be found?
mouth, skin, digestive and respiratory systems, genitourinary system (especially in the vagina)
What is the normal bacteria found on the skin? (STEP 3)
Not a very good environment for bacterial growth except for humid areas (groin, armpits, neck, etc.)
Flora here can be “résidente ou transitoire”
what are the most common ones?
staphylococcus, corynebacterium, propionibacterium (Cutibacrium acnes —> linked to acne)
What are cutaneous staph infections?
coagulase positive or negative:
- 90% of the flora found on the skin originates from the nose
- S. epidermidis Is the most common —> not a pathogen but S. aureus can be a pathogen
- 90% of S. aureus are resistant to penicillin
- can cause folliculitis, furuncles (boil), impetigo
- infections nosocomiales: SARM (resistant to meticillin)
What is acne?
most frequent skin disease
genetic and hormonal influence that favours sebum production and leads to the eventual blockage of openings of pilosebaceous units which leads to the accumulation of sebum
Cutibacterium acnes hydrolyzes glycerol and produces fatty acids which attract inflammatory cells —> apparition of papules and pustules
What is the normal bacteria found in the mouth? (STEP 3)
oral mucosa: Streptococcus salivarius, Bacteroides, yeast
teeth: Streptococcus mutans —> **caries **
What is the normal bacteria found in GI tract? (STEP 3)
Stomach:
- H. pylori –> ulcers
- pH of 2
Duodenum:
- Lactobacilli (acido-resistants)
Jejunum:
- pH 4-5
- Streptococci, lactobacilli
Ilium and colon:
- colon pH: 7
- so much bacteria
What happens when you take antibiotics?
flora is disrupted and the loss of ecological niches can favour the proliferation of C. difficile —> diarrhea in patients
- if antibiotics don’t work to treat the C. difficile.. you can resort to a fecal transplant
What is the normal bacteria found in respiratory system? (STEP 3)
Nose: Staphylococcus, streptococcus, Haemophilus
Throat and nasopharynx: similar to saliva
Trachea, bronchi, lungs: once considered to be sterile
What is the normal bacteria found in genitourinary tract? (STEP 3)
kidneys and bladder: usually sterile
ureters: staphylococcus, streptococcus, enterococcus, anaerobic bacilla
vagin: very complex
- adult: vaginal epithelium —> glycogen —> Lactobacillus —> lactic acid —> acidic pH (3.8-4.5)
- before puberty and after ménopause: no glycogen —> no Lactobacillus —> **no lactic acid —> alkaline pH (≥ 7)
What are some of the ways in which microbes can resist the immune system? (STEP 4)
Hide their vulnerable components, protect from phagocytosis, survive inside leukocytes, secrete enzymes that destroy leucocytes, interfere with antibodies and the compliment
What extracellular enzymes (4 kinds) can be secreted to help invade host tissue? (STEP 5)
- cytolysines: break cellular components (collagénase, phospholipases)
- hémolysines: destroy RBCs, alpha and beta hémolyses, strep B-hémolytiques groupes A, B, C
- coagulases et fibrinolysines: provoque formation of caillots or prevent coagulation
- leucocidines: destroy leucocytes by perforating them
What are the different types of toxins? (STEP 6)
Endotoxins and exotonins
How to endotoxins work?
naturally in gram - cell, released when it starts being attacked by WBCs/antibiotics
- Bacteremia —> sepsis —> septic shock —> dead
- Endotoxin —> inflammatory mediators, cytokines —> fever, cellular toxicity
- Endotoxin —> vasoactive mediators —> vascular problems and hypotension
- Heart/lung/kidney failure —> high mortality rate without antibiotics
How does the inflammatory reaction started by endotoxins work?
Redness, swelling, heat, pain
- can be localized or systemic, chronic or acute
- médiateurs protéiques: cytokines, chimiokines
-
médiateurs lipidiques: prostaglandines, leucotriènes
- TNF-alpha and interleukine-1 (PRO INFLAMMATORY)
- Other mediators: nitric oxide
- Involves adhesion molecules, receptors, etc. and interaction with systems
What exotoxins are secreted?
proteins, poisons (sub-unit A and B), cytotoxins (all cells), neurotoxins (nervous system), enterotoxins (attack cells lining GI tract)
What is a good thing about exotoxins?
most exotoxins can be inactivated by heat into completely safe anatoxins
What are some examples of diseases caused by exotoxins? (10)
What is tetanus?
- Clostridium tetani in contaminated soil from fecal matter
- Can stay in the ground for a long time (spores)
- Secretes a potent exotoxin (neurotoxin) which blocks nerve impulse and stops cells from relaxing leading to severe full-body spasms, paralysis, and death
- Vaccine: TDAP… booster every 10 ish years
What is botulism?
- alimentary intoxication caused by Clostridium botulinum that secretes toxine botulinique (poison)
- causes facial paralysis and cardiorespiratory problems
- without treatment: 70% mortality rate
- thankfully, it is inactivated by heat
