How do Microbes Cause Disease? Flashcards
whats a commensal?
non-pathogenic microbe that benefits from living in us but doesnt cause harm
what are attributes unique to pathogens? (5)
- cause disease in healthy, immunocompetent hosts
- breach anatomic and cellular barriers - can reach sterile body sites
- avoid and manipulate host defenses, innate and adaptive immunity
- multiply
- produce toxins and damage host
what are the different stages of disease caused by a microbe?
- *1. incubation period**
- asymptomatic period
- *2. prodromal stage**
- vauge feelings of non-specific complaints
- *3. period of illness (invasion)**
- sympotmatic and more specific signs
- effects of toxins
- *4. convalescences**
- persons of immune system responds to infection (or medical intervention)
label these pls xoxo
what are different ways of microbe transmission? (5)
what are different portal of entry for microbes? (5)
- *transmission methods:**
- direct contact with carrier
- indirect contact (cough, sneezing)
- airbourne transmission (resp. droplets, inhalation)
- vectors (insects, medical device)
- food bourne
- *portals of entry:**
- resp system (ENT) - main portal
- GI tract (oral - anal)
- genitourinary system
- skin (access to blood)
- placental
what are natural host defences / non spefific host defences?
name 7 xoxo
= non specific prevention of colonization of the host.
- normal microbial biota: compete with pathogens (GI and resp. pathway)
- **skin
- lysozyme:**tears - dissolves cell walls of bacteria
- cilia: filter and trap invading microbes
- blood proteins
- mucous and phagocytes in lungs, prevent colon.
- pH change (e.g. stomach)
- flushin of urinary tract prevents colonisation (cant stick to epithelium bc gets flushed out)
natural host defences are type of which immunity?
innate immune response
what is adherence? (by pathogens)
what are the most common adherence molecules?
Adherence: Any of several factors that enable bacteria to adhere to host surfaces as a step towards infection
most common adherence mechanism:
bacterial pathogen: produce surface molecule that will recognise specific host cell receptor
- pili and fimbriae
- outer membrane protein invasion
explain the major ways adherence can occur
adhesive hair-like structures
1. pili or fimbriae: adhesive hair-like structures formed of proteins
subunits: major subunit - pili. minor subunit - tip
- *2. afimbrial adhesin:**
- membrane or membrane anchored protein, interacting directly with host cell receptors.
- indirect interaction with hosts cell receptors via bridging molecules (e.g. fibronectin binding proteins)
- *3. biofilms: adhesion to solid surfaces and infections**
- community of bacteria that produce sugar polymer, known as extrapolymeric substance (EPS), allows biofilm to attach to a surface
explain what biofilms are particularly good at binding on?
give 4 examples of where they form
biofilms are important for adhesion on solid surfaces and infections:
- periodontal disease and dental plaque formation
- CF associated pneumonia and Pseudomonas aeruginosa infections
- chronic infections due to biofilms
- implant and catheter related infections
why are biofilm associated infections really problematic? (2)
- extreme resistance to antiobiotics and other anti-microbrial agents
- high resistance to host immune defences
how do microbes undergo local spread and invasion through degredative enzymes / spreading factors ?
explain 2 pls
bacterial patogens often produce degradative enzymes - aka spreading factors: facilitate growth and spread of pathogen (dont kill host cells)
-
hyaluronidase:
- breaks down hyaluronic acid (intracellular cement of CT). e.g. Strept. spp, Staph aureas. allows invasion further into tissues
- *2. collagenase:**
- breaks down collagen network - gives access to deeper tissues. E.g. Clostridium spp.
how does invasion of host cell oocur by bacterial invasion of host cells?
some bacteria promote their entry into non-phagocytic cells:
- *1. triggered invasion:**
- bacteria inject virulence factors into host cell cytoplasms to activate uptake by cell
- bacteria force the cell to extend local protrusion that engulf the bacterium
- = type 3 secretion system-dependent
- Salmnoella spp, Shigella flexneri
- *2. Zippered invasion:**
- bacteria produce outer membrane protein, with extracellular part exposed
- recognises receptor on target cell
- taken up by the cell
- specifc high affinity interaction between bacteria molecule and host cell receptor.
how can pathogens do invasion of host cells (overview)
- *spreading factors**
e. g: - collagenase
- hyaluronidase
- *invasion:**
- triggered invasion
- zippered invasion
what happens to microbes once gained access to lympahtic or bloodstream?
- name for bacteria / virus in blood?
- name for infection or pathogen in blood with evidence of host damage?
- microbes gain access to lymphatic or bloodsteam: spread throughout whole body
- virus / bacteria in blood: bacteraemia or viremia
- infection / pathogen causing damage in blood or lymphatic system of host: septicaemia
