Flashcards in lecture 3 - microbe-host interactions Deck (44):
what is the strongest non-covalent bond in nature?
-what is this
biotin and avidin
-biotin --> essential dietary nutrient
-avidin --> binding protein, antibacterial defence mechanism. Egg whites are rich with this
what do microbes need?
host, food, protection from predators and competitors
**normal flora and microbs
what is Normal Microbita and what relationship is this?
-collection of bacteria, archaea, and eukaryotic microbes usually colonizing our bodies
define colonization and how this occurs
- ability of a microbe to stay affixed to a body surface and replicate
-Adhesins (stick to the right place)
-susceptibility to pathogens
A condition in which pathogenic microbes penetrate host defences, enter tissues and multiply
*just because you come in contact with pathogen ("infected") doesn't mean you have disease - if body has ability to fight off pathogen, disease process will not occur
disruption of tissue or organ (pathologic state) caused by microbes or their products
-Any bacterium, virus, fungus, protozoan, or worm (helminth) that causes disease
-Parasitic relationship with its host
-Causes disease in a susceptible individual
what do the type and severity of infection depend on? 5 factors.
1. Dose (infectious)
2. Condition of the host (immunocomprimised)
3.Location in/on the host’s body: the “Portal of entry” – how does the pathogen get into your body
4. Genetic makeup of host and pathogen: the survival of the pathogen relies on the genetic make up of it and the environment
6.Host immune response
an organism’s potential to cause infection or disease
-Their lifestyle depends on infecting the host
-Attack healthy people
-Infection made worse by a weak or immature immune system
Salmonella Typhi = typhoid fever
-Only cause disease when given opportunity
-breakdown in immune system or immature immunity
Pneumocystis jirovecii = fungal infection of lungs in AIDS patients
organism is within host but cannot be detected by culture
ex) Herpes virus
Parasite is any organism that colonizes and harms its host
ectoparasite cause harm to outside of body
ex) Trichophyton rubric
endoparasite cause harm within body
ex) Wuchereria bancrofti
-enter and live inside host, aids in avoiding competition
small membrane-enclosed vacuoles
ex) Salmonella, Coxiella, Legionella
ex) Shigella, Listeria
any objective evidence of disease as noted by an observer
the subjective evidence of disease as sensed by the patient
when a disease can be identified or defined by a certain complex of signs and symptoms
what are the 5 stages of infection. Order from start to finish
1. incubation period
2. prodromal phase
time after the microbe first infects a host but before the first signs of disease
short period of vague symptoms and malaise; can serve as a warning of more symptoms to come but may not be noticed
Typical symptoms and signs of the disease appear and fever may be present
*microbe greatly out numbers immune response
Symptoms begin to subside; fever resolves.
*immune response outnumbers microbe
period after symptoms disappear and patient recovers
*immune response greatly outnumbers microbe
what are the 5 patterns of infection
5. primary - secondary
accumulated damage leads to cell death and tissue death
-Pathogen(s) stay localized
-The most common type of infection
-Spread to several sites and tissues
-Usually move via bloodstream
Ex: viral infections
Ex: Salmonella enterica serovar Typhi
-causes Typhoid fever
-Invade intestinal epithelium, spreads to macrophage, can become resident in gall bladder
-Infectious agent leaves a local infection
-Carried to other tissues
*pathogen itself stays localized but disease manifests in other areas
-In toxemia, the infection remains localized, but toxins spread to other tissues
Unusual cases: Streptococcal pharyngitis
Bacteria in throat (“Strep throat”)
Antibodies against bacterial cell wall also attack other tissues, such as heart and joints
-Multiple species contribute to infection
Example: dog bite
all sorts of different bacteria enter the wound
Can be called “polymicrobial” disease
primary - secondary infection
-Can occur due to weakened immunity
-Localized or systemic
-having one infection predisposes you to contracting another
Child scratches chickenpox (primary)
Then gets a localized Staphylococcus aureus infection (secondary)
what does "getting sick" from microbes depend on?
verdant, amount, and immunity
what weakens host defence and increases susceptibility?
-age (young and old)
-genetic and acquired immune alterations
-sugery/ organ transplants
-stress (physical/ emotional)
what are the 5 steps in pathogenesis?
-finding portal of entry (depends on virulence)
-attaching firmly (virulent factor)
-surviving host defences
-causing damage (disease) (infection)
what are the main portals of entry?
-usually same regions that harvest normal flora
Skin * most common cutaneous or membranous
how to microbes attach to host?
how do microbes survive host mechanisms?
Avoiding phagocytosis (WBC)
Avoiding death inside phagocyte
-ex) salmonella avoids being digested by macrophages even though it is “caught
Absence of specific immunity
how do microbes cause disease?
response (over-reactive immune response)
how do microbes leave host
Portals of exit
what is the portal of entry for the greatest number of pathogens?
-what type of microbes?
Examples: Streptococcal sore throat, Meningitis, Diphtheria, Whooping cough, Influenza, Measles, Mumps, Rubella, Chickenpox, Common cold, Bacteria and fungi causing pneumonia, TB
-Upper resp. tract infection (URI)
-lower resp. tract infection (LRI)
*LRI leading cause of infectious disease (tb, flu)
how do microbes enter through GI tract?
-Pathogens contained in food, drink, and other ingested substances
-can be adapted to survive digestive enzymes and pH changes; most are killed in stomach
examples: Salmonella, Shigella, Vibrio, certain strains of Escherichia coli, Poliovirus, Hepatitis A virus, Echovirus, Rotavirus, Entamoeba histolytica, Giardia lamblia
how do pathogens enter through skin and mucous membranes?
-what is the bodies reaction?
-Unbroken = a very tough barrier
-Nicks, abrasions, punctures weaken this line of defence
Eye (mucous membrane)
defence: Antigen presenting cell
-alert immune resposne
how do pathogens enter through urogenital portal?
STI's - account for 4% of all infections
-enter skin or mucosa of penis, external genitalia, vagina, cervix, and urethra
-Some can penetrate an unbroken surface
not always STI
ex) Uropathogenic E. coli - cause UTI
how do microbes cause infection in pregnancy and birth?
-cross placenta (syphilis spirochete, HIV)
-perinatally when the child is contaminated by the birth canal
*herpes is deadly to new borns