lecture 3 - microbe-host interactions Flashcards
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
- mutual relationship
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)
- environmental factors
- susceptibility to pathogens
infection
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
infectious disease
disruption of tissue or organ (pathologic state) caused by microbes or their products
pathogen
- 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.
- Dose (infectious)
- Condition of the host (immunocomprimised)
- Location in/on the host’s body: the “Portal of entry” – how does the pathogen get into your body
- Genetic makeup of host and pathogen: the survival of the pathogen relies on the genetic make up of it and the environment
- Host immune response
pathogenicity
an organism’s potential to cause infection or disease
true pathogens
- Their lifestyle depends on infecting the host
- Attack healthy people
- Infection made worse by a weak or immature immune system
Salmonella Typhi = typhoid fever
opportunistic pathogen
- Only cause disease when given opportunity
- breakdown in immune system or immature immunity
Pneumocystis jirovecii = fungal infection of lungs in AIDS patients
latent state
organism is within host but cannot be detected by culture
ex) Herpes virus
Rickettsia prowazekii
ecological parasites
pathogenic
Parasite is any organism that colonizes and harms its host
ectoparasite cause harm to outside of body
ex) Trichophyton rubric
“athletes foot”
endoparasite cause harm within body
ex) Wuchereria bancrofti
“elephantitis”
invasive pathogens
-enter and live inside host, aids in avoiding competition
small membrane-enclosed vacuoles
ex) Salmonella, Coxiella, Legionella
inside cytoplasm
ex) Shigella, Listeria
sign
any objective evidence of disease as noted by an observer
symptom
the subjective evidence of disease as sensed by the patient
syndrome
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
- incubation period
- prodromal phase
- illness phase
- decline
- convalescence
incubation period
time after the microbe first infects a host but before the first signs of disease
prodromal phase
short period of vague symptoms and malaise; can serve as a warning of more symptoms to come but may not be noticed
illness phase
Typical symptoms and signs of the disease appear and fever may be present
*microbe greatly out numbers immune response
decline
Symptoms begin to subside; fever resolves.
*immune response outnumbers microbe
convalescence
period after symptoms disappear and patient recovers
*immune response greatly outnumbers microbe
what are the 5 patterns of infection
- localized
- systemic
- focal
- mixed
- primary - secondary
necrosis
accumulated damage leads to cell death and tissue death
localized infection
- Pathogen(s) stay localized
- The most common type of infection
systemic infection
- Spread to several sites and tissues
- Usually move via bloodstream
Ex: viral infections
HIV, chickenpox
Ex: Salmonella enterica serovar Typhi
- causes Typhoid fever
- Invade intestinal epithelium, spreads to macrophage, can become resident in gall bladder
focal infection
- 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
mixed infection
-Multiple species contribute to infection
Example: dog bite
all sorts of different bacteria enter the wound
Can be called “polymicrobial” disease
primary - secondary infection
- Successive
- Can occur due to weakened immunity
- Localized or systemic
- having one infection predisposes you to contracting another
Example:
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
- underlying disease
- chemo/ immunosuppressants
- stress (physical/ emotional)
- other infections
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)
- exiting host
what are the main portals of entry?
-usually same regions that harvest normal flora
Skin * most common cutaneous or membranous
GI tract
Respiratory tract
Urogenital tract
Endogenous biota
how to microbes attach to host?
Fimbriae
Capsules
Surface proteins
Viral spikes
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
IMMUNE
how do microbes cause disease?
Direct damage
Toxins and/or
enzymes
Indirect damage Inducing inappropriate, excessive host response (over-reactive immune response)
how do microbes leave host
Portals of exit Respiratory tract, salivary glands Skin cells Fecal matter Urogenital tract Blood
what is the portal of entry for the greatest number of pathogens?
-what type of microbes?
respiratory portal
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?
- examples
- what is the bodies reaction?
- Unbroken = a very tough barrier
- Nicks, abrasions, punctures weaken this line of defence
examples:
Skin
Staphylococcus aureus
Streptococcus pyogenes
Eye (mucous membrane)
Haemophilus aegyptius
Neisseria gonorrhoeae
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 "opportunistic pathogen"
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
how do pathogens exit their host
- A parasite must have a means to leave and transmit infection again
- Usually the same door they came in by
The mechanism of exit greatly influences spread in the human population
ex) flu enters through rest. and exits
