microbes and infection Flashcards
what are the different types of microbes?
- bacteria
- fungi
- viruses
- algae
- protozoa
what are the two names of microbes?
genus and species name
how big are bacteria?
very small 1-5um
what are the three basic shapes of bacteria?
- rod: bacilli
- spherical: cocci
- spiral: sprillus
what glycoprotein does the cell wall of bacteria incorporate?
peptidoglycan
do bacteria contain a nucleus?
no
does bacteria contain membrane-bound organelles?
no
how does bacteria reproduce?
binary fission
how big is a virus?
very small 20nm-100nm
what is an obligate parasite?
it can only reproduce inside the host cell
what is a naked virus?
genetic material is surrounded by a protein coat (capsid)
what is an enveloped virus?
naked virus plus an outer membrane or envelope- derived from the plasma membrane of the previous host cell
what are the four steps of typical viral infection (lytic)?
- attachment
- penetration
- replication
- maturation and release
how do naked viruses penetrate the target cell?
engulf (endocytosis)
how do enveloped viruses penetrate the target cell?
fuse with the host cell membrane
how do naked viruses mature and release from the target cell?
trigger lysis of host cell > viral exit kills cell
how do enveloped viruses mature and release from the target cell?
bud from the host cell, taking part of the cell membrane as an envelope > usually kills the host cell
what are fungi?
eukaryotic cell with cell wall containing chitin
what do fungi feed on?
organic matter
what is a symbiotic relationship?
2 organisms living together
what are the three classes of microbes humans interact with?
- normal flora
- transient microbes
- pathogens
what are the three types of relationships possible between microbes and humans?
- commensalism
- mutualism
- parasitism
what is commensalism?
one partner benefits the other is unaffected
what is mutualism?
both partners benefit
what is parasitism?
one partner benefits at the expense of another
what is colonisation?
establishment and growth on a body surface
what are transient microbes?
temporary and remain on the body for a short time
why are transient microbes unable to colonise on body surfaces?
- can not compete with normal flora for living space and nutrients
- eliminated by bodies defences
- dislodged by human activity
what is infection?
invasion of the body by a pathogenic microbe
what is a pathogen as a microbe?
microbes that can cause an infectious disease
what is an infectious disease?
disorder of a structure or function due to damage caused by microbe
is infectious disease always transmissible?
no
what is virulence?
capacity of the pathogen to cause disease
what are some factors that can increase the chances of an infection occurring?
host susceptibility and conducive enviros
what are factors that increase a host’s susceptibility to infection?
- pre-existing poor health
- poor immune status
- immunodeficiency
- compromised barriers
- extremes of age
what are some enviro conditions that affect the conducive enviro for infection?
- health status
- reservoir of infection
- ease of pathogen transmission between hosts
what are some conducive enviro for infection?
poverty, famine, natural disasters, and conflict
what is an opportunistic pathogen?
microbe that doesn’t normally cause disease but can do so under certain circumstances
when can microbes of the normal flora cause opportunistic infection?
- ecological balance of normal flora is upset
- microbes are relocated
- host innate and/or adaptive defences are compromised
what are the steps a pathogen must take while evading host defences?
- entry to body and attach to target cells
- multiplication in body using host resources
- damage body
- shedding or exit from body in large numbers to ensure transmission to next host
what is a portal of entry for a pathogen?
the site at which a pathogen enters the body
what are some portals of entry?
skin and mucous membranes
what are some entry points for pathogens through the skin?
- hair follicles, sweat glands
- some can live in or bore through skin
- compromised barriers
what are some entry points for pathogens through the mucous membranes?
- respiratory tract
- gastrointestinal tract
- urinary
- reproductive
- conjunctiva of eyes
what is the most common portal of entry for pathogens?
respiratory tract
how do pathogens attach to establish an infection?
- must attach, many have adhesions on their surface so they can bind to surface receptors
- some bacteria secrete sticky glycocalyx that cements them
- many viruses adhere to specific molecules
what is the incubation period of an infectious disease?
the time during which the pathogen is overcoming early host defences and utilising host resources to multiply to a critical population size
what are extracellular pathogens?
majority of bacteria and fungi obtain nutrients from ECF
what are intracellular pathogens?
all viruses, some bacteria, and fungi obtain nutrients from within cells
what do the strategies or virulence factors for overcoming defences for invading pathogens include?
- overcoming innate defences such as surface barriers and phagocytes
- overcoming adaptive defences such as degrading antibodies and antigenic variation
how do some pathogens overcome surface barriers?
release enzymes that breakdown epithelial/connective tissue to invade deeper tissue
how do some bacteria resist phagocytes?
- have slippery capsules that prevent phagocytes adhering and engulfing
- some release toxins that kill phagocytes or release enzymes that inactivate digestive enzymes
what are some toxins that are released by some bacteria that kill phagocytes or inactivate digestive enzymes?
- leukocidin: kills neutrophils
- catalase: destroys lysosomal enzymes
what are some enzymes that are produced by pathogens that can destroy antibodies?
IgA proteases destory IgA antibodies in mucus at mucosal surfaces
how can damage to the host be directly caused by a pathogen?
- damage caused by enzymes or toxins
- cytopathic effects
- use of host as food source
how can damage to the host be indirectly caused by a pathogen?
- inflammation: swelling, phagocytic enzymes, complement, scarring
- antibodies and cytotoxic cells
how can enzymes released by a pathogen cause damage?
tissue damage
how can toxins released by a pathogen cause damage?
- fever
- cardiovascular and nervous system disturbances
- shock
- diarrhoea
- death
how can cytopathic effects of pathogens induce damage?
microbes activity causes damage and kills host cells
what are portals of exit for pathogens?
when pathogen leaves the body to spread to a new host
what are the most common forms of portals of exit for pathogens?
respiratory and digestive tract pathogen
what is chronic infection?
is not completely eliminated and continues to multiply slowly and cause increasing amounts of damage
what is a latent infection?
pathogen persists lifelong but does not multiply or cause damage and can be reactivated
is an acute infection short or long term?
short
when is an acute infection transmissible?
during incubation, prodromal, disease or recovery period
when can latent infections be transmitted?
cannot when not multiplying
when can chronic infections be transmitted?
always
