introduction to infection Flashcards
(21 cards)
what is an infection
invasion of host tissue by microorganisms
what are disease symptoms caused by
toxins, microbial multiplication and hosts response to invasion
environmental sources of infection
ingestion of contaminated food/water, inhalation of contaminated air and contact with contaminated surfaced e.g medical devices
transferability of microbes
physical contact e.g STI, airborne e.g chicken pox, vector e.g malaria
how patients are a source of infection
always have lots of microbes on our skin = microbiota, but not harmful. however harmful when transferred to other sites e.g UTI
what is zoonosis
how animals act as a source of disease to humans
how infections are transferred
horizontal; connect- direct, indirect and vectors. inhalation- droplets (drop down and aerosols (stay in air as cloud) ingestion vertical; mother to child before of after birth
how microbes infect us
we are exposed to them and then they adhere to us by binding to specific receptors. they then invade host cells and multiply leading to disease symptoms
what are the virulent factors
exotoxins- molecules related to increase survivability of microbe in host e.g cytolytic, toxins, super antigens or enzymes
endotoxins - molecules naturally related which host can recognise and produce a immune response against
how can microbes cause the host damage
directly- because body only responds after the microbe has damaged the body
indirectly- microbe causes such an inflammatory response that it causes damage to the host
how patient determines disease
may have 1 part of body which is more susceptible to disease than another or may have comorbities
how pathogen determines disease
virulence factors, inoculum size and whether it has antimicrobial resistance
how do we know if a patient has an infection
take a history - symptoms, and potential exposures
examination - check for organ disfunction
investigations - specific and supportive
name an couple of specific investigations
bacteriology- take a swab and check for organism growth and check if sensitive to antibiotics. also detect specific antigens or nucleic acids.
virology- e.g HIV detect viral nucleic acids or antibodies
name a couple of supportive investigations
blood count, histopathology, CPR (C protein), imaging e.g xray or chemical test e.g kidney function
what is cellulitis
severe inflammation of dermal and subcutaneous layers of the skin
features of a full blood count
white blood cell count - increased in inflammation e.c.t
white blood cell differential - types of white blood cell present
RBC count
haemoglobin - amount of oxygen carrying proteins present
haematocrit - spare RBC take up blood space
mean corpuscular volume (MCV) - measurement of RBC average size
what is the platelet count
number of platelets in blood
what are agar plates
used for culture of bacterium, is a polysaccharide from seaweed. resists digestion by bacterial enzymes, doesnt melt and often have blood in them to provide nutrients for bacteria (some bacteria inhibited by this)
what is chocolate agar
some bacteria only grow if red blood cells have been lysed related intracellular nutrients. is darker because have been lysed
how to carry out a gram stain
- prepare slide
- add crystal violet stain onto culture and then wash with water - these adhere to lipopolysacheride and peptidoglcyan walls or both + and - bacteria
- add iodine and then wash off. this will fix crystal violet on gram + bacteria
- drop alcohol to dissolve lipopolysacheride membrane and expose thin peptidoglycan wall underneath
- drop counterstain (saffron) then wash. stains gram - bacteria pink/red and is unable to bind to gram+ due to iodine meaning retains purple stain
