bacteriology Flashcards
when is blood culture used? what are the sites?
- used to determine antimicrobial resistance
- sterile sites e.g. blood and CSF
- non-sterile sites
what is the problem with non-sterile sites?
- usually a lot of bacteria here so culturing is difficult
what is serology used to determine?
the body’s response to an infection
so measuring the body’s response by doing a blood at beginning of chickenpox and at end
what do molecular techniques do?
detect resistance genes
what does antimicrobial susceptibility testing do?
used to test AB resistance
but takes a long time
what are the different types of agar?
- chocolate agar: cooked blood, let’s bacteria use blood nutrients to grow
- MacConkey agar: designed to grow gram -ve bacteria
describe the cell walls of gram +ve and -ve
gram +ve = thick wall, purple stain, retains dye
gram -ve =thin wall, pink stain, loses dye
how can different forms of staphylococci be distinguished?
coagulase test to test between coagulase +/- staphylococci
- coagulase + = staphylococci aureus
- coagulase - = common skin microbes
what is the normal presentation of staphylocci?
form clumps
look like bunches of grapes as they bud divide
what is the normal presentation of streptococci?
- generally forms chains in the gram stain
on blood agar, what are th 2 groups streptococci separate into?
- alpha haemolysis: incomplete haemolysis, turns green e.g. Strep pneumoniae
- beta haemolysis: complete haemolysis, clears agar
e. g. Group A - Strep Pyogenes, group B - strep agalactiae
what is important to remember about gram negative bacilli?
do not take up gram stain
so appear pink
e.g. E coli
what are the possible causes of diarrhoea?
- bacteria: salmonella, shigella, campylobacter, E. coli, C. difficle
- parasites: amoeba, giardia, cryptosporidium
- viruses
what does salmonella, campylobacter and virbrio cholerae look like on agar?
- salmonella: colonies are black due to hydrogen sulphide production
- campylobacter: can survive at 48 degrees so heat to kill other bacteria
- virbrio cholerae: cholera makes agar turn green
what is PPV and what does it depend on?
- depends on pre-test probability of the sample being positive
- more likely a pt is to have disease, more likely a positive test represents a true positive