Lab Exam 3 Flashcards
Scientific method steps
question research hypothesis experiment analyze data conclusion
Controlled variable
variable held constant
Independent variable
changed variable
Dependent variable
measured variable
Control treatment
part of the experiment that is kept constant, used to compare results of the changed variable experiments
Family Enterobacteriaceae characteristics
contain pathogens and non-pathogens
gram negative rods or coccobacillus
inhabit the gut of humans and animals
lactose non-fermenters are usually pathogens
family members are oxidase negative, glucose fermenters and nitrate reducers
S. aureus characteristics
yellow
growth and acid on MSA
coagulase positive
seen in skin infections and fatal septicemia
S. epidermidis
white
growth but no acid on MSA
coagulase negative
Staphylococcus characteristics
seen in clusters
normal flora of skin and nasal membranes
S. aureus is a major pathogen
Streptococcus characteristics
seen in pairs and chains
normal flora of the throat, nose, mouth and intestine
Streptococcus major pathogens
S. pyogenes
S. pneumoniae
S. agalactiae
S. faecalis
S. pyogenes
causes strep throat, can lead to scarlet fever
S. pneumoniae
causes pneumonia
S. agalactiae
causes pneumonia, endocardidis and meningitis
S. faecalis
causes endocardidis and food poisoning
Alpha hemolysis
produces greenish, brownish zone around colonies
Beta hemolysis
completely lyses blood cells around colonies
Gamma hemolysis
no hemolysis
Mannitol salt agar test
contains 7.5% salt (high)
selective for staph
Oxidase test
cyochrome oxidase reduces O2 to H2O in the final step of electron transport
positive result- black/purple within 20 sec
Catalase test
splits H2O2 to H2O and O2
Salt broth test
6.5% NaCl
Bile eschulin test
hydrolysis of eschulin results in blackened percipitate
Presumptive test
water tested for lactose fermenting bacteria, if gas is seen, there are presumed to be coliforms in the sample
Confirmed test
EMB agar inoculated with positive presumptive test samples, sample will grow if it is G- which is a coliform characteristic
Completed test
IMViC test is done on colony grown in confirmed test, inoculated onto a nutrient agar slant and Durham tube of lactose broth, if both are positive, it is a coliform (G- non spore forming rod)
Petrifilm results
blue colonies with a gas bubble are E.coli, red colonies with a gas bubble are coliforms
Glucose, lactose and sucrose fermentation tests
glucose, lactose or sucrose fermenter produces acid and gas, media color change to yellow
MRVP mixed acid fermentation test media
Media: MRVP
MRVP butanediol fermentation media
Media: MRVP
Catalase production test reagent
H2O2