Diagnosis of Bacterial Infection Flashcards
(29 cards)
what are the results of a gram stain?
pink= negative purple= positive
what substances can you culture things in?
and what human substances would you use to produce them?
solid media, liquid media, or blood
culture with: pus swab fluid- CSF, joint aspirate, urine faeces
what is the problem with diagnosis with antibody detection?
test rapid itself but it may take around 2 weeks after initial infection for antibodies to be produced
other methods of bacterial diagnosis include?
toxin detection
antigen detection
PCR
name some gram positive cocci and what colour will they stain?
staphlococci, streptococci (enterococci, like part of strep)
will stain purple
name some gram negative bacilli and what colour will they stain?
e.coli, shigella, pseudomonas, salmonella, campylobacter
gram positive cocci in:
chains=?
clusters=?
chains= strep clusters= staphlo
You have found staphlococcus under the microscope- what test would you do now?
and what bacteria is it based on the results
do coagulase/DNA test (remember- coagulate in clusters)
if coagulase +ve : s. aureus (remember +ve auras)
coagulase -ve : s. epidermidis or
you have found streptococci under the microscope- what test do you do now?
+ what do results look like?
hemolysis- alpha, beta or none
alpha- greening
beta- clearing (remember ABC)
none- no clearance or greening
Under the hemolysis test on your streptococci, there is clearance around the bacteria- what type of hemolysis is this and what test would you do now?
(A)BC
beta- clearing
lancefield grouping (A-G)
Under the hemolysis test on your streptococci, there is greening around the bacteria- what type of hemolysis is this and what test would you do now?
greening- alpha hemolysis
do the optochin resistance test
(AGRO alpha,greening,resistance to optochin)
there is an alpha hemolytic strep, and you wants to find out which strain it is. based on the optochin test- describe the results and suggest which bacteria it is.
resistant to optochin- still grows around the disk: strep viridans
not resistant- there is clearing around the disk: strep pneumonia…
you have found a gram negative bacillus under the microscope- what test would you do now and why?
appearance on MacConkey plate
as it inhibits growth of gram positive bacteria and will tell you if its a lactose fermenter or not
the bacteria is shown to be a lactose fermenter- how will it appear on the maconkey plate and what bacteria might it be?
if it goes pink, it is a lactose fermenter (sugar=pink)
if it stays pale, it is a non lactose fermenter
therefore the plate is pink and it is likely an enterobacterea (coliform) such as e.coli or klebsiella
the bacteria is shown to be a non lactose fermenter- how will it look on the macconkey plate and what test would you do? what do the results mean?
it would be clear and you would do oxidase test
oxidase positive: pseudomonas
negative: enterbacterae
gram negative bacilli non lactose fermenters include:
shigella, salmonella, pseudomonas
what plate is used to differentiate between shigella and salmonella?
XLD
(stays pink= shigella,
if goes yellow/black dots= salmonella)
example of a gram negative cocci is?
neisseria
example of a gram positive bacillus is?
listeria
why might you not see anything on the gram stain?
needs to be cultured first/too few bacteria
why might you not bother doing a gram stain?
if the sample is taken from an unsterile site, where it would have other bacteria which are not causing disease, so would be difficult to interpret results
name all the sterile site in the body?
blood, CSF, urinary tract, peritoneal cavity, pleural fluid, joints, lower respiratory tract
where would you expect to culture normal flora?
urethra, GI tract(mouth, large intestine) vagina, skin
what can we do to prevent just growing normal flora + actually grow the disease causing pathogen?
selective media (contains chemicals/pH/antibiotics to inhibit grow of others)
media containing different nutrients (blood etc)
grown at different temps
grown at in different conditions (co2, anaerobic)
