MFD practicals Flashcards
What does the enzyme urease do ?
convert urea into ammonia
What happens in the urease test?
bacteria mixed with urease
conversion of urea to ammonia
What is the significance of ammonia ?
it can raise pH
protect against caries
Which bacterium uses urease ?
helicobacter pylori
ammonia made neutralises stomach acid- allow it to survive
What does the enzyme catalase do ?
converts hydrogen peroxide into water and oxygen
What does the catalase test involve ?
drops of hydrogen peroxide on slide
add loopfuls of bacteria
see fizzing if catalase is present- liberation of oxygen
What happens in the DNase test ?
release of free nucleotides by bacteria can turn toludine blue into a pink color
What happens in the coagulase test?
latex particles covered in fibrinogen
if bacteria have coagulase- see agglutination of particles turn blue
What is the appearance of staph aureus ?
bunches of grapes
Where does staph aureus live ?
anterior nares
nasopharynx
skin
What are the properties of staph aureus that enbale it to live on the skin ?
can withstand high levels of salt
Is staph aureus commensal or opportunsitic ?
both- can cause infections when compromised host
What are some of the diseases that staph aureus can cause ?
MRSA
food poisoning
toxic shock syndrome
Is staph aureus gram positive or gram negative ?
gram positive
Which enzymes is staph aureus positive for ?
coagulase positive
catalase positive
DNase psoitive
What is the advantage of being DNase positive ?
allows bacteria to escape extracellular DNA rleeased in infection
What are some diseases oral streptococci can cause ?
infective endocarditis
Why can strep salivaris be sold as a probiotic ?
makes bacteriocns- AMPs
Which enzymes is strep salivarius positive for ?
Urease positive
What is the shape of streo salivarius ?
strips of streps
cocci
Is strep salivarius gram positive or gram negative ?
gram positive
What type of bacteria is E.coli ?
gram negative
enteric
What is e.coli mainly used for ?
lab model organism
growth
Which strains of e.coli are pathgoenic ?
those that possess the 157th version of the O polysaccharide in the LPS
What can e.coli cause ?
UTIs
foodbourne oubreaks
What is the shape of E.coli ?
rod shaped bacillus
Which agar is used to grow e.coli and what is its appearance ?
grown on macConkey agar
large red colonies
What does e.coli ferment ?
lactose
Which enzymes does e.coli possess /
catalase positive
What clues can help in species identification ?
morphology
colour
smell
What are selective media ?
they allow the growth of certian bacteria by inhibitng the growth of others
What are indcator media ?
chromogenic tests designed to identify presence of specific bacteria
What do carbohydrate test profiles do ?
each row column has a different bacteria and different substrate
phenol red- turns from red to yellow when there is fermentation of sugar to acid.
What are the advantages of broth culture ?
large amount of cells cna be cultured
easy to set up
What are the disadvantages of broth culture ?
difficult to get a pure colony
difficult to identify different bacteria in the broth
What are the uses of broth culture ?
antibiotic susceptibility testing
total viable counts
What does a high temperature do ?
above 39
inhibit the growth of most enteric bacteria
What is XLD agar used for ?
has phenol red in it
used for identification of enteric bacteria
contains sodium desoxycholate
inihibits gram positive bacteria
What is CLED agar used for ?
used for culture of bacteria from urine specimens
non-selective
What is staph agar used for ?
selective for staph aureus
high salt concentration
staphylococci can resist high salt concentrations
What are the methods of bacteria identification ?
culture
microscopy
molecular technques
Which molecular techniques can be used to identify the presence of certain bacteria ?
FISH
used to detect specific DNA sequences
PCR can be used to amplify
What does LPS consist of ?
lipid
core polysaccharide
O polsaccharide- has variants
What is significant about the 157th O antigen in E,coli ?
it is found in pathogenic e.coli
associated with outbreaks of disease
How can we detect specific antigens ?
latex agglutination
latex beads are covered in antibody for specific antigen
mix with bacterial suspension
if the bacteria express the antigen there will be agglutination
Which factor of S.aureus is responsible for food poisoning ?
enterotoxin
What substance is used for diagnostic tests of Clostriduum dificile infections ?
clostridoum toxins
find in faeces samples
Is brilliance candida agar selective or indicative ?
both
Which gene is most commonly targeted for PCR bacterial identification ?
16S rRna gene
What is meant by the specifictiy of a diagnostic test ?
How many false positives it can detect
What changes occur in beta haemolysis on blood agar ?
complete lysis of red blood cells
agar turns translucent
Which antibiotics are selective for fusobacterium ?
vancomycin
neomycin
What is FAA ?
fastidious anaerobic organism cultivation agar
What is reduced transport fluid ?
used to provide anaerobic conditions
What is MSB agar and what is it selective for ?
mits-salivarius agar
bacitracin added make it selective for strep mutans and strep sobrinus
Is MSB agar selective or indicative ?
both
What is TYCS agar ?
differnetiate strep mutans from strep sanguis
uses high sucrose content to promote glucan formation vy S mutans
Is TYCS selective or indicative ?
selective
selects for strep mutans due to high sucrose content whic is utilised to make glucans
What is blood agar ?
nutrient rich
non selective
What is alpha haemolysis ?
green colour change
hydrogen peroxide oxidising Haemoglobin
Fe3+ to Fe2+
What is beta haemolysis ?
complete lysis of RBCs
appears translucent
What is gamma haemolysis ?
no lysis
What does chlorhexidine do and what is it used for ?
reduces pahthogenic oral flora and allows the reestablishment of the normal oral flora
used for periodontal treamtent and beofre surgery to reduce bacteriaemia risk
What is the equation for CFU/ml ?
no of colonies x DF/ vol of culture plate
What does the snyder test detect ?
acidogenic and aciduric bacteria
supposed caries indicator
What are the pH indications of the snyder test ?
5.4+ blue
<3.8 yellow
3.8-5.4 Green
Which bacteria does the snyder test detect ?
lactobacillus
an acidophile
found in caries lesions- the carious lesions select for them
Why is there a colour change to yellow in the snyder test ?
lactic, acetic and formic acid
Why does P.gingivalis produce dark pigments ?
prophyryn pigments contain haem from the host
Why was there a lot of alpha haemolysis in the kiss plate ?
oral streptococci are alpha haemolytic
How can we work out CFU/ml ?
DF x number of colonies/ volume of culture plate
Which carbohydrate is fermented in the snyder test ?
glucose
Which acids are produced in the snyder test?
lactic acid
formic acid
acetic acid
What is the main function of fructans in plaque ?
energy
What type of spectrum antibiotic is methicillin ?
broad spectrum
How did MRSA acquire resistance ?
through pencillin binding protein
mecA gene
How are gram negative bacteria intrisically resistant to vancomycin ?
LPS
How does vancomycin have to be administered and why ?
IV
too big- highly glycosylated glycopeptide- too big too pass across membranes
What is amoxicillin ?
moderate spectrum antibiotic
against gram psitive bacteria
and limited gram negative bacteria
What is metronidazole ?
active agaisnt gram positive and gram negative
What is clavulanic acid ?
inhibits beta lactamases
combine with amoxicillin to make augementin
How do we carry out antibiotic sensitivty testing ?
carry out broth dilution
make serial dilutions of antibiotic
innocualte with bacteira
innocualte overnight
Is MBC or MIC usually bigger ?
MBC
What are MIC ad MBC useful for ?
drug efficacy
admistration
resistance
What does the ZOI indicate in antibiotic testing ?
sensitivity of bacteria to the antibiotic
larger the ZOI- more potent antibiotic
What does it mean if bacteria are present in the ZOI ?
they are resistant
What does PBP 2a do ?
confers resistance as it allow transpeptidase to work in the presence of methicillin
What makes staph aureus appear yellow on agar ?
makes a pigment called staphloxanthin
What is the function of staphyloxanthin ?
protects cells against oxidative stress
Which test can distinguish between staph aureus/ epidermidis ?
coagulase test- positive fro staph aureus
In what form does fluoride enter bacterial cells ?
HF- uncharged so cn corss membranes
how does vancomycin work ?
binds to peptidoglycan and interferes woth synthesis
Why is vancomycin inappropriate for e,coli infections ?
e.coli is gram negative
vancomycin cant get past the LPS
