MFD practicals Flashcards by Malaika Ahmed

What does the enzyme urease do ?

convert urea into ammonia

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What happens in the urease test?

bacteria mixed with urease

conversion of urea to ammonia

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What is the significance of ammonia ?

it can raise pH

protect against caries

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Which bacterium uses urease ?

helicobacter pylori

ammonia made neutralises stomach acid- allow it to survive

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What does the enzyme catalase do ?

converts hydrogen peroxide into water and oxygen

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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

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What happens in the DNase test ?

release of free nucleotides by bacteria can turn toludine blue into a pink color

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What happens in the coagulase test?

latex particles covered in fibrinogen

if bacteria have coagulase- see agglutination of particles turn blue

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What is the appearance of staph aureus ?

bunches of grapes

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Where does staph aureus live ?

anterior nares
nasopharynx
skin

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What are the properties of staph aureus that enbale it to live on the skin ?

can withstand high levels of salt

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Is staph aureus commensal or opportunsitic ?

both- can cause infections when compromised host

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What are some of the diseases that staph aureus can cause ?

MRSA
food poisoning
toxic shock syndrome

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Is staph aureus gram positive or gram negative ?

gram positive

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Which enzymes is staph aureus positive for ?

coagulase positive
catalase positive
DNase psoitive

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What is the advantage of being DNase positive ?

allows bacteria to escape extracellular DNA rleeased in infection

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What are some diseases oral streptococci can cause ?

infective endocarditis

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Why can strep salivaris be sold as a probiotic ?

makes bacteriocns- AMPs

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Which enzymes is strep salivarius positive for ?

Urease positive

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What is the shape of streo salivarius ?

strips of streps

cocci

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Is strep salivarius gram positive or gram negative ?

gram positive

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What type of bacteria is E.coli ?

gram negative

enteric

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What is e.coli mainly used for ?

lab model organism

growth

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Which strains of e.coli are pathgoenic ?

those that possess the 157th version of the O polysaccharide in the LPS

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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