AST Flashcards
Performed on bacteria isolated from clinical specimens
Antibiotic Susceptibility Testing
Overall profile of antimicrobial susceptibility testing, result of a specific microorganism to a battery of antimicrobial gram
Antibiogram
is the normal flora of lower gastrointestinal tract
Escherichia Coli
Characteristic of E.coli
Greenish metallic sheen, colonial macroscopic
Normal flora of Throat
Streptococcus viridans
standardized apparatus
Vortex
decrease pH, some antibiotic might be affected
It leads to decrease activity against the antibiotic Aminoglycoside, Erythromycin, Clindamycin but increased activity against Tetracyline
increase pH, some antibiotic might be affected
It leads to increase activity against the antibiotic Aminoglycoside, Erythromycin, Clindamycin but decreased activity against Tetracyline
If cation concentration decrease, what would be the effect?
Cation concentration pag decrease, increase activity of aminoglycoside against Pseudomonas aeruginosa and increase activity of tetracycline to all organism
If cation concentration increase, what would be the effect?
decrease activity amino glycoside against Pseudomonas aeruginosa, decrease activity to tetracycline to all organism.
Why Moeller Hinton agar?
It is good batch to batch in uniformity and low tetracycline sulfonamide inhibitor
Incubation atmosphere
Humidifier/ ambient air
If decrease ang atmosphere what is the effect to the carbon dioxide?
increase ang carbon dioxide, which can alter the activity of certain antibiotics
Incubation duration: Disk diffusion: __
16-18 hrs
Incubation duration: Broth diffusion: __
16-20 hrs
Thymidine content: If decrease
No effect
Thymidine content: If increase?
It leads to false resistant it affects suldonamide and trimethoprim
Measure activity of one or more antimicrobial agents (conventional susceptibility testing method is
broth dilution, agar dilution and disk diffusion
Methods that directly specific resistant mechanism
genotypic and phenotypic methods
Commercially available and widely used standard
0.5 McFarland Standard
0.5 McFarland Standard Corresponds to ____
1.5 X 108 CFU/ml
What is the preparation for Mcfarland standard?
99.5ml 1% Sulfuric Acid +
0.5 ml 1.175% Barium chloride
Antimicrobials to which the organism is intrinsically resistant are routinely excluded from the test battery (e.g., vancomycin versus gram-negative bacilli). Similarly, certain antimicrobials were developed specifically for use against particular organ- isms, but not against others (eg., ceftazidime for use against Pseudomonas aeruginosa but not against Staphylococcus aureus); such agents should be included only in the appropri- ate battery.
Organism Identification or Group
If resistance to a particular agent is common, the utility of the agent may be sufficiently limited and routine testing is not warranted. More potent antimicrobials are then included in the test battery. Conversely, more potent agents may not need to be in the test battery if susceptibility to less potent agents is highly prevalent.
Acquired Resistance Patterns Common to Local Microbial Flora
Depending on the testing method, some agents do not reliably detect resistance and should not be included in the battery.
Antimicrobial Susceptibility Testing Method Used
Some antimicrobial agents, such as nitrofurantoin, achieve effective levels only in the urinary tract and should not be included in batteries tested against bacterial isolates from other body sites
Site of Infection
Antimicrobial test batteries are selected for their ability to detect bacterial resistance to agents used by the medical staff and accessible in the pharmacy
Availability of Antimicrobial Agents in the Formulary
Commonly used in vitro tests in the laboratory
Disk diffusion method
Composition of Mueller Hinton
contains beef infusion, nucleic acid, vitamins, casein hydro nucleic acid
As the agent diffuses farther, the concentration decreases until it reaches a point when the bacterial growth is not anymore inhibited
ZONE OF INHIBITION
you should not place the antibiotic in the edge, place it in ___ to __ millimeter from the edge of petri dish. —- millimeter to avoid overlapping
you should not place the antibiotic in the edge, place it in 10 to 15 millimeter from the edge of petri dish. 24 millimeter to avoid overlapping
