antibiotic susceptibility testing and drug resistance rashmi s
TRANSCRIPT
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ANTIBIOTIC SUSCEPTIBILITY TESTING ANTIBIOTIC SUSCEPTIBILITY TESTING AND AND
DRUG RESISTANCEDRUG RESISTANCE
Rashmi S
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ANTIBIOTIC SUSCEPTIBILITY ANTIBIOTIC SUSCEPTIBILITY TESTING(AST)TESTING(AST)
DEFINITION:DEFINITION:
AST is the “study of the susceptibility AST is the “study of the susceptibility of bacteria to a specific antibiotic”of bacteria to a specific antibiotic”
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Susceptibility testing is done using following Susceptibility testing is done using following methods:methods:
Dilution methodsDilution methods
a)a) Agar dilution Agar dilution
b)b) Broth dilutionBroth dilution Diffusion methodsDiffusion methods
Disc diffusion- Kirby-Bauer method
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KIRBY –BAUER DISC KIRBY –BAUER DISC DIFFUSSION METHODDIFFUSSION METHOD
Uses small discs impregnated with antibioticsUses small discs impregnated with antibiotics These discs are placed on the surface of the These discs are placed on the surface of the
inoculated Mueller Hinton agar plate, and inoculated Mueller Hinton agar plate, and incubated at 37incubated at 37ooC for 24 hrs.C for 24 hrs.
After incubation ,plates are observed for the After incubation ,plates are observed for the zone of inhibition.zone of inhibition.
The diameter of zone of inhibition is measured The diameter of zone of inhibition is measured using a scale& compared with Kirby-Bauer chartusing a scale& compared with Kirby-Bauer chart
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Mueller Hinton Agar Plate Swabbing
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Disc Placement
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AST plate with zone of inhibition
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Measurement of zone of inhibition
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MINIMUM INHIBITORY MINIMUM INHIBITORY CONCENTRATION (MIC)CONCENTRATION (MIC)
MICMIC is the least concentration of is the least concentration of antimicrobial that will inhibit the growth of antimicrobial that will inhibit the growth of an organisman organism
Clinical use:Clinical use:
For organisms from patients suffering For organisms from patients suffering serious infection like “serious infection like “infective infective endocarditis”endocarditis”
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DRUG RESISTANCEDRUG RESISTANCE
DEFINITION:DEFINITION:
Organism develop tolerance for the drugOrganism develop tolerance for the drug
Genetic mechanism of drug resistance:Genetic mechanism of drug resistance: MutationMutation Gene TransferGene Transfer
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MUTATIONAL DRUG RESISTANCEMUTATIONAL DRUG RESISTANCE
It is of 2 typesIt is of 2 types
1.Step wise mutation1.Step wise mutation
2.One-Step mutation2.One-Step mutation
CLINICAL SIGNIFICANCE:CLINICAL SIGNIFICANCE:
Mutational resistance is of great importance in Mutational resistance is of great importance in TuberculosisTuberculosis
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DRUG RESISTANCE DUE TO GENE TRANSFERDRUG RESISTANCE DUE TO GENE TRANSFER
It can be due toIt can be due to
TransformationTransformation
ConjugationConjugation
TransductionTransduction
TranspositionTransposition
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Biochemical mechanism of Drug Biochemical mechanism of Drug ResistanceResistance
Decreased permeability to the drug.Decreased permeability to the drug. Development of alternative metabolic Development of alternative metabolic
pathway.pathway. Production of enzymes inactivating the Production of enzymes inactivating the
drugs.drugs. Modification of target site of the Modification of target site of the
antimicrobial agent.antimicrobial agent.
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