These are non- -lactamase-producing organisms and, therefore, are susceptible to amoxicillin alone. SUSCEPTIBILITY TESTING Dilution Techniques: Quantitative methods are used to determine antimicrobial minimal inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized procedure. Standardized procedures are based on a dilution method 1 (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of amoxicillin/ clavulanate potassium powder. The recommended dilution pattern utilizes a constant amoxicillin/ clavulanate potassium ratio of 2 to 1 in all tubes with varying amounts of amoxicillin. MICs are expressed in terms of the amoxicillin concentration in the presence of clavulanic acid at a constant 2 parts amoxicillin to 1 part clavulanic acid. The MIC values should be interpreted according to the following criteria: RECOMMENDED RANGES FOR AMOXICILLIN/ CLAVULANIC ACID SUSCEPTIBILITY TESTING For gram-negative enteric aerobes: MIC (µg/ mL) Interpretation . 8/ 4 Susceptible (S) 16/ 8 Intermediate (I) . 32/ 16 Resistant (R) For Staphylococcus ** and Haemophilus species: MIC (µg/ mL) Interpretation . 4/ 2 Susceptible (S) . 8/ 4 Resistant (R) ** Staphylococci which are susceptible to amoxicillin/ clavulanic acid but resistant to methicillin/ oxacillin must be considered as resistant. For Streptococcus pneumoniae from non-meningitis sources: Isolates should be tested using amoxicillin/ clavulanic acid and the following criteria should be used: MIC (µg/ mL) Interpretation . 2/ 1 Susceptible (S) 4/ 2 Intermediate (I) . 8/ 4 Resistant (R) Note: These interpretive criteria are based on the recommended doses for respiratory tract infections. | ||||
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