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[Demonstration of methicillin-resistant Staphylococci using the broth microdilution method].
Bollettino Dell'Istituto Sieroterapico Milanese
|January 1, 1987
Summary
Adding 2% NaCl to Cation Supplemented Mueller Hinton Broth (CSMHB) improves methicillin-resistant staphylococci detection. This modification enhances accuracy for penicillinase-resistant penicillins and cephalosporins without affecting aminoglycoside testing.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Antimicrobial Resistance
Context:
- Rising incidence of methicillin-resistant staphylococci (MRS) necessitates improved detection methods.
- Broth microdilution is a key susceptibility testing method for staphylococci.
- Accurate susceptibility testing is crucial for effective treatment of staphylococcal infections.
Purpose:
- To evaluate the effect of adding 2% NaCl to Cation Supplemented Mueller Hinton Broth (CSMHB) on the Minimum Inhibitory Concentrations (MICs) of various antibiotics against staphylococci.
- To determine if NaCl supplementation improves the detection of methicillin resistance in staphylococci.
- To optimize broth microdilution protocols for accurate antimicrobial susceptibility testing of staphylococci.
Summary:
- Supplementing CSMHB with 2% NaCl significantly increased oxacillin MICs in 13% of staphylococcal strains, indicating improved detection of methicillin resistance.
- NaCl addition caused substantial MIC variations for gentamicin (69% of strains) and amikacin (93% of strains).
- This variation led to altered susceptibility categorizations for oxacillin (10%), gentamicin (28%), and amikacin (41%) of the strains tested.
Impact:
- The study recommends using CSMHB with 2% NaCl for testing penicillinase-resistant penicillins and cephalosporins to enhance MRS detection.
- CSMHB without NaCl supplementation should be used for testing other antibiotics, including aminoglycosides, to maintain accurate MIC values.
- Implementing these refined broth microdilution protocols can lead to more precise antimicrobial susceptibility results, guiding clinical treatment decisions for staphylococcal infections.