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Salt-supplemented medium for testing methicillin-resistant staphylococci with newer beta-lactams
J H Jorgensen1, J S Redding, L A Maher
1Department of Pathology, University of Texas Health Science Center, San Antonio 78284-7751.
Journal of Clinical Microbiology
|September 1, 1988
Summary
Adding 2% NaCl to Mueller-Hinton broth improves detection of methicillin resistance in Staphylococcus aureus. However, salt addition does not consistently enhance beta-lactam susceptibility testing for other staphylococci.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Antimicrobial Susceptibility Testing
Background:
- Accurate antimicrobial susceptibility testing (AST) is crucial for guiding treatment of staphylococcal infections.
- Detecting methicillin resistance in Staphylococcus aureus (MRSA) is clinically significant.
- Standardized AST methods are essential for reliable results.
Purpose of the Study:
- To evaluate the impact of adding 2% NaCl to cation-supplemented Mueller-Hinton broth (CSMHB) on the AST of staphylococci.
- To determine if NaCl enhances the detection of resistance to various beta-lactam antibiotics.
Main Methods:
- Microdilution AST was performed on staphylococci using CSMHB with and without 2% NaCl.
- Susceptibility testing included cephalosporins, imipenem, amoxicillin-clavulanate, and ticarcillin-clavulanate.
- Staphylococcus aureus and coagulase-negative staphylococci were tested.
Main Results:
- In Staphylococcus aureus, 2% NaCl improved the detection of methicillin (oxacillin) resistance to cefamandole, imipenem, and ticarcillin-clavulanate.
- Resistance to amoxicillin-clavulanate was accurately determined with or without added NaCl.
- NaCl did not significantly improve beta-lactam resistance detection in coagulase-negative staphylococci.
Conclusions:
- Routine addition of 2% NaCl to oxacillin or methicillin susceptibility tests for staphylococci may be beneficial for standardization and convenience.
- NaCl supplementation does not consistently improve resistance detection for other beta-lactams in staphylococci and is not recommended for routine use with these agents.