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A simple broth-disk elution test for screening methicillin-resistant (heteroresistant) staphylococci
J R Otero1, E Amor, P Martin-Rabadan
1Servicio de Microbiología, Hospital Primero de Octubre, Madrid, Spain.
Diagnostic Microbiology and Infectious Disease
|August 1, 1987
Summary
This study evaluated a broth-disk elution test for methicillin and oxacillin resistance in Staphylococcus strains. The test accurately identified resistant and sensitive strains, classifying intermediate strains as resistant.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Antimicrobial Resistance
Background:
- Staphylococcus aureus and coagulase-negative staphylococci are significant pathogens.
- Accurate detection of methicillin and oxacillin resistance is crucial for effective treatment.
- Existing methods may require optimization for speed and accuracy.
Purpose of the Study:
- To assess the efficacy of a broth-disk elution test for detecting methicillin and oxacillin resistance.
- To compare the broth-disk elution test results with a reference method for Staphylococcus strains.
Main Methods:
- Inoculation of Staphylococcus aureus (46 strains) and coagulase-negative staphylococci (47 strains) in Mueller-Hinton broth with 4% NaCl.
- Addition of antibiotic disks to achieve critical concentrations of methicillin (10 µg/ml) or oxacillin (6 µg/ml).
- Interpretation of growth as indicative of resistance.
Main Results:
- Complete agreement with the reference method for fully resistant or fully sensitive strains.
- The broth-disk elution test classified four strains with intermediate sensitivity (two S. aureus, two coagulase-negative staphylococci) as resistant.
Conclusions:
- The broth-disk elution test is a reliable method for detecting methicillin and oxacillin resistance in Staphylococcus species.
- The test demonstrates high concordance with reference methods for susceptible and resistant isolates.
- Intermediate strains are identified as resistant, necessitating careful clinical consideration.