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Characterisation of laboratory-generated vancomycin intermediate resistant Staphylococcus aureus strains.
Pragya Bhateja1, Kedar Purnapatre, Smita Dube
1Department of Microbiology, Ranbaxy Research Laboratories R&D II, Plot No. 20, Sector 18, Udyog Vihar Industrial Area, Gurgaon 122001, Haryana, India. pragya.bhateja@ranbaxy.com
International Journal of Antimicrobial Agents
|January 19, 2006
Summary
Researchers generated vancomycin-intermediate Staphylococcus aureus (VISA) strains in vitro to study resistance. The CDC and modified agar screen methods effectively detected these VISA strains, offering insights into treatment options for MRSA infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Vancomycin is a critical antibiotic for treating methicillin-resistant Staphylococcus aureus (MRSA) infections.
- Emerging vancomycin resistance in MRSA poses a significant clinical challenge due to limited alternative therapies.
Purpose of the Study:
- To generate and characterize Staphylococcus aureus strains exhibiting reduced susceptibility to vancomycin.
- To evaluate diagnostic methods for identifying vancomycin-intermediate Staphylococcus aureus (VISA).
Main Methods:
- Serial passaging of 18 Staphylococcus aureus strains on vancomycin to induce intermediate resistance.
- Minimum Inhibitory Concentration (MIC) determination for 13 antibiotics.
- Evaluation of five detection methods: simplified population analysis, CDC method, modified vancomycin agar screen, population analysis profile (PAP), and PAP-AUC ratio.
- Assessment of phenotypic changes including doubling time, synergy with beta-lactam antibiotics, and norA efflux pump activity.
Main Results:
- Eight VISA mutants with vancomycin MICs of 8-16 µg/mL were successfully generated.
- The CDC and modified agar screen methods demonstrated high sensitivity and specificity for VISA detection.
- PAP analysis showed VISA strains with MICs ranging from 12 µg/mL to >16 µg/mL, and a PAP-AUC ratio >1.3.
- Mutants exhibited increased doubling times, synergistic responses with beta-lactam antibiotics, and in some cases, decreased oxacillin resistance or loss of norA efflux pumps.
Conclusions:
- In vitro generation of VISA strains is feasible, aiding the study of resistance mechanisms.
- Specific diagnostic methods (CDC, modified agar screen) are effective for identifying VISA.
- VISA development is associated with altered phenotypic characteristics and potential changes in antibiotic resistance profiles.