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Published on: September 25, 2014
Comparison of susceptibility test methods to detect penicillin susceptibility in Streptococcus pneumoniae isolates
Mohd Desa Mohd Nasir1, Navaratnam Parasakthi
1Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia.
Abstract:
The increasing prevalence of penicillin-resistant Streptococuus pneumoniae urges for fast and accurate susceptibility testing methods. This study evaluated the comparability of three commonly used techniques; disk diffusion, E-test and agar dilution, to detect penicillin susceptibility in clinical isolates of S. pneumoniae. Fifty pneumococcal isolates, obtained from patients at the University of Malaya Medical Centre, were selected to include both penicillin-susceptible strains and those that had decreased susceptibility (resistant and intermediate) to penicillin. The minimum inhibitory concentration (MIC) values of penicillin to serve as the reference was determined by the agar dilution method in which, based on the MIC breakpoints recommended by the National Committee for Clinical Laboratory Standards (NCCLS), 27 strains had decreased susceptibility to penicillin with 17 strains resistant and 10 intermediate. Comparing to the agar dilution method, oxacillin disk diffusion test detected all strains with decreased penicillin susceptibility as such while E-test showed a close agreement of susceptibility (92%) of the isolates to penicillin. This confirmed that oxacillin is a good screening test for S. pneumoniae isolates with decreased susceptibility to penicillin while E-test is very reliable for rapid and accurate detection of penicillin susceptibility.
Insights
Accurate penicillin susceptibility testing for Streptococcus pneumoniae is crucial. Oxacillin disk diffusion and E-test offer reliable methods for detecting resistance, aiding clinical decisions.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Penicillin-resistant Streptococcus pneumoniae poses a significant public health threat.
- Rapid and accurate susceptibility testing is essential for effective treatment.
- Current methods require evaluation for optimal clinical application.
Purpose of the Study:
- To compare the accuracy of disk diffusion, E-test, and agar dilution for penicillin susceptibility testing of S. pneumoniae.
- To evaluate the utility of oxacillin disk diffusion as a screening method.
- To assess the reliability of E-test for rapid penicillin susceptibility determination.
Main Methods:
- Agar dilution was used as the reference method to determine penicillin Minimum Inhibitory Concentration (MIC) values.
- Fifty clinical isolates of S. pneumoniae, including susceptible and resistant strains, were tested.
- Disk diffusion (oxacillin) and E-test methods were compared against the agar dilution results.
Main Results:
- Agar dilution identified 27 strains with decreased penicillin susceptibility (17 resistant, 10 intermediate).
- Oxacillin disk diffusion correctly identified all strains with decreased penicillin susceptibility.
- E-test demonstrated high agreement (92%) with the reference method for penicillin susceptibility.
Conclusions:
- Oxacillin disk diffusion is a valuable screening tool for detecting decreased penicillin susceptibility in S. pneumoniae.
- E-test provides a rapid and accurate method for determining penicillin susceptibility in S. pneumoniae.
- These validated methods can improve the management of pneumococcal infections.
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