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Penicillin-susceptible Staphylococcus aureus: susceptibility testing, resistance rates and outcome of infection
Malin Hagstrand Aldman1,2, Annette Skovby3, Lisa I Påhlman2
1a Skåne University Hospital , Clinic of Infectious Diseases , Lund , Sweden.
Background:
Staphylococcus aureus (SA) is an important human pathogen that causes both superficial and invasive infections. Penicillin is now rarely used in the treatment of SA infections due to widespread resistance and a concern about the accuracy of existing methods for penicillin susceptibility testing. The aims of the present study were to determine the frequency of penicillin-susceptible SA isolates from blood and wound cultures in Lund, Sweden, and to evaluate methods for penicillin testing in SA. We also wanted to investigate if penicillin-susceptible isolates are associated with higher mortality.
Methods:
Hundred blood culture isolates collected 2008/2009, 140 blood culture isolates from 2014/2015, and 141 superficial wound culture strains from 2015 were examined. Penicillin susceptibility was tested with disk diffusion according to EUCAST guidelines, and results were confirmed with a cloverleaf assay and PCR amplification of the BlaZ gene. Patient data for all bacteraemia cases were extracted from medical records.
Results:
The disk diffusion method with assessment of both zone size and zone edge appearance had high accuracy in our study. About 57% of bacteraemia isolates from 2008/2009 were sensitive to penicillin compared to 29% in 2014/2015 (p < .0001). In superficial wound cultures, 21% were penicillin susceptible. There was no difference in co-morbidity or mortality rates between patients with penicillin resistant and penicillin sensitive SA bacteraemia.
Conclusion:
Disk-diffusion is a simple and reliable method to detect penicillin resistance in SA, and susceptibility rates are significant. Penicillin has many theoretical advantages and should be considered in the treatment of SA bacteraemia when susceptible.
Insights
Penicillin-susceptible Staphylococcus aureus (SA) is still found in blood and wound infections. Disk diffusion is a reliable test for identifying SA penicillin susceptibility, supporting its use in treatment.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Staphylococcus aureus (SA) causes significant human infections.
- Penicillin use is limited by resistance and testing concerns.
- Accurate penicillin susceptibility testing for SA is crucial.
Purpose of the Study:
- Determine penicillin-susceptible SA frequency in Lund, Sweden.
- Evaluate penicillin susceptibility testing methods for SA.
- Investigate mortality association with penicillin-susceptible SA.
Main Methods:
- Analyzed blood and wound SA isolates (2008-2015).
- Used disk diffusion (EUCAST), cloverleaf assay, and BlaZ gene PCR.
- Extracted patient data for bacteraemia cases.
Main Results:
- Disk diffusion showed high accuracy for penicillin resistance detection.
- Penicillin susceptibility decreased from 57% (2008/2009) to 29% (2014/2015) in bacteraemia isolates.
- 21% of wound isolates were penicillin susceptible; no mortality difference observed.
Conclusions:
- Disk diffusion is a simple, reliable method for SA penicillin resistance testing.
- Significant rates of penicillin susceptibility in SA isolates persist.
- Penicillin should be considered for treating susceptible SA bacteraemia.
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