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Case Reports
. 2009 Jun;33(6):564-8.
doi: 10.1016/j.ijantimicag.2008.12.010. Epub 2009 Feb 23.

Characterisation of a Staphylococcus aureus strain with progressive loss of susceptibility to vancomycin and daptomycin during therapy

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Case Reports

Characterisation of a Staphylococcus aureus strain with progressive loss of susceptibility to vancomycin and daptomycin during therapy

Fred C Tenover et al. Int J Antimicrob Agents. 2009 Jun.

Abstract

Following an initial response to vancomycin therapy, a patient with meticillin-resistant Staphylococcus aureus (MRSA) bacteraemia developed endocarditis, failed a second course of vancomycin and then failed daptomycin therapy. An increase in the vancomycin minimum inhibitory concentrations of four consecutive MRSA blood isolates from 2 microg/mL to 8 microg/mL was shown by Etest. Population analysis of four successive blood culture isolates recovered over the 10-week period showed that the MRSA strain became progressively less susceptible to both vancomycin and daptomycin. Retrospectively, the macro Etest method using teicoplanin indicated a decrease in vancomycin susceptibility in the second blood isolate. The patient improved after treatment with various courses of trimethoprim/sulfamethoxazole, quinupristin/dalfopristin and linezolid. Early detection of vancomycin-heteroresistant S. aureus isolates, which appeared to have clinical significance in this case, continues to be a challenge for the clinical laboratory. Development of suitable practical methods for this should be given priority. Concurrent development of resistance to vancomycin and daptomycin, whilst rare, must be considered in a patient who is unresponsive to daptomycin following vancomycin therapy.

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Figures

Fig 1
Fig 1
Population analysis of four Staphylococcus aureus isolates recovered from a patient with endocarditis. Analysis was performed using brain–heart infusion agar containing serial dilutions of vancomycin. CFU, colony-forming units.
Fig 2
Fig 2
Population analysis of four Staphylococcus aureus isolates recovered from a patient with endocarditis. Analysis was performed using brain–heart infusion agar containing serial dilutions of daptomycin. CFU, colony-forming units.

References

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