Mupirocin low-level resistant MRSA: in vitro tolerance and possible implications in decolonisation treatment with mupirocin

Andrew Anyakwo, Lesley Price, Susan Lang

Research output: Contribution to conferencePosterpeer-review


Background: Nasal decolonisation of meticillin resistant S.aureus (MRSA) using mupirocin is effective for 80% of individuals, but re-lapse at 4-weeks is more frequent with strains displaying low-level mupirocin resistance (LL-MR) than those which are sensitive (MS).
Aim: To assess the in vitro ability of LL-MR MRSA to tolerate repeated exposure to mupirocin mimicking decolonisation therapy.
Method: Three clinical MRSA isolates were evaluated for tolerance to mupirocin during repeated exposure twice a day for five days. Cells of one MS and two LL-MR strains (previously demonstrated to tolerate mupirocin over 24h) were attached to mucin-coated surfaces for 4h, planktonic cells were removed and surface-adherent cells challenged with 200mg/l mupirocin (>6-fold MIC) for 1h. Adherent cells were then allowed to recover in antibiotic-free medium for 11h prior to the next treatment. After each exposure, cell viability was recorded and the extent of recovery between treatments determined, relative to untreated control.
Results: The first three doses of mupirocin inhibited the surface-adherent cells of all strains, though as the cell number increased in a maturing biofilm the impact of treatments was reduced. After five days the viable cell number of the MS strain was reduced to 15% of the control, whereas for the two LL-MR strains 39% and 43% of cells remained compared to untreated cultures.
Conclusion: LL-MR strains exhibited a greater level of tolerance to mupirocin than the MS strain in conditions mimicking decolonisation therapy. This increased tolerance might underlie the higher rate of relapse following decolonisation therapy observed with LL-MR strains.
Original languageEnglish
Publication statusPublished - 16 Nov 2014


  • mupirocin
  • MRSA
  • resistance
  • nasal decolonisation


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