1219. Effects of Iclaprim and Trimethoprim on Exotoxin Production by Methicillin-resistant Staphylococcus aureus
Session: Poster Abstract Session: Expanded Spectrum - New Antimicrobial Susceptibility Testing
Friday, October 6, 2017
Room: Poster Hall CD
  • IDWeek 2017 iclaprim poster FINAL.pdf (653.6 kB)
  • Background: Methicillin-resistant Staphylococcus aureus (MRSA) causes serious, often life-threatening, infections. Exotoxins such as alpha-hemolysin (AH), Panton Valentine leukocidin (PVL), and Toxic shock syndrome toxin 1 (TSST-1) mediate pathogenesis and inhibition of toxin production is an important consideration in choosing appropriate treatments. Vancomycin is recommended for severe MRSA infections; however, increasing vancomycin resistance, poor clinical outcomes and nephrotoxicity are serious concerns. Thus newer agents are needed, including those that block bacterial toxin production. In the current study, we compared the effects of sub-inhibitory doses (sub-MIC) of two folic acid inhibitor antibiotics (iclaprim, trimethoprim) with cell wall-active agents (nafcillin, vancomycin) on transcription and translation of AH, PVL and TSST-1 in two clinical MRSA isolates.

    Methods: Community-acquired MRSA strains 1560 (a USA400 strain; AH+, TSST-1+, PVL-) and 04014 (CDC strain 368-04; AH+, TSST-1-, PVL+) were studied. MICs were determined by standard microbroth dilution. Gene expression was studied by northern blotting and/or qRT-PCR; toxins were quantitated by ELISA (PVL and TSST-1) and rabbit erythrocyte lysate assay (AH).

    Results: In agreement with our previous findings, nafcillin increased production of AH, TSST-1, and PVL compared to untreated control cultures. In both MRSA strains, iclaprim and trimethoprim delayed the onset of mRNA production and shifted its peak production to later time points. Both iclaprim and trimethoprim suppressed AH production in both strains of MRSA and delayed, but did not reduce, maximal TSST-1 production in MRSA1560. Trimethoprim significantly increased maximal PVL production over both untreated and iclaprim-treated cultures.

    Conclusion: The folic acid antagonist antibiotics, iclaprim and trimethoprim, altered both mRNA synthesis dynamics and protein toxin production in MRSA at concentrations below those that inhibit bacterial growth.  These results, plus the fact that iclaprim is 15-fold more active than trimethoprim (MICs = 0.13 and 2.0 ug/ml, respectively), provide additional rationale for the use of iclaprim to treat complicated MRSA infections.

    Amy Bryant, PhD1, Eva Katahira, BA1, David Huang, MD, PhD, FIDSA, FACP2 and Dennis Stevens, MD, PhD1, (1)Infectious Diseases, Veterans Affairs Medical Center, Boise, ID, (2)Motif BioSciences, Princeton, NJ


    A. Bryant, Motif Biosciences: Grant Investigator , Research grant

    E. Katahira, None

    D. Huang, Motif Bio: Employee , Salary

    D. Stevens, Motif Biosciences: Grant Investigator , Research grant

    Findings in the abstracts are embargoed until 12:01 a.m. PDT, Wednesday Oct. 4th with the exception of research findings presented at the IDWeek press conferences.