JAC Advance Access originally published online on June 27, 2005
Journal of Antimicrobial Chemotherapy 2005 56(2):410-412; doi:10.1093/jac/dki236
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In vitro activity of citropin 1.1 alone and in combination with clinically used antimicrobial agents against Rhodococcus equi
ukasiak21 Institute of Infectious Diseases and Public Health, Università Politecnica delle Marche, Ancona, Italy; 2 Faculty of Pharmacy, Medical University of Gdansk, Gdansk, Poland
Received 9 November 2004; returned 8 February 2005; revised 21 May 2005; accepted 6 June 2005
* Correspondence address. Institute of Infectious Diseases and Public Health, c/o Ospedale Regionale, via Conca 71, Ancona I-60020, Italy. Tel: +39-071-5963715; Fax: +39-071-5963468; E-mail: anconacmi{at}interfree.it
Objectives: The aim of this study was to investigate the in vitro activity of citropin 1.1, an antimicrobial peptide derived from the Australian tree frog Litoria citropa, alone and in combination with ampicillin, ceftriaxone, doxycycline, netilmicin, ciprofloxacin, rifampicin, linezolid, vancomycin, clarithromycin and imipenem against 12 nosocomial isolates of Rhodococcus equi.
Methods: Antimicrobial activity of citropin 1.1 was measured by MIC, MBC, timekill studies and chequerboard titration method.
Results: All isolates were inhibited at concentrations of citropin 1.1 between 2 and 8 mg/L. Combination studies demonstrated synergy only when the peptide was combined with clarithromycin, doxycycline and rifampicin.
Conclusions: Our findings show that citropin 1.1 is active against R. equi and that its activity could be enhanced when it is combined with hydrophobic antibiotics.
Keywords: Gram-positive cocci , antimicrobial peptides , synergy , antibiotics