In vitro activity of citropin 1.1 alone and in combination with clinically used antimicrobial agents against Rhodococcus equi.
OBJECTIVE
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, time-kill 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.
Institute of Infectious Diseases and Public Health, Università Politecnica delle Marche, Ancona, Italy. anconacmi@interfree.it
Andrea
A
Giacometti
Oscar
O
Cirioni
Wojciech
W
Kamysz
Carmela
C
Silvestri
Maria Simona
MS
Del Prete
Alberto
A
Licci
Giuseppina
G
D'Amato
Jerzy
J
Lukasiak
Giorgio
G
Scalise
D000193:Actinomycetales Infections / Q000382:microbiology; D029845:Amphibian Proteins / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology*; D003428:Cross Infection / Q000382:microbiology; D004359:Drug Therapy, Combination / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D016929:Rhodococcus equi / Q000187:drug effects* / Q000302:isolation & purification
D029845:Amphibian Proteins; D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; C121829:citropin 1.1 protein, Litoria