In vitro activity and killing effect of the synthetic hybrid cecropin A-melittin peptide CA(1-7)M(2-9)NH(2) on methicillin-resistant nosocomial isolates of Staphylococcus aureus and interactions with clinically used antibiotics.

The in vitro activity of CA(1-7)M(2-9)NH(2), a 15-residue synthetic hybrid peptide derived from the sequences of cecropin A and melittin, alone and in combination with amoxicillin-clavulanate, imipenem, clarithromycin, ciprofloxacin, rifampin, and vancomycin, was investigated against 40 nosocomial isolates of methicillin-resistant Staphylococcus aureus. Antimicrobial activity of CA(1-7)M(2-9)NH(2) was measured by minimal inhibitory concentration, MBC, and time-kill studies. All isolates were inhibited at concentrations of 1 to 16 microg/mL. Combination studies performed with S. aureusATCC 43300 demonstrated synergy only when CA(1-7)M(2-9)NH(2) was combined with amoxicillin-clavulanate and imipenem. Our findings show that CA(1-7)M(2-9)NH(2) is active against methicillin-resistant S. aureusand that its activity is enhanced when it is combined with several antimicrobial agents.