In vitro resistance to daptomycin of staphylococcus aureus and enterococcus spp. strains

Daptomycin is the first antibiotic in a new class of cyclic lipopeptides, active in vitro against Gram - positive cocci. The mechanism of action is a rapid depolarization of the bacterial membrane potential, loss of cytoplasmic contents, mainly K+ ions and inhibition of protein, DNA and RNA synthesis, followed by the bacterial cell death. There were investigated 112 strains of Gram-positive cocci recommended for daptomycin susceptibility testing. Since the main clinical indications of daptomycin are the severe skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus, vancomicin-resistant enterococci and penicillinresistant Streptococcus spp, we tested daptomycin activity only in these species.

The susceptibility tests was performed by Kirby- Bauer disc-diffusion method on Muller-Hinton agar supplemented with Ca 50 mg / ml. (CAMH - Ca 2 + ) as recommended by CLSI.

During the period in which we conducted the study we isolated 112 strains of Gram-positive cocci, which we tested sensitivity to daptomycin. Resistance to Daptomycin of Staphylococcus aureus (4.11%) was lower than resistance to vancomycin (6.76%), but higher than the resistance to teicoplanin (2.71%) and linezolid (1.38%).

In our study we did not identify daptomycin resistant strains of Enterococcus spp. In severe infections that require more aggressive treatment using active antibiotics on MRSA, daptomycin is a valid therapeutic option, but a susceptibility test is required to ensure effective indication. There were no daptomycin resistant Enterococcus spp. strains