VGA-gene is responsible for the low-level resistance to quinupristin-dalfopristin among staphylococci in Greek hospitals

Abstract number: 1134_02_163

Petinaki E., Maniati M., Bersos Z., Chini V., Foka A., Maniatis A.N., Spiliopoulou I.

Objectives:

Quinupristin-dalfopristin (Q–D) is widely used for the treatment of infections caused by gram-positive cocci, except Enterococcus faecalis. Despite the prolonged use of streptogramins in animal husbandry, a limited number of staphylococcal isolates were found to be non susceptible worldwide. The purpose of this study was to investigate the rates of resistance among staphylococci to this agent in Greece, after a three year period of usage in our hospitals.

Methods:

A total of 846 staphylococci (250 S. aureus and 596 coagulase-negative staphylococci, CNS) recovered from clinical specimens of different patients in two tertiary care Greek hospitals (University Hospital of Larissa, University Hospital of Patras) during 2003–2004 were investigated for their resistance to quinupristin-dalfopristin (breakpoints for susceptibility < = 1 mg / L, resistance >4 mg / L). Identification at species level was performed by Gram stain, catalase and coagulase production, and by the API Staph system. Susceptibility to various antimicrobial agents including Q-D was assessed by disk the diffusion method. Determination of MIC to Q-D was performed by the E-test and agar dilution method. Isolates with MICs greater than 1 mg / L were examined for the presence of vatA, vatB, vatC, vga, vgaB, vgb, vgbB genes by Polymerase Chain Reactions. The clonality of isolates was studied by PFGE of chromosomal SmaI DNA digests.

Results:

All S. aureus isolates had MICs ranging from 0.19 to 0.75 mg / L (mean value: 0.25 mg / L). Among the CNS, 579 isolates expressed MICs between 0.125–1 mg / L (mean value: 0.33 mg / L), while 17 isolates had MICs that ranged from 1.5 to 4mg / L. All these 17 isolates, including one S. haemolyticus, one S.capitis, and fifteen S. epidermidis were vga-positives and expressed MLSB phenotype carrying the ermC-gene.

Conclusions:

The presence of vga-gene, conferring resistance to streptogramin A by a putative efflux mechanism is responsible for the non-susceptibility of staphylococci to quinupristin-dalfopristin in Greece.