Antimicrobial resistance and production of biofilms in clinical isolates of coagulase-negative Staphylococcus strains

Abstract

Coagulase-negative Staphylococcus (CNS) strains are frequently associated with bacteremia and hospital-acquired infections. 293 CNS strains were isolated from 744 samples from a dialysis center in S. M. de Tucumán, Argentina, from hemocultures, catheters and urine and identified as S. epidermidis, S. haemolyticus, S. saprophyticus, S. hominis and S. cohnii. 13 antibiotics were tested for antibacterial resistance. 75% of S. saprophyticus, 66% of S. epidermidis and 57% of S. haemolyticus was resistant to erythromycin and 50% of S. haemolyticus was resistant to ciprofloxacin. OXA resistance was found in 43% of S. haemolyticus. Presence of PBP 2a in OXA-R strains was confirmed with the modified agglutination assay (MRSA) and presence of the mecA gene. 15 strains with intermediate halos for vancomycin and teicoplanin showed a MIC in solid and liquid medium <or=1 microg/ml and <or=4 microg/ml respectively, which means that they were susceptible. 30% of the CNS strains produced biofilms: 42% of S. haemolyticus and 40% of S. epidermidis. 76% of the S. epidermidis and 59% of the S. haemolyticus biofilm-producing strains were isolated from catheters. The disc-diffusion technique together with the agglutination assay proved to be fast and reliable, which is of essential importance in intensive care units. Rapid identification of CNS strains, detection of resistance to methicillin and biofilm production are decisive for a prompt and appropriate antimicrobial therapy and limited use of inappropriate glycopeptides.