Incidenza della meticillino-resistenza in Staphylococcus aureus e stafilococchi coagulasi-negativi isolati da emocolture

Background: Staphylococci are major cause of nosocomial blood stream infections.This local surveillance study was carry out to monitor frequency of occurrence of Staphylococcus aureus and coagulase-negative staphylococci (CoNS) in blood stream infections and the incidence of methicillin-resistant (MET-R) strains. Materials and methods: During the period January – December 2006, 9840 blood specimens were analyzed and microrganisms from positive samples were collected. Bacterial identifications were performed according to the standard methods (Murray, 2003).We evaluated, in particular, the antibiotic-resistance phenotype of staphylococci employing disk diffusion test as suggested by the CLSI (2006). The following antimicrobial agents were tested: oxacillin, penicillin, amoxiciclin-clavulanate, cefalotin, cefamandole, imipenem, teicoplanin, linezolid, ciprofloxacin, erythromycin, clindamicin, rifampicin, trimethoprim-sulfamethoxazole, gentamicin, doxiciclin, fosfomycin. Results: The microrganisms isolated were 551: 370 Gram-positives (67%), 131 Gram-negatives (24%), 11 anaerobes (2%) and 39 mycetes (7%). In particular, 121 S. epidermidis, 75 S. aureus, 42 S. haemolyticus and other 39 CoNS were analyzed: methicillin-resistance occurred in more than 80% of S.aureus strains collected from Intensive Care Units (ICU) and in about 50 % of those isolated from other divisions. In CoNS the incidence of MET-R ranged from 30 to 80 %, the higher values were registered among S. epidermidis and S. haemolyticus. MET-R strains were characterized by high resistance rates even to ciprofloxacin (from 47 to 100%), erythromycin (from 70 to 100%), and in same cases to gentamicin (from 23 to 86%) also. Conclusions: Staphylococci are the prevalent cause of blood stream infections.The distinctive feature of MET-R strains is their resistance not only to all b-lactam antibiotics, but also to a wide range of other antimicrobial agents. However, the glycopeptide teicoplanin remains 100% effective against MET-R S.aureus and S. epidermidis strains.