SUSCEPTIBILITY OF STAPHYLOCOCCI AND ENTEROCOCCI TO GLYCOPEPTIDES COMPARISON OF 3 TEST METHODS

The significance of grampositive bacteria, especially staphylococci an d enterococci, as nosocomial pathogens has increased in the last decad e. Furthermore, resistance to commonly used antibiotics like beta-lact ams has also become more common and even resistance to glycopeptides h as been observed. We evaluated the susceptibility of 150 staphylococca l clinical isolates (52 S. epidermidis, 52 S. haemolyticus, 10 S. sapr ophyticus, 10 S. hominis, 4 S. warneri, 4 S. simulans, 4 S. capitis an d 14 S. aureus) and of 50 enterococci (49 E. faecalis, 1 E. faecium) t o the glycopeptides, vancomycin and teicoplanin. The data from the aga r dilution test used as reference method were compared with the result s from the E test and the agar disk diffusion test. Concerning vancomy cin, no resistance among all the staphylococcal isolates was observed whereas one single enterococcal strain (E. faecium) proved to be resis tant. The overall resistance of staphylococcal isolates against teicop lanin was about 10.7% (15 S. haemolyticus, 1 S. epidermidis) being mai nly due to the high proportion of S. haemolyticus strains (52 out of 1 50) among the staphylococcal isolates. Teicoplanin resistance among th e enterococci was not detected. For vancomycin, a very close correlati on between the MICs from the agar dilution test and the E test was not iced. As concerns teicoplanin, the MICs from the E-test were usually s omewhat lower than those obtained by the agar dilution test. No correl ation was found between the MICs of resistant and intermediate staphyl ococcal strains and the results from the teicoplanin agar disk diffusi on test. For routine teicoplanin susceptibility testing of staphylococ ci, the determination of the MIC (e.g. by the E test) is much more rel iable for detecting resistant strains than the agar disk diffusion tes t.