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Antimicrobial Agents and Chemotherapy, November 2000, p. 3122-3126, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Glycopeptide Susceptibility Profiles of Staphylococcus haemolyticus Bloodstream Isolates

Francesca Biavasco,* Carla Vignaroli, Raffaella Lazzarini, and Pietro E. Varaldo

Institute of Microbiology, University of Ancona, 60131 Ancona, Italy

Received 24 February 2000/Returned for modification 4 June 2000/Accepted 11 August 2000

Twelve clinical strains of Staphylococcus haemolyticus (eight methicillin resistant and three methicillin susceptible), isolated from blood cultures between 1982 and 1997, were investigated for teicoplanin and vancomycin susceptibility profiles. On the basis of conventional MIC tests and breakpoints, four isolates were susceptible (MICs, 1 to 8 µg/ml) and eight were resistant (MICs, 32 to 64 µg/ml) to teicoplanin while all were susceptible to vancomycin (MICs, 1 to 2 µg/ml). All four strains for which the conventional teicoplanin MICs were within the range of susceptibility expressed heterogeneous resistance to teicoplanin and homogeneous vancomycin susceptibility. Of the eight strains for which the conventional teicoplanin MICs were within the range of resistance, six expressed heterogeneous and two expressed homogeneous teicoplanin resistance while seven showed heterogeneous vancomycin resistance profiles (with subpopulations growing on 8 µg of the drug per ml at frequencies of >= 10-6 for six strains and 10-7 for one) and one demonstrated homogeneous vancomycin susceptibility. Of six bloodstream isolates of other staphylococcal species (S. aureus, S. epidermidis, and S. simulans), for all of which the conventional teicoplanin MICs were >= 4 µg/ml and the vancomycin MICs were <= 2 µg/ml, none exhibited heterogeneous susceptibility profiles for teicoplanin while three showed homogeneous and three showed heterogeneous susceptibility profiles for vancomycin (with subpopulations growing on 8 µg of the drug per ml found for only one strain). The results of this study indicate that a heterogeneous response to glycopeptides is a common feature of S. haemolyticus isolates and suggest that susceptibility to glycopeptides as determined by conventional MIC tests may not be predictive of the outcome of glycopeptide therapy.

* Corresponding author. Mailing address: Institute of Microbiology, University of Ancona, Via Ranieri, Monte d'Ago, 60131 Ancona, Italy. Phone: 39 071 2204697. Fax: 39 071 2204693. E-mail: f.biavasco{at}popcsi.unian.it.

Antimicrobial Agents and Chemotherapy, November 2000, p. 3122-3126, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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