The NMJI

In vitro activity of vancomycin and teicoplanin against staphylococci in intensive care units:

Infections caused by antibiotic-resistant Gram-positive bacteria, especially methicillin-resistant staphylococci, have increased during the past two decades in most areas of the world. Severe nosocomial infections caused by these organisms are treated with either vancomycin or teicoplanin.1,2 We evaluated the antimicrobial activity of vancomycin and teicoplanin against methicillin-resistant staphylococci isolated from patients in 3 surgical intensive care units (SICUs) over 4 months in Istanbul. One of the SICUs specialized in cardiovascular surgery and the other two had different fields of surgical activity.

One hundred and twenty nosocomial methicillin-resistant strains of staphylococci were isolated from clinically important materials, e.g. blood (two or more blood cultures), central venous catheter, wound and normally sterile body fluids, in the presence of clinical manifestations not attributable to other causes after at least 72 hours of hospitalization. The Bactec 9050 Blood Culture Instrument (Becton Dickinson, Baltimore, USA) was used for analysing blood cultures. There were 63 (52.5%) Staphylococcus aureus and 57 (47.5%) coagulase-negative staphylococci (CNS). All isolates were identified by conventional methods3 and confirmed by the API 32 Staph system (BioMeriéux, France). Methicillin resistance was confirmed using the oxacillin E-test (AB Biodisk, Solna, Sweden) on a medium containing 2% NaCl. After identification, all isolates were maintained in tryptic soy broth containing 10% glycerol at –70 °C until further testing. Susceptibility testing of each isolate for vancomycin and teicoplanin was performed using the E-test (AB Biodisk, Solna, Sweden) according to the National Committee for Clinical Laboratory Standards (NCCLS) guidelines.4 Staphylococcus aureus ATCC 29213 was used as the control strain.

The majority of microorganisms were isolated from the blood (n=56; 46.7%) and central venous catheters (n=29; 24.2%). The others were cultured from wounds, abscesses (n=13; 10.8%), drainage fluids (n=12; 10%) and other materials (n=10; 8.4%). There were 5 species of CNS among the isolates: Staphylococcus epidermidis (42), Staphylococcus hominis (6), Staphylococcus haemolyticus (6), Staphylococcus intermedius (2) and Staphylococcus xylosus (1). All the isolates were nosocomially acquired.

None of the 120 Staphylococcal isolates were resistant to vancomycin but 6 samples of S. haemolyticus were resistant to teicoplanin. The minimum inhibitory concentration (MIC50 and MIC90) values for S. aureus and CNS isolates were 2 µg/ml, 2 µg/ml, 2 µg/ml and 2 µg/ml for vancomycin, and 3 µg/ml, 8 µg/ml, 4 µg/ml and 8 µg/ml for teicoplanin, respectively. All the S. haemolyticus had MICs of 256 µg/ml for teicoplanin and 4 µg/ml for vancomycin.

In recent years, decreased susceptibility of S. aureus and CNS isolates to glycopeptides has been reported. Of the CNS species, S. epidermidis and S. haemolyticus are affected by the development of resistance. Although the majority of CNS remain susceptible to vancomycin, isolates with reduced susceptibility have been observed. Reduced susceptibility to teicoplanin is observed in about 30% of S. haemolyticus and less often in S. epidermidis.5

Vancomycin-intermediate or -resistant S. aureus isolates are not found in Turkey. Rarely, teicoplanin-intermediate or -resistant CNS have been detected in Turkey.6,7
Vancomycin is a good choice for the treatment of severe infections caused by CNS in SICU patients. There is a need for surveillance of nosocomial CNS developing resistance to glycopeptides.
18 March 2004