Rapid detection of vancomycin-non-susceptible Staphylococcus aureus using the spiral gradient endpoint technique.
OBJECTIVE
Several methods have been introduced for detection of vancomycin-non-susceptible Staphylococcus aureus [heterogeneous vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus (VISA)]. However, the limitations of these methods can delay appropriate therapy for the patient. This study evaluated the spiral gradient endpoint (SGE) technique for detection of hVISA/VISA.


METHODS
The SGE method was evaluated for intra-batch, inter-batch and inter-observer reproducibility in comparison with MICs determined by agar dilution. Three media, Mueller-Hinton agar, brain heart infusion agar and brain heart infusion agar with 5% glucose, were evaluated. The SGE method was compared with agar dilution for correlation of MIC and susceptibility category using control strains, clinical isolates and induced vancomycin-non-susceptible strains.


RESULTS
The SGE method had good reproducibility and there was excellent correlation of MICs generated by SGE using brain heart infusion agar with those by agar dilution (r(2) =0.950), with no difference in resistance categories generated by the two methods. All VISA isolates were correctly identified and the method allowed easy identification of hVISA by means of the trailing endpoint.


CONCLUSIONS
SGE offers a simple, rapid and cost-effective alternative method for the detection of hVISA/VISA for the routine laboratory. Early recognition of vancomycin-non-susceptible strains can allow the change to appropriate antibiotics, resulting in potentially better patient outcomes.
Doddangoudar
Vijaya C
VC
Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
O'Donoghue
Margaret M
MM
Boost
Maureen V
MV
Tsang
Dominic N C
DN
Appelbaum
Peter C
PC
D003470:Culture Media / Q000737:chemistry; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D015203:Reproducibility of Results; D013211:Staphylococcus aureus / Q000187:drug effects*; D020713:Vancomycin Resistance
D003470:Culture Media