Comparative study using various methods for identification of Staphylococcus species in clinical specimens

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Molecular Diagnostics

Background:

• Coagulase-negative staphylococci (CNS) are significant causes of nosocomial infections, necessitating rapid and accurate identification for effective patient management.
• The development of advanced identification systems, including updated VITEK 2 and BD Phoenix cards, aims to improve the diagnosis of gram-positive cocci infections.

Purpose of the Study:

• To compare the performance of the BD Phoenix and VITEK 2 automated microbiology systems with updated identification cards against the API ID32 STAPH test and a molecular method for CNS identification.
• To evaluate the accuracy of phenotypic identification methods versus genotypic analysis in differentiating Staphylococcus species.

Main Methods:

• Analysis of 86 clinical CNS isolates and 27 reference strains using BD Phoenix, VITEK 2, and API ID32 STAPH systems.
• Validation of results using a glyceraldehyde-3-phosphate dehydrogenase (gap) gene-based T-RFLP (terminal restriction fragment length polymorphism) molecular method.

Main Results:

• The updated VITEK 2 and BD Phoenix systems demonstrated comparable performance in identifying CNS.
• The API ID32 STAPH test yielded a higher number of correct identifications compared to both automated systems.
• The gap-based T-RFLP molecular method confirmed superior accuracy in identifying Staphylococcus species, excluding Staphylococcus aureus.

Conclusions:

• Newer automated systems offer improved, yet comparable, performance for CNS identification.
• The API ID32 STAPH test remains a highly accurate phenotypic method for CNS identification.
• Molecular methods, such as gap-based T-RFLP, provide the highest accuracy for species-level identification of Staphylococcus, particularly for non-aureus species.