Molecular Bacteriology in the Clinical Laboratory

Extract

Molecular diagnostic assays are becoming the “norm” in the clinical microbiology laboratory, especially in bacteriology. Routine cultures using conventional media require 24 to 72 hours or longer to generate a final report. Acid-fast bacilli (AFB) cultures for Mycobacterium tuberculosis (MTB) using standard AFB media require up to six weeks to grow and be identified. Although health care providers are aware cultures may take several days or weeks before a definitive identification and susceptibility test can be made, this turn around time is not acceptable when dealing with virulent organisms such as methicillin-resistant Staph aureus (MRSA), MTB, and vancomycin-resistant Enterococcus (VRE). Physicians need to know within hours whether their patient is suffering from a dangerous infection that requires isolation and aggressive treatment. Fortunately, there are several FDA cleared assays and platforms that can generate results of pathogenic and fastidious organisms within a few hours. For example, some of the most widely used FDA cleared in vitro molecular diagnostic systems and tests on the market are the GeneXpert® and SmartCycler® Systems by Cepheid (Sunnyvale, California), the COBAS AMPLICOR Chlamydia trachomatis (CT)/ Neisseria gonorrhoeae (NG) test by Roche Diagnostics, Inc. (Pleasanton, California), and the AMPLIFIED Mycobacterium tuberculosis Direct Test by Gen-Probe, Inc. (San Diego, California).¹ There are other assays on the market which are FDA cleared and will be mentioned briefly in this article.