Cellular fatty acid analysis in the differentiation of Clostridium in the clinical microbiology laboratory

The identification of Clostridium species can be problematic for the diagnostic microbiology laboratory. The introduction of the MIDI Microbial Identification System (MIS) has enabled personnel in diagnostic laboratories to perform cellular fatty acid analyses on a variety of microorganisms. We used the Virginia Polytechnic Institute (Blacksburg, VA) Anaerobe Library (Moore Version 3.8) to perform analyses on 216 strains representing 18 species of Clostridium. The organisms were characterized with use of traditional biochemical methods that employ prereduced anaerobically sterilized media and other reference diagnostic methods. The MIS identified 86% of the strains correctly to the species level without the need for supplemental tests, and identified an additional 6% of the strains to species levels with the aid of a few supplemental tests. Only 3% of strains were identified by genus incorrectly. The cellular fatty acid patterns of selected, medically important clostridia were so distinctive that 100% of these species were identified correctly. The MIS has many practical benefits, including speed of identification, and few disadvantages (such as equipment cost) for the clinical microbiology laboratory.