ABSTRACT
Aerobic gram-negative bacteria are ubiquitous. Many are found throughout the environment and distributed worldwide. Others are established as normal ora in human and animal mucosa, intestinal tract, and skin. Many of these bacteria are typically harmless, and several are even benecial. Others account for a large percentage of foodborne illness, and some have been identied as potential weapons of bioterrorism. The identication of these organisms is necessary in many circumstances. The clinical microbiologist identifying the pathogen responsible for the severe, bloody diarrhea of a hospitalized young child; the environmental laboratorian identifying the bacterial contaminant that forced a recall of a commercial product; and the researcher identifying and characterizing the bacteria that are degrading chemical pollutants in a river all nd themselves faced with the task of identifying aerobic gram-negative bacteria. This task can be accomplished using a variety
Introduction ......................................................................................................................................77 Characteristics for Initial Identication ........................................................................................... 79
Gram Stain .................................................................................................................................. 79 Colony Morphology ....................................................................................................................80 Pigment Production .....................................................................................................................80 Growth on MacConkey Agar ...................................................................................................... 81 Triple Sugar Iron Agar ................................................................................................................ 81 Oxidase ........................................................................................................................................ 81
Additional Conventional Biochemical Tests .................................................................................... 82 Acid from Carbohydrates ............................................................................................................ 82 Catalase ....................................................................................................................................... 82 Citrate Utilization ........................................................................................................................ 82 Decarboxylation of Lysine, Arginine, and Ornithine .................................................................. 83 Esculin Hydrolysis ...................................................................................................................... 83 Gelatin Liquefaction ....................................................................................................................84 Indole Production ........................................................................................................................84 Motility ........................................................................................................................................84 Methyl Red (MR) and Voges-Proskauer (VP) Tests ...................................................................85 Nitrate Reduction ........................................................................................................................85 Urease ..........................................................................................................................................86
Commercial Identication Systems .................................................................................................86 Molecular Testing and Analysis .......................................................................................................87 Acknowledgments ............................................................................................................................88 References ........................................................................................................................................88
of methods. It often involves a combination of conventional phenotypic tests based on biochemical reactions, commercial kits or systems, and/or molecular analysis.
