Microscopic Analysis: Morphotypes and Cellular Appendages

Microscopic analysis is a well-accepted technique in microbiology to characterize a single colony and single cell morphotypes. Although colony morphotype can be imaged by light microscopy, morphotypes of microbial cells are normally viewed by transmission electron microscopy (TEM). The specific location of proteins on microbial cell surface or inside the cells is normally detected using immunoelectron microscopy (IEM). Here we describe the technique of detection of type-specific cellular appendages that are produced by several strains of Pseudomonas aeruginosa under conditions of phosphate limitation. The ability to produce the appendages in P. aeruginosa herein described is thus far attributable only to certain multidrug-resistant strains isolated from critically ill patients. The appearance of appendages is highly suppressed in phosphate rich media and enhanced during growth in phosphate depleted media. Under these dual conditions, the absence or presence of appendages correlates with an adhesive and virulent phenotype in P. aeruginosa strains. The proper technique for appendage visualization is critical to facilitate the necessary studies to further elucidate their structure and function.