Effects of chlorhexidine diacetate on P. stutzeri ultrastructure

Electron microscopy (EM) is a useful tool for detailed ultrastructural analysis of microorganisms. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which provide information about surface and intracellular changes, can be used for studying the effects of antimicrobial agents on microorganisms. EM has previously been used to study the ultrastructural basis of the resistance of Pseudomonas aeruginosa to antiseptics, disinfectants and antibiotics, and has been widely used in this laboratory for investigating the effects of antimicrobial agents on a variety of different types of organism. X-ray microanalysis is a method of elemental analysis at the ultrastructural level and can correlate morphological appearance with chemical composition. The technique exploits the fact that different elements give off X-rays having characteristic energies when a sample is irradiated with an electron beam. The elemental composition of a sample can be determined by analysing the X-ray spectrum. An energy-dispersive X-ray analyser offers the advantage that all elements of interest are analysed simul taneously. Energy-dispersive analysis of X-ray (EDAX) is a useful technique for the localization of elements in microbial cells and has previously been used in this laboratory for studying the effects of chlorhexidine on Saccharomyces cerevisiae, P. aeruginosa bacteriophage F116 and Acantha moeba castellanii. Stable resistance to chlorhexidine has been demonstrated in some isolates of Pseudomonas stutzeri, and in this study we have used SEM, TEM and EDAX to better understand the underlying mechanisms involved.