Characterization of Pseudomonas aeruginosa Resistant to a Quaternary Ammonium Compound

We developed the resistance of Pseudomonas aeruginosa ATCC 10145 to N-dodecylpyridinium iodide (P-12), a quaternary ammonium compound (QAC), by using a standard broth dilution method and compared its characteristics with those of the sensitive strain. The minimum inhibitory concentration (MIC) against the resistant strain was 8 times higher than that against the sensitive strain and the adapted resistance to P-12 was stable. Population analysis showed that there were some variations in the extent of the resistance of P. aeruginosa to P-12. The cell surface of the resistant strain was more hydrophilic than that of the sensitive strain. In order to investigate the relationship between the resistance to P-12 and the biofilm formation of P. aeruginosa, alginic acid was isolated and its concentration was determined. The results revealed that the alginic acid was produced only in the resistant strain. Moreover, the observation by scanning electron microscope (SEM) of both strains showed that many clusters of bacteria were seen only in the resistant strain. These results suggested that not only the hydrophilic change of cell surface but also the biofilm formation is involved in the resistance of P. aeruginosa to P-12.