QAC RESISTANCE OF P. AERUGINOSA

The adaptation mechanism of Pseudomonas aeruginosa ATCC 10145 to quaternary ammonium compounds (QACs) was investigated. A P. aeruginosa strain with adapted resistance to QACs was developed by a standard broth dilution method. It was revealed that P. aeruginosa exhibited remarkable resistance to N-dodecylpyridinium iodide (P-12), whose structure is similar to that of a common disinfectant, cetylpyridinium chloride. Adapted resistance to benzalkonium chloride (BAC), which is commonly used as a disinfectant, was also observed in P. aeruginosa. Moreover, the P-12-resistant strain exhibited cross-resistance to BAC. Analysis of the outer membrane protein of the P-12-resistant strain by two-dimensional polyacrylamide gel electrophoresis showed a significant increase in the level of expression of a protein (named OprR) whose molecular mass was approximately 26 kDa. The actual function of OprR is not yet clear; however, OprR was expected to be an outer membrane-associated protein with homology to lipoproteins of other bacterial species, according to a search of the National Center for Biotechnology Information website with the BLAST program by use of the N-terminal sequence of OprR. A correlation between the level of expression of OprR and the level of resistance of P. aeruginosa to QACs was observed by using a PA2800 gene knockout mutant derived from the P-12-resistant strain. The knockout mutant recovered susceptibility not only to P-12 but also to BAC. These results suggested that OprR significantly participated in the adaptation of P. aeruginosa to QACs, such as P-12 and BAC

BACTERIAL ADAPTATION TO QAC

The adaptation of bacteria to mono-and bis-type quaternary ammonium compounds (QACs) was carried out and studied. The minimum inhibitory concentration (MIC) of bis-QACs against the bacteria in contact with bis-QACs was nearly the same as that against the control. However, the MIC of mono-QAC against the strains adapted to mono-QAC was higher than that against the control. Moreover, bis-QACs were effective against even the strains adapted to mono-QAC. As the cell surface of the strains adapted to mono-QAC changed to hydrophilic, the difference in the bacterial adaptation was thought to arise from a potent property of bis-QACs whose antimicrobial characteristics are independent of the change in the cell surface hydrophobicity

CHARACTER OF QAC RESISTANT P. AERUCINOSA

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

MICROBIAL CONTAMINATION IN HOME LAUNDRY

The hygiene levels in home laundry operations in Japan have been changing with the changes in lifestyle. Microbial transmission through home laundry has been reported, but mainly in North American and European countries. The home laundering situation in Japan is unique among many countries, and the most characteristic point is that Japanese use the leftover bath water for laundering the next day. However, such a unique custom may cause household microbial transmission. In order to clarify the link between the microbial transmission and the home laundering operation in Japan, a bacteriological investigation of various articles was done. Children's underpants, bath towels, kitchen rags, the washing machine itself and the leftover bath water were investigated. Although variations in bacterial strains were seen, many Staphylococcus spp. were isolated from every sample. Although pathogenic strains were not detected, some opportunistic pathogens were detected. Furthermore, since many bacteria were isolated from bath water, home laundering operations with the used bath water may cause microbial contamination of the laundry

Mutational Upregulation of a Resistance-Nodulation-Cell Division-Type Multidrug Efflux Pump, SdeAB, upon Exposure to a Biocide, Cetylpyridinium Chloride, and Antibiotic Resistance in Serratia marcescens▿

Serratia marcescens is an important opportunistic pathogen in hospitals, where quaternary ammonium compounds are often used for disinfection. The aim of this study is to elucidate the effect of a biocide on the emergence of biocide- and antibiotic-resistant mutants and to characterize the molecular mechanism of biocide resistance in Serratia marcescens. A quaternary ammonium compound-resistant strain, CRes01, was selected by exposing a wild-type strain of S. marcescens to cetylpyridinium chloride. The CRes01 cells exhibited 2- to 16-fold more resistance than the wild-type cells to biocides and antibiotics, including cetylpyridinium chloride, benzalkonium chloride, chlorhexidine gluconate, fluoroquinolones, tetracycline, and chloramphenicol, and showed increased susceptibilities to β-lactam antibiotics and N-dodecylpyridinium iodide. Mutant cells accumulated lower levels of norfloxacin than the parent cells in an energized state but not in a de-energized state, suggesting that the strain produced a multidrug efflux pump(s). To verify this assumption, we knocked out a putative efflux pump gene, sdeAB, in CRes01 and found that the knockout restored susceptibility to most quaternary ammonium compounds and antibiotics, to which the CRes01 strain showed resistance. On the basis of these and other results, we concluded that S. marcescens gains resistance to both biocides and antibiotics by expressing the SdeAB efflux pump upon exposure to cetylpyridinium chloride

Correlation between Resistance of Pseudomonas aeruginosa to Quaternary Ammonium Compounds and Expression of Outer Membrane Protein OprR

The adaptation mechanism of Pseudomonas aeruginosa ATCC 10145 to quaternary ammonium compounds (QACs) was investigated. A P. aeruginosa strain with adapted resistance to QACs was developed by a standard broth dilution method. It was revealed that P. aeruginosa exhibited remarkable resistance to N-dodecylpyridinium iodide (P-12), whose structure is similar to that of a common disinfectant, cetylpyridinium chloride. Adapted resistance to benzalkonium chloride (BAC), which is commonly used as a disinfectant, was also observed in P. aeruginosa. Moreover, the P-12-resistant strain exhibited cross-resistance to BAC. Analysis of the outer membrane protein of the P-12-resistant strain by two-dimensional polyacrylamide gel electrophoresis showed a significant increase in the level of expression of a protein (named OprR) whose molecular mass was approximately 26 kDa. The actual function of OprR is not yet clear; however, OprR was expected to be an outer membrane-associated protein with homology to lipoproteins of other bacterial species, according to a search of the National Center for Biotechnology Information website with the BLAST program by use of the N-terminal sequence of OprR. A correlation between the level of expression of OprR and the level of resistance of P. aeruginosa to QACs was observed by using a PA2800 gene knockout mutant derived from the P-12-resistant strain. The knockout mutant recovered susceptibility not only to P-12 but also to BAC. These results suggested that OprR significantly participated in the adaptation of P. aeruginosa to QACs, such as P-12 and BAC