Graduate Thesis Or Dissertation
 

Factors related to resisitance of bacteria to quaternary ammonium germicides

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  • This study was carried out to compare the effects of a quaternary ammonium compound (QAC) upon strains of Pseudomonas aeruginosa which were either sensitive or resistant to the germicide. The cationic QAC used was alkyldimethylbenzylammonium chloride. The resistant types were isolated from the sensitive population by selection of mutants which grew following exposure to different concentrations of germicide. A study also was made of the potentiating effect of lysozyme on the activity of QAC. An attempt was made to classify an unknown QAC-resistant bacterium isolated from sewage sludge. Germicidal activity was measured by two methods. The Weber and Black method was used to determine the germicidal effect of QAC at a low concentration (200 ppm) during various periods of exposure time. Spectrophotometric measurements of cell lysis also were used when higher concentrations of QAC and longer exposure times were employed. Results indicated that cells exposed to low concentrations of QAC were killed by lysis of cells occurred only upon the Addition of higher concentrations acting for longer exposure times. The potentiating effect of lysozyme on QAC activity was demonstrated using a modified Weber and Black method. It also was shown by means of a spectrophotometric procedure as well as manometric methods. The germicidal action of QAC toward both QAC-resistant and sensitive organisms was enhanced by addition of 0.025% lysozyme. Although the germicidal mechanism of QAC is still not understood, the penetration of QAC through the cell membrane appeared to be accelerated by the presence of lysozyme in the medium. Degradation of QAC by growing cultures of the unknown sludge bacterium was demonstrated by following the decrease in QAC concentration during the time of incubation; in 35 days, 63% of added germicide at 500 ppm was apparently degraded. Since the organism was unable to utilize QAC, as a sole source of carbon or nitrogen, it appeared that QAC molecules were either firmly absorbed on the cell surface or dissipated by an unknown mechanism within or around the cell. The unknown QAC-resistant sludge organism was classified as Aerobacter cloacea on the basis of results from usual bacteriological taxonomic tests.
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