One approach to examining errors or potential errors in aviation has focused on measuring the hazardous thought patterns of pilots. Previous research identified five thought patterns and assumed that all pilots fall into one of these categories. The current research was designed to develop and behaviorally validate a new instrument to measure hazardous thought patterns. The research confirmed previous work in finding five hazardous thought patterns. However, the research also suggested the presence of a sixth factor related to confidence/competence. The validation suggested that the individual hazardous thought patterns differentially predicted accidents and incidents. The behavioral validation also identified relationships between particular hazardous thought patterns and specific driving behaviors that supported the validity and utility of the newly designed instrument.
Chlorhexidine diacetate (CHA) and phenoxyethanol (POE) are membrane-active biocides. W e describe t h e i r effects alone and in combination on leakage from s t r a i n s of Escherichia coli and Pseudomonas aeruginosa (Table 1). Bacterial suspensions (final density lmg dry wt./ml) i n sterile w a t e r were treated at 20°C. K+ leakage w a s determined by a potassium ion-selective electrode, Rb+ by a radioactive method, and pentose against D-ribose as standard.K+ leakage w a s induced readily by low, sublethal concentrations of CHA and increased as the concentration increased up t o a maximum a t 100pg/ml. The greatest amount of K+ leakage was observed with Ps.aeruginosa strains. Leakage w a s rapid, ca. 80% of t o t a l leakage occurring within 10 min. Mutant s t r a i n s with depleted outer membrane lipopolysaccharide (LPS) w e r e r a t h e r more sensitive than parent s t r a i n s although minimum inhibitory concentrations (MICs) of CHA determined i n broth were very s i m i l a r . K+ leakage from POEtreated cells was also concentration-dependent, levelling off at ca. 1% v/v; leakage w a s rapid, with most taking place within 1 0 min, and mutant s t r a i n s w e r e r a t h e r more susceptible. A combination of CHA (100pg/ml) and POE (1% v/v) increased both t h e rate and extent of K+ leakage, with maximum effect a f t e r a contact period of 1 min.Rb+ leakage was induced readily by sublethal concentrations of CHA (lOpg/ml) o r POE (0.3%).Higher CHA concentrations had a rapid effect with m a x i m a l leakage occurring within 3 min.Little difference w a s observed between wild type s t r a i n s and t h e i r envelope mutants. Combinations of CHA (100pg/ml) and POE (1%) increased t h e rate and extent of Rb+ leakage. CHA induced a diphasic pattern of pentose leakage with a maximal effect at 100 pg/ml. N o such response was seen with POE (0 -2%). Leakage was maximal within 10 min f o r either biocide used alone, and mutant strains were slightly more sensitive than t h e corresponding parents. A combination of CHA (100 pg/ml) plus POE (1%) induced very rapid pentose leakage which reached a maximum value within 1 min. Enhanced activity is t h u s achieved by use of appropriate combinations of CHA and POE, but there is little correlation between leakage and MIC values.
Escherichia coli PC1349 and Staphylococcus aureus 6571 were sensitive to low concentrations of chlorhexidine diacetate, as determined by minimal inhibitory concentration tests. Lack of bactericidal response to 30 μg/ml was due to the fact that adsorption of biocide to the cells was very slight in suspensions of high cell density and was not due to emerging resistance. Attempts by various methods to induce stable resistance in these organisms failed, despite reports that resistant strains have been isolated.
The surfaces of mutants of Escherichia coli and Pseudomonas aeruginosa were markedly more hydrophobic than the corresponding wild types, as were the latter when the organisms were pre‐treated with chlorhexidine diacetate (CHA) or phenoxyethanol (POE). A combination of CHA and POE demonstrated that only at higher concentrations was there a marked effect on hydrophobicity compared with that of either drug used alone. The three methods used to determine hydrophobicity correlated well as long as constant conditions were employed.
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