Discussion. Part 2
In order to better characterize the relationship between P. aeruginosa and mammalian cells during infection, we examined the effect of this organism and its fractions on 3 hydrolases present in mouse monocytes. Experiments with both living and intact dead P. aeruginosa in vitro and in vivo indicated that beta glucuronidase and alkaline phosphatase were affected by intact bacteria. Although the response of beta glucuronidase varied in certain experiments, the results in table 8 clearly show inhibi tion of activity in the presence of living extracell ular organisms. The response of alkaline phosphatase suggested that both stimulation and inhibition of this enzyme occurred during infection. Viable organisms incubated with monocytes apparently did not destroy the cell’s ability to produce or activate alkaline phosphatase, despite the fact that previous manometric studies by Berk et al (1960a) had indicated that resting cells of P. aeruginosa metabolized monocytes. When monocytes were infected in vivo (table 10), acid phosphatase was depressed, while alkaline phosphatase was stimulated. This was reminiscent of the increased lactate production found with infected cells (Berk et aI, 1960a).
The response of monocytes allowed to ingest dead P. aeruginosa in vivo closely paralleled that obtained when live bacteria were used. In addition to these in vivo studies, similar experiments performed in vitro (where little or no ingestion occurred) yielded basically similar results. The results in table 3 indicate that trace amounts of piromen exerted some effect on all 3 enzymes. Beta glucuronidase appeared most susceptible to piromen. Depression of enzyme activity was not directly proportional to piromen concentration. This suggests that inhibition may be a reflection of some cell surface phenomenon, especially since it has already been demonstrated by Kerby (1952) that piromen disrupts the cell structure of leucocytes. Experiments utilizing particles of P. aeruginosa sedimented at 35,000 ref (Alexander, 1956) yielded results very similar to those with piromen. The particles were more toxic (on a nitrogen basis) for hydrolase than for succinoxidase activity. Similar studies with toxic particles from hemolytic streptococci have been reported by Roberson et al (1960). An analysis of the over-all response of P. aeruginosa-infected monocytes indicates that lactate production and alkaline phosphatase activity increase, while succinoxidase and acid phosphatase activities decrease. Cytochrome oxidase is unaffected, while the effect on beta glucuronidase is variable. It appears that certain enzymes are more susceptible to certain microorganisms than to others and that some variation may be anticipated, depending on experimental conditions. In general, the effect of either piromen or the subcellular particles seems adequate to account for the toxicity of intact P. aeruginosa. The outstanding difference between these lies in the response of alkaline phosphatase. One may suspect, however, that depression in acid phosphatase may be compensated by a corresponding increase in alkaline phosphatase.