Browsing by Subject "Bacteria -- Physiology"
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Item Physiological properties of Bacillus thuringiensis endospores(Texas Tech University, 1987-05) Wilson, Gary R.Through use of an ±n^ vitro model, survival of vegetative cells and spores of Bacillus thuringiensis within insect midgut conditions was tested. Vegetative cells would not grow in 0.1 M carbonate-buffered media above pH 9 and growth was severely impeded by incorporation of thioglycollate. Outgrowth of spores was inhibited by long-term exposure to pH 8.5 or above, but short-term exposure to carbonate buffer enhanced viable counts. A number of basic chemicals and buffers improved outgrowth with best results obtained with 0.1 M potassium carbonate at a pH of 10. The combination of trypsin, carbonate, and thioglycollate yielded the highest outgrowth rate observed. Germination rates of spores were optimized by heat shock or incubation with carbonate buffer, though most spores did not require activation for germination. To further investigate spore properties, spores from four modifications of tryptic soy agar, two low in glucose and two rich in glucose, were tested for viability and resistance to heat, UV light, and octanol. In addition, spore sizes and germination rates were determined. Spores from low-glucose media (type A spores) were smaller and less resistant to heat and UV light than were spores from high-glucose media (type B spores). Type A spores also were faster germinating and had a greater percentage viable spores than their counterparts from high-glucose media. The contributions of these traits toward adaptation to the ecological niche for spores produced within insects or within the soil is proposed.Item The contribution of quorum sensing to the pathogenesis of pseudomonas aeruginosa in burn wound infections(Texas Tech University, 2001-05) Rumbaugh, Kendra P.Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes severe infections in burned patients. In this work, we examined the contribution ofthe cell-to-cell communication systems or quorum sensing (QS) systems to the pathogenesis of P aeruginosa infection of burn wounds. For these studies, we used the thermally-injured mouse model and specific mutants that carry deletions in genes encoding specific components of the P aeruginosa QS systems {lasR, rhlR, lasl and rhll). In comparison with their parent strain (PAOl), all mutants displayed decreased lethality. The mutants were defective in their ability to spread systemically throughout the body of the mice. In addition, the lasR (PAO-Rl) and the lasl/rhll (PAO-JP2) mutants were defective in their ability to spread locally within the burned skin at 8 and 16 hours post-bum/infection. The defects in the PAO-JP2 strain were complemented upon the introduction of a plasmid carrying intact lasl and rhll genes. To determine if the defect in PAO-JP2 is due to the loss of one or more of the QScontrolled virulence factors, isogenic mutants that carry deletions in lasA, lasB, lasAAasB, toxA, lasB/toxA or rpoS were examined. With the exception of the rpoS mutant, all mutants were defective in their in vivo virulence. However, none was as severely defective as PAO-JP2. Our attempt to ascertain the role of autoinducers as virulence factors was confounded by the influence of the solvent used to purify them. Host production of cytokines in response to P aeruginosa infection in bum wounds was examined using the Multi-Probe Template/RNase protection assay. The expression of several proinflammatory and hematopoietic cytokines was up-regulated in burned mice infected with PAOl at 40 hours post-bum/infection. In contrast, the expression of most of these cytokines was not enhanced in burned mice infected with PAO-JP2. These results suggest that: (1) the QS systems play an important role in the pathogenesis of P aeruginosa in bum wound infections; (2) their effects may be contributed to by autoinducers or other, yet undefined, QS-controlled factors; and (3) QS may play a role in modulating the host immune system in response to P. aeruginosa.