| Summary: | The Burkholderia cepacia complex (BCC) is a family of Gram-negative bacteria of
evolving importance as opportunistic pathogens, particularly in patients with cystic
fibrosis (CF). BCC infections are difficult to treat and control due to the BCC's intrinsic
resistance to antibiotics and ability to spread among patients. Moreover BCC
colonization can develop into septicemia. Although recognized as a serious respiratory
pathogen, little is known about the pathogenesis of the BCC. The purpose of these
studies was to identify bacterial factors involved in BCC infection and colonization using
animal models that show differential persistence and virulence among BCC strains in a
murine host. Serial mouse passage of non-persistent BCC strain C1394 in a pulmonary
infection model resulted in its adaptation to the murine host and produced a variant,
C1394mp2 that persisted in the murine lung. The parent strain and variant were
indistinguishable by genetic typing, but differed in colonial morphology and were
compared to identify the bacterial determinants required for long-term infection in a
murine host. The parent strain, C1394 had a matte colonial phenotype, made scant
exopolysaccharide (EPS), and was lightly piliated. The variant, C1394mp2 had a shiny
colonial phenotype, produced abundant EPS, and was heavily piliated. Matte to shiny
colonial transformation was induced by growth at 42°C.
Proteomic analysis of C1394 and C1394mp2 protein profiles at 37°C revealed
increased flagellin production in C1394mp2 whereas C1394 had increased production of
metabolizing enzymes of the tricarboxylic acid cycle. Differential expression of the
stress-induced protein peroxiredoxin was observed in the proteomes of C1394 and
C1394mp2 at 37°C and 42°C respectively. Further comparisons included in vitro assays
examining host cell interactions with C1394 and C1394mp2. Though both isolates had
poor nonopsonic association with primary human phagocytic cells, C1394mp2 had even
less association than C1394. Binding assays with A549 epithelial cells also revealed
lower association with C1394mp2 than C1394. The results in this thesis identified BCC
surface determinants that were associated with a colonial morphology change, which
could be induced under stress, and correlated with long-term infection in a murine host
and decreased association with human host cells. Taken together, these results suggest putative bacterial factors that are necessary for BCC survival and chronic infections
susceptible hosts. === Medicine, Faculty of === Pathology and Laboratory Medicine, Department of === Graduate
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