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Modulation of surface antigen expression by Klebsiella pneumoniae in response to growth environment
S Camprubi1, M A Smith, J M Tomas
1Department of Microbiology, Faculty of Biology, University of Barcelona, Spain.
Abstract:
Growth in pooled human body fluids [urine, serum and peritoneal dialysate (HPD)] modulated the expression of cell envelope antigens in virulent (serotype O1:K1) and avirulent (serotype O1:K66) Klebsiella pneumoniae strains. Marked variations in the outer membrane protein (OMP) and lipopolysaccharide (LPS) profiles were noted when broth-grown cells were compared with those of bacteria cultured in body fluids. In particular, for the O1:K1 serotype strain, growth in the latter resulted in: (a) the expression of at least five iron-regulated OMPs in the 74-87 kDa range, the pattern of which was medium dependent; (b) alterations in the migration of the LPS core polysaccharide; and (c) the reversion of isogenic O-:K+ and O-:K- mutants to the O+ phenotype after growth in fresh serum but not in heat-inactivated serum, urine or HPD. Similar results were obtained for the O1:K66 serotype, although no variation in the migration of the LPS core was noted. For both O1:K1 and O1:K66 serotypes, neither the surface exposure of O1 serotype LPS nor the production of K-antigen (capsular polysaccharide) was affected by growth in body fluids. No reversion of K- mutants to the K+ phenotype was observed. These data illustrate the phenotype flexibility of this opportunistic pathogen and emphasise the crucial role of the O- rather than the K-antigen in protecting K. pneumoniae from complement-mediated serum killing.
Insights
Klebsiella pneumoniae adapts its cell envelope antigens, including outer membrane proteins and lipopolysaccharide, when grown in human body fluids. This phenotype flexibility highlights the O-antigen
Area of Science:
- Microbiology
- Immunology
- Pathogen Adaptation
Background:
- Klebsiella pneumoniae is an opportunistic pathogen.
- Cell envelope antigens play a role in bacterial virulence and host immune response.
- Understanding bacterial adaptation to host environments is crucial for developing effective treatments.
Purpose of the Study:
- To investigate how Klebsiella pneumoniae modulates its cell envelope antigen expression when grown in human body fluids.
- To compare the effects of different human body fluids (urine, serum, peritoneal dialysate) on antigen expression in virulent and avirulent strains.
- To determine the role of O-antigen and K-antigen in bacterial survival in serum.
Main Methods:
- Culturing virulent (O1:K1) and avirulent (O1:K66) Klebsiella pneumoniae strains in pooled human body fluids (urine, serum, peritoneal dialysate) and standard broth.
- Analyzing outer membrane protein (OMP) and lipopolysaccharide (LPS) profiles using gel electrophoresis.
- Assessing the reversion of O- and K-antigen deficient mutants to the O+ and K+ phenotypes after growth in different media.
- Evaluating bacterial survival in serum after growth in body fluids.
Main Results:
- Growth in human body fluids significantly altered OMP and LPS profiles compared to broth cultures.
- Specific iron-regulated OMPs were expressed in a medium-dependent manner in the O1:K1 strain.
- LPS core polysaccharide migration patterns changed in the O1:K1 strain but not in the O1:K66 strain.
- O-antigen deficient mutants reverted to O+ phenotype after growth in fresh serum, but not in heat-inactivated serum, urine, or HPD.
- K-antigen production and surface LPS exposure were unaffected by body fluid growth.
- No reversion of K- mutants to K+ phenotype was observed.
Conclusions:
- Klebsiella pneumoniae exhibits significant phenotype flexibility in response to growth in human body fluids.
- The O-antigen, rather than the K-antigen, is critical for protecting Klebsiella pneumoniae from complement-mediated killing in serum.
- These findings have implications for understanding K. pneumoniae pathogenesis and host-pathogen interactions.