A crucial step in the emergence of new waterborne and foodborne pathogens in developed countries is the evolution of durability traits that allow bacteria to survive in mass water and food distribution systems. For Escherichia coli O157:H7, a foodborne pathogen and growing public health problem, the ability to tolerate extreme acidity enables this organism to endure in foods and infect susceptible human in very low doses. In the research proposed here, the role of natural selection for acid tolerance and other aspects of durability in the external environment will be tested in an experimental system of bacterial evolution. The design simulates the transition between the two principal habitats of an enteric pathogen; the primary habitat in the intestine and the secondary habitat in the water, soil, and food. The conditions of the secondary environment will be varied to impart different selection pressures against which pathogenic strains can evolve. The environments range from relatively benign favoring growth, to a harsh environment favoring improved durability.
The specific aims are: (1) to experimentally determine how variables which influence survival in the external environment affect the direction and rate of evolution of durability; (2) to investigate the evolution of the components of durability (acid, salt, and heat tolerance, resistance to desiccation) and their correlated change with selection for single resistance factors; (3) to quantify variation in durability among E. coli from natural environments and assess the potential for emergence of new pathogenic strains; and (4) to elucidate the genetic basis of evolutionary change in durability by characterizing mutations in genes known to influence acid tolerance and other protection mechanisms. The evolved strains will be compared to the ancestral (original) strains in their durability and the costs (in terms of reduced fitness) of adaptation to the secondary environment will be assessed. In addition, the durability of E. coli from natural environments and outbreaks of disease will be compared to the evolved levels of durability. The molecular basis of evolved durability will be investigated through subtractive hybridization to identify genes that contribute to protection and cross protection against environmental challenges.
|Neupane, Mahesh; Abu-Ali, Galeb S; Mitra, Avishek et al. (2011) Shiga toxin 2 overexpression in Escherichia coli O157:H7 strains associated with severe human disease. Microb Pathog 51:466-70|
|Aref, Nasr-Eldin M; Saeed, A Mahdi (2011) Design and characterization of highly immunogenic heat-stable enterotoxin of enterotoxigenic Escherichia coli K99(+). J Immunol Methods 366:100-5|
|Johnson, J R; Delavari, P; Stell, A L et al. (2001) Molecular comparison of extraintestinal Escherichia coli isolates of the same electrophoretic lineages from humans and domestic animals. J Infect Dis 183:154-9|
|Tarr, P I; Schoening, L M; Yea, Y L et al. (2000) Acquisition of the rfb-gnd cluster in evolution of Escherichia coli O55 and O157. J Bacteriol 182:6183-91|
|Herbelin, C J; Chirillo, S C; Melnick, K A et al. (2000) Gene conservation and loss in the mutS-rpoS genomic region of pathogenic Escherichia coli. J Bacteriol 182:5381-90|
|Reid, S D; Betting, D J; Whittam, T S (1999) Molecular detection and identification of intimin alleles in pathogenic Escherichia coli by multiplex PCR. J Clin Microbiol 37:2719-22|
|Smith, K S; Jakubzick, C; Whittam, T S et al. (1999) Carbonic anhydrase is an ancient enzyme widespread in prokaryotes. Proc Natl Acad Sci U S A 96:15184-9|
|McGraw, E A; Li, J; Selander, R K et al. (1999) Molecular evolution and mosaic structure of alpha, beta, and gamma intimins of pathogenic Escherichia coli. Mol Biol Evol 16:12-22|
|Czeczulin, J R; Whittam, T S; Henderson, I R et al. (1999) Phylogenetic analysis of enteroaggregative and diffusely adherent Escherichia coli. Infect Immun 67:2692-9|
|Reid, S D; Selander, R K; Whittam, T S (1999) Sequence diversity of flagellin (fliC) alleles in pathogenic Escherichia coli. J Bacteriol 181:153-60|