Mutations in the periplasmic chaperone leading to loss of surface expression of the colonization factor CS6 in enterotoxigenic Escherichia coli (ETEC) clinical isolates.
Enterotoxigenic Escherichia coli (ETEC) cause diarrhoea by adhesion to human enterocytes by one or more colonization factors (CFs) and secretion of heat-labile (LT) and/or heat-stable (ST) enterotoxins. Expression of coli surface antigen 6 (CS6) on the bacterial surface, usually associated with ETEC strains that produce ST alone or in combination with LT, is rarely found in strains expressing only LT. However, a number of LT-only strains which are genotypically positive but phenotypically negative for CS6 have been identified. In this study, eight such strains from India and Guinea-Bissau belonging to different clones were analysed. The CS6 operon cssABCD was transcribed but protein analyses suggested that the structural subunits CssA and CssB of CS6 were absent in the periplasm. Most strains contained truncating mutations within the periplasmic chaperone-encoding gene cssC and protein modelling indicated that this severely affected the substrate-binding capacity of the chaperone. A single-nucleotide polymorphism (SNP) (A-->T) in the 5'-untranslated region of cssC distinguished the eight strains from ETEC strains that do express CS6 on the surface and may be a potential marker for ETEC strains containing phenotypically silent cssABCD. The study emphasizes the importance of using both genotypic and phenotypic methods in epidemiological studies of ETEC, e.g. for vaccine development.
Nicklasson
Matilda
M
Department of Microbiology and Immunology, Institute of Biomedicine, Göteborg University, P.O. Box 435, 405 30 Göteborg, Sweden. matilda.nicklasson@microbio.gu.se
Sjöling
Asa
A
Lebens
Michael
M
Tobias
Joshua
J
Janzon
Anders
A
Brive
Lars
L
Svennerholm
Ann-Mari
AM
D000942:Antigens, Bacterial / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D054307:Enterotoxigenic Escherichia coli / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004768:Enterotoxins; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D009876:Operon; D033903:Periplasmic Proteins / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide
D000942:Antigens, Bacterial; C098406:CS6 antigen, E coli; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D033903:Periplasmic Proteins