The capsular polysaccharide is a major determinant of serum resistance in K-1-positive blood culture isolates of Escherichia coli.
Serum resistance is a major virulence factor of gram-negative bacteria, and K-1 polysaccharide has been shown to contribute to serum resistance in selected strains. To obtain further information about the role of K-1 in serum resistance and to find out whether loss of the ability to produce K-1 can induce loss of serum resistance, we studied the serum resistance of mutants derived from completely serum-resistant, K-1-positive blood culture isolates of Escherichia coli by selection for resistance to infection with K-1 specific bacteriophages. The amounts of K-1 polysaccharide produced by wild-type strains and mutants were measured, and outer membrane protein and lipopolysaccharide (LPS) patterns were analyzed. In each group of mutants, several highly serum-sensitive strains were found. All mutant strains expressed less K-1 than did the corresponding wild-type strains. Mutants that became highly serum sensitive always had less K-1 than did mutants with less-pronounced changes of serum resistance. A few mutants derived from different wild-type strains showed increased expression of outer membrane proteins with molecular weights of about 46,000 and 67,000. All of the wild-type strains examined had smooth-type LPS, and only two mutants had altered LPS structures; alterations of mutants in outer membrane proteins and LPS could not be correlated with alterations of serum resistance. The results indicate that for K-1-positive blood culture strains of E. coli, K-1 expression is a prerequisite for serum resistance, and loss of ability to synthesize K-1 leads to loss of serum resistance.
Abteilung für Medizinische Mikrobiologie und Immunologie, Ruhr-Universität Bochum, Federal Republic of Germany.
H
H
Leying
S
S
Suerbaum
H P
HP
Kroll
D
D
Stahl
W
W
Opferkuch
D000942:Antigens, Bacterial / Q000276:immunology*; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis; D001770:Blood Bactericidal Activity; D015180:Electrophoresis, Gel, Two-Dimensional; D004926:Escherichia coli / Q000276:immunology*; D008070:Lipopolysaccharides / Q000032:analysis; D008970:Molecular Weight; D011135:Polysaccharides, Bacterial / Q000276:immunology*
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D008070:Lipopolysaccharides; D011135:Polysaccharides, Bacterial