Escherichia coli capsular polysaccharide synthesis, antibiotic susceptibility, and red blood cell agglutination

Background: Escherichia coli is a normal component of the human intestinal flora, but it is also a pathogen particularly in women with urinary tract infections, cystitis, and kidney diseases. A new capsular polysaccharide (CPS)-synthesizing variant strain of E.coli was isolated from a culturing bacterial medium containing proteose peptone No. 3 glycerin salt in our previous study. In this study, we further isolated a new E.coli variant, which produces capsular polysaccharides (CEF-CPS), using cefazolin (CEF) and examined the pathogenic characteristics of this CEF-CPS strain. Methods: Polysaccharides produced by CEF-treated E.coli were separated and purified using anion exchange resin and gel filtration column chromatographic methods. The red blood cell (RBC) agglutination assay and antibiotic susceptibility test were conducted, and serum bactericidal activity, antibiotic tolerance, and antibiotic uptake were also examined. Results: (1) Variant strains had greater RBC hemagglutination ability than parental strains. (2) The CEF-CPS variant strain showed a two-fold increase compared to the parental strain. (3) Antibiotic resistance to CEF, ampicillin, and polymyxin B was increased four-fold in the CEF-CPS variant strain. (4) Bacterial cell counts in the parental strain incubated in a medium containing gentamicin were reduced significantly, near to the undetectable level, within 4 hours. By contrast, bacterial counts of the CEF-CPS strain displayed only 50% reduction compared to the original bacterial counts under the same culture environment. Conclusion: E.coli derived from normal human intestinal flora generated a new variant strain along with the production of newly synthesized additional polysaccharides on the cell wall in the presence of CEF. Their productions can contribute to enhancing multiple-drug resistance and pathogenicity.