INFLUENCE OF SUBINHIBITORY LEVELS OF ANTIBIOTICS ON EXPRESSION OF ESCHERICHIA-COLI LIPOPOLYSACCHARIDE AND BINDING OF ANTILIPOPOLYSACCHARIDEMONOCLONAL-ANTIBODIES

The expression of Escherichia coli lipopolysaccharide (LPS) and the bi nding capacity of anti-LPS monoclonal antibodies (MAbs) to E. coli gro wn in the presence or absence of subinhibitory concentrations of vario us antibiotics was studied. Four E. coli strains (three clinical blood -culture isolates and an isogenic, non-capsulate mutant of the O18:K1 parent) were grown in the presence of the beta-lactam antibiotic, ampi cillin, the aminoglycoside gentamicin, the fluoroquinolone ciprofloxac in and chloramphenicol. The techniques of silver staining, immunoblott ing, whole-cell ELISA and flow cytometry were all used to monitor the expression of LPS on the bacteria and the binding of the anti-LPS MAbs . Treatment with ampicillin, chloramphenicol and ciprofloxacin resulte d in enhanced binding of anti-core reactive MAbs to most E. coli strai ns. Overall, treatment with gentamicin produced the least effect on MA b binding. The presence of chloramphenicol decreased the expression of high molecular mass O-antigen or increased the expression of low mole cular mass substituted E. coli LPS or both. These results further illu strate that LPS core, especially the inner-core region, becomes more a ccessible to antibodies when bacteria are grown in the presence of cer tain antibiotics. Possible synergy between antibodies and antibiotics for treatment of septicaemia and septic shock remains an intriguing po ssibility.