Enhanced binding of murine monoclonal antibodies to lipopolysaccharide structures of Enterobacteriaceae after treatment with antibiotics

Four strains of E. coli, two encapsulated and two unencapsulated, were grown in the presence or absence of the β-lactam antibiotics aztreonam, ceftazidime and ceftriaxone, the fluoroquinolone ciprofloxacin, and the aminoglycoside netilmicin. Treatment of the unencapsulated strains with β-lactams and ciprofloxacin resulted in enhanced binding of murine Mabs (all:IgM) directed to rough lipopolysaccharide structures in ELISA. However, binding of these Mabs to antibiotic treated E. coli 07K1 (bearing a thin capsule) was only slightly increased, and was unchanged in E. coli 08K49 (surrounded by a thick capsule). Treatment of bacteria with netilmicin did not result in differences in binding of these monoclonal antibodies. These results show that the inner parts of the lipopolysaccharide become more accessible to antibodies when, especially unencapsulated, bacteria are grown in the presence of certain antibiotics.