Investigation of the effect of β-lactam antibiotics and serum on growth and gene expression in Escherichia coli strain JJ1886

β-Lactamase-producing Escherichia coli strain JJ1886 is an epidemic clone with high virulence properties. Because this strain can survive in the bloodstream, we aimed here to understand how β-lactam antibiotics and human serum affect the growth and gene expression of this bacterium. We report the time-dependent growth effect of normal human serum and heat-inactivated serum, together with β-lactam antibiotics (including cefotaxime, ceftazidime, and carbenicillin), for E. coli strain JJ1886. Relative gene expression of β-lactamase-related genes (encoding the β-lactamase regulator, CTX-M-15, and peptidoglycan glycosyltransferase) and serum survival- associated genes (encoding lipoprotein NlpI, murein lipoprotein, lipopolysaccharide core heptose (I) kinase, lipopolysaccharide biosynthesis protein, capsule synthesis protein, and phosphate transport system) were investigated by RT-qPCR. Cells proliferated during the exponential growth phase when the bacterium was treated with human serum. However, cefotaxime and ceftazidime together with serum had a bactericidal effect at each of the tested time points. Downregulation was observed in gene-encoding lipoprotein NlpI as a result of treatment with carbenicillin. Serum plus cefotaxime or ceftazidime had bactericidal activities. When the bacterium was treated with human serum and β-lactam antibiotics, there were no significant changes in relative gene expression, except for the nlpI gene.