Susceptibility of Gram-negative bacteria to β-lactam antibiotics and rapid characterization of β-lactamase activity

Various species of Gram-negative bacteria were tested for susceptibility to β-lactam antibiotics and for production of β-lactamase. The rapid cephalosporin 87/312 visual test was more sensitive than either the acidometric or the iodometric test; the iodometric test was least sensitive. Characteristic β-lactamase hydrolysis product patterns were obtained by scanning mixtures of β-lactamase-producing bacteria and cephalosporin substrates. β-Lactamase could not be detected on bacterial cells by fluorescent antibody techniques. The presence of β-lactamase can be correlated with minimal inhibitory concentrations of β-lactam antibiotics only in certain Gram-negative bacilli.