Perinatal listeriosis. Tolerance of a clinical isolate of Listeria monocytogenes for ampicillin and resistance against cefotaxime.

A strain of Listeria monocytogenes isolated from a case of early onset, generalized, fatal, perinatal listeriosis in a premature infant was found to be tolerant for ampicillin and resistant against cefotaxime. A laboratory control strain of L. monocytogenes and Staphylococcus aureus control strain ATCC 25923 proved tolerant for both beta-lactam antibiotics, respectively. The combinations of ampicillin with gentamicin and cefotaxime with gentamicin resulted in additive bactericidal activity against both strains of L. monocytogenes. Based on these findings and those of the literature, it is suggested that cases of systemic listeriosis be treated with a combination of a beta-lactam antibiotic, preferably ampicillin, with an appropriate aminoglycoside, such as gentamicin.