Increased total CSF
lactate is an important
indicator differentiating bacterial from
aseptic meningitis. Bacteria can produce D- and L-
lactate; mammalian cells produce only L-
lactate. We measured D- and L-
lactate production of Streptococcus pneumoniae, Staphylococcus aureus, Neisseria meningitidis and Escherichia coli in vitro, of S. pneumoniae and E. coli in rabbit experimental
meningitis and of various common pathogens in CSF from patients with
bacterial meningitis. Despite marked in vitro production of D-
lactate by S. aureus (maximum: 4.59 mmol/l; i.e. 34.9% of total
lactate), N. meningitidis (4.62 mmol/l; i.e. 98.1%) and E. coli (3.14 mmol/l; i.e. 97.2%), minimal amounts were measured in human S. aureus (0.38 mmol/l; i.e. 1.3% of total
lactate) or N. meningitidis (0.28 mmol/l; i.e. 3.9%) and experimental E. coli
meningitis (0.75 mmol/l; i.e. 4.4%). In only 9 of 54 human CSF samples did D-
lactate exceed 0.15 mmol/l. S. pneumoniae did not produce significant amounts of D-
lactate in vitro (maximum: 0.55 mmol/l; i.e. 2.7% of total
lactate), in experimental
meningitis (0.18 mmol/l; i.e. 3%) or in human cases of
meningitis (0.28 mmol/l; i.e. 1.9%). In conclusion, increased total CSF
lactate in
meningitis consists mainly of L-
lactate and originates predominantly from host cells. CSF D-
lactate is of limited diagnostic value.