Effect of CSF on bacterial growth.

The growth patterns of five potentially pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, group B beta-hemolytic streptococcus, and Klebsiella pneumoniae) and a commonly encountered, nonpathogenic microorganism (S epidermidis) were compared using CSF, trypticase soy broth (TSB), and a phosphate buffer. Each grew less in CSF than in TSB. Escherichia coli was least affected with a median difference of 2 logarithms between CSF and TSB at 24 hours of growth, whereas S epidermidis was markedly inhibited, with a median difference of 6.85 logarithms. The differences among the remaining four organisms ranged from 3.86 to 5.94 logarithms, all significantly greater than that for E. coli. Similar results were obtained at 48 hours of growth. The non-support of bacterial growth by CSF may constitute a host defense mechanism. The basis of these observations may be the presence of inhibitors or the absence of nutrients required for bacterial growth in the CSF.