Amniotic fluid antibacterial mechanisms: newer concepts.

In this review the factors present in human amniotic fluid that may function to inhibit bacterial growth have been examined. It appears that several potential antibacterial systems are present. Lysozyme and B-lysin may significantly contribute to the killing of gram-positive bacteria. Whether or not the remaining antibacterial systems function to inhibit gram-positive organisms remains to be determined. The phosphate-sensitive bacterial inhibitor recently described in our laboratory may represent the primary defense mechanism against gram-negative bacteria in amniotic fluid. Studies are warranted to ascertain whether this antibacterial system also inhibits gram-positive bacteria. The phosphate-sensitive bacterial inhibitor is quite different from other bacterial inhibitors in at least three respects. The system is very sensitive to the ubiquitous phosphate anion. The reason for this sensitivity is unknown and is difficult to explain phylogenetically, since phosphates are present virtually everywhere. To our knowledge this is the first antibacterial system of human origin which has been shown to require a metal cation as an integral part of the bactericidal effect. The peptide component of the phosphate-sensitive bacterial inhibitor is also unique in that it is of the molecular size of antibiotics or hormones. Additionally, the peptide does not appear to contain any unusual amino acids to explain its antibacterial activity. The mechanism of bacterial destruction of the phosphate-sensitive bacterial inhibitor, and its relation to the other antibacterial systems in amniotic fluid, remain to be elucidated.