Читать книгу Genetic Disorders and the Fetus - Группа авторов - Страница 111

A number of studies have supported the original contention of antibacterial activity by demonstrating that AF contains a substance that suppresses or inhibits bacterial growth.^{391, 392} The first suggestion was lysozyme, an ubiquitous enzyme with lytic properties found in many tissues and secretions.³⁹³ Subsequent studies have suggested that zinc is an important component.^{312, 394} The antibacterial activity of zinc in AF seems to depend on a second, organic, component, which is heat stable and resists proteolytic digestion.²⁶¹ AF contains a potent antimicrobial peptide (β‐defensin‐2), the concentration of which is increased in patients with microbial infection in the amniotic cavity.³⁹⁵ Phosphate seems to reverse the AF inhibitory activity, possibly by interfering with the organic component rather than with the inorganic zinc.^{261, 354} The antimicrobial effect and bacteriolytic activity of AF have been studied on several strains.^{223, 396} Both lysozyme and β‐lysin (a bactericidal substance) have been identified as early as the second trimester. Normal bacteriolytic activities have been found in pregnancies in which respiratory distress syndrome developed in the infants. On the other hand, lack of an antimicrobial effect of AF on anaerobic bacteria may be one reason for the high incidence of spontaneous abortions in those conditions. Several findings suggest that β₂‐ microglobulin exhibits strong antibacterial activity and is upregulated in amniotic cells during bacterial infection.³⁹⁷

Other workershave concluded that AF inhibits Staphylococcus aureus throughout pregnancy, whereas clear inhibition of Escherichia coli and Streptococcus agalactiae appears during the third trimester.²⁶³ It is important to note the ineffectiveness of AF against group B streptococci, the frequently documented cases of congenital infections, and the early deleterious effects of Bacteroides fragilis, especially in the first trimester.³⁹⁸

The effect of AF on bacterial growth also has been stressed by Ismail et al.³⁹⁹ while Martius and Eschenbach⁴⁰⁰ reviewed the literature on bacteria as a cause of amnionitis associated with premature labor. Bacterial proteases and lipases could play a role in weakening fetal membranes and a genetic predisposition may have a role.

An inhibitory effect on HIV replication has been observed, and attributed at least in part to the cell‐free protein fraction of AF.⁴⁰¹