Antimicrobial Components of the Neonatal Gut Affected Upon Colonization

Abstract

Antimicrobial peptides (AMP) produced throughout our body are important effectors in the defense barrier of innate immunity. Here, we have analyzed antimicrobial activity and polypeptide composition of meconium versus neonatal feces to address the development of antimicrobial defense of the neonatal gut. Extracts of meconium exhibited antimicrobial activity against Bacillus megaterium, Escherichia coli, and group B streptococci (GBS) but not against the yeast Candida albicans. Extracts of neonatal feces were found to possess low activity against E. coli, GBS, and C. albicans. However, the anti-B. megaterium activity was higher in the fecal extracts than in meconium. All activities were reduced or abolished when salt was added to the antimicrobial assay. The AMP cathelicidin LL-37, ␣-defensin HNP-1-2, ␣-defensin HD 5, and lysozyme were identified in both meconium and fecal extracts. In addition, HNP-3 and a fragment of azurocidin were found in meconium, whereas the holoprotein azurocidin was detected in feces. In meconium, histones H2A and H4 were isolated and identified by their antimicrobial activity. Notably, LL-37 and lysozyme were found at significantly higher levels in feces than in meconium. Our findings reveal that meconium and feces contain AMP, acting in the defense of the neonatal gut, and may be implicated in the control of the initial colonization. M econium is a sterile mucilaginous material that accumulates in the fetal intestine and is expelled soon after birth. It contains secretions of intestinal glands, gut constituents (proteins, bile acids, fatty acids, and steroids), and components of amniotic fluid and vernix caseosa (1). In addition, meconium has been reported to contain proinflammatory substances, including IL-1␤, IL-6, and IL-8, compounds that are able to induce immune responses such as activation of lymphocytes and chemotaxis of neutrophils (2,3). The first microbes to colonize the intestines of newborn babies are the aerobic bacteria Escherichia coli and Streptococci. Later, the gut is colonized with anaerobic bacteria, e.g. Bacteroides, Bifidobacteria, and Clostridia. In 1-2 y, the gastrointestinal tract of infants has developed a natural microflora, which resembles the microflora of adults (4).Despite the fact that newborns have a naive adaptive immune system, infections rarely occur, indicating strong innate defense mechanisms. Several AMP have been characterized in vernix and skin of the newborn, indicating a well-developed innate immune system, which may play a pivotal role at the time of postnatal colonization. AMP are important effectors of innate immunity with the ability to kill a wide range of microbes (5). The defensins and cathelicidins are the two main families of human AMP (6,7). They are expressed at epithelial linings, i.e. the adult human gastrointestinal tract, where they are either constitutively expressed or up-regulated by bacterial factors/ products such as lipopolysaccharides and butyrate (8 -11).In the alimentary tract, polypeptides with bactericidal a...

Specificity in Killing Pathogens Is Mediated by Distinct Repertoires of Human Neutrophil Peptides

“…The contribution of histones to this activity was supported by our MIC assay on histone sulfate, which exhibited activity predominantly against M. catarrhalis and C. albicans ( table 2 ). Thus, our results support previous work on histones [25] and are in line with the emerging concept that histones function as true AMPs [23] . In fact, several histones have been found in NETs, where they contribute to bacterial and fungal killing together with other AMPs [28,29] .…”

“…The presence of histones in several fractions with antimicrobial activity against C. albicans and M. catarrhalis and previous indications of antimicrobial activity of histones [23][24][25] led us to investigate the functional role of histones as antimicrobial proteins. Thus, histone sulfate (containing H1, H2A, H2B, H3 and H4 of bovine origin) was evaluated against the 4 test microbes.…”

Murine Models of Candida Gastrointestinal Colonization and Dissemination

“…For instance, in mice, small intestinal crypts, a source of many AMPs, develop 10 to 12 days after birth, and this is accompanied by increased epithelial cell renewal (48). Of note, changes in the composition of antimicrobial peptides and in antimicrobial activity have also been noted in the intestinal lumen of human neonates (49).…”

Differential antimicrobial peptide gene expression patterns during early chicken embryological development

“…cathelicidins in the tracheal aspirates of newborn children [12] and in human meconium [13] are thought to contribute to initial microbial colonisation and the development o ntestinal homeostasis after birth [14] . Furthermore, expression of the cathelicidin gene ( CRAMP -shown to be 10-100 fold greater in neonatal mice than in the adult), is thought to provide an important compensatory neonatal innate immune defence mechanism [15] .…”