Susceptibility of preterm infants to sepsis

Antimicrobial defensePreterm infant compromised defenses
Epidermal and epithelial barriersImmature skin (3-6-cell stratum corneum and thin keratin layer)
Insensible water loss from skin and humidification systems, creating moist skin that favors the growth of microorganisms
Skin trauma from intensive care interventions
Adherence of Candida to exposed intermediate epithelial cells, favoring colonization
Enhanced adherence of Candida and GBS to buccal epithelial cells of preterm versus term infants, facilitating oral colonization
Invasive catheters and tubes
    Surface for colonization provided by intravascular catheters breaching intact epidermis
    Proliferation due to parenteral nutrition and biofilms on plastic catheters
    Colonization of endotracheal and nasogastric tubes
    Trauma from endotracheal, suctioning, and nasogastric tubes
Intact endothelial tissuesTrauma to endothelium and endocardium from central vascular catheters
Injury from hyperosmolar nutrition solutions and medications
Gastrointestinal mucosaDecreased acid production
Immature peristalsis and reduced absorption, favoring microorganism overgrowth
Thin mucin layer, leading to decreased barrier function and secretory IgA binding
Diminished number of intraepithelial lymphocytes
MicrofloraCompetitive bacterial microflora diminished by broad-spectrum antibiotics, favoring growth of resistant bacterial and fungal organisms
More commensal gram-positive organisms selected for by human milk
ComplementLower levels with decreasing gestational age
CytokinesDecreased production of IL-1, IL-8, gamma interferon, TNF-α, G-CSF, and GM-CSF
DefensinsDiminished with decreasing gestational age
NeutrophilsDecreased bone marrow storage pools and G-CSF levels
Immature neutrophil oxidative burst
Decreased numbers of azurophilic granules
Diminished granular contents (lactoferrin, defensins, lysozyme, myeloperoxidase, proteases, and cathepsin G)
Possible impairment of function by medications (steroids, H2 antagonists, lipid emulsions)
MonocytesDiminished number and function
Decreased adherence at sites of infection
Decreased opsonization and phagocytosis
Diminished gamma interferon, IL-3, and G-CSF release
T-cells, B-cells, and antibodiesDecreased numbers of lymphocytes in gastrointestinal tract
Majority of transfer of maternal IgGs after 32 weeks' gestation
Decreased production of antibodies by preterm lymphocytes