Group B streptococcal infections in neonates : Clinical and pathogenic aspects

Abstract: Clinical and pathogenic aspects of Group B streptococci (GBS), as a major pathogen responsible of invasive disease in newborn infants, were investigated.Cases of neonatal septicaemia during 1981-1994 were studied at Orebro Medical Centre Hospital. 132 children ful1filled laboratory and clinical criteria for neonatal septicaemia. The annual incidence increased significantly, from 2.3 cases during the first 7-year period to 3.3 per 1000 live births during the second 7-year period. The increase in incidence between the two 7- year periods was almost entirely due to an increase in Staphylococcus aureus ( from 9 to 32, p<O.Ol) and coagulase-negative staphylococci (CoNS) (from 7 to 20, p<0.05) and mainly affected preterm neonates 48h or more after delivery while GBS infection usually occurred in full-term children during the first 48h of life. An increased resistance among CoNS to methicillin and gentamicin was observed between the first and second 7-year period.To study the ability of GBS to adhere to the target cell, a cell-culture model with human umbilical vein endothelial cells (HUVEC) was used. Clinical isolates of serotype Ill adhered significantly (p=O.OOOl) better than other serotypes. Isogenic variants of serotype Ill with low amounts of capsule substance adhered significantly (p=O.OOl) better to the HUVEC than variants expressing high amount of capsule substance. The role of GBS capsular substance as a major virulence factor is further underlined by the fact that it impair the phagocytic capacity by polymorphonuclear leukocytes (PMNL). Growth conditions for GBS, simulating different in vivo environments, greatly affect capsule expression.The extent of and the penetration route of GBS over epithelial linings was examined with a model using Madin Darby Canine Kidney cells (MDCK). It was demonstrated that GBS can penetrate intact polarized MDCK cells by transcytosis in a selective apical-to-basolateral direction and the mechanism for this is metabolically dependent.In a chemiluminescence assay (CL), PlviNL function and opsonic capacity were shown to be significantly impaired in neonates and correlate to maturation of the newborn child. This combined defect in cellular and humoral defences may contribute to the increased susceptibility to GBS infection in preterm infants.In a prospective study in newborn having suspected sepsis, IL-6 and C-reactive protein (CRP) were measured early. Early-sampled IL-6 levels were significantly better than early-sampled CRP levels in distinguishing between mild respiratory disorders and septicaemia in the newbom child.