Abstract
Neonatal necrotising enterocolitis (NEC) is one of the most devastating diseases affecting new born premature infants [5]. Globally it affects 1-5% of all neonatal intensive care admissions and is a leading cause of neonatal morbidity and mortality. The aetiology of NEC is not entirely understood, although it is clearly a multifactorial disease involving: bacterial colonisation of the neonatal gastrointestinal tract, immune system function and immaturity of the infant. Recent practice in neonatal units has moved focus from treatment to prevention of NEC before onset of disease. Supplementation of probiotic bacteria has been identified as a protective treatment and clinical trials have identified probiotics that reduce the incidence and severity of NEC.
The commercial probiotic formulation Infloran, containing Lactobacillus acidophilus and Bifidobacterium longum ss. infantis that is currently in use in the Dunedin public hospital neonatal intensive care unit, for infants of birth low weight (< 1,500 g). In this project, the Infloran probiotics inhibited the growth of four NEC-associated strains: Cronobacter sakazakii 50, Cronobacter sakazakii 2029, Enterobacter cloacae and Klebsiella pneumoniae ss. oxytoca in vivo. Inhibition was observed in solid media and probiotic conditioned media assays where the Infloran probiotics were able to completely inhibit the growth of the NEC-associated strains, putatively by lowering the pH (~4). In vitro attachment assays on an intestinal cell line (HT-29) identified localised and diffuse adherence patterns of the NEC-associated strains. When in co-culture with the Infloran probiotics, the attachment pattern changed to an aggregative adherence pattern. This aggregative pattern was observed, regardless of the NEC-associated strain or control strain used. An In-vitro neonatal model of the intestinal lumen was created using an anaerobic atmosphere and neonatal milk formula. This neonatal formula, pre-incubated with Infloran, was able inhibit the growth of the NEC-associated strains. A larger inhibitory effect was observed with longer pre-incubation of the Infloran probiotics.
In conclusion, this project has identified mechanisms: pH modulation, co-aggregation and substrate utilisation by which Infloran exerts its protective effect on pre-term neonates at risk of NEC.