Gut bacterial activity in a cohort of preterm infants in health and disease

Beattie, Lynne Mary (2014) Gut bacterial activity in a cohort of preterm infants in health and disease. MD thesis, University of Glasgow.

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Randomised controlled trials administering probiotic supplements to preterm infants to prevent sepsis and necrotising enterocolitis are already underway, despite the lack of a robust evidence base of normative values for gut microbiota, bacterial metabolites, and markers of inflammation and immunity. There are increasing calls for observational studies to establish baseline data in these infants. Most of these studies to date have involved the measurement of these analytes individually. In the studies presented in this thesis, we measured a range of stool markers collectively in a cohort of preterm infants in health and disease.

56 infants at <32 week gestation and less than 1500g birth weight were sequentially recruited from all three Glasgow Neonatal Units within week one of life after commencement of enteral feeds. Anthropometric, dietary and treatment data were collected. Stool samples were taken once weekly for the first four weeks, testing: short chain fatty acids; calprotectin, secretory immunoglobulin A; and microbial diversity by temporal temperature gel electrophoresis.

Out of 61 live births meeting the study criteria, 56 infants were enrolled in the study, 62.5% of whom were female. 19.6% were between 24-26 weeks gestation, 28% were 26-28 weeks, 30% were 28-30 weeks, and 21% were 30-32 weeks. 5.3% were between 490-600g in birth weight, 17.8% were 600-800g, 21.4% were 801-1000g, 39.2% 1001-1250g, and 16% were between 1251-1500g. Feed regimen was heterogeneous, comprising 5 combinations of maternal, donor and formula milks. The highest social deprivation level as measured by the Carlisle ‘Depcat’ scoring system of level 7 was significantly higher in the study group than Glasgow or Scotland-wide averages. Sepsis rates were low, with a group median of only 1 per infant. Overall mortality: 7%. 32 with any NEC (56%), 20 with Bells’ ≥2a NEC. 8 (14%) with surgically treated NEC, 5 (8%) underwent ileostomy. SCFAs: (n=56) there were no correlations between gestation, weekly totals, feed type, or NEC and SCFA concentration. Acetate and lactate dominated each sample. Few significant changes were noted with respect to NEC, and these were in the less dominant SCFAs: stage 2a NEC showed higher concentrations of propionate in week 4 than week 3, and lower valerate in week 4 than 2. Stage 3b levels of isobutyrate and heptanoate were significantly lower in week 4 than 3. FC: (n=56) there were no significant differences in FC levels between each week in infants with or without NEC, although the former illustrated a trend to lower levels by week 4. There were no significant differences in NEC before and after clinical signs were apparent, or in those before NEC and after stoma formation for stage 3b NEC. However, significantly lower FC levels were noted in stage 3b NEC requiring ileostomy compared to the immediate pre-operative sample. SIgA: (n=34) Levels rose significantly week on week, and were considerably higher in weeks three and four than week one. There were no significant differences in stool SIgA concentration between infants with and without NEC. A significant increase in mean stool SIgA concentration appeared from week 2 to week 3 in NEC infants, and from week 1 to week 2 for those without. For all breastfed preterm neonates (n=6), the level of milk SIgA was significant higher on week 1 (colostrum) than week 2 and week 3. TTGE: (n=22) There was large variability between number (1-17) and species diversity (25-36 different species). Bacterial composition varied largely between the 2 sample points. No difference in species richness or similarity within the 2 feeding groups was observed. 4 bands were identified in >50% of infants. Intra-individual similarity varied greatly and ranged from a similarity index (Cs) of 0% to 66.8%. There was no statistical difference between the similarity indices of the feeding groups or between those with and without NEC. There were no significant correlations between any of the analytes.

Only extreme prematurity and extremely low birth weight were associated with NEC, which was at a strikingly high incidence. A limitation was therefore the unexpected onset of severe NEC resulting in prolonged paralytic ileus with low stool production. No correlations were found between analytes, indicating that each set of stool investigations may signify independent physiological, biochemical and immunological gut processes. Despite the severity of NEC, the levels of each analyte were remarkably consistent. High levels of deprivation within the study population may provide the constellation for an as of yet undefined genetic and epigenetic predisposition to NEC in this cohort, similar to that of other illnesses endemic to different geographical areas – notably Multiple Sclerosis in the North East of Scotland – and both follow up of these infants into childhood as well as further analysis of future inborn infants with NEC is planned.

Item Type: Thesis (MD)
Qualification Level: Doctoral
Keywords: preterm; necrotising enterocolitis; gut microbiota; gut metabolites.
Subjects: R Medicine > RJ Pediatrics > RJ101 Child Health. Child health services
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
Supervisor's Name: Edwards, Professor Christine A., Morrison, Dr. Douglas and Simpson, Dr. Judith H.
Date of Award: 2014
Depositing User: Dr Lynne M Beattie
Unique ID: glathesis:2014-5312
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 18 Nov 2014 14:18
Last Modified: 02 May 2018 14:34

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