REVIEWThe intestinal bacterial colonisation in preterm infants: A review of the literature
Introduction
The gastrointestinal tract is one of the largest organs of the body serving as an important barrier between ingested elements from the external environment and the internal milieu of the body. In children and adults, the intestine is able to discriminate between pathogenic microorganisms and the commensal intestinal microflora.1 Moreover, it is able to select the beneficial nutrients from the ingested food. In the preterm infant, these functions are not completed yet.2, 3 The development of the intestinal microflora starts at birth and is influenced by various factors such as gestational age, mode of delivery, local environment, type of feeding, and antibiotic treatment.4, 5, 6, 7, 8 In breast-fed term infants, bifidobacteria become the predominant bacteria in the intestinal microflora, whereas in formula-fed term infants the intestinal microflora becomes more diverse with, apart from bifidobacteria, also bacteroides, clostridia, enterobacteria and streptococci.9, 10, 11 Therefore, therapies have focussed on the development of a bifidogenic intestinal flora, e.g. with prebiotics and probiotics. Although recent studies with prebiotics and probiotics show promising results, more studies are needed to determine the role of prebiotics and probiotics in preterm infants.12, 13, 14, 15, 16
Bacteria in the lumen of the intestine can be grouped according to their degree of pathogenicity.17 Three groups of bacteria can be recognised: (1) beneficial, (2) potentially pathogenic and (3) pathogenic bacteria. Beneficial effects are inhibition of growth of pathogenic bacteria, production of vitamins, degrading and fermentation of food ingredients, stimulation of feeding tolerance and stimulation of immune functions. Pathogenic effects of bacteria include feeding intolerance, inflammation, infections and especially in preterm infants this can lead to necrotising enterocolitis. Potentially pathogenic bacteria belong to the normal microflora of the intestine, but may become pathogenic if present in high numbers: enterobacteria, enterococci, Escheria coli, streptococci and bacteroides. Potentially pathogenic bacteria-like proteus, staphylococci, clostridia and klebsiella, may become pathogenic, even if present in low numbers.2, 17
Due to the immaturity of the gastrointestinal tract, bacteria may translocate to systemic organs and tissues and, in combination with immaturity of the immune system, increase the risk for systemic infections.18 Especially potentially pathogenic bacteria have the potention to translocate.19 An intestinal microflora of anaerobic bacteria-like bifidobacteria and lactobacilli favours protection, because it may suppress the growth of pathogenic bacteria.20, 21
Few studies have determined the developmental aspects of the intestinal bacterial colonisation of preterm infants. As preterm infants often require intensive care treatment with an increased risk for serious infections, insight in the development of the intestinal bacterial colonisation of (preterm) infants is important. In addition, the various potential factors influencing the intestinal bacterial colonisation of these infants need to be studied. It is not known whether prematurity itself may influence the intestinal bacterial colonisation, but preterm infants experience intensive care treatment in their first days of life and it is likely that this influences the intestinal bacterial colonisation. Preterm infants often need parenteral feeding, due to the immaturity of their intestine and they often need respiratory support, they are vulnerable for infections and often require antibiotic treatment.
Increasing insight in the development of the intestinal bacterial colonisation and the factors involved might help to establish conditions in order to alter a possibly pathogenic developmental microflora to that seen in healthy term infants. The aim of this study is to review the normal development of the intestinal microflora of preterm infants and the factors influencing its development.
Section snippets
Methods of literature review
A literature search was performed by a PubMed search from January 1970 till December 2005 using the following keywords and limits:
(Intestines[mesh] OR intestin* OR gut OR gastrointestin* OR enteric) and (flora OR microbiolog* OR microbiology[sh] OR microflora OR bacteria OR bacterial OR enterobacteria* OR colonisation OR colonisation OR microbes OR microbial) and (neonat* OR infant*) AND (premature OR preterm OR pre-term OR low birth weight OR low weight OR small for gestational age) and
Results of the literature search
With the initial search, 11 relevant publications were found.4, 6, 7, 8, 22, 23, 24, 25, 26, 27, 28
The selected studies were published between 1979 and 2003. Five studies were excluded from this review because of:
- 1.
Unclear description of sampling.8, 22
- 2.
Heterogeneity of the study population.6, 7
- 3.
Lack of data on the number of infants colonised with tested bacteria.27
Characteristics of included studies
Of the six selected studies, five studies used culturing techniques on selective media to perform the colonisation pattern. One study
Bifidobacteria
In five studies bifidobacteria were determined in the faeces.4, 24, 25, 26, 28 In two of three studies, bifidobacteria were not detected directly after birth.26, 28 In these two studies, bifidobacteria increased over time. In two studies, bifidobacteria were rarely found during the whole study period.4, 24 In only one study, high numbers of bifidobacteria were found also directly after birth.25 In conclusion, low numbers of bifidobacteria are found in faeces of preterm infants.
Lactobacilli
In five studies,
Discussion
Our review has shown that colonisation of bifidobacteria and lactobacillus is delayed in preterm infants, whereas colonisation with potentially pathogenic bacteria (especially E. coli) is increased. The type of feeding did not influence the bacterial colonisation in preterm infants, but the longer time to full enteral feeding may explain this finding.26
Early introduction of enteral feedings is thought to stimulate the intestine of preterm infants. This might maximise the immune functions of the
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