Hygiene Aspects of Premature Nutrition

*Matthias Fischer and Anja Buschulte*

### **Abstract**

The very low birth weight and the not fully developed immune system make preterm infants especially susceptible to infections. Therefore microbiological food safety of preterm nutrition is a particular challenge. This is also due to the fact that breastfeeding is often not possible in these infants. There are several obstacles to breastfeeding, such as intensive care conditions and individual nutritional requirements of the newborn. The chapter covers the microbiological aspects of preterm nutrition, including quality requirements for commercial infant formulas, breastmilk fortifiers and extracted breast milk. The main pathogens of concern (e.g. *Cronobacter* spp. *Salmonella* spp. and *Clostridium botulinum*) are discussed in detail, including related food safety indicators. An important part of the chapter is devoted to the hygienic aspects of preterm formula preparation techniques, storage conditions and microbiological risks linked to certain feeding techniques (e.g. tube feeding). The risks associated with microorganisms found in commercial infant formula and in the prepared environment, as well as the risk of biofilm formation, are described. Options and requirements for risk mitigation are discussed in detail.

**Keywords:** hygiene, food safety, *Cronobacter* spp., premature nutrition, microbiological contaminants

### **1. Introduction**

The very low birth weight and the not fully developed immune system make preterm infants especially susceptible to infections. The development stage of the organ systems depends stringently on the gestation age of the newborn. This concerns also the intestinal tract and the immune system. Both are especially important for the resilience of infants to gastrointestinal infections. Regarding the intestinal tract, different aspects have a crucial influence on the immune defence. One critical aspect is that in mammals antibodies cannot pass the placenta. The newborn receives the first antibodies with the first milk of the mother, which is especially immunoglobulin enriched. Under circumstances of a mature digestion, proteins of the size of an immunoglobulin (150 to 1 Mio kDa) cannot pass the intestinal wall to enter the bloodstream. Therefore, the gut of mammals shows a different anatomy during their first days of life than the gut of adult individuals. The tight junctions seal usually the gaps between the enterocytes. These seals are quite open for the first three to four days of life to enable the antibodies of the colostrum to pass into the bloodstream.

Although this is not necessary for human neonates, the mechanism is still observed phylogenetically and is even more pronounced in preterm infants. These open tight junctions provide an option for microorganisms and toxins like endotoxins to enter the bloodstream unhindered [1, 2].

Unlike the offspring of other mammals, immune globulins of primate species can pass the placenta and are present in the bloodstream of infants immediately after birth. This has the advantage that the colostrum in humans is not an absolute requirement for the survival of the newborn. However, the antibody-enriched colostrum also provides human infants with humoral protection against intestinal infections during the first days of life. In premature births, the breastmilk is often not available or does not meet the nutritional requirements of the preterm infant and definitely does not provide the quality of a fully developed colostrum [1, 2].

The virulence of microorganisms depends on the ability to overcome the nonspecific and specific immune barriers of the host organisms, followed by the effect of specific pathogen factors, like toxins, on the target organ system or tissue. As explained before the specific and non-specific immune defences in very young infants are underdeveloped and weak. The lack of humoral immune protection is compounded by the underdeveloped acid barrier in the stomach of young children. This means pathogenic microorganisms can reach the small intestine, from where they can enter the blood system without passing the usual barriers. Thus, even bacteria with low virulence can cause significant harm to these premature organisms [1, 3].

The intestinal flora is competitive against pathogens that have reached the intestine, which provides an additional protection against gastrointestinal infections. Young children still need to develop their body flora including the gut flora. Their gut flora is not stable in the perinatal period [1]. Until now, it was assumed that the body of the newborn is sterile and that only during birth the first bacteria will colonise the skin and the enteral tract. For some years now, it has been discussed whether the fetus already comes into contact with microorganisms intrauterine [1, 4]. In any case, birth itself plays a decisive role in the colonisation of the body of the infant, as bacteria from the mother are transmitted intensively to the baby during the birth procedure [1]. Preterm infants are often not born in the natural way but by caesarean section. This way of birth already shows a retarded and different type of intestinal colonisation in term infants and is even more critical in preterm infants with regard to the formation of the intestinal microbiome.

The low birth weight and the awkward ratio of body surface to body weight make neonates more susceptible to toxin effects and low infection doses of microorganisms [5]. Moreover, the metabolic functionality in preterm infants is often not fully developed, which influences the neutralisation, turn over and excretion of bacterial toxins [6].

These special conditions meet the specific nutritional requirements of the preterm infants, often requiring individual formulas. In many cases, breastfeeding is not possible or has to be provided with extracted milk fortified with certain ingredients, and even the application of feeding tubes is also a regularly applied praxis. This requires specific hygiene precautions in the preparation, storage and application of food for preterm babies.

### **2. Types of preterm feedings**

There are different types of formula designed for preterm infants. However, the most preferable option is the feeding of breastmilk. Due to the shortened gestation

#### *Hygiene Aspects of Premature Nutrition DOI: http://dx.doi.org/10.5772/intechopen.107861*

period, the breastmilk of the mothers alone is often not sufficient for the nutritional needs of the preterm child and certain supplements (breast milk fortifiers, thickeners) have to be added [1]. The addition of powdered breastmilk fortifiers to the liquid milk bears significant hygiene risks. The breastmilk fortifiers are not sterile but have similar microbiological properties as powdered formula. The feeding practices of breastmilk to preterm infants is another hygiene issue. Direct breastfeeding is usually not possible for these patients, so milk is applied by tube feeding, syringes or baby bottles. The extraction and storage of the breastmilk pose several hygiene risks, with the addition of fortifier being only one of many other contamination sources.

In many cases, breastmilk is not available or specific nutritional needs require the use of infant formula products. From a hygiene point of view, the use of sterilised readyto-feed formula is the most recommendable option. If used as a sole source of nutrition, the contamination risks during handling and feeding are minimised. The sterilisation process guarantees the inactivation of all infectious microorganisms including spore-forming bacteria and viruses. However, the bacterial debris of these inactivated microorganisms is still in the formula but the amount is very low due to the advanced hygiene standard during the manufacturing process. A quality parameter for this kind of formula is the level of endotoxin. Endotoxins are lipopolysaccharides, which can be found as part of the cell wall of gram-negative bacteria. The group of gram-negatives includes *Enterobacteriaceae*, but also the non-fermenters, which are often detected as water bacteria in process water. Endotoxins in food are usually not an issue, as the transfer from the gut into the bloodstream is very limited. The tight junctions between the enterocytes seal the enteron very effectively, and the small amount of endotoxins, which still pass the intestinal wall, are efficiently neutralised in the liver. In young infants and especially in preterm infants, the situation is different. On one hand, the tight junctions are still open as explained earlier and on the other hand, the detoxification ability of the liver is not fully developed. If the level of endotoxins in the formula is too high, these lipopolysaccharides can enter the bloodstream. Monocytes would recognise them and start a cytokine-mediated immune response. These endotoxin levels can cause symptoms from mild sub-clinical disorders to febrile temperature. As the health status of preterm infants is quite fragile in many cases, the endotoxin-related burden is an additional factor that could influence the development of the newborn.

Powdered formula for preterm infants is available in a range of formats to meet the broad variety of the nutritional needs of prematurely born babies. Basically, the conventional starter formulas are also applicable for preterm infants. However, based on their gestational development stage, the responsible medical staff has to decide about the requirement of individually tailored diets. A variety of vitamin, mineral protein and calorie enriched formulas and fortifiers are available on the market to meet the individual nutritional needs of preterm infants. In some cases, the underdeveloped gastrointestinal tract of the baby is not able to break down proteins and carbohydrates, so the infant has to be supplied with free amino acids. In many cases, reflux might be a problem, which requires the addition of thickeners to the diet. These products are often combined or added to breastmilk or ready-to-feed formula.

Powdered infant formula is manufactured under the highest hygiene standards but is not sterile. The microbiological burden of the powder is usually low, but the reconstituted formula is an optimal growth medium where bacteria can multiply rapidly. The powdered formula differs from conventional milk powder in its composition. From a microbiological point of view, the elevated fat content is most important, because it protects bacteria in the dry environment and promotes the biofilm formation on contact surfaces. The powdered formula is produced in several steps based

on milk ingredients like skim milk powder and whey protein concentrate. These ingredients have been spray dried and are usually delivered as bulk products to the baby food manufacturer. The spray drying process is conducted in a counter flow of falling droplets against a hot air stream of more than 70°C. However, the bacteria in the droplets are protected against high temperatures due to the evaporative cooling. Therefore, spray drying is not a sufficient heat treatment to kill off microorganisms. These bulk ingredients are mixed with a range of specific nutrients like minerals, vitamins and lipids. The dosing of the especially important micro-ingredients is often done manually and bears a certain risk of contamination from the operating staff. Fat blends are often stored at higher temperatures, which make the survival of vegetative bacteria impossible, but the introduction of bacteria spores can be linked to this type of ingredient. The blending and packing operation of the baby powder is usually a fully automated step, nevertheless, contamination risks are not fully excluded. There are a number of bacteria species, which have adapted to the dry environment and are found as process contaminants in many powder factories.

The intestinal flora is an important part of the defence against gastrointestinal infections and plays an irreplaceable role in digestion and metabolism. The gut flora is labile in all infants during the first 12 months of life, but in preterm infants, this is an issue of special concern. The underdeveloped intestinal flora is seen as a factor that increases the risk for necrotising enterocolitis (NEC) and late-onset sepsis (LOS) [7]. The addition of probiotic strains to the diet of preterm infants is widely discussed. In a number of randomised clinical trials, the prophylactic effect against NEC has been shown and no adverse effects of the probiotics have been reported [8]. It is not clear whether the risk for NEC is only significantly reduced in preterm infants who receive breastmilk supplemented with probiotics. An advantage is not observed in infants fed with probiotic-enriched formula. It seems that there is a shortage of some bioactive ingredients in the formula, which are present in breastmilk [7]. However, the risk of probiotic sepsis remains one of the concerns linked to this kind of supplementation, especially in preterm infants [9–12]. Invasive diseases linked to probiotics are reported rarely and have never been seen in a randomised clinical trial [8]. However, 49 case reports on invasive diseases in children caused by probiotics have been published in the scientific literature between 1995 and 2021 according to D'Agostin et al. [9]. About 55% of the cases occurred in preterm infants and the majority developed septicaemia. All kinds of probiotics were involved in cases of invasive disease. In most cases, the outcome was favourable but in three cases there was a fatal outcome caused by *Limosilactobacillus reuteri* (formerly *Lactobacillus reuteri*), *Saccharomyces boulardii* and *Bacillus clausii* [9].

Therefore, the use of probiotics in preterm infants requires a careful assessment of benefits and risks for the individual case. Important risk factors for probiotic bacteremia are e.g. intestinal comorbidity and intravenous catheters [9].

Full-term infants who are exclusively breastfed usually have no need for additional liquid supply [13]. The fluid and electrolyte management of preterm infants is much more complex and in most cases, glucose solutions and water are supplied. In Europe, however, it is common practice to feed newborn infants herbal teas to supply the baby with fluid and relieve intestinal colic, although herbal teas are not recommended for young infants because they impair iron absorption due to the polyphenols they contain [13].

Furthermore, herbal teas often contain high levels of different bacteria species that are not eliminated during preparation and teas serve as an excellent growth medium for microorganisms.
