Brief clinical and laboratory observation

Reduction of bacterial contamination in banked human milk1

The gut microbiota is a complex system, consisting of a dynamic population of microorganisms, involved in the regulation of the host’s homeostasis. A vast number of factors are driving the gut microbiota composition including diet, antibiotics, environment, and lifestyle. However, in the past decade, a growing number of studies also focused on the role of sex in relationship to changes in the gut microbiota composition in animal experiments as well as in human beings. Despite the progress in investigation techniques, still little is known about the mechanism behind the observed sex-related differences. In this review, we summarized current knowledge on the sex-dependent differences of the intestinal commensals and discuss the probable direct impact of sex hormones and more indirect effects such as dietary habits or antibiotics. While we have to conclude limited data on specific developmental stages, a clear role for sexual hormones and most probably for testosterone emerges.

Breastfeeding is associated with considerable health benefits for infants. Aside from essential nutrients, immune cells and bioactive components, breast milk also contains a diverse range of microbes, which are important for maintaining mammary and infant health. In this review, we summarise studies that have investigated the composition of the breast milk microbiota and factors that might influence it.

We identified 44 studies investigating 3105 breast milk samples from 2655 women. Several studies reported that the bacterial diversity is higher in breast milk than infant or maternal faeces. The maximum number of each bacterial taxonomic level detected per study was 58 phyla, 133 classes, 263 orders, 596 families, 590 genera, 1300 species and 3563 operational taxonomic units. Furthermore, fungal, archaeal, eukaryotic and viral DNA was also detected. The most frequently found genera were Staphylococcus, Streptococcus Lactobacillus, Pseudomonas, Bifidobacterium, Corynebacterium, Enterococcus, Acinetobacter, Rothia, Cutibacterium, Veillonella and Bacteroides. There was some evidence that gestational age, delivery mode, biological sex, parity, intrapartum antibiotics, lactation stage, diet, BMI, composition of breast milk, HIV infection, geographic location and collection/feeding method influence the composition of the breast milk microbiota. However, many studies were small and findings sometimes contradictory. Manipulating the microbiota by adding probiotics to breast milk or artificial milk offers an exciting avenue for future interventions to improve infant health.

In planning enteral feeding in the preterm infant, decisions need to be made regarding the feeding schedule, choice of milk, and the route of administration. Feeds should be commenced within a week after birth beginning with subnutritional quantities. Preterm human milk from the infant’s own mother is the milk of choice. When full enteral feeding is established, supplementation with human milk fortifier is recommended. Donor human milk and preterm formula are alternatives. Early establishment of enteral nutrition and maintenance of optimal nutrition during infancy are important as dietary manipulations in preterm infants have potential long-term influences on their health, growth and neurodevelopment.

This study was undertaken to assess the application of the British Paediatric Association's (BPA) published guidelines to the bacteriological screening of breast milk donated to a District General Hospital milk bank.

Samples of donated milk were subjected to bacterial counts and provisional identification after both 24 and 48h incubation on cysteine lactose electrolyte-deficient (CLED) and Columbia blood agar. 21.8% (76 out of 348) donations of milk failed to reach the BPA acceptable criteria. The organisms responsible for the rejection of these samples were all evident within 24h incubation, and were not significantly confined to one medium. A large percentage of rejected samples originated from a small number of donor mothers; 63.2% came from one donor.

In applying BPA guidelines, both CLED and Columbia blood agar were found to be equally effective in screening for unacceptable organisms in prepasteurization donated breast milk. The 24h period allowed for bacteriological screening, prior to pasteurization of milk samples, was sufficient to allow the growth of all potentially pathogenic bacteria in this study. To prevent the donation of consistently contaminated milk, more active communication between the milk bank staff and the donor is recommended.

The killing activity of microwaves of 2450 MHz frequency and 600 W power on Pseudomonas aeruginosa, Escherichia coli, Enterobacter sakazakii, Klebsiella pneumoniae, Staphylococcus aureus, Candida albicans, Mycobacterium terrae and poliomyelitis vaccine-virus suspended in five infant formula preparations was investigated. The samples were brought to the boil (85–100 s depending on milk type). They had reached average temperatures of 82–93 °C at this point. Most of the vegetative organisms were killed. In those samples where growth was still detectable after microwave treatment, a significant reduction in viable micro-organisms (at least 5000-fold) was noted. We conclude that microwave heating to the boil is a convenient and fast method to reduce microbial contamination of infant feeds. However, care should be taken to ensure that milk is adequately cooled to the required temperature before it is fed to an infant.

Background: Use of human milk for preterm and high-risk neonates conveys many potential benefits but also poses practical difficulties. This prospective study examined the prevalence and degree of bacterial contamination of human milk used in the intensive care nursery.

Methods: One hundred eight milk samples collected from 40 mothers were tested for contamination. Samples from mothers whose milk showed a high degree of contamination were retested after counseling on collection methods.

Results: Only 12.5% of the samples showed no bacterial growth. Of the contaminated samples, 38% contained > 30,000 colony-forming units/ml. The most common contaminants were Staphylococcus epidermidis (82%) and Acinetobacter (9%), but other contaminants were also encountered.

Conclusions: There were not statistically identifiable common characteristics of mothers whose milk showed abundant bacterial contamination. Only 30% of these mothers showed improvement in the degree of contamination after counseling regarding techniques of milk collection.