The bacteriological screening of donated human milk: laboratory experience of British Paediatric Association's published guidelines

Staphylococcus aureus Enterotoxin Production in Raw and Pasteurized Milk: The Effect of Selected Different Storage Durations and Temperatures

Introduction:S. aureus is one of the most prevalent potential pathogenic bacteria found in DHM. Some strains produce heat stable enterotoxins that are able to survive pasteurization. These enterotoxins have been associated with gastritis and potentially necrotizing enterocolitis in preterm infants. The aim of this study is to assess the impact of different storage temperatures on Staphylococcus aureus growth and enterotoxin A and B production in raw and Holder pasteurized donor human milk (DHM). Materials and Methods: Raw and pasteurized DHM were inoculated with enterotoxin A and B producing S. aureus. Samples were incubated at 4°C (10 days), 21°C, and 37°C (18 hours). Bacterial growth and enterotoxin A and B were quantified. Results:S. aureus count increased in pasteurized DHM. Bacterial count decreased in the raw milk when incubated at 21°C and 4°C and slightly increased when incubated at 37°C. Enterotoxins A and B were only detected in pasteurized DHM at 37°C from 9 hours onward. Conclusion: This study showed that raw milk is capable of suppressing S. aureus growth compared to pasteurized DHM. It also provides a measure of assurance of the safety of raw and pasteurized DHM when refrigerated or left at room temperature for a few hours.

Improving Quality of Banked Milk: Utility of Dornic Acid Test

OBJECTIVE

To identify, if Dornic acid test done on human milk bank sample is as effective as doing routine culture, both pre and post pasteurization.

METHODS

The authors analyzed 477 samples, both pre and post pasteurization. Dornic acid measurement was performed by using N/9 NaOH and titrated to get dornicity of the sample. Senstivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) at different Dornic acid levels were calculated. To find diagnostic power of this study, ROC curve was prepared. Dornic acid for paired pre and post pasteurization were noted and analysed for statistical significance.

RESULTS

A significant growth was seen in 21% (98/477) samples with coagulase negative staphylococci and gram negative organisms being the major contaminants seen prior to pasteurization. In the index study, Dornic acidity ≥4°D had a sensitivity of 98% but very low specificity of just over 10%. However, 8°D had 92% specificity and acceptable sensitivity of 72% in comparison to gold standard microbiological criteria, making it a good test for analyzing the quality of milk before pasteurization.

CONCLUSIONS

Dornic acid test at 8°D has a very high specificity with acceptable sensitivity in comparison to dornicity at 4°D. It can be used as a simple method to select better quality of milk sample prior to pasteurization.

A retrospective audit of bacterial culture results of donated human milk in Perth, Western Australia

INTRODUCTION

The bacterial content of donated human milk is either endogenous or introduced via contamination. Defining milk bank bacterial content will allow researchers to devise appropriate tests for significant and commonly encountered organisms.

OBJECTIVE

A retrospective audit was conducted on data recorded from the Perron Rotary Express Milk Bank, King Edward Memorial Hospital, Subiaco, Western Australia. This aimed to describe the incidence of bacterial species detected in donated human milk and to identify potentially pathogenic bacteria.

MATERIAL AND METHODS

The data comprised of 2890 batches donated by 448 women between 2007 and 2011.

RESULTS

Coagulase negative Staphylococcus (CoNS) represented the highest prevalence of bacteria in donated milk, isolated from 85.5% of batches (range: 20 to 650,000CFU/mL) followed by Acinetobacter species in 8.1% of batches (range: 100 to 180,000CFU/mL). Staphylococcus aureus was the most prevalent potentially pathogenic bacteria in 5% of batches (range: 40 to 100,000CFU/mL).

CONCLUSION

Further investigation is warranted to better define the risks posed by the presence of toxin-producing S. aureus in raw and pasteurized human milk which may allow minimization of risk to the preterm infants.

Group B streptococci in milk and late neonatal infections: an analysis of cases in the literature

BACKGROUND

The source for late-onset neonatal infections (LONI) due to group B Streptococcus (GBS) has not been fully explored. We reviewed GBS LONI cases associated with contaminated breast milk to determine whether breast milk was a possible route for neonatal infection.

DATA SOURCES

A PubMed search from January 1977 to March 2013 was performed with MeSH words "Streptococcus agalactiae", "group B Streptococcus", "infection", "milk", "human", "late-onset infection" and/or "neonate"; relevant cross references were also reviewed.

RESULTS

Forty-eight documented cases of GBS LONI matched our search criteria and were retrieved from the literature. When performed, molecular typing identified clonal isolates in the neonate and milk samples taken after LONI in all cases, with the hypervirulent sequence type 17 (ST-17) clone identified in two of these cases. Caesarean delivery combined with the absence of GBS recovery from maternal samples other than milk was noted for four cases. The rate of recurrent infections was high (35%) and, together with the data reviewed, points to a potential role of breast milk in GBS LONI.

CONCLUSIONS

The cases reviewed here, together with the evidence of breast milk transmission for other pathogens, suggest that breast milk, which would account for repeated GBS transmission to the neonate, may favour gut translocation and subsequent LONI. Further investigations are nevertheless needed to study the relative importance of this contamination route compared with persistent postnatal gut colonisation and the dynamics of milk and neonatal gut colonisation.

Human milk: a source of more life than we imagine

The presence of bacteria in human milk has been acknowledged since the seventies. For a long time, microbiological analysis of human milk was only performed in case of infections and therefore the presence of non-pathogenic bacteria was yet unknown. During the last decades, the use of more sophisticated culture-dependent and -independent techniques, and the steady development of the -omic approaches are opening up the new concept of the ‘milk microbiome’, a complex ecosystem with a greater diversity than previously anticipated. In this review, possible mechanisms by which bacteria can reach the mammary gland (contamination versus active migration) are discussed. In addition, the potential roles of human milk for both infant and maternal health are summarised. A better understanding of the link between the milk microbiome and health benefit, the potential factors influencing this relationship and whether or not it can be influenced by nutrition is required to open new avenues in the field of pregnancy and lactation.

Breast, milk and microbes: a complex relationship that does not end with lactation

Until relatively recently, the extent of microbiota presence in the human breast was under-appreciated. A high-throughput sequencing study and culture-based studies have demonstrated the extensive presence of microbes in human milk, with their origin believed to be from the skin, oral cavity and via gut translocation. Since formula milk substitutes do not contain these bacteria, what benefits are denied to these infants? The addition of probiotic bacteria to some infant formula is meant to provide some benefits, but these only contain one species and the dose is relatively high compared with breast milk. Many questions of importance to women's health arise from these findings. When, how and what types of microbes colonize the breast at different stages of a woman's life, including postlactation, and what effect do they have on the host in the short and long term? This article discusses some aspects of these questions.

Bacteriological screening of donor human milk before and after Holder pasteurization

BACKGROUND

In order to ascertain any bacterial contamination of donor human milk, we cultured milk samples both before and after Holder pasteurization.

METHODS

During 2003, all frozen donor milk samples were thawed and aseptically placed in pools prior to pasteurization. All individual and pooled samples were cultured and incubated for 48 hours. Specific microbiologic identification of group B Streptococcus, Staphylococcus aureus, coagulase-negative Staphylococcus, alpha-Streptococcus, Enterococcus, and Bacillus sp. was performed. Gram-negative rods (GNRs) were subtyped but not specifically identified. Positive cultures were expressed in quantitative colony counts.

RESULTS

Samples from 303 pools and 810 individual mother's donor milk were cultured. Forty-four pools (15%) represented "preterm donor milk" from milk donated by mothers who delivered prior to 36 weeks of gestation. Before pasteurization, 185 pools (62%) grew at least one lactose-fermenting GNR, and 58 pools (19%) grew a second lactose-fermenting GNR. Forty-four percent grew a non-lactose-fermenting GNR, and 20% grew an oxidase-positive GNR. The majority (87%) were colonized with Staphylococcus. Other Gram-positive organisms identified included Enterococcus (16%), alpha-Streptococcus (8%), and S. aureus (4%). Only one milk sample was positive for methicillin-resistant S. aureus. The majority of pooled milk samples grew two or more organisms. Milk from 22% of mothers did not grow detectable bacteria on routine cultures. The bacteriologic colonization profiles of milk from mothers delivering prematurely were similar to those of mothers delivering at term. After routine Holder pasteurization of donor milk, 93% of milk samples showed no growth on routine bacterial cultures.

CONCLUSIONS

A wide variety of bacteria contaminate human milk from donor mothers. Most milk samples grew coagulase-negative Staphylococcus and Gram-negative organisms. Although normal skin flora was cultured typically from milk samples, there were also many prepasteurization milk samples contaminated with pathogenic organisms. Holder pasteurization was, however, an effective means by which to remove any detectable bacteria from samples of donor human milk.

Cold storage of human milk: effect on its bacterial composition

OBJECTIVES

In the last few years, it has been proved that human milk contains bacteria that constitute an important factor in the initiation and development of the neonatal gut microbiota. In this context, the objective of this study was to evaluate the effect of cold storage on the natural bacterial composition of breast milk.

MATERIALS AND METHODS

Breast milk samples provided by 34 healthy women and collected either by manual expression (n = 27) or breast pump (n = 7), were plated onto several culture media immediately after arrival at the laboratory (day 0) and after storage at -20 degrees C for 6 weeks. A high number of isolates from 8 of the women were identified at the species level.

RESULTS

No statistically significant differences were observed between the counts obtained at both sampling times in those media in which growth was detected. In all of the culture media, bacterial counts in pump-collected samples were higher than in those obtained by manual expression. Staphylococci and streptococci were the predominant bacteria in both fresh and frozen samples, Staphylococcus epidermidis being the most abundant species at both sampling times. Lactic acid bacteria and bifidobacteria were also present in fresh and frozen breast milk samples, but among them, only 1 species (Lactobacillus gasseri) could be isolated at both sampling times.

CONCLUSIONS

The results of this study suggest that cold storage of milk at -20 degrees C for 6 weeks does not significantly affect either the quantitative or the qualitative bacterial composition of breast milk.

A case-control study of mastitis: nasal carriage of Staphylococcus aureus

BACKGROUND

Mastitis is a common problem for breastfeeding women. Researchers have called for an investigation into the possible role of maternal nasal carriage of S. aureus in the causation of mastitis in breastfeeding women.

METHODS

The aim of the study was to investigate the role of maternal S. aureus nasal carriage in mastitis. Other factors such as infant nasal S. aureus carriage, nipple damage, maternal fatigue and oversupply of milk were also investigated. A case-control design was used. Women with mastitis (cases, n = 100) were recruited from two maternity hospitals in Melbourne, Australia (emergency departments, breastfeeding clinics and postnatal wards). Breastfeeding women without mastitis (controls, n = 99) were recruited from maternal and child health (community) centres and the rooms of a private obstetrician. Women completed a questionnaire and nasal specimens were collected from mother and baby and placed in charcoal transport medium. Women also collected a small sample of milk in a sterile jar.

RESULTS

There was no difference between nasal carriage of S. aureus in breastfeeding women with mastitis (42/98, 43%) and control women (45/98, 46%). However, significantly more infants of mothers with mastitis were nasal carriers of S. aureus (72/88, 82%) than controls (52/93, 56%). The association was strong (adjusted OR 3.23, 95%CI 1.30, 8.27) after adjustment for the following confounding factors: income, private health insurance, difficulty with breastfeeding, nipple damage and tight bra. There was also a strong association between nipple damage and mastitis (adjusted OR 9.34, 95%CI 2.99, 29.20).

CONCLUSION

We found no association between maternal nasal carriage of S. aureus and mastitis, but nasal carriage in the infant was associated with breast infections. As in other studies of mastitis, we found a strong association between nipple damage and mastitis. Prevention of nipple damage is likely to reduce the incidence of infectious mastitis. Mothers need good advice about optimal attachment of the baby to the breast and access to skilled help in the early postpartum days and weeks.

Inhibition of Staphylococcus aureus by the commensal bacteria of human milk

AIMS

To study the bacterial diversity in expressed human milk with a focus on detecting bacteria with an antimicrobial activity against Staphylococcus aureus, known as a causative agent of maternal breast infections and neonatal infections.

METHODS AND RESULTS

Random isolates (n = 509) were collected from breast milk samples (n = 40) of healthy lactating women, genotypically identified, and tested for antimicrobial activity against Staph. aureus. Commensal staphylococci (64%) and oral streptococci (30%), with Staph. epidermidis, Strep. salivarius, and Strep. mitis as the most frequent isolates, were the predominant bacterial species in breast milk. One-fifth of Staph. epidermidis and half of Strep. salivarius isolates suppressed growth of Staph. aureus. Enterococci (Ent. faecalis), isolated from 7.5% of samples, and lactic acid bacteria (LAB) (Lactobacillus rhamnosus, Lact. crispatus, Lactococcus lactis, Leuconoctoc mesenteroides), isolated from 12.5% of samples, were also effective against Staph. aureus. One L. lactis isolate was shown to produce nisin, a bacteriocin used in food industry to prevent bacterial pathogens and spoilage.

CONCLUSIONS

Expressed breast milk contains commensal bacteria, which inhibit Staph. aureus.

SIGNIFICANCE AND IMPACT OF THE STUDY

The strains inhibitory against the pathogen Staph. aureus have potential use as bacteriotherapeutic agents in preventing neonatal and maternal breast infections caused by this bacterium.

Contamination of breast milk obtained by manual expression and breast pumps in mothers of very low birthweight infants

The objective of this study was to compare the rates of bacterial contamination of expressed breast milk (EBM) obtained by manual expression and breast pumps in mothers of very low birthweight (VLBW) infants (<1501 g). This was a randomized, controlled study carried out on 28 mothers of such babies and 92 specimens of EBM were collected: 41 specimens from 13 mothers assigned to the manual group and 51 specimens from 15 mothers in the breast-pump group. EBM was cultured quantitatively by the Miles and Misra method. Breast milk expressed by breast pumps (86.3% or 44/51 specimens) had a significantly higher rate of bacterial contamination than milk expressed by the manual method (61.0% or 25/41 specimens) (P= 0.005). When breast milk was expressed in the hospital, there was no significant difference in contamination rates between the two methods. When breast milk was expressed at home, the rates of bacterial contamination by staphylococci (P= 0.003) and Gram-negative bacilli (P= 0.002) were significantly higher in the breast-pump group than the manual group. In conclusion, the rate of bacterial contamination of EBM of mothers of VLBW infants was high, especially when EBM was obtained by the breast pump or when expression was carried out at home.