Holder Pasteurization for NICU Donor Breast Milk: Does it Eliminate Pathogenic Bacterial Spores?

Updated: Dec 7, 2020


Providing donor human milk or human milk-based nutrition to NICU infants is part of your routine as a neonatal intensive care clinician. Much of that donor milk comes from vendor resources your hospital has selected, some of which use a Holder pasteurization method.

Did you know up to 7% of raw human milk samples could contain Bacillus cereus? This bacterial pathogen could be potentially harmful to an at-risk infant with a compromised immune system. And it is one that can survive the Holder pasteurization process.

Understanding donor human milk processing can aid your hospital’s decision to make the best choice for the health of your patients.

Donor breast milk processing

Donor milk processing should be a rigorous process with multiple safety steps: donor blood testing, with microbial testing on individual mother’s milk samples to discard any donor milk batches with too high a level of microorganisms (many milk banks actually skip this step). Donor milk batches that passed the milk testing are then pooled and pasteurized or sterilized based on proper food processing best practices.

Donor milk laboratories using commercial sterilization methods, such as Retort sterilization, meet modern food processing requirements, eliminate bacteria and spores, and maintain quality nutrients for neonatal growth and positive outcomes. That process currently delivers donor human milk and human milk-based nutrition to NICUs in hospitals around the world.

Some donor milk banks and laboratories use Holder pasteurization. Holder pasteurization is a traditional heat-treatment method used by some milk banks. However, pasteurization does not eliminate all thermoduric (heat-resistant) bacteria spores.1 While it does eliminate enough to satisfy existing safety requirements, and provides needed nourishment to infants, one has to ask: Is it the best choice for breast milk nutrition if there is any risk of surviving contaminants?

Holder pasteurization does not eliminate all donor milk bacteria

Holder pasteurization (HoP) is accepted as a donor breast milk pasteurization process, but it does not destroy heat-resistant bacteria such as Bacillus cereus spores. It specifically destroys high-risk bacteria and non-spore-forming bacteria.2

As a result, studies indicate up to 7% of HoP breast milk samples grow bacterial culture.3 One theory for the 7% is that the removal of competing bacteria allowed the remaining bacteria to flourish.

When donor milk is pasteurized using HoP or other pasteurization methods, it leaves a door open to bacterial spores. The problem then is three-fold:

1. Specific heat-resistant bacteria and Hepatitis B virus survive the Holder pasteurization process

2. Those same bacteria could grow again during the milk thawing and warming steps

3. A small amount of B. cereus in donor human milk can infect compromised preterm infants in the NICU

The question is, where do you draw the line? At “acceptable minimal risk,” or “no risk”?

Which bacteria survive donor milk Holder pasteurization?

A few heat-resistant bacteria and viruses able to survive the HoP process are:

Sporulating bacteria:2,3

- Bacillus Cereus: A potential source of bloodstream, lung, and central nervous system infection which can be fatal, especially for immunocompromised premature infants

Hepatitis B virus (HBV)1

- Hepatitis B: Chronic infection risk

Blood screening for HBV is not universally performed for human milk bank donor selection1 despite the fact it will not be eliminated by the HoP process.

Which donor milk process is best?

Ultimately you must make a decision for your patients. Which human milk-based nutrition resource should you use?

Informing yourself and your clinical team can make those decisions easier. Use this list as a series of questions to ask your donor human milk nutrition provider in order to make the best decision for your unit and your patients:

1. What type of heat-treatment (pasteurization or sterilization) do you use?

2. Does that method eliminate all bacteria and viruses?

3. Do you use a pooled milk testing and discard process?

4. Do you screen for HBV?

5. Does your packaged donor milk require freezing?

6. If frozen, how is your donor milk prepared for proper food transport?

7. What are recommended best practices for storage of your donor milk products?

8. How will your human milk-based nutrition product impact our workflow?

Medolac Benefit Human Milk products use an FDA-approved Retort sterilization food preparation method to eliminate all bacterial spores and viruses. Learn more about the Benefit human milk-based nutrition line for NICU infants.


1. de Oliveira et al (2009). Hepatitis B viral markers in banked human milk before and after Holder pasteurization. J Clin Virol. 2009 Aug;45(4):281-4. doi: 10.1016/j.jcv.2009.04.003. Epub 2009 May 26.

2. Escuder-vieco et al (2018). Effect of HTST and Holder pasteurization on the concentration on immunoglobulins, growth factors, and hormones in donor human milk. Frontiers in Immunology. 27 September 2018.

3. Banked human milk and quantitative risk assessment of bacillus cereus infection in premature infants: A simulation study. Canadian Journal of Infectious Diseases and Medical Microbiology. 2019; 2019: 6348281.