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Summary Cronobacter Articles Update 2016

Fatal case of bacterial infection in formula-fed baby in the USA increases urgency of circulating correct information about harmful bacteria


In June 2016, a baby less than one month old died from meningitis and sepsis in Michigan, USA. These invasive infections were caused by the rare but dangerous bacteria called Enterobacter sakazakii. As the baby’s parents said when describing the effects of the  Enterobacter infection: « We have never heard of this infection, ever … Nobody has. »  .


Confusion reigns : What is Enterobacter sakazakii and why is it such a serious problem in powdered formula?

Enterobacter sakazakii has had a confusing name change to Cronobacter sakazakii [1], but there is no confusion about the severity of infections it can cause in babies fed powdered formulas. The  World Health Organization and the Food and Agriculture Organization of the United Nations have both recognized the problem and in 2007 issued Guidelines on preparation, storage and handling of powdered infant formula. Insert hyperlink here:  

The need for safer methods of powdered formula preparation is due to the immense capacity for survival and resistance of these bacteria, and to their potential for causing life-threatening infections. These are summarised here 

Enterobacter sakazakii is a true survivor – with potentially disastrous consequences for infant health

In 2015 researchers in the USA published the results of work on the intrinsic properties of these bacteria that include « resistance to heat, ultraviolet radiation, oxygen radicals, stomach acids and pasteurization ».  This means that they are very difficult to inactivate – to kill. In addition, the stomachs of newborn babies are less acidic than those of adults, making it easier for the bacteria to multiply rapidly if they are ingested in contaminated formula.  Enterobacter sakazakii is also resistant to desiccation and can thus survive in dried powdered formula even over long periods . The bacterial cells attach to Teflon and plastics and  « can form biofilms, which render them resistant to high-level disinfection. » This means that feeding utensils such as plastic bottles and enteral feeding tubes can be a breeding ground for the bacteria to enter the baby’s stomach.

Worse still, the bacteria utilizes sialic acid in formulas that are fortified with this additive. The researchers hypothesise that « Sialic acid is an additive to powdered infant formula because of its reported ability to foster healthy brain development in the neonate.» Enterobacter sakazakii is « unique in the Cronobacter genus in that it can utilize sialic aciid for growth. » Ironically,  it is Enterobacter sakazakii  which can cause neonatal brain infections such  as meningitis, leading to brain damage. 

See  Cronobacter Species Contamination of Powdered Infant Formula and the Implications for Neonatal Health


Vital importance of testing for harmful bacteria in powdered formulas and developing methods to inactivate them

Like all industrially processed foods, powdered formulas are not sterile products because there is no final sterilization procedure. Powdered formulas may become contaminated at factory level by bacteria such as Cronobacter species, particularly Cronobacter (formerly Enterobacter) sakazakii, and species of Salmonella introduced during manufacturing processes.  Once the formula powder is mixed with water to make up the feed, even tiny amounts of these bacteria can multiply and rapidly form colonies in the warm milk and can cause severe invasive infections.

It is imperative that packages of powdered formulas should be tested regularly and reliably for the presence of Enterobacter sakazakii.  But there is also confusion about testing : the Michigan baby was fed Enfamil Gentlease powdered formula but the manufacturers, Mead Johnson, assert that there were no bacteria in the can of formula that was tested.

The article cited above at explains that Enterobacter sakazakii  is difficult to detect in powdered formula because it forms clumps and is not uniformly distributed throughout the batches « Cronobacter species tend to be non-homogeneously distributed …This property limits the utility of random sampling of powdered infant formula batches for quality assurance and public health surveillance. » See this article for discussion of the different measures for testing : “ How to tackle the problems of safety and quality of formula: examining effective measures ”


Research alerts on new methods for rapid detection or inactivation of harmful bacteria 

To tackle the difficulties of detection, researchers in many countries are working to identify improved methods, for example in South Korea.

In July 2016 researchers in South Korea developed a more sensitive testing method, explaining  that « Cronobacter species (Cronobacter spp.) are hazardous foodborne pathogens associated with baby food, powdered infant formula (PIF). » They report that their new INC-ELISA method is based on a novel immunoglobulin G (IgG), anti-Cronobacter IgG, which is able to detect seven Cronobacter spp. This « novel anti-Cronobacter IgG facilitated highly sensitive, efficient, and rapid detection of Cronobacter spp. in baby food. » However, does rapid testing mean reliable testing ? The market for new tests to detect harmful bacteria is expanding – and lucrative.

See Detection of Cronobacter Genus in Powdered Infant Formula by Enzyme-Linked Immunosorbent Assay using Anti-Cronobacter Antibody


Other researchers are developing combined treatments to kill these harmful bacteria. But because the bacteria are so resistant, a combination of three treatments is needed to prevent the bacteria from multiplying and causing infection.  However, it can be asked how the average parent or care-giver could possibly combine these complex treatments, and thus whether they are intended for use by  manufacturers, if indeed they are proven to be effective. 

​In 2016 Chinese researchers studied various treatments to ​inactivate Cronobacter/Enterobacter sakazakii. The results were published in the Journal of the Michigan based American Society of Agricultural and Biological Engineers,  with the explanation « Powdered infant formula milk is prone to Cronobacter sakazakii (C. sakazakii) contamination, which is fatal to infants. » These bacteria are heat-resistant and so various combinations were explored to reconstitute the powdered infant formula, using very hot water ranging from 60°C-75°C combined with radio frequency and hot air treatment. Water temperature of 70°C combined with radio frequency and hot air treatment achieved a reduction in Cronobacter sakazakii while retaining the quality of powdered milk formula and avoiding the protein becoming denatured. « 

See Comparison of Cronobacter sakazakii death kinetics in powdered infant formula using hot water and combined radio frequency and hot air treatment Urgency of informing about methods for safer preparation


Urgency of informing about methods for safer preparation

All the above cited articles provide robust evidence that it is more important than ever to address the problem of contamination of powdered formulas by Enterobacter sakazakii.  It is not only formula-fed premature or immuno-compromised infants and newborns who can be at risk but also infants up to one year and older babies. See WHO/FAO Enterobacter sakazakii  in powdered follow-up formulae: Meeting Report: 

 In 2016 the US CDC therefore issued a renewed alert : See  2016 alert by the US Centers for Disease Control and Prevention on the risks of harmful bacteria in formulas: 

It is significant that, also in 2016, researchers in Italy published research on precautions to be taken to protect infants fed powdered formulas, with the rationale « Powdered infant formulas are usually not sterile and may  frequently be contaminated by several bacteria strains. « They note « Contamination of powdered milk cans has been reported to range from 6.6% in Brazil to 29 % in China. » They therefore discuss the advice to parents, care-givers and health professionals to prevent foodborne infectious diseases when preparing and storing formula.

Different recommendations for preparation, handling and storage cause further confusion because manufacturers argue that the ‘killer step’ of using very hot water to prepare powdered formula may indeed inactivate the bacteria – but will also kill off the probiotic bacteria which enable manufacturers to make unsubstantiated claims for the superiority of their particular brand. See  What do we really know about probiotic bacteria and prebiotics added to formulas? Are the promotional claims made by manufacturers justified? Why are these claims banned in many countries? 

The Italian research reviews national guidance in the United Kingdom, the European Union and the US Centers for Disease Control. All of these, as well as many other countries, follow the World Health Organization’s Guidelines: Use water that has first been boiled and then cooled to no less than 70°C (158°F) to mix the powdered formula. Use formula within 2 hours of preparation. If the baby does not finish the entire bottle of formula, discard the unused formula.

See Time for the 70 °C water precautionary option in the home dilution of powdered infant formula




  • First and foremost, parents, care-givers and health professionals must be fully informed that powdered formula is not a sterile product and may contain harmful bacteria. Therefore, extra precautions must be taken to prepare, store and handle powdered formula to avoid infections that may have serious consequences ;

  •  Education to raise awareness of the risks of formula feeding, especially powdered formulas, must be increased to raise awareness and explain the reasons why it is vital that parents, care-givers and health professionals follow the WHO Guidelines :

  • Manufacturers bear the responsibility for marketing a safe product and must therefore implement « effective environmental monitoring programs, good manufacturing practice guidelines, and procedures and hazard analysis and critical control point systems to control the risk of microbiological contamination along the entire production chain. » (see Cronobacter Species Contamination of Powdered Infant Formula and the Implications for Neonatal Health  )

  • Governments should ensure that manufacturers place clear and visible warning notices on product packaging to alert product users to potential risks ;

  • Surveillance of Enterobacter sakazakii related illnesses must be intensified.  As FAO and WHO note : « Globally, there appear to be very few surveillance data for E. sakazakii (Cronobacter spp.)-related illnesses. Although a couple of passive surveillance systems exist, no active surveillance system  for  E. sakazakii (Cronobacter spp.)  disease has  been  identified. «  See WHO/FAO Enterobacter sakazakii (Cronobacter spp.) in powdered follow-up formulae: Meeting Report, page xi : 

  • Research to develop  more effective methods of testing for harmful bacteria in powdered formula should be prioritized as well as methods to inactivate any bacteria present in these products ;

  • Breastfeeding provides anti-infective agents and boosts the infant’s immature immune system. Breastfeeding must be protected, promoted and supported by governments, health care services, employers and society as a whole, so that mothers are able to breastfeed optimally. 

[1] Enterobacter sakazakii was redefined in 2008 as a species in a new genus named Cronobacter. This means that it is also referred to as Cronobacter sakazakii, or as Cronobacter species (spp.) Cronos or Cronus  was the name of the Greek Titan who devoured his own children: