Cronobacter sakazakii And The Problem Of Contamination Of Infant Formulas

Cronobacter sakazakii otherwise formerly known as Enterobacter sakazakii  is an opportunist pathogen mainly of infants and young children. It is a bacterium that causes rare but often fatal infections of the bloodstream and central nervous system particularly meningitis and necrotizing entercolitis.  It is especially associated with infants having poor or compromised immune systems. Premature infants and low birth weight neonates are very vulnerable, being most likely to contract a Cronobacter infection, although the bacteria causes illnesses in all age groups (Iversen et al., 2003).

The bacterium was first isolated in 1980 but has undergone a series of reclassifications into various genomic categories before being established in its own genus (Iversen et al., 2008).

Cronobacter sakazakii in Infant Formula

Dry infant formula is a nutritional substitute for human breast milk.  Powdered and dry infant formula is a source and vehicle for most cases of Cronobacter sakazakii infection although other sources and reservoirs exist. However, this type of infection is still very rare.

The bacterium can enter the food chain via contaminated ingredients, and from other sources during manufacture and throughout the process. The high temperatures reached during spray drying of the liquid preparation to generate the infant powders and formulas normally kill the bacteria, but there are cases of them surviving even this processing after preparation. The spray drying step serves as a form of sterilisation rather than pasteurisation and  is a critical control point or CCP in the manufacturing process and so it should be carefully monitored. However, if the powder is produced using a dry blending process, and not heated, Cronobacter bacteria can survive in the formula.

Good environmental management and control, and monitored raw material hygiene along with adherence to best practice are the main methods to reduce the prevalence of contamination in dry infant formulas by any bacteria let alone C. sakazakii.  More effective control methods are continually being developed to destroy the bacterium. Irradiation and UV light inactivation are two such techniques that have found favour in recent years. Whilst the former technique used for post-pasteurisation is controversial no-one would begrudge its application when dealing with such a devastating disease agent.

Non-thermal methods for killing Cronobacter species have also been reviewed.

Powdered infant formula is typically contaminated after production and during packaging if measures to control contamination are lax.   There are cases of C. sakazakii adapting to processing as a result of drying and surviving in the process as a response to dehydration stress. They are said to make their presence known in dry infant formula with the production of yellow pigments and colonic acid (Scheepe-Leberkuhne and Wagner 1986; Johler et al., 2010).

The primary source for infection in homes and households comes from contaminated equipment such as blenders, incubators and cooking utensils used in the preparation of liquid infant formula. There is also a  rare opportunity for contamination of the packaged formula in the home (Chen et al., 2009).

It is worth noting that Salmonella is a more dangerous disease for infant children with poorly prepared milk powders.

The web-site hosted by MarlerClarke presents a very informative description of the symptoms for Cronobacter infection which are outlined here.

Symptoms of Cronobacter Infection

Cronobacter symptoms usually include the following in infants:

• Poor feeding response
• Irritability
• Jaundice
• Grunting while breathing
• Unstable body temperature

A Cronobacter sakazakii infection can also lead to meningitis, which is the inflammation of the membranes surrounding the brain and spinal cord.  Signs of meningitis in newborns include:

• High fever
• Constant crying
• Excessive sleepiness or irritability
• Sluggishness
• Poor feeding
• A bulge in the soft spot on the top of the head
• Stiffness of the body and neck
• Seizures

The mortality rate for infants with infection by C. sakazakii is high – around 50% to 80% are reported to die and those who survive it may experience brain damage .

Treatment for Cronobacter sakazakii

A Cronobacter sakazakii infection is usually treatable with antibiotics, although some antibiotic-resistant strains have recently been discovered. If a newborn exhibits any of the above symptoms, consult a doctor to see whether the infant might need treatment.

How to Prevent a Cronobacter sakazakii Infection

The Centers For Disease Control And Prevention (CDC) recommends the following steps for preventing an Cronobacter infection in the home:

• Use hot water to make baby milk from infant formula powder—Water should reach a heat of 158°F (70°C)
• Choose an alternative to a powdered form of baby milk. Liquid formula is usually sterile.
• Follow the manufacturer’s instructions for preparing baby milk from powdered formula
• Throw out prepared formula if you don’t use it within 24 hours of preparing it
• Limit “hang time” for continuous feeding via tube to four hours.

References:

Chen, P.-C., Zahoor. T., Oh, S.-W., Kang, D.-H. (2009) Effect of heat treatment on Cronobacter spp. in reconstituted, dried infant formula: preparation guidelines for manufacturers. Lett. Appl. Microbiol. 49 pp. 730–7.

Iversen, C., Forsythe, S. (2003) Risk profile of Enterobacter sakazakii, an emergent pathogen associated with infant milk formula. Trends Food Sci. Technol. 14 pp. 443–54.

Iversen C, Mullane N, McCardell B, Tall BD, Lehner A, Fanning S, Stephan R, Joosten H. (2008). Cronobacter gen. nov., a new genus to accommodate the biogroups of Enterobacter sakazakii, and proposal of Cronobacter sakazakii gen. nov., comb. nov., Cronobacter malonaticus sp. nov., Cronobacter turicensis sp. nov., Cronobacter muytjensii sp. nov., Cronobacter dublinensis sp. nov., Cronobacter genomospecies 1, and of three subspecies, Cronobacter dublinensis subsp. dublinensis subsp. nov., Cronobacter dublinensis subsp. lausannensis subsp. nov. and Cronobacter dublinensis subsp. lactaridi subsp. nov. Int. J. Syst. Evol. Microbiol. 58  pp. 1442–7.

Johler, S., Stephan, R., Hartmann, I., Kuehner, K., Lehner, A. (2010). Genes involved in yellow pigmentation of Cronobacter sakazakii ES5 and influence of pigmentation on persistence and growth under environmental stress. Appl. Environ. Microbiol. 76 pp. 1053–1061.

Pina-Pérez, M.C., Rodrigo, D., Martinez, A. (2015)  Non-Thermal Inactivation of Cronobacter Sakazakii Infant Formula Milk: A Review. Critical Rev. in Food Science and Nutr., To be published

Scheepe-Leberkuhne, M., Wagner, F. (1986). Optimization and preliminary characterisation of an exopolysaccharide synthesized by Enterobacter sakazakii. Biotechnol Lett.  8 pp. 695–700.