Enterobacter sakazakii is a gram-negative, non-spore-forming, rod-shaped bacterium within the family Enterobacteriaceae. The organism was called "yellow-pigmented Enterobacter cloacae" until 1980 when it was renamed Enterobacter sakazakii. (1)

In the April 12th issue of Morbidity and Mortality Weekly Report, the Centers for Disease Control and Prevention (CDC) reported on a fatal case of meningitis in an intensive care nursery in Tennessee. The infecting organism was Enterobacter sakazakii, an unusual but often fatal, invasive pathogen. In the fatal Tennessee case, the infection was traced to contaminated powdered infant formula. Other infants in the same nursery were screened for E sakazakii. Of 49 screened infants, 10 events were discovered (1 proven infection, 2 assumed infections, and 7 colonizations). This report detailed for the first time a direct link to an unopened product. The manufacturer voluntarily recalled the contaminated batch of powdered formula identified as the source. (2)


The literature suggests that premature infants and those with underlying medical conditions may be at highest risk for developing E. sakazakii infection. Several outbreaks have occurred in neonatal intensive care units worldwide. The majority of cases of E. sakazakii infection reported in the literature have described infants with sepsis, meningitis, or necrotizing enterocolitis as a consequence of the infection, and the case-fatality rate among infected infants has been reported to be as high as 33%. While E. sakazakii has caused disease in all age groups, it is likely that immunocompromised or medically debilitated infants are more susceptible to infections with E. sakazakii. In addition, the stomach of newborns, especially of premature babies, is less acidic than that of adults: a possible important factor contributing to the survival of an infection with E. sakazakii in infants. (3)

Significant morbidity in the form of neurological deficits can result from infection, especially among those with bacterial meningitis and cerebritis. While the disease is usually responsive to antibiotic therapy, a number of authors have reported increasing antibiotic resistance to drugs commonly used for initial treatment of suspected Enterobacter infection. Long-term neurologic sequelae are well recognized. (3)

There is very little known about virulence factors and pathogenicity of E. sakazakii. Enterotoxin-like compounds were produced by some strains. Using tissue cultures, some strains produced a cytotoxic effect. Two strains (out of 18 isolates) were capable of causing death in suckling mice by the peroral route. Therefore, there appear to be differences in virulence among E. sakazakii strains, and some strains may be non-pathogenic. (3)

Although the reservoir of the organism is unknown in many cases, a growing number of outbreaks of infection among infants have provided compelling evidence that milk-based powdered infant formulas have served as the source of infection. In several investigations of outbreaks of E. sakazakii infection that occurred among infants in neonatal intensive care units, investigators were able to show both statistical and microbiological association between infection and powdered infant formula consumption. (3)

The FDA points out that powdered infant formulas are not commercially sterile products. Powdered milk-based infant formulas are heat-treated during processing, but unlike liquid formula products they are not subjected to high temperatures for sufficient time to make the final packaged product commercially sterile. Proper handling and use of infant formula products in the health-care setting is an important patient safety issue. Clinicians should be aware that powdered formulas are not sterile products and might contain opportunistic bacterial pathogens such as those in the family Enterobacteriacae, including E. sakazakii.

Risk for infection might depend on several factors, including the number of bacteria present in the product, handling after preparation, and underlying patient characteristics (e.g., immunosuppression, prematurity, or low birthweight). Because powdered formula is not sterile and can provide a good medium for growth, prolonged periods of storage or administration at room temperature might amplify the amount of bacteria already present. Health-care providers might be able to reduce risks for hospitalized neonates by choosing alternatives to powdered forms when possible. (4)

FDA recommends that powdered infant formulas not be used in neonatal intensive care settings unless there is no alternative available. If the only option available to address the nutritional needs of a particular infant is a powdered formula, risks of infection can be reduced by:

•Preparing only a small amount of reconstituted formula for each feeding to reduce the quantity and time that formula is held at room temperature for consumption; Minimizing the holding time, whether at room temperature or while under refrigeration, before a reconstituted formula is fed; and

•Minimizing the "hang-time" (i.e., the amount of time a formula is at room temperature in the feeding bag and accompanying lines during enteral tube feeding), with no "hang-time" exceeding 4 hours. Longer times should be avoided because of the potential for significant microbial growth in reconstituted infant formula (4)

(1) “Enterobacter sakazakii Infections Associated With the Use of Powdered Infant Formula—Tennessee, 2001”, JAMA. 2002;287:2204-2205, Vol. 287 No. 17, May 1, 2002.

(2) R. D. Baker, MD, PhD, “Infant Formula Safety”, Pediatrics, Vol. 110 No. 4, October 2002, pp. 833-835.

(3) “Enterobacter sakazakii and other microorganisms in powdered infant formula” Microbiological Risk Assessment Series 6, WORLD HEALTH ORGANIZATION, FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, 2004

(4) “Health Professionals Letter on Enterobacter sakazakii Infections Associated With use of Powdered (Dry) Infant Formulas in Neonatal Intensive Care Units”, U. S. Department of Health and Human Services, U. S. Food and Drug Administration, April 11, 2002; Revised October 10, 2002