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Thursday, February 17, 2011

Background Information on Enterobacter Sakazakii (E. sakazakii)


ISDI takes very seriously the reports identifying powdered infant formula as a source and vehicle for E. sakazakii(1) infections. Reported cases of E. sakazakii infection in which powdered infant formula was identified as a source are uncommon and have occurred mainly in hospitalised, pre-term and very low-birth weight infants; nevertheless they were serious episodes.

About E. sakazakii

  • E. sakazakii is a vegetative microorganism belonging to the family of the Enterobacteriaceae. It is an opportunistic pathogen widely found in the environment.
  • During many years the only published data on the isolation of E. sakazakii were cases of neonatal meningitis or necrotizing enterocolitis related to powdered infant formulae. This led to the establishment of a causal link. In some later cases the organism was isolated on utensils such as mixers used in bottle kitchens. Even though in some cases E. sakazakii could not be isolated from the infant formulae, a causal relationship was assumed.
  • It is, however, only very recently that information on the widespread occurrence of E. sakazakii has become available. Recent publications have demonstrated that this microorganism can be found in a wide variety of foods, water and environments including homes and hospitals.
  • The E. sakazakii has also been isolated in hospitals from clinical samples taken from adults. A recent article reported the presence of E. sakazakii in mother's milk stored in a milk bank.
  • As a widespread bacteria, E. sakazakii can also be found in infant food manufacturing environments and this is usually the source of its possible presence in the infant formula powder. In general, the very low level of E. sakazakii in powdered infant formula, or contamination through preparation equipment does not result in adverse effects unless the growth of E. sakazakii bacteria is allowed through improper handling and storage.
  • Contrary to common belief, E. sakazakii is a frequently found, ubiquitous microorganism. Further research in this field is continuing and is expected to provide additional information on the widespread distribution of this organism and contribute to the better understanding on exposure.
How does E. sakazakii behave? Is it heat-resistant?

  • E. sakazakii grows very rapidly in reconstituted infant formulae kept at room temperature. It is particularly well adapted to growth at temperatures around 37 – 44°C.
  • Certain strains show an increased tolerance and resistance to temperatures around 50 – 60°C. In different publications, this characteristic has been referred to as “thermo-tolerance”, and has lead to the misunderstanding that this microorganism is heat-resistant.
  • As shown in different publications, E. sakazakii is not heat-resistant and is readily killed at temperatures above 60°C, as applied in industrial processes, e.g. pasteurisation. This fact is acknowledged by governmental agencies such as the US-FDA and is not a point of debate among experts.

The vast majority of E. sakazakii infections occur in hospital neonatal intensive care units. Risk of infection arises when reconstituted formula is kept at room temperature (or warmer) for prolonged periods of time. Improved training and hygiene in hospitals are critically important in avoiding E. sakazakii outbreaks.
  • Health professionals should receive training and effective risk management guidelines on optimum hygiene practices for handling, storage and preparation of formula. Following the comprehensive instructions on manufacturers’ labels best prevents the presence and growth of pathogenic bacteria in formula.
  • Hospitals must also ensure good hygiene in their preparation areas, including an anti-bacterial treatment before preparing the formula, and a concerted effort to minimize the time between preparation and consumption.
  • ISDI strongly supports the use of freshly reconstituted infant formula as a means to eliminate these problems.
  • ISDI questions the WHO-FAO report’s recommendation to use boiling water in the preparation of infant formula and strongly discourages this practice. Water at 100°C can scald an infant and lead to nutritional damage.
  • Breastfeeding should be recommended as the ideal to mothers in all instances. Those who cannot, or choose not to, breastfeed should receive accurate information and education about good hygiene practices concerning the preparation and use of formula. Mothers should be taught to correctly prepare and use formula before leaving hospital, when necessary.

Infant food manufacturers take extensive measures at the factory level to ensure the highest level of product quality and safety.
  • ISDI member companies strictly comply with national legislation and international recommendations based on scientific expertise to provide safe and nutritionally adapted infant food.
  • Along with their normal strict hygiene standards, manufacturers take additional actions to minimise possible contamination of powder products, including with Enterobacteriacea.
  • These include a series of rigorous processes that prevent contamination from production to the point of purchase by the consumer. For example, manufacturers:
    • Closely monitor ingredients, especially those added after the final step of heat-processing;
    • Take extensive measures to minimise Enterobacteriaceae or coliforms in the manufacturing environment to prevent post-process contamination;
    • Train personnel to ensure that hygiene control measures are understood and closely followed; and
    • Test finished products to confirm the effectiveness of these procedures.
April 2004