Effects of Preculturing Conditions on Lag Time and Specific Growth Rate of Enterobacter sakazakii in Reconstituted Powdered Infant Formula

Abstract

Enterobacter sakazakii can be present, although in low levels, in dry powdered infant formulae, and it has been linked to cases of meningitis in neonates, especially those born prematurely. In order to prevent illness, product contamination at manufacture and during preparation, as well as growth after reconstitution, must be minimized by appropriate control measures. In this publication, several determinants of the growth of E. sakazakii in reconstituted infant formula are reported. The following key growth parameters were determined: lag time, specific growth rate, and maximum population density. Cells were harvested at different phases of growth and spiked into powdered infant formula. After reconstitution in sterile water, E. sakazakii was able to grow at temperatures between 8 and 47°C. The estimated optimal growth temperature was 39.4°C, whereas the optimal specific growth rate was 2.31 h ؊1 . The effect of temperature on the specific growth rate was described with two secondary growth models. The resulting minimum and maximum temperatures estimated with the secondary Rosso equation were 3.6°C and 47.6°C, respectively. The estimated lag time varied from 83.3 ؎ 18.7 h at 10°C to 1.73 ؎ 0.43 h at 37°C and could be described with the hyperbolic model and reciprocal square root relation. Cells harvested at different phases of growth did not exhibit significant differences in either specific growth rate or lag time. Strains did not have different lag times, and lag times were short given that the cells had spent several (3 to 10) days in dry powdered infant formula. The growth rates and lag times at various temperatures obtained in this study may help in calculations of the period for which reconstituted infant formula can be stored at a specific temperature without detrimental impact on health.Enterobacter sakazakii is a motile, peritrichous, gram-negative rod that occasionally causes neonatal meningitis and sepsis, with mortality rates of 40 to 80% (3). The recovery of E. sakazakii from samples of commercially available dry powdered infant formulae has been reported (4,8,9). E. sakazakii organisms in infant formula have been associated with outbreaks of meningitis, sepsis, and necrotizing enterocolitis in premature and full-term infants, particularly those with predisposing medical conditions (17). Although the levels of E. sakazakii occurring in dry powdered infant formula are generally very low, reconstituted infant formula is a good medium for growth. When present in dry formula, E. sakazakii may grow during preparation, cooling, storage, and holding of the bottles, increasing the probability of illness. Occasional contamination of dried infant formula during manufacture is a source of the microorganism's occurrence in reconstituted product. However, as E. sakazakii has been detected in various other dry environments (7), contamination may also occur during reconstitution of dried infant formula in hospitals or at home.In order to prevent illness, product contamination at manufacture and/or during preparat...

Cronobacter Sakazakii: An Emerging Contaminant in Pediatric Infant Milk Formula

“…Large amounts of powdered substitutes for breast milk should be obtained from different sources to be analyzed for the presence of this bacterium 78 . It has been suggested that thermal treatment of rehydrated PIF may be a practical way of minimizing neonatal risk to C. sakazakii infection [79][80][81] . Simmons et al has recommended using refrigeration and limiting hang time to prevent or retard the growth of C. sakazakii 5 .…”

Development of a Novel Screening Method for the Isolation of “ Cronobacter ” spp. ( Enterobacter sakazakii )

“…This corresponds to a final concentration of 10 4 CFU ml Ϫ1 after preenrichment of the sample in buffered peptone water (BPW) (CM0509; Oxoid AG, Pratteln, Switzerland). The level of competitive flora in PIF is generally low (8), the lag time for desiccated cells to recover after rehydration of PIF at 37°C has been estimated as 0.254 h (15), and the approximate doubling time at 37°C in infant formula for Cronobacter spp. is 20 min (10).…”

Comparison of Two Optical-Density-Based Methods and a Plate Count Method for Estimation of Growth Parameters of Bacillus cereus

“…These parameters can be determined using different techniques. Plate counting can be used to generate the data points max and by fitting of the growth curve (15,33). Often, automated optical density (OD) measurements are used to determine parameters for growth as they allow quicker data generation with less need for human resources (22).…”