Reservoir and routes of transmission of Enterobacter sakazakii (Cronobacter spp.) in a milk powder-producing plant

Abstract

Several outbreaks of Cronobacter spp. (Enterobacter sakazakii) have been described as food-borne illness in neonates and infants. Powdered infant formula has been identified as a source of infection, especially in hospital nurseries, where a bulk of formula nutrient is prepared for the whole day and instructions for preparation are not always followed correctly. Neonates who are underweight or immunosuppressed are especially at risk for an E. sakazakii infection. Considering that milk powder is the main ingredient of powdered infant formula, we analyzed the incidence and distribution of E. sakazakii in a milk powder-producing plant. We looked specifically at the spray-drying towers and roller dryers. Selected isolates from samples taken from the environment and final product were typed by pulsed-field gel electrophoresis to investigate the epidemiology of the organism within the production area of the plant. Seven pulsed-field gel electrophoresis types were detected in the spray-drying area, which presumably entered the plant through an aperture for process air and an improperly controlled roller shutter. Furthermore, textile filters for exhaust air of both the spray-drying towers were identified as internal reservoirs of the pathogen. For economic reasons, powder from the textile filters is reintroduced into the product flow; this can contaminate the final product. For the production of milk powder to be used as an ingredient of powdered infant formula, it was suggested to terminate the process of reintroducing the filtered powder into the product flow. A second transmission route was identified in the roller dryer section of the factory. It could be shown that contaminated milk concentrate could pass the process unheated, thus leading to a contamination of the product with E. sakazakii.

Insights into the Emergent Bacterial Pathogen Cronobacter spp., Generated by Multilocus Sequence Typing and Analysis

“…ST1 is a dominant ST consisting of strains isolated from across the world over a period of more than 25 years. These have been mainly isolated from PIF and clinical cases, and also more recently from milk powder processing factories in Germany and Australia (Craven et al, 2010; Jacobs et al, 2011), apart from a few food isolates. ST14, which is a SLV ( ppsA allele) of ST1 was isolated from infant formula (Caubilla-Barron et al, 2007).…”

Diversity of the Cronobacter Genus as Revealed by Multilocus Sequence Typing

“…Twelve strains of C. sakazakii that were isolated from PIF collected in 12 countries were shown to be ST4. Fifteen strains which had been isolated from milk-processing factories, including roller dryers, tanker bays, and spray dryers, in Australia and Germany (6,21) were revealed to be ST4. Other nonclinical sources included isolates from weaning food, chocolate (44), and a washing brush (46).…”

Powdered Infant Formula

“…Some contamination of the fi nished product was traced to the dry blending of ingredients. A number of studies have shown that the supply air is a potential vehicle for Cronobacter contamination and confi rmed that the organism is dispersed widely in milk powder factories Hein et al 2009 ;Craven et al 2010 ;Reich et al 2010 ;Jacobs et al 2011 ). These early studies on strain persistence should be considered along with more recent observations of C. sakazakii ST4 presence in manufacturing plants and fi nished products.…”

“…These were divided into 13 pulsetypes. Although the original studies by Craven et al ( 2010 ) and Jacobs et al ( 2011 ) did not speciate the Cronobacter strains, these have now been reanalysed using MLST (Sonbol et al 2013 ). It revealed that C. sakazakii was the predominant Cronobacter species isolated from the 6 factories and that nearly a third of the strains (21/72) were C. sakazakii clonal complex ST4, the lineage associated with neonatal meningitis.…”

“…from 100 locations of fi ve milk powder factories in Australia; there were additional strains which could not be pulsetyped. Similarly, Jacobs et al ( 2011 ) analysed environmental and fi nal product samples from a milk powder manufacturing plant over a 4-year period (2005)(2006)(2007)(2008)(2009) in Germany. Eighty-one Cronobacter strains were isolated from the spray-drying area and the roller-drying area.…”