NTU Undergraduates' research April 2014 - Biosciences | Page 125

Stress Survival of Cronobacter spp.
Ben Stephens
Abstract
Cronobacter is a relatively newly described genus containing ten species to date including
Cronobacter sakazakii formerly known as Enterobacter sakazakii. C. sakazakii has been known to
cause bacteraemia, necrotizing enterocolitis and infant meningitis in neonates and is often linked to
the consumption of infant formula (PIF) this has led to much research into the stress survival and
tolerances of this species; this report aims to study the stress responses across the whole genus and
use this data to examine an infant milk preparation machine specifically designed to sterilise milk of
any harmful organisms. It was found that previous reports of C. sakazakii showed the organism to be
a highly resistant bacteria when compared to other Enterobacteriaceae and the resistances are
present across the entire genus. Cronobacter was found to only result in <1 log-cycle reduction over
24 hours when in a desiccated state and reconstituted in infant milk formula and at 560C over a 60
minute period D-values of 24.49-42.86 were reported. The only case in which the organism was
destroyed to undetectable levels was in an acidified TSB medium at pH3. These levels of tolerance
were found to be sufficient for the bacteria to persist in environments leading up to and including
ingestion particularly when in an infant milk formula which conferred greater resistance to
Cronoabacter.