NTU Undergraduates' research April 2014 - Biosciences | Page 97

Serratia marcescens is an opportunistic bacterium of increasing
clinical importance, particularly within neonatal intensive care units
(NICU). While the use of powered infant milk has garnered much
attention as a source of contamination, enteral feeding tubes have
also been shown to be a loci for contamination.
Alexander Fezovich
Abstract
This study tested 12 pathogenic strains of Serratia marcescens and found them to
exhibit a notable sensitivity to acidic stress compared to other species of
Enterbacteriaceae, with no viable cells isolated after 120 minutes of incubation at
pH2 in TSB for the majority of strains. However, a marked increase was seen
when strains where tested as a biofilm, increasing percentage survival from no
viable cells with planktonic cells to 0.014% as a biofilm. Furthermore, incubation
with various brands of infant ready to feed formula milk showed an increase in
survival from 0.008% in TSB to 0.61% in Cow and Gate milk, 0.31% in Atpamil
milk and 0.028% in SMA milk. This therefore raises concerns over the use of
infant formula milks in NICUs with neonates who are already susceptible to
infection.
Additionally, an alternative, high throughput method to viable counts is tested to
determine bacterial cell numbers and its accuracy, precision and sensitivity are
discussed and compared with viable counts.