Salmonella typhimurium DT104 strain has emerged as a global human and veterinary public health concern because of its antibiotic resistance and extensive host range. Although it is thought to be more virulent, to date, factors relevant to its virulence have not been fully elucidated. Thus, understanding how this strain forms biofilms on hydrophobic surfaces will add to current knowledge on its possible virulence mechanism.
METHODS: Biofilm-forming abilities of clinical isolates of S. typhimurium DT104 from human and animal sources on hydrophobic inanimate surfaces were assessed by absorbance at 600 nm of
crystal violet-bound cells recovered from 96-well tissue culture plates after growth in a nutrient-rich growth medium and various adjusted media; and scanning electron microscopy based on standard procedures.
RESULTS: In the nutrient-rich growth medium, Luria-Bertani (LB), biofilms were formed in small quantities, preferentially on
polystyrene (p<0.05), and followed different time courses. Significantly lower amounts of biofilms were formed on
polystyrene when a nutrient-deficient growth medium (adherence test medium) was used. Inclusion of
D-(+)-mannose in LB at a concentration of 100 mM significantly (p<0.05) inhibited biofilm formation on
polystyrene.
D-(+)-glucose relatively enhanced biofilm formation but
D-(-)-mannitol only insignificantly influenced the process. The action of
mannose on polyvinly
chloride (
PVC) was insignificant, suggesting that its action may be surface-dependent. Additionally,
glucose significantly reduced biofilm growths of 2 of the isolates and only that of the
PVC-loving strain T980021 on
polystyrene and
PVC, respectively. At the concentration tested, unlike
xylose, both
D-mannose and
D-glucose significantly (p<0.05) inhibited bacterial growth, providing a possible mechanism for their inhibitory action on biofilm formation by S. typhimurium. While stress of
starvation resulted in significant reduction in biofilm formation on
polystyrene in all but the
PVC-loving strain T980021, high osmolarity had little effect on the quantity of biofilm formed on
polystyrene. The extent of primary attachment to
polystyrene as well as their capacity to form biofilm did not correlate with their cell surface hydrophobicity and exopolysaccharide production.
CONCLUSIONS: