Salmonella enterica is of significant concern to the food industry
with respect to both public health and the costs associated with regulatory
compliance and recalls. Biofilm formation represents an important mechanism by
which this species persists in food-related environments. We investigated the in vitro biofilm forming capacity of 20 Salmonella enterica strains representing
different subspecies (I, IIIa, IIIb, IV and VI) from a range of food-related
sources. In addition the strains were characterized for the carriage of seven
virulence genes and for resistance to 13 antibiotics. The S. enterica subspecies IIIa, IIIb, IV and VI strains (with 1
exception) formed significantly (p<0.05) more biofilm in the assay used than
S. enterica subspecies I strains
(with 2 exceptions). An association (both positive and negative) between the
carriage of particular virulence genes and/or resistance to particular
antibiotics with the extent of biofilm formation within subspecies was
apparent. We further investigated the link between antibiotic resistance and
biofilm formation by transforming two
strains of each subspecies (one relatively stronger and one relatively weaker
biofilm former) with plasmids carrying ampicillin resistance, kanamycin
resistance or both ampicillin and kanamycin resistance. The introduction of
antibiotic resistance changed biofilm formation in most strains, either
positively or negatively, and in both a strain and antibiotic specific manner.
This work suggests that antibiotic resistance can significantly influence
biofilm formation by Salmonella enterica. This finding has implications
for the persistence and spread of this pathogen in food related environments
and may result in the emergence of new strains of greater public health
concern.