Genotypic and phenotypic characteristics associated with biofilm formation in Escherichia coli and Salmonella spp. Isolated from ulam in Terengganu

Abstract

Nowadays, the foodborne outbreaks associated with fresh produces, including ulam, are increasing worldwide. The biofilm formation or bacterial attachment to plant surface is the initial step towards the contamination in fresh produce. The biofilm phenotype of bacteria grown on congo red agar is termed as red, dry and rough (rdar) morphotype. The binding of congo red dye with both biological proteins and inert surfaces is due to the presence of curli fimbriae and cellulose as the main extracellular components. The objective of this study was to determine the rdar morphotypes, biofilm ability and the role of csgA gene of Escherichia coli and Salmonella spp. isolated from ulam or Malaysian herbs. A total of 29 isolates, including 23 E. coli and 6 Salmonella spp. were analyzed for their ability to produce biofilm by colony morphology test, microtiter plate biofilm assay and qualitative biofilm test (pellicle formation). The presence of the csgA gene of E. coli was identified by PCR, which demonstrated the potential gene that able to produce curli fimbriae. Results revealed that 16 (69.6%) E. coli isolates were categorized as strong biofilm producers, 2 (8.7%) as moderate biofilm producers, 3 (13%) as weak biofilm producers, whereas 2 (8.7%) as negative biofilm producers (did not produce biofilm). While 4 (66.7%) Salmonella spp. isolates were identified as strong biofilm producers, 1 (16.7%) as moderate biofilm producers and 1 (16.7%) as negative biofilm producers. Majority of the E. coli strains (69.6%) were identified as strong biofilm producers and able to express rdar morphotypes. The ability of the of E. coli and Salmonella spp. isolates to form biofilm reveals the ability of these isolates to persist on the fresh vegetables and become hosts for the disease transmission to humans or/and animals.