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.

Antibiotic Susceptibility and Antimicrobial Activity of Lactic Acid Bacteria from Malaysian Fermented Foods Against Biofilm-Forming Escherichia coli Strains

“…The agar plates were allowed to diffuse at room temperature (25 ± 2°C) for 2 hours and then incubated in an upright position at 37°C for 24 hours. The results were determined by measuring the diameter of the growth inhibition zones in millimetres (mm) [24].…”

“…The four bacterial cultures identified using the API 50 CHL method were further analysed using Polymerase Chain Reaction (PCR) following method established by Bahri, [24]. Genomic DNA was extracted from 24-hour bacterial cultures using the innuPREP bacteria DNA kit (Analytik Jena), following the manufacturer's instruction.…”

“…The sequence was then identified using the Basic Local Alignment Search Tool Nucleotide (BLASTn) against the GenBank database of the National Centre for Biotechnology Information (NCBI), with the setting of 16S ribosomal RNA gene sequences (Bacteria and Archaea) in the database and highly similar sequences (Megablast) were chosen. The top 10 sequences were selected and used to build the phylogenetic tree using the neighbour joining method [24].…”

“…The isolated LAB strains were screened for antimicrobial activity against selected E. coli strains previously isolated from ulam-ulam, a Malaysian salad, in a study by Anis Athirah [24]. These E. coli strains were known to form biofilms.…”