Salmonella enterica serotype Enteritidis is an important alimentary pathogen that recently gained special attention due to the ability of a large number of strains to form biofilms. Qualitative testing of biofilm forming ability was performed by observing the morphotype of the colonies on Congo Red agar and by conducting the pellicle test, while quantitative testing was carried out by Cristal violet assay on microtiter plates. A total of 14 isolates of S. Enteritidis were tested for biofilm forming ability, while Salmonella Enteritidis ATTC 13076 was used as the reference strain. Based on the morphotype of colonies cultivated on Congo Red agar at 25°C incubation temperature, among tested isolates three morphotypes were detected – red, dry and rough (rdar), brown, dry and rough (bdar) and smooth and white (saw). Half of the tested isolates demonstrated rdar morphotype. All isolates that showed a specific morphotype at this incubation temperature also formed the corresponding type of pellicle at the air-liquid interface. Additionally, comparing OD (optical density) values obtained by crystal violet test between groups of isolates that represent one of the three detected morphotypes (rdar, bdar and saw), statistically significant differences were detected. Based on OD values obtained by crystal violet test at both applied incubation temperatures, isolates were classified into three categories, regarding their ability to form biofilms: strong, moderate and weak biofilm producers. By comparing the amounts of the biofilms formed after 48h at 25°C and 37°C, statistically significant differences were noted (P<0.05). In this research we presented micrographs and a reconstruction of three-dimensional projections of biofilm developing phases of rdar morphotype isolates, which were obtained using confocal laser scanning microscopy.
