In vitro estimation of the infectious potential of the enterococcal strain by an analysis of monocytes’ response to the formed biofilm

The aim of our study was to assess the possibility of predicting Enterococcus faecalis pathogenicity based on morphological changes of monocytes interacting with of bacteria and their adherence to biofilm. Changes in the size and granularity of monocytes, as well as their adherence to biofilm were assessed using FACScan flow cytometer after 1h co-incubation of monocytes and enterococcal biofilm in 37°C. The obtained results were validated with respect to monocytes incubated without bacteria. The most prominent changes in size of monocytes were observed in the case of commensal bacteria. The interaction with bacteria isolated from the blood stream and urine caused comparable changes in the size of THP-1 cells and were smaller than the changes of cells incubated with commensal bacteria. Changes in THP-1 granularity were comparable regardless of the source of bacteria forming biofilm. The parameter which differed the most was connected to the adherence index relating to the monocytes remaining on the surface of biofilm after 1h of incubation. Taking into consideration the obtained results, we conclude that changes in the morphology of monocytes can be treated as a tool assessing the potential pathogenicity of the bacteria. What is more, the adhesive properties towards bacterial biofilm alone might be considered as a tool allowing for the assessment of the pathogenicity of the isolated strain bypassing time-consuming techniques.

Influence of synthetic peptide inducers on antibacterial activity of enterococci

Antibacterial activity of probiotic enterococci is often related to the production of bacteriocins. There is a variety of Enterococcus faecium strains which synthesise one or several enterocins including A, B, P, 96, L50AB and others. In this work we have analysed the probiotic strain E. faecium L3 whose genome contained the genes encoding enterocins А, В and a three-component regulatory system. All these genes were found to be expressed in enterococcal strain L3. Antimicrobial activity of the strain tested on the strains of Listeria monocytogenes and Streptococcus agalactiae was pheromone dependent. Chemically synthesised cyclic peptides (analogues and shorter derivates of EntF) with different molecular structures were able to increase the antagonistic activity of the strain E. faecium L3 in contrast to the strain E. faecium SF68, which does nоt have genes encoding enterocins А and В.

Biocontrol of Psychrotrophic Enterotoxigenic Bacillus cereus in a Nonfat Hard Cheese by an Enterococcal Strain–Producing Enterocin AS-48

Bacillus cereus is a food poisoning bacterium of great concern, especially in milk products. In this study, we describe the efficient control of the psychrotrophic and toxigenic strain B. cereus LWL1 in milk and in a nonfat hard cow's cheese by the enterocin AS-48 producer strain Enterococcus faecalis A-48-32 (Bac+). No viable B. cereus cells were detected after 72 h incubation in milk coinoculated with the AS-48–producing strain and B. cereus. Diarrheic toxin production was also markedly inhibited by the Bac+ strain to eightfold lower levels compared with control cultures of B. cereus. In cheeses manufactured by inoculation with a commercial starter (about 6.8 log CFU/ml) and B. cereus (about 4 log CFU/ml), the latter reached 6.27 log CFU/g after 5 days of maturation, and approximately 8 log CFU/g after 15 days. However, in cheeses made from milk inoculated with the starter along with a mixture of E. faecalis–B. cereus (2/1 ratio), counts of B. cereus decreased by approximately 1.0, 2.0, 4.32, and 5.6 log units with respect to control cheeses after 5, 10, 15, and 30 days of ripening, respectively. Growth of E. faecalis A-48-32 was associated with enterocin AS-48 production and persistence in cheese. Interestingly, growth of starter cultures was not affected by the Bac+ strain, and neither was lactic acid production. These results clearly indicate that E. faecalis A-48-32 produced satisfactory amounts of bacteriocin in cheese and support the potential use of AS-48–producing strains as culture adjuncts to inhibit B. cereus during cheese manufacture and ripening.