Method: MS (ATCC 25175) as well as the probiotics Lactobacillus rhamnosus LC705, Lactobacillus rhamnosus LR32, Lactobacillus casei LC11, Lactobacillus casei 431, Lactobacillus fermentum PCC, Lactobacillus rhamnosus GG were grown anaerobically overnight, washed twice, re-suspended in PBS and suspensions’ absorbance at 600nm was adjusted to 0.25 (±0.05). For co-aggregation assays probiotics were mixed with MS in equal volumes. Absorbances (600nm) of both single and mixture suspensions were determined at baseline, after 2h, 4h and 24h, respectively. Gram staining and light microscopic evaluation were performed in parallel. Auto-aggregation ratios were calculated as [(A0-At)/A0]×100; A0 and At: absorbance of single strain suspension at baseline and different time-points, respectively. Co-aggregation ratios were calculated as [((Apro+AMS)/2)-Amix)/(Apro+AMS)/2]×100; Apro, AMS and Amix: absorbance of various probiotics, MS and their mixtures, respectively at various time-points. All assays were performed at 20°C and repeated in six independent experiments.
Result: Auto-aggregation ratios [mean (SD)] significantly increased with time for all strains (p<0.05; repeated measures ANOVA) reaching 52 (37)-90 (11)% at 24h. Co-aggregation ratios between probiotics and MS were low at all time-points varying from 3 (9)-23 (33)%. No significant differences in co-aggregation ratios between the tested probiotics or between various time-points could be observed (p>0.05; ANOVA). Light microscopic analysis also revealed an increasing auto-aggregation over time. In mixtures, auto-aggregation predominated over co-aggregation.
Conclusion: All tested strains showed high auto-aggregation but none of probiotics showed remarkable co-aggregation with MS.