In lactobacilli the aggregation phenotype is linked to their ability to colonize the intestinal and urogenital tracts and to counteract pathogenic bacteria. In all available complete genome sequences of Lactobacillus delbrueckii ssp. bulgaricus there are at least two genes putatively related to aggregation, one of which is annotated as aggregation-promoting factor (apf). Here we report the results from the in silico analysis of this gene and its product. The apf gene was present in the genome of all 70 tested L. delbr. ssp. bulgaricus strains. Its expression was confirmed for a selection of five strains with aggregation phenotype and two aggregation-negative strains. The mature Apf protein had a length of 257-284 amino acids with predicted molecular weight in the range of 28.64-30.36 kDa and isoelectric point of 10.6 ± 0.1, showing some similarity to Apf1 and Apf2 from L. johnsonii NCC533 and Apf1 and Apf2 from L. gasseri which are similar in size (28-35 kDa) and share a similar high isoelectric point (pI > 9). Predictive analyzes have indicated that Apf is a secretory protein. The 30 amino acid signal peptide and the predicted cleavage site in the pre-protein suggested that it was processed by Type I Signal protease. In the mature Apf protein a glutamine-rich N-terminal region was followed by an unusual lysine/alanine-rich region with variable length, supposed to be positively charged under physiological conditions, interacting with bacterial teichoic acids. The alignment of the C-termini of the Apf proteins showed similarity to conserved C-terminal domains in aggregation-related proteins in other lactobacilli such as Apf1 of Lactobacillus johnsonii ATCC 11506 and the secretory protein Sep of L. fermentum BR11, that may be involved in non-covalent binding to carbohydrates. The C-terminal anchor and the cationic domain in Apf may serve as mediators of physical cell-to-cell interaction in L. delbr. ssp. bulgaricus.

Due to their antimicrobial activity Enterococcus faecium strains have a growing record of use as beneficial adjunct cultures in animal nutrition or components of probiotic preparations for humans. However, safety concerns accompany the application of enterococci, as clinical strains associated with infection have been isolated, especially antibiotic resistant cultures. With the increasing availability of whole genome sequencing (WGS), valuable safety data can be extracted in the early phase of development of the probiotic dossier of an E. faecium strain. Here we report the results of initial safety assessment of E. faecium LBB.E81 by selecting accessible commercial antibiotic susceptibility test and WGS. Testing against a panel of antibiotic substances showed that E. faecium LBB.E81 was susceptible to all antimicrobials with the exception of its intrinsic, non-transferable resistance to nitrofurantoin. The identified antibiotic resistance genes of E. faecium LBB.E81 aac(6')-Ii, msrC and efmA belonged to a group of intrinsic non-transferable factors contributing to the lower susceptibility of the E. faecium species to aminoglycoside and macrolide antibiotics but with minimal inhibitory concentrations for E. faecium LBB.E81 below the threshold values determined for resistant strains. The only potential virulence factor genes found in the genome of E. faecium LBB.E81 were a defective acm (collagen-binding adhesin) and efaA fm (antigen Alike protein) without any evidence for its involvement in pathogenicity. Other hospital associated virulence factor genes of E. faecium such as IS16, hyl, asa-type genes, cyl; gelE and fsr, sprE and esp(fm) were found to be absent in E. faecium LBB.E81.

Introduction: The gram-negative bacterium Porphyromonas gingivalis is a major causative agent of periodontitis in adults. It is also associated with disorders of the cardiovascular and endocrine systems, rheumatoid arthritis, pancreatic cancer, and Alzheimer’s disease. Lactic acid bacteria (LAB) present in the oral cavity or introduced as probiotic preparations can support successful treatment of periodontitis due to their antagonism with the pathogen. Aim: The aim of this study was in vitro assessment of the antimicrobial activity of Lactobacillus spp. and Streptococcus thermophilus against P. gingivalis. Materials and methods: The antimicrobial effect of lactobacilli or S. thermophilus from the LBB Culture collection against P. gingivalis DSM 20709 was evaluated with the well diffusion assay on Wilkins Chalgren blood agar. Inhibition of the pathogen was evaluated by measuring the diameter of clear zones around the wells. Results: Application of milk fermented with selected LAB resulted in а bacteriostatic effect. The most active culture was S. thermophilus 187/4, followed by L. delbr. ssp. bulgaricus (LBB.B1054, C3/2 and LBB.B120), L. helveticus LBB.H48/1 and L. rhamnosus I-1/13. The respective reconstituted freeze-dried preparations had a stronger inhibitory effect on the pathogen with the formation of clear bactericidal zones. The effect of milk acidified with lactic acid was apparent with minimal bactericidal zone observed at concentration of 0.1%. The effectiveness of the assay was confirmed with Elgydium and Eludril. Conclusions:P. gingivalis DSM 20709 was sensitive to the metabolites produced in fermented milk by selected strains of L. delbr. ssp. bulgaricus, L. helveticus, L. rhamnosus, and S. thermophilus. Reconstituted freeze dried fermented milk had а stronger inhibitory effect compared to fresh samples. Lactic acid produced by lactic acid bacteria was the key component for inhibition of the pathogen.