Among Streptococcus thermophilus cultures, the principle component of yoghurt and cheese starters, a minority of strains forms the group of ‘H’-strains which show an unusually high acidification rate, grow faster and coagulate milk 3–5 hours earlier than the typical S. thermophilus cultures. A large-scale screening study was performed to select ‘H’-strains of S. thermophilus from more than 100 samples of home-made yoghurt, industrial yoghurt starters and single cultures, maintained in the LBB culture collection. Only four strains – LBB.TN1, LBB.M23, LBB.M34 and LBB.M60 – were isolated/selected due to their ability to form large yellowish colonies on milk agar, supplemented with beta-glycerophosphate and bromocresol purple. While in general S. thermophilus is described as a species with limited proteolytic capacity and in contrast to all other tested S. thermophilus cultures, the four selected strains invariably gave positive amplification product with the polymerase chain reaction when primers, specific for the membrane proteinase-coding gene prtS were used. The macrorestriction profiles of the genomic DNA of the four strains confirmed that they are non-isogenic and not related to each other. When grown in milk and compared to the control industrial strain LBB.A, the four strains showed a dramatically faster acidification, coagulating milk within four hours. The application of strain TN1 or M23 as adjunct culture to industrial yoghurt starter LBB.BY5-12 resulted in shortening the fermentation time with more than 30 min.

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 A – like 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.

The urgent need of research of new approaches to control bacterial disease on economical important crops, focuses our attention on bacteriophages as alternative biocontrol agents. Thus, the purpose of this paper is to present the isolation and initial characterization of three bacteriophages (SfXv124t/1, 2 and 3) isolated from rhizosphere soil of a healthy tomato plant in Bulgaria that are capable to lyse three phytopathogenic bacteria. The initial characterization includes determination of: their host range, plaque morphology, optimal storage temperature of pure phage lysates, their sensitivity to UV light, thermal inactivation, optimal multiplicity of infection (MOI) and virion morphology. The obtained results showed that one of the phage isolates was capable to lyse wild strains from three phytopathogenic bacterial species: Xanthomonas vesicatoria, Xanthomonas euvesicatoria and Xanthomonas gardneri, and the two remaining phages were active against X. vesicatoria and X. euvesicatoria. On X. vesicatoria lawn, the phages produced the same plaque types that differed only in their size. Storage at 4 °C for 26 days did not lead to decrease in phage titer as opposed to storage at 28 °C followed by decrease to varying degree for all three phages. The results obtained after exposure of the phage lysates to sunlight (UVA + B) and UVC light in separate experiments showed that UVC had a potent phagocidal effect as after 50 min of exposure there were no viable phages in the samples. UVA an UVB had lethal effect for two of the phage isolates and absolutely no lethal effect for the third one as after 50 min of exposure to sunlight there was no decrease in the initial phage titer. Phage isolates were tested for their thermal inactivation after incubation of pure phage lysates at three different temperatures: 55 °C, 75 °C and 95 °C for a period of 10 and 30 min. The most lethal temperature turned out to be 95 °C as after 10 min there were no viable phages in the samples. Phage isolate SfXv124t/1 was the most susceptible as its titer decreased by 1 lg after 10 min of incubation at 55 °C and by another 1 lg after 30 min. The most thermally resistant isolate was SfXv124t/3 as its titer remained stable after 30 min of incubation at 55 °C and decreased only by lg after incubation at 75 °C for 10 min. The optimal MOI for SfXv124t/3 was 0,01 (tested range 0,01–100) with maximal phage titer, reported at the 24th hour of incubation. TEM micrographs of the same isolates reveals that it belongs to family Podoviridae.