Evaluation of antimicrobial activity and antibiotic susceptibility profiles of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains isolated from commercial yoghurt starter cultures

Abstract

This research investigated the antimicrobial activity and antibiotic susceptibilities of nine Lactobacillus delbrueckii subsp. bulgaricus strains and nine Streptococcus thermophilus strains isolated from commercial yoghurt cultures. The antimicrobial activities of overnight culture strains against Bacillus cereus CECT 131, Bacillus subtilis ATCC 6633, Campylobacter jejuni NCTC 11351, Candida albicans ATCC 14053, Enterobacter aerogenes ATCC 13048, Escherichia coli ATCC 25922, Listeria monocytogenes ATCC 7644, Pseudomonas aeruginosa ATCC 9027, Salmonella typhimurium ATCC 14028 and Staphylococcus aureus ATCC 12600 were investigated using the disc diffusion method. The antibiotic resistance/susceptibility profiles of the strains were determined using antibiotic discs, which included ampicillin (10µg), ampicillin (25µg), bacitracin (10µg), clindamycin (2µg), clindamycin (10µg), erythromycin (10µg), erythromycin (15µg), gentamicin (10µg), gentamicin (120µg), nalidixic acid (30µ), neomycin (10µg), novobiocin (5µg), oxacillin (1µg), penicillin (10units), streptomycin (25µg), streptomycin (300µg), tetracycline (30µg) and vancomycin (30µg). The results of the study showed that while the Streptococcus thermophilus strain SY8, Lactobacillus bulgaricus strains LY6, LY8, LY9 and LY10 showed antimicrobial activity for all test microorganisms, Streptococcus thermophilus SY5 strains showed the weakest antimicrobial effect. All the Lactobacillus bulgaricus and Streptococcus thermophilus strains were resistant to oxacillin (1μg) and nalidixic acid (30μg). Indeed, the highest antibiotic susceptibility was seen with antibiotics such as ampicillin (25μg), clindamycin (10μg) and erythromycin (15μg).

Bioactive Peptides from Liquid Milk Protein Concentrate by Sequential Tryptic and Microbial Hydrolysis

“…The zone of inhibition has an increasing trend with the increase in the concentration of trypsin for all microorganisms. The antibacterial activity of Lactobacillus bulgaricus and Streptococcus thermophilus against all mentioned microorganisms has been reported by other investigators [118,119]. During microbial fermentation, the reduction of pH [120] or the generation of new antibacterial peptides or bacteriocin [120,121] may offer antibacterial activity against all mentioned microorganisms.…”

“…On the other hand, the biochemical characteristics of the bacteriocin produced by Lactobacillus bulgaricus are generally class IV bacteriocin [124]. It has been reported that the bacteriocin produced by Streptococcus thermophilus was less active against Staphylococcus aureus [118,119,123] and Bacillus cereus [118,119] than against Listeria monocytogenes. On the other hand, the bacteriocin produced by Lactobacillus bulgaricus was less active for inhibiting Staphylococcus aureus than Listeria monocytogenes and Bacillus cereus [118,119].…”

“…It has been reported that the bacteriocin produced by Streptococcus thermophilus was less active against Staphylococcus aureus [118,119,123] and Bacillus cereus [118,119] than against Listeria monocytogenes. On the other hand, the bacteriocin produced by Lactobacillus bulgaricus was less active for inhibiting Staphylococcus aureus than Listeria monocytogenes and Bacillus cereus [118,119]. It is noted that the value of the zone of inhibition is not changed in a significant way in LMPC-T-F G compared to LMPC-T-F.…”

Investigation of memory-enhancing effects of Streptococcus thermophilus EG007 in mice and elucidating molecular and metagenomic characteristics using nanopore sequencing

“…Similarly, in previous studies, abundance of genus Olsenella was positively correlated to gut inflammation and STH infection, which also significantly reduced following clearance of the infections 95 , 96 . The reduction of these microbes might be associated with the antagonistic effect of S. thermophilus against various pathogens 97 as the presence of several kinds of putative bacteriocin clusters in the EG007 genome was also identified. A number of studies have proposed the functions of probiotics in a decrease of proinflammatory microbes and increase of microbiota with anti-inflammatory activities, which might in turn prevented the pathogenesis of neurodegeneration via the MGB axis 33 , 98 .…”

Selection of potential probiotics with cholesterol-lowering properties for probiotic yoghurt production

“…In addition, the viability of L. fermentum KUB-D18, L. pentosus HM04-25, and L. pentosus HM04-3 was determined in selective MRS media with 30 µg/mL of vancomycin. Yoghurt starter could not growth on vancomycin supplement (30 µg/mL) (Yerlikaya et al., 2020). All cultures on MRS agar plates were incubated at 37 °C for 18 h.…”