In recent years, the consumers’ interest in health-promoting foods containing probiotics has risen due to probiotics’ capability to promote human health (Nair and Dubhashi 2016). Probiotics are defined as living microorganisms that, when given in sufficient number, confer a health benefit to the host (Hill et al. 2014). Probiotics are generally applied in the fermentation of foods as starter cultures and are considered safe with application in the food industry. The most widely used probiotic in the food industry is lactic acid bacteria (LAB). LAB is a heterogeneous group composed of Gram-positive, non-spore-forming bacteria, including
A worldwide spectrum of
Furthermore, the efficacy of probiotics has been proved to be species- or even strain-dependent, as different LAB strains can affect hosts in different ways (Cani and Van Hul 2015). Isolation and identification of such wild LAB from traditional dairy foods can be a good opportunity to develop new starter cultures and new probiotics (Bao et al. 2012). Consequently, exploration for new probiotics, especially from the relatively undeveloped rural areas, has become a hot research topic (Bajaj et al. 2014; Gupta and Bajaj 2016).
Chinese traditional buffalo milk is a kind of fermented yogurt with a unique flavor, which is made from raw milk of buffalo raised in the Changjiang river basin and fermented in clay pots by natural LAB. It is different from the yogurt products in Northwest China made from the raw milk of yak, cow, and sheep as the primary raw material. Rare reports have been available on the usage of Chinese traditional fermented buffalo milk as a potential probiotic carrier so far. A detailed study on the probiotic potential of Chinese traditional fermented buffalo milk can provide valuable information and clarify its potential use in a broader range.
Although LAB is generally considered safe to consume in the food industry, a series of
This study’s objecives were to provide a more comprehensive investigation of the probiotic properties of LAB strains obtained from Chinese traditional fermented buffalo milk through various
Five home-made traditional fermented buffalo milk was collected from the households of Digang Town, Fanchang County (E 118°20″, N 31°08″), Wuhu City, Anhui Province, China. The samples did not deteriorate, showed porcelain white, had milk fragrance, and no peculiar smell. To enrich LAB, the samples were added at 2% volume into 50 ml de Man, Rogosa, and Sharpe (MRS, Qingdao Hope Bio-Technology Co., Ltd.). The sample suspensions of an appropriate dilution were inoculated onto MRS plates (containing 1% CaCO3), and placed in an anaerobic environment for culture at 37°C for 48 h. The separate white colonies, which showed calcium-dissolving circle by streaking on the MRS plate were selected and purified. Biochemical features were used for the identification of isolated LAB. All the experiments in this study have been carried out in triplicates.
Adhesion to HT-29 cell was performed following the method described previously (Lee et al. 2015) with minor modifications. Human colon cancer cells HT-29 (Hunan Fenghui Bio-technology Co., Ltd.) were maintained in Dulbecco’s Modified Eagle Medium F-12 (DMEM/F12, Gibco, USA), supplemented with 10% (v/v) fetal bovine serum (Zhengjiang Tianhang Biotechnology Co., Ltd.) in a carbon dioxide incubator of 5% CO2 at 37°C for 48 h. The HT-29 cells were harvested and added into the 24-well plate (2 × 106 cells/well), and grown for 48 h. The medium was refreshed daily. A volume of 0.5 ml LAB (1 × 108 CFU/ml) was added into the wells, and the suspension was incubated at 37°C for 2 h. The wells were washed with PBS three times, then the cells were treated with Triton X-100 (BioFRoxx, Germany), and the bacteria were inoculated on the MRS agar plate. The number of the adherent bacterial cells was counted on the plates and the adhesion rate was calculated.
The determination of resistance to simulated gastrointestinal juices was carried out according to the method described previously with minor modifications (Cao et al. 2018; Iraporda et al. 2019). The cultures of LAB strains incubated in MRS broth, supplemented with 0.1% (w/v) ascorbic acid at 37°C for 48 h on anaerobic condition were centrifuged at 10,000 ×
2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was assessed according to the methodology used (Yu et al. 2018) with slight modifications. 0.2 ml of LAB culture (1 × 109 CFU/ml) was mixed with 1 ml DPPH solution in methanol (100 µM). After being placed against exposure to light at 37°C for 20 minutes, the mixture was centrifugated at 8,000 ×
Antibacterial activities of LAB strains were investigated by a disc diffusion method (Piyadeatsoontorn et al. 2019) with some modifications. The pathogens were used as indicator strains in this study, including
The LAB strain isolated was subjected to the 16S rRNA gene identification at the species level. The genomic DNA was extracted according to the manufacturer’s instructions of the bacterial DNA extraction kit purchased from TIANGEN Biotech Co., Ltd., and the 16S rRNA gene was amplified with universal primers 27F (5’-AGAGTTGATCCTGGCTCAG-3’) and 1492R (5’-GGTATCCTTGTTACTACTT-3’) by using gradient PCR instrument (ABI, USA) (Piyadeatsoontorn et al. 2019). A total volume of 50 μl consisted of 1.0 μl template DNA, 1.0 μl Taq DNA polymer, 5.0 μl 10 × PCR buffer, 1.0 μl 10 mM dNTP, 1.5 μl 10 μM upstream and downstream primers, respectively, 39.0 μl ddH2O. The thermal cycling parameters were as follows: initial denaturation at 95°C for 300 s, 35 denaturation cycles at 95°C for 30 s, annealing at 58°C for 30 s, elongation at 72°C for 90 s, and final elongation at 72°C for 420 s. Three microliters of PCR amplicons were visualized at 100 V for 1 h by using 1% agarose for electrophoresis. The PCR product was sent to Shanghai Personal Gene Technology Co., Ltd. for sequencing. The 16S rRNA gene sequences were compared and matched using BLAST with the available sequences in NCBI Gen-Bank. The homology of the target gene sequence was analyzed, and the phylogenetic tree was constructed by MEGA 7.0 with bootstrap values based on 1,000 replications. The sequence identified was uploaded to the NCBI Gene Bank database.
Observations on the morphology of isolated LAB strains exhibiting probiotic potential by SEM were conducted as described previously (Prasanna and Charalampopolous 2018). The LAB strains were placed in the incubator at 37°C for 18 h. The cultures were centrifuged at 8,000 ×
The growth curve and acid production curve were drawn based on the method described (Xia et al. 2019) with modifications. The fresh culture of isolated LAB strain was subcultured twice for 24 h and added into the conical flask (250 ml) containing 150 ml MRS broth at 2% inoculation amount for static culture in an anaerobic incubator (Shanghai Longyue Biotechnology Co., Ltd.). Two milliliters of culture were taken out through the rubber gloves fixed and sealed on the operating hole left on the anaerobic incubator quickly and carefully every 2 h until 24 h, and try not to shake the conical flask to keep the static condition. The absorbance value at 600 nm and pH value were measured. The growth curve and acid production curve were drawn according to the absorbance value at 600 nm, and pH value, respectively, determined at different culture times.
According to Bacon et al. (2003), the heat resistance test was performed with modifications. The strain was cultured in MRS broth until the absorbance value at 600 nm reached 1.5 at 37°C anaerobically. A total of 1 ml culture was inoculated into 4 ml PBS solution and treated in the water bath at 40, 50, 60, 70, or 80°C for 3 minutes, respectively. As soon as the heating was over, the solution was immediately cooled on ice and diluted to 10−1, 10−2, 10−3, 10−4, and 10−5, subsequently. The sample suspensions of appropriate dilution were plated onto MRS and placed in the incubator at 37°C for 18 h anaerobically.
BSH activity was performed as described by Shehata et al. (2016). The LAB strain was incubated in the incubator at 37°C for 18 h, and the culture was coated on the MRS plate with 0.5% (w/v) sodium taurodeoxycholic acid (TDCA) or MRS plate without TDCA, followed by incubation at 37°C for 72 h anaerobically. The appearance of precipitation indicated the BSH activity of the strain.
Biofilm formation on the glass and plastic surfaces was detected according to Gheziel et al. (2019). After LAB incubation the bio-film rings were collected, washed with distilled water, and stained with crystal violet (0.5%, v/v). Followed by dissolving the biofilms with acetic acid (30%, v/v), the absorbance value at 590 nm was measured. LAB was defined as strongly biofilm formation (OD590 > 0.2), weakly biofilm formation (0.1 < OD590 < 0.2), or no bio-film formation (OD590 < 0.1).
According to Adesulu-Dahunsi et al. (2018), the EPS production capability was detected. The strain was cultured in an MRS broth medium with 2% sucrose (w/v) at 37°C for 18 h. After the culture was centrifugated at 8,000 ×
The hemolysis test was assessed according to Menezes et al. (2020). The appearance of the hydrolytic circle (β-hemolysis) was regarded as a positive result. The appearance of the green circle (α-hemolysis) or no hydrolytic circle appearing (γ-hemolysis) was regarded as non-hemolysis.
Antibiotic susceptibility was assessed as Maldonado et al. (2012) with minor modifications. Under aseptic condition, 100 μl of LAB culture (1 × 107 CFU/ml) was coated on MRS plate. After 5 min, the discs containing antibiotics were placed on the plate, and the media were incubated at 37°C for 24 h. Types and dosages of antibiotics were as follows: metronidazole 5 μg, chloramphenicol 30 μg, streptomycin 10 μg, kanamycin 30 μg, ampicillin 10 μg, gentamicin 10 μg, tetracycline 30 μg, erythromycin 15 μg, rifampicin 5 μg, ciprofloxacin 5 μg, doxycycline 30 μg, vancomycin 30 μg. The diameter of the inhibition zone was measured with a vernier caliper, and the results were declared in accordance with the microbiological breakpoints for antimicrobials issued (CLSI 2012).
Biogenic amines production was investigated following Bover-Cid and Holzapfel (1999). Pyridoxal-5-phosphate (0.005%) was added to the medium as a cofactor for decarboxylation reaction, and the pH was adjusted to 5.3. The LAB strain was streaked on MRS plate supplemented with amino acids (lysine, histidine, arginine, tyrosine, and ornithine) (Beijing Solarbio Science & Technology Co., Ltd.) at 0.5% final concentration. Bromocresol purple was used as a color indicator, and the plate was placed in the incubator at 37°C for 72 h, subsequently. The positive result was confirmed by changing the indicator from yellow to purple.
Enzyme production was determined by using an API-ZYM kit (Biomerieux, France). After incubation of the strain, the culture was centrifuged at 4°C at 12,000 ×
Experiments were conducted in triplicate in our research, and all data were expressed as means and standard deviation. SPSS version 23.0 was employed for data analysis. One-way ANOVA estimated the difference with Duncan’s multiple range tests, and statistical significance was set at
Through preliminary screening of LAB, out of a total of 22 isolates, 11 isolated strains were putatively identified as LAB (Table I), and their adhesion to HT-29 cells was evaluated. The results are shown in Table II. The adhesion rate to HT-29 cell ranged from 2.47 ± 0.46% to 11.50 ± 1.22%. Among the 11 LAB strains, six strains displayed strong adhesion capacity to HT-29 cells, including WDS-3, WDS-4, WDS-7, WDS-9, WDS-10, and WDS-18. WDS-4 had the strongest adhesion capacity to HT-29 cells with an adhesion rate of 11.50 ± 1.22%.
Physiological and biochemical features of 11 isolated strains.
Characteristic | WDS | WDS-7 |
---|---|---|
Glucose gas production | − | − |
Gelatin | 3 | − |
Nitrate reduction | − | − |
Catalase | − | − |
Arginine hydrolysis | − | − |
Motile | − | − |
H2S production | − | − |
Indole | − | − |
15°C growth test | − | − |
45°C growth test | + | + |
Arabinose | 3 | − |
Cellobiose | 7 | − |
Esculin | 5 | − |
Fructose | + | + |
Gluconate | 4 | − |
Lactose | 9 | + |
Mannose | 6 | + |
Mannitol | 1 | − |
Sorbitol | − | − |
Melezitose | − | − |
Melibiose | 5 | − |
Raffinose | 3 | − |
Rhamnose | − | − |
Salicin | 6 | − |
Glucose | + | + |
Sucrose | 8 | + |
Trehalose | 6 | − |
Xylose | − | − |
Ribose | − | − |
Maltose | 8 | − |
WDS – WDS-2, WDS-3, WDS-4, WDS-8, WDS-9, WDS-10, WDS-11, WDS-15, WDS-18, WDS-20; 10 isolates
+ – positive or weakly positive reaction
– – negative reaction
number – the number of positive reactions
Adhesion rate to HT-29 cells of 11 isolated LAB strains.
Strains | Adhesion capacity to HT-29 Cell (%) |
---|---|
WDS-2 | 3.79 ± 0.72a |
WDS-3 | 9.65 ± 1.50bcd |
WDS-4 | 11.50 ± 1.22e |
WDS-7 | 10.74 ± 0.99cde |
WDS-8 | 2.47 ± 0.46a |
WDS-9 | 9.43 ± 0.93bc |
WDS-10 | 8.99 ± 1.05b |
WDS-11 | 3.32 ± 0.50a |
WDS-15 | 2.92 ± 0.80a |
WDS-18 | 11.23 ± 0.71de |
WDS-20 | 4.16 ± 0.37a |
LGG | 15.56 ± 1.31f |
Results are expressed as the mean ± SD.
– different letters along the column represent statistical significance (
Tolerance to artificial simulated gastrointestinal conditions of six selected LAB strains is presented in Table III. In general, six selected strains exhibited a good tolerance to artificial simulated gastrointestinal conditions. After treatment with artificial simulated gastric juice for 3 h, the survival rate of six LAB strains decreased with the growth reduction ranging from 18.66% to 29.06%. WDS-3 showed the best tolerance to artificial simulated gastric juice with an 81.34 ± 4.41 survival rate. Subsequently, after treatment with artificial simulated intestinal juice for 5 h, the growth reduction ranged from 29.44% to 39.96%. WDS-3 also displayed the best tolerance to artificial simulated intestinal juice, showing a 70.56 ± 4.49% survival rate. Due to their high tolerance to artificial simulated gastrointestinal conditions, WDS-3, WDS-4, WDS-7, WDS-9, WDS-10, and WDS-18 were chosen for further testing.
Tolerance to artificial simulated gastrointestinal conditions of six isolated LAB strains.
Strains | Artificial simulated gastric juice, 3 h, survival rate (%) | Artificial simulated intestinal juice, 5 h survival rate (%) |
---|---|---|
WDS-3 | 81.34 ± 4.40b | 70.56 ± 4.49b |
WDS-4 | 77.45 ± 3.66ab | 62.36 ± 3.06ab |
WDS-7 | 78.99 ± 3.98ab | 67.81 ± 3.57ab |
WDS-9 | 76.95 ± 2.03ab | 66.19 ± 3.48ab |
WDS-10 | 70.94 ± 4.27a | 60.04 ± 1.25a |
WDS-18 | 71.29 ± 2.13a | 60.75 ± 5.17a |
LGG | 84.72 ± 4.96b | 77.75 ± 4.25c |
Results are expressed as the mean ± SD.
– different letters along the column represent statistical significance (
Antioxidant activities including DPPH radical scavenging, ABTS+ radical scavenging, and superoxide anion scavenging were assayed in this study. The results are presented in Table IV. In general, WDS-4, WDS-7, and WDS-18 exhibited prominent antioxidant activities with significantly higher DPPH, ABTS+, and superoxide anion scavenging activities than those of the reference strain LGG (
Antioxidant capacities of six isolated LAB strains.
Strains | Antioxidant capacities (%) | ||
---|---|---|---|
DPPH scavenging activity | ABTS+ scavenging activity | Superoxide anion scavenging activity | |
WDS-3 | 19.32 ± 1.24ab | 52.35 ± 2.47b | 41.31 ± 2.64a |
WDS-4 | 31.04 ± 1.71c | 65.20 ± 2.38d | 49.72 ± 1.63b |
WDS-7 | 30.15 ± 2.24c | 68.31 ± 1.50d | 48.92 ± 1.36b |
WDS-9 | 18.09 ± 1.78a | 40.78 ± 1.43a | 40.77 ± 1.85a |
WDS-10 | 22.08 ± 1.61b | 49.01 ± 1.72b | 41.94 ± 1.69a |
WDS-18 | 32.00 ± 2.71c | 56.97 ± 1.68c | 48.68 ± 1.33b |
LGG | 21.32 ± 1.13ab | 51.94 ± 2.04b | 40.12 ± 1.07a |
Results are expressed as the mean ± SD.
– different letters along the column represent statistical significance (
The inhibition activity of three isolated strains against four pathogens including
Due to the efficient adhesion to HT-29 cells, prominent antioxidant activity, and remarkable antimicrobial activity, the WDS-7 strain was selected to be identified by the 16S rRNA gene sequencing. The 16S rRNA gene sequence of the WDS-7 strain was uploaded to NCBI (the accession No. MN 759441), and the sequence similarity comparison was performed with BLAST. The phylogenetic tree of strain is shown in Fig. 2. The homology of WDS-7 and
The micrographs of
The growth curve of
The heat resistance of
The cell survival rates after heat treatment of
Strains | Temperature (°C) | |||
---|---|---|---|---|
50 | 60 | 70 | 80 | |
WDS-7 | 91.81 ± 7.43% | 12.38 ± 2.33%* | ≈ 0% | 0% |
LGG | 83.38 ± 7.32% | 4.79 ± 0.93% | ≈ 0% | 0% |
Results are expressed as the mean ± SD.
– along the column represent statistical significance (
The BSH activity of
The ability of
Biofilm formation by
Strains | Biofilm formation | |
---|---|---|
Glass | Plastic | |
WDS-7 | + | ++ |
LGG | + | + |
+ and ++ represent mild biofilm producer (0.1 < OD590 < 0.2) and strong biofilm producer (OD590 > 0.2), respectively
The EPS production by
The antibiotic susceptibility of
Antibiotic susceptibility of
Strains | Antibiotic susceptibility | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Metronidazole | Chloramphenicol | Streptomycin | Kanamycin | Ampicillin | Gentamicin | Tetracycline | Erythromycin | Rifampicin | Ciprofloxacin | Doxycycline | Vancomycin | |
WDS-7 | R | S | R | R | S | R | I | S | S | I | S | R |
LGG | R | S | R | R | S | R | S | S | S | S | S | R |
R, I, and S represent resistance, intermediate susceptibility, and susceptibility to the antibiotic, respectively
The enzyme production by
Enzyme production by
Enzyme | Strains | |
---|---|---|
LGG | WDS-7 | |
Alkaline phosphatase | 1 | 1 |
Esterase | 2 | 1 |
Esterase lipase | 1 | 2 |
Lipase | 0 | 0 |
Leucine arylamidase | 2 | 4 |
Valine arylamidase | 3 | 2 |
Cystine arylamidase | 1 | 0 |
Trypsin | 0 | 0 |
α-Chymotrypsin | 0 | 0 |
Acid phosphatase | 2 | 0 |
Naphthol-AS-BI-phosphohydrolase | 2 | 2 |
α-Galactosidase | 1 | 3 |
β-Galactosidase | 2 | 4 |
β-Glucuronidase | 0 | 0 |
α-Glucosidase | 2 | 2 |
β-Glucosidase | 1 | 0 |
N-Acetyl-b-glucosaminidase | 0 | 0 |
α-Mannosidase | 0 | 0 |
α-Fucosidase | 1 | 0 |
Control | 0 | 0 |
0: 0 nmol, 1: 5 nmol, 2: 10 nmol, 3: 20 nmol, 4: 30 nmol, 5: 40 nmol
Adhesion to the intestinal mucosa is vital for cultivating probiotics, as it is a prerequisite for colonization in the gastrointestinal tract (Papadimitriou et al. 2015). Georgalaki et al. (2017) reported that the adhesion rate of
The candidate selected as probiotic should survive under high acid conditions and maintain high cell concentration within 2–3 hours of transit in the stomach. Similarly, a potential probiotic is considered is considered to show tolerance to bile salt in the human gut (Kandylis et al. 2016). Son et al. (2017) found that
Probiotics with antioxidant activity benefit the host by destroying and neutralizing free radicals (Talebi et al. 2018). At present, DPPH and ABTS+ free radical scavenging activities are important tools to evaluate the antioxidant activity of probiotics. Das et al. (2020) investigated the antioxidant activities of eight
Antimicrobial activity is an important criterion when screening potential probiotics, as antimicrobial activity prevents potentially harmful intestinal microorganisms from colonizing the host’s intestinal mucosa (Gheziel et al. 2019). Edalati et al. (2019) discovered that
A microbial growth curve can provide useful helpful information for understanding microbial growth trends and selecting the optimal growth stage (Yang et al. 2018). Rapid growth and low pH of the culture may constitute an important feature for the industrial production of a potential probiotic strain. Yang et al. (2021) described that eight
Potential probiotic must be able to withstand the harsh conditions e.g., heat, often encountered in food processing, to be successfully applied in functional foods. Ren et al. (2018) found most
The positive results showing the presence of precipitation around the colonies on MRS agar plate containing TDCA by LAB are advantageous for probiotics as it can help to detoxify bile salt by producing BSH activity (Sharma et al. 2021). It was observed that
The ability to form biofilm is another desirable characteristic of probiotics. Biofilms are complex multi-species communities that are closely linked to the surface. Therefore, screening of potential probiotic strains usually involves the determination of its biofilm formation capacity (Muruzović et al. 2018). Among five LAB strains isolated from Algerian infant feces,
Probiotics possessing the capability of EPS production are considered an advantage (Bermúdez-Humarán and Langella 2011). Comparatively with the rest of the cultures,
In terms of antibiotic resistance, potential probiotic exhibiting sensitivity to antibiotics is preferable for application. Our findings were similar to the antibiotic resistance of
The absence of biogenic amines production in
The lack of harmful activities, such as β-glucuronidase activity, must also be included in the safety assessment. In present study,
In this work,