BackgroundConsumers are increasingly demanding for natural and beneficial foods, in order to improve their health and well-being. Probiotics play an important role in such demand, and dairy foods are commonly used as vehicles for such bacteria, represented predominantly by lactic acid bacteria. Due to consumers demand, food industry is constantly looking for novel bacterial strains, leading to studies that aims the isolation and characterization of their beneficial features. This study aimed to characterize the naturally occurring lactic acid bacteria obtained from a dairy environment, in order to assess their potential use as probiotics.ResultsPreliminary screening and PCR analysis, based on 16S rRNA sequencing, were applied to select and identify 15 LAB strains from the genera Lactobacillus (n = 11), Pediococcus (n = 2) and Weissella (n = 2). All strains showed resistance to low pH and the evaluated bile salt concentrations in vitro. The API ZYM test characterized the enzymatic activity of the strains, and a high β-galactosidase activity was observed in 13 strains. All strains presented resistance to simulated gastric (3 h) and intestinal (4 h) conditions in vitro, the ability to auto- and co-aggregate with indicator microorganisms and a high cell surface hydrophobicity. Most of the strains were positive for map and EFTu beneficial genes. All strains exhibited strong deconjugation of bile salts in vitro and all assimilated lactose.ConclusionsThe phenotypes exhibited in vitro and the presence of beneficial genes revealed the beneficial potential of the studied strains, demanding further analyses in a food matrix and in vivo to allow the development of a functional product, with health-related properties.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1356-8) contains supplementary material, which is available to authorized users.

This study aimed to assess the safety aspects of 15 lactic acid bacteria (LAB) strains previously isolated from a dairy environment with relation to their beneficial features. LAB strains were assessed using phenotypic methods according to their production of virulence factors at 25°C and 37°C, as well as by examining their potential resistance to 15 antibiotics. Polymerase chain reaction (PCR) was also used to identify the presence of 50 genes associated with virulence factors and antibiotic resistance in the strains. None of the strains presented hemolytic activity or the production of gelatinase, lipase, deoxyribonuclease, or the tested biogenic amines. Based on the disk diffusion assay, all strains were resistant to oxacillin and sulfa/trimethoprim. Further, some were resistant to gentamicin (14), clindamycin (11), vancomycin (9), rifampicin (8), erythromycin (5), tetracycline (4), ampicillin (2), and chloramphenicol (1); no strain was resistant to imipenem. Regarding virulence-and antibiotic-resistance-related genes, 19 out of 50 tested genes were present in some strains; there was a variable association of expression. Based on the obtained data, the isolates presented relatively safe characteristics and behavior, findings that should lead to further studies to assess their potential usage as beneficial cultures in the food industry. Keywords Lactic acid bacteria. Virulence factors. Antibiotic resistance Highlights • The safety aspects of LAB isolated from a dairy environment was evaluated. • Presence of 49 virulence factors and antibiotic resistance genes was studied. • Physiological expression of virulence factors, biogenic amine, and antibiotic resistance was tested.

Scientific studies demonstrate the importance of intestinal microbiota to human health and how probiotic microorganisms can positively affect health when administered regularly and in adequate amounts. Probiotic bacteria can be part of fermented products and their functional importance is associated mainly with their metabolism. They are thought to benefit individuals to maintain their health and also to strengthen resistance against various types of diseases. The acceptance of probiotic cultures and products by consumers increased when these bacteria were marketed as natural cultures that help in digestion and health. Considering this, the food industry has an increasing demand for new candidates as probiotic cultures, and the dairy industry has a particular interest for fermented milks and other dairy products, since these are the most common food vehicles for probiotic cultures. Therefore, the dairy industries are increasingly seeking to improve their products with these beneficial bacteria. However, the legal peculiarities and excess of control agencies in Brazil makes the registration of these products and the collection of data very complex. Prospective analysis suggests that probiotic foods have the potential to effect a considerable expansion of the dairy industry, allowing the dairy sector to grow and for these products to be increasingly sought by consumers globally. For this, not only actions on research and innovation are necessary, but also official clarifications on the claims for considerations of microbiological security and functionality of these products. This review aims to elucidate important probiotic research regarding the isolation and characterization of beneficial cultures in Brazil, and to demonstrate the relevance of the dairy chain as a potential source of novel cultures for the development of new probiotic products to expand the Brazilian dairy industry.

BackgroundBacteriocins produced by lactic acid bacteria (LAB) can be considered as viable alternatives for food safety and quality, once these peptides present antimicrobial activity against foodborne pathogens and spoilage bacteria. Fermented foods, such as artisanal sausages and cured meats, are relevant sources of LAB strains capable of producing novel bacteriocins, with particular interest by the food industry.ResultsThree LAB strains (firstly named as Lactobacillus curvatus 12, L. curvatus 36 and Weissella viridescens 23) were obtained from calabresa by presenting promising bacteriocinogenic activity, distinct genetic profiles (rep-PCR, RAPD, bacteriocin-related genes) and wide inhibitory spectrum. Among these strains, L. curvatus 12 presented higher bacteriocin production, reaching 25,000 AU/mL after incubation at 25, 30 and 37 °C and 6, 9 and 12 h. Partially purified bacteriocins from L. curvatus 12 kept their inhibitory activity after elution with isopropanol at 60% (v/v). Bacteriocins produced by this strain were purified by HPLC and sequenced, resulting in four peptides with 3102.79, 2631.40, 1967.06 and 2588.31 Da, without homology to known bacteriocins.ConclusionsLAB isolates obtained from calabresa presented high inhibitory activity. Among these isolates, bacteriocins produced by L. curvatus 12, now named as L. curvatus UFV-NPAC1, presented the highest inhibitory performance and the purification procedures revealed four peptides with sequences not described for bacteriocins to date.Electronic supplementary materialThe online version of this article (10.1186/s12866-019-1436-4) contains supplementary material, which is available to authorized users.

Monitoring the populations of probiotic strains of the species Lactobacillus casei in food is required by food industries in order to assure that a minimum concentration of these organisms will be ingested by consumers. In this context, Petrifilm™ AC plates can be used along with selective culture media to allow the enumeration of specific groups of lactic acid bacteria. The present study aimed to assess chemical substances as selective agents for Lb. casei in order to propose a selective culture medium to be used with Petrifilm™ AC plates as an alternative protocol for the enumeration of probiotic strains of this species in fermented milk. Twenty-six probiotic and starter cultures (including six strains of Lb. casei) were plated on de Man Rogosa and Sharpe (MRS) agar with distinct concentrations of nalidixic acid, bile, lithium chloride, metronidazole, sodium propionate, and vancomycin. Vancomycin at 10 mg/L demonstrated selective activity for Lb. casei. In addition, 2,3,5-triphenyltetrazolium chlorine was identified as a compound that did not inhibit Lb. casei, and Petrifilm™ AC plates used with MRS and vancomycin at 10 mg/L (MRS-V) demonstrated more colonies of this organism when incubated under anaerobic conditions than aerobic conditions. Acidophilus milk and yoghurt were prepared, added to Lb. casei strains, and stored at 4 °C. Lb. casei populations were monitored using MRS-V and MRTLV by conventional plating and associated with Petrifilm™ AC plates. All correlation indices between counts obtained by conventional plating and Petrifilm™ AC were significant (p < 0.05), but the best performance was observed for growth on MRS-V. The obtained data indicate the efficiency of using MRS-V associated with Petrifilm™ AC plates for the enumeration of Lb. casei strains in fermented milk. However, the selective potential of this culture medium must be evaluated considering the specific strains of Lb. casei and the starter cultures inoculated in the fermented milk that requires monitoring.