Comparison of the sensitivity of commercial strains and infant isolates of bifidobacteria to antibiotics and bacteriocins

Antibacterial Activity of Chinese Red Propolis against Staphylococcus aureus and MRSA

The antibacterial activity of propolis has long been of great interest, and the chemical composition of propolis is directly dependent on its source. We recently obtained a type of propolis from China with a red color. Firstly, the antibacterial properties of this unusual propolis were determined against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA). Studies on its composition identified and quantified 14 main polyphenols of Chinese red propolis extracts (RPE); quantification was carried out using liquid chromatography triple quadrupole tandem mass spectrometry (LC-QQQ-MS/MS) and RPE was found to be rich in pinobanksin, pinobanksin-3-acetate, and chrysin. In vitro investigations of its antibacterial activity revealed that its activity against S. aureus and MRSA is due to disruption of the cell wall and cell membrane, which then inhibits bacterial growth. Despite its similar antibacterial activities against S. aureus and MRSA, metabolomic analysis further revealed the effects of RPE on bacteria metabolism were different. The untargeted metabolomic results showed that a total of 7 metabolites in 12 metabolic pathways had significant changes (Fold change > 2, p < 0.05 *) after RPE treatment in S. aureus, while 11 metabolites in 9 metabolic pathways had significant changes (Fold change > 2, p < 0.05 *) after RPE treated on MRSA. Furthermore, RPE downregulated several specific genes related to bacterial biofilm formation, autolysis, cell wall synthesis, and bacterial virulence in MRSA. In conclusion, the data obtained indicate that RPE may be a promising therapeutic agent against S. aureus and MRSA.

In Vitro Selective Growth-Inhibitory Activities of Phytochemicals, Synthetic Phytochemical Analogs, and Antibiotics against Diarrheagenic/Probiotic Bacteria and Cancer/Normal Intestinal Cells

A desirable attribute of novel antimicrobial agents for bacterial diarrhea is decreased toxicity toward host intestinal microbiota. In addition, gut dysbiosis is associated with an increased risk of developing intestinal cancer. In this study, the selective growth-inhibitory activities of ten phytochemicals and their synthetic analogs (berberine, bismuth subsalicylate, ferron, 8-hydroxyquinoline, chloroxine, nitroxoline, salicylic acid, sanguinarine, tannic acid, and zinc pyrithione), as well as those of six commercial antibiotics (ceftriaxone, ciprofloxacin, chloramphenicol, metronidazole, tetracycline, and vancomycin) against 21 intestinal pathogenic/probiotic (e.g., Salmonella spp. and bifidobacteria) bacterial strains and three intestinal cancer/normal (Caco-2, HT29, and FHs 74 Int) cell lines were examined in vitro using the broth microdilution method and thiazolyl blue tetrazolium bromide assay. Chloroxine, ciprofloxacin, nitroxoline, tetracycline, and zinc pyrithione exhibited the most potent selective growth-inhibitory activity against pathogens, whereas 8-hydroxyquinoline, chloroxine, nitroxoline, sanguinarine, and zinc pyrithione exhibited the highest cytotoxic activity against cancer cells. None of the tested antibiotics were cytotoxic to normal cells, whereas 8-hydroxyquinoline and sanguinarine exhibited selective antiproliferative activity against cancer cells. These findings indicate that 8-hydroxyquinoline alkaloids and metal-pyridine derivative complexes are chemical structures derived from plants with potential bioactive properties in terms of selective antibacterial and anticancer activities against diarrheagenic bacteria and intestinal cancer cells.

Characterization and screening of the potential probiotic lactic acid bacteria and Bifidobacterium strains isolated of different biotopes

The use of lactic acid bacteria (LAB) and bifidobacteria species as probiotics may help to reduce antibiotic use for therapeutic, prophylactic and growth promotion in animal husbandry. The choice of the starter cultures has a critical impact on the palatability, processability and nutritional attributes of fermented products. In our research, the aim of this study was to screen and select potent probiotic LAB and Bifidobacterium strains isolated from different niches and to evaluate their characteristic features. A total of fourteen LAB and fifty-four Bifidobacterium were isolated from four fresh cows and camel’s milk, and twenty stool samples of healthy new born infants were identified and characterized by morphology and biochemical tests in order to select most suitable strains according to their technological characteristics including probiotic proprieties, antibiotics resistance and in vitro antagonism against food-poisoning bacteria. When the results of tolerance to both gastric and bile juices are taken together it appears that between fourteen LAB and forty-five, the strain B. longum BHI 07 has significantly the highest ability to survive during gastrointestinal transit (P < 0.05). Therefore, the mixed cultures of Bf. longum strains with LAB strains were more active against pathogenic bacteria than the pure one. These results show that bifidobacteria isolated from infants may be useful for improving probiotic formulae with respect to protection against pathogenic bacteria responsible of infection.

Study of the Ability of Bifidobacteria of Human Origin to Prevent and Treat Rotavirus Infection Using Colonic Cell and Mouse Models

Rotavirus is the leading cause of severe acute gastroenteritis among children worldwide. Despite effective vaccines, inexpensive alternatives such as probiotics are needed. The aim of this study was to assess the ability of probiotic candidate Bifidobacterium thermophilum RBL67 to inhibit rotavirus infection. Bacterial adhesion to intestinal cells and interference with viral attachment were evaluated in vitro. B. thermophilum RBL67 displayed adhesion indexes of 625 ± 84 and 1958 ± 318 on Caco-2 and HT-29 cells respectively and was comparable or superior to four other bifidobacteria, including B. longum ATCC 15707 and B. pseudolongum ATCC 25526 strains. Incubation of B. thermophilum RBL67 for 30 min before (exclusion) and simultaneously (competition) with human rotavirus strain Wa decreased virus attachment by 2.0 ± 0.1 and 1.5 ± 0.1 log₁₀ (by 99.0% and 96.8% respectively). Displacement of virus already present was negligible. In CD-1 suckling mice fed B. thermophilum RBL67 challenged with simian rotavirus SA-11, pre-infection feeding with RBL 67 was more effective than post-infection feeding, reducing the duration of diarrhea, limiting epithelial lesions, reducing viral replication in the intestine, accelerating recovery, and stimulating the humoral specific IgG and IgM response, without inducing any adverse effect. B. thermophilum RBL67 had little effect on intestinal IgA titer. These results suggest that humoral immunoglobulin might provide protection against the virus and that B. thermophilum RBL67 has potential as a probiotic able to inhibit rotavirus infection and ultimately reduce its spread.

In Vitro Antibacterial Mechanism of Action of Crude Garlic (Allium sativum) Clove Extract on Selected Probiotic Bifidobacterium Species as Revealed by SEM, TEM, and SDS-PAGE Analysis

There has been much research on the effects of garlic (Allium sativum) on numerous pathogens, but very few, if any, studies on its effect on beneficial, probiotic bifidobacteria. We have recently shown that garlic exhibits antibacterial activity against bifidobacteria. The mechanism by which garlic kills bifidobacteria is yet to be elucidated. This study sought to determine the mechanism of action of garlic clove extract on selected Bifidobacterium species using scanning and transmission electron microscopy and SDS-PAGE analysis. SEM micrographs revealed unusual morphological changes such as cell elongation, cocci-shaped cells with cross-walls, and distorted cells with bulbous ends. With TEM, observed changes included among others, condensation of cytoplasmic material, disintegration of membranes, and loss of structural integrity. SDS-PAGE analysis did not reveal any differences in whole-cell protein profiles of untreated and garlic clove extract-treated cells. The current study is the first to reveal the mechanism of action of garlic clove extract on probiotic Bifidobacterium species. The results indicate that garlic affects these beneficial bacteria in a manner similar to that exhibited in pathogens. These results therefore further highlight that caution should be taken especially when using raw garlic and probiotic bifidobacteria simultaneously as viability of these bacteria could be reduced by allicin released upon crushing of garlic cloves, thereby limiting the health benefits that the consumer anticipate to gain from probiotics.

Physiological and Structural Differences Between Enterococcus faecalis JH2-2 and Mutant Strains Resistant to (P)-Divercin RV41

The aim of this study was to show the differences that could exist at the physiological and structural levels between Enterococcus faecalis JH2-2 (wild type) and three mutant strains resistant to divercin RV41. These mutant strains were recently isolated and characterized for their intermediate resistance to recombinant DvnRV41; a subclass IIa bacteriocin produced by Escherichia coli. These mutant strains were named 35A1 (altered in gene coding phosphoesterase activity), 35H1 (altered in gene coding σ(54) factor) and 36H4 (altered in gene coding glycerophosphodiesterase). The growth and resistance of each strain were tested against lysozyme. The inhibitory substance did not show any cross-resistance but exhibited an additive effect ascribed to the combined action of lysozyme and (P)-DvnRV41. The use of Fourier transform infrared spectroscopy (FT-IR) allowed to unravelling differences at the structural levels between the aforementioned strains. Thus, mutants 35H1 and 36H4 showed clear differences from mutant 35A1 and wild-type strain. These differences were located, mainly in the fatty acid region and in the polysaccharide composition. This study contributes to understanding more the resistance/sensitivity of Ent. faecalis to (P)-DvnRV41, a subclass IIa bacteriocin.

Maximum-biomass concentration prediction for Bifidobacteria in the pH-controlled fed-batch culture

Our objective was to systematically study the relationship between maximum biomass concentration of different Bifidobacteria and total-acid anions accumulation, and develop a prediction equation for the maximum biomass concentration in the fed-batch culture at pH-controlled 7·0. The accumulation of acid anions and the consumption of nutrients of various strains were evaluated. In addition, minimum inhibitory concentrations (MICs) of acid anions on a range of strains were examined at pH 7·0. The inhibition of acid anions, which had the same MIC as sodium chloride, was due to the osmotic pressure under pH 7·0 conditions. Moreover, the concentration of total-acid anions completely inhibiting each strain in the fed-batch culture at pH-controlled 7·0 had no significant differences with the MIC of acid anions for the corresponding strains. The osmotic pressures under two conditions were not significantly different. Finally, the maximum biomass concentration of Bifidobacteria was found to be closely related to biomass yield per unit of acid anion produced (YX/P ) and MIC (C) which were needed for the prediction, and different strains exhibited marked correlation (P ˂ 0·01, R = 0·985). An equation for the prediction of the maximum biomass concentration was developed as follows: Xmax -X0  = (0·71 ± 0·03)·YX/P ·C.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides further insights into the inhibition of Bifidobacteria by dissociated acid anions (the dissociated form) at pH 7·0. The high correlation between different strains suggested that the equation established in this paper is appropriate for different strains of Bifidobacteria. The prediction equation could be used to guide practical production in the preparation of materials, the control of the end of fermentation and production plans for further products such as freeze-dried powder of Bifidobacteria or food fermentation.

Symbiotic maple saps minimize disruption of the mice intestinal microbiota after oral antibiotic administration

This study was undertaken to evaluate the in vivo impact of new symbiotic products based on liquid maple sap or its concentrate. Sap and concentrate, with or without inulin (2%), were inoculated with Bifidobacterium lactis Bb12 and Lactobacillus rhamnosus GG valio at initial counts of 2-4 × 10(8) cfu mL(-1). The experiments started with intra-gastric administration of antibiotic (kanamycin 40 mg in 0.1 cc) (to induce microbiota disturbance and/or diarrhea) to 3-to-5-week-old C57BL/6 female mice followed by a combination of prebiotic and probiotics included in the maple sap or its concentrate for a week. The combination inulin and probiotics in maple sap and concentrate appeared to minimize the antibiotic-induced breakdown of mice microbiota with a marked effect on bifidobacterium and bacteroides levels, thus permitting a more rapid re-establishment of the baseline microbiota levels. Results suggest that maple sap and its concentrate represent good candidates for the production of non-dairy functional foods.

In silico assigned resistance genes confer Bifidobacterium with partial resistance to aminoglycosides but not to β-lactams

Bifidobacteria have received significant attention due to their contribution to human gut health and the use of specific strains as probiotics. It is thus not surprising that there has also been significant interest with respect to their antibiotic resistance profile. Numerous culture-based studies have demonstrated that bifidobacteria are resistant to the majority of aminoglycosides, but are sensitive to β-lactams. However, limited research exists with respect to the genetic basis for the resistance of bifidobacteria to aminoglycosides. Here we performed an in-depth in silico analysis of putative Bifidobacterium-encoded aminoglycoside resistance proteins and β-lactamases and assess the contribution of these proteins to antibiotic resistance. The in silico-based screen detected putative aminoglycoside and β-lactam resistance proteins across the Bifidobacterium genus. Laboratory-based investigations of a number of representative bifidobacteria strains confirmed that despite containing putative β-lactamases, these strains were sensitive to β-lactams. In contrast, all strains were resistant to the aminoglycosides tested. To assess the contribution of genes encoding putative aminoglycoside resistance proteins in Bifidobacterium sp. two genes, namely Bbr_0651 and Bbr_1586, were targeted for insertional inactivation in B. breve UCC2003. As compared to the wild-type, the UCC2003 insertion mutant strains exhibited decreased resistance to gentamycin, kanamycin and streptomycin. This study highlights the associated risks of relying on the in silico assignment of gene function. Although several putative β-lactam resistance proteins are located in bifidobacteria, their presence does not coincide with resistance to these antibiotics. In contrast however, this approach has resulted in the identification of two loci that contribute to the aminoglycoside resistance of B. breve UCC2003 and, potentially, many other bifidobacteria.

Transcriptome analysis and physiology of Bifidobacterium longum NCC2705 cells under continuous culture conditions

A central issue in the use of probiotics in food and food supplements is their sensitivity to many environmental stress factors. The resistance of probiotic cells to lethal stress can be improved by application of homologous or heterologous sub-lethal stress during culture. This screening procedure is generally performed using batch cultures. Continuous cultures could be a suitable and more efficient method to test different stress factors on one culture instead of repeating several batch cultures. However, before testing stresses using continuous cultures, the physiological stability of continuously produced cells over a considered time period must be first evaluated. A continuous culture of Bifidobacterium longum NCC2705 was maintained for 211 h at a dilution rate of 0.1 per h, mimicking a deceleration growth phase culture. Stable viable cell counts were measured over the culture period, decreasing only moderately from 8.8 to 8.6 log10 cfu/ml. A slight shift in metabolite production, characterized by increased lactate and decreased acetate, formate and ethanol concentrations was observed. Susceptibilities to antibiotics and stress conditions were stable (cefotaxim, ampicillin, ceftazidime) or moderately affected (simulated gastric juices, heat, bile salts, tetracycline, chloramphenicol, penicillin, vancomycin and neomycin) over culturing time. Comparison of gene transcription profiles between samples collected after 31 h of continuous culture and samples collected after 134 and 211 h revealed only limited changes in expression of 1.0 and 3.8% of total genes, respectively. Based on these results, we propose that continuous culture can be used to produce bacterial cells with stable physiological properties suitable for fast and efficient screening of sub-lethal stress conditions.

Development of Class IIa Bacteriocins as Therapeutic Agents

Class IIa bacteriocins have been primarily explored as natural food preservatives, but there is much interest in exploring the application of these peptides as therapeutic antimicrobial agents. Bacteriocins of this class possess antimicrobial activity against several important human pathogens. Therefore, the therapeutic development of these bacteriocins will be reviewed. Biological and chemical modifications to both stabilize and increase the potency of bacteriocins are discussed, as well as the optimization of their production and purification. The suitability of bacteriocins as pharmaceuticals is explored through determinations of cytotoxicity, effects on the natural microbiota, and in vivo efficacy in mouse models. Recent results suggest that class IIa bacteriocins show promise as a class of therapeutic agents.

Susceptibility of bifidobacteria of animal origin to selected antimicrobial agents

Strains of the genus Bifidobacterium are frequently used as probiotics, for which the absence of acquired antimicrobial resistance has become an important safety criterion. This clarifies the need for antibiotic susceptibility data for bifidobacteria. Based on a recently published standard for antimicrobial susceptibility testing of bifidobacteria with broth microdilution method, the range of susceptibility to selected antibiotics in 117 animal bifidobacterial strains was examined. Narrow unimodal MIC distributions either situated at the low-end (chloramphenicol, linezolid, and quinupristin/dalfopristin) or high-end (kanamycin, neomycin) concentration range could be detected. In contrast, the MIC distribution of trimethoprim was multimodal. Data derived from this study can be used as a basis for reviewing or verifying present microbiological breakpoints suggested by regulatory agencies to assess the safety of these micro-organisms intended for the use in probiotics.

Effect of antimicrobial peptides divergicin M35 and nisin A on Listeria monocytogenes LSD530 potassium channels

The aim of this work was to study the effect of antimicrobial peptides: divergicin M35 and nisin A on Listeria monocytogenes LSD 530 potassium (K+) channels: ATP-sensitive (K ATP), calcium-activated (BK Ca), and depolarization-activated (Kv) types. Increase on K+ efflux and inhibition of cellular growth were observed after adding K+ channel activators pinacidil, NS1619, and cromakalim to divergicin M35. Increase in K+ efflux from log-phase cells was about 18 +/- 1.1, 11 +/- 0.63, and nmol mg(-1) of cell dry weight (CDW) for pinacidil and NS1619, respectively, over the efflux obtained with divergicin M35 alone. Increases in K+ efflux obtained by adding the same K+ channel activators to nisin A fit a completely different profile. Divergicin M35 activates K+ channels, particularly of the Kv and BK Ca types and to a lesser extent the K ATP type, causing K+ efflux and consequently cell death.

Genetic and phenotypic diversity of Bifidobacterium thermacidophilum fecal isolates from newborns

This study was undertaken to genetically identify and phenotypically characterize 14 bifidobacteria isolated from 20 breast-fed newborns. These isolates showed 98%–99% similarity to Bifidobacterium thermacidophilum subsp. suis based on 16S rDNA. Further analysis by pulsed-field gel electrophoresis of chromosomal DNA digested with XbaI revealed 4 distinct restriction patterns. The predominant pattern, shared by 8 (57%) isolates, produced a macro-restriction profile with about 13 large fragments ranging in size from >242.5 to 23.1 kb, whereas the other 6 displayed 3 distinct restriction profiles all characterized by more micro- than macro-restriction, with fragments ranging in size from 97 to 9.4 kb. Phenotypic characteristics, including carbohydrate fermentation profile, maximal growth temperature, and antibiotic susceptibility, varied widely even among strains showing the same restriction profile. The presence of B. thermacidophilum in stools of newborn infants may indicate the potential of these bacteria for aiding the development of the intestinal ecosystem.

In vitro inhibition activity of nisin A, nisin Z, pediocin PA-1 and antibiotics against common intestinal bacteria

AIMS

To evaluate the sensitivity of 21 common intestinal bacteria to six antibiotics and three broad-spectrum bacteriocins (nisins Z and A and pediocin PA-1).

METHODS AND RESULTS

Neutralized cell-free culture supernatants containing active bacteriocins, and antibiotics were tested with the agar diffusion test and the disc-diffusion method, respectively. The tested intestinal strains showed high sensitivity to most antibiotics except for streptomycin and oxacillin. Nisins A and Z (8 mug per well) had similar activity spectra and inhibited all Gram-positive intestinal bacteria at different levels (except Streptococcus salivarius), with bifidobacteria (except Bifidobacterium breve and Bif. catenulatum), Collinsella aerofaciens and Eubacterium biforme being the most sensitive strains, but they were not active against Gram-negative bacteria. Surprisingly, none of the tested strains were inhibited by pediocin PA-1 (16 mug per well).

CONCLUSION

Pediocin PA-1 which is very active against Listeria spp. and other food pathogens did not inhibit major intestinal species in the human intestine in contrast to both nisins A and Z.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our data suggest that pediocin PA-1 has potential to inhibit Listeria within the intestinal microbiota without altering commensal bacteria.

Probiotics: from research to consumer

Intestinal microflora has metabolic, trophic and protective functions, and can be modified in pathological conditions and by the exogenous administration of probiotics. Probiotics are defined as living microorganisms which resist gastric, bile, and pancreatic secretions, attach to epithelial cells and colonize the human intestine. In the last twenty years research has been focused on the identification of the role of planktonic flora and adhesive bacteria in health and disease, and on the requisite of bacterial strains to become probiotic product which can be marketed. Probiotics can be commercialized either as nutritional supplements, pharmaceuticals or foods, but the marketing as a pharmaceutical product requires significant time, complex and costly research, and the demonstration of a well-defined therapeutic target. This review examines the sequential steps of research which, from the identification of a possible probiotic strain, lead to its production and marketing, summarizing the whole process existing behind its development, through its growth in laboratory, the studies performed to test its resistance to human secretions and stability, microencapsulation technologies, and safety tests.

Antibiotic susceptibility profile of bifidobacteria as affected by oxgall, acid, and hydrogen peroxide stress

The effects of acid, oxgall, and H(2)O(2) on susceptibilities to antibiotics and nisin were examined for 13 strains of bifidobacteria. Susceptibilities to ampicillin, cloxacillin, penicillin, vancomycin, kanamycin, neomycin, paramomycin, streptomycin, chloramphenicol, erythromycin, tetracycline, and nisin A were assayed by a microdilution broth method. Acid-, oxgall- and H(2)O(2)-stressed variants were produced and assayed. Exposure to a pH of 2.0 for 60 min reduced susceptibilities to cloxacillin and nisin A but increased susceptibilities to ampicillin, vancomycin, aminoglycosides, chloramphenicol, and erythromycin in a strain-dependent manner. Exposure to oxgall (0.3%) for 90 min increased susceptibilities to cell wall-directed antibiotics and aminoglycosides but increased resistances to tetracycline and nisin A. Oxidative stress increased the susceptibilities of 70% of the strains to ampicillin and chloramphenicol, of 50% of the strains to cloxacillin and tetracycline, and of 40% of the strains to erythromycin but did not affect susceptibilities to vancomycin, kanamycin, and nisin A. This study shows that exposure of bifidobacteria to stressful conditions resembling those in the gastrointestinal tract may substantially modify their susceptibilities to antibiotics and may thus affect their probiotic capacities, especially when they are used for the management of intestinal infections and antibiotic-associated diarrhea.

Comparison of three test media for antimicrobial susceptibility testing of bifidobacteria using the Etest method

The performance of three test media for antimicrobial susceptibility testing of bifidobacteria using the Etest was compared. All Bifidobacterium strains (n=42) displayed good growth on trypticase-phytone-yeast extract agar (TPY). Most strains showed good growth on lactic acid bacteria susceptibility test medium supplemented with cysteine (LSM+cys); Bifidobacterium bifidum showed moderate growth. Growth of seven strains was inadequate on Brucella blood agar (BRU) and an additional eight strains showed moderate growth. The minimum inhibitory concentrations (MICs) for tetracycline were highest on BRU and lowest on LSM+cys (agreement 57%), whereas the MICs for streptomycin were lowest on BRU and highest on TPY (agreement 40%). Occasional mismatches (agreement 71-91%) between the test media were also detected for the beta-lactam antibiotics. This study describes test medium-dependent variation of MICs and the applicability of LSM+cys for antimicrobial susceptibility testing of bifidobacteria.

Acquisition of bile salt resistance promotes antibiotic susceptibility changes in bifidobacterium

The effect of acquired resistance to bile on the antimicrobial sensitivity of two Bifidobacterium strains (Bifidobacterium animalis IPLA4549 and Bifidobacterium longum NIZO B667) was studied. The MICs of 23 different antibiotics belonging to the most clinically important groups were determined by using the Etest method, which comprises nonporous plastic strips calibrated with a predefined gradient of antibiotic concentrations covering 15 twofold dilutions. The strains were sensitive to most antibiotics assayed, although they tolerated relatively high concentrations of gentamicin, kanamycin, streptomycin, polymyxin B, and ciprofloxacin (from 32 to more than 1,024 microg/ml). One of the bile-adapted strains was more strongly resistant to ceftazidime than was its parent bile-sensitive strain, and the other bile-adapted strain had increased resistance to tetracyclines. Therefore, to test the possibility that the acquisition of stable resistance to bile could be associated with a general increase in resistance to some antibiotics, we analyzed the sensitivities of four additional pairs of parent strains and their bile-adapted derivatives to ceftazidime and three tetracyclines (doxycycline, minocycline, and tetracycline). Three of the bile-resistant derivatives had increased resistance to ceftazidime (more than 256-fold) compared with their parents, and two had enhanced resistance to tetracyclines (at least 12-fold). Thus, the acquisition of bile salts resistance in Bifidobacterium induced modifications of the antibiotic resistance patterns. These results suggest that adaptation of probiotics to bile could also change their potential impact on intestinal microbiota, and this possibility deserves further attention.