In vitro assessment of antimicrobial activity of carvacrol, thymol and cinnamaldehyde towards Salmonella serotype Typhimurium DT104: effects of pig diets and emulsification in hydrocolloids

Reduction of Salmonella enterica serovar enteritidis colonization in 20-day-old broiler chickens by the plant-derived compounds trans-cinnamaldehyde and eugenol

The efficacies of trans-cinnamaldehyde (TC) and eugenol (EG) for reducing Salmonella enterica serovar Enteritidis colonization in broiler chickens were investigated. In three experiments for each compound, 1-day-old chicks (n = 75/experiment) were randomly assigned to five treatment groups (n = 15/treatment group): negative control (-ve S. Enteritidis, -ve TC, or EG), compound control (-ve S. Enteritidis, +ve 0.75% [vol/wt] TC or 1% [vol/wt] EG), positive control (+ve S. Enteritidis, -ve TC, or EG), low-dose treatment (+ve S. Enteritidis, +ve 0.5% TC, or 0.75% EG), and high-dose treatment (+ve S. Enteritidis, +ve 0.75% TC, or 1% EG). On day 0, birds were tested for the presence of any inherent Salmonella (n = 5/experiment). On day 8, birds were inoculated with ∼8.0 log(10) CFU S. Enteritidis, and cecal colonization by S. Enteritidis was ascertained (n = 10 chicks/experiment) after 24 h (day 9). Six birds from each treatment group were euthanized on days 7 and 10 after inoculation, and cecal S. Enteritidis numbers were determined. TC at 0.5 or 0.75% and EG at 0.75 or 1% consistently reduced (P < 0.05) S. Enteritidis in the cecum (≥3 log(10) CFU/g) after 10 days of infection in all experiments. Feed intake and body weight were not different for TC treatments (P > 0.05); however, EG supplementation led to significantly lower (P < 0.05) body weights. Follow-up in vitro experiments revealed that the subinhibitory concentrations (SICs, the concentrations that did not inhibit Salmonella growth) of TC and EG reduced the motility and invasive abilities of S. Enteritidis and downregulated expression of the motility genes flhC and motA and invasion genes hilA, hilD, and invF. The results suggest that supplementation with TC and EG through feed can reduce S. Enteritidis colonization in chickens.

Sub-lethal levels of carvacrol reduce Salmonella Typhimurium motility and invasion of porcine epithelial cells

The European ban on the use of antibiotic growth promotors has increased the search for new alternatives to prevent pig intestinal microbial diseases and to stimulate growth. The addition of essential oils or components thereof, such as carvacrol, to pig feed is a promising alternative. In this report we determined the effect of sub-lethal concentrations of carvacrol on Salmonella Typhimurium. At concentrations where growth of Salmonella was not inhibited, carvacrol completely inhibited motility of the bacterium. This loss of motility was not due to the loss of the flagellum or to ATP shortage upon carvacrol treatment. Adhesion of Salmonella to IPEC-J2, porcine intestinal epithelial cells, was not affected by carvacrol but invasion was significantly reduced. In addition, the epithelial gene expression of porcine β-defensin 2, an innate immune response to Salmonella infection, was reduced when Salmonella was exposed to carvacrol. This indicates that invasion but not adhesion of Salmonella triggers the porcine β-defensin 2 expression of porcine epithelial cells.

Study of the chemical composition and antimicrobial activities of ethanolic extracts from roots of Scutellaria baicalensis Georgi

Scutellaria baicalensis Georgi (SBG), commonly named Huangqin, showed strong in vitro antimicrobial effects. However, limited research is available to systematically evaluate the effects of extraction methods on the phytochemical composition of SBG and its associated antimicrobial effects. In addition, limited studies have tested SBG as a natural antimicrobial agent on fresh produce such as tomatoes. In the current study, powered roots of SBG were extracted with 60, 80, and 100% ethanol, and their antiviral and antibacterial activities were evaluated. SBG ethanol extracts (SBGEEs) at 6.25 mg/mL showed limited antiviral activities against coliphage MS2 and hepatitis A virus. The SBG 80% ethanol extract (SBG80%EE) exhibited the lowest minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) against six foodborne pathogens. SBG80%EE had the highest contents of flavonoids and phenolic acids determined by high-performance liquid chromatography (HPLC). Among these bioactive compounds, ferulic acid had the lowest MIC and MBC values, 0.4 and 1.0 mg/mL, respectively, followed by baicalein and baicalin. Washing with SBG80%EE (12.5 mg/mL) resulted in >1 log reduction of Salmonella enterica serovars Typhimurium, Kentucky, Senftenberg, and Enteritidis on surface-inoculated grape tomatoes. None of SBGEE solutions changed the total phenolic content, color, or pH values of grape tomatoes. The quantification of these antimicrobial flavonoids and phenolic acids is important to maintain the quality and antimicrobial efficacy of SBG extracts. In addition, the application of SBG on tomatoes has provided valuable insights on the potential usage of this antimicrobial extract.

The antimicrobial activities of the cinnamaldehyde adducts with amino acids

Cinnamaldehyde is a well-established natural antimicrobial compound. It is probable for cinnamaldehyde to react with amino acid forming Schiff base adduct in real food system. In this paper, 9 such kind of adducts were prepared by the direct reaction of amino acids with cinnamaldehyde at room temperature. Their antimicrobial activities against Bacillus subtilis, Escherichia coli and Saccharomyces cerevisiae were evaluated with benzoic acid as a reference. The adducts showed a dose-dependent activities against the three microbial strains. Both cinnamaldehyde and their adducts were more active against B. subtilis than on E. coli, and their antimicrobial activities were higher at lower pH. Both cinnamaldehyde and its adducts were more active than benzoic acid at the same conditions. The adduct compound A was non-toxic by primary oral acute toxicity study in mice. However, in situ effect of the adduct compound A against E. coli was a little lower than cinnamaldehyde in fish meat. This paper for the first time showed that the cinnamaldehyde adducts with amino acids had similar strong antimicrobial activities as cinnamaldehyde, which may provide alternatives to cinnamaldehyde in food to avoid the strong unacceptable odor of cinnamaldehyde.

Influence of probiotics in different energy and nutrient density diets on growth performance, nutrient digestibility, meat quality, and blood characteristics in growing-finishing pigs

The study was conducted to determine the effects of probiotics (Bacillus subtilis endospore and Clostridium butyricum endospore complex) supplementation and different energy and nutrient densities on growth performance, nutrient digestibility, and meat quality in growing-finishing pigs. A total of 96 pigs with initial BW of 47.50 ± 1.14 kg were used in a 10-wk experiment. Pigs were randomly allotted to 1 of 4 treatments in a 2 × 2 factorial arrangement of treatments with 2 levels of energy and nutrient density (low and high energy, CP, and Lys) and 0.2% probiotics according to their sex and BW (6 pens, with 2 gilts and 2 barrows/pen). From 0 to 5 wk, ADG and G:F, as well as the apparent total tract digestibility (ATTD) of N and energy, were improved (P < 0.05) in the probiotic groups and in the high-energy and high-nutrient-density groups. From 6 to 10 wk, ADG and G:F, as well as the ATTD of DM, N, and energy, were increased (P < 0.01) when pigs were fed the high-energy and high-nutrient-density diets. Pigs fed the probiotic supplement or the high-energy and high-nutrient-density diets had increased (P < 0.01) ADG and G:F overall. Moreover, pigs fed the high-energy and high-nutrient-density diets had increased (P < 0.05) meat color scores, marbling scores, drip loss values, pH, and LM area (P < 0.05) compared with those fed the low-energy and low-nutrient-density diets, whereas the probiotic treatment groups had increased (P < 0.01) meat color scores, marbling scores, and redness values. The lightness and yellowness values in the low-energy and low-nutrient-density dietary treatments were greater (P < 0.05) than those in the high-energy and high-nutrient-density dietary treatments. Interactive effects of dietary energy and nutrient density and probiotics were also observed (P < 0.05) on the digestibility of N at wk 10 and energy at wk 5, as well as on meat firmness at the end of the experiment. In conclusion, dietary supplementation of probiotics increased growth performance throughout the experiment and exerted beneficial effects on ATTD. Meat quality was improved when pigs were fed high-energy and high-nutrient-density diets.

Use of natural antimicrobials to increase antibiotic susceptibility of drug resistant bacteria

Plant-derived antibacterial compounds may be of value as a novel means for controlling antibiotic resistant zoonotic pathogens which contaminate food animals and their products. Individual activity of natural antimicrobials (eugenol, thymol, carvacrol, cinnamaldehyde, allyl isothiocyanate (AIT)) and activity when paired with an antibiotic was studied using broth microdilution and checkerboard methods. In the latter assays, fractional inhibitory concentration (FIC) values were calculated to characterize interactions between the inhibitors. Bacteria tested were chosen because of their resistance to at least one antibiotic which had a known genetic basis. Substantial susceptibility of these bacteria toward the natural antimicrobials and a considerable reduction in the minimum inhibitory concentrations (MIC's) of the antibiotics were noted when paired combinations of antimicrobial and antibiotic were used. In the interaction study, thymol and carvacrol were found to be highly effective in reducing the resistance of Salmonella Typhimurium SGI 1 (tet A) to ampicillin, tetracycline, penicillin, bacitracin, erythromycin and novobiocin (FIC<0.4) and resistance of Streptococcus pyogenes ermB to erythromycin (FIC<0.5). With Escherichia coli N00 666, thymol and cinnamaldehyde were found to have a similar effect (FIC<0.4) in reducing the MIC's of ampicillin, tetracycline, penicillin, erythromycin and novobiocin. Carvacrol, thymol (FIC<0.3) and cinnamaldehyde (FIC<0.4) were effective against Staphylococcus aureus blaZ and in reducing the MIC's of ampicillin, penicillin and bacitracin. Allyl isothiocyanate (AIT) was effective in reducing the MIC of erythromycin (FIC<0.3) when tested against S. pyogenes. Fewer combinations were found to be synergistic when the decrease in viable population (log DP) was calculated. Together, fractional inhibitory concentrations < or = 0.5 and log DP<-1 indicated synergistic action between four natural antimicrobials and as many as three antibiotics to which these bacteria were normally resistant.

Investigations on the effects of dietary essential oils and different husbandry conditions on the gut ecology in piglets after weaning

Essential oils (EO) are being considered as possible alternatives to in-feed antibiotic growth promoters in pig nutrition. The effects of an EO mixture consisting of limonene, eugenol and pinene (10.0, 2.0, and 4.8 mg/kg diet, resp.) on gut physiology and ecology were studied in piglets. The experiment was conducted at low (commercial farm) and high hygienic conditions (experimental farm), to elucidate interactions between EO supplementation and husbandry methods. Piglets were weaned at 28 days of age, when they were offered either a control diet (C) or C with EO. Four piglets were sacrificed in each group on day 29, 30, 33 and 39. Digesta from the third distal part of the small intestine and from the colon were sampled and analysed for pH, dry matter, lactic acid, short chain fatty acids and ammonia concentrations. Enterobacteria, enterococci, lactobacilli and yeast counts were obtained by plating. Genomic DNA was extracted from digesta and polymerase chain reaction—denaturing gradient gel electrophoresis was performed. Individual microbial communities were identified at each farm. Age affected the intestinal parameters. No effects of the EO with exception for a significant reduction in colon bacterial diversity at 39 days of age could be recorded at experimental farm.

Antibacterial effect of plant-derived antimicrobials on major bacterial mastitis pathogens in vitro

The objective of this study was to investigate the antimicrobial effect of plant-derived antimicrobials including trans-cinnamaldehyde (TC), eugenol, carvacrol, and thymol on major bacterial mastitis pathogens in milk. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the aforementioned compounds on Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Staphylococcus aureus, and Escherichia coli were determined. In addition, the bactericidal kinetics of TC on the aforementioned pathogens and the persistence of the antimicrobial activity of TC in milk over a period of 2 wk were investigated. All 4 plant-derived molecules exhibited antimicrobial activity against the 5 mastitis pathogens tested, but TC was most effective in killing the bacteria. The MIC and MBC of TC on Staph. aureus, E. coli, and Strep. uberis were 0.1 and 0.45%, respectively, whereas that on Strep. agalactiae and Strep. dysgalactiae were 0.05 and 0.4%, respectively. The MIC and MBC of the other 3 molecules ranged from 0.4 to 0.8% and 0.8 to 1.5%, respectively. In time-kill assays, TC at the MBC reduced the bacterial pathogens in milk by 4.0 to 5.0 log(10) cfu/mL and to undetectable levels within 12 and 24 h, respectively. The antimicrobial effect of TC persisted for the duration of the experiment (14 d) without any loss of activity. Results of this study suggest that TC has the potential to be evaluated as an alternative or adjunct to antibiotics as intramammary infusion to treat bovine mastitis.