Rabin Gyawali

Impact of plant derivatives on the growth of foodborne pathogens and the functionality of probiotics

Numerous studies have been published on the antimicrobial and antioxidant properties of various plant components. However, there is relatively little information on the impact of such components on the enhancement of probiotics and production of antimicrobial compounds from these probiotics. Hence, this paper focuses on the influence of plant-derived components against pathogens, enhancement of cell viability and functionality of probiotics, and potential applications of such components in food safety and human health.

Antimicrobial Activity of Copper Alone and in Combination with Lactic Acid against Escherichia coli O157:H7 in Laboratory Medium and on the Surface of Lettuce and Tomatoes

The objective of this study was to evaluate the effect of copper alone and in combination with lactic acid against E. coli O157:H7 in laboratory medium and on the surface of lettuce and tomatoes. Four strains of E. coli O157:H7 were individually inoculated into BHI broth containing different concentrations of copper (5, 10, 20, and 40 ppm, w/v), lactic acid (0.1 and 0.2%, v/v), and their combinations. After incubation, aliquots of 1 mL from each sample were withdrawn and plated on BHI agar to determine the bacterial population. Significant growth inhibition (P < 0.05) was observed with a combination treatment of copper (40 ppm) and lactic acid (0.2%). The population of E. coli O157:H7 was reduced by 3.93 and 3.39 log on the surface of lettuce and tomato samples, respectively, when treated with the same combination. This indicates that combination of copper and lactic acid could be used as an effective solution to inhibit E. coli O157:H7 on fresh produce.

Behavior and changes in cell morphology of Escherichia coli O157:H7 in liquid medium and skim milk in the presence of caffeine

The objective of this study was to investigate the antibacterial effect of caffeine on the behavior and changes in cell morphology of E. coli O157:H7 in a liquid medium and in skim milk. The inhibitory effect of caffeine at different concentrations was determined by inoculating E. coli O157:H7 in laboratory medium and skim milk samples. Samples were incubated at 37ºC for 48 h, and E. coli O157:H7 population was enumerated. Our results showed that caffeine significantly (P < 0.05) inhibited the growth of E. coli O157:H7 in laboratory medium and milk samples. A greater than 3.0 log CFU ml−1 inhibition was observed in milk containing 5.0 g/L caffeine within 12 h of incubation. Moreover, using flow cytometry, marked changes in the morphology of E. coli O157:H7 were also observed. Caffeine has potential as an antimicrobial agent and could be used as an effective natural additive to improve the safety of food products.

Evaluating the Effectiveness of Essential Oils and Combination of Copper and Lactic Acid on the Growth of E. coli O157:H7 in Laboratory Medium

In this study, we compared the effectiveness of armoise and clove bud essential oils (EOs) and the combination of low concentrations of copper (Cu) and lactic acid (LA) against E. coli O157:H7 in a laboratory medium. Three strains of Escherichia coli O157:H7 (ATCC700599, ATCC51659, and ATCC43895) were used in this study. Antibacterial activity was determined by measuring the turbidity of a broth medium and by determination of bacterial populations. Our results showed that armoise (0.15% v/v), clove bud (0.1% v/v) EOs, or Cu (50 ppm) in combination with LA (0.2% v/v) caused a minimum 5.0 log reduction of E. coli O157:H7 in the laboratory medium. Cu in combination with LA may thus be preferable to EOs in food in order to control the growth of foodborne pathogens. In addition, the combination treatment of Cu and LA could provide the food industry with a practical approach to reducing the risk of foodborne pathogens.

Inclusion of Oat in Feeding Can Increase the Potential Probiotic Bifidobacteria in Sow Milk

Simple Summary In this study we isolated and characterized potential probiotic bifidobacteria from sow milk. The bifidobacterial population in milk has been attributed to the existence of prebiotic oat in feeding systems. Since breast feeding protects the newborns against several infectious diseases, milk from sows fed with oat could improve the health of piglets. Abstract The objectives of this study were to (i) investigate the impact of feeding oat on the population of bifidobacteria and (ii) evaluate their probiotic potential. In this study, we investigated the effects of supplementing sows’ gestation and lactation feed with 15% oat (prebiotic source) on the levels of probiotic population in milk. We found that dietary inclusion of oat during lactation and gestation resulted in increased levels of bifidobacteria compared to lactobacilli in sow milk. Furthermore bifidobacteria within the sow milk samples were further evaluated for probiotic potential based on aggregating properties, and acid- and bile-tolerance after exposure to hydrochloric acid (pH 2.5) and bile salts (0%, 0.25%, 0.50%, 1.0% and 2.0%). All isolates survived under the condition of low pH and bile 2.0%. Autoaggregation ability ranged from 17.5% to 73%. These isolates also showed antimicrobial activity against E. coli O157:H7. Together our results suggest that inclusion of oat in feeding systems could have the potential to improve the intestinal health of piglets by increasing the population of bifidobacteria.

Chapter 26 – Antimicrobials from herbs, spices, and plants

Due to recent outbreaks by foodborne pathogens, food safety has started to gain much more attention from consumers and food industry. Foodborne pathogens are becoming resistant to food preservation methods and antibiotics. However, synthetic and chemical preservatives have negative impact on health. Natural antimicrobials have potential health benefits and they can improve the flavor and aroma of products. Plant extracts, herbs, and spices are generally recognized as safe (GRAS) and have antimicrobial effects against foodborne pathogens. Essential oils (EOs) extracted from plants and their active ingredients have also shown antioxidant and antimicrobial activities against several harmful microorganisms. However, these natural ingredients lose activity in food products during processing and handling since these ingredients could interact with food compounds. Therefore, nanoencapsulation of natural antimicrobials could help to protect the antimicrobial efficacy and increase the shelf-life of food products. The aim of this chapter is to discuss the role of several natural products and nanoencapsulation strategies to enhance the efficacy of these products. We discuss several methods of encapsulation processes and their activity in growth media and food systems.

Inactivation of Cronobacter sakazakii in reconstituted infant milk formula by plant essential oils

This study aimed to screen the in vitro antimicrobial activity of 10 plant essential oils (EOs) against 4 Cronobacter sakazakii strains, and use these oils or their combination to control C. sakazakii cocktail at low (3 log 10 CFU/ml) and high (6 log 10 CFU/ml) contamination levels in reconstituted infant milk formula (RIMF). Cinnamon and fir oils were the most inhibitory to C. sakazakii strains with inhibition zone of 32 to 40 mm at 20 µl/disc (the minimum inhibitory concentrations were 0.16 and 0.625 µl/ml, respectively). The addition of each of cinnamon or fir oil at 1% (v/v) reduced the C. sakazakii numbers in RIMF by 0.7-0.8 log 10 CFU/ml when inoculated with high contamination level and by 2.5-3.1 log 10 CFU/ml when inoculated with low contamination level. However, the combination of cinnamon and fir oils reduced C. sakazakii numbers at both inoculum levels to undetectable levels after 3 h of incubation at 37°C. The results of the current study indicated that a combination of cinnamon and fir oils has a potent antimicrobial activity which may potentially be used to control C. sakazakii in RIMF.

Use of Phytone Peptone to Optimize Growth and Cell Density of Lactobacillus reuteri

The objective of this study was to determine the use of phytone peptone to optimize the growth and cell density of Lactobacillus reuteri. Four strains of L. reuteri (DSM 20016, SD 2112, CF 2-7F, and MF 2-3,) were used in this study. An overnight culture of individual strains was inoculated into fresh basal media with various protein sources (peptone, tryptone, proteose peptone #3, phytone peptone, tryptic soy broth, yeast extract, and beef extract). Samples were then mixed well and incubated at 37 °C for 15 h. Bacterial growth was monitored by measuring turbidity (optical density 610 nm) at different time intervals during the incubation period. At the end of incubation, samples were plated on de-Man Rogosa Sharpe (MRS) agar to determine the bacterial population. Our results showed that phytone peptone promoted the growth of L. reuteri (p < 0.05) by 1.4 log CFU/mL on average compared to the control samples. Therefore, phytone peptone could be included in laboratory media to enhance growth and increase the cell density of L. reuteri.

Decontamination of Escherichia coli O157:H7 from Leafy Green Vegetables Using Ascorbic Acid and Copper Alone or in Combination with Organic Acids

The objective of this study was to determine the efficacy of ascorbic acid and copper alone or in combination with organic acids in decontaminating leafy greens (cilantro, parsley, and dill) that were artificially contaminated with Escherichia coli O157:H7. Samples were individually submerged in an approximately 8 log CFU/mL cocktail suspension consisting of three E. coli O157:H7 strains. To allow attachment, inoculated samples were air dried under a biosafety hood for 2 h before exposure to various treatment solutions. Individual samples were then treated with either alone or with a combination solution of ascorbic, acetic, lactic, copper, or water (control). Our results indicated that a reduction of at least 2.0 CFU/g of E. coli O157:H7 was achieved when a combination of 0.2 % ascorbic with acetic acid and 50 ppm copper with 0.2 % lactic acid were applied. These results demonstrated that combination treatments could be useful in improving the microbial safety of cilantro, parsley, and dill.

Interaction Between Bifidobacterium and Medical Drugs

Probiotics are live microorganisms which when administered in adequate amounts confer beneficial health benefits to the host. However, commonly consumed medical drugs may interact with probiotic bacteria and influence their viability and functionality. The objective of this study was to determine the impact of commonly administered medical drugs on the survival of Bifidobacterium. Five strains of Bifidobacterium (B. breve, B. longum, B. infantis, B. adolescentis, and B. bifidium) were individually grown in MRS broth at 37 °C for next day use. One tablet of commonly used medical drug (Aleve, Aspirin, Tylenol, Hydro, Lisinopril, Metformin, Metoprolol, or Glipizide) was completely dissolved into batches of 9 mL MRS broth then samples were inoculated with 1 mL of overnight grown cultures. Samples were incubated at 37 °C for 2 h and bacterial populations were determined immediately after exposure to medical drugs and after 2 h of incubation. Our result showed a decrease in bifidobacteria population by an average of 3.0 ± 0.25 log CFU/mL in the presence of tested drugs. Arthritis drug (Aleve, Aspirin, and Tylenol) showed higher killing effect on bifidobacteria compared to other tested drugs. These findings suggested that intake of common medical drugs may decrease the viability of probiotic bacteria and may reflect their contribution to human health. The intake of probiotic dietary supplements and functional foods may reduce the negative effect of medical drugs on probiotics.