Santos García

Extracts of Edible and Medicinal Plants Damage Membranes of Vibrio cholerae

ABSTRACT The use of natural compounds from plants can provide an alternative approach against food-borne pathogens. The mechanisms of action of most plant extracts with antimicrobial activity have been poorly studied. In this work, changes in membrane integrity, membrane potential, internal pH (pHin), and ATP synthesis were measured in Vibriocholerae cells after exposure to extracts of edible and medicinal plants. A preliminary screen of methanolic, ethanolic, and aqueous extracts of medicinal and edible plants was performed. Minimal bactericidal concentrations (MBCs) were measured for extracts showing high antimicrobial activity. Our results indicate that methanolic extracts of basil (Ocimum basilicum L.), nopal cactus (Opuntia ficus-indica var. Villanueva L.), sweet acacia (Acacia farnesiana L.), and white sagebrush (Artemisia ludoviciana Nutt.) are the most active against V. cholera, with MBCs ranging from 0.5 to 3.0 mg/ml. Using four fluorogenic techniques, we studied the membrane integrity of V. cholerae cells after exposure to these four extracts. Extracts from these plants were able to disrupt the cell membranes of V. cholerae cells, causing increased membrane permeability, a clear decrease in cytoplasmic pH, cell membrane hyperpolarization, and a decrease in cellular ATP concentration in all strains tested. These four plant extracts could be studied as future alternatives to control V. cholerae contamination in foods and the diseases associated with this microorganism.

Microbiological survey of retail herbs and spices from Mexican markets.

In the present study, 304 samples of herbs and spices (garlic powder, cumin seeds, black pepper, oregano, and bay leaves) widely used in Mexico were analyzed for the presence of Bacillus cereus, Salmonella Typhi, Shigella dysenteriae, Escherichia coli, total and fecal coliforms, total mesophilic aerobic organisms, and fungi. Samples were nonpackaged or packaged in polyethylene bags or glass containers. High levels (10(5) to 10(7) CFU/g) of mesophilic aerobic microorganisms were found in most of the samples of garlic powder, cumin seed, and black pepper. Lower levels (<102 CFU/g) were found in oregano and bay leaves. Total and fecal coliforms counts were dependent on the type of packaging. More than 70% of the polyethylene-packaged samples had less than 10(3) CFU/g of microorganisms. Glass and nonpackaged spices showed lower levels of these microorganisms. B. cereus was present in 32 samples of which most were polyethylene packaged. The other pathogenic bacteria were not detected. Aspergillus niger was detected in 29% of the samples, Rhizopus sp. in 19%, and Penicillum sp. and Cunninghamella in 8%.

Microbiological condition of ground meat retailed in Monterrey, Mexico.

Eighty-eight samples of ground meat were randomly collected from retail stores in the metropolitan area of Monterrey, Mexico, and were analyzed for microbial contamination. Methods were those recommended by the Mexican regulation and/or the U.S. Food and Drug Administration. Over 75% of the samples contained > 10(5) total mesophilic microorganisms per g, and over 40% had >10(6) total coliforms per g. Fecal coliforms were present in most samples. Staphylococcus aureus was detected in 2.3% of the samples, Salmonella spp. in 11.4%, Listeria spp. in 62%, and L. monocytogenes in 16%. Escherichia coli was detected in 76% of samples, but none was serotype O157:H7. Shigella spp. was not found in any sample. Fusarium spp. and Mucor spp. were detected in 3.4% of the samples, and low levels of yeast in 93%. The microbiological quality of the ground meat analyzed was unsatisfactory, and the product could be an important cause of food poisoning.

Microbiologically safe foods.

The book begins with a general discussion of microbial hazards and their public health ramifications. It then moves on to survey the production processes of different food types, including dairy, eggs, beef, poultry, and fruits and vegetables, pinpointing potential sources of human foodborne diseases. The authors address the growing market in processed foods as well novel interventions such as innovative food packaging and technologies to reduce spoilage organisms and prolong shelf life. Each chapter also describes the ormal flora of raw product, spoilage issues, pathogens of concern, sources of contamination, factors that influence survival and growth of pathogens and spoilage organisms, indicator microorganisms, approaches to maintaining product quailty and reducing harmful microbial populations, microbial standards for end-product testing, conventional microbiological and molecular methods, and regulatory issues.

Mycotoxins in Mexico: epidemiology, management, and control strategies.

Mycotoxin-producing molds species are extremely common. Many of them provoke serious diseases in humans and animals. These toxins occur, with varying severity, in agricultural products. Since Mexico is a big crops producer, the importance of the presence of these toxins is high. Currently, the Mexican regulation establishes limits only for aflatoxins in cereals and cereal products. No limits are set for other mycotoxins. Epidemiological data although limited, has shown that an important number of samples contain mycotoxin limits above those established abroad. Several strategies for reducing contamination have been conducted in the country such as development of hybrid corn, control of insect population, use of natural products, and modification of nixtamalization and extraction procedures. Although significant research on this field has been conducted, there is still a great need for information to determine the incidence of mycotoxins in Mexican products.

Inhibition of Growth, Enterotoxin Production, and Spore Formation of Clostridium perfringens by Extracts of Medicinal Plants

The extracts of 14 plants used in the traditional medicine of Mexico were evaluated for their effects on the growth, spore formation, and enterotoxin production of Clostridium perfringens type A. The extracts of Psidium guajava L., Haemotoxylon brasiletto, and Euphobia prostata were the most effective inhibitors of growth, spore formation, and enterotoxin production. No enterotoxins were detected when extracts were added to the media at less than the MIC for growth.

Cross protection by heat and cold shock to lethal temperatures in Clostridium perfringens

A heat shock pre-treatment of Clostridium perfringens provides protection against lethality from subsequent exposure to cold shock and vice versa. Heat shocked cells were more cold tolerant (one log reduction in 65 min) than control cells (one log reduction in 34 min). On the other hand, cold-shocked cells were more thermotolerant (D55= 17 min) than the control (D55= 6.5 min). The addition of chloramphenicol (an inhibitor of protein synthesis) in the experiments indicates that synthesis of new proteins was necessary for cross protection between both treatments.

Extracts of Edible and Medicinal Plants in Inhibition of Growth, Adherence, and Cytotoxin Production of Campylobacter jejuni and Campylobacter coli

UNLABELLED Campylobacter spp. is recognized as one of the most common cause of food-borne bacterial gastroenteritis in humans. Campylobacter infection causes campylobacteriosis, which can range from asymptomatic to dysentery-type illnesses with severe complications, such as Guillian-Barre syndrome. Epidemiological studies have revealed that consumption of poultry products is an important risk factor of this disease. Adherence and cytotoxic activity of the bacteria to host mucosal surfaces have been proposed to be critical steps in pathogenesis. Innovative tools for controlling Campylobacter, such as natural products from plants, represent good alternatives for use in foods or as therapeutic agents. In this study, 28 edible or medicinal plants species were analyzed for their bactericidal effects on the growth of Campylobacter jejuni and C. coli. The extracts of Acacia farnesiana, Artemisia ludoviciana, Opuntia ficus-indica, and Cynara scolymus were the most effective against these microorganisms at minimal bactericidal concentrations (MBCs) of 0.3, 0.5, 0.4, and 2.0 mg/mL, respectively. No effect on growth was detected with lower concentrations of extract (25%, 50%, or 75% of the MBC) added to the media. The effect of each extract (75% of the MBC) on adherence and cytotoxicity of C. jejuni and C. coli was evaluated in Vero cells. Adherence of Campylobacter to Vero cells was significantly affected by all the extracts. Cytotoxic activity of bacterial cultures was inhibited by A. farnesiana and A. ludoviciana. These plant extracts are potential candidates to be studied for controlling Campylobacter contamination in foods and the diseases associated with this microorganism. PRACTICAL APPLICATION Innovative tools for controlling Campylobacter, such as natural products from plants, represent good alternatives for use in foods or as therapeutic agents. The extracts of Acacia farnesiana, Artemisia ludoviciana, Opuntia ficus-indica, and Cynara scolymus were the most effective against these microorganisms. Adherence and cytotoxic activity of the bacteria to host mucosal surfaces which are critical steps in pathogenesis were decreased by these extracts. Our results point to these plants as potential candidates for the control of Campylobacter contamination in foods, the treatment of the diseases associated with this microorganism, and as feed supplements to reduce on-farm prevalence of Campylobacter.

Decontamination of Salmonella, Shigella, and Escherichia coli O157:H7 from leafy green vegetables using edible plant extracts.

UNLABELLED Fresh cilantro, parsley, and spinach are products that are regularly consumed fresh, but are difficult to decontaminate, as a result, they are common vehicles of transmission of enteropathogenic bacteria. In this study, the efficacy of plant extracts as alternatives for disinfection of cilantro, parsley, and spinach that were artificially contaminated with Salmonella, Escherichia coli O157:H7, and Shigella sonnei was determined. Edible plant extracts obtained using ethanol as the extraction solvent were tested to determine the minimum bactericidal concentration (MBC) and those that exhibited the lowest MBC were selected for further studies. Leaves of fresh greens were washed with sterile water and dried. For seeding, leaves were submerged in suspensions of 2 different concentrations of bacteria (1.5 × 10(8) and 1 × 10(5) ), dried, and then stored at 4 °C until use. To determine the effects of the extracts, inoculated leafy greens were submerged in a container and subjected to treatments with chlorine, Citrol®, or selected plant extracts. Each treatment type was stored at 4 °C for 0, 1, 5, and 7 d, and the bacterial counts were determined. From the 41 plant extracts tested, the extracts from oregano leaves and from the peel and pulp of limes were found to be as effective as chlorine or Citrol® in reducing by > 2 logs, the population of pathogenic bacteria on leafy greens and therefore, may be a natural and edible alternative to chemicals to reduce the risk of Salmonella, E. coli O157:H7 and S. sonnei contamination on leafy vegetables. PRACTICAL APPLICATION The antimicrobial efficacy of the extracts of Mexican lime and oregano was clearly demonstrated on cilantro, parsley, and spinach. The extracts of Mexican lime and oregano provide alternatives to chlorine to significantly reduce bacterial pathogens that have been associated with outbreaks from contaminated leafy green vegetables. A simple, low cost, and labor-saving extraction system for production of the extracts was used.

Edible Active Coatings Based on Pectin, Pullulan, and Chitosan Increase Quality and Shelf Life of Strawberries (Fragaria ananassa).

Edible active coatings (EACs) based on pectin, pullulan, and chitosan incorporated with sodium benzoate and potassium sorbate were employed to improve the quality and shelf life of strawberries. Fruits were washed, disinfected, coated by dipping, packed, and stored at 4 °C for 15 d. Application of EACs reduced (P < 0.05) weight loss and fruit softening and delayed alteration of color (redness) and total soluble solids content. In contrast, pH and titratable acidity were not affected (P > 0.05) throughout storage, and ascorbic acid content was maintained in pectin-EAC coated strawberries. Microbiological analyses showed that application of EACs reduced (P < 0.05) microbial growth (total aerobic counts, molds, and yeasts) on strawberries. Chitosan-EAC coated strawberries presented the best results in microbial growth assays. Sensory quality (color, flavor, texture, and acceptance) improved and decay rate decreased (P < 0.05) in pectin-EAC, pullulan-EAC, and chitosan-EAC coated strawberries. In conclusion, EACs based on polysaccharides improved the physicochemical, microbiological, and sensory characteristics, increasing the shelf life of strawberries from 6 (control) to 15 d (coated fruits).