Norma Heredia

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%.

Antimicrobial activity of extracts of three major plants from the Chihuahuan desert

Dilution methods were employed to determine the effect of ethanolic extracts of Agave lecheguilla Torr. (Agavaceae), Baccharis glutinosa Pers. (Compositae) and Larrea tridentata (DC.) Cov. (Zygophyllaceae) on growth of yeasts, molds and bacteria. The three extracts analyzed showed good antimicrobial activity against more than one organism. The minimal inhibitory concentration of the extracts was also determined.

Elevation of the heat resistance of vegetative cells and spores of Clostridium perfringens type A by sublethal heat shock

The degree of heat resistance conferred on Clostridium perfringens by a heat shock, the kinetics of this development, and its duration were determined. A sublethal heat shock at 55°C for 30 min increased the heat tolerance of vegetative cells at least two- to threefold. The acquired tolerance was maintained for 2 h after the heat shock treatment. Heat shock applied for the first hour of incubation produced spores more tolerant to heat than the spores of the control. Acquired thermotolerance is of importance in the case of this organism because of its inherently high optimal growth temperature.

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.

Detection of enterotoxigenic Clostridium perfringens in spices used in Mexico by dot blotting using a DNA probe

Several reports on the microbiology of spices and herbs indicate the presence of Clostridium perfringens, a spore-forming foodborne pathogen responsible for gastrointestinal disease. In the present study, a total of 380 samples of spices and herbs (cumin seed, black pepper, oregano, garlic powder, and bay leaves) widely used in Mexico were analyzed for the presence of C. perfringens, and the enterotoxigenicity of the isolates was determined by a dot-blot technique using an enterotoxin degoxigenin-labeled DNA probe. C. perfringens counts varied from <100 to 433 CFU/g in garlic powder, from <100 to 200 CFU/g in black pepper, from <100 to 433 CFU/g in cumin seed, from <100 to 340 CFU/g in oregano, and from < 100 to 450 CFU/g in bay leaves. The dot-blot technique detected the enterotoxin gene in 8 (4.25%) of 188 confirmed isolates of C. perfringens. dot-blot.

Traditional Uses and Scientific Knowledge of Medicinal Plants from Mexico and Central America

ABSTRACT The regions of Mexico and Central America contain some of the most biologically diverse collections of vegetation in the world. Within these area, a wide variety of plant preparation have been used to treat illnesses for several centuries with vast ethnobotanical knowledge existing in the region since pre-Columbian times. Despite reports about the current medicinal use of more than 1000 plant species in Mexico, less than 20 percent of these species have been scientifically studied to validate the use of the plant materials. This review discusses the traditional use and scientific knowledge of some of the most commonly used medicinal plants in Mexico and Central America.