Bacteria and Sprouts
Bacteria and Its Relationship with Sprouts
General Information about Bacteria
Bacteria is the plural of bacterium. Bacteria are microscopic unicellular organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera. Bacteria fall into one of two groups, Archaebacteria (ancient forms thought to have evolved separately from other bacteria) and Eubacteria.
Bacteria were the only form of life on earth for 2 billion years. They were first observed by Antony van Leeuwenhoek in the 17th cent.
Bacteria are remarkably adaptable to diverse environmental conditions: they are found in the bodies of all living organisms and on all parts of the earth-in land terrains and ocean depths, in arctic ice and glaciers, in hot springs, and even in the stratosphere. There are more bacteria, as separate individuals, than any other type of organism; there can be as many as 2.5 billion bacteria in one gram of fertile soil.
Bacteria are grouped in a number of different ways. Most bacteria are of one of three typical shapes-rod-shaped (bacillus), round (coccus, e.g., streptococcus), and spiral (spirillum). An additional group, vibrios, appear as incomplete spirals. The cytoplasm and plasma membrane of most bacterial cells are surrounded by a cell wall. Many bacteria, chiefly the bacillus and spirillum forms, are motile, swimming about by whip-like movements of flagella; other bacteria have rigid rod-like protuberances called pili that serve as tethers.
Some bacteria (those known as aerobic forms) can function metabolically only in the presence of free or atmospheric oxygen; others (anaerobic bacteria) cannot grow in the presence of free oxygen but obtain oxygen from compounds. Facultative anaerobes can grow with or without free oxygen; obligate anaerobes are poisoned by oxygen.
In bacteria the genetic material is organized in a continuous strand of DNA. This circle of DNA is localized in an area called the nucleoid, but there is no membrane surrounding a defined nucleus as there is in the cells of fungi, plants, and animals. In addition to the nucleoid, the bacterial cell may include one or more plasmids, separate circular strands of DNA that can replicate independently, and that are not responsible for the reproduction of the organism.
Reproduction is chiefly by binary fission, cell division yielding identical daughter cells. Some bacteria reproduce by budding or fragmentation. Despite the fact that these processes should produce identical generations, the rapid rate of mutation possible in bacteria makes them very adaptable. Under unfavorable conditions some bacteria form highly resistant spores with thickened coverings, within which the living material remains dormant in altered form until conditions improve. Others can withstand serious damage by repairing their own DNA.
Most bacteria live off other organisms. Most of these are saprobes, bacteria that live off dead organic matter. The bacteria that cause disease are heterotrophic parasites. There are also many non-disease-causing bacterial parasites, many of which are helpful to their hosts. These include the “normal flora” of sprouts or the human body. Autotrophic bacteria manufacture their own food by the processes of photosynthesis and chemosynthesis.
Harmless and beneficial bacteria far outnumber harmful varieties. Because they are capable of producing so many enzymes necessary for the building up and breaking down of organic compounds, bacteria are employed extensively by humans-for soil enrichment with leguminous crops, for preservation by pickling, for fermentation (as in the manufacture of alcoholic beverages, vinegar, and certain cheeses), for decomposition of organic wastes (in septic tanks, in some sewage disposal plants, and in agriculture for soil enrichment) and toxic wastes, and for many other specialized processes.
Bacterial parasites that cause disease are called pathogens. Animal diseases caused by bacteria include tuberculosis, cholera, syphilis, typhoid fever, and tetanus. Among bacterial plant diseases that affect sprouts are Erwinia Carotovora and Pseudomonas Fluorescents.
Some bacteria attack the tissues directly; others produce poisonous substances called toxins. Natural defense against harmful bacteria is provided by antibodies. Certain bacterial diseases, e.g., tetanus, can be prevented by injection of antitoxin or of serum containing antibodies against specific bacterial antigens; immunity to some can be induced by vaccination; and certain specific bacterial parasites are killed by antibiotics.
New strains of more virulent bacterial pathogens, many of them resistant to antibiotics, have emerged in recent years. Many believe this to be due to the overuse of antibiotics, both in prescriptions for minor, self-limiting ailments and as growth enhancers in livestock; such overuse increases the likelihood of bacterial mutations. For example, a variant of the normally harmless Escherichia coli has caused serious illness and death in victims of food poisoning.
Sprouts and Foodborne Illness
An estimated 76 million cases of foodborne diseaseoccur each year in the United States. The great majority of these cases are mildand cause symptoms for only a day or two. Some cases are more serious, andthe U.S. Centers for Disease Control estimates that there are 325,000 hospitalizations and 5,000 deaths relatedto foodborne diseases each year. The most severe cases tend to occur inthe very old, the very young, those who have an illness already that reducestheir immune system function, and in healthy people exposed to a very high doseof an organism.
All produce, including sprouts, can become contaminatedwith foodborne pathogens. Nearly all of the sprout related outbreaks havebeen traced back to pathogens in the seed which can multiply over 1,000,000 foldwhen given the ideal growing conditions provided by the process ofsprouting. This can be enough hospitalize or be fatal to even the healthiest ofpeople.
Microbiological surveys have shown the presence of avariety of foodborne pathogens in sprouts. Salmonella, Listeria monocytogenes,Staphylococcus aureus, Bacilluscereus and Aeromonas hydrophila have been isolated from sproutedseeds, including alfalfa, mung bean, cress, soybean, and mustard (Beuchat,1996). Escherichia coli O157, various serotypes of Salmonella, andBacillus cereus have been the causative agents of documented outbreaks offoodborne illness associated with sprouts (Jackson, 1998).
Other pathogens that been identified as being apotential source of increased risk due to their ability to proliferate duringsprouting include Yersinia enterocolitica and Shigella.
Commercial sprout growers recognize their specialresponsibility in protecting the public and have become the most well informed,responsible members of the produce industry.