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LESSON 1 MICROORGANISMS IMPORTANT IN FOOD MICROBIOLOGY

Introduction

Microorganisms are tiny, mostly one-celled organisms capable of rapid reproduction under proper growth conditions. Those microorganisms important in the food industry include the bacteria, viruses, yeasts, molds, and protozoans. Many are helpful and serve useful functions such as causing breads to rise, fermenting sugars to alcohol, assisting in the production of cheese from milk, and decaying organic matter to replenish nutrients in the soil. Microorganisms can also cause foods to spoil and make them inedible. Spoilage organisms cost the food industry millions of dollars each year. Microorganisms can also be harmful. These are called pathogens and cause 24 to 81 million cases of foodborne illness. These forms of life, some so small that 25,000 of them placed end to end would not span one inch, were little known until the last century. Antony van Leeuwenhoek and others discovered "very little animalcules' in rain water viewed through crude microscopes. We now know that microorganisms occur everywhere on the skin, in the air, in the soil, and on nearly all objects. It was not until Pasteur proved that microorganisms could be eliminated from a system, such as a can of food, and sealed out (hermetically sealed), that man could exert control over the microbes in his environment.

UNIT I MICROORGANISMS IMPORTANT IN FOOD MICROBIOLOGY

fission, by budding as in the case of yeasts, or by means of spores borne on fruiting structures depending on the organism. Protozoa are single-celled organisms such as the amoeba which can cause disease in humans and animals. They possess cell structure similar to higher, more complex organisms. Microorganisms are referred to by their scientific names which are often very descriptive. The first part of the name, the genus, is capitalized such as Streptococcus, spherical cells which occur in strips, Lactobacillus which are rod-shaped organisms commonly found in milk, or Pediococcus spherical cells which ferment pickles. The second part of the name is not capitalized and gives added information. Both parts of the name are underlined or italicized as in the case of Saccharomyces cerevisiae, yeast which commonly ferments sausage. Microorganisms either can be beneficial or harmful. Harmful effects of microorganisms include

FOOD MICROBIOLOGY

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spoilage of foods food borne toxification food borne infections viral borne infections

Beneficial effects results from the use of microoganisms to utilize carbohydrates and product fermented foods, which include

Terminology

Bacteria are single-celled microorganisms found in nearly all natural environments. Outward appearances of the cell such as size, shape, and arrangement are referred to as morphology. Morphological types are grouped into the general categories of spherical (the cocci), cylindrical (the rods) and spiral. The cocci may be further grouped by their tendencies to cluster. Diplococci attach in pairs, streptococci in chains, staphylococci bunch like grapes, and sarcinae produce a cuboidal arrangement. Bacterial cells have definite characteristic structures such as the cell wall, cytoplasm, and nuclear structures. Some also possess hairlike appendages for mobility called flagella, fimbriae which aid in attachment, plus cytoplasmic and membranous inclusions for regulating life processes. Viruses are extremely small parasites. They require living cells of plants, animals, or bacteria for growth. The virus is mainly a packet of genetic material which must be reproduced by the host. Yeast and mold are fungi which do not contain chlorophyls. They range in size from single-celled organisms to large mushrooms. Although some are multi celled, they are not differentiated into roots, stems and leaves. The true fungi produce masses of filamentous hyphae which form the mycelium. Depending on the organism, they may reproduce by

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Cheese Yogurt Fermented sausages Wine Beer Pickles Sour kraut Tea Coffee Cocoa

Microorganisms are ubiquitous. There are very few places on the planet where they cannot be found. Recent research on organisms known as Extremophiles has shown that they can grow in the geysers in Yellowstone, in the Great Salt Lake, and in vents 1.5 miles below the ocean surface along the Juan de Fuca Ridge. Almost every surface of an object is covered with microorganisms including the surfaces of foods. The majority of these organisms are harmless (nonpathogenic); however, a few types can cause problems if they are ingested. A variety of organisms inhabit the digestive tract. These organisms are known collectively as normal flora. The body has a variety of mechanisms to protect against pathogenic (disease producing) organisms. One of the most important is the hydrochloric acid that is produced in the

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stomach. Most pathogenic organisms require environments that are basic (pH above 7.0). An important exception is Helicobacter pylori, bacteria that have evolved a mechanism that allows it to thrive in the stomach. Food poisoning is most likely to occur when a very large meal is ingested. It takes more time for the acid level of the stomach to rise to a pH of 1.5 when a large amount of food has been consumed. During this time the microorganisms can grow to a quantity that is large enough to produce disease symptoms. People with reduced stomach acid due to the use of antacids or acid reduction drugs must be particularly aware of microorganism contamination since they lack the acid to protect against infection. Most foodborne microorganisms remain in the digestive tract; however, a few species can enter the bloodstream which produces widespread disease. Microorganisms that remain in the digestive tract cause their pathogenic effects by entering the epithelial cells that line the digestive tract. These organisms commonly produce diarrhea which can be accompanied by other symptoms such as nausea, vomiting or abdominal cramping. Treatment of these diseases is difficult because antibiotics remain in the digestive system for such as short period of time if diarrhea is present. These conditions are usually self-limiting and end in a few days. Use of antidiarrheal medications is not recommended because they can prolong infection but preventing the organisms from being washed out of the digestive system. Organisms can remain in the digestive system for days or weeks after the acute phase of the disease has ended. These organisms continue to be shed from the body in the feces and care must be taken to avoid reinfection or spread of the disease. Careful hand washing has been shown to be the most effective preventative strategy. Advantages of Using Microorganisms for Food Production Examination candidates should be able to explain the advantages of using microorganisms for food production rapid population growth, ease of manipulation; predictable and reliable product independent of climate; use of waste products from other industrial processes. These are listed on page 28 of the biology syllabus Aspects meriting particular emphasis include their prodigious population growth potential, their ability to grow on a range of cheap materials (which may otherwise be industrial waste) and the potential for processing of the raw product into a variety of nutritious formulations for specific purposes. Illustrations such as the following may help students to appreciate the reasons for the interest in the potential for using microorganisms in food production With a generation time of twenty minutes, and with no limiting factors, a single bacterium, with a biomass of only l012 g, would produce 22 x 1025 tonnes of biomass - 4000 times the mass of our planet - within two days. In other terms, a bacterium could, in a non-restricting environment, produce 1011 times its own biomass of protein alone in a single day. The potential for the application of modem biotechnology towards solving global food shortage, though a vast scenario could form the basis of thought-provoking classroom discussion and/or topic work widely different areas of

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exportable biotechnology are, of course involved. Some of the most significant developments are agricultural (such as the use of transgenic plants, animals and bacteria, of transplanted embryos and of micropropagation) but this is higher tier material. Teachers may prefer to limit discussion at this stage to the possible impact of microbial fermentation processes Many of the issues involved in the application of these processes are, in any case, common to other fields of biotechnological innovation. Background The global shortage of dietary protein has been particularly apparent since the 1950's. Animal protein is expensive to produce and this, together with other practical problems such as transport, the need for refrigeration and the dwindling of fish stocks, makes it largely unavailable in many developing countries. Supplying vegetable protein can be almost as problematic, especially in the face of soil impoverishment, drought and other adverse climatic circumstances. In terms of energy efficiency, it clearly makes sense to use microorganisms, rather than conventionally-farmed animals or plants, to produce food. Energy conversion factors, growth rates and technical feasibility are far from being the only considerations, however. Economic, political and social pressures may provide enormous obstacles. In the 1970's and 1980's, a number of companies tried to harness the astonishing potential of microorganisms to increase their biomass and their ability to grow on cheap organic foods. One idea was to produce animal food to replace imported soya bean and fish meal products. The most widely documented example is the ICI Pruteen TM project. Investing well over £ 100 million, the company overcame formidable development problems to achieve a technological triumph. However, high production costs and falling prices of competing products meant that Pruteen TM, although nutritionally excellent, was far more expensive than the imported materials it was meant to replace. The project had to be abandoned for these purely economic reasons and the plant was demolished. Attempts by other companies to produce microbial protein using oil as substrate failed following the steep rise in oil prices in the 1970's. Other economic considerations come into play when attempts are made to replace imported materials, for the effects on the economy of the exporting country can be severe. Also, some countries which badly need more food and which have ample supplies of cheap carbohydrates which can be used as food in fermenters, cannot afford the high setting-up costs. Safety aspects are clearly very important; at present nearly all of the SCP products available globally are rigorous criteria regarding safety and nutrition, any novel material has to be acceptable in terms of taste, appearance and texture. Even the name of a product can deter consumers - for example, if it is implied that they are being invited to eat bacteria! The nutritional value of a food which no-one will eat is nil. Experience in food aid programmes has shown that nutrition problems could be solved by adding microbial protein powders to local traditional foods to be invalid Much attention is now given to these consumer-led aspects when presenting new foods such as Quorn TM.

FOOD MICROBIOLOGY

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Some Pathogenic Food-Borne Microorganisms

FOOD MICROBIOLOGY

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Bacillus cereus Campylobacter jejuni Clostridium botulinum Clostridium perfringens Escherichia coli Listeria monocytogenes Salmonella Salmonella enteritidis Shigella Staphylococcus aureus Vibrio parahaemolyticus Vibrio cholerae Vibrio cholerae Serogroup O1 Vibrio cholerae Serogroup Non-O1 Yersinia enterocolitica Cladosporium Rhizopus Lactobacillus acidophilus

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Some Microorganisms in Fermented Foods and Related Products

FOOD MICROBIOLOGY

Foods and Products Dairy Products Cheeses (ripened) Kefir Kumiss Taette Yogurt Meat and Fish Products Country-cured hams Dry sausages Fish sauces Izushi Nonbeverage Plant Products Cocoa beans Coffee beans Kimchi Miso Olives Poi Sauerkraut Soy sauce Tempeh Breads Idli Rolls, cakes, etc. San Francisco Sourdough bread Sour pumpernickel

Raw Ingredients Milk, curd Milk Mare's milk Milk Milk, milk solids

Fermenting Organisms Streptococcus spp., Leuconostoc spp. Streptococcus lactis, Lactobacillus bulgaricus, Candida spp. Lactobacillus bulgaricus, L. leichmannii, Candida spp. S. lactis var. taette S. thermophilus, L. bulgaricus

Location Produced Worldwide Primarily southwestern Asia Russia Scandinavia Worldwide

Pork hams Pork, beef Small fish Fresh fish, rice, vegetables

Aspergillus, Penicillium spp. Pediococcus cerevisiae Halophilic Bacillus spp. Lactobacillus spp.

Southern USA Europe, USA Southeast Asia Japan

Cacao fruits (pods) Coffee cherries Cabbage and other vegetables Soybeans Green olives Taro roots Cabbage Soybeans Soybeans Rice and bean flour Wheat flours Wheat flour Wheat flour

Candida krusei, Geotrichum spp. Erwinia dissolvens, Saccharomyces spp. Lactic acid bacteria Leuconostoc mesenteroides, Lactobacillus plantarum Lactic acid bacteria Leuconostoc mesenteroides, Lactobacillus plantarum A. oryzae or A. soyae, S. rouxii, Lactobacillus delbrueckii Rhizopus oligosporus, R. oryzae Leuconostoc mesenteroides Saccharomyces cerevisiae S. exiguus, Lactobacillus sanfrancisco Leuconostoc mesenteroides

African, South America Brazil, Congo, Hawaii, India Korea

Aspergillus oryzae, Saccharomyces spp. Primarily Japan Worldwide Hawaii Worldwide Japan, China, USA Indonesia, New Guinea, Surinam Southern India Worldwide Northern California Switzerland, other areas

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Yeasts in Alcoholic Beverages

FOOD MICROBIOLOGY

Beverage Beer and Wine

Yeast

Method of Preparation Molasses, sassafras bark, wintergreen bark, and sarsaparilla root added for flavor; yeast added; incubated aerobically. Germinated barley releases starches and amylase enzymes (malting). Enzymes in malt hydrolyze starch to fermentable sugars (mashing). Liquid (wort) sterilized. Hops (flowers) added for flavor. Yeast added, incubated at 37o-49o C. Germinated barley releases starches and amylase enzymes (malting). Enzymes in malt hydrolyze starch to fermentable sugars (mashing). Liquid (wort) sterilized. Hops (flowers) added for flavor. Yeast added, incubated at 50o-70o C. Aspergillus oryzae converts starch in steamed rice into sugar; yeast added; incubated at 20oC.

Function of Yeast Converts sugar into carbon dioxide by aerobic metabolism; 0.03% alcohol. Converts sugar into alcohol and carbon dioxide; 4% alcohol. Yeast grows on bottom of fermenting vessel. Converts sugar into alcohol; 6% alcohol. Yeast grows at top of fermentation vessel.

Root beer (preSaccharomyces 1905 and cerevisiae homemade)

Beer

Saccharomyces carlsbergensis (bottom yeast)

Ale

Saccharomyces cerevisiae (top yeast)

Sake

Saccharomyces cerevisiae

Wine, natural

Saccharomyces cerevisiae

Strain of grape provides various flavors and sugar concentrations. Grapes crushed into must; sulfur dioxide added to inhibit wild Converts grape sugar yeast; yeast added. Red wines: incubated at into alcohol; 14% or less 25oC. Aged in oak for 3-5 years and in bottle alcohol for 5-15 years. White wines: incubated at 10o15oC. Aged 2-3 years in bottle. Saccharomyces beticus As natural wine, with additional surface oC. Alcohol added to 18%- grows as surface film, growth (flor) at 27 producing aldehydes 21%. from alcohol. As natural wine, with secondary fermentation in bottle. 2.5% sugar and yeast added to bottled wine; incubated at 15o C; bottle inverted to collect yeast in neck. In secondary fermentation, produces carbon dioxide; yeast settles quickly.

Wine, sherry

Saccharomyces cerevisiae and Saccharomyces beticus or Saccharomyces bayanus

Wine, sparkling Saccharomyces (champagne) cerevisiae Distilled Beverages Rum, Jamaica Wild yeast Saccharomyces cerevisiae Saccharomyces cerevisiae

Cane molasses inoculated from pervious Converts sugar to fermentation. Oak aging adds color. Distilled alcohol; 50-95% alcohol. to concentrate. Fruits pressed; yeast added. Distilled to concentrate alcohol, blended with other brandies. Wort (see beer) is fermented by yeast. Distilled to concentrate alcohol; aged in charred oak barrels. Converts sugar into alcohol; 40%-43% alcohol. Converts sugar to alcohol; 50%-95% alcohol.

Brandy

Whiskey

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Some Microbial Enzymes Produced Commercially

FOOD MICROBIOLOGY

Enzyme

Microorganism

Use of Enzyme Baking: Flour supplement Starch: Cold-water laundry Textiles: Desizing agent Food: Converts starch to glucose Pharmaceuticals: Digestive aid used when eating beans (Beano® ) Brewing: Converts starch to maltose Food: Liquid coffee concentrate Food: Making cheese curd Pharmaceuticals: Dextran Brewing: "Lite" beer Brewing: Degradation of barley cell walls Food: Glucose removal from egg solids Pharmaceuticals: Test papers Candy: Prevents granulation in soft center Food: Artificial honey Dairy: Prevents crystallization of lactose in ice cream and concentrated milk Pharmaceuticals: Digestive aid used when eating dairy products (Lactaid® ) Dairy: Flavor production in cheese Wine and juice: Clarification Pharmaceuticals: Diagnostic agent Brewing: Beer stabilizer Baking: Bread making Food: Meat tenderizer Pharmaceuticals: Digestive aid Textiles: Desizing agent Pharmaceutical: Lysis of embolisms and thrombolisms Laundry: Added to detergents

alpha-Amylose

Aspergillus niger Aspergillus oryzae

beta-Amylase Cellulase Chymosin (rennin) Dextransucrase Glucanase beta-Glucanase

Bacillus subtilis Trichoderma viride Escherichia coli (recombinant) Leuconostoc mesenteroides Saccharomyces (recombinant) Bacillus subtilis Aspergillus niger

Glucose oxidase Aspergillus niger Invertase Lactase Lactase Lipase Pectinase Penicillinase Saccharomyces cerevisiae Saccharomyces fragilis Escherichia coli Aspergillus niger Aspergillus niger Bacillus subtilis

Protease

Aspergillus oryzae

Streptokinase Subtilisins

Group C beta-hemolytic Streptococcus Bacillus subtilis

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Some Cheeses and the Microorganisms Used in Their Production

Foodborne Microbial Intoxications

Disease Food Involved Prevention Clinical Features Onset and Duration Carcinogenic effects have indefinite onset; direct toxicity to animals usually sudden Onset: 8-16 hours Duration: Less than 1 day Onset: 2 hours - 6 days Duration: Weeks

FOOD MICROBIOLOGY

Type of Cheese

Cheese Name Parmesan Romano

Microorganisms Lactobacillus bulgaricus Streptococcus lactis Streptococcus cremoris Streptococcus thermophilus Streptococcus lactis Streptococcus cremoris Streptococcus durans Streptococcus thermophilus Lactobacillus helveticus Propionibacterium shermanii Streptococcus lactis Streptococcus cremoris Penicillium roqueforti Streptococcus lactis Streptococcus cremoris Penicillium camemberti Penicillium candidum Brevibacterium linens Streptococcus lactis Leuconostoc citrovorum

Very hard, ripened

Moldy Aflatoxin grains, poisoning peanuts

Hard, ripened

Cheddar Colby Edam Gouda Gruyere Swiss Gorgonzola Monterey Roquefort Brie Camembert Limburger Cottage

Avoid Low doses eating may induce contaminate liver cancer; d grains, high doses peanut cause general products liver damage Cramps, Refrigeratio diarrhea, n of foods nausea, vomiting Proper Difficulty canning swallowing, procedures; double boiling food vision, before respiratory consumptio paralysis n

Bacillus cereus intoxicatio n

Custard, cereal, starchy foods

Semisoft, ripened Soft, ripened Soft, ripened Soft, unripened

Botulism

Canned foods

Carnivoro us tropical fish in Tingling, which Avoid rash, fever, Ciguatera dinoflagell eating large breathing ate toxin tropical fish discomfort is concentrat ed Moldy grains Avoid Burning eating abdominal contaminate pain, d grains hallucinations

Onset: 2-6 hours Duration: Up to 2 weeks

Onset: 1-2 hours Ergotism Duration: Months Onset: 1 Stop Blurred Methyl Freshwate week dumping vision, mercury r or ocean Duration: mercury numbness, poisoning fish May be into waters apathy, coma chronic Mushroom Amanita poisoning species Bivalve mollusks Paralytic during red mollusk tide poisoning (dinoflagel late blooms) Avoid eating poisonous mushrooms Avoid eating mollusks during red tide Onset: less Vomiting, than 1 day liver necrosis, Duration: neurotoxic Less than 10 effects days Tingling, rash, fever, respiratory paralysis Onset: Less than 1 hour Duration: Less than 12 hours Onset: Several

Scombroid Histamine Refrigeratio Headache, poisoning like n of fish cramps,

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Summaries of Bacterial Disease Acquired Through the Alimentary Route Acute Gastrointestinal Disease

FOOD MICROBIOLOGY

Clinical Disease

Causative Organism

Incubation Period Communicable Period For duration of active infection and as long as salmonellae are shed

Treatment None; Use of antimicrobial agents may prolong fecal excretion of organisms

Salmonellosis

Salmonella 8-10 hours, may species be delayed for 48 (many serotypes) hours or more

Shigellosis (bacillary dysentery)

Shigella dysenteriae 1-4 days, not more As long as organisms are Ciprofloxacin or other Shigella flexneri than 7 days in feces fluoroquinolone Shigella boydii Shigella sonnei 2-4 days Not known; probably while organisms are present in feces Not known if communicable Fluid replacement Erythromycin Tetracycline Ciprofloxacin Bismuth sulfate + metronidazole, amoxicillin

Campylobacter Gastroenteritis jejuni Gastritis Peptic Ulcer Helicobacter pylori

Unknown

Gastroenteritis

Yersinia enterocolitica

2-7 days

Trimethoprimsulfamethoxazole As long as organisms are Gentamicin in feces Cefotaxime Ciprofloxacin

I f c i n C u e b M i r b a M u t p i a i nw t n e t o s a s d y coil lilcto ih E t r t x nP o u t o neooi rdcin

Clinical Disease Causative Organism Incubation Period 2-3 days, few hours during outbreak of cholera Communicable Period While organisms are present are present in vomitus and feces; may persist in intestinal tract for several weeks after recovery Not communicable from person to person Not communicable from person to person Not communicable from person to person As long as patients shed organisms and endospores contaminate environment Treatment Fluid and electrolyte replacement, Tetracyclines None Supportive Supportive Stop antimicrobial agents, Metronidazole or vancomycin if severe

Cholera

Vibrio cholerae

Gastroenteritis Gastroenteritis Gastroenteritis

Vibrio 8-48 hours parahaemolyticus Clostridium perfringens Bacillus cereus 2-4 days 2-4 days

Pseudomembranous Clostridium colitis difficile

Undefined

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Enteric Infections Caused by Escherichia coli

FOOD MICROBIOLOGY

Clinical Disease

Causative Organism Incubation Period

Communicable Period

Treatment

Travelers' diarrhea Enterotoxigenic Escherichia coli Travelers' diarrhea Enteroaggregative Escherichia coli Gastroenteritis dysentery Enteroinvasive Escherichia coli

12-72 hours Generally not communicable Primarily supportive, from person to person Trimethoprimsulfamethoxazole 1-3 days 2-3 days Generally not communicable Ciprofloxacin from person to person As long as organisms are in feces Ampicillin Fluid and electrolyte replacement Antimicrobial therapy depends on testing of isolated organism Supportive

Epidemic diarrhea Enteropathogenic in nurseries Escherichia coli

2-4 days As long as babies remain maximum of symptomatic and adult carrier 3 weeks or environmental source remains undetected As long as organisms are in feces

Hemorrhagic colitis

Enterohemorrhagic 3-5 days Escherichia coli

Disease Caused by Ingestion of Preformed Toxin

Clinical Disease Staphylococcal intoxication Botulism

Causative Organism Incubation Period Staphylococcus aureus enterotoxin Clostridium botulinum enterotoxin 1-6 hours

Communicable Period

Treatment

Not communicable from person to Supportive person Not communicable from person to Antitoxin person

12-36 hours

Infectious Systemic Diseases

Clinical Disease Causative Organism Incubation Period 1-2 weeks, sometimes 3 weeks Communicable Period Through active infection, and as long as salmonellae are shed in excreta; 10 present of convalescents shed bacilli up to 3 months, 2-5 percent become permanent carriers Through active infection and for as long as salmonellae are shed in excreta; carrier rate is variable Treatment Ciprofloxacin,Ceftriaxone Chloramphenicol Ampicillin Trimethoprimsulfamethoxazole Ciprofloxacin Ceftriaxone Chloramphenicol Ampicillin Trimethoprimsulfamethoxazole Ciprofloxacin,Ceftriaxone Chloramphenicol Ampicillin Trimethoprimsulfamethoxazole Doxycyclines + rifampin or gentamicin Ampicillin,Trimethoprimsulfamethoxazole

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Typhoid fever Salmonella typhi

Paratyphoid fever

Salmonella enteritidis var paratyphi A or B

1-10 days

Salmonella septicemia

Salmonella choleraesuis

1-10 days

Through active infection and for as long as salmonellae are shed in excreta; carrier rate is variable

Brucellosis

Brucella abortus Brucella melitensis 1-3 weeks Brucella suis Brucella canis Listeria monocytogenes 3-70 days

Not ordinarily communicable from person to person To fetus, during maternal bacteremic phase

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Listeriosis

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Viral Diseases Acquired Through the Alimentary Route

Clinical Disease Poliomyelitis Coxsackievirus Diseases Echovirus Diseases Viral Gastroenteritis Viral Gastroenteritis Viral Gastroenteritis Viral Hepatitis Causative Organism Poliovirus Coxsackieviruses Echoviruses Rotaviruses Adenoviruses Norwalk virus group Caliciviruses Astroviruses Hepatitis A virus Incubation Period Usually 1-2 weeks, may range from 3 days to 4-5 weeks 3-5 days Unknown 24-48 hours 3-10 days 24-48 hours 1-3 days 24-36 hours 15-45 days Communicable Period Before onset of symptoms and during infection Treatment None specific

FOOD MICROBIOLOGY

During acute, febrile stage of illness None specific During acute febrile stage of illness None specific Through first week of illness May be up to 2 weeks 2-3 days after onset of illness Unknown During incubation period and possibly through first week of symptoms During incubation period and possibly through first week of symptoms None specific None specific None specific None specific

Viral Hepatitis

Hepatitis E virus

4-8 weeks

None specific

Summary

Any small organism viewed only with a microscope could be categorized as a microorganism or microbe. In food, the microorganisms of concern are bacteria, yeasts and molds, although viruses and parasites are also important2. Bacteria are single celled and rod, spherical or ovoid in shape. Some species of bacteria also produce spores, some of which are resistant to heat and chemicals3. Yeasts are also usually one cell, but they are larger than bacteria. Food and beverage with a lower pH (or higher acidity) are more likely to spoil from yeast growth. Molds are multicellular microorganisms that grow by producing thread-like mycelial filaments3. They are more likely to grow on food stuffs such as breads, nuts, and cheeses that are low in moisture content. They are widely distributed in our environment. Some common living places of microbes are air, water, soil, plants, animals, human beings, sewage, fertilizer, food ingredients, processing equipment, and packaging materials. The microbes found in food include those associated with the raw material, those acquired during harvesting, handling, and processing, and those surviving any preservation treatment and storage1. Food handlers can transmit microorganisms. In fact, humans are the major source of food contamination3. Their hands, hair, breath as well as their unguarded coughs and sneezes can contaminate food. Microorganisms may have different functions in food. They may remain inert, serve a useful function, cause spoilage, or become a health hazard 1. Useful microbes are those which produce desirable changes in food, such as converting milk to cheese, grape juice to wine, and cabbage to sauerkraut. Spoilage microbes are those that cause deterioration which is manifested by alterations in the appearance, texture, odor, or flavor of the food. Pathogenic microbes are those toxigenic and invasive microorganisms which can multiply in food and/or the human body and cause foodborne illness. Four basic systems are often used to control microbes in food. They are (1) prevent contamination; (2) remove contaminants; (3) inhibit growth; and (4) destroy contaminates 1. In most cases, two or more of these systems are used in combination to control the microbial level in food. For example, optimum quality and shelf-life of fresh-squeezed citrus juice can be achieved by (1) good hygiene and sanitation practices to prevent contamination; (2) effective sorting, washing, sanitizing, and extraction to remove fruit surface microbes; and (3) proper refrigeration to inhibit the growth of microbes during storage, distribution, and retail.

Questions

Q. What are microorganisms? Q. What do they do in our food? Q. How to control microorganisms? Q. Describe Foodborne Microbial Intoxications. Q. What is the advantage of using microorganisms for food production?

References

· Information/Elements-Food-Micro.html · Frazier W.C., West Hoff D.C. Food Microbiology, 4th Ed

Reprint (1995) Tata McGraw Hill Publishing Co. Ltd. New Delhi.

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