Restaurant and other institutional chefs, home cooks and anyone else involved in the preparation of food must be vigilant in their war on the bacteria that cause food poisoning. And all eaters must be aware of potential problems. Unfortunately, bacteria can contaminate food without making their presence known — until it's too late.

The problem of harmful bacteria in the American food supply has become so acute that the USDA began posting safe-handling labels on all packages of fresh and frozen meat and poultry in 1994.

Of course, not all bacteria are bad. Many are beneficial — make that indispensable — to the food industry. For example, LACTIC ACID bacteria are used in the manufacture of sour cream, buttermilk, yogurt, cheese, even sauerkraut. And acetobacter is used in the production of vinegar.

Those most apt to cause grief:

CAMPYLOBACTER JEJUNI:

What it is: This bug causes a severe gastrointestinal upset that lasts a week or more.

Bacterial source: Raw poultry and meat, unpasteurized milk.

Symptoms of Campylobacteriosis: Abdominal cramps, diarrhea, fever and, in intense episodes, bloody stools.

How soon symptoms occur: Within two to five days.

Preventives: Use pasteurized milk only; cook poultry well done and red meat until it shows the merest tinge of pink in the center (160°F. on a meat thermometer). Hamburger and meat loaves should be brown clear through. Also, keep counters, cutting boards and implements scrupulously clean, and wash hands well after handling raw meat or poultry.

CLOSTRIDIUM BOTULINUM:

What it is: The bacterium itself doesn't kill, but the toxin it produces causes the deadly botulism.

Bacterial source: Improperly canned low-acid foods (soups; vegetables such as peas, beans and corn; ripe olives; tuna; liver pâté), also hams, luncheon meats, shellfish, sausage, smoked and salted fish. The spores of C. botulinum multiply in low-acid foods in the absence of air, producing a poison so powerful minute amounts of it can kill. Sadly, the C. botulinum toxin often gives no clue of its presence; the food may look, smell and taste okay. Most outbreaks of botulism can be traced to faulty home-canned food, but commercial processors are sometimes fallible, too.

Symptoms of botulism: Double vision, difficulty in speaking or swallowing, progressive respiratory paralysis. If symptoms occur, get medical help at once.

How soon symptoms occur: Within four to thirty-six hours.

Preventives: Fortunately, heat deactivates botulism toxin — usually ten minutes of hard boiling will do the job. Still, if you doubt the safety of a particular food or can of food, get rid of it immediately — where neither people nor animals can get at it. Don't taste and do wash your hands thoroughly with soap and hot water after handling any suspicious food. The best policy always: When in doubt, throw it out.

CLOSTRIDIUM PERFRINGENS:

What it is: Nicknamed the cafeteria bug, C. perfringens is responsible for about 10 percent of all cases of food poisoning.

Bacterial source: Perishable foods, especially large batches of meat or poultry left at room temperature for longer than two hours.

Symptoms of C. perfringens food poisoning: Vomiting, diarrhea, abdominal cramps. In most cases, symptoms last about a day and, except in the elderly or infirm, are rarely serious enough to require medical attention.

How soon symptoms occur: Within eight to twelve hours.

Preventives: Keep cold foods cold and hot foods hot. When refrigerating large batches of hot food, divide among small containers so the food will chill fast.

ESCHERICHIA COLI:

What it is: Always considered a benign, indeed beneficial bug that lived quietly in the intestine synthesizing B VITAMINS, E. coli has suddenly turned vicious. Or rather, a killer strain (E. coli 0157:h7) has surfaced, the culprit behind a hemorrhagic form of food poisoning that began appearing in the early 1980s in Canada and the United States. Those felled by the disease shared one thing: They'd all eaten rare hamburgers at fast-food restaurants. Sad to say, several children died from eating the tainted burgers. Recently, there's been a shocking increase in E. coli food poisonings (even traced to unpasteurized apple cider pressed from unwashed windfalls possibly contaminated with deer feces). The young are particularly hard hit by hemorrhagic E. coli, as are the elderly and infirm.

Bacterial source: Unpasteurized milk, undercooked meats (particularly hamburgers and all-beef hot dogs).

Symptoms of hemorrhagic E. coli food poisoning: Vomiting, bloody diarrhea, intense abdominal cramps and, in young children, sometimes kidney failure. Old people may suffer strokes or seizures (from blood clots on the brain). This acute food poisoning can last ten days or more, it can require hospitalization and it can kill.

How soon symptoms occur: Within three to four days.

Preventives: Drink pasteurized milk only. Handle raw meats carefully and cook them thoroughly (with hamburgers, this means until brown in the center). Never thaw frozen meat at room temperature (freezing does not kill E. coli ) or let raw meat stand at room temperature for more than two hours. When putting groceries away, refrigerate perishables immediately. Use ground meat within three days of purchase and frozen patties within four months. Finally, keep kitchen counters, cutting boards and utensils spotless. And wash your hands well in hot, soapy water after handling raw meat.

LISTERIA MONOCYTOGENES:

What it is: This form of food poisoning seems to target pregnant women and their fetuses, infants, the elderly and cancer and AIDS patients, as well as others with weakened immune systems. But anyone  can get listeriosis.

Bacterial source: Unpasteurized milk and milk products; fresh, soft cheeses (particularly Mexican types like queso blanco and queso fresco ), also feta, Brie, Camembert, Roquefort and other blues; seafood; frozen cooked shrimp, crab and surimi; even such deli items as coleslaw and cold cuts. Finally, sloppy food handling, which can cause cross-contamination of food.

Symptoms of listeriosis: Nausea, vomiting, fever, headache and, occasionally, miscarriage, meningitis, septicemia, infant or fetal death.

How soon symptoms occur: Usually within two to three days of eating the contaminated food although the illness may take a month to develop.

Preventives: Avoid unpasteurized milk and milk products. Cook all meat thoroughly (to 160°F. although chefs and devotees of juicily red meat will probably throw up their hands in horror). Cook all fish to 160°F. (no more raw or rare fresh fish) and cook all poultry to 180°F. Keep hot foods good and hot (above 140°F.) and cold foods well chilled (below 40°F.).

SALMONELLA:

What it is: With salmonella now rampaging through America's henhouses, many favorite recipes — eggnog, mayonnaises or ice creams made with raw eggs — must be abandoned. Meringue pie toppings are risky, too, if made with fresh eggs, and soft-cooked eggs are out. Salmonella is not a single bacterium but a cast of thousands that accounts for about half the cases of food poisoning. Regardless of which salmonella is the culprit, all cause the same intestinal flulike symptoms.

Bacterial source: Raw or undercooked poultry and eggs; raw milk and dairy products; raw or undercooked meats and shrimp; and, finally, untidy cooking procedures.

Symptoms of salmonella poisoning: Nausea, vomiting, stomach cramps, fever, headache.

How soon symptoms occur: Within six to forty-eight hours.

Preventives: Rinse poultry, meat and shrimp well in cold water before you cook them (this sends some of the bugs down the drain). Never taste anything containing raw egg (no more bowl licking!); cook eggs until the yolks set and poultry until a meat thermometer, inserted in the fleshiest part of a thigh, not touching bone, registers 180°F. Cook meat to an internal temperature of 160°F. or more. Finally, keep counters, cutting boards, knives and other implements immaculate, washing them with hot soapy water or perhaps a diluted bleach solution as soon as you've finished working with raw eggs, meat or poultry. Lather your hands well, too.

SHIGELLA:

What it is: The medical name for the dysentery this pathogen causes is shigellosis.

Bacterial source: Dairy products; poultry; potato, pasta and other bland salads. Contaminated by careless cooks or handlers, food, if not refrigerated, allows shigella to grow, and outbreaks of shigellosis will surely follow.

Symptoms of shigellosis: Diarrhea, abdominal cramps, vomiting, fever and sometimes blood, mucus and/or pus in stools.

How soon symptoms occur: Within one to seven days.

Preventives: Keeping the cook and kitchen squeaky clean; also refrigerating all perishables promptly and properly.

STAPHYLOCOCCUS AUREUS:

What it is: The " turista bug" that so often plagues travelers. Actually, it's not the bug that makes you sick but the toxin it manufactures. S. aureus lives in the respiratory tract, so if a chef or waiter sneezes into food — particularly a PROTEIN-rich one — he contaminates it (he also contaminates it if he has infected sores on his hands). If the food is then not kept hot enough or cold enough, the bugs will thrive, producing their special brand of poison. Once staph toxins are present in food, no amount of cooking will destroy them.

Bacterial source: Meats, poultry, egg products, cream-filled cakes and pastries, GELATINS, cream sauces, creamed foods and bland salads (potato, macaroni, chicken, tuna, shrimp, etc.) that are allowed to stand too long at room temperature or, worse, as sometimes happens on cruise ships, are left to languish on a buffet under the downpouring sun. Such foods are warm and moist, the perfect breeding ground for bacteria.

Symptoms of Staphylococcal food poisoning: The "trots," stomach cramps, vomiting, fever.

How soon symptoms occur: Anywhere from a half hour to eight hours after eating contaminated food. The good news is that these bouts rarely last more than a day or two and although they can make you wish you were dead, they're almost never fatal.

Preventives: Keep hot foods hissing hot, cold foods icy cold. Also, thaw frozen food in the refrigerator, never at room temperature. Finally, refrigerate leftovers ASAP.

VIBRIO VULNIFICUS:

What it is: This microbe lives in coastal waters and in warm weather can infect seafood and, ultimately, those who eat it. People at greatest risk are those with weakened immune systems, scanty stomach acid or liver problems. Vibrio infections strike abruptly with chills and fever. The best preventive? Avoid raw fish or shellfish taken in summer from shallow inshore waters.

YERSINIA ENTEROCOLITICA:

Both food- and waterborne, Y. enterocolitica has occasionally infected livestock (beef, lamb and pork) and is passed along to humans through improperly cooked meat. It thrives at room temperature, even in the refrigerator but, fortunately, is destroyed by heat.

Bacterial source: Raw meat, water, improperly handled nonfat dry milk reconstituted, tofu packed in contaminated water, chocolate syrup, raw vegetables, unpasteurized milk and milk products.

Symptoms of Y. enterocolitica food poisoning: Fever, diarrhea and intense abdominal pain on the lower, right-hand side that mimics appendicitis (more than a few healthy appendixes have been removed because of wrong diagnoses). Y. enterocolitica infections, a major cause of enterocolitis in children, have also led to terminal ileitis, liver and spleen abscesses, septicemia and arthritis.

How soon symptoms occur: Two to three days after eating or drinking contaminated food or water.

Preventives: Keep kitchen and kitchen equipment immaculate, paying particular attention to implements and cutting boards used to prepare food that will be eaten raw. Avoid unpurified water, unpasteurized milk and milk products. Cook all meats thoroughly (to 160°F.).