Microbiology of Food

Many human foods are produced using microorganisms or microbial products including bread, sourdough bread, buttermilk, yogurt, green olives, pickles, soy sauce, poi, cheeses, beer, and wine.

Infections by food-borne pathogens are very common worldwide, and in the United States as well. It is estimated that in the US, food borne diseases cause 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths each year. While known pathogens (eg. Salmonella, Listeria, and Toxoplasma) cause about 25% of these deaths, the remaining three-quarters are caused by usually unidentified or unknown agents.

More than 200 human diseases are known to be transmissible by food. Such diseases may be bacterial, viral, parasitic, or caused by bacterial toxins or prions (in the case of BSE). Many of the common food borne pathogens of today (eg. Listeria, Campylobacter, E. coli 0157:H7, and Cyclospora) were not even recognized 20 years ago. Of the approximately 1,400 deaths that occur annually in the US due to acute gastroenteritis, 67% are traceable to food borne infection.

A list of some food groups and the pathogens that may be associated with them include:

Grains:

mycotoxins such as ergot (Claviceps purpurea on rye) and aflatoxin from Aspergillus flavus on peanuts)
Bread spoilage from fungi such as Rhizopus, Penicillium, Aspergillus and Monilia

Fruits and Vegetables:

A variety of potentially pathogenic organisms can occur on the surfaces of fruits and vegetables, including bacteria, protozoa, and helminth ova. Such contamination is particularly common in areas where human or animal manure is used to fertilize vegetables grown for human consumption. Vegetables that may be consumed without cooking ( eg. radishes, lettuce, carrots) are a particular problem. An example is the contamination of watercress by Fasciola hepatica. Most fruits are relatively free of pathogens, the occurrence of Cyclospora on berries being an exception.

Spoilage of food is caused by a variety of microorganisms. A partial list includes:

Food Spoilage Microorganisms
Food	Type of Spoliage	Microorganism
bacon, sausages	greening	Lactobacillus ; Leuconostoc
bread	ropiness (stringy)	Bacillus subtilis
bread	molding	Penicillium ; Rhizopus; Aspergillus
canned goods	molding	yeasts
fresh fish	rotting	Micrococcus ; Serratia ; Pseudomonas ; Flavobacterium
eggs	greening	Pseudomonas ; Proteus
fresh meats	slimyness	Flavobacterium ; Pseudomonas
fresh meats	putrefaction	Bacillus ; Pseudomonas ; coliforms
milk	souring	Lactobacillus ; Streptococcus
milk	roppy spoilage	Alcaligenes
milk	gassy spoilage	Bacillus ; Clostridiium
preserves	molding	Aspergillus ; Penicillium; yeasts
butter and oils	rancidity	Pseudomonas
fruits & leafy vegetables	soft rot	Erwinia
potatoes	rotting	Erwinia
potatoes	potato blight	Phytophthora
melons	soft rot	Fusarium and Rhizopus
tomatoes	soft rot	Fusarium and Rhizopus

Meat and Poultry:

Trichinella spirallis (pork and bearmeat), Taenia solium (pork), and T. saginata (beef), may all be transmitted by meat.

Salmonella and Campylobacter are especially strongly associated with poultry and eggs.

Enterotoxigenic Escherichia coli in beef has caused numerous human infections (and some deaths) recently.

Fish and Shellfish:

Vibrio parahemolyticus, Vibrio choleri, and Salmonella typhimurium in shellfish.

Paragonomus westermanni (Lung fluke) in crayfish and freshwater crabs

Schistosoma , Chlonorchis, and Diphyllobothrium latum in fish

Milk:

Mycobacterium bovis, Brucella abortus, Listeria monocytogenes, Staphylococcus aureus, Coxiella burnetii, and Salmonella can all be transmitted by contaminated milk.