Bacterial Food Spoilers

Spore-forming bacteria are usually associated with spoilage of heat-treated foods because their spores can survive high processing temperatures. These Gram-positive bacteria may be strict anaerobes or facultative (capable of growth with or without oxygen). Some spore-formers are thermophilic, preferring growth at high temperatures (as high as 55ºC). Some anaerobic thermophiles produce hydrogen sulphide (Desulfotomaculum) and others produce hydrogen and carbon dioxide (Thermoanaerobacterium) during growth on canned/ hermetically sealed foods kept at high temperatures, for example, soups sold in vending machines.

Other thermophiles (Bacillus and Geobacillus spp.) cause a flat sour spoilage of high or low pH canned foods with little or no gas production, and one species causes ropiness in bread held at high ambient temperatures. Mesophilic anaerobes, growing at ambient temperatures, cause several types of spoilage of vegetables (Bacillus spp.); putrefaction of canned products, early blowing of cheeses, and butyric acid production in canned vegetables and fruits (Clostridium spp.); and "medicinal" flavors in canned low-acid foods (Alicyclobacillus). Psychrotolerant sporeformers produce gas and sickly odors in chilled meats and brine-cured hams (Clostridium spp.) while others produce off-odors and gas in vacuum-packed, chilled foods and milk (Bacillus spp.).

Lactic acid bacteria (LAB) are a group of Gram-positive bacteria, including species of Lactobacillus, Pediococcus, Leuconostoc and Oenococcus, some of which are useful in producing fermented foods such as yogurt and pickles. However, under low oxygen, low temperature, and acidic conditions, these bacteria become the predominant spoilage organisms on a variety of foods. Erwinia carotovora is one of the most important bacteria causing soft rot of vegetables in the field or stored at ambient temperatures.