In such environments, yeasts or molds predominate. However, bacteria find conditions of low pH, moisture, or temperature and high salt or sugar unfavorable. Since bacteria grow faster, they greatly outnumber yeasts and molds in most foods. Yeasts and molds grow on most foods, on equipment, and building surfaces where there are small amounts of nutrient and moisture. They reproduce by spores that are frequently present as green or black masses on the protruding hyphae. Molds can thrive in conditions too adverse for bacteria or yeasts. The chains usually have numerous branches, called hyphae. Molds as found on bread, fruit, damp paper, or other surfaces are actually composed of millions of microscopic cells joined together to form chains.
In budding each cell can produce several buds, or swellings, which break away to form new, fully formed daughter cells. Yeasts are oval-shaped and slightly larger than bacteria. Most sporulating bacteria that grow in the presence of air belong to the Genus Bacillus, and most that grow only in the absence of air belong to the Genus Clostridium. Among the bacteria, sporulation is not a means of reproduction since each cell forms a single spore which later germinates into a single cell again. When conditions become favorable, the spores germinate, with each spore again becoming a vegetative cell with the ability to reproduce. Spore forms preserve the bacteria from starvation, drying, freezing, chemicals, and heat. Vegetative cells form spores under adverse conditions as a means of survival. Some rod-shaped bacteria are capable of existing in two forms, dormant spores and active vegetative cells. If there are 1000 original cells instead of a single one, there will be over 1 billion cells in 5 hours. Under ideal conditions, this doubling may occur as frequently as every 15 minutes, so that within 5 hours there will be more than a million cells from the original single cell. The two cells then divide to become 4, 4 become 8, and so forth. All bacteria reproduce by dividing into two cells. To see them, you need a microscope that magnifies about 1000-fold. There are thousands of species of bacteria, but all are single-celled and fall into three basic shapes: spherical, straight rods, and spiral rods. Most are harmless, many are highly beneficial, some indicate the probable presence of filth, disease organisms, spoilage and a few cause disease. Bacteriaīacteria are the most important microorganisms to the food processor.
The tiniest life forms are bacteria, yeasts, molds, and viruses, termed “microorganisms” because of their size (micro meaning small and organism meaning living being).