Either the organism is not filamentous or it is filamentous but not strictly a fungus. Bacteria Bacteria represent a very ancient group of organisms, perhaps as old as four billion years. Colonies of bacteria are composed of minute spore-like cells that together form a slimy mass. Such colonies never contain hyphae and are thus easily distinguished from those of true moulds. Bacterial cells, rarely more than 1 um in diameter, are difficult to examine, even with a good microscope, and are best seen when stained.
Many bacteria are motile and swim vigorously.
Actinomycetes These organisms are usually classified as bacteria but have filaments like fungi. The filaments are seldom more than 1 um in diameter, however, and are thus considerably narrower than those of moulds. Yeasts Yeasts are true fungi, but in lacking hyphae cannot be classed as moulds. They resemble bacteria in forming pasty or slimy colonies of spore-like cells, but differ in having these cells much larger, usually 2 um or more broad. Reproduction of yeasts is usually by budding, a process where a smaller cell appears to bubble slowly out of the parent cell.