d. Reproduction. Most bacteria reproduce by binary fission. One organism
divides to form two new organisms. The time required for fission will vary from eight
minutes to as long as six hours. If all cells of each succeeding generation divided every
twenty minutes, then one bacterial cell would result in sixty-five billion cells in twelve
e. Optimum Growth Conditions. Bacteria generally have a poorer tolerance
for salt and sugar than most other microorganisms. Most species of bacteria have an
optimum pH range between pH 6.0 to pH 8.5. Bacteria generally will not grow in as
wide a range of moisture conditions and temperatures as will yeasts and molds.
MICROORGANISMS SMALLER THAN BACTERIA
There are two groups of microorganisms smaller in size than most bacteria.
They are of little importance as spoilage organisms but are of considerable importance
as pathogenic organisms in food.
a. Rickettsiae. Rickettsiae are smaller in size than other bacteria but are larger
than viruses. Rickettsiae cause such diseases as typhus, Rocky Mountain spotted
fever, and Q fever. Q fever is now considered to be one of the major milk-borne
diseases in this country.
b. Viruses. Viruses are our smallest group. They cause many diseases in
animals, humans, and plants. A bacteriophage is a type of virus that destroys bacteria.
Bacteriophages are very important in the brewing industry and dairy industry, since they
will destroy beneficial bacteria that are essential to the fermentation and souring
Molds (division Eumycetes) are multicellular microorganisms that form
filamentous branching growths known as mycelia (singular, mycelium). See figure 1-3.
Figure 1-3. Molds.