4 ◾ Fundamental Food Microbiology
easily available, which stimulated many inquisitive minds to observe and describe the creatures
they discovered under a microscope. By 1838, Ehrenberg (who introduced the term bacteria) had
proposed at least 16 species in four genera, and by 1875, Ferdinand Cohn had developed the preliminary classification system of bacteria. Cohn was also the first to discover that some bacteria
produced spores. Although, like bacteria, the existence of submicroscopic viruses was recognized
in the mid-19th century, they were observed only after the invention of the electron microscope
in the 1940s.
Where Are they Coming from?
Following Leeuwenhoek’s discovery, although there were no bursts of activity, some scientific
minds were curious to determine from where the animalcules, observed to be present in many different objects, were emanating. 1–3 Society had just emerged from the Renaissance period, and science, known as experimental philosophy, was in its infancy. The theory of spontaneous generation,
that is, the generation of some form of life from nonliving objects, had many powerful followers
among the educated and elite classes. Since the time of the Greeks, the emergence of maggots from
dead bodies and spoiled flesh was thought to be a result of spontaneous generation. However, in
approximately 1665, Redi disproved that theory by showing that the maggots in spoiled meat and
fish could only appear if flies were allowed to contaminate them. The advocates of the spontaneous
generation theory argued that the animalcules could not regenerate by themselves (biogenesis), but
they were present in different things only through abiogenesis (spontaneous generation). In 1749,
Turbevill Needham showed that boiled meat and meat broth, following storage in covered flasks,
could have the presence of animalcules within a short time. This was used to prove the appearance
of these animalcules by spontaneous generation. Lazzaro Spallanzani (1765) showed that boiling
the meat infusion in broth in a flask and sealing the flask immediately prevented the appearance
of these microscopic organisms, thereby disproving Needham’s theory.
This was the time when Antoine Laurent Lavoisier and his coworkers showed the need of oxygen for life. The believers of abiogenesis rejected Spallanzani’s observation, suggesting that there
was not enough vital force (oxygen) present in the sealed flask for animalcules to appear through
spontaneous generation. Later, Schulze (1830), by passing air through acid; Theodore Schwann
(1838), by passing air through red-hot tubes; and Schröeder (1854), by passing air through cotton showed that bacteria failed to appear in a boiled meat infusion even in the presence of air.
Finally, in 1861, Louis Pasteur demonstrated that, in a boiled infusion, bacteria could grow only
if the infusions were contaminated with bacteria carried by dust particles in the air. 1,4 His careful
and controlled studies proved that bacteria were able to reproduce (biogenesis), and life could not
originate by spontaneous generation. John Tyndall, in 1870, showed that a boiled infusion could
be stored in dust-free air in a box without microbial growth.
What Are their Functions?
The involvement of invisible organisms in many diseases in humans was suspected as early as the
13th century by Roger Bacon. In the 16th century, Girolamo Fracastoro of Verona suggested
that many human diseases were transmitted from person to person by small creatures. This was
also indicated by Kircher in 1658. In 1762, von Plenciz of Vienna suggested that different invisible organisms were responsible for different diseases. Theodore Schwann (1837) and Hermann
easily available, which stimulated many inquisitive minds to observe and describe the creatures
they discovered under a microscope. By 1838, Ehrenberg (who introduced the term bacteria) had
proposed at least 16 species in four genera, and by 1875, Ferdinand Cohn had developed the preliminary classification system of bacteria. Cohn was also the first to discover that some bacteria
produced spores. Although, like bacteria, the existence of submicroscopic viruses was recognized
in the mid-19th century, they were observed only after the invention of the electron microscope
in the 1940s.
Where Are they Coming from?
Following Leeuwenhoek’s discovery, although there were no bursts of activity, some scientific
minds were curious to determine from where the animalcules, observed to be present in many different objects, were emanating. 1–3 Society had just emerged from the Renaissance period, and science, known as experimental philosophy, was in its infancy. The theory of spontaneous generation,
that is, the generation of some form of life from nonliving objects, had many powerful followers
among the educated and elite classes. Since the time of the Greeks, the emergence of maggots from
dead bodies and spoiled flesh was thought to be a result of spontaneous generation. However, in
approximately 1665, Redi disproved that theory by showing that the maggots in spoiled meat and
fish could only appear if flies were allowed to contaminate them. The advocates of the spontaneous
generation theory argued that the animalcules could not regenerate by themselves (biogenesis), but
they were present in different things only through abiogenesis (spontaneous generation). In 1749,
Turbevill Needham showed that boiled meat and meat broth, following storage in covered flasks,
could have the presence of animalcules within a short time. This was used to prove the appearance
of these animalcules by spontaneous generation. Lazzaro Spallanzani (1765) showed that boiling
the meat infusion in broth in a flask and sealing the flask immediately prevented the appearance
of these microscopic organisms, thereby disproving Needham’s theory.
This was the time when Antoine Laurent Lavoisier and his coworkers showed the need of oxygen for life. The believers of abiogenesis rejected Spallanzani’s observation, suggesting that there
was not enough vital force (oxygen) present in the sealed flask for animalcules to appear through
spontaneous generation. Later, Schulze (1830), by passing air through acid; Theodore Schwann
(1838), by passing air through red-hot tubes; and Schröeder (1854), by passing air through cotton showed that bacteria failed to appear in a boiled meat infusion even in the presence of air.
Finally, in 1861, Louis Pasteur demonstrated that, in a boiled infusion, bacteria could grow only
if the infusions were contaminated with bacteria carried by dust particles in the air. 1,4 His careful
and controlled studies proved that bacteria were able to reproduce (biogenesis), and life could not
originate by spontaneous generation. John Tyndall, in 1870, showed that a boiled infusion could
be stored in dust-free air in a box without microbial growth.
What Are their Functions?
The involvement of invisible organisms in many diseases in humans was suspected as early as the
13th century by Roger Bacon. In the 16th century, Girolamo Fracastoro of Verona suggested
that many human diseases were transmitted from person to person by small creatures. This was
also indicated by Kircher in 1658. In 1762, von Plenciz of Vienna suggested that different invisible organisms were responsible for different diseases. Theodore Schwann (1837) and Hermann