Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Cold, common

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CCohn, Ferdinand JuliusOHN, FERDINANDJULIUS(1828-1898)

German microbiologist

Ferdinand Cohn, a founder of modern microbiology, became

the first to recognize and study bacteriology as a separate sci-

ence. Cohn developed a system for classifying bacteriaand

discovered the importance of heat-resistant endospores.

Additionally, Cohn recognized that both pathogens and non-

pathogens could be found in drinking water and spoke of the

importance of analyzing drinking water. Finally, Cohn worked

with Robert Kochon the development of the etiology of the

anthraxbacillus.

Cohn initially began his studies in botany at the

University of Breslau in 1844. After being denied entry into

the doctoral program in 1846 because of his Jewish heritage,

Cohn moved to Berlin. There he completed his doctoral

degree in 1847, at the age of 19, on the structure and germi-

nation of seeds.

After returning to Breslau in 1849, Cohn was presented

with a top of the line microscopefrom his father. There he

studied the cell biology of plants including the growth and

division of plant cells, plasma streaming, cell differentiation,

and cellular structures. In time, Cohn’s studies were redirected

toward algae, protozoa, fungi, and bacteria. His efforts on the

developmental and sexual cycles of these microorganismsled

to important advancements in cell biology.

At that time, bacteriology was an emerging field and

although scientists knew that bacteria existed, they had failed

to isolate bacteria in pure cultures. Scientists began to name

bacteria without regard for someone else that had already

observed and named the very same bacteria. Moreover, scien-

tists believed bacteria to be a single species and that variations

observed were due to different stages of development. Cohn

recognized that bacteria could not be classified as a single

species and developed a system for classifying them. He pro-

posed that bacteria could be divided into groups based on

whether they had similar development, chemical make-up, or

descent. In 1875, he defined bacteria as “chlorophyll-less cells

of characteristic shape that multiply by cross division and live

as singe cells, filamentous cell chains, or cell aggregates.”

Eventually he extended his definition to include that “bacteria

can be divided into distinct species with typical characteristics,

which are transmitted to the following generations when bacte-

ria multiply and that variations exist within each species.”

After comprehensive studies of bacteria, Cohn believed

that bacteria were related to algae and should thus be classified

in the plant kingdom. Additionally, Cohn studied the growth of

bacteria and found that in some bacteria organic substances

were broken down in the presence of nitrogen. He also claimed

that carbon dioxide could not be utilized as a carbon source in

bacteria. It was not until 1890 when Sergei N. Winogradsky

disproved this statement and discovered autotrophy.

Cohn’s initial classification of bacteria consisted of four

groups based on shape: Sphaerobacteria (sphere-shaped),

Microbacteria (rod-shaped), Desmobacteria (filamentous),

and Spirobacteria (screw-like shaped). Of those four groups

the genus Micrococcuswas classified as Sphaerobacteria,

Bacterium was classified as Microbacteria, Bacillus and

Vibriowere classified as Desmobacteria, and Spirillumand

Spirochaetawere classified as Spirobacteria. Some of the gen-

era could be further divided into subcategories.

Through the studies of Bacillus subtilisCohn was able

to disprove the earlier theory of spontaneous generation. Cohn

recognized that some solutions were easily sterilized by heat,

requiring only a few minutes of boiling, while other solutions

required several hours of boiling. He found that still others,

such as hay infusions, could not be sterilized at all. Cohn dis-

covered heat-resistant structures called endospores, not spon-

taneous generation, were responsible for tainting sterilized

cultures. Endospores are not killed in boiling water while the

vegetative cells are. It was the heat resistant endospores from

which bacteria grew, discounting the old theory of sponta-

neous generation.

Early on Cohn assisted in diagnosing fungal infections

of crops and provided treatment options to the farmers for

these plant diseases. Additionally, Cohn recognized that water

sources were capable of harboring and transferring infectious

diseases to humans. It was Robert Koch who first identified

the pathogen that caused cholera in the drinking water; how-

ever, Cohn also analyzed the drinking water and found disease

and non-disease causing microorganisms. Cohn developed a

system for chemical analysis of water and claimed that drink-

ing water should be monitored for microorganisms on a regu-

lar basis.

Later when Robert Koch was studying anthrax bacil-

lus, Koch sought the help of Cohn. Cohn realized the impor-

tance of studying the disease causing anthrax bacillus and

worked with Koch to further investigate the etiology of the

bacteria. In 1875, Cohn founded the journal Beitrage zur

Biologie der Pflanzenand published Koch’s findings on

anthrax bacillus in 1877.

See alsoWater quality; Cell cycle and cell division; History of

microbiology

CCold, commonOLD, COMMON

Dedicated researchers have searched for a cure or even an

effective treatment for the common cold (rhinitis) for years.

Discovering or constructing the agent that will be universally

lethal to all the cold-causing viruseshas been fruitless. A drug

that will kill only one or two of the viruses would be of little

use since the patient would not know which of the viruses was

the one that brought on his cold.

The common cold differs in several ways from

influenzaor the flu. Cold symptoms develop gradually and are

relatively mild. The flu has a sudden onset and has more seri-

ous symptoms the usually put the sufferer to bed, and the flu

lasts about twice as long as the cold. Also influenza can be

fatal, especially to elderly persons, though the number of

influenza viruses is more limited than the number of cold

viruses, and vaccines are available against certain types of flu.

Rhinoviruses, adenoviruses, influenza viruses, parain-

fluenza viruses, syncytial viruses, echoviruses, and coxsackie

viruses—all have been implicated as the agents that cause the

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