(I) B. Development of microbiology in 19th (Golden era of microbiology -1857 to 1954)

 

Development of microbiology in 19^th (Golden era of microbiology -1857 to 1954)

Discovery of microbial role in transformation of organic matter:

Germ theory of fermentation :

After the controversy over spontaneous generation, the role of microorganism in the transformation of organic matter was found out.

The two types of chemical changes in the organic matter; fermentation and putrefaction.

Fermentation is defined as the process  that results in the formation of alcohol or organic acids.

Putrefaction is a process of decomposition that results in the formation of ill smelling products, occasionally in meat as a consequence of proteins degradation.

Germ theory states that the fermentation process is caused due to microorganism (involvement of microorganism in fermentation).

Fermentation as biological process was recognized in 1837 by three scientists: Latour, Schwann, Kutzing. 

They independently proposed that microscopic yeast cells were responsible for the conversion of sugars to ethyl alcohol and carbon dioxide.

Mean while Louis Pasteur (1856-57) worked on ethanol fermentation. 

A French wine industry was producing a bad quality, sour taste wine. 

Pasteur was called on by French wine industry to solve this problem .

After microscopic observation Pasteur found the presence of another types of bacteria in wine.

 The bacteria were lactic acid bacteria. 

Because of production of lactic acid by these bacteria the wine had sour taste.

 Thus in order to kill those bacteria contaminating wine, Pasteur designed a process of gentle heating.

Pasteur found the presence of contaminating bacteria in grape mash(grape mash is used as a principal raw material for the production of wine).

Thus, he gave a temperature of 60⁰C for 30 minutes to grape mash. 

This heating process killed the contaminating microbes. 

Then this grape mash was inoculated with pure culture of yeast. 

Also, Pasteur gave this heat treatment to wine for its preservation for long period of time. 

After this the quality of wine was improved.

Thus Pasteur became the national hero after developing this techniques for the control of growth of undesirable microbes in wine. 

The process is now called as ‘pasteurization’ in the honors if its inventor Louis Pasteur.

Today, this techniques is used to preserve the milk and milk products in dairy industry.

 For milk the pasteurization temperature is 145⁰ F(63⁰C) for 30 minutes or 161⁰ F (714.7⁰C) for 15 to 30 sec. 

Pasteurization of milk only kills the pathogenic microorganism present in milk.

 But all microorganism are not necessarily killed. Hence this is a partial sterilization process.

Pasteur worked on various fermentation processes like lactic acid, alcoholic, and butyric acid fermentations. 

During his investigations he discovered  some interesting points;

1).      Each type of fermentation is the result of microbial activity.

2)      During fermentation microbes produce specific type  of end products using substrate like sugar.

3)      For fermentation microbes required a specific environment.

 

Discovery of anaerobic life:

Pasteur published several research paper on fermentation during his studies. 

He continued his study on  fermentation  for 20 years.

 During his studies on butyric acid fermentation, Pasteur discovered the anerobic  life in microbes. 

Because in this process, the microbes were unable  to survive in the presence of air .

On the basis  of these  observation , Pasteur coined the term aerobic and anerobic.

 Aerobic are capable of growth only in presence of oxygen. 

Anerobic can grow only in the absence of oxygen.

Physiological significance of fermentation :

During his studies on fermentation, Pasteur described the physiological significance of fermentation process. 

He described the fermentation process as the energy-yielding metabolism for the fermenting microbes. 

He also stated that fermentation is a less energy yielding metablic process than aerobic respiration.

The discovery of the role of microbes in the causation of disease:

Germ theory of disease:

The theory says that the microbes are responsible for the production of disease. 

To prove this theory , many scientists were working . 

For the first time Agostine Bassi (1834) proved the presence of fungi in silkworms, which caused disease in silkwarms. 

This discovery was followed by the isolation of a fungus from human skin disease by Johann Schonelin. 

M.J. Berkeley discovered the role of pathogen in disease of silkworms that threatened to ruin French wine industry.

For the first time the role of bacteria as a causative agent was given by Robert Koch( 1843-1910). 

Robert Koch , a German physician neglected his medical practice and diverted to studies in new science of bacteriology. 

Robert Koch was working on anthrax disease of animals. 

To prove the bacteria are responsible for the anthrax disease, he performed an experiment.

From the observations of results, Robert Koch published four important criteria called Koch’s postulates.

Robert Koch’s postulates are as follows:

1)     In every case of disease , a specific microorganism must be present in infected man or animal and must be absent in healthy individuals.

2)      The microbes can be isolated from infected animal and grown in pure culture in laboratory.

3)      The injection of pure culture in healthy , normal animal will produce disease in that animal again.

4)      The same type of microbes can be recovered (isolated) from this experimentally infected animal again.

 

With his anthrax discoveries , Koch was the first to prove that one kind of microbes causes one definite kind of disease.

 Later he and his colleagues discovered the bacteria that causes cholera and tuberculosis. ( At that time when Koch’s postulates were formulated , true viral pathogens were unknown. But after the discovery of viruses, agents that do not grow in laboratory on artificial media, as do bacteria, has required some modification of Koch’s postulates. Also we know that , one microbe can cause several disease and there are some disease caused by more than one microbes.).

Similar type of postulates was formulated in 1937 by T.M. River, after the discovery of viruses as causative agents. 

Rivers’s postulates applicable to both animal and plant viruses are as fallows:

1.The viral agent must be found either in diseased host’s body fluids or in the cells showing specific lesions.

2.  The viral agent obtained from the infected host’s must produce the specific disease in a suitable healthy animal or plant: or provide evidence of infection in the form of formation of antibodies aginst viruses.

3. Similar material from such newely infected animal or plants, in turn , must be capable of producing the same disease in other healthyhosts.

 

 

In 1892 , Dmitri Ivanovski discovered that the causative agent of tobacco mosic disease could be transmitted by the filtered juice from  a diseased plant ( the filter was known to prevent the entry of bacteria). 

It was shown later that the material that passed through the filter contained diseased- causing agents, which was much smaller than bacteria. 

Thomas J. Burrill, an American botanist, found a bacterium known to cause a disease of pear trees called as fire blight. 

Another American, Theobald Smith proved the transmission of microbes by arthropods (vectors) . 

Smith’s discovery successfully  prevented the spread of disease such as malaria, yellow fever and sleeping sickness.

In 1900, an army surgeon named Walter Reed proved that the virus responsible for yellow fever was carried by certain  mosquitoes.

 Subsequent mosquito control  programs virtually eliminated the epidemic yellow fever from Cuba and area of central and south America and  made it possible to complete the Panama Canal.

Development in disease prevention:

With the knowledge of disease causing microbes, scientists focused their attention on the prevention and treatment . 

Several methods were adopted such as antisepsis, immunization and chemotherapy.

Surgical antisepsis: 

Sepsis means the toxic effects of disease causing agents on the body during infection, while 

antisepsis means measure that stops these effects by preventing infection. 

Thus the measures used to prevent microbial infection during surgery called surgical antisepsis.

 It was practiced even before the germ theory of disease was proved. 

Joseph Lister, an English surgeon was  searching for a way to prevent infection by microbes at the time of surgery. 

In 1860s , the deaths from infection following surgery were frequent , for example about 45% of Lister’s patients died due to surgical infection.

Lister used carbolic acid( phenol), which was known to kill bacteria. 

He used a dilute solution of phenol to soak surgical equipments and to spray in the operation room. 

With the success of this technique, it was immediately accepted by other surgeons, who also got remarkable results. 

Lister ‘s finding were the origin of present day aseptic techniques that prevent infection. 

A variety of chemical and physical agent are available today that can reduce the number of microorganism in operating rooms, nurseries for premature infants etc.

Vaccination or Immunization: 

The process of vaccination was introduced by Edward Jenner in 1798.

 He immunized the people with small pox. 

Edward Jenner observed that the boys working with cows were not susceptible to small pox disease.

 But the other boys did suffer from small pox disease very soon.

 Edward Jenner tried to find the reason for this. 

Then he realized that, some material must have been getting transferred from the cows (which were suffering from cow pox disease) to the boys, which were in contact with these diseased cows.

Considering this point Edward Jenner vaccinated a boy named James Phipps, by inoculating the cowpox material. 

And they did not get small pox i.e. he developed resistance against small pox disease.

The principle of vaccination was not well understood that time.

 It was later on explained and demonstrated by Louis Pasteur.

Louis Pasteur also worked on the cause and prevention of disease .

 During his work on infectious diseases, in 1880, he isolated the bacterium responsible for chicken cholera and grew it in pure culture. 

To prove that he had really isolated the organism responsible for chicken  cholera, Pasteur arranged for public demonstration where he repeated an experiment .

 In which he inoculated his old pure culture in chickens.

 But the chickens failed to get sick and die. 

Thus, Pasteur found that he used accidently the old culture of chickens  cholera organism for inoculation.

 As the culture were old they lost their virulence power (i.e. ability to produce disease). Hence, the chickens survived.

Several weeks later Pasteur repeated the same experiment using two groups of chickens.

 One group of chickens had been inoculated with old culture of chickens cholera organism. 

The second group of chickens was not inoculated . 

After an interval of few weeks, both  the group of chickens was  inoculated with fresh culture of organism.

This time the second group (i.e. which were  inoculated previously with the old cultures) survived.

The result puzzled the Pasteur, but he soon found the explanation that bacteria lose the ability to produce disease(that is, lose their virulence or could become avirulent ) if they are grown for several weeks (old culture) .

 Thus these bacteria could not produce disease. But after inoculation in body, it stimulates the host  body to produce some substance, hence body remain prepared to fight against incoming infection by virulent bacteria. 

Thus whenever, the virulent organism(bacteria) enter in a body again, they are removed from the body immediately. 

Therefore , the chickens which were inoculated previously with old  cultures, survived after the reinoculation of virulent bacteria.

Now a days, we know that the body’s immune system (protective agency of the body) is stimulated by first exposure to organism.

This experiment of Pasteur gave the complete explanation of the principle of vaccination which was introduced by Edward Jenner . 

Pasteur called  the avirulent culturea as vaccines and immunized as vaccination.

Next Pasteur prepared vaccine against hydrophobia or  rabies- a disease transmitted to people by a bite of rabid animal such as dogs, cats, and other animals.

 Although the  causative agent of the disease was not known, Pasteur felt strongly that it was microorganisms. 

He inoculated rabbits with saliva from rabid dogs, dried them for several days, and mixed the powder in to liquid. This preparation was used as vaccine for the inoculation in dogs. This mixture protected inoculated dogs from rabies.

From the first time it was tested on a boy named Joseph Meister who was bitten by a rabid wolf and his family requested Pasteur to inoculated the child. Pasteur was a chemist and not a physician hence he was not accustomed to  treating humans. The worried Pasteur inoculated the boy for a week and later boy  did not die.

Pasteur also saved most of a group of Russian peasants bitten by a rabid wolf. The czar(is a Russian word for ruler or emperor)  sent him 100000francs. This money and along with their donations from around the world , was the beginning of the world famous Pasteur Institute in Paris.