Microbiology deals with the study of microscopic organisms. The diagnostic microbiology laboratory involves in the identification of infectious agents.
The procedures involved in the microbiological analysis varies from one branch to another. For example, examination of parasites are totally different from the routine diagnostic procedures employed in bacteriology and virology.
Identification of the infectious agent is the principle function of the diagnostic microbiology laboratory, moreover, the diagnostic laboratory also provides guidance in therapeutic management.
For example, in case of bacterial infections the laboratory provides information regarding the most effective antimicrobial agent and its dosage to be used for the particular patient.
HISTORY OF MICROBIOLOGY
As microbes are invisible to the unaided eye, definitive knowledge about them had to await the development of microscopes. The credit for having first observed and reported bacteria belongs to Antony van Leeuwenhoek, whose hobby was grinding lenses and observing diverse materials through them. Leeuwenhoek coined the word of ‘little animalcules’ as he called them, represented only curiosity of nature.
The development of microbiology as a scientific discipline dates back to Louis Pasteur (1822-95). Though trained as a chemist, his studies on fermentation led him to take an interest in microoganisms. The basic principles and techniques of microbiology were evolved by Pasteur during his enquiry into the origin of microbes, he introduced techniques of sterilisation and developed the steam steriliser, hot-air oven and autoclave. He also established the differing growth needs of different bacteria.
He attenuated cultures of the anthrax bacillus by incubation at high temperature (42-43°C) and proved that inoculation of such cultures in animals induced specific protection against anthrax. It was Pasteur who coined the term vaccine for prophylactic preparations to commemorate the first of such 4preparations, namely cowpox, employed by Jenner for protection against smallpox.
Pasteur and Koch had many disciples who discovered the causative agents of several bacterial infections. In 1874 Hansen described the leprosy bacillus; in 1879 Neisser described the Gonococcus; in 1881 Ogston discovered the Staphylococcus; in 1884 Loeffler observed the tetanus bacillus in soil; in 1886 Frenkel described the Pneumococcus; in 1887 Bruce identified the causative agent of Malta fever; in 1905 Schaudinn and Hoffmann discovered the spirochaete of syphilis.
Roux and Yersin (1888) identified a new mechanism of pathogenesis when they discovered the diphtheria toxin. Similar toxins were identified in tetanus and some other bacteria. The toxins were found to be specifically neutralised by these antitoxins.
The causative agents of various infectious disease were being reported by different investigators in such profusion that it was necessary to introduce criteria for proving. These criteria, first indicated by Henle, were enunciated by Koch and are known as “Koch's postulates”.
- The bacterium should be constantly associated with the lesions of the disease.
- It should be possible to isolate the bacterium in pure culture from the lesions.
- Inoculation of such pure culture into suitable laboratory animal should reproduce the lesions of the disease.
- It should be possible to reisolate the bacterium in pure culture from the lesions produced in the experimental animals.
- The specific antibodies to the bacterium should be demonstrable in the serum of patient suffering from the disease.
The next major discovery in immunity was Pasteur's development of vaccines for chicken-cholera, anthrax and rabies. Pfeiffer (1893) demonstrated bactericidal effect in vivo by injecting live cholera vibrios intraperitoneally in guinea pigs previously injected with killed vibrios. The vibrios were shown to undergo lysis.
Apart from the obvious benefits such as specific methods of diagnosis, prevention and control of infectious disease, medical microbiology has contributed to scientific knowledge and human welfare in many other ways.