Medical microbiology is the biological study of bacteria, viruses, fungi, protozoa, and algae which are collectively called microorganisms, and unlike macroscopic organisms that are readily visible, these require magnification to be seen with the help of a microscope.
A microorganism is one of a very diverse group of organisms that typically are microscopic and occur as independent, rapidly producing units that are comparatively less complex than plants and animals and exists almost everywhere. The easy way to remember these features is
M = Microscopic
I = Independent units
C = Complex (less)
R = Rapid growth rates
O = Omnipresent (present everywhere)
MICROBIOLOGY AND PATIENT
Medical microbiology is concerned with etiology, pathogenesis, laboratory diagnosis, and treatment of infections in an individual and with the epidemiology and control of infection in the community. The ideal bacteriological management of a patient with infection consists of the following steps:
- Establishment of a clinical diagnosis
- Isolation of causative agent
- Determination of antibiotic susceptibility in laboratory and administration of the effective drug
- Monitoring of therapy
- Measurement of antimicrobial agents in body fluid
- Confirmation of bacteriological cure.
The treating physician often identifies the disease-causing organism on the basis of his clinical findings and accordingly treats the patient. There are many clinical conditions that are manifested only by fever and can be caused by a large number of organisms. The laboratory comes to the aid of a physician in all such cases. Many times even when the clinical syndrome is diagnosed such as sore throat, urinary tract infection, and acute diarrhea, it becomes difficult to prescribe the most appropriate chemotherapeutic agent because of a large number of organisms that can cause these syndromes. Laboratory investigation provides the information regarding organisms as well as the drug to be used
Predicting Antibiotic Sensitivity
For many organisms, it is not essential to perform antibiotic sensitivity every time these are isolated from a clinical sample because a bacteriology laboratory, on the basis of its experience in that area can always predict with a fairly high degree of accuracy, the useful drugs for a particular type of infection.
Organisms with Predictable Sensitivity
Bacterium like Streptococcus pyogenes which commonly causes sore throat is almost always sensitive to penicillin and Yersinia pestis and many other gram-negative bacilli are invariably resistant to penicillin. Similarly, organism like Haemophilus influenza is almost always sensitive to cotrimoxazole, chloramphenicol, ampicillin, and tetracycline. Regular patterns of sensitivity to many chemotherapeutic agents can be shown for streptococci, pneumococci, Yersinia, Salmonella, and Clostridium.
Thus, every regional microbiological laboratory should have and provide this information. Many times an infection is of such a nature that the antimicrobial agent given alone fails to eradicate the infection. Combination therapy is usually the answer to such problems and only a bacteriology laboratory can provide the best combination. It can also be first detected only in a laboratory that a combination of drugs shall result in a synergistic or an antagonistic effect.