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The term “microorganism” derives from Greek, where “mikro” means small and “organismos” means living being. A microorganism, therefore, refers to a living organism too small to be seen with the naked eye. Microorganisms are diverse, including bacteria, fungi, parasites, and viruses. It is believed that bacteria evolved from the earliest life forms approximately 4 billion years ago.
Microorganisms exist everywhere - in soil, water, thermal springs, the deepest points of the oceans, the highest mountain peaks, plants, animals, and the human body. It is estimated that there are about 5x10³⁰ bacteria on Earth. While the vast majority of microorganisms are harmless, a very small proportion can cause disease in humans.
History of Microorganisms
Before their discovery in the 17th century, knowledge about microorganisms was purely speculative. In the 1st century BC, Marcus Terentius Varro, a Roman scholar, warned people against settling near swamps, stating: “Tiny creatures, invisible to the eye, float in the air and enter the body through the mouth and nose, causing serious diseases.” Similarly, scientists from the Islamic world — such as Avicenna (Ibn Sina), Al-Razi, and Ibn Zuhr — suggested the existence of microorganisms centuries before they were visually identified.
History of Microbiology
The turning point came in the 17th century with Antonie van Leeuwenhoek, who, in 1676, observed microorganisms for the first time using a microscope he designed himself. However, the founders of modern microbiology are considered to be Louis Pasteur and Robert Koch in the 19th century. With the formal establishment of microbiology as a scientific discipline, rapid and continuous developments followed, shaping it into the advanced field it is today.
Microorganisms and Humans
Trillions of microorganisms live on the human skin, in the nose, throat, intestines, and genital area. One gram of human feces contains approximately 90 billion bacteria. These microorganisms are beneficial to human health - without them, life would not be possible.
What is Clinical Microbiology?
Microbiology encompasses several fields, including human health, veterinary science, agriculture, and industry. The branch of microbiology concerned with human health and medicine is known as clinical microbiology.
Clinical Microbiology and Infectious Diseases
The primary field of study for microbiology is the laboratory. Closely associated with it is the discipline of infectious diseases, which forms an inseparable pair. While microbiology focuses on identifying microorganisms and their characteristics, infectious disease specialists are responsible for the diagnosis and treatment of patients.
Demonstrating Microorganisms
Microorganisms can be visualized directly under a microscope or by using specific staining techniques. They can also be cultured and identified in nutrient media, known as culture media. When direct observation is not possible, indirect evidence - such as antigen or antibody detection - is used for identification.
Sample Collection in Clinical Microbiology
The most critical step in clinical microbiology is obtaining a proper specimen from the correct site while avoiding contamination with normal body flora. For example, in a patient with a throat infection, a sterile swab similar to a cotton applicator is used to collect a sample from the tonsils and inflamed areas of the pharynx, avoiding contact with the lips, tongue, or oral mucosa. The swab is then immediately placed into a transport medium.
As another example, for urine cultures, the midstream urine sample is preferred. After voiding the initial portion of urine, the middle stream is collected in a sterile container, and the final portion is discarded.
For samples taken from sterile body sites such as blood, cerebrospinal fluid, pleural fluid, or tissue, maintaining sterility is of utmost importance. For instance, when collecting a blood culture, contamination from skin flora must be prevented. The skin is first disinfected with an antiseptic, and blood is drawn using a sterile syringe before being transferred into the culture bottle.
Examination Methods in Clinical Microbiology
Traditional methods such as microscopic examination, culturing microorganisms in media, and performing antibiotic susceptibility tests remain the gold standard in microbiological analysis.
In addition to these conventional methods, indirect techniques such as antigen detection and antibody testing are also used to identify microorganisms.
One of the most well-known molecular diagnostic methods today is the polymerase chain reaction (PCR) technique, which gained worldwide recognition during the COVID-19 pandemic. PCR enables the detection of various microorganisms by amplifying their genetic material, and this field is referred to as molecular biology.
Microorganisms are a part of every moment of our lives - life without them is unimaginable. However, pathogenic microorganisms can occasionally cause disease. In such cases, clinical microbiology plays a vital role in diagnosing and managing infections effectively.
