Microscopy and Culture

Microscopy and Culture

What is microscopy and culture?

To ascertain the cause of an infection, it may be necessary to cultivate body fluids and tissue specimens in a laboratory setting. This procedure allows for the identification and evaluation of bacteria and fungal infections.

Microscopy enables the detection and identification of microorganisms, facilitating the diagnosis of diseases in tissue samples.

What does it reveal?

- Pathogens, the microorganisms responsible for illnesses, are classified into several groups based on their type. The primary categories include viruses, bacteria, and chlamydia (a bacterium resembling a virus). Other groups encompass parasites such as eggs, larvae, and protozoa, which are single-celled organisms like amoebas.

- Bacterial identification typically involves culturing (growing bacteria in the lab). This process involves isolating and examining a purified group of non-contaminated bacteria for comparison.

- Fungi can also be cultured and purified similarly to bacteria, although this method is less common.

- Viruses and chlamydia present challenges for analysis, often requiring advanced laboratory techniques. In some cases, diagnosing these microorganisms may involve testing the patient's blood for antibodies.

- Worms, larvae, eggs, and protozoa are easily identifiable under a microscope by trained microbiologists without the need for further examination.

Bacterial Culture

The body's exterior surfaces, including hair, skin, and mucous membranes in the nose, throat, intestines, stomach, and reproductive organs, harbor numerous bacteria. Under normal circumstances, these bacteria are harmless and even contribute to maintaining a healthy body by preventing harmful bacteria.

If a physician suspects bacterial infection, they typically collect a sample from the suspected site of infection, such as stools for intestinal infections or urine for bladder or kidney infections. This sample, along with patient details, is then sent to a microbiology laboratory for culturing.

Various methods exist for cultivating cultures in the lab. Samples can be obtained from blood, saliva, or other bodily areas like the mouth, skin, outer ear canal, throat, and wounds.

How is culture produced?

Upon arrival at the laboratory, the sample is spread onto a special gel, such as agar, in a plastic dish (culture dish), which is then covered.

To provide additional nourishment, extracts of live substances like meat, bread, or chocolate may be added to the gel. If a particular bacterium is suspected, the gel may be supplemented with specific substances to encourage its growth while inhibiting others.

The culture is then incubated in a heated environment at around 100°F (about 35°C), optimal for the growth of disease-causing bacteria. While multiple bacteria may grow, the pathogen responsible for the disease typically dominates compared to non-pathogens.

How is bacterial microscopy performed?

Bacteria from the culture are transferred to a small glass slide, dried, and stained to enhance visualization.

The Gram stain, a common staining method, distinguishes bacteria as Gram-positive or Gram-negative. The following are examples of frequently encountered Gram-positive and Gram-negative bacteria and associated diseases.

Gram-positive bacteria:

- Staphylococci: causing pneumonia, toxic shock syndrome, and skin infections.
- Streptococci: causing blood poisoning and throat infections.
- Anthrax, Bacilli, and Clostridium: causing tetanus and gangrene.

Gram-negative bacteria:

- Salmonella, Shigella, and Campylobacter: causing gastrointestinal infections.
- Legionella: causing Legionnaires' disease.
- Meningococcus: causing meningitis.
- Gonorrhea bacteria: causing gonorrhea.

Numerous Gram-negative bacteria also cause urinary tract infections and septicemia in chronically ill individuals.

Identification of other bacteria may involve assessing their ability to ferment different types of sugars.

How is fungal and protozoan microscopy performed?

- Microorganisms slightly larger than bacteria can be visualized using microscopy. For instance, oral candidiasis (thrush) can be identified from mouth or genital samples.

- Protozoa responsible for amoebic dysentery, malaria, or trichomoniasis can be isolated from stools, blood samples, or discharge.

- Parasites like roundworm and hookworm are often identifiable by examining eggs or worms in stools.

- Smaller microorganisms such as chlamydia, rickettsiae, and viruses are detected through blood samples analyzed for antibodies against the microorganism.

How is cell and tissue (histology) testing performed?

Microscopy is crucial for studying tissue structure and cells with abnormal appearances, aiding in cancer diagnosis, among other applications.

Upon receiving a biopsy (tissue sample), the pathologist divides it into small pieces and fixes them in formalin or a similar substance.

The fixed tissue is then embedded in paraffin, sliced into extremely thin sections, stained for enhanced visualization, and examined under a microscope.

Specialized staining techniques may be employed to detect specific types of cells.

While the tissue test results may take up to a week or longer, urgent cases may yield results within half an hour by freezing the tissue before sectioning, allowing for rapid analysis.