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Secrets of Microbes: How to Identify Mysterious Bacteria by Colonizing Forms?
In microbiology, colonization morphology refers to the visual appearance of bacteria or fungi on culture media. Examining colonization morphology is the first step in identifying unknown microorganisms. By systematically assessing the appearance of a colony, microbiologists are able to select appropriate tests to determine the specific identity of the microorganism based on characteristics such as size, shape, color, transparency, and consistency that provide clues as to its identity.
Microbiological testing procedures
When a sample comes to the microbiology laboratory, it is first inoculated into an agar medium and placed in an incubator to encourage the growth of microorganisms. Because the appearance of microbial colonies changes as they grow, examination of colonial morphology is required at specific times after inoculation. Readings are usually taken 18 to 24 hours after inoculation, although times may vary for slower growing organisms such as fungi.
Microbiologists carefully observe the appearance of the colonies, noting specific characteristics such as size, color, shape, consistency and transparency.
Transparency can be described as transparent, translucent, or opaque. Typically, staphylococci are opaque, while many streptococci are often translucent. The overall shape of a colony can be characterized as round, irregular, or small dot-shaped (such as pinpoints). Another identifying characteristic is the vertical growth or bulge of the colony, which can be assessed by tilting the agar medium to one side and appearing as flat, ridged, convex, rounded (very convex), depressed (with a depression in the center), or It is expressed by bulging (a bulge in the center), etc.
Colonial edges can be characterized by terms such as smooth, rough, irregular and filamentous.
Consistency and special indicators
Check the consistency by physically touching the colon with sterile tools. Can be described with mini-phrases like crispy, creamy, sticky, and dry. Staphylococci usually have a creamy texture, while some Neisseria species are more sticky, and colonies of Diphtheriae and beta-hemolytic Streptococci are often dry. The bacteria that produce the capsule usually have a slippery (mucus-like) consistency.
When certain microorganisms grow on blood agar, they may digest the blood in the medium, causing significant hemolysis on the agar plate. Within the context of colonial forms, hemolysis is divided into three types: alpha hemolysis, beta hemolysis and gamma hemolysis. Alpha hemolysis is when the blood is partially digested, causing the surrounding colonies to turn green; beta hemolysis is when the organism completely digests the blood, leaving a clear area around each colony; organisms that do not develop hemolysis are called gamma hemolysis.
For example, Clostridium difficile, which causes gas gangrene, is known for producing "dual zones" of complete and incomplete hemolysis.
Odor and other characteristics
The smell of culture is sometimes seen as part of the colonial formation. While it is not recommended to intentionally sniff microbial cultures, some microorganisms produce distinctive odors, such as Pseudomonas aeruginosa, which gives off a grape-like aroma, Staphylococcus aureus, which has an odor similar to old socks, and Proteus, which alternates between Described as rancid or like chocolate cake.
Other unique features of the colonial form include motility and the production of color pigments. Pseudomonas aeruginosa produces cyanobacteria and xanthophyll pigments, which give the colonies a green sheen, while some Chromobacteriaceae produce an orange-red pigment called procidin.
Explanation and application
Colonial morphology is the first step in identifying microbial species from clinical samples. Based on the visual appearance of the colonization, microbiologists can narrow down the list of possible organisms and thus select the appropriate test to provide a definitive diagnosis. The results of hemolysis observations are very useful in identifying specific bacteria such as Streptococci, which are classified based on their hemolytic reaction.
For example, Streptococcus pyogenes, which causes sore throat and scarlet fever, exhibits beta hemolysis, while Streptococcus pneumoniae exhibits alpha hemolysis.
Although automated techniques such as MALDI-TOF are increasingly used in clinical laboratories to identify microorganisms, colonization morphology can still be useful in distinguishing potential pathogens from normal flora, as determination of normal flora is usually not required identification, while assessment of colonial morphology can further confirm identity when results from automated techniques are equivocal.
This series of inspections and comparisons not only gives us a deeper understanding of the diversity of microorganisms, but also brings more space for thinking. What role do these microorganisms play in the environment we live in?
