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Did you know how a piece of agar can be the key to identifying pathogenic bacteria?
In microbiology, colonization morphology refers to the visual appearance of bacterial or fungal communities on agar plates. Examining colonization morphology is the first step in identifying unknown microorganisms. Systematic assessment of the appearance of a community, focusing on aspects such as size, shape, color, opacity, and consistency, provides clues that help determine the identity of organisms and allows microbiologists to select appropriate tests for conclusive determination. Identify.
When the test material arrives at the microbiology laboratory, it is inoculated onto an agar plate and placed in an incubator to encourage microbial growth. Because the appearance of the microbial community changes with growth, examine colonization morphology a specific time after inoculation, usually 18 to 24 hours after inoculation but sometimes varies based on slower growing organisms such as fungi.
The microbiologist will carefully examine the appearance of the colony, noting specific characteristics such as size, color, shape, consistency, and opacity. The inspection team may use a hand mirror or magnifying glass to view the colony in greater detail. Opacity is described as transparent, translucent, or opaque. Staphylococcus aureus is usually opaque, while many Streptococci are translucent.
The overall shape of the colony can be described as round, irregular, or punctate (like pinpoints). Assessing the vertical growth or elevation of a community is another identifying characteristic, examined by tilting an agar plate sideways and calling it flat, humped, raised, domed (very raised), depressed (with a depression in the center), or raised ( There is a bulge in the center). The edges of a colony can be described individually using terms such as smooth, rough, irregular, and filamentous.
Bacillus anthracis is striking for its filamentous appearance, sometimes described as resembling a Medusa head.
Consistency is checked by physically manipulating the colonies with sterilized tools, using terms such as brittle, creamy, sticky and dry. Staphylococcus aureus is considered to have a creamy consistency, while some Neisseria species are slimy, and colonies of diphtheriae and beta-hemolytic streptococci are often dry.
Bacteria that produce biofilms often have a slimy (slimy) consistency. When some microorganisms grow on blood agar, they may digest the blood in the medium, causing hemolysis (destruction of red blood cells) visible on the agar plates. In colonial morphology, hemolysis is divided into three types: alpha, beta, and gamma hemolysis. In alpha hemolysis, the blood is partially digested, causing the area around the colony to turn green; while in beta hemolysis, the organism completely digests the blood, leaving a clear area around the three-dimensional colony.
Organisms that do not produce hemolysis are called gamma hemolytic.
Anaerobic bacteria that produce "dual-zone" complete and incomplete hemolysis Necrotrophic fasciitis are noteworthy. The smell of culture is sometimes considered part of colonial morphology. Although it is not recommended to intentionally smell microbial cultures, certain organisms produce distinctive odors that can be detected during routine inspection of cultures.
For example, Pseudomonas aeruginosa has a grape-like odor; while Staphylococcus aureus has been described as smelling like old socks; and Proteus odor can be described as rotten or similar to chocolate cake.
Other unique features of colonial morphology include motility and pigment production. Pseudomonas aeruginosa produces cyanine and chlorophyll, which give the colony a green sheen.
Some Serratia samples produce an orange-red pigment called dwarfism. And organisms with circular motility, such as Proteobacteria, exhibit growth in concentric waves extending from the site of inoculation.
Explanation
Colonial morphology serves as a first step in identifying microbial species from clinical samples. Based on the visual appearance of the community, microbiologists can narrow down the list of possible organisms and thereby select the appropriate test to provide a definitive diagnosis. For example, if a microbiologist observes a community that resembles Staphylococcus aureus, a catalytic enzyme test may be performed to confirm whether it belongs to the genus Staphylococcus aureus and a coagulase test to confirm that it is a coagulase-negative S. aureus Cocci are also more pathogenic species, such as S. aureus.
The observation of hemolysis is also very useful in the initial identification of streptococci, which are classified according to their hemolytic reaction. For example, Streptococcus pyogenes, which causes sore throats and scarlet fever, shows beta hemolysis, while Streptococcus pneumoniae, which can cause pneumonia and meningitis, shows alpha hemolysis. Highly pathogenic Staphylococcus aureus usually shows beta hemolysis, whereas skin-resident Staphylococcus epidermidis shows weak or no hemolysis at all.
Although automated techniques such as MALDI-TOF are increasingly used to identify microorganisms in clinical laboratories, colonization morphology remains useful for distinguishing potential pathogens that require identification from normal flora that do not require definitive identification, and is used in automated techniques Confirm identification when failure to provide unambiguous results.
In the world of microorganisms, have you ever thought about what role these tiny colonies of bacteria play in our health?
