
Mycoplasma is a unique group of bacteria known for its small size and unusual characteristics, often associated with diseases in humans and animals. Despite its simplicity, Mycoplasma’s biology is quite interesting. Let’s explore its habitat, morphology, culture, and biochemical features in clear terms.Mycoplasma is also called Pleuropneumonia-Like Organisms (PPLO) because they were first discovered in relation to pleuropneumonia in cattle.
Table of Contents
Habitat of Mycoplasma
Pleuropneumonia-Like Organisms typically lives in parasitic or commensal relationships with other organisms, often residing in mucous membranes. These bacteria thrive in environments such as the respiratory, urogenital, and gastrointestinal tracts of both humans and animals.
In humans, species like Pleuropneumonia-Like Organisms pneumoniae inhabit the respiratory system, where they can cause conditions like atypical pneumonia.
In animals, Pleuropneumonia-Like Organisms species are found in livestock and poultry, affecting the respiratory and reproductive systems.
These bacteria favor warm, moist environments and depend on their hosts for nutrients. They are mostly found within tissues rather than external environments like water or soil.
Morphology of Mycoplasma

Pleuropneumonia-Like Organisms stands out due to its extremely small size and lack of a rigid cell wall.
Size
These bacteria are among the smallest organisms, measuring just 0.2 to 0.3 micrometers. Their tiny size allows them to pass through filters that usually trap bacteria.
Shape
Pleuropneumonia-Like Organisms lacks a fixed shape due to the absence of a cell wall, giving them a flexible, variable form (pleomorphic). They can appear round, filamentous, or irregular in shape, making them more adaptable and harder for the immune system to detect.
No Cell Wall
Unlike most bacteria, Pleuropneumonia-Like Organisms doesn’t have a cell wall, making it resistant to antibiotics that target cell walls, like penicillin. However, this also makes them more susceptible to environmental stressors like dehydration.
Culture of Mycoplasma
Culturing Pleuropneumonia-Like Organisms in the lab is difficult because of their small size and complex nutritional needs. Since they lack a cell wall and rely heavily on their hosts, they require very specific growth conditions.
Growth Medium
Pleuropneumonia-Like Organisms needs nutrient-rich media, often supplemented with animal-derived components like serum to provide essential nutrients such as cholesterol. A common medium is PPLO broth (Pleuropneumonia-Like Organism broth), containing peptones, yeast extract, and serum for optimal growth.
Agar Plates

On solid media, Pleuropneumonia-Like Organisms forms tiny colonies that resemble “fried eggs” under the microscope. These colonies take several days (2 to 7) to become visible, reflecting their slow growth rate.
Biochemical Characteristics of Mycoplasma
Pleuropneumonia-Like Organisms has several distinct biochemical traits, mainly due to its lack of a cell wall and its reliance on host organisms for nutrients.
Energy Metabolism
Pleuropneumonia-Like Organisms can grow in both oxygen-rich and oxygen-poor environments (facultative anaerobes). They typically use fermentation to produce energy, breaking down glucose into lactic acid. Some species, like Mycoplasma pneumoniae, can also metabolize oxygen, depending on their surroundings.
No Peptidoglycan
Without a cell wall, Pleuropneumonia-Like Organisms doesn’t produce peptidoglycan, which is why antibiotics that inhibit cell wall synthesis, like penicillin, are ineffective against them.
Sterol Dependence
Uniquely, Pleuropneumonia-Like Organisms requires sterols, such as cholesterol, in its membrane to maintain structure. These sterols strengthen the flexible membrane, compensating for the lack of a cell wall.
Urease Activity
Certain species of Pleuropneumonia-Like Organisms, like Mycoplasma hominis, can break down urea to produce ammonia and carbon dioxide, which is used in the lab to identify them.
Adhesion and Invasion
Mycoplasma uses specialized structures like adhesins to attach to host cells. For example, Pleuropneumonia-Like Organisms pneumoniae adheres to respiratory cells, allowing it to evade immune defenses and cause infections. In some cases, Mycoplasma can invade host cells, leading to persistent infections.
Conclusion
Mycoplasma is a distinctive group of bacteria that stands out for its small size, lack of a cell wall, and dependence on host organisms. These bacteria inhabit the respiratory, urogenital, and gastrointestinal systems of humans and animals, often causing infections. Culturing them in the lab requires specific growth conditions, and their unique biochemical characteristics, such as sterol dependence and resistance to cell wall-targeting antibiotics, make them fascinating subjects in microbiology research.
Frequently Asked Questions (FAQ)
What do you mean by Agar plates ?
Agar plates are petri dishes containing agar, a gelatinous substance used as a growth medium for microorganisms in biological research and laboratory experiments.
Define Peptidoglycan ?
Peptidoglycan is a mesh-like polymer made of sugars and amino acids that gives structural support and shape to bacterial cell walls.
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