Model Answer
0 min readIntroduction
Mycoplasmas are the smallest known self-replicating bacteria, belonging to the class Mollicutes. A defining characteristic of Mycoplasmas, differentiating them from other bacteria, is the complete absence of a cell wall. This structural peculiarity makes them naturally resistant to many common antibiotics, such as beta-lactams, which target cell wall synthesis. These organisms are highly adaptable, often living as parasites or commensals. Their widespread distribution and ability to infect a broad range of hosts, including humans, animals, and plants, make them significant pathogens causing a variety of serious diseases across different biological kingdoms, impacting health, agriculture, and animal husbandry globally.
Mycoplasma: A Versatile Pathogen
Mycoplasmas are unique prokaryotes with small genomes and an elastic membrane, but no rigid cell wall. This flexibility allows them to penetrate host cells and tissues, contributing to their pathogenicity. They often cause chronic, persistent infections due to their ability to evade host immune responses and antibiotic treatments.
Diseases in Humans
Mycoplasma species are responsible for various infections in humans, primarily affecting the respiratory and urogenital tracts. Their lack of a cell wall complicates treatment, making diagnosis and management challenging.
- Respiratory Infections: Mycoplasma pneumoniae is a well-known human pathogen causing respiratory tract infections. It is a leading cause of "walking pneumonia" (atypical pneumonia), which presents with milder but persistent symptoms like a dry cough, fever, and headache, often not requiring hospitalization. It can also lead to tracheobronchitis and, in severe cases, complications like asthma attacks, pleural effusion, and even encephalitis.
- Urogenital Infections: Species such as Mycoplasma genitalium and Mycoplasma hominis are associated with infections of the urinary and genital tracts. M. genitalium can cause urethritis, cervicitis, and pelvic inflammatory disease (PID), often mimicking sexually transmitted infections. M. hominis can lead to postpartum fever and infections in individuals with weakened immune systems.
- Other Complications: In rare instances, mycoplasma infections can lead to systemic complications, including arthritis, hemolytic anemia, and certain skin conditions like Stevens-Johnson syndrome.
Diseases in Animals
Mycoplasmas inflict substantial economic losses in the livestock industry by causing a range of chronic and acute diseases in various animal species.
- Cattle: Mycoplasma bovis is a major pathogen in cattle, causing several severe conditions. It is frequently implicated in bovine respiratory disease (BRD) in calves, which can be particularly resistant to standard antibiotic treatments. Other significant diseases include mastitis (inflammation of the udder) in dairy cows, leading to reduced milk production and quality; arthritis, causing lameness; and, less commonly, otitis media (ear infections) and reproductive issues. Mycoplasma mycoides subspecies mycoides is the causative agent of Contagious Bovine Pleuropneumonia (CBPP), a highly fatal and economically devastating disease.
- Poultry: In poultry, Mycoplasma gallisepticum causes Chronic Respiratory Disease (CRD) in chickens and infectious sinusitis in turkeys, leading to reduced egg production, poor weight gain, and increased mortality. Mycoplasma synoviae can cause infectious synovitis, affecting joints and tendons.
- Pigs: Mycoplasma hyopneumoniae is the primary cause of enzootic pneumonia in pigs, a chronic respiratory disease that significantly impacts pig growth and productivity. Mycoplasma hyosynoviae and Mycoplasma hyorhinis are associated with arthritis in pigs.
Diseases in Plants
Mycoplasma-like organisms (MLOs), now often referred to as phytoplasmas, are obligate parasites that cause a wide array of devastating diseases in plants, impacting agricultural yields globally. They are typically transmitted by insect vectors, mainly leafhoppers and psyllids.
- Sandal Spike Disease: This severe disease affects sandalwood trees in India, characterized by a reduction in leaf size, shortening of internodes, and a 'spiky' appearance, eventually leading to the death of the tree. Mycoplasma-like bodies are consistently associated with this disease.
- Little Leaf of Brinjal: Caused by phytoplasmas, this disease results in significantly reduced and distorted leaves, often accompanied by bushy growth and sterility in brinjal (eggplant) plants, leading to severe crop losses.
- Citrus Greening (Huanglongbing): One of the most destructive diseases of citrus worldwide, it is caused by fastidious, unculturable bacteria (often phytoplasmas or closely related wall-less bacteria). Symptoms include yellowing of leaves, stunted growth, fruit malformation, and eventual tree decline, transmitted by citrus psyllids.
- Witches' Broom: This symptom, caused by various phytoplasmas, involves the abnormal proliferation of shoots and branches, leading to a broom-like appearance in affected woody plants like apple and jujube.
- Aster Yellows: Affecting a broad range of herbaceous plants, including important agricultural crops like carrots, lettuce, and celery, Aster Yellows causes stunting, yellowing, and abnormal flower development (phyllody), where floral parts transform into leaf-like structures.
Conclusion
In conclusion, Mycoplasma species, characterized by their lack of a cell wall, are highly adaptable and significant pathogens causing a diverse range of serious diseases across humans, animals, and plants. From "walking pneumonia" in humans to devastating respiratory and reproductive disorders in livestock, and debilitating diseases like citrus greening and sandal spike in plants, their impact is profound. The unique biological features of Mycoplasmas, particularly their cell wall deficiency, render them resistant to many conventional antibiotics and present considerable challenges for diagnosis, treatment, and disease management strategies in medical, veterinary, and agricultural fields.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.