Mycoplasma: Characteristics and Infections

• Mycoplasma are the smallest free-living bacteria, able to grow in a cell-free medium.
• Mycoplasma gets its name from its fungus-like branching filaments and the plasticity of its shape
• Mycoplasma can be saprophytic, parasitic or pathogenic.

Categories of Infections

• Mycoplasma causes pneumonia, specifically M. pneumoniae.
• Mycoplasma causes urogenital infections, specifically M. genitalium.

Characteristics of Mycoplasma

• Mycoplasma lacks cell walls.
• They are pleomorphic, having no fixed shape or size, and have a flexible cell membrane allowing them to change shape.
• Mycoplasma lacks cell wall precursors like muramic acids and diaminopimelic acid.
• The cells are bound by a soft, triminar membrane containing sterols.
• They are also known as pleuropneumoniae-like organisms (PPLO).
• Mycoplasma can pass through filters.
• Mycoplasma is resistant to antibiotics due to their lack of a cell wall.
• Some species of Mycoplasma are zoonotic, meaning they can be transmitted from animals to humans.

Morphology

• Mycoplasma appears as granules and filaments of various sizes.
• They come in coccoid, balloon, disc, ring, or star-shaped forms.
• Filaments are slender and show branching.
• Multiplication occurs through binary fission.
• Mycoplasma is gram-negative but stains better with Giemsa stain.

Classification

• M. pneumoniae is an established pathogen that causes pneumonia and colonizes in the oropharynx.
• M. hominis and M. genitalium are established pathogens that cause genital infections and colonize in the genital tract.

Antigenic Properties

• The antigenic properties of Mycoplasma are mainly glycolipids and proteins.
• Glycolipid antigens are identified by complement fixation.
• Protein antigens are detected by ELISA.

Resistance

• Mycoplasma is destroyed at 45 degrees in 15 minutes.
• They can be lysed by surface-active agents and lipolytic agents such as taurocholate and digitonin.
• Mycoplasma is resistant to penicillin and cephalosporins and lysozymes that act on cell walls.
• Mycoplasma is sensitive to tetracyclines, erythromycin, and other macrolides.

Pathogenicity

• Pathogenic Mycoplasma exhibits host specificity.
• They produce infections by adhering to the mucosa of respiratory, gastrointestinal, and genitourinary tracts.
• Mycoplasma causes two types of infection.
• Mycoplasmal pneumonia (primary atypical pneumonia or PAP) is caused by M. pneumoniae; the disease is typically tracheobronchitis.
• The incubation period for Mycoplasmal pneumonia is 1–3 weeks.
• Onset of M. pneumoniae infection is gradual, with fever, malaise, headache, and sore throat.
• Paroxysmal cough may occur with blood–tinged sputum.
• The disease is characterized by minimum respiratory signs on physical examination but marked by radiological evidence of consolidation.
• Consolidation is usually patchy, involving one of the lower lobe, starting at the helium and funning out to the periphery
• The disease is usually self-limiting, with recovery in 1–2 weeks.
• Mycoplasmas tend to cause severe and prolonged infections in HIV-infected and other immunodeficient subjects.

Laboratory Diagnosis

• Specimens are taken via throat swab inoculated on sterile transport media.
• Culture is done using Hayflick medium; the colonies show a fried egg appearance.
• Molecular methods such as PCR are used.
• Serology is performed.