Mycoplasma and L-Forms

Mycoplasmas are cultivated on fluid (PPLO broth) or solid (PPLO agar) media enriched with 20% horse or human serum and yeast extract, with antibiotics added as selective agents. Colonies appear after 2–6 days of incubation, ranging 10–600 µm in size with a typical 'fried egg' appearance — a dense central zone growing into the agar surrounded by a flatter peripheral zone.

Colonies are best studied after staining by the Dienes method, where an agar block containing the colony is covered with a coverslip bearing dried methylene blue/azure stain. Colonies cannot be picked with a loop; subculture is done by cutting an agar block and rubbing it onto fresh plates. No turbidity is seen in liquid medium despite growth.

M. pneumoniae causes community-acquired atypical pneumonia, tracheobronchitis or bronchiolitis, though pneumonia develops in only 5–10% of infected persons; acute pharyngitis may also occur. After inhalation of respiratory aerosols, the organism attaches to host epithelial cells via adhesins and accessory proteins, inducing ciliostasis, local inflammation and tissue destruction (partly mediated by hydrogen peroxide release).

A recently described exotoxin, CARDS toxin (Community-Acquired Respiratory Distress Syndrome toxin), also contributes to epithelial damage. The organism replicates intracellularly, contributing to chronicity and difficulty of eradication. Spread throughout households is common; incubation period is 2–3 weeks.

Because Mycoplasma lacks a cell wall, none of the beta-lactam antibiotics is effective. Oral erythromycin or newer macrolides (azithromycin, clarithromycin) have long been the drugs of choice for mycoplasmal respiratory infections. Tetracyclines are also active. Fluoroquinolones (levofloxacin, moxifloxacin) are bactericidal but generally less potent in vitro than macrolides. Supportive measures (cough suppressants, antipyretics, analgesics) address systemic symptoms.

L-form bacteria (also called L-phase bacteria, L-phase variants, or cell wall-deficient/CWD bacteria) are strains of otherwise walled bacteria that lack cell walls. First isolated in 1935 by Emmy Klieneberger-Nobel, named after the Lister Institute in London.

Two types exist: unstable L-forms — spheroplasts capable of dividing but able to revert to the original walled morphology — and stable L-forms, which cannot revert. L-forms can be generated in the laboratory from species like Bacillus subtilis or E. coli by inhibiting peptidoglycan synthesis (antibiotics) or treating with lysozyme. Species implicated in chronic disease as L-forms include Bacillus anthracis, Treponema pallidum, Mycobacterium tuberculosis, Helicobacter pylori, Rickettsia prowazekii, and Borrelia burgdorferi. Although L-forms can derive from Gram-positive or Gram-negative parent bacteria, they always stain Gram-negative on Gram testing due to the absent cell wall.

Because symptoms are often milder than the degree of radiographic infiltrate would suggest, patients frequently remain ambulatory and continue daily activities despite having pneumonia.

Yes — many patients with M. pneumoniae infection develop cold agglutinins (autoantibodies against red blood cell I antigen), which can support the clinical diagnosis, though this finding is not universally present or fully specific.

L-forms are thought to be implicated in some chronic or relapsing infections since their lack of a cell wall makes them resistant to cell-wall-active antibiotics and harder to detect by conventional culture, though their clinical significance remains an area of ongoing study.