What is mycoplasma?

Definition

Mycoplasma is a bacterial genus belonging to the class
Mollicutes. A number of Mycoplasma species have been established
as human pathogens, including pneumoniae,
hominis, and genitalium.

Natural Habitat and Features

Mycoplasma has been isolated from humans and animals including
cows, dogs, cats, pigs, horses, poultry, sheep, goats, and small rodents.
Mycoplasma is the smallest bacteria that can live
independently. It has a small genome size that is in the lower limit of complexity
necessary for self-replicating organisms. Mycoplasma can survive
in the presence or absence of oxygen.

Mycoplasma lacks a cell wall, so it does not react in a Gram’s
stain and is not susceptible to antibiotics that target cell walls. It
has a specialized organelle, or tip, that provides motility and mediates bacterial
interactions with its host cells. Adherence proteins allow
Mycoplasma attachment to cells lining the respiratory and
genitourinary tracts, acting like a parasite on the surface of its host cells and
using their precursors for production of its genetic material. Some species
(pneumoniae, genitalium,
fermentans, penetrans, and
gallisepticum, a poultry pathogen) can invade host cells and
live intracellularly.

Mycoplasma produces hydrogen peroxide and superoxide, substances that cause injuries to the mucosal surface; the activation of inflammatory mediators is associated with its infectious process. Mycoplasma is challenging to grow in culture; thus, bacterial identification mainly depends on molecular-biochemical techniques.

Pathogenicity and Clinical Significance

Although there are seven Mycoplasma species detected in the
human genitourinary tract, only three species (genitalium,
hominis, and Ureaplasma species) are
associated with urogenital disease. Nonchlamydial nongonococcal urethritis in men
may result from genitalium and Ureaplasma
species. Genitalium has also been isolated from the urogenital
tract of women with cervicitis and pelvic inflammatory
disease. Genitalium and
Ureaplasma species have also been implicated in extragenital
infections.

Hominis and Ureaplasma species have been
implicated in chorioamnionitis, endometritis, pyelonephritis, postpartum or postabortum fevers, neonatal
meningitis, pneumonia, bacteremia, and arthritis
(specifically, hominis in postpartum women and
Ureaplasma species in sexually acquired reactive
arthritis).

Hominis has been related to extragenital infections, including
sepsis, hematoma infection, vascular and catheter-related infections, sternal wound infections following
thoracic surgery, prosthetic valve endocarditis, brain abscesses, and pneumonia.
These infections occurred mainly through the spread of bacteria in the bloodstream
and mostly in immunocompromised persons who had injuries of anatomical barriers
and had polytrauma.

Pneumoniae causes lung infections, often called atypical
pneumonia or walking pneumonia. It is transmitted through
respiratory droplets between persons. At highest risk for infection are those
persons who are in close contact with others, including those who live, work, or
perform activities in crowded places such as schools, homeless shelters,
hospitals, prisons, and dormitories. Other risk factors for
Mycoplasma respiratory infection include smoking and lower
levels of preexisting immunoglobulin G levels. Mycoplasma
pneumonia has pulmonary manifestations (such as nonproductive cough) and
extrapulmonary manifestations (such as cardiologic, neurologic, and dermatologic
symptoms). There is no age or gender predilection for the disease. Although people
of all ages are at risk, infection rarely occurs in children younger than five
years of age.

Drug Susceptibility

Hominis is treated with tetracycline,
the drug of choice, usually for seven days, but the duration of treatment is based
on observations of symptom resolution and clinical judgment. Resistant strains
have been reported, and alternate choices of antibiotics include clindamycin and
fluoroquinolones (such as gatifloxacin and moxifloxacin).

Ureaplasma infections are treated with tetracycline or
erythromycin, the drugs of choice. A seven day course of doxycycline can be used
for treatment of urethritis caused by Ureaplasma species.
Alternative antimicrobials for Ureaplasma include
fluoroquinolones (such as levofloxacin and ofloxacin) and chloramphenicol.
Clinical observations are important in considering treatment duration.

Neonatal meningitis caused by hominis and Ureaplasma species is often treated with tetracyclines, despite contraindications for use in children. Alternative medications for use in children include chloramphenicol for both bacteria, clindamycin for hominis, and erythromycin for Ureaplasma species. Lower respiratory infections in newborns can be treated with azithromycin or erythromycin. The suggested duration of treatment for Mycoplasma infections in newborns is ten to fourteen days.

Genitalium and pneumonia are treated with macrolides (such as azithromycin, clarithromycin, and erythromycin), fluoroquinolones (such as levofloxacin and moxifloxacin), and tetracyclines (such as doxycycline). The duration of treatment ranges from five to fourteen days, depending on what antibiotic is used.

Bibliography

Blanchard, Alain, and Cecile M. Bebear. “Mycoplasmas of Humans.” In Molecular Biology and Pathogenicity of Mycoplasmas, edited by Shmuel Razin and Richard Herrmann. New York: Kluwer Academic, 2002.

Johannson, Karl-Erik, and Bertil Petterrson. “Taxonomy of Mollicutes.” In Molecular Biology and Pathogenicity of Mycoplasmas, edited by Shmuel Razin and Richard Herrmann. New York: Kluwer Academic, 2002.

Mandell, Lionel A., et al. “Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community Acquired Pneumonia in Adults.” Clinical Infectious Diseases 44 (2007): S27-S72.

Ryan, Kenneth J. “ Mycoplasma and Ureaplasma.” In Sherris Medical Microbiology, edited by Kenneth J.Ryan and C. George Ray. 5th ed. New York: McGraw-Hill, 2010.