Mycoplasma pneumoniae
by Kaniz Khalfia
Background
Mycoplasma pneumoniae is unique because of its small genome and physical size. The bacterium contains only 500-2300 Kba in its genome that produces about 700 different proteins. Its reduced genome has been clearly mapped. M. pneumoniae size range from 0.2 to 0.8 micrometer and are capable of passing through most filters designed to remove bacteria. The bacterium is the smallest living organism capable of replicating itself. The bacterium lacks a cell wall but has a three layered cell membrane with sterols. It can take on any shape from cocci to filamentous. An agar plates the colonies have a specific fried egg look. It lives mainly as a parasite in humans where it can maintain its osmotic balance with its environment. It has a strict dependence on the host for nutrients. They grow aerobically and use glucose as its main food source but need the host for amino acids, lipids, nucleotides and sterols.
Disease
M. pneumoniae is generally referred to as primary atypical or walking pneumonia because the symptoms are not as sever as pneumonia. The symptoms include a dry hacking cough, fever, and headache. The symptoms will last for about 2 to 3 weeks.
M. pneumoniae affects people worldwide. Typically only 33 % of people who have M. pneumoniae will get atypical pneumonia. The majority, 77 %, will come down with an upper tract infection (tracheaobronchitis). M. pneumoniae is transmitted through aerosol droplets. The bacterium is capable of infecting anyone at any time but it has a pattern of coming in the fall and winter and causing an outbreak every 4 to 8 years, although more tight communities occur more frequently. The pathogen rarely occurs on children less than 4 years of age. Since the bacterium lacks a cell wall, B-lactums are futile against them. The body’s immune system is responsible for killing the pathogen. There were 2 million cases in the US with 100,000 requiring hospitalization. The mortality rate is very low with only occasional fatalities among the elderly and sickle cell anemia persons.
Virulence
The bacterium evolved by loosing its genes converting it from a free-living microbe into a pathogen. It needs the host’s nutrients in order to survive. The bacterium latches itself onto the host epithelial cells by a 160 kDa type 1 pilli. The pilli, located on a specific organelle on the polar region of the bacterium, attaches to the sialic residues that are present on epithelial cells. It then begins to colonize creating a cascade of problems to the host. M. pneumoniae stops the cilliary movement and produces hydrogen peroxides and superoxides as metabolic waste that kill the epithelial and neighboring cells. The inactive cilia of the epithelium cells produce non-productive coughs, fever and sore throat. It also causes an immune repose monopolizing the immune systems but through antigenic variations it capable of avoiding being phagocytized. By monopolizing the immune system the pathogen is capable of making the host susceptible to other pathogens. Other virulence factors include its ability to deplete nearby cells of nutrients.
Treatment
The antibiotic usually given is tetracycline and erythromycin. Penicillins are useless because the bacterium lacks a cell wall. The body’s own immune systems will eventually take care of the disease. There are no vaccines available for the disease.
The last outbreak of Mycoplasma pneumoniae occurred in 1993 in Ohio, Texas and New York.
Ohio
From June 15th to September 8th, 47 staff members and clients in a shelter for disabled adults came down with acute respiratory infection caused by mycoplasma pneumonia. Patients suffered from fever and headache of which, 15 % required hospitalization.
Texas
From August 1st through November 15th, 215 workers of 4500 had Mycoplasma infections in a tertiary care center. Patients suffered from abrupt onset of headache, shaking chills, and severe malaise, followed by fever and cough. Only 2 % required hospitalization.
New York
From August 1st to October 26th, 48 out 189 people came down with an acute respiratory infection in an autism center in upstate New York. Six percent of the patients required hospitalization.
References
http://meded.ucsd.edu/isp/1999/CAP/mycoplas.html
http://www.emedicine.com/EMERG/topic467.htm
http://www.cdc.gov/ncidod/dbmd/diseaseinfo/mycoplasmapneum_t.htm