This webpage was produced as an assignment for an undergraduate course at Davidson College.
An infection of Legionella pneumophila leads to the syndrome known as Legionnaire’s disease. This sickness is characterized by severe pneumonia accompanied by alveolitis and bronchiolitis (Rathore and Alvarez, 2006). Like any other bacterial infection, the most obvious and most effective treatment is antibiotic therapy. The most effective antibiotics for the treatment of Legionnaire’s disease are those that can achieve high intracellular concentrations because the pathogens are usually hiding inside vacuoles in cells. The best antibiotics of this type are quinolones, ketolides and macrolides. Azithromycin and rifampin are the two most effective specific antibodies which are often taken together to combat severe infections (2006).
Researchers test the effectiveness of an antibody at suppressing an infection by measuring the colony-forming units grown in media (Horwitz and Silverstein, 1983). By this method it was shown that erythromycin and rifampin were able to stop L. pneumophila growth whether taken immediately before, after or two days after an infection. The actions of these antibiotic treatments are also reversible: after the antibodies are removed from the infection, growth resumes within two days (1983). This fact stresses the importance that a patient consistently take their antibiotics for the suggested two to three week treatment period (Rathore and Alvarez, 2006). If they stop taking their medication even a day or two before the infection is cleared, it can easily re-infect the vulnerable vascular tissues.
L. pneumophila grown on plates (like above) are used to test in vitro reactions to antibiotics. Image in public domain.
Possibility of a Vaccine
While antibiotics are clearly the most obvious choice for clearing a bacterial infection like Legionnaire’s disease, there is also the possibility of an effective vaccine. Research has shown that immunization of guinea pigs with both an avirulent mutant form of L. pneumophila and with the major secretory protein of L. pneumophila can lead to protection against a lethal dose of the unattenuated pathogen (Blander and Horwitz, 1989). The ability of a single protein from the bacteria to impart sufficient protective memory gives great hope for the possibility of a human vaccine. The chance of such a vaccine being developed is slim, though, because of the rarity and unpredictability of this disease. Only 8,000 to 18,000 cases arise in America each year, usually occurring as outbreaks in isolated areas (Rathore and Alvarez, 2006). While these conditions don’t warrant universal immunization, research shows that such a vaccine would theoretically be possible should the outbreaks of Legionnaire’s disease become more widespread.
Blander SJ and MA Horwitz. 1989. Vaccination with the major secretory protein of Legionella pneumophila induces cell-mediated and protective immunity in a guinea pig model of Legionnaire’s disease. Journal of Experimental Medicine 169:691-705.
Horwitz MA and SC Silverstein. 1983. Intracellular multiplication of Legionnaires’ disease bacteria (Legionella pneumophila) in human monocytes is reversibly inhibited by erythromycin and rifampin. J. Clin. Invest. 71:15-26.
Rathore M and A Alvarez. 2006 May 15. eMedicine: Legionella infection. <http://www.emedicine.com/ped/topic1288.htm>. Accessed 2007 April 29.
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