Loeffler, Friedrich August Johannes (1852-1915)

German physician

Friedrich August Loeffler was a German physician who turned his career path to focus on microbiology after becoming an assistant to Robert Koch. Loeffler is accredited with the discovery of several microorganisms including Loefflerella mallei, the etiological agent of glanders, Corynebacterium diphtheriae, the infectious organism of diphtheria; and Erysipelothrix rhusiopathiae, the infectious agent that causes cholera in swine. In addition to his discoveries of bacteria, Loeffler determined that foot-and-mouth disease was due to an infectious microorganism smaller than any bacteria (a virus).

Friedrich Loeffler began his studies in medicine at the University of Würzburg but then transferred to the Army Medical School shortly before the Franco-Prussian War. In 1872, Loeffler received his medical degree and then worked as an assistant physician in Berlin at the Charté Hospital. Beginning in 1876, he worked as a public health officer and military surgeon in Potsdam and Hannover. This lasted until 1879, when he moved to Berlin and continued his work at the Kaiserliches Gesundheitsamt.

Friedrich Loeffler's transfer brought him under the supervision of Robert Koch. Loeffler and Georg Graffky began assisting Koch on his research of bacteria. Loeffler first began his bacteriological studies researching effective methods of disinfection. During his studies, Loeffler discovered Loefflerella mallei, bacteria that causes glanders, a disease seen mainly in horses. To determine the exact bacteria that causes glanders, Loeffler applied what has come to be known as Koch's postulates. Initially, Loeffler isolated the infectious agent from the horse and grew it in a pure culture of blood serum. Next, Loeffler injected the bacteria into healthy horses, which then showed symptoms of the disease. Finally, Loeffler once again isolated the bacteria from the once healthy horses. In addition to discovering Loefflerella mallei, Loeffler discovered the infectious agent that causes cholera in swine.

In 1884, after a long struggle to decipher the etiological agent that causes diphtheria, Loeffler isolated Corynebacterium diphtheriae in pure culture from the throat of humans. Problems pinpointing the exact microorganism that causes diphtheria stemmed from the fact that many different microorganisms inhabited the throats of diphtheria patients. Loeffler undertook the task of isolating pure cultures of bacteria to determine the exact etiological agent of diphtheria. Loeffler found that certain throat infections were due to streptococcal infections, which are now known to cause scarlet fever. He reasoned that the Streptococcus bacteria were not responsible for causing diphtheria because when injected into healthy animals, the bacteria did not produce symptoms characteristic of the disease. Additionally, the Streptococcus was not always abundant in diphtheria patients. The Streptococcus appeared to be secondary to rod shaped bacteria. When these rod shaped bacteria, called bacillus, were isolated in pure culture and injected into healthy animals, the animals exhibited the characteristic signs of human diphtheria, including the pseudomembrane in the throat of the patients that suffocate to death. Additionally, Loeffler determined that toxins produced by the infectious agent were the cause of destruction to internal organs. He reasoned that the toxins released entered the blood stream and traveled to other organs thereby poisoning them. Emile Roux and Yersin proved this theory of toxins to be correct. Loeffler made a surprising discovery when he was able to isolate the diphtheria bacillus from healthy individuals. He then determined that not all people who carry infectious microorganisms contract the disease.

Also in 1884, Loeffler began his new career as hygienic director with his first directorship position being at the First Garrison Hospital. There he was able to continue his bacteriological research in conjunction with lecturing on sanitation. Two years later, he became part of the faculty at the University of Berlin. By 1888, he had transferred to the University of Greifswald where he spent the next 25 years.

At the University of Greifswald, Loeffler studied Salmonella typhi-murium, the bacteriological agent that causes mouse typhoid but does not infect other animals. This research was intended to control the exuberant mouse population that was threatening to destroy the crops of Greece. Loeffler effectively killed the mice by contaminating their food sources with the bacteria.

In 1898, Friedrich Loeffler, in conjunction with Paul Frosch, determined a filterable agent proving smaller than any bacteria previously discovered caused foot-and-mouth disease. This was the first hint that viruses existed. At that time, Loeffler was working at the University of Greifswald as head of the department of hygiene. Loeffler moved his laboratory to the island of the Insel Riems in order to safely continue his research on the disease. In 1913, Loeffler's research took a back seat to his new position as director of the Robert Koch Institute in Berlin. Once World War I began, all research on the Insel Riems ceased. Loeffler worked for the army to implement proper hygiene regimens until his death in 1915.

See also Coryneform bacteria; Streptococci and streptococcal infections