Treponema pallidum is considered a gram-negative bacterium even though it lacks lipopolysaccharide in its outer membrane – a characteristic found in other gram-negative bacteria. Most Treponema pallidum cells are not easily stained by Gram staining, but rather Silver impregnation stain and Ryu’s stain are better for staining T. pallidum cells. Because it is gram-negative, a bright red or pink stain is visible when stained.

Treponema pallidum is a spirochaete bacterium. This means that is it part of the Spirochaetes phylum and has long, helically coiled cells.

Treponema pallidum was observed by Dr. David Cox, a member of the CDC using a scanning electron microscope (SEM). The spiral shape is evident in the photograph and the picture was taken on top of a culture of cotton-tail rabbit epithelium cells. In this image, the bacteria were not stained.

Treponema pallidum is an extremely interesting case when it pertains to bacterium identification. The results above show that Treponema pallidum is negative for both Gram-positive and Gram-negative. This is because Gram-staining is not an effective test in determining whether a bacterium is Treponema pallidum. Even though it is normally described as a Gram-negative bacteria, it lacks lipopolysaccharide in its outer membrane which is a key characteristic of Gram-negative bacteria. The best phenotypical characteristic for Treponema pallidum is that it cannot be identified using standard tests. As already discussed, Treponema pallidum cells are not easily stained by Gram staining, but rather Silver impregnation stain and Ryu’s stain are better for staining T. pallidum cells. An example of a gram-negative bacterium stained using Ryu’s stain is shown in the picture below. Treponema pallidum is unique in the sense that it can’t be identified by standard tests and upon making that cell positive, there was a significant jump from 10% to 99% Treponema pallidum.

Positive tests: Not identifiable by standard tests, Motility Test, Spirochete

Negative tests: Gram-stain test, Coccus, Curved bacilli, Gram positive, Gram negative

Treponema pallidum is found in the chancre in the early stages of the disease. This is usually the first manifestation of syphilis. It can then invade the bloodstream. Most organs in the body can be invaded, however, it most commonly invades the lymph nodes, skin, and the central nervous system. In the latter stages of syphilis, Treponema pallidum invades the vasa vasorum of the aorta and the arteries.

The best antibiotic for Treponema pallidum is antibiotic penicillin known as Benzathine penicillin G. This is the best and most common treatment for Treponema pallidum. Treponema pallidum has a drug susceptibility to Treponema ssp. Including the drug Abacavir.