What are cell wall-deficient bacteria?
Cell wall-deficient bacteria are microscopic single-celled organisms (prokaryotes). The bacteria discussed in this education module are unlike most other bacteria - precisely because they lack a cell wall. Having lost their cell wall during evolution, these bacteria appear microscopically as pleomorphic and spheroid.
The most prominent bacteria of this group, those that colonize or infect humans, are the Mycoplasma species, and the Ureaplasma species.
Characteristics
These bacteria are:
- Highly fastidious
- Slow growers
- Very small in cell size (0.3 x 0.8 μm)1
- A small genome (the minimum number of genes or DNA to support life)
- Mostly facultative anaerobes (requiring something "extra" for growth - like fatty acids, sterols [eg, cholesterol], and nucleic acid precursor molecules
- Known for having a long incubation period between exposure and symptom development - often gradual, a "slow onset" - taking weeks, not days
In addition, these microorganisms cannot be detected using the standard Gram stain and routine culture procedures. Specific media formulations can yield the growth of typical "fried egg-type" colonies. This appearance differs from the raised, circular, convex growth typically seen with many bacterial colonies having cell walls. (Laboratory methods will be discussed in the "Diagnosis of Infection" topic section.)
1. Tille PM. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier. 2022.
3. CDC/Forrester. Image #10935. "Under a magnification of 500X, four times greater than PHIL 10934, this photograph revealed some of the morphologic features exhibited by a single, large-sized, Ureaplasma urealyticum colony." PHIL public domain. Created 1973. Accessed December 29, 2023. hhttps://phil.cdc.gov/Details.aspx?pid=10935
