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Chlamydiae, rickettsiae, and their cell wall defective variants
Abstract:
Inapparent chlamydial and rickettsial infections are an important source of the dissemination of the parasites and may cause explosive outbreaks of severe diseases in man and animal. However, it is engimatic how these obligate intracellular microbes induce latency and why or how inapparent infections convert into active disease. Currently, microbiologists believe that chlamydiae and rickettsiae are gram-negative bacteria unique in their intracellular habitat. This review presents evidence that these organisms have another peculiarity; namely, defective cell walls present throughout much of their life cycle. In this survey, the properties of the small and large forms of chlamydiae and rickettsiae are reexamined with regard to the current knowledge of cell wall defective variants of free-living bacteria. Data are presented in support of the concept that chlamydiae and rickettsiae are cell wall defective microbes whose small 'bacterial' forms have lost the ability to reproduce as bacteria during evolution; the large forms including ultrafilterable phases of the life cycle of these parasites are responsible for inapparent infections of healthy carriers, whereas conversion into small 'bacterial forms may cause, under appropriate conditions manifest diseases. This concept may provide challenging and profitable directions in the search to explain puzzling phenomena associated with chlamydiae and rickettsiae.
Insights
Chlamydial and rickettsial infections can cause severe disease outbreaks. This review suggests these microbes may be cell wall defective, explaining their latency and ability to cause active infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Cell Biology
Background:
- Inapparent chlamydial and rickettsial infections are significant sources of disease dissemination in humans and animals.
- The mechanisms by which these obligate intracellular microbes establish latency and transition to active disease remain poorly understood.
- Current understanding classifies chlamydiae and rickettsiae as unique Gram-negative bacteria residing intracellularly.
Purpose of the Study:
- To reexamine the properties of chlamydial and rickettsial life cycle forms.
- To present evidence supporting a novel concept regarding the nature of these microbes.
- To offer a new perspective on the pathogenesis of chlamydial and rickettsial infections.
Main Methods:
- Review of existing literature and data on chlamydiae and rickettsiae.
- Comparison of chlamydial and rickettsial forms with cell wall defective variants of free-living bacteria.
- Analysis of life cycle characteristics, including small and large forms and ultrafilterable phases.
Main Results:
- Evidence suggests chlamydiae and rickettsiae possess defective cell walls throughout much of their life cycle.
- The small 'bacterial' forms may have evolved to lose their ability to reproduce independently.
- Large forms and ultrafilterable phases are implicated in maintaining inapparent infections in healthy carriers.
Conclusions:
- Chlamydiae and rickettsiae are proposed to be cell wall defective microbes.
- The transition between large (inapparent) and small (potentially pathogenic) forms may explain disease manifestation.
- This cell wall defect concept offers a new framework for understanding latency and disease conversion in these infections.